WorldWideScience

Sample records for plasma sheet reconnection

  1. Alfven Waves in a Plasma Sheet Boundary Layer Associated with Near-Tail Magnetic Reconnection

    Institute of Scientific and Technical Information of China (English)

    YUAN Zhi-Gang; DENG Xiao-Hua; PANG Ye; LI Shi-You; WANG Jing-Fang

    2007-01-01

    We report observations from Geotail satellite showing that large Poynting fluxes associated with Alfven waves in the plasma sheet boundary layer(PSBL) occur in the vicinity of the near-tail reconnection region on 10 December 1996.During the period of large Poynting fluxex,Geotail also observed strong tailward plasma flws.These observations demonstrate the importance of near-tail reconnection process as the energy source of Alfven waves in the PSBL.Strong tailward(Earthward)plasma flows ought to be an important candidate in generating Alfven waves.Furthermore,the strong pertutbations not only of the magnetic field but also of the electric field observed in the PSBL indicate that the PSBL plays an important role in the generation and propagation of the energy flux associated with Alfven waves.

  2. Three-dimensional particle simulation of plasma instabilities and collisionless reconnection in a current sheet

    Energy Technology Data Exchange (ETDEWEB)

    Horiuchi, Ritoku; Sato, Tetsuya [Theory and Computer Simulation Center, National Inst. for Fusion Science, Toki, Gifu (Japan)

    1999-06-01

    Generation of anomalous resistivity and dynamical development of collisionless reconnection in the vicinity of a magnetically neutral sheet are investigated by means of a three-dimensional particle simulation. For no external driving source, two different types of plasma instabilities are excited in the current layer. The lower hybrid drift instability (LHDI) is observed to grow in the periphery of current layer in an early period, while a drift kink instability (DKI) is triggered at the neutral sheet in a late period as a result of the nonlinear deformation of the current sheet by the LHDI. A reconnection electric field grows at the neutral sheet in accordance with the excitation of the DKI. When an external driving field exists, the convective electric field penetrates into the current layer through the particle kinetic effect and collisionless reconnection is triggered by the convective electric field earlier than the DKI is excited. It is also found that the anisotropic ion distribution is formed through the anomalous ion heating by the DKI. (author)

  3. Modeling the Self-organized Critical Behavior of the Plasma Sheet Reconnection Dynamics

    Science.gov (United States)

    Klimas, Alex; Uritsky, Vadim; Baker, Daniel

    2006-01-01

    Analyses of Polar UVI auroral image data reviewed in our other presentation at this meeting (V. Uritsky, A. Klimas) show that bright night-side high-latitude UV emissions exhibit so many of the key properties of systems in self-organized criticality (SOC) that an alternate interpretation has become virtually impossible. It is now necessary to find and model the source of this behavior. We note that the most common models of self-organized criticality are numerical sandpiles. These are, at root, models that govern the transport of some quantity from a region where it is loaded to another where it is unloaded. Transport is enabled by the excitation of a local threshold instability; it is intermittent and bursty, and it exhibits a number of scale-free statistical properties. Searching for a system in the magnetosphere that is analogous and that, in addition, is known to produce auroral signatures, we focus on the reconnection dynamics of the plasma sheet. In our previous work, a driven reconnection model has been constructed and has been under study. The transport of electromagnetic (primarily magnetic) energy carried by the Poynting flux into the reconnection region of the model has been examined. All of the analysis techniques, and more, that have been applied to the auroral image data have also been applied to this Poynting flux. Here, we report new results showing that this model also exhibits so many of the key properties of systems in self-organized criticality that an alternate interpretation is implausible. Further, we find a strong correlation between these key properties of the model and those of the auroral UV emissions. We suggest that, in general, the driven reconnection model is an important step toward a realistic plasma physical model of self-organized criticality and we conclude, more specifically, that it is also a step in the right direction toward modeling the multiscale reconnection dynamics of the magnetotail.

  4. Modeling the Self-organized Critical Behavior of Earth's Plasma Sheet Reconnection Dynamics

    Science.gov (United States)

    Klimas, Alexander J.

    2006-01-01

    Analyses of Polar UVI auroral image data show that bright night-side high-latitude W emissions exhibit so many of the key properties of systems in self-organized criticality that an alternate interpretation has become virtually impossible. These analyses will be reviewed. It is now necessary to find and model the source of this behavior. We note that the most common models of self-organized criticality are numerical sandpiles. These are, at root, models that govern the transport of some quantity from a region where it is loaded to another where it is unloaded. Transport is enabled by the excitation of a local threshold instability; it is intermittent and bursty, and it exhibits a number of scale-free statistical properties. Searching for a system in the magnetosphere that is analogous and that, in addition, is known to produce auroral signatures, we focus on the reconnection dynamics of the magnetotail plasma sheet. In our previous work, a driven reconnection model has been constructed and has been under study. The transport of electromagnetic (primarily magnetic) energy carried by the Poynting flux into the reconnection region of the model has been examined. All of the analysis techniques (and more) that have been applied to the auroral image data have also been applied to this Poynting flux. New results will be presented showing that this model also exhibits so many of the key properties of systems in self-organized criticality that an alternate interpretation is implausible. A strong correlation between these key properties of the model and those of the auroral UV emissions will be demonstrated. We suggest that, in general, the driven reconnection model is an important step toward a realistic plasma physical model of self-organized criticality and we conclude, more specifically, that it is also a step in the right direction toward modeling the multiscale reconnection dynamics of the magnetotail.

  5. Plasmoid ejection and secondary current sheet generation from magnetic reconnection in laser-plasma interaction.

    Science.gov (United States)

    Dong, Quan-Li; Wang, Shou-Jun; Lu, Quan-Ming; Huang, Can; Yuan, Da-Wei; Liu, Xun; Lin, Xiao-Xuan; Li, Yu-Tong; Wei, Hui-Gang; Zhong, Jia-Yong; Shi, Jian-Rong; Jiang, Shao-En; Ding, Yong-Kun; Jiang, Bo-Bin; Du, Kai; He, Xian-Tu; Yu, M Y; Liu, C S; Wang, Shui; Tang, Yong-Jian; Zhu, Jian-Qiang; Zhao, Gang; Sheng, Zheng-Ming; Zhang, Jie

    2012-05-25

    Reconnection of the self-generated magnetic fields in laser-plasma interaction was first investigated experimentally by Nilson et al. [Phys. Rev. Lett. 97, 255001 (2006)] by shining two laser pulses a distance apart on a solid target layer. An elongated current sheet (CS) was observed in the plasma between the two laser spots. In order to more closely model magnetotail reconnection, here two side-by-side thin target layers, instead of a single one, are used. It is found that at one end of the elongated CS a fanlike electron outflow region including three well-collimated electron jets appears. The (>1 MeV) tail of the jet energy distribution exhibits a power-law scaling. The enhanced electron acceleration is attributed to the intense inductive electric field in the narrow electron dominated reconnection region, as well as additional acceleration as they are trapped inside the rapidly moving plasmoid formed in and ejected from the CS. The ejection also induces a secondary CS.

  6. Reconnection in thin current sheets

    Science.gov (United States)

    Tenerani, Anna; Velli, Marco; Pucci, Fulvia; Rappazzo, A. F.

    2016-05-01

    It has been widely believed that reconnection is the underlying mechanism of many explosive processes observed both in nature and laboratory, but the question of reconnection speed and initial trigger have remained mysterious. How is fast magnetic energy release triggered in high Lundquist (S) and Reynolds (R) number plasmas?It has been shown that a tearing mode instability can grow on an ideal timescale, i.e., independent from the the Lundquist number, once the current sheet thickness becomes thin enough, or rather the inverse aspect ratio a/L reaches a scale a/L~S-1/3. As such, the latter provides a natural, critical threshold for current sheets that can be formed in nature before they disrupt in a few Alfvén time units. Here we discuss the transition to fast reconnection extended to simple viscous and kinetic models and we propose a possible scenario for the transition to explosive reconnection in high-Lundquist number plasmas, that we support with fully nonlinear numerical MHD simulations of a collapsing current sheet.

  7. Fluctuation dynamics in reconnecting current sheets

    Science.gov (United States)

    von Stechow, Adrian; Grulke, Olaf; Ji, Hantao; Yamada, Masaaki; Klinger, Thomas

    2015-11-01

    During magnetic reconnection, a highly localized current sheet forms at the boundary between opposed magnetic fields. Its steep perpendicular gradients and fast parallel drifts can give rise to a range of instabilities which can contribute to the overall reconnection dynamics. In two complementary laboratory reconnection experiments, MRX (PPPL, Princeton) and VINETA.II (IPP, Greifswald, Germany), magnetic fluctuations are observed within the current sheet. Despite the large differences in geometries (toroidal vs. linear), plasma parameters (high vs. low beta) and magnetic configuration (low vs. high magnetic guide field), similar broadband fluctuation characteristics are observed in both experiments. These are identified as Whistler-like fluctuations in the lower hybrid frequency range that propagate along the current sheet in the electron drift direction. They are intrinsic to the localized current sheet and largely independent of the slower reconnection dynamics. This contribution characterizes these magnetic fluctuations within the wide parameter range accessible by both experiments. Specifically, the fluctuation spectra and wave dispersion are characterized with respect to the magnetic topology and plasma parameters of the reconnecting current sheet.

  8. Observation of a planetward ion beam in the plasma sheet boundary layer at Saturn following tail reconnection

    Science.gov (United States)

    Jackman, C. M.

    2014-04-01

    We present an interval of data from 2006 when the Cassini spacecraft was located 32 RS (1 RS = 60268km) downtail, at a local time of 22:00 hrs and a latitude of 13.8°. The interval in question displayed a range of dynamic behaviour, including a southward turning of the tail magnetic field, indicative of a dipolarization, and an energetic, fast, planetward beam of ions. Preliminary interpretation of this event suggests that it represents a reconnection-driven ion beam in Saturn's magnetotail plasma sheet boundary layer. This event is explored using several of the Cassini instruments to build up a picture of the reconfiguration of the tail in terms of local and global effects.

  9. Self-regulation of the reconnecting current layer in relativistic pair plasma reconnection

    CERN Document Server

    Zenitani, S

    2008-01-01

    We investigate properties of the reconnecting current layer in relativistic pair plasma reconnection. We found that the current layer self-regulates its thickness when the current layer runs out current carriers and so relativistic reconnection retains a fast reconnection rate. Constructing a steady state Sweet-Parker model, we discuss conditions for the current sheet expansion. Based on the energy argument we conclude that the incompressible assumption is invalid in relativistic Sweet-Parker reconnection. The guide field cases are more incompressible than the anti-parallel cases, and we find a more significant current sheet expansion.

  10. Fast magnetic reconnection in laser-produced plasma bubbles

    OpenAIRE

    Fox, W.; Bhattacharjee, A.; Germaschewski, K.

    2011-01-01

    Recent experiments have observed magnetic reconnection in high-energy-density, laser-produced plasma bubbles, with reconnection rates observed to be much higher than can be explained by classical theory. Based on fully kinetic particle simulations we find that fast reconnection in these strongly driven systems can be explained by magnetic flux pile-up at the shoulder of the current sheet and subsequent fast reconnection via two-fluid, collisionless mechanisms. In the strong drive regime with ...

  11. Reconnection at 3D Magnetic Null Points: Effect of Current Sheet Asymmetry

    CERN Document Server

    Wyper, Peter F

    2013-01-01

    Asymmetric current sheets are likely to be prevalent in both astrophysical and laboratory plasmas with complex three dimensional (3D) magnetic topologies. This work presents kinematic analytical models for spine and fan reconnection at a symmetric 3D null with asymmetric current sheets. Asymmetric fan reconnection is characterized by an asymmetric reconnection of flux past each spine line and a bulk flow of plasma across the null point. In contrast, asymmetric spine reconnection is inherently equal and opposite in how flux is reconnected across the fan plane. The higher modes of spine reconnection also include localized wedges of vortical flux transport in each half of the fan. In this situation, two definitions for reconnection rate become appropriate: a local reconnection rate quantifying how much flux is genuinely reconnected across the fan plane and a global rate associated with the net flux driven across each semi-plane. Through a scaling analysis it is shown that when the ohmic dissipation in the layer ...

  12. Tail reconnection region versus auroral activity inferred from conjugate ARTEMIS plasma sheet flow and auroral observations

    Science.gov (United States)

    Nishimura, Y.; Lyons, L. R.; Xing, X.; Angelopoulos, V.; Donovan, E. F.; Mende, S. B.; Bonnell, J. W.; Auster, U.

    2013-09-01

    sheet flow bursts have been suggested to correspond to different types of auroral activity, such as poleward boundary intensifications (PBIs), ensuing auroral streamers, and substorms. The flow-aurora association leads to the important question of identifying the magnetotail source region for the flow bursts and how this region depends on magnetic activity. The present study uses the ARTEMIS spacecraft coordinated with conjugate ground-based auroral imager observations to identify flow bursts beyond 45 RE downtail and corresponding auroral forms. We find that quiet-time flows are directed dominantly earthward with a one-to-one correspondence with PBIs. Flow bursts during the substorm recovery phase and during steady magnetospheric convection (SMC) periods are also directed earthward, and these flows are associated with a series of PBIs/streamers lasting for tens of minutes with similar durations to that of the series of earthward flows. Presubstorm onset flows are also earthward and associated with PBIs/streamers. The earthward flows during those magnetic conditions suggest that the flow bursts, which lead to PBIs and streamers, originate from further downtail of ARTEMIS, possibly from the distant-tail neutral line (DNL) or tailward-retreated near-Earth neutral line (NENL) rather than from the nominal NENL location in the midtail. We find that tailward flows are limited primarily to the substorm expansion phase. They continue throughout the period of auroral poleward expansion, indicating that the expansion-phase flows originate from the NENL and that NENL activity is closely related to the auroral expansion of the substorm expansion phase.

  13. Fast magnetic reconnection in laser-produced plasma bubbles.

    Science.gov (United States)

    Fox, W; Bhattacharjee, A; Germaschewski, K

    2011-05-27

    Recent experiments have observed magnetic reconnection in high-energy-density, laser-produced plasma bubbles, with reconnection rates observed to be much higher than can be explained by classical theory. Based on fully kinetic particle simulations we find that fast reconnection in these strongly driven systems can be explained by magnetic flux pileup at the shoulder of the current sheet and subsequent fast reconnection via two-fluid, collisionless mechanisms. In the strong drive regime with two-fluid effects, we find that the ultimate reconnection time is insensitive to the nominal system Alfvén time.

  14. Reconnection at three dimensional magnetic null points: Effect of current sheet asymmetry

    Science.gov (United States)

    Wyper, P. F.; Jain, Rekha

    2013-05-01

    Asymmetric current sheets are likely to be prevalent in both astrophysical and laboratory plasmas with complex three dimensional (3D) magnetic topologies. This work presents kinematic analytical models for spine and fan reconnection at a radially symmetric 3D null (i.e., a null where the eigenvalues associated with the fan plane are equal) with asymmetric current sheets. Asymmetric fan reconnection is characterized by an asymmetric reconnection of flux past each spine line and a bulk flow of plasma across the null point. In contrast, asymmetric spine reconnection is characterized by the reconnection of an equal quantity of flux across the fan plane in both directions. The higher modes of spine reconnection also include localized wedges of vortical flux transport in each half of the fan. In this situation, two definitions for reconnection rate become appropriate: a local reconnection rate quantifying how much flux is genuinely reconnected across the fan plane and a global rate associated with the net flux driven across each semi-plane. Through a scaling analysis, it is shown that when the ohmic dissipation in the layer is assumed to be constant, the increase in the local rate bleeds from the global rate as the sheet deformation is increased. Both models suggest that asymmetry in the current sheet dimensions will have a profound effect on the reconnection rate and manner of flux transport in reconnection involving 3D nulls.

  15. Reconnection at three dimensional magnetic null points: Effect of current sheet asymmetry

    Energy Technology Data Exchange (ETDEWEB)

    Wyper, P. F.; Jain, Rekha [School of Mathematics and Statistics, University of Sheffield, Sheffield, South Yorkshire S3 7RH (United Kingdom)

    2013-05-15

    Asymmetric current sheets are likely to be prevalent in both astrophysical and laboratory plasmas with complex three dimensional (3D) magnetic topologies. This work presents kinematic analytical models for spine and fan reconnection at a radially symmetric 3D null (i.e., a null where the eigenvalues associated with the fan plane are equal) with asymmetric current sheets. Asymmetric fan reconnection is characterized by an asymmetric reconnection of flux past each spine line and a bulk flow of plasma across the null point. In contrast, asymmetric spine reconnection is characterized by the reconnection of an equal quantity of flux across the fan plane in both directions. The higher modes of spine reconnection also include localized wedges of vortical flux transport in each half of the fan. In this situation, two definitions for reconnection rate become appropriate: a local reconnection rate quantifying how much flux is genuinely reconnected across the fan plane and a global rate associated with the net flux driven across each semi-plane. Through a scaling analysis, it is shown that when the ohmic dissipation in the layer is assumed to be constant, the increase in the local rate bleeds from the global rate as the sheet deformation is increased. Both models suggest that asymmetry in the current sheet dimensions will have a profound effect on the reconnection rate and manner of flux transport in reconnection involving 3D nulls.

  16. Plasma compression in magnetic reconnection regions in the solar corona

    CERN Document Server

    Provornikova, Elena; Lukin, Vyacheslav S

    2016-01-01

    It has been proposed that particles bouncing between magnetized flows converging in a reconnection region can be accelerated by the first order Fermi mechanism. Analytical considerations of this mechanism have shown that the spectral index of accelerated particles is related to the total plasma compression within the reconnection region similarly to the case of diffusive shock acceleration mechanism. As a first step to investigate the efficiency of Fermi acceleration in reconnection regions in producing hard energy spectra of particles in the solar corona, we explore the degree of plasma compression that can be achieved at reconnection sites. In particular, we aim to determine the conditions for the strong compressions to form. Using a two-dimensional resistive MHD numerical model we consider a set of magnetic field configurations where magnetic reconnection can occur including a Harris current sheet, a force-free current sheet, and two merging flux ropes. Plasma parameters are taken to be characteristic of t...

  17. Theory of magnetic reconnection in solar and astrophysical plasmas.

    Science.gov (United States)

    Pontin, David I

    2012-07-13

    Magnetic reconnection is a fundamental process in a plasma that facilitates the release of energy stored in the magnetic field by permitting a change in the magnetic topology. In this paper, we present a review of the current state of understanding of magnetic reconnection. We discuss theoretical results regarding the formation of current sheets in complex three-dimensional magnetic fields and describe the fundamental differences between reconnection in two and three dimensions. We go on to outline recent developments in modelling of reconnection with kinetic theory, as well as in the magnetohydrodynamic framework where a number of new three-dimensional reconnection regimes have been identified. We discuss evidence from observations and simulations of Solar System plasmas that support this theory and summarize some prominent locations in which this new reconnection theory is relevant in astrophysical plasmas.

  18. TURBULENT RECONNECTION IN RELATIVISTIC PLASMAS AND EFFECTS OF COMPRESSIBILITY

    Energy Technology Data Exchange (ETDEWEB)

    Takamoto, Makoto [Max-Planck-Institut für Kernphysik, Heidelberg (Germany); Inoue, Tsuyoshi [Division of Theoretical Astronomy, National Astronomical Observatory of Japan (Japan); Lazarian, Alexandre, E-mail: mtakamoto@eps.s.u-tokyo.ac.jp, E-mail: tsuyoshi.inoue@nao.ac.jp, E-mail: alazarian@facstaff.wisc.edu [Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706 (United States)

    2015-12-10

    We report on the turbulence effects on magnetic reconnection in relativistic plasmas using three-dimensional relativistic resistive magnetohydrodynamics simulations. We found that the reconnection rate became independent of the plasma resistivity due to turbulence effects similarly to non-relativistic cases. We also found that compressible turbulence effects modified the turbulent reconnection rate predicted in non-relativistic incompressible plasmas; the reconnection rate saturates, and even decays, as the injected velocity approaches to the Alfvén velocity. Our results indicate that compressibility cannot be neglected when a compressible component becomes about half of the incompressible mode, occurring when the Alfvén Mach number reaches about 0.3. The obtained maximum reconnection rate is around 0.05–0.1, which will be able to reach around 0.1–0.2 if injection scales are comparable to the sheet length.

  19. Magnetohydrodynamic simulation of reconnection in turbulent astrophysical plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Widmer, Fabien

    2016-07-19

    Turbulence is ubiquitous at large-Reynolds-number astrophysical plasmas like in the Solar corona. In such environments, the turbulence is thought to enhance the energy conversion rate by magnetic reconnection above the classical model predictions. Since turbulence cannot be simulated together with the large scale behaviour of the plasma, magnetic reconnection is studied through the average properties of turbulence. A Reynolds-averaged turbulence model is explored in which turbulence is self-sustained and -generated by the large scales (mean-) field inhomogeneities. Employing that model, the influence of turbulence is investigated by large-scale MHD numerical simulations solving evolution equations of the energy and cross-helicity of the turbulence together with the MHD equations. Magnetic reconnection is found to be either rapidly enhanced or suppressed by turbulence depending on the turbulence timescale. If the turbulence timescale is self-consistently calculated, reconnection is always strongly enhanced. Since the solar corona bears strong guide magnetic fields perpendicular to the reconnecting magnetic fields, the influences of a strong guide field on turbulent reconnection is separately investigated. A slow down of reconnection, obtained in the presence of a finite guide field, can be understood by a finite residual helicity working against the enhancement of reconnection by the turbulence. The influence of turbulence on magnetic reconnection is further studied by means of high resolution simulations of plasmoid-unstable current sheets. These simulations revealed the importance of turbulence for reaching fast reconnection.

  20. Unsteady magnetic reconnection in laboratory experiments with current sheets

    Science.gov (United States)

    Frank, Anna

    2009-11-01

    According to present notion, unsteady magnetic reconnection in current sheets (CS) is basic to dramatic natural phenomena: solar and stellar flares, substorms in the Earth and other planetary magnetospheres, as well as to disruptive instabilities in tokamak plasmas. We present a review of laboratory experiments studying evolution of CS formed in 3D and 2D magnetic configurations with an X line, in the CS-3D device. Usually CS exists during an extended period in a metastable stage, without essential changes of its structure and parameters. Under certain conditions this stage may be suddenly interrupted by unsteady phase of magnetic reconnection, which manifests itself in a rapid change of the magnetic field topology, current redistribution, excitation of pulsed electric fields, and other dynamic effects. The unsteady phase results in effective conversion of magnetic energy into the energy of plasma and accelerated particles, and may finally bring about the CS disruption. In the context of the solar flares, a metastable CS is associated with a pre-flare situation, while CS disruption -- with the flare itself. The physical mechanisms triggering the unsteady magnetic reconnection in the laboratory produced current sheets are discussed. Supported by the Russian Foundation for Basic Research (project # 09-02-00971).

  1. Numerical study of magnetic reconnection process near in- terplanetary current sheet

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The third order accurate upwind compact difference scheme has been applied to the numerical study of the magnetic reconnection process possibly occurring near the interplanetary current sheet, under the framework of the two-dimensional compressible magnetohydrodynamics (MHD). Our results here show that the driven reconnection near the current sheet can occur within 10-30 min for the interplanetary high magnetic Reynolds number, RM =2 000-10 000, the stable magnetic reconnection structure can be formed in hour-order of magnitude, and there are some ba- sic properties such as the multiple X-line reconnections, vortical velocity structures, filament current systems, split-ting and collapse of the high-density plasma bulk. These results are helpful in understanding and identifying the magnetic reconnection phenomena near the interplanetary current sheets.

  2. Fast Magnetic Reconnection: Bridging Laboratory and Space Plasma Physics

    Energy Technology Data Exchange (ETDEWEB)

    Bhattacharjee, Amitava [University New Hampshire- Durham

    2012-02-16

    Recent developments in experimental and theoretical studies of magnetic reconnection hold promise for providing solutions to outstanding problems in laboratory and space plasma physics. Examples include sawtooth crashes in tokamaks, substorms in the Earth’s Magnetosphere, eruptive solar flares, and more recently, fast reconnection in laser-produced high energy density plasmas. In each of these examples, a common and long-standing challenge has been to explain why fast reconnection proceeds rapidly from a relatively quiescent state. In this talk, we demonstrate the advantages of viewing these problems and their solutions from a common perspective. We focus on some recent, surprising discoveries regarding the role of secondary plasmoid instabilities of thin current sheets. Nonlinearly, these instabilities lead to fast reconnection rates that are very weakly dependent on the Lundquist number of the plasma.

  3. "Ideally" unstable current sheets and the triggering of fast magnetic reconnection

    CERN Document Server

    Tenerani, Anna; Pucci, Fulvia; Landi, Simone; Rappazzo, Antonio Franco

    2016-01-01

    Magnetic reconnection is thought to be the dynamical mechanism underlying many explosive phenomena observed both in space and in the laboratory, though the question of how fast magnetic reconnection is triggered in such high Lundquist ($S$) number plasmas has remained elusive. It has been well established that reconnection can develop over timescales faster than those predicted traditionally once kinetic scales are reached. It has also been shown that, within the framework of resistive Magnetohydrodynamics (MHD), fast reconnection is achieved for thin enough sheets via the onset of the so-called plasmoid instability. The latter was discovered in studies specifically devoted to the Sweet-Parker current sheet, either as an initial condition or an apparent transient state developing in nonlinear studies. On the other hand, a fast tearing instability can grow on an ideal, i.e., $S$-independent, timescale (dubbed "ideal" tearing) within current sheets whose aspect ratio scales with the macroscopic Lundquist number...

  4. Relativistic Magnetic Reconnection in Pair Plasmas in Three Dimensions

    CERN Document Server

    Kagan, Daniel; Spitkovsky, Anatoly

    2012-01-01

    We investigate guide-field magnetic reconnection and particle acceleration in relativistic pair plasmas with three-dimensional particle-in-cell (PIC) simulations of a kinetic-scale current sheet in a periodic geometry at low magnetizations. The tearing instability is the dominant mode in the current sheet for all guide field strengths, while the linear kink mode is less important even without guide field. Oblique modes seem to be suppressed entirely. In its nonlinear evolution, the reconnection layer develops a network of interconnected and interacting magnetic flux ropes. As smaller flux ropes merge into larger ones, the reconnection layer evolves toward a three-dimensional, disordered state in which the resulting flux rope segments contain magnetic substructure on plasma skin depth scales. Embedded in the flux ropes, we detect spatially and temporally intermittent sites of dissipation reflected in peaks in the parallel electric field. Magnetic dissipation and particle acceleration persist until the end of t...

  5. Magnetotail Current Sheet Thinning and Magnetic Reconnection Dynamics in Global Modeling of Substorms

    Science.gov (United States)

    Kuznetsova, M. M.; Hesse, M.; Rastaetter, L.; Toth, G.; DeZeeuw, D. L.; Gombosi, T. I.

    2008-01-01

    Magnetotail current sheet thinning and magnetic reconnection are key elements of magnetospheric substorms. We utilized the global MHD model BATS-R-US with Adaptive Mesh Refinement developed at the University of Michigan to investigate the formation and dynamic evolution of the magnetotail thin current sheet. The BATSRUS adaptive grid structure allows resolving magnetotail regions with increased current density up to ion kinetic scales. We investigated dynamics of magnetotail current sheet thinning in response to southwards IMF turning. Gradual slow current sheet thinning during the early growth phase become exponentially fast during the last few minutes prior to nightside reconnection onset. The later stage of current sheet thinning is accompanied by earthward flows and rapid suppression of normal magnetic field component $B-z$. Current sheet thinning set the stage for near-earth magnetic reconnection. In collisionless magnetospheric plasma, the primary mechanism controlling the dissipation in the vicinity of the reconnection site is non-gyrotropic effects with spatial scales comparable with the particle Larmor radius. One of the major challenges in global MHD modeling of the magnetotail magnetic reconnection is to reproduce fast reconnection rates typically observed in smallscale kinetic simulations. Bursts of fast reconnection cause fast magnetic field reconfiguration typical for magnetospheric substorms. To incorporate nongyritropic effects in diffusion regions we developed an algorithm to search for magnetotail reconnection sites, specifically where the magnetic field components perpendicular to the local current direction approaches zero and form an X-type configuration. Spatial scales of the diffusion region and magnitude of the reconnection electric field are calculated self-consistently using MHD plasma and field parameters in the vicinity of the reconnection site. The location of the reconnection sites and spatial scales of the diffusion region are updated

  6. Three-dimensional geometry of magnetic reconnection induced by ballooning instability in a generalized Harris sheet

    Science.gov (United States)

    Zhu, Ping; Bhattacharjee, Amitava; Sangari, Arash; Wang, Zechen; Bonofiglo, Phillip

    2017-02-01

    We report for the first time the intrinsically three-dimensional (3D) geometry of the magnetic reconnection process induced by ballooning instability in a generalized Harris sheet. The spatial distribution and the structure of the quasi-separatrix layers, as well as their temporal emergence and evolution, indicate that the associated magnetic reconnection can only occur in a 3D geometry, which is irreducible to that of any two-dimensional reconnection process. Such a finding provides a new perspective to the long-standing controversy over the substorm onset problem and elucidates the combined roles of reconnection and ballooning instabilities. It also connects to the universal presence of 3D reconnection processes previously discovered in various natural and laboratory plasmas.

  7. ISEE 3 observations during a plasma sheet encounter at 140 earth radii - Evidence for enhancement of reconnection at the distant neutral line

    Science.gov (United States)

    Scholer, M.; Terasawa, T.; Baker, D. N.; Zwickl, R. D.; Gloeckler, G.; Hovestadt, D.; Smith, E. J.; Tsurutani, B. T.

    1986-01-01

    A plasma sheet encounter of the ISEE-3 spacecraft in the distant tail at 140 earth radii on March 20, 1983 is studied using magnetic field, energetic particle, and plasma electron data sets. The H-component magnetograms from auroral magnetometer stations, intensity-time profiles, high resolution magnetic field measurements, and electron and proton angular distributions are analyzed. The dynamics of the plasma sheet displayed by the strong tailward and earthward directed ion beams, large northward and southward magnetic fields excursions, and short tailward and earthward plasma flows are described.

  8. Observations of Magnetic Reconnection and Plasma Dynamics in Mercury's Magnetosphere

    Science.gov (United States)

    DiBraccio, Gina A.

    Mercury's magnetosphere is formed as a result of the supersonic solar wind interacting with the planet's intrinsic magnetic field. The combination of the weak planetary dipole moment and intense solar wind forcing of the inner heliosphere creates a unique space environment, which can teach us about planetary magnetospheres. In this work, we analyze the first in situ orbital observations at Mercury, provided by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. Magnetic reconnection and the transport of plasma and magnetic flux are investigated using MESSENGER Magnetometer and Fast Imaging Plasma Spectrometer measurements. Here, we report our results on the effect of magnetic reconnection and plasma dynamics on Mercury's space environment: (1) Mercury's magnetosphere is driven by frequent, intense magnetic reconnection observed in the form of magnetic field components normal to the magnetopause, BN, and as helical bundles of flux, called magnetic flux ropes, in the cross-tail current sheet. The high reconnection rates are determined to be a direct consequence of the low plasma beta, the ratio of plasma to magnetic pressure, in the inner heliosphere. (2) As upstream solar wind conditions vary, we find that reconnection occurs at Mercury's magnetopause for all orientations of the interplanetary magnetic field, independent of shear angle. During the most extreme solar wind forcing events, the influence of induction fields generated within Mercury's highly conducting core are negated by erosion due to persistent magnetopause reconnection. (3) We present the first observations of Mercury's plasma mantle, which forms as a result of magnetopause reconnection and allows solar wind plasma to enter into the high-latitude magnetotail through the dayside cusps. The energy dispersion observed in the plasma mantle protons is used to infer the cross-magnetosphere electric field, providing a direct measurement of solar wind momentum

  9. Measurement of ion velocity profiles in a magnetic reconnection layer via current sheet jogging

    Science.gov (United States)

    Stein, G.; Yoo, J.; Yamada, M.; Ji, H.; Dorfman, S.; Lawrence, E.; Myers, C.; Tharp, T.

    2011-10-01

    In many laboratory plasmas, constructing stationary Langmuir and Mach probe arrays with resolution on the order of electron skin depth is technically difficult, and can introduce significant plasma perturbations. However, complete two- dimensional profiles of plasma density, electron temperature, and ion flow are important for studying the transfer of energy from magnetic fields to particles during magnetic reconnection. Through the use of extra ``Shaping Field'' coils in the Magnetic Reconnection Experiment (MRX) at the Princeton Plasma Physics Laboratory, the inward motion of the current sheet in the reconnection layer can be accelerated, or ``jogged,'' allowing the measurement of different points across the sheet with stationary probes. By acquiring data from Langmuir probes and Mach probes at different locations in the MRX with respect to the current sheet center, profiles of electron density and temperature and a vector plot of two-dimensional ion velocity in the plane of reconnection are created. Results from probe measurements will be presented and compared to profiles generated from computer simulation.

  10. Magnetic reconnection between colliding magnetized laser-produced plasma plumes.

    Science.gov (United States)

    Fiksel, G; Fox, W; Bhattacharjee, A; Barnak, D H; Chang, P-Y; Germaschewski, K; Hu, S X; Nilson, P M

    2014-09-05

    Observations of magnetic reconnection between colliding plumes of magnetized laser-produced plasma are presented. Two counterpropagating plasma flows are created by irradiating oppositely placed plastic (CH) targets with 1.8-kJ, 2-ns laser beams on the Omega EP Laser System. The interaction region between the plumes is prefilled with a low-density background plasma and magnetized by an externally applied magnetic field, imposed perpendicular to the plasma flow, and initialized with an X-type null point geometry with B=0 at the midplane and B=8  T at the targets. The counterflowing plumes sweep up and compress the background plasma and the magnetic field into a pair of magnetized ribbons, which collide, stagnate, and reconnect at the midplane, allowing the first detailed observations of a stretched current sheet in laser-driven reconnection experiments. The dynamics of current sheet formation are in good agreement with first-principles particle-in-cell simulations that model the experiments.

  11. Reconnection current sheet structure in a turbulent medium

    Directory of Open Access Journals (Sweden)

    E. T. Vishniac

    2012-11-01

    Full Text Available In the presence of turbulence, magnetic field lines lose their dynamical identity and particles entrained on field lines diffuse through space at a rate determined by the amplitude of the turbulence. In previous work (Lazarian and Vishniac, 1999; Kowal et al., 2009; Eyink et al., 2011 we showed that this leads to reconnection speeds which are independent of resistivity. In particular, in Kowal et al. (2009 we showed that numerical simulations were consistent with the predictions of this model. Here we examine the structure of the current sheet in simulations of turbulent reconnection. Laminar flows consistent with the Sweet-Parker reconnection model produce very thin and well ordered currents sheets. On the other hand, the simulations of Kowal et al. (2009 show a strongly disordered state even for relatively low levels of turbulence. Comparing data cubes with and without reconnection, we find that large scale field reversals are the cumulative effect of many individual eddies, each of which has magnetic properties which are not very different from turbulent eddies in a homogeneous background. This implies that the properties of stationary and homogeneous MHD turbulence are a reasonable guide to understanding turbulence during large scale magnetic reconnection events. In addition, dissipation and high energy particle acceleration during reconnection events take place over a macroscopic volume, rather than being confined to a narrow zone whose properties depend on microscopic transport coefficients.

  12. Formation and Reconnection of Three-Dimensional Current Sheets in the Solar Corona

    Science.gov (United States)

    Edmondson, J. K.; Antiochos, S. K.; DeVore, C. R.; Zurbuchen, T. H.

    2010-01-01

    Current-sheet formation and magnetic reconnection are believed to be the basic physical processes responsible for much of the activity observed in astrophysical plasmas, such as the Sun s corona. We investigate these processes for a magnetic configuration consisting of a uniform background field and an embedded line dipole, a topology that is expected to be ubiquitous in the corona. This magnetic system is driven by a uniform horizontal flow applied at the line-tied photosphere. Although both the initial field and the driver are translationally symmetric, the resulting evolution is calculated using a fully three-dimensional magnetohydrodynamic (3D MHD) simulation with adaptive mesh refinement that resolves the current sheet and reconnection dynamics in detail. The advantage of our approach is that it allows us to apply directly the vast body of knowledge gained from the many studies of 2D reconnection to the fully 3D case. We find that a current sheet forms in close analogy to the classic Syrovatskii 2D mechanism, but the resulting evolution is different than expected. The current sheet is globally stable, showing no evidence for a disruption or a secondary instability even for aspect ratios as high as 80:1. The global evolution generally follows the standard Sweet- Parker 2D reconnection model except for an accelerated reconnection rate at a very thin current sheet, due to the tearing instability and the formation of magnetic islands. An interesting conclusion is that despite the formation of fully 3D structures at small scales, the system remains close to 2D at global scales. We discuss the implications of our results for observations of the solar corona. Subject Headings: Sun: corona Sun: magnetic fields Sun: reconnection

  13. THEMIS multispacecraft observations of a reconnecting magnetosheath current sheet with symmetric boundary conditions and a large guide field

    Science.gov (United States)

    Øieroset, M.; Phan, T. D.; Shay, M. A.; Haggerty, C. C.; Fujimoto, M.; Angelopoulos, V.; Eastwood, J. P.; Mozer, F. S.

    2017-08-01

    We report three spacecraft observations of a reconnecting magnetosheath current sheet with a guide field of unity, with THEMIS D (THD) and THEMIS E (THE)/THEMIS A (THA) observing oppositely directed reconnection exhausts, indicating the presence of an X line between the spacecraft. The near-constant convective speed of the magnetosheath current sheet allowed the direct translation of the observed time series into spatial profiles. THD observed asymmetries in the plasma density and temperature profiles across the exhaust, characteristics of symmetric reconnection with a guide field. The exhausts at THE and THA, on the other hand, were not the expected mirror image of the THD exhaust in terms of the plasma and field profiles. They consisted of a main outflow at the center of the current sheet, flanked by oppositely directed flows at the two edges of the current sheet, suggesting the presence of a second X line, whose outflow wraps around the outflow from the first X line.

  14. Cause of sudden magnetic reconnection in a laboratory plasma.

    Science.gov (United States)

    Choi, S; Craig, D; Ebrahimi, F; Prager, S C

    2006-04-14

    The cause for sudden reconnection in reversed field pinch plasmas is determined experimentally for two cases: large reconnection events (the sawtooth crash) and small reconnection events during improved confinement. We measure the term in the MHD equations which represents the driving (or damping) of edge tearing modes due to the axisymmetric magnetic field. The term is negative for large reconnection events (the modes are stable, implying that reconnection may be driven by nonlinear coupling to other modes) and positive for small reconnection events (modes are unstable, reconnection is spontaneous).

  15. Introduction to Plasma Dynamo, Reconnection and Shocks

    Energy Technology Data Exchange (ETDEWEB)

    Intrator, Thomas P. [Los Alamos National Laboratory

    2012-08-30

    In our plasma universe, most of what we can observe is composed of ionized gas, or plasma. This plasma is a conducting fluid, which advects magnetic fields when it flows. Magnetic structure occurs from the smallest planetary to the largest cosmic scales. We introduce at a basic level some interesting features of non linear magnetohydrodynamics (MHD). For example, in our plasma universe, dynamo creates magnetic fields from gravitationally driven flow energy in an electrically conducting medium, and conversely magnetic reconnection annihilates magnetic field and accelerates particles. Shocks occur when flows move faster than the local velocity (sonic or Alfven speed) for the propagation of information. Both reconnection and shocks can accelerate particles, perhaps to gigantic energies, for example as observed with 10{sup 20} eV cosmic rays.

  16. Exploring reconnection, current sheets, and dissipation in a laboratory MHD turbulence experiment

    Science.gov (United States)

    Schaffner, D. A.

    2015-12-01

    The Swarthmore Spheromak Experiment (SSX) can serve as a testbed for studying MHD turbulence in a controllable laboratory setting, and in particular, explore the phenomena of reconnection, current sheets and dissipation in MHD turbulence. Plasma with turbulently fluctuating magnetic and velocity fields can be generated using a plasma gun source and launched into a flux-conserving cylindrical tunnel. No background magnetic field is applied so internal fields are allowed to evolve dynamically. Point measurements of magnetic and velocity fluctuations yield broadband power-law spectra with a steepening breakpoint indicative of the onset of a dissipation scale. The frequency range at which this steepening occurs can be correlated to the ion inertial scale of the plasma, a length which is characteristic of the size of current sheets in MHD plasmas and suggests a connection to dissipation. Observation of non-Gaussian intermittent jumps in magnetic field magnitude and angle along with measurements of ion temperature bursts suggests the presence of current sheets embedded within the turbulent plasma, and possibly even active reconnection sites. Additionally, structure function analysis coupled with appeals to fractal scaling models support the hypothesis that current sheets are associated with dissipation in this system.

  17. In situ observations of reconnection and associated particle energization in turbulent plasmas

    Science.gov (United States)

    Retinò, A.; Sundkvist, D.; Vaivads, A.; Sahraoui, F.

    2012-04-01

    Magnetic reconnection occurs in turbulent plasma within a large number of volume-filling thin current sheets. Such reconnection efficiently dissipates the magnetic energy of turbulent plasma, resulting in substantial particle heating. Turbulent reconnection is also considered to play an important role for the acceleration of supra-thermal particles. Yet the details of energy dissipation and particle energization during turbulent reconnection, as well their dependence on turbulence properties, are not completely understood from an experimental point of view due to the scarcity of in situ observations. Here we present recent Cluster spacecraft observations of reconnection in different near-Earth turbulent regions (solar wind, magnetosheath, magnetotail) and we discuss the properties of particle energization therein.

  18. Explosive Turbulent Magnetic Reconnection

    OpenAIRE

    Higashimori, Katsuaki; Yokoi, Nobumitsu; Hoshino, Masahiro

    2013-01-01

    We report simulation results for turbulent magnetic reconnection obtained using a newly developed Reynolds-averaged magnetohydrodynamics model. We find that the initial Harris current sheet develops in three ways, depending on the strength of turbulence: laminar reconnection, turbulent reconnection, and turbulent diffusion. The turbulent reconnection explosively converts the magnetic field energy into both kinetic and thermal energy of plasmas, and generates open fast reconnection jets. This ...

  19. Nonlinear magnetic reconnection in low collisionality plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Ottaviani, M. [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking; Porcelli, F. [Politecnico di Torino, Turin (Italy)

    1994-07-01

    The magnetic reconnection in collisionless regimes, where electron inertia is responsible for the decoupling of the plasma motion from that of the field lines, is discussed. Since the linear theory of m=1 modes breaks down for very small magnetic island widths, a non linear analysis is called for. Thus, the behaviour of a collisionless, 2-D fluid slab model in the limit {rho}/d -> 0, is analyzed. The main result is that, when the island size is larger than the linear layer but smaller than the equilibrium scale length, the reconnection rate exhibits a quasi-explosive time behaviour, during which a current density sub-layer narrower than the skin depth is formed. It is believed that the inclusion of the electron initial term in Ohm`s law opens the possibility to understand the rapidity of relaxation process observed in low collisionality plasmas. 7 refs., 6 figs.

  20. Heating Mechanisms in the Low Solar Atmosphere through Magnetic Reconnection in Current Sheets

    Science.gov (United States)

    Ni, Lei; Lin, Jun; Roussev, Ilia I.; Schmieder, Brigitte

    2016-12-01

    We simulate several magnetic reconnection processes in the low solar chromosphere/photosphere; the radiation cooling, heat conduction and ambipolar diffusion are all included. Our numerical results indicate that both the high temperature (≳8 × 104 K) and low temperature (˜104 K) magnetic reconnection events can happen in the low solar atmosphere (100-600 km above the solar surface). The plasma β controlled by plasma density and magnetic fields is one important factor to decide how much the plasma can be heated up. The low temperature event is formed in a high β magnetic reconnection process, Joule heating is the main mechanism to heat plasma and the maximum temperature increase is only several thousand Kelvin. The high temperature explosions can be generated in a low β magnetic reconnection process, slow and fast-mode shocks attached at the edges of the well developed plasmoids are the main physical mechanisms to heat the plasma from several thousand Kelvin to over 8 × 104 K. Gravity in the low chromosphere can strongly hinder the plasmoid instability and the formation of slow-mode shocks in a vertical current sheet. Only small secondary islands are formed; these islands, however, are not as well developed as those in the horizontal current sheets. This work can be applied to understand the heating mechanism in the low solar atmosphere and could possibly be extended to explain the formation of common low temperature Ellerman bombs (˜104 K) and the high temperature Interface Region Imaging Spectrograph (IRIS) bombs (≳8 × 104) in the future.

  1. Formation of electron energy spectra during magnetic reconnection in laser-produced plasma

    Science.gov (United States)

    Huang, Kai; Lu, Quanming; Huang, Can; Dong, Quanli; Wang, Huanyu; Fan, Feibin; Sheng, Zhengming; Wang, Shui; Zhang, Jie

    2017-10-01

    Energetic electron spectra formed during magnetic reconnection between two laser-produced plasma bubbles are investigated by the use of two-dimensional particle-in-cell simulations. It is found that the evolution of such an interaction between the two plasma bubbles can be separated into two distinct stages: squeezing and reconnection stages. In the squeezing stage, when the two plasma bubbles expand quickly and collide with each other, the magnetic field in the inflow region is greatly enhanced. In the second stage, a thin current sheet is formed between the two plasma bubbles, and then, magnetic reconnection occurs therein. During the squeezing stage, electrons are heated in the perpendicular direction by betatron acceleration due to the enhancement of the magnetic field around the plasma bubbles. Meanwhile, non-thermal electrons are generated by the Fermi mechanism when these electrons bounce between the two plasma bubbles approaching quickly and get accelerated mainly by the convective electric field associated with the plasma bubbles. During the reconnection stage, electrons get further accelerated mainly by the reconnection electric field in the vicinity of the X line. When the expanding speed of the plasma bubbles is sufficiently large, the formed electron energy spectra have a kappa distribution, where the lower energy part satisfies a Maxwellian function and the higher energy part is a power-law distribution. Moreover, the increase in the expanding speed will result in the hardening of formed power-law spectra in both the squeezing and reconnection stages.

  2. Plasma Astrophysics, part II Reconnection and Flares

    CERN Document Server

    Somov, Boris V

    2007-01-01

    This well-illustrated monograph is devoted to classic fundamentals, current practice, and perspectives of modern plasma astrophysics. The first part is unique in covering all the basic principles and practical tools required for understanding and working in plasma astrophysics. The second part presents the physics of magnetic reconnection and flares of electromagnetic origin in space plasmas within the solar system; single and double stars, relativistic objects, accretion disks, and their coronae are also covered. This book is designed mainly for professional researchers in astrophysics. However, it will also be interesting and useful to graduate students in space sciences, geophysics, as well as advanced students in applied physics and mathematics seeking a unified view of plasma physics and fluid mechanics.

  3. MHD simulations of three-dimensional resistive reconnection in a cylindrical plasma column

    Science.gov (United States)

    Striani, E.; Mignone, A.; Vaidya, B.; Bodo, G.; Ferrari, A.

    2016-11-01

    Magnetic reconnection is a plasma phenomenon where a topological rearrangement of magnetic field lines with opposite polarity results in dissipation of magnetic energy into heat, kinetic energy and particle acceleration. Such a phenomenon is considered as an efficient mechanism for energy release in laboratory and astrophysical plasmas. An important question is how to make the process fast enough to account for observed explosive energy releases. The classical model for steady state magnetic reconnection predicts reconnection times scaling as S1/2 (where S is the Lundquist number) and yields time-scales several order of magnitude larger than the observed ones. Earlier two-dimensional MHD simulations showed that for large Lundquist number the reconnection time becomes independent of S (`fast reconnection' regime) due to the presence of the secondary tearing instability that takes place for S ≳ 1 × 104. We report on our 3D MHD simulations of magnetic reconnection in a magnetically confined cylindrical plasma column under either a pressure balanced or a force-free equilibrium and compare the results with 2D simulations of a circular current sheet. We find that the 3D instabilities acting on these configurations result in a fragmentation of the initial current sheet in small filaments, leading to enhanced dissipation rate that becomes independent of the Lundquist number already at S ≃ 1 × 103.

  4. Final Report: Laboratory Studies of Spontaneous Reconnection and Intermittent Plasma Objects

    Energy Technology Data Exchange (ETDEWEB)

    Egedal-Pedersen, Jan [Massachusetts Institute of Technology; Porkolab, Miklos [Massachusetts Institute of Technology

    2011-05-31

    The study of the collisionless magnetic reconnection constituted the primary work carried out under this grant. The investigations utilized two magnetic configurations with distinct boundary conditions. Both configurations were based upon the Versatile Toroidal Facility (VTF) at the MIT Plasma Science and Fusion Center and the MIT Physics Department. The NSF/DOE award No. 0613734, supported two graduate students (now Drs. W. Fox and N. Katz) and material expenses. The grant enabled these students to operate the VTF basic plasma physics experiment on magnetic reconnection. The first configuration was characterized by open boundary conditions where the magnetic field lines interface directly with the vacuum vessel walls. The reconnection dynamics for this configuration has been methodically characterized and it has been shown that kinetic effects related to trapped electron trajectories are responsible for the high rates of reconnection observed. This type of reconnection has not been investigated before. Nevertheless, the results are directly relevant to observations by the Wind spacecraft of fast reconnection deep in the Earth magnetotail. The second configuration was developed to be relevant to specifically to numerical simulations of magnetic reconnection, allowing the magnetic field-lines to be contained inside the device. The configuration is compatible with the presence of large current sheets in the reconnection region and reconnection is observed in fast powerful bursts. These reconnection events facilitate the first experimental investigations of the physics governing the spontaneous onset of fast reconnection. In the Report we review the general motivation of this work and provide an overview of our experimental and theoretical results enabled by the support through the awards.

  5. Detection of thin current sheets and associated reconnection in the Earth's turbulent magnetosheath using cluster multi-point measurements

    Science.gov (United States)

    Chasapis, Alexandros; Retino, Alessandro; Sahraoui, Fouad; Greco, Antonella; Vaivads, Andris; Sundkvist, David; Canu, Patrick

    2013-04-01

    Magnetic reconnection occurs in turbulent plasma within a large number of volume-filling thin current sheets and is one major candidate for energy dissipation of turbulent plasma. Such dissipation results in particle heating and non-thermal particle acceleration. In situ observations are needed to study the detailed properties of thin current sheets and associated reconnection, in order to determine its importance as a dissipation mechanism at small scales. In particular, multi-point measurements are crucial to unambiguously identify spatial scales (e.g current sheet thickness) and estimate key quantities such as E*J. Here we present a study of the properties of thin current sheets detected in the Earths magnetosheath downstream of the quasi-parallel shock by using Cluster spacecraft data. The current sheets were detected by the rotation of the magnetic field as computed by four-point measurements. We study the distribution of current sheets as a function of the magnetic shear angle θ, their duration and the waiting time between consecutive current sheets. We found that high shear (θ > 90 degrees) current sheets show different properties with respect to low shear current sheets (θ < 90 degrees). These high-shear current sheets account for about ˜ 20% of the total and have an average thickness comparable to the ion inertial length. We also compare our four-point detection method with other single-point methods (e.g. Partial Variance of Increments - PVI) and we discuss the results of such comparison.

  6. Slowing of Magnetic Reconnection Concurrent with Weakening Plasma Inflows and Increasing Collisionality in Strongly Driven Laser-Plasma Experiments.

    Science.gov (United States)

    Rosenberg, M J; Li, C K; Fox, W; Zylstra, A B; Stoeckl, C; Séguin, F H; Frenje, J A; Petrasso, R D

    2015-05-22

    An evolution of magnetic reconnection behavior, from fast jets to the slowing of reconnection and the establishment of a stable current sheet, has been observed in strongly driven, β≲20 laser-produced plasma experiments. This process has been inferred to occur alongside a slowing of plasma inflows carrying the oppositely directed magnetic fields as well as the evolution of plasma conditions from collisionless to collisional. High-resolution proton radiography has revealed unprecedented detail of the forced interaction of magnetic fields and super-Alfvénic electron jets (V_{jet}∼20V_{A}) ejected from the reconnection region, indicating that two-fluid or collisionless magnetic reconnection occurs early in time. The absence of jets and the persistence of strong, stable magnetic fields at late times indicates that the reconnection process slows down, while plasma flows stagnate and plasma conditions evolve to a cooler, denser, more collisional state. These results demonstrate that powerful initial plasma flows are not sufficient to force a complete reconnection of magnetic fields, even in the strongly driven regime.

  7. Magnetic reconnection rate in space plasmas: a fractal approach.

    Science.gov (United States)

    Materassi, Massimo; Consolini, Giuseppe

    2007-10-26

    Magnetic reconnection is generally discussed via a fluid description. Here, we evaluate the reconnection rate assuming a fractal topology of the reconnection region. The central idea is that the fluid hypothesis may be violated at the scales where reconnection takes place. The reconnection rate, expressed as the Alfvén Mach number of the plasma moving toward the diffusion region, is shown to depend on the fractal dimension and on the sizes of the reconnection or diffusion region. This mechanism is more efficient than prediction of the Sweet-Parker model and even Petschek's model for finite magnetic Reynolds number. A good agreement also with rates given by Hall MHD models is found. A discussion of the fractal assumption on the diffusion region in terms of current microstructures is proposed. The comparison with in-situ satellite observations suggests the reconnection region to be a filamentary domain.

  8. New aspects of plasma sheet dynamics - MHD and kinetic theory

    Directory of Open Access Journals (Sweden)

    H. Wiechen

    Full Text Available Magnetic reconnection is a process of fundamental importance for the dynamics of the Earth's plasma sheet. In this context, the development of thin current sheets in the near-Earth plasma sheet is a topic of special interest because they could be a possible cause of microscopic fluctuations acting as collective non-idealness from a macroscopic point of view. Simulations of the near-Earth plasma sheet including boundary perturbations due to localized inflow through the northern (or southern plasma sheet boundary show developing thin current sheets in the near-Earth plasma sheet about 810 RE tailwards of the Earth. This location is largely independent from the localization of the perturbation. The second part of the paper deals with the problem of the macroscopic non-ideal consequences of microscopic fluctuations. A new model is presented that allows the quantitative calculation of macroscopic non-idealness without considering details of microscopic instabilities or turbulence. This model is only based on the assumption of a strongly fluctuating, mixing dynamics on microscopic scales in phase space. The result of this approach is an expression for anomalous non-idealness formally similar to the Krook resistivity but now describing the macroscopic consequences of collective microscopic fluctuations, not of collisions.

    Key words. Magnetospheric physics (plasma sheet · Space plasma physics (kinetic and MHD theory; magnetic reconnection

  9. Nonthermal Particle Acceleration in 3D Relativistic Magnetic Reconnection in Pair Plasma

    Science.gov (United States)

    Werner, Gregory R.; Uzdensky, Dmitri A.

    2017-07-01

    As a fundamental process converting magnetic to plasma energy in high-energy astrophysical plasmas, relativistic magnetic reconnection is a leading explanation for the acceleration of particles to the ultrarelativistic energies that are necessary to power nonthermal emission (especially X-rays and gamma-rays) in pulsar magnetospheres and pulsar wind nebulae, coronae and jets of accreting black holes, and gamma-ray bursts. An important objective of plasma astrophysics is therefore the characterization of nonthermal particle acceleration (NTPA) effected by reconnection. Reconnection-powered NTPA has been demonstrated over a wide range of physical conditions using large 2D kinetic simulations. However, its robustness in realistic 3D reconnection—in particular, whether the 3D relativistic drift-kink instability (RDKI) disrupts NTPA—has not been systematically investigated, although pioneering 3D simulations have observed NTPA in isolated cases. Here, we present the first comprehensive study of NTPA in 3D relativistic reconnection in collisionless electron-positron plasmas, characterizing NTPA as the strength of 3D effects is varied systematically via the length in the third dimension and the strength of the guide magnetic field. We find that, while the RDKI prominently perturbs 3D reconnecting current sheets, it does not suppress particle acceleration, even for zero guide field; fully 3D reconnection robustly and efficiently produces nonthermal power-law particle spectra closely resembling those obtained in 2D. This finding provides strong support for reconnection as the key mechanism powering high-energy flares in various astrophysical systems. We also show that strong guide fields significantly inhibit NTPA, slowing reconnection and limiting the energy available for plasma energization, yielding steeper and shorter power-law spectra.

  10. Explosive turbulent magnetic reconnection.

    Science.gov (United States)

    Higashimori, K; Yokoi, N; Hoshino, M

    2013-06-21

    We report simulation results for turbulent magnetic reconnection obtained using a newly developed Reynolds-averaged magnetohydrodynamics model. We find that the initial Harris current sheet develops in three ways, depending on the strength of turbulence: laminar reconnection, turbulent reconnection, and turbulent diffusion. The turbulent reconnection explosively converts the magnetic field energy into both kinetic and thermal energy of plasmas, and generates open fast reconnection jets. This fast turbulent reconnection is achieved by the localization of turbulent diffusion. Additionally, localized structure forms through the interaction of the mean field and turbulence.

  11. Three-dimensional evolution of a relativistic current sheet: triggering of magnetic reconnection by the guide field.

    Science.gov (United States)

    Zenitani, S; Hoshino, M

    2005-08-26

    The linear and nonlinear evolution of a relativistic current sheet of pair (e(+/-)) plasmas is investigated by three-dimensional particle-in-cell simulations. In a Harris configuration, it is obtained that the magnetic energy is fast dissipated by the relativistic drift kink instability (RDKI). However, when a current-aligned magnetic field (the so-called "guide field") is introduced, the RDKI is stabilized by the magnetic tension force and it separates into two obliquely propagating modes, which we call the relativistic drift-kink-tearing instability. These two waves deform the current sheet so that they trigger relativistic magnetic reconnection at a crossover thinning point. Since relativistic reconnection produces a lot of nonthermal particles, the guide field is of critical importance to study the energetics of a relativistic current sheet.

  12. Plasma Relaxation Dynamics Moderated by Current Sheets

    Science.gov (United States)

    Dewar, Robert; Bhattacharjee, Amitava; Yoshida, Zensho

    2014-10-01

    Ideal magnetohydrodynamics (IMHD) is strongly constrained by an infinite number of microscopic constraints expressing mass, entropy and magnetic flux conservation in each infinitesimal fluid element, the latter preventing magnetic reconnection. By contrast, in the Taylor-relaxed equilibrium model all these constraints are relaxed save for global magnetic flux and helicity. A Lagrangian is presented that leads to a new variational formulation of magnetized fluid dynamics, relaxed MHD (RxMHD), all static solutions of which are Taylor equilibrium states. By postulating that some long-lived macroscopic current sheets can act as barriers to relaxation, separating the plasma into multiple relaxation regions, a further generalization, multi-relaxed MHD (MRxMHD), is developed. These concepts are illustrated using a simple two-region slab model similar to that proposed by Hahm and Kulsrud--the formation of an initial shielding current sheet after perturbation by boundary rippling is calculated using MRxMHD and the final island state, after the current sheet has relaxed through a reconnection sequence, is calculated using RxMHD. Australian Research Council Grant DP110102881.

  13. Magnetic Reconnection in a Compressible MHD Plasma

    Science.gov (United States)

    Hesse, Michael; Birn, Joachim; Zenitani, Seiji

    2011-01-01

    Using steady-state resistive MHD, magnetic reconnection is reinvestigated for conditions of high resistivity/low magnetic Reynolds number, when the thickness of the diffusion region is no longer small compared to its length. Implicit expressions for the reconnection rate and other reconnection parameters are derived based on the requirements of mass, momentum, and energy conservation. These expressions are solved via simple iterative procedures. Implications specifically for low Reynolds number/high resistivity are being discussed

  14. On the ions acceleration via collisionless magnetic reconnection in laboratory plasmas

    Science.gov (United States)

    Cazzola, E.; Curreli, D.; Markidis, S.; Lapenta, G.

    2016-11-01

    This work presents an analysis of the ion outflow from magnetic reconnection throughout fully kinetic simulations with typical laboratory plasma values. A symmetric initial configuration for the density and magnetic field is considered across the current sheet. After analyzing the behavior of a set of nine simulations with a reduced mass ratio and with a permuted value of three initial electron temperatures and magnetic field intensity, the best ion acceleration scenario is further studied with a realistic mass ratio in terms of the ion dynamics and energy budget. Interestingly, a series of shock wave structures are observed in the outflow, resembling the shock discontinuities found in recent magnetohydrodynamic simulations. An analysis of the ion outflow at several distances from the reconnection point is presented, in light of possible laboratory applications. The analysis suggests that magnetic reconnection could be used as a tool for plasma acceleration, with applications ranging from electric propulsion to production of ion thermal beams.

  15. On the ions acceleration via collisionless magnetic reconnection in laboratory plasmas

    CERN Document Server

    Cazzola, Emanuele; Markidis, Stefano; Lapenta, Giovanni

    2016-01-01

    This work presents an analysis of the ion outflow from magnetic reconnection throughout fully kinetic simulations with typical laboratory plasmas values. A symmetric initial configuration for the density and magnetic field is considered across the current sheet. After analyzing the behavior of a set of nine simulations with a reduced mass ratio and with a permuted value of three initial electron temperature and magnetic field intensity, the best ion acceleration scenario is further studied with a realistic mass ratio in terms of the ion dynamics and energy budget. Interestingly, a series of shock waves structures are observed in the outflow, resembling the shock discontinuities found in recent magnetohydrodynamic (MHD) simulations. An analysis of the ion outflow at several distances from the reconnection point is presented, in light of possible laboratory applications. The analysis suggests that magnetic reconnection could be used as a tool for plasma acceleration, with applications ranging from electric prop...

  16. Fast reconnection in relativistic plasmas: the magnetohydrodynamics tearing instability revisited

    Science.gov (United States)

    Del Zanna, L.; Papini, E.; Landi, S.; Bugli, M.; Bucciantini, N.

    2016-08-01

    Fast reconnection operating in magnetically dominated plasmas is often invoked in models for magnetar giant flares, for magnetic dissipation in pulsar winds, or to explain the gamma-ray flares observed in the Crab nebula; hence, its investigation is of paramount importance in high-energy astrophysics. Here we study, by means of two-dimensional numerical simulations, the linear phase and the subsequent non-linear evolution of the tearing instability within the framework of relativistic resistive magnetohydrodynamics (MHD), as appropriate in situations where the Alfvén velocity approaches the speed of light. It is found that the linear phase of the instability closely matches the analysis in classical MHD, where the growth rate scales with the Lundquist number S as S-1/2, with the only exception of an enhanced inertial term due to the thermal and magnetic energy contributions. In addition, when thin current sheets of inverse aspect ratio scaling as S-1/3 are considered, the so-called ideal tearing regime is retrieved, with modes growing independently of S and extremely fast, on only a few light crossing times of the sheet length. The overall growth of fluctuations is seen to solely depend on the value of the background Alfvén velocity. In the fully non-linear stage, we observe an inverse cascade towards the fundamental mode, with Petschek-type supersonic jets propagating at the external Alfvén speed from the X-point, and a fast reconnection rate at the predicted value {R}˜ (ln S)^{-1}.

  17. Observational Study on Current Sheet of Magnetic Reconnection in Two Solar Eruptions

    Science.gov (United States)

    Qiang-wei, Cai; Ning, Wu; Jun, Lin

    2016-07-01

    The coronal magnetic configuration behind coronal mass ejections (CMEs) can commonly be stretched severely, thus to push the magnetic fields with opposite polarities to approach each other, and to form a current sheet of magnetic reconnection. The current sheet in solar eruptions is not only an important region to convert the magnetic free energy into thermal energy, plasma kinetic energy, and energetic particle beams, but also plays a role to connect CMEs and flares. In the CME events of 2003 January 3 and 2003 November 4, the development of current sheet has been observed in both cases. We have investigated the dynamic features and physical properties of current sheet in the two events, based on the data of LASCO (Large Angle and Spectrometric Coronagraph) and UVCS (Ultraviolet Coronagraph Spectrometer) on board of SOHO (Solar and Heliospheric Observatory), and the Hα data from BBSO (Big Bear Solar Observatory) and YNAO (Yunnan Astronomical Observatory). The existence of ions with a high degree of ionization, such as Fe+17 and Si+11, indicates a high temperature up to 3×106 ∼5×106 K in the region of current sheet. A direct measurement shows that the thickness of current sheet varies between 1.3×104 and 1.1×105 km, which increases first and then decreases with time. Using the CHIANTI code (v.7.1), we have further calculated the average values of electron temperature and corresponding emission measure (EM) respectively to be 3.86×106 K and 6.1×1024 cm-5 in the current sheet of the 2003 January 3 event. We also find that the current sheet twisted forth and back quasi-periodically during the eruption event on 2003 November 4 by analyzing the observational data from SOHO/UVCS.

  18. An Intrinsically Three-Dimensional Magnetic Reconnection Process in a Generalized Harris Sheet

    CERN Document Server

    Zhu, Ping; Wang, Zechen; Bonofiglo, Phillip

    2016-01-01

    A magnetic reconnection process in the generalized Harris sheet has been revealed to be intrinsically three-dimensional both geometrically and dynamically despite the spatial invariance of the original current sheet in the equilibrium current direction. The spatial distribution and structure of the quasi-separatrix layers, as well as their temporal emergence and evolution, indicate that the associated magnetic reconnection can only occur in a three-dimensional geometry which is irreducible to a two-dimensional reconnection process. Such a three-dimensional reconnection process is induced by the nonlinear development of an ideal MHD ballooning instability in the generalized Harris sheet, which is itself an intrinsically three-dimensional dynamic process.

  19. Bulk ion acceleration and particle heating during magnetic reconnection in a laboratory plasma

    Energy Technology Data Exchange (ETDEWEB)

    Yoo, Jongsoo; Yamada, Masaaki; Ji, Hantao; Jara-Almonte, Jonathan; Myers, Clayton E. [Center for Magnetic Self-Organization, Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

    2014-05-15

    Bulk ion acceleration and particle heating during magnetic reconnection are studied in the collisionless plasma of the Magnetic Reconnection Experiment (MRX). The plasma is in the two-fluid regime, where the motion of the ions is decoupled from that of the electrons within the ion diffusion region. The reconnection process studied here is quasi-symmetric since plasma parameters such as the magnitude of the reconnecting magnetic field, the plasma density, and temperature are compatible on each side of the current sheet. Our experimental data show that the in-plane (Hall) electric field plays a key role in ion heating and acceleration. The electrostatic potential that produces the in-plane electric field is established by electrons that are accelerated near the electron diffusion region. The in-plane profile of this electrostatic potential shows a “well” structure along the direction normal to the reconnection current sheet. This well becomes deeper and wider downstream as its boundary expands along the separatrices where the in-plane electric field is strongest. Since the in-plane electric field is 3–4 times larger than the out-of-plane reconnection electric field, it is the primary source of energy for the unmagnetized ions. With regard to ion acceleration, the Hall electric field causes ions near separatrices to be ballistically accelerated toward the outflow direction. Ion heating occurs as the accelerated ions travel into the high pressure downstream region. This downstream ion heating cannot be explained by classical, unmagnetized transport theory; instead, we conclude that ions are heated by re-magnetization of ions in the reconnection exhaust and collisions. Two-dimensional (2-D) simulations with the global geometry similar to MRX demonstrate downstream ion thermalization by the above mechanisms. Electrons are also significantly heated during reconnection. The electron temperature sharply increases across the separatrices and peaks just outside of the

  20. Explosive Magnetic Reconnection in Double-current Sheet Systems: Ideal versus Resistive Tearing Mode

    Science.gov (United States)

    Baty, Hubert

    2017-03-01

    Magnetic reconnection associated with the tearing instability occurring in double-current sheet systems is investigated within the framework of resistive magnetohydrodynamics (MHD) in a two-dimensional Cartesian geometry. A special emphasis on the existence of fast and explosive phases is taken. First, we extend the recent theory on the ideal tearing mode of a single-current sheet to a double-current layer configuration. A linear stability analysis shows that, in long and thin systems with (length to shear layer thickness) aspect ratios scaling as {S}L9/29 (S L being the Lundquist number based on the length scale L), tearing modes can develop on a fast Alfvénic timescale in the asymptotic limit {S}L\\to ∞ . The linear results are confirmed by means of compressible resistive MHD simulations at relatively high S L values (up to 3× {10}6) for different current sheet separations. Moreover, the nonlinear evolution of the ideal double tearing mode (IDTM) exhibits a richer dynamical behavior than its single-tearing counterpart, as a nonlinear explosive growth violently ends up with a disruption when the two current layers interact trough the merging of plasmoids. The final outcome of the system is a relaxation toward a new state, free of magnetic field reversal. The IDTM dynamics is also compared to the resistive double tearing mode dynamics, which develops in similar systems with smaller aspect ratios, ≳ 2π , and exhibits an explosive secondary reconnection, following an initial slow resistive growth phase. Finally, our results are used to discuss the flaring activity in astrophysical magnetically dominated plasmas, with a particular emphasis on pulsar systems.

  1. Electrodynamics in a Very Thin Current Sheet Leading to Magnetic Reconnection

    Science.gov (United States)

    Singh, Nagendra; Deverapalli, Chakri; Khazanov, George

    2006-01-01

    We study the formation of a very thin current sheet (CS) and associated plasma electrodynamics using three-dimensional (3-D) particle-in-cell simulations with ion to electron mass ratio M/m=1836. The CS is driven by imposed anti-parallel magnetic fields. The noteworthy features of the temporal evolution of the CS are the following: (i) Steepening of the magnetic field profile B,(z) in the central part of the CS, (ii) Generation of three-peak current distribution with the largest peak in the CS center as B,(z) steepens, (iii) Generation of converging electric fields forming a potential well in the CS center in which ions are accelerated. (iv) Electron and ion heating in the central part of the CS by current-driven instabilities (CDI). (v) Re-broadening of the CS due to increased kinetic plasma pressure in the CS center. (vi) Generation of electron temperature anisotropy with temperature perpendicular to the magnetic field being larger than the parallel one. (vii) Current disruption by electron trapping in an explosively growing electrostatic instability (EGEI) and electron tearing instability (ETI). (viii)The onset of EGEI coincides with an increase in the electron temperature above the temperature of the initially hot ions as well as the appearance of new shear in the electron drift velocity. (ix) Bifurcation of the central CS by the current disruption. (x) Magnetic reconnection (MR) beginning near the null in B, and spreading outward. (xi) Generation of highly energized electrons reaching relativistic speeds and having isotropic pitch-angle distribution in the region of reconnected magnetic fields. We compare some of these features of the current sheet with results from laboratory and space experiments.

  2. Electrodynamics in a very thin current sheet leading to magnetic reconnection

    Directory of Open Access Journals (Sweden)

    N. Singh

    2006-01-01

    Full Text Available We study the formation of a very thin current sheet (CS and associated plasma electrodynamics using three-dimensional (3-D particle-in-cell simulations with ion to electron mass ratio M/m=1836. The CS is driven by imposed anti-parallel magnetic fields. The noteworthy features of the temporal evolution of the CS are the following: (i Steepening of the magnetic field profile Bx(z in the central part of the CS, (ii Generation of three-peak current distribution with the largest peak in the CS center as Bx(z steepens, (iii Generation of converging electric fields forming a potential well in the CS center in which ions are accelerated. (iv Electron and ion heating in the central part of the CS by current-driven instabilities (CDI. (v Re-broadening of the CS due to increased kinetic plasma pressure in the CS center. (vi Generation of electron temperature anisotropy with temperature perpendicular to the magnetic field being larger than the parallel one. (vii Current disruption by electron trapping in an explosively growing electrostatic instability (EGEI and electron tearing instability (ETI. (viiiThe onset of EGEI coincides with an increase in the electron temperature above the temperature of the initially hot ions as well as the appearance of new shear in the electron drift velocity. (ix Bifurcation of the central CS by the current disruption. (x Magnetic reconnection (MR beginning near the null in Bx and spreading outward. (xi Generation of highly energized electrons reaching relativistic speeds and having isotropic pitch-angle distribution in the region of reconnected magnetic fields. We compare some of these features of the current sheet with results from laboratory and space experiments.

  3. Reconnection dynamics with secondary tearing instability in compressible Hall plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Z. W., E-mail: zwma@zju.edu.cn; Wang, L. C.; Li, L. J. [Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China)

    2015-06-15

    The dynamics of a secondary tearing instability is systematically investigated based on compressible Hall magnetohydrodynamic. It is found that in the early nonlinear phase of magnetic reconnection before onset of the secondary tearing instability, the geometry of the magnetic field in the reconnection region tends to form a Y-type structure in a weak Hall regime, instead of an X-type structure in a strong Hall regime. A new scaling law is found that the maximum reconnection rate in the early nonlinear stage is proportional to the square of the ion inertial length (γ∝d{sub i}{sup 2}) in the weak Hall regime. In the late nonlinear phase, the thin elongated current sheet associated with the Y-type geometry of the magnetic field breaks up to form a magnetic island due to a secondary tearing instability. After the onset of the secondary tearing mode, the reconnection rate is substantially boosted by the formation of the X-type geometries of magnetic field in the reconnection regions. With a strong Hall effect, the maximum reconnection rate linearly increases with the increase of the ion inertial length (γ∝d{sub i})

  4. Magnetic configuration of the distant plasma sheet - ISEE 3 observations

    Science.gov (United States)

    Slavin, J. A.; Smith, E. J.; Daly, P. W.; Sanderson, T. R.; Wenzel, K.-P.; Lepping, R. P.

    1987-01-01

    The influence of the IMF orientation and magnitude and substorm activity on the magnetic configuration of the central plasma sheet at 20-240 earth radii down the geomagnetic tail is investigated on the basis of ISEE-3 data. The results are presented graphically, and high-speed antisolar bulk flows threaded by southward magnetic fields are shown to be present in the distant plasma sheet after periods of substorm activity and southward IMF Bz. The effective dayside reconnection efficiency is estimated as 25 + or - 4 percent, in good agreement with theoretical models.

  5. Study of Local Reconnection Physics in a Laboratory Plasma

    Energy Technology Data Exchange (ETDEWEB)

    Hantao Ji; Troy Carter; Scott Hsu; Masaaki Yamada

    2001-06-11

    A short review of physics results obtained in the Magnetic Reconnection Experiment (MRX) is given with an emphasis on the local features of magnetic reconnection in a controlled environment. Stable two-dimensional current sheets are formed and sustained by induction using two internal coils. The observed reconnection rates are found to be quantitatively consistent with a generalized Sweet-Parker model which incorporates compressibility, unbalanced upstream-downstream pressure, and the effective resistivity. The latter is significantly enhanced over its classical values in the low collisionality regime. Strong local ion heating is measured by an optical probe during the reconnection process, and at least half of the increased ion energy must be due to nonclassical processes, consistent with the resistivity enhancement. Characteristics of high-frequency electrostatic and electromagnetic fluctuations detected in the current sheet suggest presence of the lower-hybrid-drift-like waves with significant magnetic components. The detailed structures of the current sheet are measured and compared with Harris theory and two-fluid theory.

  6. Laboratory study of magnetic reconnection with a density asymmetry across the current sheet.

    Science.gov (United States)

    Yoo, Jongsoo; Yamada, Masaaki; Ji, Hantao; Jara-Almonte, Jonathan; Myers, Clayton E; Chen, Li-Jen

    2014-08-29

    The effects of a density asymmetry across the current sheet on anti-parallel magnetic reconnection are studied systematically in a laboratory plasma. Despite a significant density ratio of up to 10, the in-plane magnetic field profile is not significantly changed. On the other hand, the out-of-plane Hall magnetic field profile is considerably modified; it is almost bipolar in structure with the density asymmetry, as compared to quadrupolar in structure with the symmetric configuration. Moreover, the ion stagnation point is shifted to the low-density side, and the electrostatic potential profile also becomes asymmetric with a deeper potential well on the low-density side. Nonclassical bulk electron heating together with electromagnetic fluctuations in the lower hybrid frequency range is observed near the low-density-side separatrix. The dependence of the ion outflow and reconnection electric field on the density asymmetry is measured and compared with theoretical expectations. The measured ion outflow speeds are about 40% of the theoretical values.

  7. Magnetic Reconnection

    Energy Technology Data Exchange (ETDEWEB)

    Masaaki Yamada, Russell Kulsrud and Hantao Ji

    2009-09-17

    We review the fundamental physics of magnetic reconnection in laboratory and space plasmas, by discussing results from theory, numerical simulations, observations from space satellites, and the recent results from laboratory plasma experiments. After a brief review of the well-known early work, we discuss representative recent experimental and theoretical work and attempt to interpret the essence of significant modern findings. In the area of local reconnection physics, many significant findings have been made with regard to two- uid physics and are related to the cause of fast reconnection. Profiles of the neutral sheet, Hall currents, and the effects of guide field, collisions, and micro-turbulence are discussed to understand the fundamental processes in a local reconnection layer both in space and laboratory plasmas. While the understanding of the global reconnection dynamics is less developed, notable findings have been made on this issue through detailed documentation of magnetic self-organization phenomena in fusion plasmas. Application of magnetic reconnection physics to astrophysical plasmas is also brie y discussed.

  8. Strongly Driven Magnetic Reconnection in a Magnetized High-Energy-Density Plasma

    Science.gov (United States)

    Fiksel, G.; Barnak, D. H.; Chang, P.-Y.; Haberberger, D.; Hu, S. X.; Ivancic, S.; Nilson, P. M.; Fox, W.; Deng, W.; Bhattacharjee, A.; Germaschewski, K.

    2014-10-01

    Magnetic reconnection in a magnetized high-energy-density plasma is characterized by measuring the dynamics of the plasma density and magnetic field between two counter-propagating and colliding plasma flows. The density and magnetic field were profiled using the 4 ω angular filter refractometry and fast proton deflectometry diagnostics, respectively. The plasma flows are created by irradiating oppositely placed plastic targets with 1.8-kJ, 2-ns laser beams on the OMEGA EP Laser System. The two plumes are magnetized by an externally controlled magnetic field with an x-type null point geometry with B = 0 at the midplane and B = 8 T at the targets. The interaction region is pre-filled with a low-density background plasma. The counterflowing super-Alfvénic plasma plumes sweep up and compress the magnetic field and the background plasma into a pair of magnetized ribbons, which collide, stagnate, and reconnect at the midplane, allowing for the first detailed observation of a stretched current sheet in laser-driven reconnection experiments. The measurements are in good agreement with first-principles particle-in-cell simulations. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944 and NLUF Grant DE-SC0008655.

  9. Particle heating and acceleration during collisionless reconnection in a laboratory plasma

    Science.gov (United States)

    Yoo, Jongsoo

    2013-10-01

    Particle heating and acceleration during magnetic reconnection is studied in the collisionless plasma of the Magnetic Reconnection Experiment (MRX). For ion heating and acceleration, the role of the in-plane (Hall) electric field is emphasized. An in-plane electrostatic potential profile is established by electron acceleration near the X-point. The potential profile shows a well structure along the direction normal to the reconnection current sheet that becomes deeper and wider downstream as its boundary expands along the separatrices where the in-plane electric field is strongest. The Hall electric field ballistically accelerates ions near the separatrices toward the outflow direction. After ions are accelerated, they are heated as they travel into the high-pressure downstream region due to an effect called re-magnetization. Electrons are also significantly heated during reconnection. The electron temperature sharply increases across the separatrices and peaks just outside of the electron diffusion region. Classical Ohmic dissipation based on the perpendicular Spitzer resistivity is too small to compensate for the energy loss by parallel heat conduction, indicating the presence of anomalous electron heating. Finally, a total energy inventory is calculated based on analysis of the Poynting, enthalpy, flow energy, and heat flux in the measured diffusion layer. More than half of the incoming magnetic energy is converted to particle energy during reconnection. The author thanks contributions from M. Yamada, H. Ji, J. Jara-Almonte, and C. E. Myers. This work is supported by DOE and NSF.

  10. Fast reconnection in relativistic plasmas: the magnetohydrodynamics tearing instability revisited

    CERN Document Server

    Del Zanna, L; Landi, S; Bugli, M; Bucciantini, N

    2016-01-01

    Fast reconnection operating in magnetically dominated plasmas is often invoked in models for magnetar giant flares, for magnetic dissipation in pulsar winds, or to explain the gamma-ray flares observed in the Crab nebula, hence its investigation is of paramount importance in high-energy astrophysics. Here we study, by means of two dimensional numerical simulations, the linear phase and the subsequent nonlinear evolution of the tearing instability within the framework of relativistic resistive magnetohydrodynamics, as appropriate in situations where the Alfven velocity approaches the speed of light. It is found that the linear phase of the instability closely matches the analysis in classical MHD, where the growth rate scales with the Lundquist number S as S^-1/2, with the only exception of an enhanced inertial term due to the thermal and magnetic energy contributions. In addition, when thin current sheets of inverse aspect ratio scaling as S^-1/3 are considered, the so-called "ideal" tearing regime is retriev...

  11. Magnetic Reconnection: A Fundamental Process in Space Plasmas

    Science.gov (United States)

    Hesse, Michael

    2010-01-01

    For many years, collisionless magnetic reconnect ion has been recognized as a fundamental process, which facilitates plasma transport and energy release in systems ranging from the astrophysical plasmas to magnetospheres and even laboratory plasma. Beginning with work addressing solar dynamics, it has been understood that reconnection is essential to explain solar eruptions, the interaction of the solar wind with the magnetosphere, and the dynamics of the magnetosphere. Accordingly, the process of magnetic reconnection has been and remains a prime target for space-based and laboratory studies, as well as for theoretical research. Much progress has been made throughout the years, beginning with indirect verifications by studies of processes enabled by reconnection, such as Coronal Mass Ejections, Flux Transfer Events, and Plasmoids. Theoretical advances have accompanied these observations, moving knowledge beyond the Sweet-Parker theory to the recognition that other, collisionless, effects are available and likely to support much faster reconnect ion rates. At the present time we are therefore near a break-through in our understanding of how collisionless reconnect ion works. Theory and modeling have advanced to the point that two competing theories are considered leading candidates for explaining the microphysics of this process. Both theories predict very small spatial and temporal scales. which are. to date, inaccessible to space-based or laboratory measurements. The need to understand magnetic reconnect ion has led NASA to begin the implementation of a tailored mission, Magnetospheric MultiScale (MMS), a four spacecraft cluster equipped to resolve all relevant spatial and temporal scales. In this presentation, we present an overview of current knowledge as well as an outlook towards measurements provided by MMS.

  12. Magnetic Reconnection Onset via Disruption of a Forming Current Sheet by the Tearing Instability.

    Science.gov (United States)

    Uzdensky, D A; Loureiro, N F

    2016-03-11

    The recent realization that Sweet-Parker current sheets are violently unstable to the secondary tearing (plasmoid) instability implies that such current sheets cannot occur in real systems. This suggests that, in order to understand the onset of magnetic reconnection, one needs to consider the growth of the tearing instability in a current layer as it is being formed. Such an analysis is performed here in the context of nonlinear resistive magnetohydrodynamics for a generic time-dependent equilibrium representing a gradually forming current sheet. It is shown that two onset regimes, single-island and multi-island, are possible, depending on the rate of current sheet formation. A simple model is used to compute the criterion for transition between these two regimes, as well as the reconnection onset time and the current sheet parameters at that moment. For typical solar corona parameters, this model yields results consistent with observations.

  13. Effects of auroral potential drops on plasma sheet dynamics

    Science.gov (United States)

    Xi, Sheng; Lotko, William; Zhang, Binzheng; Wiltberger, Michael; Lyon, John

    2016-11-01

    The reaction of the magnetosphere-ionosphere system to dynamic auroral potential drops is investigated using the Lyon-Fedder-Mobarry global model including, for the first time in a global simulation, the dissipative load of field-aligned potential drops in the low-altitude boundary condition. This extra load reduces the field-aligned current (j||) supplied by nightside reconnection dynamos. The system adapts by forcing the nightside X line closer to Earth, with a corresponding reduction in current lensing (j||/B = constant) at the ionosphere and additional contraction of the plasma sheet during substorm recovery and steady magnetospheric convection. For steady and moderate solar wind driving and with constant ionospheric conductance, the cross polar cap potential and hemispheric field-aligned current are lower by approximately the ratio of the peak field-aligned potential drop to the cross polar cap potential (10-15%) when potential drops are included. Hemispheric ionospheric Joule dissipation is less by 8%, while the area-integrated, average work done on the fluid by the reconnecting magnetotail field increases by 50% within |y| < 8 RE. Effects on the nightside plasma sheet include (1) an average X line 4 RE closer to Earth; (2) a 12% higher mean reconnection rate; and (3) dawn-dusk asymmetry in reconnection with a 17% higher rate in the premidnight sector.

  14. THIN CURRENT SHEETS AND ASSOCIATED ELECTRON HEATING IN TURBULENT SPACE PLASMA

    Energy Technology Data Exchange (ETDEWEB)

    Chasapis, A.; Retinò, A.; Sahraoui, F.; Canu, P. [Laboratoire de Physique des Plasmas, Ecole Polytechnique, Palaiseau, F-91128 (France); Vaivads, A.; Khotyaintsev, Yu. V. [Swedish Institute of Space Physics, Uppsala (Sweden); Sundkvist, D. [Space Sciences Laboratory, University of California, Berkeley, CA (United States); Greco, A. [Dipartimento di Fisica, Universita della Calabria (Italy); Sorriso-Valvo, L., E-mail: alexandros.chasapis@lpp.polytechnique.fr [IMIP-CNR, U.O.S. LICRYL di Cosenza (Italy)

    2015-05-01

    Intermittent structures, such as thin current sheets, are abundant in turbulent plasmas. Numerical simulations indicate that such current sheets are important sites of energy dissipation and particle heating occurring at kinetic scales. However, direct evidence of dissipation and associated heating within current sheets is scarce. Here, we show a new statistical study of local electron heating within proton-scale current sheets by using high-resolution spacecraft data. Current sheets are detected using the Partial Variance of Increments (PVI) method which identifies regions of strong intermittency. We find that strong electron heating occurs in high PVI (>3) current sheets while no significant heating occurs in low PVI cases (<3), indicating that the former are dominant for energy dissipation. Current sheets corresponding to very high PVI (>5) show the strongest heating and most of the time are consistent with ongoing magnetic reconnection. This suggests that reconnection is important for electron heating and dissipation at kinetic scales in turbulent plasmas.

  15. Hamiltonian vortices and reconnection in a magnetized plasma

    NARCIS (Netherlands)

    Kuvshinov, B. N.; Lakhin, V. P.; Pegoraro, F.; Schep, T. J.

    1998-01-01

    Hamiltonian vortices and reconnection in magnetized plasmas are investigated analytically and numerically using a two-fluid model. The equations are written in the Lagrangian form of three fields that are advected with different velocities. This system can be considered as a generalization and exten

  16. A multi-model plasma simulation of collisionless magnetic reconnection

    Science.gov (United States)

    Datta, I. A. M.; Shumlak, U.; Ho, A.; Miller, S. T.

    2016-10-01

    Collisionless magnetic reconnection is a process relevant to many areas of plasma physics in which energy stored in magnetic fields within highly conductive plasmas is rapidly converted to plasma energy. A full understanding of this phenomenon, however, is currently incomplete as models developed to date have difficulty explaining the fast reconnection rates often seen in nature, such as in the case of solar flares. Therefore, this behavior represents an area of much research in which various plasma models have been tested in order to understand the proper physics explaining the reconnection process. In this research, the WARPXM code developed at the University of Washington is used to study the problem using a hybrid multi-model simulation employing Hall-MHD and two-fluid plasma models. The simulation is performed on a decomposed domain where different plasma models are solved in different regions, depending on a trade-off between each model's physical accuracy and associated computational expense in each region. The code employs a discontinuous Galerkin (DG) finite element spatial discretization coupled with a Runge-Kutta scheme for time advancement and uses boundary conditions to couple the different plasma models. This work is supported by a Grant from the United States Air Force Office of Scientific Research.

  17. Collisionless reconnection: Mechanism of self-ignition in thin current sheets

    OpenAIRE

    2010-01-01

    The spontaneous onset of magnetic reconnection in thin plane collisionless current sheets is shown to result from a thermal-anisotropy driven non-relativistic magnetic electron Weibel-mode, generating seed-magnetic field X-points in the centre of the current layer. The proposed mechanism is of larger generality. It also works in the presence of magnetic guide fields.

  18. Collisionless reconnection: Mechanism of self-ignition in thin current sheets

    CERN Document Server

    Treumann, R A; Baumjohann, W

    2010-01-01

    The spontaneous onset of magnetic reconnection in thin collisionless current sheets is shown to result from a thermal-anisotropy driven magnetic Weibel-mode, generating seed-magnetic field {\\sf X}-points in the centre of the current layer.

  19. Collisionless reconnection: mechanism of self-ignition in thin plane homogeneous current sheets

    Science.gov (United States)

    Treumann, R. A.; Nakamura, R.; Baumjohann, W.

    2010-10-01

    The spontaneous onset of magnetic reconnection in thin plane collisionless current sheets is shown to result from a thermal-anisotropy driven non-relativistic magnetic electron Weibel-mode, generating seed-magnetic field X-points in the centre of the current layer. The proposed mechanism is of larger generality. It also works in the presence of magnetic guide fields.

  20. Thin Current Sheets and Associated Electron Heating in Turbulent Space Plasma

    Science.gov (United States)

    Chasapis, A.; Retinò, A.; Sahraoui, F.; Vaivads, A.; Khotyaintsev, Yu. V.; Sundkvist, D.; Greco, A.; Sorriso-Valvo, L.; Canu, P.

    2015-05-01

    Intermittent structures, such as thin current sheets, are abundant in turbulent plasmas. Numerical simulations indicate that such current sheets are important sites of energy dissipation and particle heating occurring at kinetic scales. However, direct evidence of dissipation and associated heating within current sheets is scarce. Here, we show a new statistical study of local electron heating within proton-scale current sheets by using high-resolution spacecraft data. Current sheets are detected using the Partial Variance of Increments (PVI) method which identifies regions of strong intermittency. We find that strong electron heating occurs in high PVI (>3) current sheets while no significant heating occurs in low PVI cases (5) show the strongest heating and most of the time are consistent with ongoing magnetic reconnection. This suggests that reconnection is important for electron heating and dissipation at kinetic scales in turbulent plasmas.

  1. Suppression of Collisionless Magnetic Reconnection in Asymmetric Current Sheets

    Science.gov (United States)

    Liu, Yi-Hsin; Hesse, Michael

    2016-01-01

    Using fully kinetic simulations, we study the suppression of asymmetric reconnection in the limit where the diamagnetic drift speed >> Alfven speed and the magnetic shear angle is moderate. We demonstrate that the slippage between electrons and the magnetic flux mitigates the suppression and can even result in fast reconnection that lacks one of the outflow jets. Through comparing a case where the diamagnetic drift is supported by the temperature gradient with a companion case that has a density gradient instead, we identify a robust suppression mechanism. The drift of the x-line is slowed down locally by the asymmetric nature of the x-line, and then the x-line is run over and swallowed by the faster-moving following flux.

  2. Forced current sheet structure, formation and evolution: application to magnetic reconnection in the magnetosphere

    Directory of Open Access Journals (Sweden)

    V. I. Domrin

    2004-07-01

    Full Text Available By means of a simulation model, the earlier predicted nonlinear kinetic structure, a Forced Kinetic Current Sheet (FKCS, with extremely anisotropic ion distributions, is shown to appear as a result of a fast nonlinear process of transition from a previously existing equilibrium. This occurs under triggering action of a weak MHD disturbance that is applied at the boundary of the simulation box. In the FKCS, current is carried by initially cold ions which are brought into the CS by convection from both sides, and accelerated inside the CS. The process then appears to be spontaneously self-sustained, as a MHD disturbance of a rarefaction wave type propagates over the background plasma outside the CS. Comparable to the Alfvénic discontinuity in MHD, transformation of electromagnetic energy into the energy of plasma flows occurs at the FKCS. But unlike the MHD case, ``free" energy is produced here: dissipation should occur later, through particle interaction with turbulent waves generated by unstable ion distribution being formed by the FKCS action. In this way, an effect of magnetic field ``annihilation" appears, required for fast magnetic reconnection. Application of the theory to observations at the magnetopause and in the magnetotail is considered.

  3. Particle Acceleration and Plasma Dynamics during Magnetic Reconnection in the Magnetically-dominated Regime

    CERN Document Server

    Guo, Fan; Daughton, William; Li, Hui

    2015-01-01

    Magnetic reconnection is thought to be the driver for many explosive phenomena in the universe. The energy release and particle acceleration during reconnection have been proposed as a mechanism for producing high-energy emissions and cosmic rays. We carry out two- and three-dimensional kinetic simulations to investigate relativistic magnetic reconnection and the associated particle acceleration. The simulations focus on electron-positron plasmas starting with a magnetically dominated, force-free current sheet ($\\sigma \\equiv B^2/(4\\pi n_e m_e c^2) \\gg 1$). For this limit, we demonstrate that relativistic reconnection is highly efficient at accelerating particles through a first-order Fermi process accomplished by the curvature drift of particles along the electric field induced by the relativistic flows. This mechanism gives rise to the formation of hard power-law spectra $f \\propto (\\gamma-1)^{-p}$ and approaches $p = 1$ for sufficiently large $\\sigma$ and system size. Eventually most of the available magne...

  4. The Onset of Magnetic Reconnection: Tearing Instability in Current Sheets with a Guide Field

    Science.gov (United States)

    Daldorff, Lars K. S.; Klimchuk, James A.; Leake, James E.; Knizhnik, Kalman

    2017-08-01

    Magnetic reconnection is fundamental to many solar phenomena, ranging from coronal heating, to jets, to flares and CMEs. A poorly understood yet crucial aspect of reconnection is that it does not occur until magnetic stresses have built to sufficiently high levels for significant energy release. If reconnection were to happen too soon, coronal heating would be weak and flares would be small. As part of our program to study the onset conditions for magnetic reconnection, we have investigated the instability of current sheets to tearing. Surprisingly little work has been done on this problem for sheets that include a guide field, i.e., for which the field rotates by less than 180 degrees. This is the most common situation on the Sun. We present numerical 3D resistive MHD simulations of several sheets and show how the behavior depends on the shear angle (rotation). We compare our results to the predictions of linear theory and discuss the nonlinear evolution in terms of plasmoid formation and the interaction of different oblique tearing modes. The relevance to the Sun is explained.

  5. Scaling of Magnetic Reconnection in Relativistic Collisionless Pair Plasmas

    Science.gov (United States)

    Liu, Yi-Hsin; Guo, Fan; Daughton, William; Li, Hui; Hesse, Michael

    2015-01-01

    Using fully kinetic simulations, we study the scaling of the inflow speed of collisionless magnetic reconnection in electron-positron plasmas from the non-relativistic to ultra-relativistic limit. In the anti-parallel configuration, the inflow speed increases with the upstream magnetization parameter sigma and approaches the speed of light when sigma is greater than O(100), leading to an enhanced reconnection rate. In all regimes, the divergence of the pressure tensor is the dominant term responsible for breaking the frozen-in condition at the x-line. The observed scaling agrees well with a simple model that accounts for the Lorentz contraction of the plasma passing through the diffusion region. The results demonstrate that the aspect ratio of the diffusion region, modified by the compression factor of proper density, remains approximately 0.1 in both the non-relativistic and relativistic limits.

  6. Conversion of magnetic energy in the magnetic reconnection layer of a laboratory plasma.

    Science.gov (United States)

    Yamada, Masaaki; Yoo, Jongsoo; Jara-Almonte, Jonathan; Ji, Hantao; Kulsrud, Russell M; Myers, Clayton E

    2014-09-10

    Magnetic reconnection, in which magnetic field lines break and reconnect to change their topology, occurs throughout the universe. The essential feature of reconnection is that it energizes plasma particles by converting magnetic energy. Despite the long history of reconnection research, how this energy conversion occurs remains a major unresolved problem in plasma physics. Here we report that the energy conversion in a laboratory reconnection layer occurs in a much larger region than previously considered. The mechanisms for energizing plasma particles in the reconnection layer are identified, and a quantitative inventory of the converted energy is presented for the first time in a well-defined reconnection layer; 50% of the magnetic energy is converted to particle energy, 2/3 of which transferred to ions and 1/3 to electrons. Our results are compared with simulations and space measurements, for a key step towards resolving one of the most important problems in plasma physics.

  7. Physical processes of driven magnetic reconnection in collisionless plasmas: Zero guide field case

    Science.gov (United States)

    Cheng, C. Z.; Inoue, S.; Ono, Y.; Horiuchi, R.

    2015-10-01

    The key physical processes of the electron and ion dynamics, the structure of the electric and magnetic fields, and how particles gain energy in the driven magnetic reconnection in collisionless plasmas for the zero guide field case are presented. The key kinetic physics is the decoupling of electron and ion dynamics around the magnetic reconnection region, where the magnetic field is reversed and the electron and ion orbits are meandering, and around the separatrix region, where electrons move mainly along the field line and ions move mainly across the field line. The decoupling of the electron and ion dynamics causes charge separation to produce a pair of in-plane bipolar converging electrostatic electric field ( E→ e s ) pointing toward the neutral sheet in the magnetic field reversal region and the monopolar E→ e s around the separatrix region. A pair of electron jets emanating from the reconnection current layer generate the quadrupole out-of-plane magnetic field, which causes the parallel electric field ( E→ || ) from E→ i n d to accelerate particles along the magnetic field. We explain the electron and ion dynamics and their velocity distributions and flow structures during the time-dependent driven reconnection as they move from the upstream to the downstream. In particular, we address the following key physics issues: (1) the decoupling of electron and ion dynamics due to meandering orbits around the field reversal region and the generation of a pair of converging bipolar electrostatic electric field ( E→ e s ) around the reconnection region; (2) the slowdown of electron and ion inflow velocities due to acceleration/deceleration of electrons and ions by E→ e s as they move across the neutral sheet; (3) how the reconnection current layer is enhanced and how the orbit meandering particles are accelerated inside the reconnection region by E→ i n d ; (4) why the electron outflow velocity from the reconnection region reaches super-Alfvenic speed

  8. Thin current sheets caused by plasma flow gradients in space plasma

    Science.gov (United States)

    Nickeler, D.; Wiegelmann, T.

    2011-12-01

    To understand complex space plasma systems like the solar wind-magnetosphere coupling, we need to have a good knowledge of the slowly evolving equilibrium state. The slow change of external constraints on the system (for example boundary conditions or other external parameters) lead in many cases to the formation of current sheets. These current sheets can trigger micro-instabilities, which cause resistivity on fluid scales. Consequently resistive instabilities like magnetic reconnection can occur and the systems evolves dynamically. Therefore such a picture of quasi-magneto-hydro-static changes can explain the quasy-static phase of many space plasma before an eruption occurs. Within this work we extend the theory by the inclusion of a nonlinear stationary plasma flows. Our analysis shows that stationary plasma flows with strong flow gradients (for example the solar wind magnetosphere coupling) can be responsible for the existence or generation of current sheets.

  9. Heating mechanisms in the low solar atmosphere through magnetic reconnection in current sheets

    CERN Document Server

    Ni, Lei; Roussev, Ilia I; Schmieder, Brigitte

    2016-01-01

    We simulate several magnetic reconnection processes in the low solar chromosphere/photosphere, the radiation cooling, heat conduction and ambipolar diffusion are all included. Our numerical results indicate that both the high temperature($ \\gtrsim 8\\times10^4$~K) and low temperature($\\sim 10^4$~K) magnetic reconnection events can happen in the low solar atmosphere ($100\\sim600$~km above the solar surface). The plasma $\\beta$ controlled by plasma density and magnetic fields is one important factor to decide how much the plasma can be heated up. The low temperature event is formed in a high $\\beta$ magnetic reconnection process, Joule heating is the main mechanism to heat plasma and the maximum temperature increase is only several thousand Kelvin. The high temperature explosions can be generated in a low $\\beta$ magnetic reconnection process, slow and fast-mode shocks attached at the edges of the well developed plasmoids are the main physical mechanisms to heat the plasma from several thousand Kelvin to over $8...

  10. Collisionless reconnection: mechanism of self-ignition in thin plane homogeneous current sheets

    Directory of Open Access Journals (Sweden)

    R. A. Treumann

    2010-10-01

    Full Text Available The spontaneous onset of magnetic reconnection in thin plane collisionless current sheets is shown to result from a thermal-anisotropy driven non-relativistic magnetic electron Weibel-mode, generating seed-magnetic field X-points in the centre of the current layer. The proposed mechanism is of larger generality. It also works in the presence of magnetic guide fields.

  11. Pulsar scintillations from corrugated reconnection sheets in the ISM

    CERN Document Server

    Pen, Ue-Li

    2013-01-01

    We show that surface waves along interstellar current sheets closely aligned with the line of sight lead to pulsar scintillation properties consistent with those observed. By contrast with previously considered scintillation drivers, our mechanism naturally produces the length and density scales of the ISM scattering lenses that are required to explain the magnitude and dynamical spectrum of the scintillations. In our picture, the parts of warm ionized interstellar medium that are responsible for the scintillations are relatively quiescent, with scintillation and scattering resulting from weak waves propagating along magnetic domain boundary current sheets, which are both expected from helicity conservation and have been observed in numerical simulations. The model quantitatively predicts the spacing and amplitudes of inverted parabolic arcs seen in Fourier-transformed dynamical spectra of strongly scintillating pulsars. Multi-frequency, multi-epoch low frequency VLBI observations can quantitatively test this...

  12. The Link Between Shocks, Turbulence, and Magnetic Reconnection in Collisionless Plasmas

    Science.gov (United States)

    Karimabadi, H.; Roytershteyn, V.; Vu, H. X.; Omelchenko, Y. A.; Scudder, J.; Daughton, W.; Dimmock, A.; Nykyri, K.; Wan, M.; Sibeck, D.; Tatineni, M.; Majumdar, A.; Loring, B.; Geveci, B.

    2014-01-01

    Global hybrid (electron fluid, kinetic ions) and fully kinetic simulations of the magnetosphere have been used to show surprising interconnection between shocks, turbulence and magnetic reconnection. In particular collisionless shocks with their reflected ions that can get upstream before retransmission can generate previously unforeseen phenomena in the post shocked flows: (i) formation of reconnecting current sheets and magnetic islands with sizes up to tens of ion inertial length. (ii) Generation of large scale low frequency electromagnetic waves that are compressed and amplified as they cross the shock. These 'wavefronts' maintain their integrity for tens of ion cyclotron times but eventually disrupt and dissipate their energy. (iii) Rippling of the shock front, which can in turn lead to formation of fast collimated jets extending to hundreds of ion inertial lengths downstream of the shock. The jets, which have high dynamical pressure, 'stir' the downstream region, creating large scale disturbances such as vortices, sunward flows, and can trigger flux ropes along the magnetopause. This phenomenology closes the loop between shocks, turbulence and magnetic reconnection in ways previously unrealized. These interconnections appear generic for the collisionless plasmas typical of space, and are expected even at planar shocks, although they will also occur at curved shocks as occur at planets or around ejecta.

  13. Laboratory Study Of Magnetic Reconnection With A Density Asymmetry Across The Current Sheet

    Energy Technology Data Exchange (ETDEWEB)

    Yoo, Joseph; Yamada, Massaaki; Ji, Hantao; Meyers,, Clayton E.; Jara-Almonte,; Chen, Li-Jen

    2014-04-18

    The effects of an upstream density asymmetry on magnetic reconnection are studied systematically in a laboratory plasma. Despite a significant upstream density asymmetry of up to 10, the reconnecting magnetic field pro file is not signifi cantly changed. On the other hand, the out-of-plane magnetic field profile is considerably modified; it is almost bipolar in structure with the density asymmetry, as compared to the quadrupolar structure in the symmetric configuration. The in-plane ion flow pattern and the electrostatic potential pro file are also affected by the density asymmetry. Strong bulk electron heating is observed near the low-density-side separatrix together with electromagnetic fluctuations in the lower hybrid frequency range. The dependence of the ion outflow and reconnection electric field on the density asymmetry is measured and compared with theoretical expectations.

  14. Cluster multi-point observations of the magnetotail plasma sheet

    Science.gov (United States)

    Henderson, Paul David

    This thesis presents observations of the terrestrial magnetotail plasma sheet made by the European Space Agency Cluster mission. The Cluster mission is composed of four identical spacecraft, the first such multi-spacecraft mission, and enables, for the first time, the disambiguation of time versus space phenomena. Using the data from 2003, when the spacecraft were at their smallest average separation to date, many small-scale processes, both microphysical and macrophysical, are investigated. In the first study presented, two small flux ropes, a possible signature of multiple X-line reconnection, are investigated. By the development and utilisation of various multi-spacecraft methods, the currents and magnetic forces internal and external to the flux ropes, as well as the internal structure of the flux ropes, are investigated. In addition, a theory of their early evolution is suggested. In the second study presented, various terms of the generalised Ohm's law for a plasma are determined, including, for the first time, the divergence of the full electron pressure tensor, during the passage past the spacecraft of an active reconnection X-line. It is found that the electric field contribution from the divergence of the electron pressure tensor is anti-correlated with the contribution from the Hall term in the direction normal to the neutral sheet. In addition, further signatures of reconnection are quantified, such as parallel electric field generation and Hall quadrupolar magnetic field and current systems. In the final study presented, the anti-correlation between the divergence of the electron pressure tensor and Hall terms is investigated further. It is found that the anti-correlation is general, appearing in the direction normal to the neutral sheet because of a cross tail current. In a simple magnetohydrostatic treatment, a force balance argument leads to the conclusion that the gradient of the anti-correlation is a function of the ratio of the electron to ion

  15. Pressure-driven reconnection and quasi periodical oscillations in plasmas

    Science.gov (United States)

    Paccagnella, R.

    2014-03-01

    This paper presents a model for an ohmically heated plasma in which a feedback exists between thermal conduction and transport, on one side, and the magneto-hydro-dynamical stability of the system, on the other side. In presence of a reconnection threshold for the magnetic field, a variety of periodical or quasi periodical oscillations for the physical quantities describing the system are evidenced. The model is employed to interpret the observed quasi periodical oscillations of electron temperature and perturbed magnetic field around the so called "Single Helical" state in the reversed field pinch, but its relevance for other periodical phenomena observed in magnetic confinement systems, especially in tokamaks, is suggested.

  16. Disruption of sheet-like structures in Alfvénic turbulence by magnetic reconnection

    Science.gov (United States)

    Mallet, A.; Schekochihin, A. A.; Chandran, B. D. G.

    2017-07-01

    We propose a mechanism whereby the intense, sheet-like structures naturally formed by dynamically aligning Alfvénic turbulence are destroyed by magnetic reconnection at a scale \\hat{λ }_D, larger than the dissipation scale predicted by models of intermittent, dynamically aligning turbulence. The reconnection process proceeds in several stages: first, a linear tearing mode with N magnetic islands grows and saturates, and then the X-points between these islands collapse into secondary current sheets, which then reconnect until the original structure is destroyed. This effectively imposes an upper limit on the anisotropy of the structures within the perpendicular plane, which means that at scale \\hat{λ }_D the turbulent dynamics change: at scales larger than \\hat{λ }_D, the turbulence exhibits scale-dependent dynamic alignment and a spectral index approximately equal to -3/2, while at scales smaller than \\hat{λ }_D, the turbulent structures undergo a succession of disruptions due to reconnection, limiting dynamic alignment, steepening the effective spectral index and changing the final dissipation scale. The scaling of \\hat{λ }_D with the Lundquist (magnetic Reynolds) number S_{L_\\perp } depends on the order of the statistics being considered, and on the specific model of intermittency; the transition between the two regimes in the energy spectrum is predicted at approximately \\hat{λ }_D˜ S_{L_\\perp }^{-0.6}. The spectral index below \\hat{λ }_D is bounded between -5/3 and -2.3. The final dissipation scale is at \\hat{λ }_{η ,∞}˜ S_{L_\\perp }^{-3/4}, the same as the Kolmogorov scale arising in theories of turbulence that do not involve scale-dependent dynamic alignment.

  17. Dependence of anomalous resistivity on bulk drift velocity of electrons in the reconnecting current sheets in solar flares

    Institute of Scientific and Technical Information of China (English)

    Gui-Ping Wu; Guang-Li Huang; Hai-Sheng Ji

    2010-01-01

    Anomalous resistivity is critical for triggering fast magnetic reconnection in the nearly collisionless coronal plasma.Its nonlinear dependence on bulk drift velocity is usually assumed in MHD simulations.However,the mechanism for the production of anomalous resistivity and its evolution is still an open question.We numerically solved the one dimension Vlasov equation with the typical solar coronal parameters and realistic mass ratios to infer the relationship between anomalous resistivity and bulk drift velocity of electrons in the reconnecting current sheets as well as its nonlinear characteristics.Our principal findings are summarized as follows: 1)the relationship between the anomalous resistivity and bulk drift velocity of electrons relative to ions may be described as ηmax = 0.03724(vd/ve)5.702 Ω m for vd/ve in the range of 1.4-2.0 and ηmax = 0.8746(vd/ve)1.284 Ωm for vd/ve in the range of 2.5-4.5; 2)if drift velocity is just slightly larger than the threshold of ion-acoustic instability,the anomalous resistivity due to the wave-particle interactions is enhanced by about five orders as compared with classic resistivity due to Coulomb collisions.With the increase of drift velocity from 1.4ve to 4.5ve,the anomalous resistivity continues to increase 100 times; 3)in the rise phase of unstable waves,the anomalous resistivity has the same order as the one estimated from quasi-linear theory; after saturation of unstable waves,the anomalous resistivity decreases at least about one order as compared with its peak value; 4)considering that the final velocity of electrons ejected out of the reconnecting current sheet(RCS)decreases with the distance from the neutral point in the neutral plane,the anomalous resistivity decreases with the distance from the neutral point,which is favorable for the Petschek-like reconnection to take place.

  18. Magnetic reconnection during magnetospheric substorms

    Science.gov (United States)

    Baker, Daniel N.

    1996-01-01

    The near earth reconnection model of substorms represents an attempt to place a broad range of observations into a consistent framework. The roles and requirements of reconnection are discussed. High speed plasma sheet flows, thin current sheet instability, substorm triggering, plasmoids and flux ropes in the distant tail, and magnetohydrodynamic simulations are discussed. Substorms are global, coherent sequences of processes involving solar wind/magnetosphere/ionosphere interaction. Magnetic reconnection is required to explain different dayside and polar cap phenomena, which required nightside reconnection. The modification and expansion of the standard near earth neutral line (NENL) model can integrate breakup arcs, current disruption, current wedge features, and localized plasma flows into the magnetic reconnection framework.

  19. On the nature of the plasma sheet boundary layer

    Energy Technology Data Exchange (ETDEWEB)

    Hones, E.W. Jr. (Mission Research Corp., Los Alamos, NM (USA) Los Alamos National Lab., NM (USA))

    1990-01-01

    The regions of the plasma sheet adjacent to the north and south lobes of the magnetotail have been described by many experimenters as locations of beams of energetic ions and fast-moving plasma directed primarily earthward and tailward along magnetic field lines. Measurements taken as satellites passed through one or the other of these boundary layers have frequently revealed near-earth mirroring of ions and a vertical segregation of velocities of both earthward-moving and mirroring ions with the fastest ions being found nearest the lobe-plasma sheet interface. These are features expected for particles from a distant tail source {bar E} {times} {bar B} drifting in a dawn-to-dusk electric field and are consistent with the source being a magnetic reconnection region. The plasma sheet boundary layers are thus understood as separatrix layers, bounded at their lobeward surfaces by the separatrices from the distant neutral line. This paper will review the observations that support this interpretation. 10 refs., 7 figs.

  20. The effects of plasma beta and anisotropy instabilities on the dynamics of reconnecting magnetic fields in the heliosheath

    CERN Document Server

    Schoeffler, K M; Swisdak, M

    2011-01-01

    The plasma {\\beta} (the ratio of the plasma pressure to the magnetic pressure) of a system can have a large effect on its dynamics as high {\\beta} enhances the effects of pressure anisotropies. We investigate the effects of {\\beta} in a system of stacked current sheets that break up into magnetic islands due to magnetic reconnection. We find significant differences between {\\beta} 1. At low {\\beta} growing magnetic islands are modestly elongated and become round as contraction releases magnetic stress and reduces magnetic energy. At high {\\beta} the increase of the parallel pressure in contracting islands causes saturation of modestly elongated islands as island cores approach the marginal firehose condition. Only highly elongated islands reach finite size. The kinking associated with the Weibel and firehose instabilities prevents full contraction of these islands, leading to a final state of highly elongated islands in which further reconnection is suppressed. The results are directly relevant to reconnecti...

  1. MHD simulations of three-dimensional Resistive Reconnection in a cylindrical plasma column

    CERN Document Server

    Striani, Edoardo; Vaidya, Bhargav; Bodo, Gianluigi; Ferrari, Attilio

    2016-01-01

    Magnetic reconnection is a plasma phenomenon where a topological rearrangement of magnetic field lines with opposite polarity results in dissipation of magnetic energy into heat, kinetic energy and particle acceleration. Such a phenomenon is considered as an efficient mechanism for energy release in laboratory and astrophysical plasmas. An important question is how to make the process fast enough to account for observed explosive energy releases. The classical model for steady state magnetic reconnection predicts reconnection times scaling as $S^{1/2}$ (where $S$ is the Lundquist number) and yields times scales several order of magnitude larger than the observed ones. Earlier two-dimensional MHD simulations showed that for large Lundquist number the reconnection time becomes independent of $S$ ("fast reconnection" regime) due to the presence of the secondary tearing instability that takes place for $S \\gtrsim 1 \\times 10^4$. We report on our 3D MHD simulations of magnetic reconnection in a magnetically confin...

  2. Ion Beams in the Plasma Sheet Boundary Layer

    Science.gov (United States)

    Birn, J.; Hesse, M.; Runov, A.; Zhou, X.

    2015-12-01

    We explore characteristics of energetic particles in the plasma sheet boundary layer associated with dipolarization events, based on simulations and observations. The simulations use the electromagnetic fields of an MHD simulation of magnetotail reconnection and flow bursts as basis for test particle tracing. They are complemented by self-consistent fully electrodynamic particle-in-cell (PIC) simulations. The test particle simulations confirm that crescent shaped earthward flowing ion velocity distributions with strong perpendicular anisotropy can be generated as a consequence of near tail reconnection, associated with earthward flows and propagating magnetic field dipolarization fronts. Both PIC and test particle simulations show that the ion distribution in the outflow region close to the reconnection site also consist of a beam superposed on an undisturbed population; this beam, however, does not show strong perpendicular anisotropy. This suggests that the crescent shape is created by quasi-adiabatic deformation from ion motion along the magnetic field toward higher field strength. The simulation results compare favorably with ``Time History of Events and Macroscale Interactions during Substorms" (THEMIS) observations.

  3. Sheet Plasma Produced by Hollow Cathode Discharge

    Institute of Scientific and Technical Information of China (English)

    张龙; 张厚先; 杨宣宗; 冯春华; 乔宾; 王龙

    2003-01-01

    A sheet plasma is produced by a hollow cathode discharge under an axial magnetic field.The plasma is about 40cm in length,4 cm in width and 1cm in thickness.The electron density is about 108cm-3.The hollow cathode is made to be shallow with a large opening,which is different from the ordinary deep hollow cathode.A Langmuir probe is used to detect the plasma.The electron density and the spatial distribution of the plasma change when voltage,pressure and the magnetic field vary.A peak and a data fluctuation at about 200 G-300 G are observed in the variation of electron density(or thickness of the sheet plasma)with the magnetic field.Our work will be helpful in characterizing the sheet plasma and will make the production of dense sheet plasma more controllable.

  4. A laboratory study of asymmetric magnetic reconnection in strongly driven plasmas.

    Science.gov (United States)

    Rosenberg, M J; Li, C K; Fox, W; Igumenshchev, I; Séguin, F H; Town, R P J; Frenje, J A; Stoeckl, C; Glebov, V; Petrasso, R D

    2015-02-04

    Magnetic reconnection, the annihilation and rearrangement of magnetic fields in a plasma, is a universal phenomenon that frequently occurs when plasmas carrying oppositely directed field lines collide. In most natural circumstances, the collision is asymmetric (the two plasmas having different properties), but laboratory research to date has been limited to symmetric configurations. In addition, the regime of strongly driven magnetic reconnection, where the ram pressure of the plasma dominates the magnetic pressure, as in several astrophysical environments, has also received little experimental attention. Thus, we have designed the experiments to probe reconnection in asymmetric, strongly driven, laser-generated plasmas. Here we show that, in this strongly driven system, the rate of magnetic flux annihilation is dictated by the relative flow velocities of the opposing plasmas and is insensitive to initial asymmetries. In addition, out-of-plane magnetic fields that arise from asymmetries in the three-dimensional plasma geometry have minimal impact on the reconnection rate, due to the strong flows.

  5. Anomalous-plasmoid-ejection-induced secondary magnetic reconnection: modeling solar flares and coronal mass ejections by laser–plasma experiments

    Institute of Scientific and Technical Information of China (English)

    Quanli; Dong; Dawei; Yuan; Shoujun; Wang; Xun; Liu; Yutong; Li; Xiaoxuan; Lin; Huigang; Wei; Jiayong; Zhong; Shaoen; Jiang; Yongkun; Ding; Bobin; Jiang; Kai; Du; Yongjian; Tang; Mingyang; Yu; Xiantu; He; Neng; Hua; Zhanfeng; Qiao; Kuixi; Huang; Ming; Chen; Jianqiang; Zhu; Gang; Zhao; Zhengming; Sheng; Jie; Zhang

    2013-01-01

    The driving mechanism of solar flares and coronal mass ejections is a topic of ongoing debate, apart from the consensus that magnetic reconnection plays a key role during the impulsive process. While present solar research mostly depends on observations and theoretical models, laboratory experiments based on high-energy density facilities provide the third method for quantitatively comparing astrophysical observations and models with data achieved in experimental settings.In this article, we show laboratory modeling of solar flares and coronal mass ejections by constructing the magnetic reconnection system with two mutually approaching laser-produced plasmas circumfused of self-generated megagauss magnetic fields. Due to the Euler similarity between the laboratory and solar plasma systems, the present experiments demonstrate the morphological reproduction of flares and coronal mass ejections in solar observations in a scaled sense,and confirm the theory and model predictions about the current-sheet-born anomalous plasmoid as the initial stage of coronal mass ejections, and the behavior of moving-away plasmoid stretching the primary reconnected field lines into a secondary current sheet conjoined with two bright ridges identified as solar flares.

  6. Magnetic reconnection and tearing in a 3D current sheet about a solar coronal null

    Science.gov (United States)

    Pontin, David; Wyper, Peter

    2014-06-01

    Three-dimensional magnetic null points are ubiquitous in the solar corona and in any generic mixed-polarity magnetic field. We discuss the nature of flux transfer during reconnection an isolated coronal null point, that occurs across the fan plane when a current sheet forms about the null. We then go on to discuss the breakup of the current sheet via a non-linear tearing-type instability and show that the instability threshold corresponds to a Lundquist number comparable to the 2D case. We also discuss the resulting topology of the magnetic field, which involves a layer in which open and closed magnetic fields are effectively mixed, with implications for particle transport.

  7. 3-d resistive MHD simulations of magnetic reconnection and the tearing mode instability in current sheets

    CERN Document Server

    Murphy, G C; Pelletier, Guy

    2008-01-01

    Magnetic reconnection plays a critical role in many astrophysical processes where high energy emission is observed, e.g. particle acceleration, relativistic accretion powered outflows, pulsar winds and probably in dissipation of Poynting flux in GRBs. The magnetic field acts as a reservoir of energy and can dissipate its energy to thermal and kinetic energy via the tearing mode instability. We have performed 3d nonlinear MHD simulations of the tearing mode instability in a current sheet. Results from a temporal stability analysis in both the linear regime and weakly nonlinear (Rutherford) regime are compared to the numerical simulations. We observe magnetic island formation, island merging and oscillation once the instability has saturated. The growth in the linear regime is exponential in agreement with linear theory. In the second, Rutherford regime the island width grows linearly with time. We find that thermal energy produced in the current sheet strongly dominates the kinetic energy. Finally preliminary ...

  8. Current sheet flapping motions in the tailward flow of magnetic reconnection

    Science.gov (United States)

    Wu, Mingyu; Lu, Quanming; Volwerk, Martin; Vörös, Zoltán.; Ma, Xuanye; Wang, Shui

    2016-08-01

    The feature and origin of current sheet flapping motions are one of most interesting issues of magnetospheric dynamics. In this paper we report the flapping motion of the current sheet detected in the tailward flow of a magnetic reconnection event on 7 February 2009. This flapping motion with frequency about 12 mHz was accompanied by magnetic turbulence. The observations by the tail-elongated fleet of five Time History of Events and Macroscale Interactions during Substorms probes indicate that these flapping oscillations were rather confined within the tailward flow than were due to a global process. This flapping motion could be due to the instability driven by the free energy associated with the ion temperature anisotropy in the tailward flow. Our observations indicate that the flapping motion in the tailward flow could have a different generation mechanism with that in the earthward flow.

  9. Secondary magnetic islands generated by the Kelvin-Helmholtz instability in a reconnecting current sheet.

    Science.gov (United States)

    Fermo, R L; Drake, J F; Swisdak, M

    2012-06-22

    Magnetic islands or flux ropes produced by magnetic reconnection have been observed on the magnetopause, in the magnetotail, and in coronal current sheets. Particle-in-cell simulations of magnetic reconnection with a guide field produce elongated electron current layers that spontaneously produce secondary islands. Here, we explore the seed mechanism that gives birth to these islands. The most commonly suggested theory for island formation is the tearing instability. We demonstrate that in our simulations these structures typically start out, not as magnetic islands, but as electron flow vortices within the electron current sheet. When some of these vortices first form, they do not coincide with closed magnetic field lines, as would be the case if they were islands. Only after they have grown larger than the electron skin depth do they couple to the magnetic field and seed the growth of finite-sized islands. The streaming of electrons along the magnetic separatrix produces the flow shear necessary to drive an electron Kelvin-Helmholtz instability and produce the initial vortices. The conditions under which this instability is the dominant mechanism for seeding magnetic islands are explored.

  10. Patchy Reconnection in the Solar Corona

    CERN Document Server

    Guidoni, Silvina E

    2011-01-01

    Supra-arcade downflows (SADs) and supra-arcade downflowing loops (SADLs) descending from reconnection regions toward solar post-flare arcades seem to be two different observational signatures of retracting, isolated reconnected flux tubes with irreducible three-dimensional geometries. This dissertation describes work in refining and improving a novel model of patchy reconnection, where only a small bundle of field lines is reconnected across a current sheet and forms a reconnected thin flux tube. Traditional models have not been able to explain why some of the observed SADs appear to be hot and relatively devoid of plasma. The present work shows that plasma depletion naturally occurs in flux tubes that are reconnected across nonuniform current sheets and slide trough regions of decreasing magnetic field magnitude. Moreover, through a detailed theoretical analysis of generalized thin flux tube equations, we show that the addition to the model of pressure-driven parallel dynamics, as well as temperature-depende...

  11. Coupling between reconnection and Kelvin-Helmholtz instabilities in collisionless plasmas

    Directory of Open Access Journals (Sweden)

    D. Grasso

    2009-04-01

    Full Text Available In a collisionless plasma, when reconnection instability takes place, strong shear flows may develop. Under appropriate conditions these shear flows become unstable to the Kelvin-Helmholtz instability. Here, we investigate the coupling between these instabilities in the framework of a four-field model. Firstly, we recover the known results in the low β limit, β being the ratio between the plasma and the magnetic pressure. We concentrate our attention on the dynamical evolution of the current density and vorticity sheets which evolve coupled together according to a laminar or a turbulent regime. A three-dimensional extension in this limit is also discussed. Secondly, we consider finite values of the β parameter, allowing for compression of the magnetic and velocity fields along the ignorable direction. We find that the current density and vorticity sheets now evolve separately. The Kelvin-Helmholtz instability involves only the vorticity field, which ends up in a turbulent regime, while the current density maintains a laminar structure.

  12. Thin current sheets in collisionless plasma: Equilibrium structure, plasma instabilities, and particle acceleration

    Energy Technology Data Exchange (ETDEWEB)

    Zelenyi, L. M.; Malova, H. V.; Artemyev, A. V.; Popov, V. Yu.; Petrukovich, A. A. [Russian Academy of Sciences, Space Research Institute (Russian Federation)

    2011-02-15

    The review is devoted to plasma structures with an extremely small transverse size, namely, thin current sheets that have been discovered and investigated by spacecraft observations in the Earth's magnetotail in the last few decades. The formation of current sheets is attributed to complicated dynamic processes occurring in a collisionless space plasma during geomagnetic perturbations and near the magnetic reconnection regions. The models that describe thin current structures in the Earth's magnetotail are reviewed. They are based on the assumption of the quasi-adiabatic ion dynamics in a relatively weak magnetic field of the magnetotail neutral sheet, where the ions can become unmagnetized. It is shown that the ion distribution can be represented as a function of the integrals of particle motion-the total energy and quasi-adiabatic invariant. Various modifications of the initial equilibrium are considered that are obtained with allowance for the currents of magnetized electrons, the contribution of oxygen ions, the asymmetry of plasma sources, and the effects related to the non-Maxwellian particle distributions. The theoretical results are compared with the observational data from the Cluster spacecraft mission. Various plasma instabilities developing in thin current sheets are investigated. The evolution of the tearing mode is analyzed, and the parameter range in which the mode can grow are determined. The paradox of complete stabilization of the tearing mode in current sheets with a nonzero normal magnetic field component is thereby resolved based on the quasi-adiabatic model. It is shown that, over a wide range of current sheet parameters and the propagation directions of large-scale unstable waves, various modified drift instabilities-kink and sausage modes-can develop in the system. Based on the concept of a turbulent electromagnetic field excited as a result of the development and saturation of unstable waves, a mechanism for charged particle

  13. Time window for magnetic reconnection in plasma configurations with velocity shear.

    Science.gov (United States)

    Faganello, M; Califano, F; Pegoraro, F

    2008-10-24

    It is shown that the rate of magnetic field line reconnection can be clocked by the evolution of the large-scale processes that are responsible for the formation of the current layers where reconnection can take place. In unsteady plasma configurations, such as those produced by the onset of the Kelvin-Helmholtz instability in a plasma with a velocity shear, qualitatively different magnetic structures are produced depending on how fast the reconnection process develops on the external clock set by the evolving large-scale configuration.

  14. Spatial distribution of Mercury's flux ropes and reconnection fronts: MESSENGER observations

    Science.gov (United States)

    Sun, W. J.; Fu, S. Y.; Slavin, J. A.; Raines, J. M.; Zong, Q. G.; Poh, G. K.; Zurbuchen, T. H.

    2016-08-01

    We perform a statistical study of flux ropes and reconnection fronts based on MErcury Surface, Space ENviroment, GEochemistry, and Ranging (MESSENGER) magnetic field and plasma observations to study the implications for the spatial distribution of reconnection sites in Mercury's near magnetotail. The results show important differences of temporal and spatial distributions as compared to Earth. We have surveyed the plasma sheet crossings between -2 RM and -3 RM downtail from the planet, i.e., the location of Near-Mercury Neutral Line (NMNL). Plasma sheets were defined to be regions with β ≥ 0.5. Using this definition, 39 flux ropes and 86 reconnection fronts were identified in the plasma sheet. At Mercury, the distributions of flux ropes and reconnection fronts show clear dawn-dusk asymmetry with much higher occurrence rate on the dawnside plasma sheet than on the duskside. This suggests that magnetic reconnection in Mercury's magnetotail occurs more frequently in the dawnside than in the duskside plasma sheet, which is different than the observations in Earth's magnetotail showing more reconnection signatures in the duskside plasma sheet. The distribution of plasma sheet thickness shows that plasma sheet near the midnight is the thinnest part and does not show obvious asymmetry. Thus, the reasons that cause magnetic reconnection to preferentially occur on the dawnside of the magnetotail at Mercury may not be the plasma sheet thickness and require further study. The peak occurrence rates of flux ropes and reconnection fronts in Mercury's plasma sheet are ~ 60 times higher than that of Earth's values, which we interpret to be due to the highly variable magnetospheric conditions at Mercury. Such higher occurrence rate of magnetic reconnection would generate more plasma flows in the dawnside plasma sheet than in the duskside. These plasma flows would mostly brake and initiate the substorm dipolarization on the postmidnight sector at Mercury rather than the

  15. Effects on magnetic reconnection of a density asymmetry across the current sheet

    Directory of Open Access Journals (Sweden)

    K. G. Tanaka

    2008-08-01

    Full Text Available The magnetopause (MP reconnection is characterized by a density asymmetry across the current sheet. The asymmetry is expected to produce characteristic features in the reconnection layer. Here we present a comparison between the Cluster MP crossing reported by Retinò et al. (2006 and virtual observations in two-dimensional particle-in-cell simulation results. The simulation, which includes the density asymmetry but has zero guide field in the initial condition, has reproduced well the observed features as follows: (1 The prominent density dip region is detected at the separatrix region (SR on the magnetospheric (MSP side of the MP. (2 The intense electric field normal to the MP is pointing to the center of the MP at the location where the density dip is detected. (3 The ion bulk outflow due to the magnetic reconnection is seen to be biased towards the MSP side. (4 The out-of-plane magnetic field (the Hall magnetic field has bipolar rather than quadrupolar structure, the latter of which is seen for a density symmetric case. The simulation also showed rich electron dynamics (formation of field-aligned beams in the proximity of the separatrices, which was not fully resolved in the observations. Stepping beyond the simulation-observation comparison, we have also analyzed the electron acceleration and the field line structure in the simulation results. It is found that the bipolar Hall magnetic field structure is produced by the substantial drift of the reconnected field lines at the MSP SR due to the enhanced normal electric field. The field-aligned electrons at the same MSP SR are identified as the gun smokes of the electron acceleration in the close proximity of the X-line. We have also analyzed the X-line structure obtained in the simulation to find that the density asymmetry leads to a steep density gradient in the in-flow region, which may lead to a non-stationary behavior of the X-line when three-dimensional freedom is taken into account.

  16. A Simple, Analytical Model of Collisionless Magnetic Reconnection in a Pair Plasma

    Science.gov (United States)

    Hesse, Michael; Zenitani, Seiji; Kuznetova, Masha; Klimas, Alex

    2011-01-01

    A set of conservation equations is utilized to derive balance equations in the reconnection diffusion region of a symmetric pair plasma. The reconnection electric field is assumed to have the function to maintain the current density in the diffusion region, and to impart thermal energy to the plasma by means of quasi-viscous dissipation. Using these assumptions it is possible to derive a simple set of equations for diffusion region parameters in dependence on inflow conditions and on plasma compressibility. These equations are solved by means of a simple, iterative, procedure. The solutions show expected features such as dominance of enthalpy flux in the reconnection outflow, as well as combination of adiabatic and quasi-viscous heating. Furthermore, the model predicts a maximum reconnection electric field of E(sup *)=0.4, normalized to the parameters at the inflow edge of the diffusion region.

  17. Particle Heating and Energization During Magnetic Reconnection Events in MST Plasmas

    Science.gov (United States)

    Dubois, Ami M.; Almagri, A. F.; Anderson, J. K.; den Hartog, D. J.; Forest, C.; Nornberg, M.; Sarff, J. S.

    2015-11-01

    Magnetic reconnection plays an important role in particle transport, energization, and acceleration in space, astrophysical, and laboratory plasmas. In MST reversed field pinch plasmas, discrete magnetic reconnection events release large amounts of energy from the equilibrium magnetic field, resulting in non-collisional ion heating. However, Thomson Scattering measures a decrease in the thermal electron temperature. Recent fast x-ray measurements show an enhancement in the high energy x-ray flux during reconnection, where the coupling between edge and core tearing modes is essential for enhanced flux. A non-Maxwellian energetic electron tail is generated during reconnection, where the power law spectral index (γ) decreases from 4.3 to 1.8 and is dependent on density, plasma current, and the reversal parameter. After the reconnection event, γ increases rapidly to 5.8, consistent with the loss of energetic electrons due to stochastic thermal transport. During the reconnection event, the change in γ is correlated with the change in magnetic energy stored in the equilibrium field, indicating that the released magnetic energy may be an energy source for electron energization. Recent experimental and computational results of energetic electron tail formation during magnetic reconnection events will be presented. This work is supported by the U.S. DOE and the NSF.

  18. Thermal-inertial effects on magnetic reconnection in relativistic pair plasmas.

    Science.gov (United States)

    Comisso, Luca; Asenjo, Felipe A

    2014-07-25

    The magnetic reconnection process is studied in relativistic pair plasmas when the thermal and inertial properties of the magnetohydrodynamical fluid are included. We find that in both Sweet-Parker and Petschek relativistic scenarios there is an increase of the reconnection rate owing to the thermal-inertial effects, both satisfying causality. To characterize the new effects we define a thermal-inertial number which is independent of the relativistic Lundquist number, implying that reconnection can be achieved even for vanishing resistivity as a result of only thermal-inertial effects. The current model has fundamental importance for relativistic collisionless reconnection, as it constitutes the simplest way to get reconnection rates faster than those accessible with the sole resistivity.

  19. Development of a new experimental device for long-duration magnetic reconnection in weakly ionized plasma

    Science.gov (United States)

    Yanai, Ryoma; Kaminou, Yasuhiro; Nishida, Kento; Inomoto, Michiaki

    2016-10-01

    Magnetic reconnection is a universal phenomenon which determines global structure and energy conversion in magnetized plasmas. Many experimental studies have been carried out to explore the physics of magnetic reconnection in fully ionized condition. However, it is predicted that the behavior of magnetic reconnection in weakly ionized plasmas such as solar chromosphere plasma will show different behavior such as ambipolar diffusion caused by interaction with neutral particles. In this research, we are developing a new experimental device to uncover the importance of ambipolar diffusion during magnetic reconnection in weakly ionized plasmas. We employ an inverter-driven rotating magnetic fields technique, which is used for generating steady azimuthal plasma current, to establish long-duration ( 1 ms) anti-parallel reconnection with magnetic field of 5 mT in weakly ionized plasma. We will present development status and initial results from the new experimental setup. This work was supported by JSPS A3 Foresight Program ``Innovative Tokamak Plasma Startup and Current Drive in Spherical Torus'', Giant-in Aid for Scientific Research (KAKENHI) 15H05750, 15K14279, 26287143 and the NIFS Collaboration Research program (NIFS14KNWP004).

  20. Magnetic reconnection in turbulent space plasmas: null-points or pinches?

    Science.gov (United States)

    Olshevsky, Vyacheslav; Lapenta, Giovanni; Markidis, Stefano; Divin, Andrey

    2014-05-01

    We report particle-in-cell simulations of magnetic reconnection in the configuration containing both null-points and pinches. All indicators suggest that secondary magnetic reconnection driven by kinking of the pinches plays a dominant role in the energetics of the system. While there is no substantial energy dissipation in the vicinity of X-type null-points. Such reconnection results in tremendous release of magnetic energy, generation of suprathermal particles and waves. Similar scenario may take place in turbulent space plasmas, where current channels and twisted magnetic fields are detected.

  1. 3D reconnection due to oblique modes: a simulation of Harris current sheets

    Directory of Open Access Journals (Sweden)

    G. Lapenta

    2000-01-01

    Full Text Available Simulations in three dimensions of a Harris current sheet with mass ratio, mi/me = 180, and current sheet thickness, pi/L = 0.5, suggest the existence of a linearly unstable oblique mode, which is independent from either the drift-kink or the tearing instability. The new oblique mode causes reconnection independently from the tearing mode. During the initial linear stage, the system is unstable to the tearing mode and the drift kink mode, with growth rates that are accurately described by existing linear theories. How-ever, oblique modes are also linearly unstable, but with smaller growth rates than either the tearing or the drift-kink mode. The non-linear stage is first reached by the drift-kink mode, which alters the initial equilibrium and leads to a change in the growth rates of the tearing and oblique modes. In the non-linear stage, the resulting changes in magnetic topology are incompatible with a pure tearing mode. The oblique mode is shown to introduce a helical structure into the magnetic field lines.

  2. 太阳爆发过程中的大尺度磁重联电流片:理论和观测%Large-Scale Reconnecting Current Sheets in Solar Eruptions: Theories and Observations

    Institute of Scientific and Technical Information of China (English)

    吴宁; 李燕; 沈呈彩; 林隽

    2012-01-01

    从理论和观测两个方面来介绍和讨论出现在太阳爆发过程中的磁重联电流片及其物理本质和动力学特征.首先介绍在理论研究和理论模型中,磁重联电流片是如何在爆发磁结构当中形成并发展的,对观测研究有什么指导意义.然后介绍观测工作是从哪几个方面对理论模型预测的电流片进行证认和研究的.第三,将介绍观测研究给出了哪些过去所没有能够预期的结果,这些结果对深入研究耀斑-CME电流片以及其中的磁重联过程的理论工作有什么重要的、挑战性的意义.第四,讨论最新的与此有关的理论研究和数值实验.最后,对未来的研究方向和重要课题进行综述和展望.%Magnetic reconnection is a fundamental process with a rich variety of aspects and applications in astrophysical, space, and laboratory plasmas. It is at the core of many dynamic phenomena in the universe, including solar eruptions, geomagnetic substorms, and tokamak disruption. Most of the universe is in the form of a plasma threaded by a magnetic field. When twisted or sheared, the field lines may reconnect rapidly, converting magnetic energy into heat and kinetic energy. Because these phenomena often occur in environments of very high electric conductivity, the process of energy conversion is usually confined to a small local region, such as an X-type neutral point, a current sheet, or a quasi-separatrix layer. It is traditionally expected that the current sheet is too thin to be observable since its thickness is believed to be roughly the proton Larmor radius, which is about tens of meters in the coronal environment. This view is based on magnetic reconnection on small scales in the laboratory or on quasi-static process in space (with timescale of tens of hours or even a few days). This could be true as well in the solar eruption in the case that the classical Spitzer resistivity dominates the diffusion process. However, CME/fiare current

  3. 3D magnetic field configuration of small-scale reconnection events in the solar plasma atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    Shimizu, T., E-mail: shimizu@solar.isas.jaxa.jp [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan); Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2015-10-15

    The outer solar atmosphere, i.e., the corona and the chromosphere, is replete with small energy-release events, which are accompanied by transient brightening and jet-like ejections. These events are considered to be magnetic reconnection events in the solar plasma, and their dynamics have been studied using recent advanced observations from the Hinode spacecraft and other observatories in space and on the ground. These events occur at different locations in the solar atmosphere and vary in their morphology and amount of the released energy. The magnetic field configurations of these reconnection events are inferred based on observations of magnetic fields at the photospheric level. Observations suggest that these magnetic configurations can be classified into two groups. In the first group, two anti-parallel magnetic fields reconnect to each other, yielding a 2D emerging flux configuration. In the second group, helical or twisted magnetic flux tubes are parallel or at a relative angle to each other. Reconnection can occur only between anti-parallel components of the magnetic flux tubes and may be referred to as component reconnection. The latter configuration type may be more important for the larger class of small-scale reconnection events. The two types of magnetic configurations can be compared to counter-helicity and co-helicity configurations, respectively, in laboratory plasma collision experiments.

  4. Three-dimensional dynamics of collisionless magnetic reconnection in large-scale pair plasmas.

    Science.gov (United States)

    Yin, L; Daughton, W; Karimabadi, H; Albright, B J; Bowers, Kevin J; Margulies, J

    2008-09-19

    Using the largest three-dimensional particle-in-cell simulations to date, collisionless magnetic reconnection in large-scale electron-positron plasmas without a guide field is shown to involve complex interaction of tearing and kink modes. The reconnection onset is patchy and occurs at multiple sites which self-organize to form a single, large diffusion region. The diffusion region tends to elongate in the outflow direction and become unstable to secondary kinking and formation of "plasmoid-rope" structures with finite extent in the current direction. The secondary kink folds the reconnection current layer, while plasmoid ropes at times follow the folding of the current layer. The interplay between these secondary instabilities plays a key role in controlling the time-dependent reconnection rate in large-scale systems.

  5. Thermomechanical processing of plasma sprayed intermetallic sheets

    Energy Technology Data Exchange (ETDEWEB)

    Hajaligol, Mohammad R. (Midlothian, VA); Scorey, Clive (Cheshire, CT); Sikka, Vinod K. (Oak Ridge, TN); Deevi, Seetharama C. (Midlothian, VA); Fleischhauer, Grier (Midlothian, VA); Lilly, Jr., A. Clifton (Chesterfield, VA); German, Randall M. (State College, PA)

    2001-01-01

    A powder metallurgical process of preparing a sheet from a powder having an intermetallic alloy composition such as an iron, nickel or titanium aluminide. The sheet can be manufactured into electrical resistance heating elements having improved room temperature ductility, electrical resistivity, cyclic fatigue resistance, high temperature oxidation resistance, low and high temperature strength, and/or resistance to high temperature sagging. The iron aluminide has an entirely ferritic microstructure which is free of austenite and can include, in weight %, 4 to 32% Al, and optional additions such as .ltoreq.1% Cr, .gtoreq.0.05% Zr .ltoreq.2% Ti, .ltoreq.2% Mo, .ltoreq.1% Ni, .ltoreq.0.75% C, .ltoreq.0.1% B, .ltoreq.1% submicron oxide particles and/or electrically insulating or electrically conductive covalent ceramic particles, .ltoreq.1% rare earth metal, and/or .ltoreq.3% Cu. The process includes forming a non-densified metal sheet by consolidating a powder having an intermetallic alloy composition such as by roll compaction, tape casting or plasma spraying, forming a cold rolled sheet by cold rolling the non-densified metal sheet so as to increase the density and reduce the thickness thereof and annealing the cold rolled sheet. The powder can be a water, polymer or gas atomized powder which is subjecting to sieving and/or blending with a binder prior to the consolidation step. After the consolidation step, the sheet can be partially sintered. The cold rolling and/or annealing steps can be repeated to achieve the desired sheet thickness and properties. The annealing can be carried out in a vacuum furnace with a vacuum or inert atmosphere. During final annealing, the cold rolled sheet recrystallizes to an average grain size of about 10 to 30 .mu.m. Final stress relief annealing can be carried out in the B2 phase temperature range.

  6. A statistical survey of reconnection exhausts in the solar wind based on the Riemannian decay of current sheets

    Science.gov (United States)

    Sasunov, Yu. L.; Semenov, V. S.; Heyn, M. F.; Erkaev, N. V.; Kubyshkin, I. V.; Slivka, K. Yu.; Korovinskiy, D. B.; Khodachenko, M. L.

    2015-10-01

    We present a statistical study of the magnetic reconnection exhausts in solar wind. Observational data are compared with the analytical model based on the Riemann analysis of tangential discontinuity decay forced by finite X-line reconnection of skewed magnetic fields. Statistical analysis is based on 51 events of the solar wind reconnection listed in Phan et al. (2009). The best agreement of the observed and analytically predicted values is achieved for the rotational angle of the tangential magnetic field component with correlation coefficient reaching the value of 0.97. The lowest correlation coefficient of 0.87 is obtained for the exhaust flow plasma temperature. It is found that proton temperature increases at the exhaust boundary while electron temperature stays unchanged. This may indicate that heating and acceleration processes operate on the proton scale. Exhaust boundaries are identified as tangential discontinuities, except one particular event, where Alfvén discontinuity and slow shock were detected instead. Hence, the impulsive reconnection may be supposed in that case rather than steady state one. Exhaust regions extending up to 690RE, registered in some observations, do not necessarily imply X-lines of similar length. They could be explained alternatively by reconnection of skewed magnetic fields. The numerical modeling of the interplanetary coronal mass ejection (ICME) propagating in the solar wind reveals that the resistance force, impeding the ICME motion, may be reduced significantly (three times in our simulations) by means of the magnetic reconnection at the leading edge. Thus, reconnection may substantially increase ICME velocity and travel distance.

  7. A model of global magnetic reconnection rate in relativistic collisionless plasmas

    CERN Document Server

    Liu, Yi-Hsin; Guo, Fan; Daughton, William; Li, Hui

    2016-01-01

    A model of global magnetic reconnection rate in relativistic collisionless plasmas is developed and validated by the fully kinetic simulation. Through considering the force balance at the upstream and downstream of the diffusion region, we show that the global rate is bounded by a value $\\sim 0.3$ even when the local rate goes up to $\\sim O(1)$ and the local inflow speed approaches the speed of light in strongly magnetized plasmas. The derived model is general and can be applied to magnetic reconnection under widely different circumstances.

  8. Z箍缩等离子体磁重联现象%Magnetic reconnection in Z-pinch plasmas

    Institute of Scientific and Technical Information of China (English)

    但加坤; 段书超; 章征伟

    2012-01-01

    Effects of magnetic reconnection on coronal plasma acceleration and energy balance have been discussed. Acceleration of coronal plasma to the array axis can be divided into two stages. Firstly, coronal plasma is pushed radially inward the array axis mainly by global magnetic force or thermal force, depending on the wire number. Secondly, plasma jets are accelerated to Alfven speed by magnetic reconnection, eventually reaching the array axis as precursor pinch. The thickness of the reconnection layer that is comparable to the ion inertial length indicates the motions of electrons and ions are decoupled in the current sheet. Strong radial electric field produced by charge separation converts magnetic energy to axial kinetic energy of plasmas, and thermalization of radial and axial kinetic energy accounts for radiation yield. For facilities with 1 MA drive leve l, the energy of electromagnetic pulse produced by magnetic reconnection can reach 1 kJ.%分析了磁重联对晕等离子体加速和能量平衡过程的影响.分析表明晕等离子体向轴心的加速过程分为两个阶段:第一阶段晕等离子体在磁压或热压(依赖于丝数)作用下向轴心运动;第二阶段晕等离子体由于磁重联过程被加速到阿尔芬速度,并到达轴心形成先驱等离子体.估算表明重联层的厚度与离子的惯性长度具有相同的数量级,电流片内电子运动和离子的运动是解耦合的.在内爆滞止阶段电荷分离产生强的径向电场,这个电场将磁能转化为等离子体轴向(z方向)动能,内爆动能和轴向动能共同转化为X射线辐射能,以此解释了X射线能量大于内爆动能这一观测结果.分析了磁重联电磁脉冲的性质,对于(1) MA驱动条件,电磁脉冲的总能量可达kJ量级.

  9. Global reconnection topology as inferred from plasma observations inside Kelvin-Helmholtz vortices

    Directory of Open Access Journals (Sweden)

    M. B. Bavassano Cattaneo

    2010-04-01

    Full Text Available During a long lasting period of northward interplanetary magnetic field and high solar wind speed (above 700 km/s, the Cluster spacecraft go across a number of very large rolled-up Kelvin-Helmholtz (KH vortices at the dusk magnetopause, close to the terminator. The peculiarity of the present event is a particular sequence of ions and electrons distribution functions observed repeatedly inside each vortex. In particular, whenever Cluster crosses the current layer inside the vortices, multiple field-aligned ion populations appear, suggesting the occurrence of reconnection. In addition, the ion data display a clear velocity filter effect both at the leading and at the trailing edge of each vortex. This effect is not present in the simultaneous electron data. Unlike other KH studies reported in the literature in which reconnection occurs within the vortices, in the present event the observations are not compatible with local reconnection, but are accounted for by lobe reconnection occurring along an extended X-line at the terminator in the Southern Hemisphere. The reconnected field lines "sink" across the magnetopause and then convect tailward-duskward where they become embedded in the vortices. Another observational evidence is the detected presence of solar wind plasma on the magnetospheric side of the vortices, which confirms unambiguously the occurrence of mass transport across the magnetopause already reported in the literature. The proposed reconnection scenario accounts for all the observational aspects, regarding both the transport process and the kinetic signatures.

  10. Plasma and Energetic Particle Behaviors During Asymmetric Magnetic Reconnection at the Magnetopause

    Science.gov (United States)

    Lee, S. H.; Zhang, H.; Zong, Q.-G.; Otto, A.; Sibeck, D. G.; Wang, Y.; Glassmeier, K.-H.; Daly, P.W.; Reme, H.

    2014-01-01

    The factors controlling asymmetric reconnection and the role of the cold plasma population in the reconnection process are two outstanding questions. We present a case study of multipoint Cluster observations demonstrating that the separatrix and flow boundary angles are greater on the magnetosheath than on the magnetospheric side of the magnetopause, probably due to the stronger density than magnetic field asymmetry at this boundary. The motion of cold plasmaspheric ions entering the reconnection region differs from that of warmer magnetosheath and magnetospheric ions. In contrast to the warmer ions, which are probably accelerated by reconnection in the diffusion region near the subsolar magnetopause, the colder ions are simply entrained by ??×?? drifts at high latitudes on the recently reconnected magnetic field lines. This indicates that plasmaspheric ions can sometimes play only a very limited role in asymmetric reconnection, in contrast to previous simulation studies. Three cold ion populations (probably H+, He+, and O+) appear in the energy spectrum, consistent with ion acceleration to a common velocity.

  11. Turbulent reconnection and its implications

    Science.gov (United States)

    Lazarian, A.; Eyink, G.; Vishniac, E.; Kowal, G.

    2015-01-01

    Magnetic reconnection is a process of magnetic field topology change, which is one of the most fundamental processes happening in magnetized plasmas. In most astrophysical environments, the Reynolds numbers corresponding to plasma flows are large and therefore the transition to turbulence is inevitable. This turbulence, which can be pre-existing or driven by magnetic reconnection itself, must be taken into account for any theory of magnetic reconnection that attempts to describe the process in the aforementioned environments. This necessity is obvious as three-dimensional high-resolution numerical simulations show the transition to the turbulence state of initially laminar reconnecting magnetic fields. We discuss ideas of how turbulence can modify reconnection with the focus on the Lazarian & Vishniac (Lazarian & Vishniac 1999 Astrophys. J. 517, 700–718 ()) reconnection model. We present numerical evidence supporting the model and demonstrate that it is closely connected to the experimentally proven concept of Richardson dispersion/diffusion as well as to more recent advances in understanding of the Lagrangian dynamics of magnetized fluids. We point out that the generalized Ohm's law that accounts for turbulent motion predicts the subdominance of the microphysical plasma effects for reconnection for realistically turbulent media. We show that one of the most dramatic consequences of turbulence is the violation of the generally accepted notion of magnetic flux freezing. This notion is a cornerstone of most theories dealing with magnetized plasmas, and therefore its change induces fundamental shifts in accepted paradigms, for instance, turbulent reconnection entails reconnection diffusion process that is essential for understanding star formation. We argue that at sufficiently high Reynolds numbers the process of tearing reconnection should transfer to turbulent reconnection. We discuss flares that are predicted by turbulent reconnection and relate this process to

  12. Magnetic reconnection in high-energy-density plasmas in the presence of an external magnetic field

    Science.gov (United States)

    Fox, W.; Bhattacharjee, A.; Fiksel, G.; Nilson, P.; Hu, S.; Chang, P.-Y.; Barnak, D.; Betti, R.

    2012-10-01

    Magnetic reconnection has recently been observed and studied in high-energy-density, laser-produced plasmas. These experiments are interesting both for obtaining fundamental data on reconnection, and may also be relevant for inertial fusion, as this magnetic reconnection geometry, with multiple, colliding, magnetized plasma bubbles, occurs naturally inside ICF hohlraums. We present initial results of experiments conducted on the OMEGA EP facility on magnetic reconnection between colliding, magnetized blowoff plasmas. While in previous experiments the magnetic fields were self-generated in the plasma by the Biermann battery effect, in these experiments the seed magnetic field is generated by pulsing current through a pair of external foils using the MIFEDS current generator (Magneto-Inertial Fusion Electrical Discharge System) developed at LLE. Time-resolved images of the magnetic fields and plasma dynamics are obtained from proton radiography and x-ray self-emission, respectively. We present initial results of the experiments, including comparison to ``null'' experiments with zero MIFEDS magnetic field, and associated modeling using the radiation-hydro code DRACO and the particle-in-cell code PSC.

  13. Heat Transfer and Reconnection Diffusion in Turbulent Magnetized Plasmas

    CERN Document Server

    Lazarian, A

    2011-01-01

    It is well known that magnetic fields constrain motions of charged particles, impeding the diffusion of charged particles perpendicular to magnetic field direction. This modification of transport processes is of vital importance for a wide variety of astrophysical processes including cosmic ray transport, transfer of heavy elements in the interstellar medium, star formation etc. Dealing with these processes one should keep in mind that in realistic astrophysical conditions magnetized fluids are turbulent. In this review we single out a single transport process, namely, heat transfer and consider how it occurs in the presence of the magnetized turbulence. We show that the ability of magnetic field lines to constantly change topology and connectivity is at the heart of the correct description of the 3D magnetic field stochasticity in turbulent fluids. This ability is ensured by fast magnetic reconnection in turbulent fluids and puts forward the concept of reconnection diffusion at the core of the physical pictu...

  14. Quasi-Separatrix Layers and Line-tied Reconnection in Collisionless Plasmas

    Science.gov (United States)

    Billey, Zachary; Zweibel, Ellen; Finn, John; Daughton, William

    2015-11-01

    Many plasmas undergoing magnetic reconnection have boundaries that have constant magnetic flux on the dynamical timescales of the system, such as coronal loops and planetary magnetospheres. Systems where the boundary magnetic flux is constant are called line-tied systems. We conduct collisionless fully 3D particle-in-cell simulations in slab geometry to study how line-tying changes the dynamics relative non-tied systems. We confirm Quasi-Separatrix Layers (QSLs) as a model for predicting potential reconnection sites in 3D systems. Based on this theory, we use line-integrated diagnostics to investigate the collisionless physics relating to the parallel electric field. Here we find non-gyrotopic terms in the pressure tensor are important at the center of the reconnection layer. We investigate the effect of varying the length of the line-tied plasma on the growth rate and reconnection process and compare oblique modes with equivalent periodic systems. We discuss the extension into collisionless regimes of the geometric width vs tearing width theory, developed to explain line-tied suppression of tearing in MHD reconnection. Work supported by the NSF and U.S. DoE through CMSO.

  15. Thermal Structure and Dynamics in Supra-arcade Downflows and Flare Plasma Sheets

    Science.gov (United States)

    Reeves, K.; Hanneman, W.; Freed, M.; McKenzie, D. E.

    2014-12-01

    During a long duration solar flare, a hot plasma sheet is commonly formed above the flare loops. Often produced within this sheet are down-flowing voids referred to as supra-arcade downflows, thought to be the products of a patchy reconnection process. Models differ on the question of whether the downflows should be hotter than the surrounding plasma or not. We use imaging data from Hinode/XRT and SDO/AIA to determine the thermal structure of the plasma sheet and downflows. We find that the temperatures of the plasma within the downflows are either roughly the same as or lower than the surrounding fan plasma. This result implies that a mechanism for forming the voids that involves a sunward directed hydrodynamic shock pattern combined with perpendicular magnetic shock is unlikely. Additionally, we use the high cadence AIA data to trace the velocity fields in these regions through the use of a local correlation tracking algorithm. Through these measurements, we can determine areas of diverging velocity fields, as well as velocity shear fields and correlate them with temperature changes in order to understand the heating mechanisms in the plasma sheet. This work is supported by under contract SP02H1701R from Lockheed-Martin to SAO, contract NNM07AB07C from NASA to SAO and NASA grant numbers NNX13AG54G and NNX14AD43G

  16. Energetic electron spectra in Saturn's plasma sheet

    Science.gov (United States)

    Carbary, J. F.; Paranicas, C.; Mitchell, D. G.; Krimigis, S. M.; Krupp, N.

    2011-07-01

    The differential spectra of energetic electrons (27-400 keV) in Saturn's plasma sheet can be characterized by power law or kappa distributions. Using all available fluxes from 2005 to 2010, fits to these distributions reveal a striking and consistent pattern of radial dependence in Saturn's plasma sheet (∣z∣ constant throughout the Cassini mission. Inward of about 10 RS, the presence of the electron radiation belts and losses of lower-energy electrons to the gas and grain environment give rise to the very hard spectra in the inner magnetosphere, while the hard spectra in the outer magnetosphere may derive from auroral acceleration at high latitudes. The gradual softening of the spectra from 20 to 10 RS is explained by inward radial diffusion.

  17. Reconnection and electron temperature anisotropy in sub-proton scale plasma

    NARCIS (Netherlands)

    Haynes, C.T.; Burgess, D.; Camporeale, E.

    2014-01-01

    Turbulent behavior at sub-proton scales in magnetized plasmas is important for a full understanding of the energetics of astrophysical flows such as the solar wind. We study the formation of electron temperature anisotropy due to reconnection in the turbulent decay of sub-proton scale fluctuations u

  18. Erratum: A Simple, Analytical Model of Collisionless Magnetic Reconnection in a Pair Plasma

    Science.gov (United States)

    Hesse, Michael; Zenitani, Seiji; Kuznetsova, Masha; Klimas, Alex

    2011-01-01

    The following describes a list of errata in our paper, "A simple, analytical model of collisionless magnetic reconnection in a pair plasma." It supersedes an earlier erratum. We recently discovered an error in the derivation of the outflow-to-inflow density ratio.

  19. Final Technical Report: Magnetic Reconnection in High-Energy Laser-Produced Plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Germaschewski, Kai [Univ. of New Hampshire, Durham, NH (United States); Fox, William [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Bhattacharjee, Amitava [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)

    2017-04-06

    This report describes the final results from the DOE Grant DE-SC0007168, “Fast Magnetic Reconnection in HED Laser-Produced Plasmas.” The recent generation of laboratory high-energy-density physics facilities has opened significant physics opportunities for experimentally modeling astrophysical plasmas. The goal of this proposal is to use these new tools to study fundamental problems in plasma physics and plasma astrophysics. Fundamental topics in this area involve study of the generation, amplification, and fate of magnetic fields, which are observed to pervade the plasma universe and govern its evolution. This project combined experiments at DOE laser facilities with kinetic plasma simulation to study these processes. The primary original goal of the project was to study magnetic reconnection using a new experimental platform, colliding magnetized laser-produced plasmas. However through a series of fortuitous discoveries, the work broadened out to allow significant advancement on multiple topics in laboratory astrophysics, including magnetic reconnection, Weibel instability, and collisionless shocks.

  20. Magnetic reconnection from a multiscale instability cascade.

    Science.gov (United States)

    Moser, Auna L; Bellan, Paul M

    2012-02-15

    Magnetic reconnection, the process whereby magnetic field lines break and then reconnect to form a different topology, underlies critical dynamics of magnetically confined plasmas in both nature and the laboratory. Magnetic reconnection involves localized diffusion of the magnetic field across plasma, yet observed reconnection rates are typically much higher than can be accounted for using classical electrical resistivity. It is generally proposed that the field diffusion underlying fast reconnection results instead from some combination of non-magnetohydrodynamic processes that become important on the 'microscopic' scale of the ion Larmor radius or the ion skin depth. A recent laboratory experiment demonstrated a transition from slow to fast magnetic reconnection when a current channel narrowed to a microscopic scale, but did not address how a macroscopic magnetohydrodynamic system accesses the microscale. Recent theoretical models and numerical simulations suggest that a macroscopic, two-dimensional magnetohydrodynamic current sheet might do this through a sequence of repetitive tearing and thinning into two-dimensional magnetized plasma structures having successively finer scales. Here we report observations demonstrating a cascade of instabilities from a distinct, macroscopic-scale magnetohydrodynamic instability to a distinct, microscopic-scale (ion skin depth) instability associated with fast magnetic reconnection. These observations resolve the full three-dimensional dynamics and give insight into the frequently impulsive nature of reconnection in space and laboratory plasmas.

  1. The effect of electron thermal conduction on plasma pressure gradient during reconnection of magnetic field lines

    Energy Technology Data Exchange (ETDEWEB)

    Chu, T.K.

    1987-12-01

    The interplay of electron cross-field thermal conduction and the reconnection of magnetic field lines around an m = 1 magnetic island prior to a sawtooth crash can generate a large pressure gradient in a boundary layer adjacent to the reconnecting surface, leading to an enhanced gradient of poloidal beta to satisfy the threshold condition for ideal MHD modes. This narrow boundary layer and the short onset time of a sawtooth crash can be supported by fine-grained turbulent processes in a tokamak plasma. 11 refs.

  2. Study of energy conversion and partitioning in the magnetic reconnection layer of a laboratory plasma

    Energy Technology Data Exchange (ETDEWEB)

    Yamada, Masaaki; Yoo, Jongsoo; Jara-Almonte, Jonathan; Ji, Hantao; Kulsrud, Russell M.; Myers, Clayton E. [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Daughton, William [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

    2015-05-15

    While the most important feature of magnetic reconnection is that it energizes plasma particles by converting magnetic energy to particle energy, the exact mechanisms by which this happens are yet to be determined despite a long history of reconnection research. Recently, we have reported our results on the energy conversion and partitioning in a laboratory reconnection layer in a short communication [Yamada et al., Nat. Commun. 5, 4474 (2014)]. The present paper is a detailed elaboration of this report together with an additional dataset with different boundary sizes. Our experimental study of the reconnection layer is carried out in the two-fluid physics regime where ions and electrons move quite differently. We have observed that the conversion of magnetic energy occurs across a region significantly larger than the narrow electron diffusion region. A saddle shaped electrostatic potential profile exists in the reconnection plane, and ions are accelerated by the resulting electric field at the separatrices. These accelerated ions are then thermalized by re-magnetization in the downstream region. A quantitative inventory of the converted energy is presented in a reconnection layer with a well-defined, variable boundary. We have also carried out a systematic study of the effects of boundary conditions on the energy inventory. This study concludes that about 50% of the inflowing magnetic energy is converted to particle energy, 2/3 of which is ultimately transferred to ions and 1/3 to electrons. Assisted by another set of magnetic reconnection experiment data and numerical simulations with different sizes of monitoring box, it is also observed that the observed features of energy conversion and partitioning do not depend on the size of monitoring boundary across the range of sizes tested from 1.5 to 4 ion skin depths.

  3. Observation of ion acceleration and heating during collisionless magnetic reconnection in a laboratory plasma.

    Science.gov (United States)

    Yoo, Jongsoo; Yamada, Masaaki; Ji, Hantao; Myers, Clayton E

    2013-05-24

    The ion dynamics in a collisionless magnetic reconnection layer are studied in a laboratory plasma. The measured in-plane plasma potential profile, which is established by electrons accelerated around the electron diffusion region, shows a saddle-shaped structure that is wider and deeper towards the outflow direction. This potential structure ballistically accelerates ions near the separatrices toward the outflow direction. Ions are heated as they travel into the high-pressure downstream region.

  4. 3D magnetic field configuration of small-scale reconnection events in the solar plasma atmosphere

    CERN Document Server

    Shimizu, T

    2015-01-01

    The outer solar atmosphere, i.e., the corona and the chromosphere, is replete with small energy-release events, which are accompanied by transient brightening and jet-like ejections. These events are considered to be magnetic reconnection events in the solar plasma, and their dynamics have been studied using recent advanced observations from the Hinode spacecraft and other observatories in space and on the ground. These events occur at different locations in the solar atmosphere, and vary in their morphology and amount of the released energy. The magnetic field configurations of these reconnection events are inferred based on observations of magnetic fields at the photospheric level. Observations suggest that these magnetic configurations can be classified into two groups. In the first group, two anti-parallel magnetic fields reconnect to each other, yielding a 2D emerging flux configuration. In the second group, helical or twisted magnetic flux tubes are parallel or at a relative angle to each other. Reconne...

  5. Electron acceleration in collisionless shocks and magnetic reconnection by laser-produced plasma ablation

    Science.gov (United States)

    Park, Jaehong; Spitkovksy, Anatoly; Fox, Will; Bhattacharjee, Amitava

    2016-10-01

    We perform particle-in-cell simulations of collisionless shocks and magnetic reconnection generated by ablated plasma expanding into a magnetized background plasma. We find: (1) The simulated proton radiography produces different morphology of the shock structure depending on the orientation of the magnetic field and can be used to identify a shock in the experiment. Electrons are accelerated by the whistler waves generated at oblique sites of the shock. (2) Forced collisionless magnetic reconnection is induced when the expanding plumes carry opposite magnetic polarities and interact with a background plasma. Electrons are accelerated at the reconnection X line and reveal a power-law distribution as the plasma beta is lowered, β = 0.08 . As the plasma beta is increased, β = 0.32 , the 1st order Fermi mechanism against the two plasma plumes contributes to the electron acceleration as well as the X line acceleration. Using 3-D simulations, we also explore the effect of 3-D instabilities (Weibel instability or drift-kink) on particle acceleration and magnetic field annihilation between the colliding magnetized plumes

  6. On the 3-dimensional structure of plasmoids. [in near-earth plasma sheets

    Science.gov (United States)

    Hughes, W. J.; Sibeck, D. G.

    1987-01-01

    The hypothesis that the IMF penetrates plasmoids causing them to be three- rather than two-dimensional is tested by comparing observations of By within plasmoids and related tail structures to upstream IMF By data. The magnetic topologies that result from the mergings of closed plasma sheet flux tubes and open tail lobe flux tubes at a near-earth neutral line, and merging near the tail flanks are described and studied. The particle signals and isotropic electron distributions are examined. It is observed that the IMF By penetrates plasmoids and that their structure is three-dimensional. In the three-dimensional model of plasmoids the reconnected plasma sheet field lines form a magnetic flux-ropelike structure. The three-dimensional model is utilized to analyze stagnant, slowly moving and earthward moving structures.

  7. Three-dimensional shock formation in the spontaneous fast reconnection evolution

    Science.gov (United States)

    Kondoh, K.; Ugai, M.; Shimizu, T.

    2011-12-01

    Shock structure associated with magnetic reconnection is studied using three-dimensional magneto-hydro-dynamics simulations on the basis of the spontaneous fast reconnection model. In the two-dimensional reconnection, the angle between the slow shock pair (thickness of the plasma sheet) is smaller (thinner) in the region with higher reconnection rate. On the other hand, in the three-dimensional reconnection, the reconnection rate in the diffusion region is not uniform in the direction of sheet current, and the angle between the shock pair at the center of the diffusion region should be smallest. However, the profile of the angle in the direction of sheet current is not satisfied with this relationship. It is shown that this structure is caused by the inflow from the direction of the positive and negative sheet current and the inflow of the magnetic flux accompanied with it.

  8. Cassini in situ observations of long-duration magnetic reconnection in Saturn's magnetotail

    CERN Document Server

    Arridge, Christopher S; Jackman, Caitriona M; Poh, Gang-Kai; Slavin, James A; Thomsen, Michelle F; André, Nicolas; Jia, Xianzhe; Kidder, Ariah; Lamy, Laurent; Radioti, Aikaterina; Reisenfeld, Dan B; Sergis, Nick; Volwerk, Martin; Walsh, Andrew P; Zarka, Philippe; Coates, Andrew J; Dougherty, Michele K

    2015-01-01

    Magnetic reconnection is a fundamental process in solar system and astrophysical plasmas, through which stored magnetic energy associated with current sheets is converted into thermal, kinetic and wave energy. Magnetic reconnection is also thought to be a key process involved in shedding internally produced plasma from the giant magnetospheres at Jupiter and Saturn through topological reconfiguration of the magnetic field. The region where magnetic fields reconnect is known as the diffusion region and in this letter we report on the first encounter of the Cassini spacecraft with a diffusion region in Saturn's magnetotail. The data also show evidence of magnetic reconnection over a period of 19 h revealing that reconnection can, in fact, act for prolonged intervals in a rapidly rotating magnetosphere. We show that reconnection can be a significant pathway for internal plasma loss at Saturn. This counters the view of reconnection as a transient method of internal plasma loss at Saturn. These results, although d...

  9. Plasma streams in the Hermean dayside magnetosphere: solar wind injection through the reconnection region

    CERN Document Server

    Varela, J; Moncuquet, M

    2016-01-01

    The aim of this research is to simulate the interaction of the solar wind with the magnetic field of Mercury and to study the particle fluxes between the magnetosheath and the planet surface. We simulate the magnetosphere structure using the open source MHD code PLUTO in spherical geometry with a multipolar expansion of the Hermean magnetic field (Anderson, B. J. et al, 2012). We perform two simulations with realistic solar wind parameters to study the properties of a plasma stream originated in the reconnection region between the interplanetary and the Hermean magnetic field. The plasma precipitates along the open magnetic field lines to the planet surface showing a fast expansion, rarefaction and cooling. The plasma stream is correlated with a flattening of the magnetic field observed by MESSENGER due to the adjacency of the reconnection region where the solar wind is injected to the inner magnetosphere.

  10. Observation of Multiple Reconnections during Self-organization Process of High Temperature Fusion Plasma

    Science.gov (United States)

    Park, H. K.; Tobias, B.; Choi, M. J.; Yun, G. S.; Domier, C. W.; Luhmann, N. C., Jr.; Munsat, T.; Donné, A. J. H.; Spakman, G. W.; Textor Team

    2011-10-01

    Images of a high resolution 2-D Electron Cyclotron Emission Imaging (ECEI) diagnostic shows evidence of multiple magnetic reconnection processes during the internal disruption of a high temperature tokamak plasmas. The disruption induces magnetic self-organization of the toroidal plasma being accompanied by successive or simultaneous multiple layer reconnection. The degree of asymmetric deformation of the internal magnetic structure (m/n=1/1 mode) prior to temperature crash influences the outcome of the disruptive behavior. The observation is critical for the building block of first principle theoretical modeling of the sawtooth oscillation in current driven toroidal plasmas and the understandings can be applied to the impulsive disruptive behavior in flares of the solar, accretion disk and stellar coronae, Earth magnetospheric storms, and controlled fusion. Work supported by the NRF of Korea, the US DOE, the NWO of the Netherlands, and the EURATOM-FOM association.

  11. IMF dependence of energetic oxygen and hydrogen ion distributions in the near-Earth plasma sheet

    Science.gov (United States)

    Luo, Hao; Kronberg, Elena; Nykyri, Katariina; Daly, Patrick; Chen, Gengxiong; Du, Aimin; Ge, Yasong

    2017-04-01

    Energetic ion distributions in the near-Earth plasma sheet can provide important information for understanding the entry of ions into the magnetosphere, and their transportation, acceleration, and losses in the near-Earth region. In this study, 11 years of energetic proton and oxygen observations (> 100 keV) from Cluster/RAPID were used to statistically study the energetic ion distributions in the near-Earth region. The dawn-dusk asymmetries of the distributions in three different regions (dayside magnetosphere, near-Earth nightside plasma sheet, and tail plasma sheet) are examined in northern and southern hemispheres. The results show that the energetic ion distributions are influenced by the dawn-dusk IMF direction. The enhancement of intensity largely correlates with the location of the magnetic reconnection at the magnetopause and the consequent formation of a diamagnetic cavity in the same quadrant of the magnetosphere. The results imply that substorm-related processes in the magnetotail are not the only source of energetic ions in the dayside and the near-Earth plasma sheet. We propose that large-scale cusp diamagnetic cavities can be an additional source and can thus significantly affect the energetic ion population in the magnetosphere. We also believe that the influence of the dawn-dusk IMF direction should not be neglected in models of the particle population in the magnetosphere.

  12. Turbulent magnetic fluctuations in laboratory reconnection

    Science.gov (United States)

    Von Stechow, Adrian; Grulke, Olaf; Klinger, Thomas

    2016-07-01

    The role of fluctuations and turbulence is an important question in astrophysics. While direct observations in space are rare and difficult dedicated laboratory experiments provide a versatile environment for the investigation of magnetic reconnection due to their good diagnostic access and wide range of accessible plasma parameters. As such, they also provide an ideal chance for the validation of space plasma reconnection theories and numerical simulation results. In particular, we studied magnetic fluctuations within reconnecting current sheets for various reconnection parameters such as the reconnection rate, guide field, as well as plasma density and temperature. These fluctuations have been previously interpreted as signatures of current sheet plasma instabilities in space and laboratory systems. Especially in low collisionality plasmas these may provide a source of anomalous resistivity and thereby contribute a significant fraction of the reconnection rate. We present fluctuation measurements from two complementary reconnection experiments and compare them to numerical simulation results. VINETA.II (Greifswald, Germany) is a cylindrical, high guide field reconnection experiment with an open field line geometry. The reconnecting current sheet has a three-dimensional structure that is predominantly set by the magnetic pitch angle which results from the superposition of the guide field and the in-plane reconnecting field. Within this current sheet, high frequency magnetic fluctuations are observed that correlate well with the local current density and show a power law spectrum with a spectral break at the lower hybrid frequency. Their correlation lengths are found to be extremely short, but propagation is nonetheless observed with high phase velocities that match the Whistler dispersion. To date, the experiment has been run with an external driving field at frequencies higher than the ion cyclotron frequency f_{ci}, which implies that the EMHD framework applies

  13. Magnetic Reconnection in the Heliospheric Current Sheet: The Implications of the Different Environments Seen by the VoyagerSpacecraft

    Science.gov (United States)

    Swisdak, M. M.; Drake, J. F.; Opher, M.

    2014-12-01

    The magnetic field abutting the heliospheric current sheet (HCS) is primarily in the azimuthal direction, either east-to-west or west-to-east. Mis-alignment of the solar rotational and magnetic axesleads to the characteristic ballerina-skirt shape of the HCS and during the solar cycle there can be large excursions in the sheet's latitudinal extent. Voyager 2's observations of energetic electrondropouts are related to its crossing of this boundary. Magnetic reconnection is also thought to occur as the HCS compresses and narrows between the termination shock and the heliopause. Near theequator the two HCS field alignments are present in roughly equal amounts, while near the edges the distribution can be considerably skewed. This will lead to substantial differences in the environmentsof the two Voyager spacecraft since Voyager 1 is north of the equator, but firmly in the sector region, while Voyager 2 is south of the equator and skirting the edges of the sector region. We presentparticle-in-cell simulations demonstrating the consequences of the reconnection of asymmetric amounts of flux. In particular, we will discuss Voyager 2's remaining time in the heliosphere -- including theimplications for the solar wind velocity, energetic particle transport, and the expected structure of Voyager 2's heliopause crossing -- and compare it with the data collected from Voyager 1.

  14. Start-Time of Magnetic Reconnection in Interplanetary Space

    Institute of Scientific and Technical Information of China (English)

    范全林; 魏奉思; 冯学尚

    2003-01-01

    Start-time of magnetic reconnection under typical interplanetary parameters has been numerically simulated by using the two-dimensional compressible magnetohydrodynamic equations with a third-order compact upwind scheme. Magnetic reconnection would occur near the interplanetary current sheet impacted by a plasmoid.Its initiation is associated with the interplanetary plasma parameter β and the momentum of the plasmoid.The higher the β value is, the faster the reconnection takes place. Meanwhile the reconnection occurs earlier with increasing the plasmoid momentum, and increasing driving velocity is more effective in initializing the reconnection than that of the plasma density when the other factors are kept to be the same. The evolution of the reconnection with the heliocentric distance is also investigated.

  15. Shocks and Thermal Conduction Fronts in Retracting Reconnected Flux Tubes

    CERN Document Server

    Guidoni, Silvina

    2010-01-01

    We present a model for plasma heating produced by time-dependent, spatially localized reconnection within a flare current sheet separating skewed magnetic fields. The reconnection creates flux tubes of new connectivity which subsequently retract at Alfv\\'enic speeds from the reconnection site. Heating occurs in gas-dynamic shocks which develop inside these tubes. Here we present generalized thin flux tube equations for the dynamics of reconnected flux tubes, including pressure-driven parallel dynamics as well as temperature dependent, anisotropic viscosity and thermal conductivity. The evolution of tubes embedded in a uniform, skewed magnetic field, following reconnection in a patch, is studied through numerical solutions of these equations, for solar coronal conditions. Even though viscosity and thermal conductivity are negligible in the quiet solar corona, the strong gas-dynamic shocks generated by compressing plasma inside reconnected flux tubes generate large velocity and temperature gradients along the t...

  16. ADVECTIVE TRANSPORT OF INTERSTELLAR PLASMA INTO THE HELIOSPHERE ACROSS THE RECONNECTING HELIOPAUSE

    Energy Technology Data Exchange (ETDEWEB)

    Strumik, M.; Grzedzielski, S.; Czechowski, A.; Macek, W. M.; Ratkiewicz, R. [Space Research Centre, Polish Academy of Sciences, Bartycka 18A, 00-716 Warsaw (Poland)

    2014-02-10

    We discuss results of magnetohydrodynamical model simulations of plasma dynamics in the proximity of the heliopause (HP). The model is shown to fit details of the magnetic field variations observed by the Voyager 1 spacecraft during the transition from the heliosphere to the local interstellar medium (LISM). We propose an interpretation of magnetic field structures observed by Voyager 1 in terms of fine-scale physical processes. Our simulations reveal an effective transport mechanism of relatively dense LISM plasma across the reconnecting HP into the heliosphere. The mechanism is associated with annihilation of magnetic sectors in the heliospheric plasma near the HP.

  17. Magnetic reconnection triggering magnetohydrodynamic instabilities during a sawtooth crash in a Tokamak plasma.

    Science.gov (United States)

    Chapman, I T; Scannell, R; Cooper, W A; Graves, J P; Hastie, R J; Naylor, G; Zocco, A

    2010-12-17

    Thomson scattering measurements with subcentimeter spatial resolution have been made during a sawtooth crash in a Mega Ampere Spherical Tokamak fusion plasma. The unparalleled resolution of the temperature profile has shed new light on the mechanisms that underlie the sawtooth. As magnetic reconnection occurs, the temperature gradient at the island boundary increases. The increased local temperature gradient is sufficient to make the helical core unstable to ideal magnetohydrodynamic instabilities, thought to be responsible for the rapidity of the collapse.

  18. Nonthermal Electron Energization from Magnetic Reconnection in Laser-Driven Plasmas.

    Science.gov (United States)

    Totorica, Samuel R; Abel, Tom; Fiuza, Frederico

    2016-03-04

    The possibility of studying nonthermal electron energization in laser-driven plasma experiments of magnetic reconnection is studied using two- and three-dimensional particle-in-cell simulations. It is demonstrated that nonthermal electrons with energies more than an order of magnitude larger than the initial thermal energy can be produced in plasma conditions currently accessible in the laboratory. Electrons are accelerated by the reconnection electric field, being injected at varied distances from the X points, and in some cases trapped in plasmoids, before escaping the finite-sized system. Trapped electrons can be further energized by the electric field arising from the motion of the plasmoid. This acceleration gives rise to a nonthermal electron component that resembles a power-law spectrum, containing up to ∼8% of the initial energy of the interacting electrons and ∼24% of the initial magnetic energy. Estimates of the maximum electron energy and of the plasma conditions required to observe suprathermal electron acceleration are provided, paving the way for a new platform for the experimental study of particle acceleration induced by reconnection.

  19. Washer-Gun Plasma Source for Magnetic Reconnection Experiments on VTF

    Science.gov (United States)

    Vrublevskis, A.; Egedal, J.; Fox, W.; Katz, N.; Le, A.; Porkolab, M.

    2009-11-01

    We present a recently built electrostatic washer-gun plasma source for the Versatile Toroidal Facility (VTF). The source produces plasmas with estimated densities of ˜10^19 m^- 3 and electron temperatures of ˜5-20 eV. The present plasma source for VTF is microwave-induced electron cyclotron resonant breakdown and requires a strong toroidal magnetic field, which acts as a guide field in reconnection experiments. The gun will allow reconnection experiments with no guide field. The source is based on the design developed by Sterling Scientific [1, 2]. To operate, gas is injected into a channel formed by a stack of alternating molybdenum and boron nitride washers with a molybdenum electrode washer at each end. A capacitor bank is discharged through these electrodes and the gas. The resulting plasma escapes the channel into the main chamber of the experiment. If available, we will present data on argon plasma produced by the gun inside the VTF. [1ex] [1] G. Fiksel, et al., Plasma Sources Sci. Technol., 5, 78 (1996)[0ex] [2] D. Hartog et al., Plasma Sources Sci. Technol., 6, 492 (1997)

  20. High-beta plasma blobs in the morningside plasma sheet

    Directory of Open Access Journals (Sweden)

    G. Haerendel

    Full Text Available Equator-S frequently encountered, i.e. on 30% of the orbits between 1 March and 17 April 1998, strong variations of the magnetic field strength of typically 5–15-min duration outside about 9RE during the late-night/early-morning hours. Very high-plasma beta values were found, varying between 1 and 10 or more. Close conjunctions between Equator-S and Geotail revealed the spatial structure of these "plasma blobs" and their lifetime. They are typically 5–10° wide in longitude and have an antisymmetric plasma or magnetic pressure distribution with respect to the equator, while being altogether low-latitude phenomena 
    (≤ 15°. They drift slowly sunward, exchange plasma across the equator and have a lifetime of at least 15–30 min. While their spatial structure may be due to some sort of mirror instability, little is known about the origin of the high-beta plasma. It is speculated that the morningside boundary layer somewhat further tailward may be the source of this plasma. This would be consistent with the preference of the plasma blobs to occur during quiet conditions, although they are also found during substorm periods. The relation to auroral phenomena in the morningside oval is uncertain. The energy deposition may be mostly too weak to generate a visible signature. However, patchy aurora remains a candidate for more disturbed periods.

    Key words. Magnetospheric physics (plasma convection; plasma sheet; plasma waves and instabilities

  1. MULTIPLE PLASMA EJECTIONS AND INTERMITTENT NATURE OF MAGNETIC RECONNECTION IN SOLAR CHROMOSPHERIC ANEMONE JETS

    Energy Technology Data Exchange (ETDEWEB)

    Singh, K. A. P.; Nishida, K.; Shibata, K. [Kwasan and Hida Observatories, Graduate School of Science, Kyoto University, Yamashina, Kyoto 607-8471 (Japan); Isobe, H. [Unit of Synergetic Study for Space, Kyoto University, Yamashina, Kyoto 607-8471 (Japan); Nishizuka, N., E-mail: singh@kwasan.kyoto-u.ac.jp, E-mail: nishida@kwasan.kyoto-u.ac.jp, E-mail: shibata@kwasan.kyoto-u.ac.jp, E-mail: isobe@kwasan.kyoto-u.ac.jp, E-mail: nishizuka.naoto@jaxa.jp [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara-shi, Kanagawa 229-8510 (Japan)

    2012-11-01

    The recent discovery of chromospheric anemone jets with the Solar Optical Telescope (SOT) on board Hinode has shown an indirect evidence of magnetic reconnection in the solar chromosphere. However, the basic nature of magnetic reconnection in chromosphere is still unclear. We studied nine chromospheric anemone jets from SOT/Hinode using Ca II H filtergrams, and we found multiple bright, plasma ejections along the jets. In most cases, the major intensity enhancements (larger than 30% relative to the background intensity) of the loop correspond to the timing of the plasma ejections. The typical lifetime and size of the plasma ejecta are about 20-60 s and 0.3-1.5 Mm, respectively. The height-time plot of jet shows many sub-structures (or individual jets) and the typical lifetime of the individual jet is about one to five minutes. Before the onset of the jet activity, a loop appears in Ca II H and gradually increases in size, and after few minutes several jets are launched from the loop. Once the jet activity starts and several individual jets are launched, the loop starts shrinking with a speed of {approx}4 km s{sup -1}. In some events, a downward moving blob with a speed of {approx}35 km s{sup -1} was observed, associated with the upward moving plasma along one of the legs of the loop hosting the jets. The upward moving plasma gradually developed into jets. Multiple plasma ejections in chromospheric anemone jet show the strongly time-dependent as well as intermittent nature of magnetic reconnection in the solar chromosphere.

  2. Collisionless Magnetic Reconnection as an Ion Acceleration Mechanism of Low- β Laboratory Plasmas

    Science.gov (United States)

    Cazzola, Emanuele; Curreli, Davide; Lapenta, Giovanni

    2016-10-01

    In this work we present the results from a series of fully-kinetic simulations of magnetic reconnection under typical laboratory plasma conditions. The highly-efficient energy conversion obtained from this process is of great interest for applications such as future electric propulsion systems and ion beam accelerators. We analysed initial configurations in low-beta conditions with reduced mass ratio of mi = 512me at magnetic fields between 200G and 5000G and electron temperatures between 0.5 and 10eV. The initial ion density and temperature are kept uniform and equal to 1019 m-3 and 0.0215eV (room temperature) respectively. The analysis has shown that the reconnection process under these conditions can accelerate ions up to velocities as high as a significant fraction of the inflow Alfven speed. The configuration showing the best scenario is further studied with a realistic mass ratio in terms of energetics and outflow ion momentum, with the latter featured by the traditionally used specific impulse. Finally, a more detailed analysis of the reconnection outflow has revealed the formation of different interesting set of shock structures, also recently seen from MHD simulations of relativistic plasmas and certainly subject of future more careful attention. The present work has been possible thanks to the Illinois-KULeuven Faculty/PhD Candidate Exchange Program. Computational resources provided by the PRACE Tier-0 machines.

  3. The Dynamical Generation of Current Sheets in Astrophysical Plasma Turbulence

    CERN Document Server

    Howes, Gregory G

    2016-01-01

    Turbulence profoundly affects particle transport and plasma heating in many astrophysical plasma environments, from galaxy clusters to the solar corona and solar wind to Earth's magnetosphere. Both fluid and kinetic simulations of plasma turbulence ubiquitously generate coherent structures, in the form of current sheets, at small scales, and the locations of these current sheets appear to be associated with enhanced rates of dissipation of the turbulent energy. Therefore, illuminating the origin and nature of these current sheets is critical to identifying the dominant physical mechanisms of dissipation, a primary aim at the forefront of plasma turbulence research. Here we present evidence from nonlinear gyrokinetic simulations that strong nonlinear interactions between counterpropagating Alfven waves, or strong Alfven wave collisions, are a natural mechanism for the generation of current sheets in plasma turbulence. Furthermore, we conceptually explain this current sheet development in terms of the nonlinear...

  4. Boosting Magnetic Reconnection by Viscosity and Thermal Conduction

    CERN Document Server

    Minoshima, Takashi; Imada, Shinsuke

    2016-01-01

    Nonlinear evolution of magnetic reconnection is investigated by means of magnetohydrodynamic simulations including uniform resistivity, uniform viscosity, and anisotropic thermal conduction. When viscosity exceeds resistivity (the magnetic Prandtl number Prm > 1), the viscous dissipation dominates outflow dynamics and leads to the decrease in the plasma density inside a current sheet. The low-density current sheet supports the excitation of the vortex. The thickness of the vortex is broader than that of the current for Prm > 1. The broader vortex flow more efficiently carries the upstream magnetic flux toward the reconnection region, and consequently boosts the reconnection. The reconnection rate increases with viscosity provided that thermal conduction is fast enough to take away the thermal energy increased by the viscous dissipation (the fluid Prandtl number Pr < 1). The result suggests the need to control the Prandtl numbers for the reconnection against the conventional resistive model.

  5. Three-dimensional Spontaneous Magnetic Reconnection

    Science.gov (United States)

    Beresnyak, Andrey

    2017-01-01

    Magnetic reconnection is best known from observations of the Sun where it causes solar flares. Observations estimate the reconnection rate as a small, but non-negligible fraction of the Alfvén speed, so-called fast reconnection. Until recently, the prevailing pictures of reconnection were either of resistivity or plasma microscopic effects, which was contradictory to the observed rates. Alternative pictures were either of reconnection due to the stochasticity of magnetic field lines in turbulence or the tearing instability of the thin current sheet. In this paper we simulate long-term three-dimensional nonlinear evolution of a thin, planar current sheet subject to a fast oblique tearing instability using direct numerical simulations of resistive-viscous magnetohydrodynamics. The late-time evolution resembles generic turbulence with a ‑5/3 power spectrum and scale-dependent anisotropy, so we conclude that the tearing-driven reconnection becomes turbulent reconnection. The turbulence is local in scale, so microscopic diffusivity should not affect large-scale quantities. This is confirmed by convergence of the reconnection rate toward ∼ 0.015{v}{{A}} with increasing Lundquist number. In this spontaneous reconnection, with mean field and without driving, the dissipation rate per unit area also converges to ∼ 0.006ρ {v}{{A}}3, and the dimensionless constants 0.015 and 0.006 are governed only by self-driven nonlinear dynamics of the sheared magnetic field. Remarkably, this also means that a thin current sheet has a universal fluid resistance depending only on its length to width ratio and to {v}{{A}}/c.

  6. Dynamics of a reconnection-driven runaway ion tail in a reversed field pinch plasma

    Science.gov (United States)

    Anderson, J. K.; Kim, J.; Bonofiglo, P. J.; Capecchi, W.; Eilerman, S.; Nornberg, M. D.; Sarff, J. S.; Sears, S. H.

    2016-05-01

    While reconnection-driven ion heating is common in laboratory and astrophysical plasmas, the underlying mechanisms for converting magnetic to kinetic energy remain not fully understood. Reversed field pinch discharges are often characterized by rapid ion heating during impulsive reconnection, generating an ion distribution with an enhanced bulk temperature, mainly perpendicular to magnetic field. In the Madison Symmetric Torus, a subset of discharges with the strongest reconnection events develop a very anisotropic, high energy tail parallel to magnetic field in addition to bulk perpendicular heating, which produces a fusion neutron flux orders of magnitude higher than that expected from a Maxwellian distribution. Here, we demonstrate that two factors in addition to a perpendicular bulk heating mechanism must be considered to explain this distribution. First, ion runaway can occur in the strong parallel-to-B electric field induced by a rapid equilibrium change triggered by reconnection-based relaxation; this effect is particularly strong on perpendicularly heated ions which experience a reduced frictional drag relative to bulk ions. Second, the confinement of ions varies dramatically as a function of velocity. Whereas thermal ions are governed by stochastic diffusion along tearing-altered field lines (and radial diffusion increases with parallel speed), sufficiently energetic ions are well confined, only weakly affected by a stochastic magnetic field. High energy ions traveling mainly in the direction of toroidal plasma current are nearly classically confined, while counter-propagating ions experience an intermediate confinement, greater than that of thermal ions but significantly less than classical expectations. The details of ion confinement tend to reinforce the asymmetric drive of the parallel electric field, resulting in a very asymmetric, anisotropic distribution.

  7. Excitation of electrostatic waves in the electron cyclotron frequency range during magnetic reconnection in laboratory overdense plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Kuwahata, A., E-mail: kuwahata@ts.t.u-tokyo.ac.jp [Graduate School of Engineering, The University of Tokyo, Tokyo 113-8656 (Japan); Igami, H. [National Institute for Fusion Science, Toki 509-5292 (Japan); Kawamori, E. [Institute of Space and Plasma Sciences, National Cheng Kung University, Tainan 70101, Taiwan (China); Kogi, Y. [Fukuoka Institute of Technology, Fukuoka 811-0295 (Japan); Inomoto, M.; Ono, Y. [Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa 277-8561 (Japan)

    2014-10-15

    We report the observation of electromagnetic radiation at high harmonics of the electron cyclotron frequency that was considered to be converted from electrostatic waves called electron Bernstein waves (EBWs) during magnetic reconnection in laboratory overdense plasmas. The excitation of EBWs was attributed to the thermalization of electrons accelerated by the reconnection electric field around the X-point. The radiative process discussed here is an acceptable explanation for observed radio waves pulsation associated with major flares.

  8. Diagnostics of solar flare reconnection

    Directory of Open Access Journals (Sweden)

    M. Karlický

    2004-01-01

    Full Text Available We present new diagnostics of the solar flare reconnection, mainly based on the plasma radio emission. We propose that the high-frequency (600-2000 MHz slowly drifting pulsating structures map the flare magnetic field reconnection. These structures correspond to the radio emission from plasmoids which are formed in the extended current sheet due to tearing and coalescence processes. An increase of the frequency drift of the drifting structures is interpreted as an increase of the reconnection rate. Using this model, time scales of slowly drifting pulsating structure observed during the 12 April 2001 flare by the Trieste radiopolarimeter with high time resolution (1 ms are interpreted as a radio manifestation of electron beams accelerated in the multi-scale reconnection process. For short periods Fourier spectra of the observed structure have a power-law form with power-law indices in the 1.3-1.6 range. For comparison the 2-D MHD numerical modeling of the multi-scale reconnection is made and it is shown that Fourier spectrum of the reconnection dissipation power has also a power-law form, but with power-law index 2. Furthermore, we compute a time evolution of plasma parameters (density, magnetic field etc in the 2-D MHD model of the reconnection. Then assuming a plasma radio emission from locations, where the 'double-resonance' instability generates the upper-hybrid waves due to unstable distribution function of suprathermal electrons, we model radio spectra. Effects of the MHD turbulence are included. The resulting spectra are compared with those observed. It is found, that depending on model parameters the lace bursts and the decimetric spikes can be reproduced. Thus, it is shown that the model can be used for diagnostics of the flare reconnection process. We also point out possible radio signatures of reconnection outflow termination shocks. They are detected as type II-like herringbone structures in the 200-700 MHz frequency range. Finally

  9. Formation and evolution of flapping and ballooning waves in magnetospheric plasma sheet

    Science.gov (United States)

    Ma, J. Z. G.; Hirose, A.

    2016-05-01

    By adopting Lembége & Pellat's 2D plasma-sheet model, we investigate the flankward flapping motion and Sunward ballooning propagation driven by an external source (e.g., magnetic reconnection) produced initially at the sheet center. Within the ideal MHD framework, we adopt the WKB approximation to obtain the Taylor-Goldstein equation of magnetic perturbations. Fourier spectral method and Runge-Kutta method are employed in numerical simulations, respectively, under the flapping and ballooning conditions. Studies expose that the magnetic shears in the sheet are responsible for the flapping waves, while the magnetic curvature and the plasma gradient are responsible for the ballooning waves. In addition, the flapping motion has three phases in its temporal development: fast damping phase, slow recovery phase, and quasi-stabilized phase; it is also characterized by two patterns in space: propagating wave pattern and standing wave pattern. Moreover, the ballooning modes are gradually damped toward the Earth, with a wavelength in a scale size of magnetic curvature or plasma inhomogeneity, only 1-7% of the flapping one; the envelops of the ballooning waves are similar to that of the observed bursty bulk flows moving toward the Earth.

  10. Three-dimensional relativistic pair plasma reconnection with radiative feedback in the Crab Nebula

    Energy Technology Data Exchange (ETDEWEB)

    Cerutti, B. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Werner, G. R.; Uzdensky, D. A. [Center for Integrated Plasma Studies, Physics Department, University of Colorado, UCB 390, Boulder, CO 80309-0390 (United States); Begelman, M. C., E-mail: bcerutti@astro.princeton.edu, E-mail: greg.werner@colorado.edu, E-mail: uzdensky@colorado.edu, E-mail: mitch@jila.colorado.edu [JILA, University of Colorado and National Institute of Standards and Technology, UCB 440, Boulder, CO 80309-0440 (United States)

    2014-02-20

    The discovery of rapid synchrotron gamma-ray flares above 100 MeV from the Crab Nebula has attracted new interest in alternative particle acceleration mechanisms in pulsar wind nebulae. Diffuse shock-acceleration fails to explain the flares because particle acceleration and emission occur during a single or even sub-Larmor timescale. In this regime, the synchrotron energy losses induce a drag force on the particle motion that balances the electric acceleration and prevents the emission of synchrotron radiation above 160 MeV. Previous analytical studies and two-dimensional (2D) particle-in-cell (PIC) simulations indicate that relativistic reconnection is a viable mechanism to circumvent the above difficulties. The reconnection electric field localized at X-points linearly accelerates particles with little radiative energy losses. In this paper, we check whether this mechanism survives in three dimension (3D), using a set of large PIC simulations with radiation reaction force and with a guide field. In agreement with earlier works, we find that the relativistic drift kink instability deforms and then disrupts the layer, resulting in significant plasma heating but few non-thermal particles. A moderate guide field stabilizes the layer and enables particle acceleration. We report that 3D magnetic reconnection can accelerate particles above the standard radiation reaction limit, although the effect is less pronounced than in 2D with no guide field. We confirm that the highest-energy particles form compact bunches within magnetic flux ropes, and a beam tightly confined within the reconnection layer, which could result in the observed Crab flares when, by chance, the beam crosses our line of sight.

  11. Three-dimensional Relativistic Pair Plasma Reconnection with Radiative Feedback in the Crab Nebula

    Science.gov (United States)

    Cerutti, B.; Werner, G. R.; Uzdensky, D. A.; Begelman, M. C.

    2014-02-01

    The discovery of rapid synchrotron gamma-ray flares above 100 MeV from the Crab Nebula has attracted new interest in alternative particle acceleration mechanisms in pulsar wind nebulae. Diffuse shock-acceleration fails to explain the flares because particle acceleration and emission occur during a single or even sub-Larmor timescale. In this regime, the synchrotron energy losses induce a drag force on the particle motion that balances the electric acceleration and prevents the emission of synchrotron radiation above 160 MeV. Previous analytical studies and two-dimensional (2D) particle-in-cell (PIC) simulations indicate that relativistic reconnection is a viable mechanism to circumvent the above difficulties. The reconnection electric field localized at X-points linearly accelerates particles with little radiative energy losses. In this paper, we check whether this mechanism survives in three dimension (3D), using a set of large PIC simulations with radiation reaction force and with a guide field. In agreement with earlier works, we find that the relativistic drift kink instability deforms and then disrupts the layer, resulting in significant plasma heating but few non-thermal particles. A moderate guide field stabilizes the layer and enables particle acceleration. We report that 3D magnetic reconnection can accelerate particles above the standard radiation reaction limit, although the effect is less pronounced than in 2D with no guide field. We confirm that the highest-energy particles form compact bunches within magnetic flux ropes, and a beam tightly confined within the reconnection layer, which could result in the observed Crab flares when, by chance, the beam crosses our line of sight.

  12. Magnetic turbulence in the plasma sheet

    CERN Document Server

    Vörös, Z; Nakamura, R; Runov, A; Zhang, T L; Eichelberger, H U; Treumann, R A; Georgescu, E; Balogh, A; Klecker, B; R`eme, H

    2004-01-01

    Small-scale magnetic turbulence observed by the Cluster spacecraft in the plasma sheet is investigated by means of a wavelet estimator suitable for detecting distinct scaling characteristics even in noisy measurements. The spectral estimators used for this purpose are affected by a frequency dependent bias. The variances of the wavelet coefficients, however, match the power-law shaped spectra, which makes the wavelet estimator essentially unbiased. These scaling characteristics of the magnetic field data appear to be essentially non-steady and intermittent. The scaling properties of bursty bulk flow (BBF) and non-BBF associated magnetic fluctuations are analysed with the aim of understanding processes of energy transfer between scales. Small-scale ($\\sim 0.08-0.3$ s) magnetic fluctuations having the same scaling index $\\alpha \\sim 2.6$ as the large-scale ($\\sim 0.7-5$ s) magnetic fluctuations occur during BBF-associated periods. During non-BBF associated periods the energy transfer to small scales is absent, ...

  13. Gyrophase bunched ions in the plasma sheet

    Science.gov (United States)

    Wang, Zhiqiang; Zhai, Hao; Gao, Zhuxiu; Huang, Chaoyan

    2017-01-01

    Gyrophase bunched ions were first detected in the upstream region of the Earth's bow shock in the early 1980s which is formed by the microphysical process associated with reflected solar wind ions at the bow shock. Inside the magnetosphere, the results of computer simulations demonstrated that nonlinear wave-particle interaction can also result in the gyrophase bunching of particles. However, to date direct observations barely exist regarding this issue occurred inside the magnetosphere. In this paper, we report for the first time an event of gyrophase bunched ions observed in the near-Earth plasma sheet. The nongyrotropic distributions of ions were closely accompanied with the electromagnetic waves at the oxygen cyclotron frequency. The phase of bunched ions and the phase of waves mainly have very narrow phase differences (helicity with respect to the propagation direction, which agrees with the characteristic of electromagnetic ion cyclotron waves. The observation of O+ ions composition suggests that the oxygen band waves are excited due to the enhancements of the O+ ion density. This study suggests that the gyrophase bunching is a significant nonlinear effect that exists not only in the bow shock but also in the inner magnetosphere.

  14. The extent of power-law energy spectra in collisionless relativistic magnetic reconnection in pair plasmas

    CERN Document Server

    Werner, G R; Cerutti, B; Nalewajko, K; Begelman, M C

    2014-01-01

    Using two-dimensional particle-in-cell simulations, we characterize the energy spectra of particles accelerated by relativistic magnetic reconnection (without guide field) in collisionless electron-positron plasmas, for a wide range of upstream magnetizations $\\sigma$ and system sizes $L$. The particle spectra are well-represented by a power law $\\gamma^{-\\alpha}$, with a combination of exponential and super-exponential high-energy cutoffs, proportional to $\\sigma$ and $L$, respectively. For large $L$ and $\\sigma$, the power-law index $\\alpha$ approaches about 1.2.

  15. Non-Thermal Electron Energization from Magnetic Reconnection in Laser-Driven Plasmas

    CERN Document Server

    Totorica, Samuel; Fiuza, Frederico

    2016-01-01

    The possibility of studying non-thermal electron energization in laser-driven plasma experiments of magnetic reconnection is studied using two- and three-dimensional particle-in-cell simulations. It is demonstrated that non-thermal electrons with energies more than an order of magnitude larger than the initial thermal energy can be produced in plasma conditions currently accessible in the laboratory. Electrons are accelerated by the reconnection electric field, being injected at varied distances from the X-points, and in some cases trapped in plasmoids, before escaping the finite-sized system. Trapped electrons can be further energized by the electric field arising from the motion of the plasmoid. This acceleration gives rise to a non-thermal electron component that resembles a power-law spectrum, containing up to ~ 8% of the initial energy of the interacting electrons and ~ 24 % of the initial magnetic energy. Estimates of the maximum electron energy and of the plasma conditions required to observe suprather...

  16. Relativistic magnetic reconnection in collisionless ion-electron plasmas explored with particle-in-cell simulations

    CERN Document Server

    Melzani, Mickaël; Folini, Doris; Winisdoerffer, Christophe; Favre, Jean M

    2014-01-01

    Magnetic reconnection is a leading mechanism for magnetic energy conversion and high-energy non-thermal particle production in a variety of high-energy astrophysical objects, including ones with relativistic ion-electron plasmas (e.g., microquasars or AGNs) - a regime where first principle studies are scarce. We present 2D particle-in-cell (PIC) simulations of low $\\beta$ ion-electron plasmas under relativistic conditions, i.e., with inflow magnetic energy exceeding the plasma rest-mass energy. We identify outstanding properties: (i) For relativistic inflow magnetizations (here $10 80$), the reconnection electric field is sustained more by bulk inertia than by thermal inertia. It challenges the thermal-inertia-paradigm and its implications. (iii) The inflows feature sharp transitions at the entrance of the diffusion zones. These are not shocks but results from particle ballistic motions, all bouncing at the same location, provided that the thermal velocity in the inflow is far smaller than the inflow E cross...

  17. Magnetic field generation, Weibel-mediated collisionless shocks, and magnetic reconnection in colliding laser-produced plasmas

    Science.gov (United States)

    Fox, W.; Bhattacharjee, A.; Fiksel, G.

    2016-10-01

    Colliding plasmas are ubiquitous in astrophysical environments and allow conversion of kinetic energy into heat and, most importantly, the acceleration of particles to extremely high energies to form the cosmic ray spectrum. In collisionless astrophysical plasmas, kinetic plasma processes govern the interaction and particle acceleration processes, including shock formation, self-generation of magnetic fields by kinetic plasma instabilities, and magnetic field compression and reconnection. How each of these contribute to the observed spectra of cosmic rays is not fully understood, in particular both shock acceleration processes and magnetic reconnection have been proposed. We will review recent results of laboratory astrophysics experiments conducted at high-power, inertial-fusion-class laser facilities, which have uncovered significant results relevant to these processes. Recent experiments have now observed the long-sought Weibel instability between two interpenetrating high temperature plasma plumes, which has been proposed to generate the magnetic field necessary for shock formation in unmagnetized regimes. Secondly, magnetic reconnection has been studied in systems of colliding plasmas using either self-generated magnetic fields or externally applied magnetic fields, and show extremely fast reconnection rates, indicating fast destruction of magnetic energy and further possibilities to accelerate particles. Finally, we highlight kinetic plasma simulations, which have proven to be essential tools in the design and interpretation of these experiments.

  18. Fast magnetic reconnection supported by sporadic small-scale Petschek-type shocks

    Energy Technology Data Exchange (ETDEWEB)

    Shibayama, Takuya, E-mail: shibayama@stelab.nagoya-u.ac.jp; Nakabou, Takashi [Institute for Space-Earth Environmental Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan); Kusano, Kanya [Institute for Space-Earth Environmental Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan); Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Kanazawa-ku, Yokohama, Kanagawa 236-0001 (Japan); Miyoshi, Takahiro [Department of Physical Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526 (Japan); Vekstein, Grigory [Jodrell Bank Centre for Astrophysics, University of Manchester, Manchester M13 9PL (United Kingdom)

    2015-10-15

    Standard magnetohydrodynamic (MHD) theory predicts reconnection rate that is far too slow to account for a wide variety of reconnection events observed in space and laboratory plasmas. Therefore, it was commonly accepted that some non-MHD (kinetic) effects play a crucial role in fast reconnection. A recently renewed interest in simple MHD models is associated with the so-called plasmoid instability of reconnecting current sheets. Although it is now evident that this effect can significantly enhance the rate of reconnection, many details of the underlying multiple-plasmoid process still remain controversial. Here, we report results of a high-resolution computer simulation which demonstrate that fast albeit intermittent magnetic reconnection is sustained by numerous small-scale Petschek-type shocks spontaneously formed in the current sheet due to its plasmoid instability.

  19. Magnetic reconnection: from MHD to QED

    Science.gov (United States)

    Bulanov, S. V.

    2017-01-01

    The paper examines the prospects of using laser plasmas for studying novel regimes of the magnetic field line reconnection and charged particle acceleration. Basic features of plasma dynamics in the three-dimensional configurations relevant to the formation of current sheets in a plasma are addressed by analyzing exact self-similar solutions of the magneto-hydrodynamics and electron magneto-hydrodynamics equations. Then the magnetic field annihilation in the ultrarelativistic limit is considered, when the opposite polarity magnetic field is generated in collisionless plasma by multiple laser pulses, in the regime with a dominant contribution of the displacement current exciting a strong large-scale electric field. This field leads to the conversion of the magnetic energy into the kinetic energy of accelerated particles inside a thin current sheet. Charged particle acceleration during magnetic field reconnection is discussed when radiation friction and quantum electrodynamics effects become dominant.

  20. Magnetic reconnection: from MHD to QED

    CERN Document Server

    Bulanov, S V

    2016-01-01

    The paper examines the prospects of using laser plasmas for studying novel regimes of the magnetic field line reconnection and charged particle acceleration. Basic features of plasma dynamics in the three-dimensional configurations relevant to the formation of current sheets in a plasma are addressed by analyzing exact self-similar solutions of the magneto-hydrodynamics and electron magneto-hydrodynamics equations. Then the magnetic field annihilation in the ultrarelativistic limit is considered, when the opposite polarity magnetic field is generated in collisionless plasma by multiple laser pulses, in the regime with a dominant contribution of the displacement current exciting a strong large-scale electric field. This field leads to the conversion of the magnetic energy into the kinetic energy of accelerated particles inside a thin current sheet. Charged particle acceleration during magnetic field reconnection is discussed when radiation friction and quantum electrodynamics effects become dominant.

  1. Particle-in-cell simulations of Magnetic Field Generation, Evolution, and Reconnection in Laser-driven Plasmas

    Science.gov (United States)

    Matteucci, Jack; Moissard, Clément; Fox, Will; Bhattacharjee, Amitava

    2016-10-01

    The advent of high-energy-density physics facilities has introduced the opportunity to experimentally investigate magnetic field dynamics relevant to both ICF and astrophysical plasmas. Recent experiments have demonstrated magnetic reconnection between colliding plasma plumes, where the reconnecting magnetic fields were self-generated in the plasma by the Biermann battery effect. In this study, we simulate these experiments from first principles using 2-D and 3-D particle-in-cell simulations. Simulations self-consistently demonstrate magnetic field generation by the Biermann battery effect, followed by advection by the Hall effect and ion flow. In 2-D simulations, we find in both the collisionless case and the semi-collisional case, defined by eVi × B >> Rei /ne (where Rei is the electron ion momentum transfer) that quantitative agreement with the generalized Ohm's law is only obtained with the inclusion of the pressure tensor. Finally, we document that significant field is destroyed at the reconnection site by the Biermann term, an inverse, `anti-Biermann' effect, which has not been considered previously in analysis of the experiment. The role of the anti-Biermann effect will be compared to standard reconnection mechanisms in 3-D reconnection simulations. This research used resources of the ORLC Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. DoE under Contract No. DE-AC05-00OR22725.

  2. Hard X-Ray Burst Detected From Caltech Plasma Jet Experiment Magnetic Reconnection Event

    Science.gov (United States)

    Marshall, Ryan S.; Bellan, Paul M.

    2016-10-01

    In the Caltech plasma jet experiment a 100 kA MHD driven jet becomes kink unstable leading to a Rayleigh-Taylor instability that quickly causes a magnetic reconnection event. Movies show that the Rayleigh-Taylor instability is simultaneous with voltage spikes across the electrodes that provide the current that drives the jet. Hard x-rays between 4 keV and 9 keV have now been observed using an x-ray scintillator detector mounted just outside of a kapton window on the vacuum chamber. Preliminary results indicate that the timing of the x-ray burst coincides with a voltage spike on the electrodes occurring in association with the Rayleigh-Taylor event. The x-ray signal accompanies the voltage spike and Rayleigh-Taylor event in approximately 50% of the shots. A possible explanation for why the x-ray signal is sometimes missing is that the magnetic reconnection event may be localized to a specific region of the plasma outside the line of sight of the scintillator. The x-ray signal has also been seen accompanying the voltage spike when no Rayleigh-Taylor is observed. This may be due to the interframe timing on the camera being longer than the very short duration of the Rayleigh-Taylor instability.

  3. Particle-in-Cell Simulations of Collisionless Magnetic Reconnection with a Non-Uniform Guide Field

    CERN Document Server

    Wilson, Fiona; Hesse, Michael; Harrison, Michael G; Stark, Craig R

    2015-01-01

    Results are presented of a first study of collisionless magnetic reconnection starting from a recently found exact nonlinear force-free Vlasov-Maxwell equilibrium. The initial state has a Harris sheet magnetic field profile in one direction and a non-uniform guide field in a second direction, resulting in a spatially constant magnetic field strength as well as a constant initial plasma density and plasma pressure. It is found that the reconnection process initially resembles guide field reconnection, but that a gradual transition to anti-parallel reconnection happens as the system evolves. The time evolution of a number of plasma parameters is investigated, and the results are compared with simulations starting from a Harris sheet equilibrium and a Harris sheet plus constant guide field equilibrium.

  4. Nonlinear regimes of forced magnetic reconnection

    Energy Technology Data Exchange (ETDEWEB)

    Vekstein, G., E-mail: g.vekstein@manchester.ac.uk [JBCA, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL (United Kingdom); STEL, Nagoya University, Nagoya, Aichi 464-8601 (Japan); Kusano, K. [STEL, Nagoya University, Nagoya, Aichi 464-8601 (Japan)

    2015-09-15

    This letter presents a self-consistent description of nonlinear forced magnetic reconnection in Taylor's model of this process. If external boundary perturbation is strong enough, nonlinearity in the current sheet evolution becomes important before resistive effects come into play. This terminates the current sheet shrinking that takes place at the linear stage and brings about its nonlinear equilibrium with a finite thickness. Then, in theory, this equilibrium is destroyed by a finite plasma resistivity during the skin-time, and further reconnection proceeds in the Rutherford regime. However, realization of such a scenario is unlikely because of the plasmoid instability, which is fast enough to develop before the transition to the Rutherford phase occurs. The suggested analytical theory is entirely different from all previous studies and provides proper interpretation of the presently available numerical simulations of nonlinear forced magnetic reconnection.

  5. Activation of MHD reconnection on ideal timescales

    CERN Document Server

    Landi, S; Del Zanna, L; Tenerani, A; Pucci, F

    2016-01-01

    Magnetic reconnection in laboratory, space and astrophysical plasmas is often invoked to explain explosive energy release and particle acceleration. However, the timescales involved in classical models within the macroscopic MHD regime are far too slow to match the observations. Here we revisit the tearing instability by performing visco-resistive two-dimensional numerical simulations of the evolution of thin current sheets, for a variety of initial configurations and of values of the Lunquist number $S$, up to $10^7$. Results confirm that when the critical aspect ratio of $S^{1/3}$ is reached in the reconnecting current sheets, the instability proceeds on ideal (Alfv\\'enic) macroscopic timescales, as required to explain observations. Moreover, the same scaling is seen to apply also to the local, secondary reconnection events triggered during the nonlinear phase of the tearing instability, thus accelerating the cascading process to increasingly smaller spatial and temporal scales. The process appears to be ro...

  6. A new magnetic reconnection paradigm: Stochastic plasmoid chains

    Science.gov (United States)

    Loureiro, Nuno

    2015-11-01

    Recent analytical and numerical research in magnetic reconnection has converged on the notion that reconnection sites (current sheets) are unstable to the formation of multiple magnetic islands (plasmoids), provided that the system is sufficiently large (or, in other words, that the Lundquist number of the plasma is high). Nonlinearly, plasmoids come to define the reconnection geometry. Their nonlinear dynamics is rather complex and best thought of as new form of turbulence whose properties are determined by continuous plasmoid formation and their subsequent ejection from the sheet, as well as the interaction (coalescence) between plasmoids of different sizes. The existence of these stochastic plasmoid chains has powerful implications for several aspects of the reconnection process, from determining the reconnection rate to the details and efficiency of the energy conversion and dissipation. In addition, the plasmoid instability may also directly bear on the little understood problem of the reconnection trigger, or onset, i.e., the abrupt transition from a slow stage of energy accumulation to a fast (explosive) stage of energy release. This talk will first provide a brief overview of these recent developments in the reconnection field. I will then discuss recent work addressing the onset problem in the context of a forming current sheet which becomes progressively more unstable to the plasmoid instability. Work partially supported by Fundação para a Ciência e Tecnologia via Grants UID/FIS/50010/2013 and IF/00530/2013.

  7. Plasmoid Instability in High-Lundquist-Number Magnetic Reconnection

    CERN Document Server

    Huang, Yi-Min

    2013-01-01

    Our understanding of magnetic reconnection in resistive magnetohydrodynamics has gone through a fundamental change in recent years. The conventional wisdom is that magnetic reconnection mediated by resistivity is slow in laminar high Lundquist ($S$) plasmas, constrained by the scaling of the reconnection rate predicted by Sweet-Parker theory. However, recent studies have shown that when $S$ exceeds a critical value $\\sim10^{4}$, the Sweet-Parker current sheet is unstable to a super-Alfv\\'enic plasmoid instability, with a linear growth rate that scales as $S^{1/4}$. In the fully developed statistical steady state of two-dimensional resistive magnetohydrodynamic simulations, the normalized average reconnection rate is approximately 0.01, nearly independent of $S$, and the distribution function $f(\\psi)$ of plasmoid magnetic flux $\\psi$ follows a power law $f(\\psi)\\sim\\psi^{-1}$. When Hall effects are included, the plasmoid instability may trigger onset of Hall reconnection even when the conventional criterion f...

  8. A Theoretical Model of Pinching Current Sheet in Low-beta Plasmas

    CERN Document Server

    Takeshige, Satoshi; Shibata, Kazunari

    2015-01-01

    Magnetic reconnection is an important physical process in various explosive phenomena in the universe. In the previous studies, it was found that fast re- connection takes place when the thickness of a current sheet becomes on the order of a microscopic length such as the ion larmor radius or the ion inertial length. In this study, we investigated the pinching process of a current sheet by the Lorentz force in a low-{\\beta} plasma using one-dimensional magnetohydrodynam- ics (MHD) simulations. It is known that there is an exact self-similar solution for this problem that neglects gas pressure. We compared the non-linear MHD dynamics with the analytic self-similar solution. From the MHD simulations, we found that with the gas pressure included the implosion process deviates from the analytic self-similar solution as t {\\rightarrow} t 0, where t 0 is the explosion time when the thickness of a current sheet of the analytic solution becomes 0. We also found a pair of MHD fast-mode shocks are generated and propaga...

  9. Physical Conditions in the Reconnection Layer in Pulsar Magnetospheres

    CERN Document Server

    Uzdensky, Dmitri A

    2012-01-01

    The magnetosphere of a rotating pulsar naturally develops a current sheet beyond the light cylinder (LC). Magnetic reconnection in this current sheet inevitably dissipates a nontrivial fraction of the pulsar spin-down power within a few LC radii. We develop a basic physical picture of reconnection in this environment and discuss its implications for the observed pulsed gamma-ray emission. We argue that reconnection proceeds in the plasmoid-dominated regime, via an hierarchical chain of multiple secondary islands/flux ropes. The inter-plasmoid reconnection layers are subject to strong synchrotron cooling, leading to significant plasma compression. Using the conditions of pressure balance across these current layers, the balance between the heating by magnetic energy dissipation and synchrotron cooling, and Ampere's law, we obtain simple estimates for key parameters of the layers --- temperature, density, and layer thickness. In the comoving frame of the relativistic pulsar wind just outside of the equatorial c...

  10. Collective dynamics of bursty particle precipitation initiating in the inner and outer plasma sheet

    Science.gov (United States)

    Uritsky, V. M.; Donovan, E.; Klimas, A. J.; Spanswick, E.

    2009-02-01

    Using multiscale spatiotemporal analysis of bursty precipitation events in the nighttime aurora as seen by the POLAR UVI instrument, we report a set of new statistical signatures of high- and low-latitude auroral activity, signaling a strongly non-uniform distribution of dissipation mechanism in the plasma sheet. We show that small-scale electron emission events that initiate in the equatorward portion of the nighttime auroral oval (scaling mode A1) have systematically steeper power-law slopes of energy, power, area, and lifetime probability distributions compared to the events that initiate at higher latitudes (mode B). The low-latitude group of events also contain a small but energetically important subpopulation of substorm-scale disturbances (mode A2) described by anomalously low distribution exponents characteristic of barely stable thermodynamic systems that are prone to large-scale sporadic reorganization. The high latitude events (mode organized critical (SOC) behavior. The low- and high latitude events have distinct inter-trigger time statistics, and are characterized by significantly different MLT distributions. Based on these results we conjecture that the inner and outer portions of the plasma sheet are associated with two (or more) mechanisms of collective dynamics that may represent an interplay between current disruption and magnetic reconnection scenarios of bursty energy conversion in the magnetotail.

  11. Quantitative study of guide-field effects on Hall reconnection in a laboratory plasma.

    Science.gov (United States)

    Tharp, T D; Yamada, M; Ji, H; Lawrence, E; Dorfman, S; Myers, C E; Yoo, J

    2012-10-19

    The effect of guide field on magnetic reconnection is quantitatively studied by systematically varying an applied guide field in the Magnetic Reconnection Experiment (MRX). The quadrupole field, a signature of two-fluid reconnection at zero guide field, is altered by a finite guide field. It is shown that the reconnection rate is significantly reduced with increasing guide field, and this dependence is explained by a combination of local and global physics: locally, the in-plane Hall currents are reduced, while globally guide field compression produces an increased pressure both within and downstream of the reconnection region.

  12. Electron scale nested quadrupole Hall field in Cluster observations of magnetic reconnection

    CERN Document Server

    Jain, Neeraj

    2014-01-01

    This Letter presents the first evidence of a new and unique feature of spontaneous reconnection at multiple sites in electron current sheet, viz. nested quadrupole structure of Hall field at electron scales, in Cluster observations. The new nested quadrupole is a consequence of electron scale processes in reconnection. Whistler response of the upstream plasma to the interaction of electron flows from neighboring reconnection sites produces a large scale quadrupole Hall field enclosing the quadrupole fields of the multiple sites, thus forming a nested structure. Electron-magnetohydrodynamic simulations of an electron current sheet yields mechanism of the formation of nested quadrupole.

  13. Thickness of Heliospheric Current and Plasma Sheets: Dependence on Distance

    Science.gov (United States)

    Zhou, X.; Smith, E. J.; Winterhalter, D.; McComas, D. J.; Skoug, R. M.; Goldstein, B. E.; Smith, C. W.

    2005-05-01

    Heliospheric current sheets (HCS) are well defined structures that separate the interplanetary magnetic fields with inverse polarities. Surrounded by heliospheric plasma sheets (HPS), the current sheets stretch throughout the heliosphere. Interesting questions that still remain unanswered include how the thickness of these structures will change along the distance? And what determines the thickness of these structures? To answer these fundamental questions, we have carried out a study of the HCS and HPS using recent Ulysses data near 5 AU. When the results were compared with earlier studies at 1 AU using ISEE-3 data, they were surprising and unexplained. Although the plasma sheet grew thicker, the embedded current sheet grew thinner! Using data under the same (or very similar) circumstances, we have extended the analysis in two ways. First, the same current-plasma sheets studied at 5 AU have been identified at 1 AU using ACE data. Second, data obtained while Ulysses was en-route to Jupiter near 3 AU have been analyzed. This three-point investigation reveals the thickness variation along the distance and enables the examination of the controller of this variation.

  14. Generation of Alfvenic Waves and Turbulence in Magnetic Reconnection Jets

    Science.gov (United States)

    Hoshino, M.

    2014-12-01

    The magneto-hydro-dynamic (MHD) linear stability for the plasma sheet with a localized bulk plasma flow parallel to the neutral sheet is investigated. We find three different unstable modes propagating parallel to the anti-parallel magnetic field line, and we call them as "streaming tearing'', "streaming sausage'', and "streaming kink'' mode. The streaming tearing and sausage modes have the tearing mode-like structure with symmetric density fluctuation to the neutral sheet, and the streaming kink mode has the asymmetric fluctuation. The growth rate of the streaming tearing mode decreases with increasing the magnetic Reynolds number, while those of the streaming sausage and kink modes do not strongly depend on the Reynolds number. The wavelengths of these unstable modes are of the order of the thickness of plasma sheet, which behavior is almost same as the standard tearing mode with no bulk flow. Roughly speaking the growth rates of three modes become faster than the standard tearing mode. The situation of the plasma sheet with the bulk flow can be realized in the reconnection exhaust with the Alfvenic reconnection jet, and the unstable modes may be regarded as one of the generation processes of Alfvenic turbulence in the plasma sheet during magnetic reconnection.

  15. Turbulent Plasmoid Reconnection

    CERN Document Server

    Widmer, Fabien; Yokoi, Nobumitsu

    2016-01-01

    The plasmoid instability may lead to fast magnetic reconnection through long current sheets(CS). It is well known that large-Reynolds-number plasmas easily become turbulent. We address the question whether turbulence enhances the energy conversion rate of plasmoid-unstable current sheets. We carry out appropriate numerical MHD simulations, but resolving simultaneously the relevant large-scale (mean-) fields and the corresponding small-scale, turbulent, quantities by means of direct numerical simulations (DNS) is not possible. Hence we investigate the influence of small scale turbulence on large scale MHD processes by utilizing a subgrid-scale (SGS) turbulence model. We verify the applicability of our SGS model and then use it to investigate the influence of turbulence on the plasmoid instability. We start the simulations with Harris-type and force-free CS equilibria in the presence of a finite guide field in the direction perpendicular to the reconnection plane. We use the DNS results to investigate the growt...

  16. The Onset of Magnetic Reconnection in Tail-Like Equilibria

    Science.gov (United States)

    Hesse, Michael; Birn, Joachim; Kuznetsova, Masha

    1999-01-01

    Magnetic reconnection is a fundamental mode of dynamics in the magnetotail, and is recognized as the basic mechanisms converting stored magnetic energy into kinetic energy of plasma particles. The effects of the reconnection process are well documented by spacecraft observations of plasmoids in the distant magnetotail, or bursty bulk flows, and magnetic field dipolarizations in the near Earth region. Theoretical and numerical analyses have, in recent years, shed new light on the way reconnection operates, and, in particular, which microscopic mechanism supports the dissipative electric field in the associated diffusion region. Despite this progress, however. the question of how magnetic reconnection initiates in a tail-like magnetic field with finite flux threading the current i.sheet remains unanswered. Instead, theoretical studies supported by numerical simulations support the point-of-view that such plasma and current sheets are stable with respect to collisionless tearing mode. In this paper, we will further investigate this conclusion, with emphasis on the question whether it remains valid in plasma sheets with embedded thin current sheets. For this purpose, we perform particle-in-cell simulations of the driven formation of thin current sheets, and their subsequent evolution either to equilibrium or to instability of a tearing-type mode. In the latter case we will pay particular attention to the nature of the electric field contribution which unmagnetizes the electrons.

  17. The study of magnetic reconnection in solar spicules

    CERN Document Server

    Fazel, Z

    2014-01-01

    This work is devoted to study the magnetic reconnection instability under solar spicule conditions. Numerical study of the resistive tearing instability in a current sheet is presented by considering the magnetohydrodynamic (MHD) framework. To investigate the effect of this instability in a stratified atmosphere of solar spicules, we solve linear and non-ideal MHD equations in the x-z plane. In the linear analysis it is assumed that resistivity is only important within the current sheet, and the exponential growth of energies takes place faster as plasma resistivity increases. We are interested to see the occurrence of magnetic reconnection during the lifetime of a typical solar spicule.

  18. Physics and Dynamics of Current Sheets in Pulsed Plasma Thrusters

    Science.gov (United States)

    2007-11-02

    pulsed plasma thruster. A simple experiment would involve measuring the impulse bit of a coaxial gas-fed pulsed plasma thruster operated in both positive...Princeton, NJ, 2002. [2] J. Marshal. Performance of a hydromagnetic plasma gun . The Physics of Fluids, 3(1):134–135, January-February 1960. [3] R.G. Jahn...Jahn and K.E. Clark. A large dielecteic vacuum facility. AIAA Jour- nal, 1966. [16] L.C. Burkhardt and R.H. Lovberg. Current sheet in a coaxial plasma

  19. Iris si iv line profiles: An indication for the plasmoid instability during small-scale magnetic reconnection on the sun

    CERN Document Server

    Innes, Davina; Huang, YiMin; Bhattacharjee, Amitava

    2015-01-01

    Our understanding of the process of fast reconnection has undergone a dramatic change in the last 10 years driven, in part, by the availability of high-resolution numerical simulations that have consistently demonstrated the break-up of current sheets into magnetic islands, with reconnection rates that become independent of Lundquist number, challenging the belief that fast magnetic reconnection in flares proceeds via the Petschek mechanism that invokes pairs of slow-mode shocks connected to a compact diffusion region. The reconnection sites are too small to be resolved with images but these reconnection mechanisms, Petschek and the plasmoid instability, have reconnection sites with very different density and velocity structures and so can be distinguished by high-resolution line-profiles observations. Using IRIS spectroscopic observations we obtain a survey of typical line profiles produced by small-scale events thought to be reconnection sites on the Sun. Slit-jaw images are used to investigate the plasma h...

  20. Plasma-Jet Forming of Sheet Metal Shapes

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Plasma-jet forming is a newly proposed flexible sheet metal forming process. A non-transferred arc plasma torch is used as a controllable heat source to produce internal stress in sheet metals, causing plastic deformation without the necessity of hard tooling. This method has potential for rapid prototyping of sheet metal parts by reducing development costs and lead times. A robotic system has been used to perform simple linear bends in several different alloys. In order to develop a controllable process and to improve the forming accuracy, the effects of various process parameters on the obtained shape changes and on the resulting structure and properties have been studied. The overall goal is to understand the roles of the forming parameters and their inter-relationship in optimizing the forming procedure-a high forming speed without damage to the material structure or properties.

  1. Multiwavelength Observations of Supersonic Plasma Blob Triggered by Reconnection Generated Velocity Pulse in AR10808

    CERN Document Server

    Srivastava, A K; Murawski, K; Kumar, Pankaj

    2012-01-01

    Using multi-wavelength observations of Solar and Heliospheric Observatory (SoHO)/Michelson Doppler Imager (MDI), Transition Region and Coronal Explorer (TRACE) 171 \\AA, and H$\\alpha$ from Culgoora Solar Observatory at Narrabri, Australia, we present a unique observational signature of a propagating supersonic plasma blob before an M6.2 class solar flare in AR10808 on 9th September 2005. The blob was observed between 05:27 UT to 05:32 UT with almost a constant shape for the first 2-3 minutes, and thereafter it quickly vanished in the corona. The observed lower bound speed of the blob is estimated as $\\sim$215 km s$^{-1}$ in its dynamical phase. The evidence of the blob with almost similar shape and velocity concurrent in H$\\alpha$ and TRACE 171 \\AA\\ supports its formation by multi-temperature plasma. The energy release by a recurrent 3-D reconnection process via the separator dome below the magnetic null point, between the emerging flux and pre-existing field lines in the lower solar atmosphere, is found to be...

  2. Geomagnetic activity effects on plasma sheet energy conversion

    Directory of Open Access Journals (Sweden)

    M. Hamrin

    2010-10-01

    Full Text Available In this article we use three years (2001, 2002, and 2004 of Cluster plasma sheet data to investigate what happens to localized energy conversion regions (ECRs in the plasma sheet during times of high magnetospheric activity. By examining variations in the power density, E·J, where E is the electric field and J is the current density obtained by Cluster, we have studied the influence on Concentrated Load Regions (CLRs and Concentrated Generator Regions (CGRs from variations in the geomagnetic disturbance level as expressed by the Kp, the AE, and the Dst indices. We find that the ECR occurrence frequency increases during higher magnetospheric activities, and that the ECRs become stronger. This is true both for CLRs and for CGRs, and the localized energy conversion therefore concerns energy conversion in both directions between the particles and the fields in the plasma sheet. A higher geomagnetic activity hence increases the general level of energy conversion in the plasma sheet. Moreover, we have shown that CLRs live longer during magnetically disturbed times, hence converting more electromagnetic energy. The CGR lifetime, on the other hand, seems to be unaffected by the geomagnetic activity level. The evidence for increased energy conversion during geomagnetically disturbed times is most clear for Kp and for AE, but there are also some indications that energy conversion increases during large negative Dst. This is consistent with the plasma sheet magnetically mapping to the auroral zone, and therefore being more tightly coupled to auroral activities and variations in the AE and Kp indices, than to variations in the ring current region as described by the Dst index.

  3. Localized electron heating during magnetic reconnection in MAST

    Science.gov (United States)

    Yamada, T.; Tanabe, H.; Watanabe, T. G.; Hayashi, Y.; Imazawa, R.; Inomoto, M.; Ono, Y.; Gryaznevich, M.; Scannell, R.; Michael, C.; The MAST Team

    2016-10-01

    Significant increase in the plasma temperature above 1 keV was measured during the kilogauss magnetic field reconnection of two merging toroidal plasmas under the high-guide field and collision-less conditions. The electron temperature was observed to peak significantly at the X-point inside the current sheet, indicating Joule heating caused by the toroidal electric field along the X-line. This peaked temperature increases significantly with the guide field, in agreement with the electron mean-free path calculation. The slow electron heating in the downstream suggests energy conversion from ions to electrons through ion-electron collisions in the bulk plasma as the second electron heating mechanism in the bulk plasma. The electron density profile clearly reveals the electron density pile-up / fast shock structures in the downstream of reconnection, suggesting energy conversion from ion flow energy to ion thermal energy as well as significant ion heating by reconnection outflow.

  4. Magnetic reconnection in plasma under inertial confinement fusion conditions driven by heat flux effects in Ohm's law.

    Science.gov (United States)

    Joglekar, A S; Thomas, A G R; Fox, W; Bhattacharjee, A

    2014-03-14

    In the interaction of high-power laser beams with solid density plasma there are a number of mechanisms that generate strong magnetic fields. Such fields subsequently inhibit or redirect electron flows, but can themselves be advected by heat fluxes, resulting in complex interplay between thermal transport and magnetic fields. We show that for heating by multiple laser spots reconnection of magnetic field lines can occur, mediated by these heat fluxes, using a fully implicit 2D Vlasov-Fokker-Planck code. Under such conditions, the reconnection rate is dictated by heat flows rather than Alfvènic flows. We find that this mechanism is only relevant in a high β plasma. However, the Hall parameter ωcτei can be large so that thermal transport is strongly modified by these magnetic fields, which can impact longer time scale temperature homogeneity and ion dynamics in the system.

  5. Magnetic reconnection in plasma under inertial confinement fusion conditions driven by heat flux effects in Ohm's law

    CERN Document Server

    Joglekar, A S; Fox, W; Bhattacharjee, A

    2015-01-01

    In the interaction of high-power laser beams with solid density plasma there are a number of mechanisms that generate strong magnetic fields. Such fields subsequently inhibit or redirect electron flows, but can themselves be advected by heat fluxes, resulting in complex interplay between thermal transport and magnetic fields.We show that for heating by multiple laser spots reconnection of magnetic field lines can occur, mediated by these heat fluxes, using a fully implicit 2D Vlasov-Fokker-Planck code. Under such conditions, the reconnection rate is dictated by heat flows rather than Alfv\\`enic flows. We find that this mechanism is only relevant in a high $\\beta$ plasma. However, the Hall parameter $\\omega_c \\tau_{ei}$ can be large so that thermal transport is strongly modified by these magnetic fields, which can impact longer time scale temperature homogeneity and ion dynamics in the system.

  6. Density Enhancements and Voids following Patchy Reconnection

    CERN Document Server

    Guidoni, S E

    2011-01-01

    We show, through a simple patchy reconnection model, that retracting reconnected flux tubes may present elongated regions relatively devoid of plasma, as well as long lasting, dense central hot regions. Reconnection is assumed to happen in a small patch across a Syrovatski\\'i (non-uniform) current sheet (CS) with skewed magnetic fields. The background magnetic pressure has its maximum at the center of the CS plane, and decreases toward the edges of the plane. The reconnection patch creates two V-shaped reconnected tubes that shorten as they retract in opposite directions, due to magnetic tension. One of them moves upward toward the top edge of the CS, and the other one moves downward toward the top of the underlying arcade. Rotational discontinuities (RDs) propagate along the legs of the tubes and generate parallel super-sonic flows that collide at the center of the tube. There, gas dynamics shocks that compress and heat the plasma are launched outwardly. The descending tube moves through the bottom part of t...

  7. Sustained lobe reconnection in Saturn's magnetotail

    Science.gov (United States)

    Thomsen, M. F.; Jackman, C. M.; Mitchell, D. G.; Hospodarsky, G.; Kurth, W. S.; Hansen, K. C.

    2015-12-01

    The degree to which solar wind driving may affect Saturn's magnetosphere is not yet fully understood. We present observations that suggest that under some conditions the solar wind does govern the character of the plasma sheet in Saturn's outer magnetosphere. On 16 September 2006, the Cassini spacecraft, at a radial distance of 37 Rs near local midnight, observed a sunward flowing ion population for ~5 h, which was accompanied by enhanced Saturn Kilometric Radiation emissions. We interpret this beam as the outflow from a long-lasting episode of Dungey-type reconnection, i.e., reconnection of previously open flux containing magnetosheath material. The beam occurred in the middle of a several-day interval of SKR activity and enhanced lobe magnetic field strength, apparently caused by the arrival of a solar wind compression region with significantly higher than average dynamic pressure. The arrival of the high-pressure solar wind also marked a change in the composition of the plasma-sheet plasma, from water-group-dominated material clearly of inner-magnetosphere origin to material dominated by light-ion composition, consistent with captured magnetosheath plasma. This event suggests that under the influence of prolonged high solar wind dynamic pressure, the tail plasma sheet, which normally consists of inner-magnetospheric plasma, is eroded away by ongoing reconnection that then involves open lobe field lines. This process removes open magnetic flux from the lobes and creates a more Earth-like, Dungey-style outer plasma sheet dominantly of solar wind origin. This behavior is potentially a recurrent phenomenon driven by repeating high-pressure streams (corotating interaction regions) in the solar wind, which also drive geomagnetic storms at Earth.

  8. Comparison of plasma sheet ion composition with the IMF and solar wind plasma

    Science.gov (United States)

    Lennartsson, W.

    Plasma sheet energetic ion data (0.1- to 16 keV/e) obtained by the Plasma Composition Experiment on ISEE-1 between 10 and 23 earth radii are compared with concurrent IMF and solar wind plasma data. The densities of H(+) and He(++) ions in the plasma sheet are found to be the highest, and the most nearly proportional to the solar wind density, when the IMF B(z) is not northward. The density of terrestrial O(+) ions increases strongly with increasing magnitude of the IMF, in apparent agreement with the notion that the IMF plays a fundamental role in the electric coupling between the solar wind and the ionosphere.

  9. Final Scientific Report: Experimental Investigation of Reconnection in a Line-tied Plasma

    Energy Technology Data Exchange (ETDEWEB)

    Forest, Cary [Univ. of Wisconsin, Madison, WI (United States)

    2016-10-25

    This grant used funding from the NSF/DoE Partnership on Plasma Science to investigate magnetic reconnection phenomena in a line-tied pinch experiment. The experiment was upgraded from a previous device intended to study fusion plasma-related instabilities to a new configuration capable of studying a number of new, previously unstudied configurations. A high spatial and time resolution array of magnetic probes was constructed to measure time evolving structures present as instability and turbulence developed. The most important new equilibrium made possible by this grant was a Zero-Net-Current equilibrium that models the footpoint twisting of solar flux tubes that occurs prior to solar eruptions (flares and coronal mass ejections). This new equilibrium was successfully created in the lab, and it exhibited a host of instabilities. In particular, at low current when the equilibrium was not overly stressed, a saturated internal kink mode oscillation was observed. At high current, 2 D magnetic turbulence developed which we attribute to the lack of a equilibrium brought about by a subcritical transition to turbulence. A second set of experiments involved the turbulent interactions of a collection of flux tubes all being twisted independently, a problem known as the Parker Problem. Current profiles consisting of 2, 3 and 4 guns were used to impose a fine scale drive, and resulted in a new experimental platform in which the injection scale of the magnetic turbulence could be controlled. First experiments in this configuration support the conclusion that an inverse cascade of magnetic energy occurred which self-organized the plasma into a nearly axisymmetric current distribution.

  10. Particle Acceleration and Heating by Turbulent Reconnection

    CERN Document Server

    Vlahos, Loukas; Isliker, Heinz; Tsiolis, Vassilios; Anastasiadis, Anastasios

    2016-01-01

    Turbulent flows in the solar wind, large scale current sheets, multiple current sheets, and shock waves lead to the formation of environments in which a dense network of current sheets is established and sustains "turbulent reconnection". We constructed a 2D grid on which a number of randomly chosen grid points are acting as {\\bf scatterers} (i.e.\\ magnetic clouds or current sheets). In particular, we study how test particles respond inside this collection of scatterers. We study the energy gain of individual particles, the evolution of their energy distribution, their escape time distribution and we determine the transport coefficients from the particle dynamics. We have shown that our model describes very well the second order Fermi energization of non relativistic plasmas in open or periodic numerical boxes, when using magnetic clouds as scatterers. Replacing the "magnetic clouds" with current sheets, we have proven that the processes are much more efficient and particle heating and acceleration depends on...

  11. Three-dimensional Geometry of a Current Sheet in the High Solar Corona: Evidence for Reconnection in the Late Stage of the Coronal Mass Ejections

    Science.gov (United States)

    Kwon, Ryun-Young; Vourlidas, Angelos; Webb, David

    2016-07-01

    Motivated by the standard flare model, ray-like structures in the wake of coronal mass ejections (CMEs) have been often interpreted as proxies of the reconnecting current sheet connecting the CME with the postflare arcade. We present the three-dimensional properties of a post-CME ray derived from white light images taken from three different viewing perspectives on 2013 September 21. By using a forward modeling method, the direction, cross section, and electron density are determined within the heliocentric distance range of 5-9 R ⊙. The width and depth of the ray are 0.42 ± 0.08 R ⊙ and 1.24 ± 0.35 R ⊙, respectively, and the electron density is (2.0 ± 0.5) × 104 cm-3, which seems to be constant with height. Successive blobs moving outward along the ray are observed around 13 hr after the parent CME onset. We model the three-dimensional geometry of the parent CME with the Gradual Cylindrical Shell model and find that the CME and ray are coaxial. We suggest that coaxial post-CME rays, seen in coronagraph images, with successive formation of blobs could be associated with current sheets undergoing magnetic reconnection in the late stage of CMEs.

  12. Magnetic reconnection associated fluctuations in the deep magnetotail: ARTEMIS results

    Directory of Open Access Journals (Sweden)

    Z. Vörös

    2011-11-01

    Full Text Available On the basis of ARTEMIS two-probe mission magnetic reconnection (MR outflow associated magnetic fluctuations and turbulence are analyzed on 19 February 2011. In the deep-tail, at distances between X = 45 – 51 RE, evidence for reconnection associated plasma sheet thinning was found, accompanied by heating of the plasma sheet. Correlated flow and field reversals and the large-scale Hall-effect signatures indicated the presence of the reconnection X-line. Within fast reconnection plasma outflows, magnetic fluctuations exhibit the same spectral scaling features and kinked spectra as magnetic fluctuations in the solar wind or in various parts of geospace. It was shown that the proton scale magnetic fluctuations are constrained by oblique firehose, proton cyclotron and mirror instability thresholds. For parallel plasma β|| > 1, where the thresholds converge, perpendicular magnetic fluctuations are enhanced. Magnetic compressibility decreases with the distance to the neutral sheet, however, near the instability thresholds it is comparable to the values obtained in the solar wind.

  13. Energetic electron bursts in the plasma sheet and their relation with BBFs

    Science.gov (United States)

    Duan, A. Y.; Cao, J. B.; Dunlop, M.; Wang, Z. Q.

    2014-11-01

    We studied energetic electron bursts (EEBs) (40-250 keV) in the plasma sheet (PS) and their relation to bursty bulk flows (BBFs) using the data recorded by Cluster from 2001 to 2009. The EEBs in the PS can be classified into four types. Three types of EEBs are dispersionless, including EEBs accompanied with BBFs (V > 250 km/s) but without dipolarization front (DF); EEBs accompanied with both dipolarization front (DF) and BBF; and EEBs accompanied with DF and fast flow with V EEB, i.e., EEBs not accompanied with BBFs and DFs, is dispersed. The energetic electrons (40-130 keV) can be easily transported earthward by BBFs due to the strong dawn-dusk electric field embedded in BBFs. The DFs in BBFs can produce energetic electrons (40 to 250 keV). For the EEBs with DF and BBFs, the superposed epoch analyses show that the increase of energetic electron flux has two phases: gradual increase phase before DF and rapid increase phase concurrent with DF. In the PS around x = -18 RE, 60%-70% of EEBs are accompanied with BBFs, indicating that although hitherto there have been various acceleration mechanisms of energetic electrons, most of the energetic electrons in the PS are related with magnetic reconnection, and they are produced either directly by magnetic reconnection or indirectly by the DFs within BBFs. In the BBF's braking region of -12 RE EEBs are accompanied with BBFs. The corresponding ratio between EEBs and BBFs shows a dawn-dusk asymmetry.

  14. 3-D Magnetospheric Field and Plasma Containing Thin Current Sheets

    Science.gov (United States)

    Zaharia, S.; Cheng, C. Z.; Maezawa, K.; Wing, S.

    2002-05-01

    In this study we present fully-3D self-consistent solutions of the magnetosphere by using observation-based plasma pressure distributions and computational boundary conditions based on the T96 magnetospheric field model. The pressure profiles we use are either taken directly from observations (GEOTAIL pressure data in the plasma sheet and DMSP ionospheric pressure) or empirical (Spence-Kivelson formula for pressure on the midnight equatorial line). The 3-D solutions involve solving 2 coupled elliptic equations in a flux coordinate systems, with the magnetic field expressed by two Euler potentials and using appropriate boundary conditions for both the closed- and open-field regions derived from the empirical field model. We look into how the self-consistent magnetic field and current structures change under different external conditions, and we discuss the appearance of thin cross-tail current sheets during disturbed magnetospheric times.

  15. Singular Sheet Etching of Graphene with Oxygen Plasma

    Institute of Scientific and Technical Information of China (English)

    Haider Al-Mumen; Fubo Rao; Wen Li; Lixin Dong

    2014-01-01

    This paper reports a simple and controllable post-synthesis method for engineering the number of graphene layers based on oxygen plasma etching. Singular sheet etching (SSE) of graphene was achieved with the optimum process duration of 38 seconds. As a demonstration of this SSE process, monolayer graphene films were produced from bilayer graphenes. Experimental investigations verified that the oxygen plasma etching removes a single layer graphene sheet in an anisotropic fashion rather than anisotropic mode. In addition, etching via the oxygen plasma at the ground electrodes introduced fewer defects to the bottom graphene layer compared with the conventional oxygen reactive ion etching using the powered electrodes. Such defects can further be reduced with an effective annealing treatment in an argon environment at 900-1000◦C. These results demonstrate that our developed SSE method has enabled a microelectronics manufacturing compatible way for single sheet precision subtraction of graphene layers and a potential technique for producing large size graphenes with high yield from multilayer graphite materials.

  16. Analysis of radiation performances of plasma sheet antenna

    Science.gov (United States)

    Yin, Bo; Zhang, Zu-Fan; Wang, Ping

    2015-12-01

    A novel concept of plasma sheet antennas is presented in this paper, and the radiation performances of plasma sheet antennas are investigated in detail. Firstly, a model of planar plasma antenna (PPA) fed by a microstrip line is developed, and its reflection coefficient is computed by the JE convolution finite-difference time-domain method and compared with that of the metallic patch antenna. It is found that the design of PPA can learn from the theory of the metallic patch antenna, and the impedance matching and reconstruction of resonant frequency can be expediently realized by adjusting the parameters of plasma. Then the PPA is mounted on a metallic cylindrical surface, and the reflection coefficient of the conformal plasma antenna (CPA) is also computed. At the same time, the influence of conformal cylinder radius on the reflection coefficient is also analyzed. Finally, the radiation pattern of a CPA is given, the results show that the pattern agrees well with the one of PPA in the main radiation direction, but its side lobe level has deteriorated significantly.

  17. Plasma physics. Stochastic electron acceleration during spontaneous turbulent reconnection in a strong shock wave.

    Science.gov (United States)

    Matsumoto, Y; Amano, T; Kato, T N; Hoshino, M

    2015-02-27

    Explosive phenomena such as supernova remnant shocks and solar flares have demonstrated evidence for the production of relativistic particles. Interest has therefore been renewed in collisionless shock waves and magnetic reconnection as a means to achieve such energies. Although ions can be energized during such phenomena, the relativistic energy of the electrons remains a puzzle for theory. We present supercomputer simulations showing that efficient electron energization can occur during turbulent magnetic reconnection arising from a strong collisionless shock. Upstream electrons undergo first-order Fermi acceleration by colliding with reconnection jets and magnetic islands, giving rise to a nonthermal relativistic population downstream. These results shed new light on magnetic reconnection as an agent of energy dissipation and particle acceleration in strong shock waves.

  18. Causes of plasma flow bursts and dayside auroral transients: An evaluation of two models invoking reconnection pulses and changes in the Y component of the magnetosheath field

    Energy Technology Data Exchange (ETDEWEB)

    Lockwood, M. [Rutherford Appleton Lab., Didcot (United Kingdom); Cowley, S.W.H. [Imperial College, London (United Kingdom); Sandholt, P.E. [Univ. of Oslo (Norway)] [and others

    1995-05-01

    The authors apply two models to interpret data observed by the EISCAT radar, and sky cameras, which observe bursty plasma flow events in conjunction with auroral transients near 630{angstrom}. One model argues the flows are caused by enhanced reconnection events at the magnetopause. The other argues they result from an increase in field line curvature forces associated with magnetosheath fields. The authors conclude that only the reconnection model can reliably explain the observed data.

  19. Survey of Galileo Plasma Observations in Jupiter's Plasma Sheet

    Science.gov (United States)

    Bagenal, Fran; Wilson, Robert J.; Siler, Scott; Paterson, William R.; Kurth, William S.

    2016-01-01

    The plasma science (PLS) Instrument on the Galileo spacecraft (orbiting Jupiter from December 1995 to September 2003) measured properties of the ions that were trapped in the magnetic field. The PLS data provide a survey of the plasma properties between approx. 5 and 30 Jupiter radii [R(sub J)] in the equatorial region. We present plasma properties derived via two analysis methods: numerical moments and forward modeling. We find that the density decreases with radial distance by nearly 5 orders of magnitude from approx. 2 to 3000 cm(exp.-3) at 6R(sub j) to approx. 0.05cm(sub -3) at 30 R(sub j). The density profile did not show major changes from orbit to orbit, suggesting that the plasma production and transport remained constant within about a factor of 2. The radial profile of ion temperature increased with distance which implied that contrary to the concept of adiabatic cooling on expansion, the plasma heats up as it expands out from Io's orbit (where TI is approx.60-80 eV) at approx. 6R(sub j) to a few keV at 30R(sub j).There does not seem to be a long-term, systematic variation in ion temperature with either local time or longitude. This latter finding differs from earlier analysis of Galileo PLS data from a selection of orbits. Further examination of all data from all Galileo orbits suggests that System Ill variations are transitory on timescales of weeks, consistent with the modeling of Cassini Ultraviolet Imaging Spectrograph observations. The plasma flow is dominated by azimuthal flow that is between 80% and 100% of corotation out to 25 R(sub j).

  20. The use of the power density for identifying reconnection regions

    Science.gov (United States)

    Hamrin, M.; Andersson, L.; Vaivads, A.; Pitkänen, T.; Gunell, H.

    2015-10-01

    In the vicinity of magnetic reconnection, magnetic energy is transferred into kinetic energy. A reconnection region hence corresponds to a load, and it should manifest itself as large and positive values of the power density, E·J ≫ 0, where E is the electric field and J the current density. In this article we analyze Cluster plasma sheet data from 2001-2004 to investigate the use of the power density for identifying possible magnetic reconnection events from large sets of observed data. From theoretical arguments we show that an event with E·J≳20 pW/m3 in the Earth's magnetotail observed by the Cluster instruments (X potential reconnection regions, but selected events must be reviewed separately to confirm any possible reconnection signatures by looking for other signatures such as Hall electric and magnetic fields and reconnection jets. The power density can be computed from multispacecraft data, and we argue that the power density can be used as a tool for identifying possible reconnection events from large sets of data, e.g., from the Cluster and the Magnetospheric Multiscale missions.

  1. Magnetic reconnection at 3D null points: effect of magnetic field asymmetry

    Science.gov (United States)

    Al-Hachami, A. K.; Pontin, D. I.

    2010-03-01

    Context. The magnetic field in many astrophysical plasmas, for example in the solar corona, is known to have a highly complex - and clearly three-dimensional - structure. Turbulent plasma motions in high-β regions where field lines are anchored, such as the solar interior, can store large amounts of energy in the magnetic field. This energy can only be released when magnetic reconnection occurs. Reconnection may only occur in locations where huge gradients of the magnetic field develop, and one candidate for such locations are magnetic null points, known to be abundant for example in the solar atmosphere. Reconnection leads to changes in the topology of the magnetic field, and energy being released as heat, kinetic energy and acceleration of particles. Thus reconnection is responsible for many dynamic processes, for instance flares and jets. Aims: The aim of this paper is to investigate the properties of magnetic reconnection at a 3D null point, with respect to their dependence on the symmetry of the magnetic field around the null. In particular we examine the rate of reconnection of magnetic flux at the null point, as well as how the current sheet forms and its properties. Methods: We use mathematical modelling and finite difference resistive MHD simulations. Results: It is found that the basic structure of the mode of magnetic reconnection considered is unaffected by varying the magnetic field symmetry, that is, the plasma flow is found to cross both the spine and fan of the null. However, the peak intensity and dimensions of the current sheet are dependent on the symmetry/asymmetry of the field lines. As a result, the reconnection rate is also found to be strongly dependent on the field asymmetry. Conclusions: The symmetry/asymmetry of the magnetic field in the vicinity of a magnetic null can have a profound effect on the geometry of any associated reconnection region, and the rate at which the reconnection process proceeds.

  2. Interchange Reconnection Alfven Wave Generation

    CERN Document Server

    Lynch, B J; Li, Y

    2014-01-01

    Given recent observational results of interchange reconnection processes in the solar corona and the theoretical development of the S-Web model for the slow solar wind, we present further analysis of the 3D MHD simulation of interchange reconnection by Edmondson et al. (Astrophys. J. 707, 1427, 2009). Specifically, we analyze the consequences of the dynamic streamer belt jump that corresponds to flux opening by interchange reconnection. Information about the magnetic field restructuring by interchange reconnection is carried throughout the system by Alfven waves propagating away from the reconnection region, distributing the shear and twist imparted by the driving flows, including shedding the injected stress-energy and accumulated magnetic helicity along newly-open field lines. We quantify the properties of the reconnection-generated wave activity in the simulation. There is a localized high frequency component associated with the current sheet/reconnection site and an extended low frequency component associ...

  3. Space weather. Ionospheric control of magnetotail reconnection.

    Science.gov (United States)

    Lotko, William; Smith, Ryan H; Zhang, Binzheng; Ouellette, Jeremy E; Brambles, Oliver J; Lyon, John G

    2014-07-11

    Observed distributions of high-speed plasma flows at distances of 10 to 30 Earth radii (R(E)) in Earth's magnetotail neutral sheet are highly skewed toward the premidnight sector. The flows are a product of the magnetic reconnection process that converts magnetic energy stored in the magnetotail into plasma kinetic and thermal energy. We show, using global numerical simulations, that the electrodynamic interaction between Earth's magnetosphere and ionosphere produces an asymmetry consistent with observed distributions in nightside reconnection and plasmasheet flows and in accompanying ionospheric convection. The primary causal agent is the meridional gradient in the ionospheric Hall conductance which, through the Cowling effect, regulates the distribution of electrical currents flowing within and between the ionosphere and magnetotail.

  4. Current sheets at three-dimensional magnetic nulls: Effect of compressibility

    CERN Document Server

    Pontin, D I; Galsgaard, K

    2007-01-01

    The nature of current sheet formation in the vicinity of three-dimensional magnetic null points is investigated. The particular focus is upon the effect of the compressibility of the plasma on the qualitative and quantitative properties of the current sheet. It is found that as the incompressible limit is approached, the collapse of the null point is suppressed, and instead an approximately planar current sheet aligned to the fan plane is present. Both the peak current and peak reconnection rate are reduced. The results imply that previous analytical solutions for steady-state reconnection at fan current sheets are dynamically accessible, while spine current sheet solutions are not.

  5. Critical Differences of Asymmetric Magnetic Reconnection from Standard Models

    Science.gov (United States)

    Nitta, S.; Wada, T.; Fuchida, T.; Kondoh, K.

    2016-09-01

    We have clarified the structure of asymmetric magnetic reconnection in detail as the result of the spontaneous evolutionary process. The asymmetry is imposed as ratio k of the magnetic field strength in both sides of the initial current sheet (CS) in the isothermal equilibrium. The MHD simulation is carried out by the HLLD code for the long-term temporal evolution with very high spatial resolution. The resultant structure is drastically different from the symmetric case (e.g., the Petschek model) even for slight asymmetry k = 2. (1) The velocity distribution in the reconnection jet clearly shows a two-layered structure, i.e., the high-speed sub-layer in which the flow is almost field aligned and the acceleration sub-layer. (2) Higher beta side (HBS) plasma is caught in a lower beta side plasmoid. This suggests a new plasma mixing process in the reconnection events. (3) A new large strong fast shock in front of the plasmoid forms in the HBS. This can be a new particle acceleration site in the reconnection system. These critical properties that have not been reported in previous works suggest that we contribute to a better and more detailed knowledge of the reconnection of the standard model for the symmetric magnetic reconnection system.

  6. Anisotropic ion heating and tail generation during tearing mode magnetic reconnection in a high-temperature plasma.

    Science.gov (United States)

    Magee, R M; Den Hartog, D J; Kumar, S T A; Almagri, A F; Chapman, B E; Fiksel, G; Mirnov, V V; Mezonlin, E D; Titus, J B

    2011-08-05

    Complementary measurements of ion energy distributions in a magnetically confined high-temperature plasma show that magnetic reconnection results in both anisotropic ion heating and the generation of suprathermal ions. The anisotropy, observed in the C(+6) impurity ions, is such that the temperature perpendicular to the magnetic field is larger than the temperature parallel to the magnetic field. The suprathermal tail appears in the majority ion distribution and is well described by a power law to energies 10 times the thermal energy. These observations may offer insight into the energization process.

  7. Cassini in situ observations of long-duration magnetic reconnection in Saturn’s magnetotail

    Science.gov (United States)

    Arridge, C. S.; Eastwood, J. P.; Jackman, C. M.; Poh, G.-K.; Slavin, J. A.; Thomsen, M. F.; André, N.; Jia, X.; Kidder, A.; Lamy, L.; Radioti, A.; Reisenfeld, D. B.; Sergis, N.; Volwerk, M.; Walsh, A. P.; Zarka, P.; Coates, A. J.; Dougherty, M. K.

    2016-03-01

    Magnetic reconnection is a fundamental process in solar system and astrophysical plasmas, through which stored magnetic energy associated with current sheets is converted into thermal, kinetic and wave energy. Magnetic reconnection is also thought to be a key process involved in shedding internally produced plasma from the giant magnetospheres at Jupiter and Saturn through topological reconfiguration of the magnetic field. The region where magnetic fields reconnect is known as the diffusion region and in this letter we report on the first encounter of the Cassini spacecraft with a diffusion region in Saturn’s magnetotail. The data also show evidence of magnetic reconnection over a period of 19 h revealing that reconnection can, in fact, act for prolonged intervals in a rapidly rotating magnetosphere. We show that reconnection can be a significant pathway for internal plasma loss at Saturn. This counters the view of reconnection as a transient method of internal plasma loss at Saturn. These results, although directly relating to the magnetosphere of Saturn, have applications in the understanding of other rapidly rotating magnetospheres, including that of Jupiter and other astrophysical bodies.

  8. The statistical studies of the inner boundary of plasma sheet

    Directory of Open Access Journals (Sweden)

    J. B. Cao

    2011-02-01

    Full Text Available The penetration of plasma sheet ions into the inner magnetosphere is very important to the inner magnetospheric dynamics since plasma sheet ions are one of the major particle sources of ring current during storm times. However, the direct observations of the inner boundary of the plasma sheet are fairly rare due to the limited number of satellites in near equatorial orbits outside 6.6 RE. In this paper, we used the ion data recorded by TC-1 from 2004 to 2006 to study the distribution of inner boundary of ion plasma sheet (IBIPS and for the first time show the observational distribution of IBIPS in the equatorial plane. The IBIPS has a dawn-dusk asymmetry, being farthest to the Earth in the 06:00 08:00 LT bin and closest to the Earth in the 18:00–20:00 LT bin. Besides, the IBIPS has also a day-night asymmetry, which may be due to the fact that the ions on the dayside are exposed more time to loss mechanisms on their drift paths. The radial distance of IBIPS decrease generally with the increase of Kp index. The mean radial distance of IBIPS is basically larger than 6.6 RE during quiet times and smaller than 6.6 RE during active times. When the strength of convection electric field increases, the inward shift of IBIPS is most significant on the night side (22:00–02:00 LT. For Kp ≤ 0+, only 16% of IBIPSs penetrate inside the geosynchronous orbit. For 2 ≤ Kp < 3+, however, 70% of IBIPSs penetrate inside the geosynchronous orbit. The IBIPS has weak correlations with the AE and Dst indexes. The average correlation coefficient between Ri and Kp is −0.58 while the correlation coefficient between Ri and AE/Dst is only −0.29/0.17. The correlation coefficients are local time dependent. Particularly, Ri and Kp are highly correlated (r=−0.72 in the night sector, meaning that the radial distance of IBIPS

  9. SIMULTANEOUS OBSERVATION OF RECONNECTION INFLOW AND OUTFLOW ASSOCIATED WITH THE 2010 AUGUST 18 SOLAR FLARE

    Energy Technology Data Exchange (ETDEWEB)

    Takasao, Shinsuke; Shibata, Kazunari [Kwasan and Hida Observatories, Kyoto University, Yamashina, Kyoto 607-8471 (Japan); Asai, Ayumi; Isobe, Hiroaki, E-mail: takasao@kwasan.kyoto-u.ac.jp [Unit of Synergetic Studies for Space, Kyoto University, Yamashina, Kyoto 607-8471 (Japan)

    2012-01-20

    We report the simultaneous extreme-ultraviolet observation of magnetic reconnection inflow and outflow in a flare on 2010 August 18 observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. We found that during the rise phase of the flare, some plasma blobs appeared in the sheet structure above the hot loops. The plasma blobs were ejected bidirectionally along the sheet structure (outflow), at the same time as the threads visible in extreme-ultraviolet images moved toward the sheet structure (inflow). The upward and downward ejection velocities are 220-460 km s{sup -1} and 250-280 km s{sup -1}, respectively. The inflow speed changed from 90 km s{sup -1} to 12 km s{sup -1} in 5 minutes. By using these velocities, we estimated the nondimensional reconnection rate, which we found to vary during this period from 0.20 to 0.055. We also found that the plasma blobs in the sheet structure collided or merged with each other before they were ejected from the sheet structure. We hypothesize that the sheet structure is the current sheet and that these plasma blobs are plasmoids or magnetic islands, which could be important for understanding the dynamics of the reconnection region.

  10. Magnetic reconnection: from the Sweet-Parker model to stochastic plasmoid chains

    Science.gov (United States)

    Loureiro, N. F.; Uzdensky, D. A.

    2016-01-01

    Magnetic reconnection is the topological reconfiguration of the magnetic field in a plasma, accompanied by the violent release of energy and particle acceleration. Reconnection is as ubiquitous as plasmas themselves, with solar flares perhaps the most popular example. Other fascinating processes where reconnection plays a key role include the magnetic dynamo, geomagnetic storms and the sawtooth crash in tokamaks. Over the last few years, the theoretical understanding of magnetic reconnection in large-scale fluid systems has undergone a major paradigm shift. The steady-state model of reconnection described by the famous Sweet-Parker (SP) theory, which dominated the field for  ˜50 years, has been replaced with an essentially time-dependent, bursty picture of the reconnection layer, dominated by the continuous formation and ejection of multiple secondary islands (plasmoids). Whereas in the SP model reconnection was predicted to be slow, a major implication of this new paradigm is that reconnection in fluid systems is fast (i.e. independent of the Lundquist number), provided that the system is large enough. This conceptual shift hinges on the realization that SP-like current layers are violently unstable to the plasmoid (tearing) instability—implying, therefore, that such current sheets are super-critically unstable and thus can never form in the first place. This suggests that the formation of a current sheet and the subsequent reconnection process cannot be decoupled, as is commonly assumed. This paper provides an introductory-level overview of the recent developments in reconnection theory and simulations that led to this essentially new framework. We briefly discuss the role played by the plasmoid instability in selected applications, and describe some of the outstanding challenges that remain at the frontier of this subject. Amongst these are the analytical and numerical extension of the plasmoid instability to (i) 3D and (ii) non-magnetohydrodynamics (MHD

  11. Plasma Jog Experiments on MRX in Collaboration with MMS team

    Science.gov (United States)

    Yamada, Masaaki; Yoo, Jongsoo; Tharp, Tim; Ji, Hantao; Lawrence, Eric

    2011-10-01

    In the Magnetic Reconnection Experiment (MRX), a multi-probe mock-up system is utilized to investigate the fine structure of the diffusion region of the reconnection layer and to identify data signatures which indicate the nearby presence of a reconnection neutral sheet. The reconnection layer is swept through the probe system in controlled speeds of 0.01-0.2 of the Alfvén velocity. This situation is very similar to the space measurements in which the current sheet moves with respect to satellites as expected in the Magnetosphere Multi-scale Satellite (MMS) cluster configuration. The main objectives of the proposed joint research are (1) to compare basic properties of the reconnection regions in the neutral sheet of space and laboratory plasmas, (2) to study their roles in the process of magnetic reconnection, and (3) to measure fine scale profiles of the thin electron diffusion layer. A series of the first results from the experimental campaign are presented.

  12. Localization of the magnetic reconnection zone during sawtooth crashes in tokamak plasmas

    NARCIS (Netherlands)

    Munsat, T.; Park, H. K.; Classen, I.G.J.; Domier, C.W.; Donne, A. J. H.; N C Luhmann Jr.,; Mazzucato, E.; van de Pol, M.J.

    2007-01-01

    Recent 2D spatially and temporally resolved measurements of electron temperature fluctuations in the tokamak core have revealed new information on the dynamics of the sawtooth crash. Measures of poloidal localization of the reconnection zone are achieved through direct analysis of the 2D data and th

  13. Magnetic reconnection and stochastic plasmoid chains in high-Lundquist-number plasmas

    KAUST Repository

    Loureiro, N. F.

    2012-04-13

    A numerical study of magnetic reconnection in the large-Lundquist-number (S), plasmoid-dominated regime is carried out for S up to 10 7. The theoretical model of Uzdensky [Phys. Rev. Lett. 105, 235002 (2010)] is confirmed and partially amended. The normalized reconnection rate is Ẽ eff ∼ 0.02 independently of S for S ≫ 10 4. The plasmoid flux (ψ) and half-width (w x) distribution functions scale as f (ψ) ∼ - ψ -2 and f (w x) ∼ w x -2. The joint distribution of ψ and w x shows that plasmoids populate a triangular region w x ≲ψ/B 0, where B 0 is the reconnecting field. It is argued that this feature is due to plasmoid coalescence. Macroscopic "monster" plasmoids with w x ∼ 10 % of the system size are shown to emerge in just a few Alfvén times, independently of S, suggesting that large disruptive events are an inevitable feature of large-S reconnection. © 2012 American Institute of Physics.

  14. Casimir effects for a flat plasma sheet: I. Energies

    Energy Technology Data Exchange (ETDEWEB)

    Barton, G [Department of Physics and Astronomy, University of Sussex, Brighton BN1 9QH (United Kingdom)

    2005-04-01

    We study a fluid model of an infinitesimally thin plasma sheet occupying the xy plane, loosely imitating a single base plane from graphite. In terms of the fluid charge e/a{sup 2} and mass m/a{sup 2} per unit area, the crucial parameters are q nsce 2{pi}e{sup 2}/mc{sup 2}a{sup 2}, a Debye-type cutoff K{identical_to}{radical}(4{pi})/a on surface-parallel normal-mode wavenumbers k, and X nsce K/q. The cohesive energy {beta} per unit area is determined from the zero-point energies of the exact normal modes of the plasma coupled to the Maxwell field, namely TE and TM photon modes, plus bound modes decaying exponentially with vertical bar zvertical bar. Odd-parity modes (with E{sub x,y}(z = 0) = 0) are unaffected by the sheet except for their overall phases, and are irrelevant to {beta}, although the following paper shows that they are essential to the fields (e.g. to their vacuum expectation values), and to the stresses on the sheet. Realistically one has X >> 1, the result {beta} {approx} {Dirac_h}cq{sup 1/2}K{sup 5/2} is nonrelativistic, and it comes from the surface modes. By contrast, X << 1 (nearing the limit of perfect reflection) would entail {beta} {approx} -{Dirac_h}cqK{sup 2}log(1/X): contrary to folklore, the surface energy of perfect reflectors is divergent rather than zero. An appendix spells out the relation, for given k, between bound modes and photon phase-shifts. It is very different from Levinson's theorem for 1D potential theory: cursory analogies between TM and potential scattering are apt to mislead.

  15. Thin current sheets caused by plasma flow gradients in space and astrophysical plasma

    Directory of Open Access Journals (Sweden)

    D. H. Nickeler

    2010-08-01

    Full Text Available Strong gradients in plasma flows play a major role in space and astrophysical plasmas. A typical situation is that a static plasma equilibrium is surrounded by a plasma flow, which can lead to strong plasma flow gradients at the separatrices between field lines with different magnetic topologies, e.g., planetary magnetospheres, helmet streamers in the solar corona, or at the boundary between the heliosphere and interstellar medium. Within this work we make a first step to understand the influence of these flows towards the occurrence of current sheets in a stationary state situation. We concentrate here on incompressible plasma flows and 2-D equilibria, which allow us to find analytic solutions of the stationary magnetohydrodynamics equations (SMHD. First we solve the magnetohydrostatic (MHS equations with the help of a Grad-Shafranov equation and then we transform these static equilibria into a stationary state with plasma flow. We are in particular interested to study SMHD-equilibria with strong plasma flow gradients perpendicular to separatrices. We find that induced thin current sheets occur naturally in such situations. The strength of the induced currents depend on the Alfvén Mach number and its gradient, and on the magnetic field.

  16. Experimental demonstration of the role of electron pressure in fast magnetic reconnection with a guide field

    Science.gov (United States)

    Fox, W.; Sciortino, F.; von Stechow, A.; Jara-Almonte, J.; Yoo, J.; Ji, H.; Yamada, M.

    2016-10-01

    We report detailed laboratory observations of the structure of reconnection current sheets in a two-fluid plasma regime with a guide magnetic field, conducted on the Magnetic Reconnection Experiment. We observe in the laboratory for the first time the quadrupolar electron pressure variation in the ion-diffusion region, as originally predicted by extended MHD simulation. We quantitatively analyze the parallel and perpendicular force balance, and observe the projection of the electron pressure gradient parallel to the B field balances the parallel electric field. The resulting cross-field electron jets in the reconnection layer are diamagnetic in origin. Electron density variations are observed to dominate temperature variations and may provide a new diagnostic of reconnection with finite guide field for fusion experiments and spacecraft missions. Supported by Max-Planck Princeton Center for Plasma Physics.

  17. Fan-shaped jets in three dimensional reconnection simulation as a model of ubiquitous solar jets

    CERN Document Server

    Jiang, Rong Lin; Isobe, Hiroaki; Fang, Cheng

    2010-01-01

    Magnetic reconnection is a fundamental process in space and astrophysical plasmas in which oppositely directed magnetic fields changes its connectivity and eventually converts its energy into kinetic and thermal energy of the plasma. Recently, ubiquitous jets (for example, chromospheric anemone jets, penumbral microjets, umbral light bridge jets) have been observed by Solar Optical Telescope on board the satellite Hinode. These tiny and frequently occurring jets are considered to be a possible evidence of small-scale ubiquitous reconnection in the solar atmosphere. However, the details of three dimensional magnetic configuration are still not very clear. Here we propose a new model based on three dimensional simulations of magnetic reconnection using a typical current sheet magnetic configuration with a strong guide field. The most interesting feature is that the jets produced by the reconnection eventually move along the guide field lines. This model provides a fresh understanding of newly discovered ubiquit...

  18. The history of re-connection and the concept of the solar wind plasma with relatively small electrical conductivity

    Science.gov (United States)

    Chertkov, A. D.

    1995-01-01

    Petschek's 're-connection' model, aspiring to be universal, treated as a boundary problem meets unresolvable difficulties connected with impossibility to specify correctly boundary and initial conditions. This problem was incorrectly formulated. Hence, ineradicable logarithmic singularities occurred on the boundary surfaces. Attempts to eliminate them by incorporating the finite electrical conductivity are incorrect. This should lead to the change in the equation type, boundary condition type and in consequence to the change in solutions. Besides, the slow mode shocks cannot be driven by small internal source. As an alternative a new plasma concept is suggested. The state of fully ionized plasma in space depends completely on the entropy of the plasma heating source and on the process in which plasma is involved. The presumptive source of the solar wind creation - the induction electric field of the solar origin - has very low entropy. The state of plasma should be very far from the thermodynamic equilibrium. Debye's screening is not complete. The excitation of the powerful resonant self-consistent electric fields in plasma provides low electric conductivity. The MHD problems should be treated in frameworks of dissipative theories.

  19. The role of lateral magnetic reconnection in solar eruptive events

    Directory of Open Access Journals (Sweden)

    A. Soenen

    2009-10-01

    Full Text Available On 10–11 December 2005 a slow CME occurred in between two coronal streamers in the Western Hemisphere. SOHO/MDI magnetograms show a multipolar magnetic configuration at the photosphere consisting of a complex of active regions located at the CME source and two bipoles at the base of the lateral coronal streamers. White light observations reveal that the expanding CME affects both of the lateral streamers and induces the release of plasma within or close to them. These transient phenomena are possibly due to magnetic reconnections induced by the CME expansion that occurs either inside the streamer current sheet or between the CME flanks and the streamer. Our observations show that CMEs can be associated to not only a single reconnection process at a single location in the corona, but also to many reconnection processes occurring at different times and locations around the flux rope. Numerical simulations are used to demonstrate that the observed lateral reconnections can be reproduced. The observed secondary reconnections associated to CMEs may facilitate the CME release by globally decreasing the magnetic tension of the corona. Future CME models should therefore take into account the lateral reconnection effect.

  20. Kinetic simulations of secondary reconnection in the reconnection jet

    Science.gov (United States)

    Huang, S. Y.; Zhou, M.; Yuan, Z. G.; Fu, H. S.; He, J. S.; Sahraoui, F.; Aunai, N.; Deng, X. H.; Fu, S.; Pang, Y.; Wang, D. D.

    2015-08-01

    Magnetic reconnection, as one important energy dissipation process in plasmas, has been extensively studied in the past several decades. Magnetic reconnection occurring in the downstream of a primary X line is referred to as secondary reconnection. In this paper, we used kinetic simulations to investigate the secondary reconnection in detail. We found that secondary reconnection is reversed by the compression caused by the outflowing jet originating from the primary reconnection site, which results in the erosion of the magnetic island between the two X lines within ~3 ωci-1. We show the observational signatures expected in electromagnetic fields and plasma measurements in the Earth's magnetotail, associated with this mechanism. These simulation results could be applied to interpret the signatures associated with the evolution of earthward magnetic islands in the Earth's magnetotail.

  1. Peristaltic Pumping near Post-CME Supra-Arcade Current Sheets

    CERN Document Server

    Scott, Roger B; McKenzie, David E

    2013-01-01

    Measurements of temperature and density near supra-arcade current sheets suggest that plasma on unreconnected field lines may experience some degree of "pre-heating" and "pre-densification" prior to their reconnection. Models of patchy reconnection allow for heating and acceleration of plasma along reconnected field lines but do not offer a mechanism for transport of thermal energy across field lines. Here we present a model in which a reconnected flux tube retracts, deforming the surrounding layer of unreconnected field. The deformation creates constrictions that act as peristaltic pumps, driving plasma flow along affected field lines. Under certain circumstances these flows lead to shocks that can extend far out into the unreconnected field, altering the plasma properties in the affected region. These findings have direct implications for observations in the solar corona, particularly in regard to such phenomena as high temperatures near current sheets in eruptive solar flares and wakes seen in the form of ...

  2. Nonthermally Dominated Electron Acceleration during Magnetic Reconnection in a Low-beta Plasma

    Energy Technology Data Exchange (ETDEWEB)

    Li, Xiaocan [Los Alamos National Laboratory

    2015-07-21

    This work was motivated by electron acceleration during solar flares. After some introductory remarks on proposed particle acceleration mechanisms and questions needing answers, dynamic simulations and simulation results are presented including energy spectra and the formation of the power law distribution. In summary, magnetic reconnection is highly efficient at converting the free magnetic energy stored in a magnetic shear and accelerating electrons to nonthermal energies in low-β regime. The nonthermal electrons have a dominant fraction and form power-law energy spectra with spectral index p ~ 1 in low-β regime. Electrons are preferentially accelerated along the curvature drift direction along the electric field induced by the reconnection outflow. The results can be applied to explain the observations of electron acceleration during solar flares.

  3. Central Plasma Sheet Ion Properties as Inferred from Ionospheric Observations

    Science.gov (United States)

    Wing, Simon; Newell, Patrick T.

    1998-01-01

    A method of inferring central plasma sheet (CPS) temperature, density, and pressure from ionospheric observations is developed. The advantage of this method over in situ measurements is that the CPS can be studied in its entirely, rather than only in fragments. As a result, for the first time, comprehensive two-dimensional equatorial maps of CPS pressure, density, and temperature within the isotropic plasma sheet are produced. These particle properties are calculated from data taken by the Special Sensor for Precipitating Particles, version 4 (SSJ4) particle instruments onboard DMSP F8, F9, F10, and F11 satellites during the entire year of 1992. Ion spectra occurring in conjunction with electron acceleration events are specifically excluded. Because of the variability of magnetotail stretching, the mapping to the plasma sheet is done using a modified Tsyganenko [1989] magnetic field model (T89) adjusted to agree with the actual magnetotail stretch at observation time. The latter is inferred with a high degree of accuracy (correlation coefficient -0.9) from the latitude of the DMSP b2i boundary (equivalent to the ion isotropy boundary). The results show that temperature, pressure, and density all exhibit dawn-dusk asymmetries unresolved with previous measurements. The ion temperature peaks near the midnight meridian. This peak, which has been associated with bursty bulk flow events, widens in the Y direction with increased activity. The temperature is higher at dusk than at dawn, and this asymmetry increases with decreasing distance from the Earth. In contrast, the density is higher at dawn than at dusk, and there appears to be a density enhancement in the low-latitude boundary layer regions which increases with decreasing magnetic activity. In the near-Earth regions, the pressure is higher at dusk than at dawn, but this asymmetry weakens with increasing distance from the Earth and may even reverse so that at distances X less than approx. 10 to -12 R(sub E

  4. Experimental investigation of a 1 kA/cm² sheet beam plasma cathode electron gun.

    Science.gov (United States)

    Kumar, Niraj; Pal, Udit Narayan; Pal, Dharmendra Kumar; Prajesh, Rahul; Prakash, Ram

    2015-01-01

    In this paper, a cold cathode based sheet-beam plasma cathode electron gun is reported with achieved sheet-beam current density ∼1 kA/cm(2) from pseudospark based argon plasma for pulse length of ∼200 ns in a single shot experiment. For the qualitative assessment of the sheet-beam, an arrangement of three isolated metallic-sheets is proposed. The actual shape and size of the sheet-electron-beam are obtained through a non-conventional method by proposing a dielectric charging technique and scanning electron microscope based imaging. As distinct from the earlier developed sheet beam sources, the generated sheet-beam has been propagated more than 190 mm distance in a drift space region maintaining sheet structure without assistance of any external magnetic field.

  5. Mechanism of Radial Redistribution of Energetic Trapped Ions Due to m=2/n=1 Internal Reconnection in Joint European Torus Shear Optimized Plasmas

    Energy Technology Data Exchange (ETDEWEB)

    N.N. Gorelenkov; A. Gondhalekar; A.A. Korotkov; S.E. Sharapov; D. Testa; and Contributors to the EFDA-JET Workprogramme

    2002-01-18

    Internal radial redistribution of MeV energy ICRF-driven hydrogen minority ions was inferred from neutral particle analyzer measurements during large amplitude MHD activity leading to internal reconnection in Shear Optimized plasmas in the Joint European Torus (JET). A theory is developed for energetic ion redistribution during a reconnection driven by an m=2/n=1 internal kink mode. Plasma motion during reconnection generates an electric field which can change the energy and radial position of the energetic ions. The magnitude of ion energy change depends on the value of the safety factor at the plasma core from which the energetic ions are redistributed. A relation is found for corresponding change in canonical momentum. P(subscript phi), which leads to radial displacement of the ions. The model yields distinctive new features of energetic ion redistribution under such conditions. Predicted characteristics of ion redistribution are compared with the NPA measurements, and good correlation is found. Sometimes fast ions were transported to the plasma edge due to interaction with a long-lived magnetic island which developed after the reconnection and had chirping frequency in the laboratory frame. Convection of resonant ions trapped in a radially moving phase-space island is modeled to understand the physics of such events.

  6. Conceptual design of the three-dimensional magnetic field configuration relevant to the magnetopause reconnection in the SPERF

    Science.gov (United States)

    Aohua, MAO; Yang, REN; Hantao, JI; Peng, E.; Ke, HAN; Zhibin, WANG; Qingmei, XIAO; Liyi, LI

    2017-03-01

    A new ground-based experimental device, the Space Plasma Environment Research Facility (SPERF), is being designed at Harbin Institute of Technology in China, with Asymmetric REconnection eXperiment-3 Dimensional (AREX-3D) as one of the experimental components to study the asymmetric reconnection dynamics relevant to the interaction between the interplanetary and magnetospheric plasmas. The asymmetry in the designed magnetic reconnection process not only refers to the distinct plasma parameters designed for the two upstream regions across the current sheet, but also refers to the inhomogeneity in the direction along the current sheet resulting from the designed 3D magnetic field geometry. These two asymmetries are fundamental features of the reconnection process at the Earth’s magnetopause. In experiment, the reconnection process is driven by a set of flux cores through coil-current-ramp-up from the ‘magnetosheath-side’ to interact with a dipole magnetic field generated by the Dipole Research EXperiment (DREX) coil on the ‘magnetosphere-side’. The AREX-3D will be able to investigate a range of important reconnection issues in 3D magnetic field geometry that is relevant to the Earth’s magnetopause. A wide range of plasma parameters can be achieved through inductive plasma generation with flux cores on the ‘magnetosheath-side’ and electron cyclotron resonance (ECR) with microwave sources on the ‘magnetosphere-side’, e.g. high (low) plasma density at experimental magnetosheath (dipole) side. Different reconnection regimes and geometries can be produced by adjusting plasma parameters and coil setups as well as coil current waveforms. The three-dimensional magnetic field configurations in the SPERF relevant to the dayside magnetopause reconnection are discussed in detail.

  7. Separatrices: the crux of reconnection

    CERN Document Server

    Lapenta, Giovanni; Divin, Andrey; Newman, David; Goldman, Martin

    2014-01-01

    Reconnection is one of the key processes in astrophysical and laboratory plasmas: it is the opposite of a dynamo. Looking at energy, a dynamo transforms kinetic energy in magnetic energy while reconnection takes magnetic energy and returns is to its kinetic form. Most plasma processes at their core involve first storing magnetic energy accumulated over time and then releasing it suddenly. We focus here on this release. A key concept in analysing reconnection is that of the separatrix, a surface (line in 2D) that separates the fresh unperturbed plasma embedded in magnetic field lines not yet reconnected with the hotter exhaust embedded in reconnected field lines. In kinetic physics, the separatrices become a layer where many key processes develop. We present here new results relative to the processes at the separatrices that regulate the plasma flow, the energisation of the species, the electromagnetic fields and the instabilities developing at the separatrices.

  8. Collisionless magnetic reconnection under anisotropic MHD approximation

    Science.gov (United States)

    Hirabayashi, Kota; Hoshino, Masahiro

    We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless magneto-hydro-dynamic (MHD) simulations based on the double adiabatic approximation, which is an important step to bridge the gap between the Petschek-type MHD reconnection model accompanied by a pair of slow shocks and the observational evidence of the rare occasion of in-situ slow shock observation. According to our results, a pair of slow shocks does form in the reconnection layer. The resultant shock waves, however, are quite weak compared with those in an isotropic MHD from the point of view of the plasma compression and the amount of the magnetic energy released across the shock. Once the slow shock forms, the downstream plasma are heated in highly anisotropic manner and a firehose-sense (P_{||}>P_{⊥}) pressure anisotropy arises. The maximum anisotropy is limited by the marginal firehose criterion, 1-(P_{||}-P_{⊥})/B(2) =0. In spite of the weakness of the shocks, the resultant reconnection rate is kept at the same level compared with that in the corresponding ordinary MHD simulations. It is also revealed that the sequential order of propagation of the slow shock and the rotational discontinuity, which appears when the guide field component exists, changes depending on the magnitude of the guide field. Especially, when no guide field exists, the rotational discontinuity degenerates with the contact discontinuity remaining at the position of the initial current sheet, while with the slow shock in the isotropic MHD. Our result implies that the slow shock does not necessarily play an important role in the energy conversion in the reconnection system and is consistent with the satellite observation in the Earth's magnetosphere.

  9. Activation of MHD reconnection on ideal timescales

    Science.gov (United States)

    Landi, S.; Papini, E.; Del Zanna, L.; Tenerani, A.; Pucci, F.

    2017-01-01

    Magnetic reconnection in laboratory, space and astrophysical plasmas is often invoked to explain explosive energy release and particle acceleration. However, the timescales involved in classical models within the macroscopic MHD regime are far too slow to match the observations. Here we revisit the tearing instability by performing visco-resistive two-dimensional numerical simulations of the evolution of thin current sheets, for a variety of initial configurations and of values of the Lunquist number S, up to 107. Results confirm that when the critical aspect ratio of S 1/3 is reached in the reconnecting current sheets, the instability proceeds on ideal (Alfvénic) macroscopic timescales, as required to explain observations. Moreover, the same scaling is seen to apply also to the local, secondary reconnection events triggered during the nonlinear phase of the tearing instability, thus accelerating the cascading process to increasingly smaller spatial and temporal scales. The process appears to be robust, as the predicted scaling is measured both in inviscid simulations and when using a Prandtl number P  =  1 in the viscous regime.

  10. The Role of Magnetic Reconnection in Solar Activity

    Science.gov (United States)

    Antiochos, Spiro; DeVore, C. R.

    2008-01-01

    The central challenge in solar/heliospheric physics is to understand how the emergence and transport of magnetic flux at the photosphere drives the structure and dynamics that we observe in the corona and heliosphere. This presentation focuses on the role of magnetic reconnection in determining solar/heliospheric activity. We demonstrate that two generic properties of the photospheric magnetic and velocity fields are responsible for the ubiquitous reconnection in the corona. First, the photospheric velocities are complex, which leads to the injection of energy and helicity into the coronal magnetic fields and to the efficient, formation of small-scale structure. Second, the flux distribution at the photosphere is multi-polar, which implies that topological discontinuities and, consequently, current sheets, must be present in the coronal magnetic field. We: present numerical simulations showing that photospherically-driven reconnection is responsible for the heating and dynamics of coronal plasma, and for the topology of the coronal/heliospheric magnetic field.

  11. Current sheets with inhomogeneous plasma temperature: Effects of polarization electric field and 2D solutions

    Energy Technology Data Exchange (ETDEWEB)

    Catapano, F., E-mail: menacata3@gmail.com; Zimbardo, G. [Dipartimento di Fisica, Università della Calabria, Rende, Cosenza (Italy); Artemyev, A. V., E-mail: ante0226@gmail.com; Vasko, I. Y. [Space Research Institute, RAS, Moscow (Russian Federation)

    2015-09-15

    We develop current sheet models which allow to regulate the level of plasma temperature and density inhomogeneities across the sheet. These models generalize the classical Harris model via including two current-carrying plasma populations with different temperature and the background plasma not contributing to the current density. The parameters of these plasma populations allow regulating contributions of plasma density and temperature to the pressure balance. A brief comparison with spacecraft observations demonstrates the model applicability for describing the Earth magnetotail current sheet. We also develop a two dimensional (2D) generalization of the proposed model. The interesting effect found for 2D models is the nonmonotonous profile (along the current sheet) of the magnetic field component perpendicular to the current sheet. Possible applications of the model are discussed.

  12. Whistler Mode Waves in Collisionless Magnetic Reconnection

    Institute of Scientific and Technical Information of China (English)

    GUO Jun; LU Quan-Ming; WANG Shui; WANG Yu-Ming; DOU Xian-Kang

    2004-01-01

    A 21/2-dimensional electromagnetic particle-in-cell (PIC) simulation code is used to investigate the wave phenomena in the plasma sheet of collisionless magnetic reconnection. The results show that these waves have the following characteristics: they are right-hand circularity polarized, with propagation direction nearly parallel to local magnetic field, and frequency between 0.07 and 0.17 times of local electron cyclotron frequency. Therefore we conclude that such waves are Whistler waves, and their possible excitation mechanisms are also discussed.

  13. The auroral and ionospheric flow signatures of dual lobe reconnection

    Directory of Open Access Journals (Sweden)

    S. M. Imber

    2006-11-01

    Full Text Available We present the first substantial evidence for the occurrence of dual lobe reconnection from ionospheric flows and auroral signatures. The process of dual lobe reconnection refers to an interplanetary magnetic field line reconnecting with lobe field lines in both the northern and southern hemispheres. Two bursts of sunward plasma flow across the noon portion of the open/closed field line boundary (OCB, indicating magnetic flux closure at the dayside, were observed in SuperDARN radar data during a period of strongly northward IMF. The OCB is identified from spacecraft, radar backscatter, and auroral observations. In order for dual lobe reconnection to take place, we estimate that the interplanetary magnetic field clock angle must be within ±10° of zero (North. The total flux crossing the OCB during each burst is small (1.8% and 0.6% of the flux contained within the polar cap for the two flows. A brightening of the noon portion of the northern auroral oval was observed as the clock angle passed through zero, and is thought to be due to enhanced precipitating particle fluxes due to the occurrence of reconnection at two locations along the field line. The number of solar wind protons captured by the flux closure process was estimated to be ~2.5×1030 (4 tonnes by mass, sufficient to populate the cold, dense plasma sheet observed following this interval.

  14. Magnetospheric Magnetic Reconnection with Southward IMF by a 3D EMPM Simulation

    Science.gov (United States)

    Nishikawa, K.-I.; Yan, X. Y.; Cai, D. S.; Lembege, B.

    2004-01-01

    We report our new simulation results on magnetospheric magnetic reconnection with southward IMF using a 3D EMPM model, with greater resolution and more particles using the parallelized 3D HPF TRISTAN code on VPP5000 supercomputer. Main parameters used in the new simulation are: domain size is 215 x 145 x 145, grid size = 0.5 Earth radius, initial particle number is 16 per cell, the IMF is southward. Arrival of southward IMF will cause reconnection in the magnetopause, thus allowing particles to enter into the inner magnetosphere. Sunward and tailward high particle flow are observed by satellites, and these phenomena are also observed in the simulation near the neutral line (X line) of the near-Earth magnetotail. This high particle flow goes along with the reconnected island. The magnetic reconnection process contributes to direct plasma entry between the magnetosheath to the inner magnetosphere and plasma sheet, in which the entry process eats the magnetosheath plasma to plasma sheet temperatures. We investigate magnetic, electric fields, density, and current during this magnetic reconnection with southward IMF. Further investigation with this simulation will provide insight into unsolved problems, such as the triggering of storms and substorms, and the storm-substorm relationship. New results will be presented at the meeting.

  15. Spatial variation of eddy-diffusion coefficients in the turbulent plasma sheet during substorms

    Directory of Open Access Journals (Sweden)

    M. Stepanova

    2009-04-01

    Full Text Available Study of the plasma turbulence in the central plasma sheet was performed using the Interball-Tail satellite data. Fluctuations of the plasma bulk velocity in the plasma sheet were deduced from the measurements taken by the Corall instrument for different levels of geomagnetic activity and different locations inside the plasma sheet. The events that satisfied the following criteria were selected for analysis: number density 0.1–10 cm−3, ion temperature T≥0.3 keV, and average bulk velocity ≤100 km/s. It was found that the plasma sheet flow generally appears to be strongly turbulent, i.e. is dominated by fluctuations that are unpredictable. Corresponding eddy-diffusion coefficients in Y- and Z-direction in the GSM coordinate system were derived using the autocorrelation time and rms velocity. Statistical studies of variation of the eddy-diffusion coefficients with the location inside the plasma sheet showed a significant increase in these coefficients in the tailward direction. During substorms this dependence shows strong increase of eddy-diffusion in the central part of the plasma sheet at the distances of 10–30 Earth's radii. This effect is much stronger for Y-components of the eddy-diffusion coefficient, which could be related to the geometry of the plasma sheet, allowing more room for development of eddies in this direction.

  16. Fractal Reconnection in Solar and Stellar Environments

    CERN Document Server

    Shibata, Kazunari

    2016-01-01

    Recent space based observations of the Sun revealed that magnetic reconnection is ubiquitous in the solar atmosphere, ranging from small scale reconnection (observed as nanoflares) to large scale one (observed as long duration flares or giant arcades). Often the magnetic reconnection events are associated with mass ejections or jets, which seem to be closely related to multiple plasmoid ejections from fractal current sheet. The bursty radio and hard X-ray emissions from flares also suggest the fractal reconnection and associated particle acceleration. We shall discuss recent observations and theories related to the plasmoid-induced-reconnection and the fractal reconnection in solar flares, and their implication to reconnection physics and particle acceleration. Recent findings of many superflares on solar type stars that has extended the applicability of the fractal reconnection model of solar flares to much a wider parameter space suitable for stellar flares are also discussed.

  17. A statistical study on the correlations between plasma sheet and solar wind based on DSP explorations

    Directory of Open Access Journals (Sweden)

    G. Q. Yan

    2005-11-01

    Full Text Available By using the data of two spacecraft, TC-1 and ACE (Advanced Composition Explorer, a statistical study on the correlations between plasma sheet and solar wind has been carried out. The results obtained show that the plasma sheet at geocentric distances of about 9~13.4 Re has an apparent driving relationship with the solar wind. It is found that (1 there is a positive correlation between the duskward component of the interplanetary magnetic field (IMF and the duskward component of the geomagnetic field in the plasma sheet, with a proportionality constant of about 1.09. It indicates that the duskward component of the IMF can effectively penetrate into the near-Earth plasma sheet, and can be amplified by sunward convection in the corresponding region at geocentric distances of about 9~13.4 Re; (2 the increase in the density or the dynamic pressure of the solar wind will generally lead to the increase in the density of the plasma sheet; (3 the ion thermal pressure in the near-Earth plasma sheet is significantly controlled by the dynamic pressure of solar wind; (4 under the northward IMF condition, the ion temperature and ion thermal pressure in the plasma sheet decrease as the solar wind speed increases. This feature indicates that plasmas in the near-Earth plasma sheet can come from the magnetosheath through the LLBL. Northward IMF is one important condition for the transport of the cold plasmas of the magnetosheath into the plasma sheet through the LLBL, and fast solar wind will enhance such a transport process.

  18. Three-dimensional relativistic pair plasma reconnection with radiative feedback in the Crab Nebula

    CERN Document Server

    Cerutti, Benoit; Uzdensky, Dmitri A; Begelman, Mitchell C

    2013-01-01

    The discovery of rapid synchrotron gamma-ray flares above 100 MeV from the Crab Nebula has attracted new interest in alternative particle acceleration mechanisms in pulsar wind nebulae. Diffuse shock-acceleration fails to explain the flares because particle acceleration and emission occur during a single or even sub-Larmor timescale. In this regime, the synchrotron energy losses induce a drag force on the particle motion that balances the electric acceleration and prevents the emission of synchrotron radiation above 160 MeV. Previous analytical studies and 2D particle-in-cell (PIC) simulations indicate that relativistic reconnection is a viable mechanism to circumvent the above difficulties. The reconnection electric field localized at X-points linearly accelerates particles with little radiative energy losses. In this paper, we check whether this mechanism survives in 3D, using a set of large PIC simulations with radiation reaction force and with a guide field. In agreement with earlier works, we find that t...

  19. A study of the formation and dynamics of the Earth's plasma sheet using ion composition data

    Science.gov (United States)

    Lennartsson, O. W.

    1994-01-01

    Over two years of data from the Lockheed Plasma Composition Experiment on the ISEE 1 spacecraft, covering ion energies between 100 eV/e and about 16 keV/e, have been analyzed in an attempt to extract new information about three geophysical issues: (1) solar wind penetration of the Earth's magnetic tail; (2) relationship between plasma sheet and tail lobe ion composition; and (3) possible effects of heavy terrestrial ions on plasma sheet stability.

  20. The Pressure Limitations on Flux Pile-up Reconnection

    Science.gov (United States)

    Litvinenko, Yuri E.

    1999-05-01

    The problem of the plasma pressure limitations on the rapidity of flux pile-up magnetic reconnection is re-examined, following the claim made by Jardine and Allen (1998) that the limitations can be removed by relaxing the assumption of zero-vorticity two-dimensional plasma flows. It is shown that for a two-dimensional stagnation point flow with nonzero vorticity the magnetic merging rate cannot exceed the Sweet-Parker scaling in a low-beta plasma. The pressure limitation appears to be much less restrictive for weak three-dimensional flux pile-up, provided the perturbation length scale in the third dimension is much less than the global length scale. The actual reconnection rate in the latter case, however, is much lower than this upper estimate unless the current sheet width is also much less than the global scale.

  1. Radiative Magnetic Reconnection in Astrophysics

    CERN Document Server

    Uzdensky, Dmitri A

    2015-01-01

    I review a new rapidly growing area of high-energy plasma astrophysics --- radiative magnetic reconnection, i.e., a reconnection regime where radiation reaction influences reconnection dynamics, energetics, and nonthermal particle acceleration. This influence be may be manifested via a number of astrophysically important radiative effects, such as radiation-reaction limits on particle acceleration, radiative cooling, radiative resistivity, braking of reconnection outflows by radiation drag, radiation pressure, viscosity, and even pair creation at highest energy densities. Self-consistent inclusion of these effects in magnetic reconnection theory and modeling calls for serious modifications to our overall theoretical approach to the problem. In addition, prompt reconnection-powered radiation often represents our only observational diagnostic tool for studying remote astrophysical systems; this underscores the importance of developing predictive modeling capabilities to connect the underlying physical condition...

  2. Experimental Verification of the Role of Electron Pressure in Fast Magnetic Reconnection with a Guide Field.

    Science.gov (United States)

    Fox, W; Sciortino, F; V Stechow, A; Jara-Almonte, J; Yoo, J; Ji, H; Yamada, M

    2017-03-24

    We report detailed laboratory observations of the structure of a reconnection current sheet in a two-fluid plasma regime with a guide magnetic field. We observe and quantitatively analyze the quadrupolar electron pressure variation in the ion-diffusion region, as originally predicted by extended magnetohydrodynamics simulations. The projection of the electron pressure gradient parallel to the magnetic field contributes significantly to balancing the parallel electric field, and the resulting cross-field electron jets in the reconnection layer are diamagnetic in origin. These results demonstrate how parallel and perpendicular force balance are coupled in guide field reconnection and confirm basic theoretical models of the importance of electron pressure gradients for obtaining fast magnetic reconnection.

  3. Dynamo-driven plasmoid formation from a current-sheet instability

    Science.gov (United States)

    Ebrahimi, F.

    2016-12-01

    Axisymmetric current-carrying plasmoids are formed in the presence of nonaxisymmetric fluctuations during nonlinear three-dimensional resistive MHD simulations in a global toroidal geometry. We utilize the helicity injection technique to form an initial poloidal flux in the presence of a toroidal guide field. As helicity is injected, two types of current sheets are formed from (1) the oppositely directed field lines in the injector region (primary reconnecting current sheet), and (2) the poloidal flux compression near the plasma edge (edge current sheet). We first find that nonaxisymmetric fluctuations arising from the current-sheet instability isolated near the plasma edge have tearing parity but can nevertheless grow fast (on the poloidal Alfven time scale). These modes saturate by breaking up the current sheet. Second, for the first time, a dynamo poloidal flux amplification is observed at the reconnection site (in the region of the oppositely directed magnetic field). This fluctuation-induced flux amplification increases the local Lundquist number, which then triggers a plasmoid instability and breaks the primary current sheet at the reconnection site. The plasmoids formation driven by large-scale flux amplification, i.e., a large-scale dynamo, observed here has strong implications for astrophysical reconnection as well as fast reconnection events in laboratory plasmas.

  4. Sub-Grid-Scale Description of Turbulent Magnetic Reconnection in Magnetohydrodynamics

    CERN Document Server

    Widmer, Fabien; Yokoi, Nobumitsu

    2015-01-01

    Magnetic reconnection requires, at least locally, a non-ideal plasma response. In collisionless space and astrophysical plasmas, turbulence could permit this instead of the too rare binary collisions. We investigated the influence of turbulence on the reconnection rate in the framework of a single fluid compressible MHD approach. The goal is to find out, whether unresolved, sub-grid for MHD simulations, turbulence can enhance the reconnection process in high Reynolds number astrophysical plasma. We solve, simultaneously with the grid-scale MHD equations, evolution equations for the sub-grid turbulent energy and cross helicity according to Yokoi's model (Yokoi (2013)) where turbulence is self-generated and -sustained through the inhomogeneities of the mean fields. Simulations of Harris and force free sheets confirm the results of Higashimori et al. (2013) and new results are obtained about the dependence on resistivity for large Reynolds number as well as guide field effects. The amount of energy transferred f...

  5. Magnetic reconnection at 3D null points: effect of magnetic field asymmetry

    CERN Document Server

    Al-Hachami, A K

    2009-01-01

    The aim of this paper is to investigate the properties of magnetic reconnection at a 3D null point, with respect to their dependence on the symmetry of the magnetic field around the null. In particular we examine the rate of flux transport across the null point with symmetric/asymmetric diffusion regions, as well as how the current sheet forms in time, and its properties. Mathematical modelling and finite difference resistive MHD simulations are used. It is found that the basic structure of the mode of magnetic reconnection considered is unaffected by varying the magnetic field symmetry, that is, the plasma flow is found cross both the spine and fan of the null. However, the peak intensity and dimensions of the current sheet are dependent on the symmetry/ asymmetry of the field lines. As a result, the reconnection rate is also found to be strongly dependent on the field asymmetry.

  6. Ion beta dependence on the development of Alfvénic fluctuations in reconnection jets

    Science.gov (United States)

    Higashimori, Katsuaki; Hoshino, Masahiro

    2015-03-01

    The generation of magneto-hydro-dynamic (MHD) to ion-scale fluctuations in collisionless magnetic reconnection is discussed using a two-dimensional electromagnetic hybrid code. It is shown that reconnection jets become turbulent specifically in low beta conditions, βi0dynamics in the plasma sheet boundary layer (PSBL) and a current sheet. We suggest that PSBL ion dynamics play an important part in excitation and suppression of waves. PSBL beam ions drive Alfvén waves in MHD to ion scale, kλicorrelated with that of inflowing ions, the waves decay by cyclotron damping as the value of the inflow ion beta increases. Local linear analysis suggests that this damping signature changes in βi0˜0.1-0.2 and suppresses the wave activity of Alfvén modes in high beta reconnection jets.

  7. Three-Dimensional Turbulent Reconnection Induced by the Plasmoid Instability

    Science.gov (United States)

    Bhattacharjee, A.; Huang, Y. M.

    2014-12-01

    It has been established that the Sweet-Parker current layer in high-Lundquist-number reconnection is unstable to the super-Alfvenic plasmoid instability. Past two-dimensional magnetohydrodynamic simulations have demonstrated that the plasmoid instability leads to a new regime in which the Sweet-Parker current layer evolves into a chain of plasmoids connected by secondary current sheets and the averaged reconnection rate becomes nearly independent of the Lundquist number. In a three-dimensional configuration with a guide field, the additional degree of freedom allows plasmoid instabilities to grow at oblique angles [S. Baalrud et al. Phys. Plasmas 19, 022101 (2012)] and develop the complex dynamics of flux ropes which overlap, cause field-line stochasticization, and self-generate a turbulent state. Three-dimensional simulations in the high-Lundquist-number regime show the formation of cigar-shaped eddies elongated in the direction of the local magnetic field, which is a signature of anisotropic MHD turbulence. Furthermore, the energy fluctuation spectra are found to satisfy power laws in the inertial range. The averaged 3D reconnection rate in the self-generated turbulent state is of the order of a hundredth of the characteristic Alfven speed, which is an order of magnitude lower than the reconnection rate reported in recent studies of externally driven 3D turbulent reconnection. The physical reasons for these differences will be discussed.

  8. A new fast reconnection model in a collisionless regime

    CERN Document Server

    Tsiklauri, David

    2008-01-01

    Based on the first principles (by balancing the advection with the electron pressure tensor in the generalised Ohm's law, and using the conservation of mass) a simple model of magnetic reconnection in a collisionless regime is formulated. In addition to its importance from the fundamental point of view, the collisionless reconnection model offers a much faster reconnection rate ($M_{c'less}={(d_i/2)}^{1/2}$) than Sweet-Parker's classical one ($M_{sp}=S^{-1/2}$). The width of the diffusion region (current sheet) in the collisionless regime is found to be $\\delta_{c'less}={(d_i/2)}^{1/2}L$, which is much larger than the Sweet-Parker width ($\\delta_{sp}=S^{-1/2}L$) for the space plasma conditions. Amongst other issues, this alleviates e.g. the problem of interpretation of solar flares by means of reconnection, as for the typical solar coronal parameters the obtained collisionless reconnection time can be $< 10$ minutes, as opposed to Sweet-Parker's equivalent value of $<$ year. The new theoretical reconnec...

  9. Local Dynamics and Global Size Coupling during Magnetic Reconnection

    Science.gov (United States)

    Jacobson, C. M.; Breslau, J. A.; Jardin, S. C.; Ji, H.

    2008-11-01

    Magnetic reconnection is an important physical process not only in small systems such as laboratory plasmas, but also in large systems such as solar flares. The reconnection rate increases with resistivity η and decreases with the current sheet length L. Recent experimental results suggest that these parameters are not independent, but anti-correlate such that ηL is kept roughly constant; thus the reconnection rate is a function of both local dynamics and global size [1]. In order to verify these results and further extend the system size, a numerical MHD model [2] is used. This code allows simulation of either two-fluid or single-fluid resistive MHD reconnection of colliding flux tubes on a 2D grid. The resistivity and system size are systematically varied, and scalings of the ion skin depth, collisionality, and reconnection rate due to these quantities are presented. Results are compared to experimental data, and findings are projected to solar flare scales. [1] A. Kuritsyn et al. Geophys. Res. Lett. 34, L16106 (2007) [2] J. A. Breslau and S. C. Jardin, Comput. Phys. Commun. 151, 8 (2003)

  10. Conditions for substorm onset by the fast reconnection mechanism

    Directory of Open Access Journals (Sweden)

    M. Ugai

    2008-12-01

    Full Text Available The fast reconnection mechanism, involving slow shocks and Alfvénic fast plasma jets, is most responsible for the explosive conversion of magnetic energy associated with geomagnetic substorms and solar flares. In this paper, the spontaneous fast reconnection model is applied to well-known phenomena of substorms. When the east-west width of the tail current sheet becomes 3–4 times larger than its north-south thickness, the fast reconnection mechanism can fully be established, which may lead to substorm onset. The resulting Alfvénic jet can exactly explain, both qualitatively and quantitatively, the in-situ satellite observations of the traveling compression regions (TCRs associated with large-scale plasmoids propagating down the tail. Also, the earthward fast reconnection jet causes drastic magnetic field dipolarization, so that the sheet current ahead of the magnetic loop of closed field lines suddenly turns its direction toward the loop footpoint and a large-scale current wedge is formed according to the growth of field-aligned currents. It is demonstrated that an MHD generator arises ahead of the magnetic loop and drives the current wedge to distinctly enhance the current density in a pair of thin layers of the loop footpoint, giving rise to drastic heating in the form of two ribbons.

  11. Magnetic Reconnection with Strong Synchrotron Cooling in Pulsar Magnetospheres

    Science.gov (United States)

    Uzdensky, Dmitri; Spitkovsky, Anatoly

    2012-10-01

    The magnetosphere of a rotating pulsar naturally develops a current sheet beyond the light cylinder (LC). Magnetic reconnection in this current sheet inevitably dissipates a nontrivial fraction of the pulsar spin-down power within a few LC radii. In this presentation, a basic physical picture of reconnection in this environment is developed. It is shown that reconnection proceeds in the plasmoid-dominated regime, via an hierarchical chain of multiple secondary islands/flux ropes. The inter-plasmoid reconnection layers are subject to strong synchrotron cooling, leading to significant plasma compression. The basic parameters of these current layers --- temperature, density, and layer thickness --- are estimated in terms of the upstream magnetic field. It is argued that, after accounting for the bulk Doppler boosting, the synchrotron and inverse-Compton emission mechanisms can explain the observed pulsed high-energy (GeV) and VHE (˜ 100 GeV) radiation, respectively. The motions of the secondary plasmoids may contribute to the pulsar's radio emission.

  12. The formation and evolution of reconnection-driven slow-mode shocks in a partially ionised plasma

    CERN Document Server

    Hillier, Andrew; Nakamura, Naoki

    2016-01-01

    The role of slow-mode MHD shocks in magnetic reconnection is one of great importance for energy conversion and transport, but in many astrophysical plasmas the plasma is not fully ionised. In this paper, we investigate, using numerical simulations, the role of collisional coupling between a proton-electron charge-neutral fluid and a neutral hydrogen fluid for the 1D Riemann problem initiated in a constant pressure and density background state by a discontinuity in the magnetic field. This system, in the MHD limit, is characterised by two waves: a fast-mode rarefaction wave that drives a flow towards a slow-mode MHD shock. The system evolves through four stage: initiation, weak coupling, intermediate coupling and a quasi steady state. The initial stages are characterised by an over-pressured neutral region that expands with characteristics of a blast wave. In the later stages, the system tends towards a self-similar solution where the main drift velocity is concentrated in the thin region of the shock front. D...

  13. Solar flare mechanism based on magnetic arcade reconnection and island merging

    Energy Technology Data Exchange (ETDEWEB)

    C.Z. Chen; G.S. Choe

    2000-06-15

    The authors propose a model describing physical processes of solar flares based on resistive reconnection of magnetic field subject to continuous increase of magnetic shear in the arcade. The individual flaring process consists of magnetic reconnection of arcade field lines, generation of magnetic islands in the magnetic arcade, and coalescence of magnetic islands. When a magnetic arcade is sheared (either by foot point motion or by flux emergence), a current sheet is formed and magnetic reconnection can take place to form a magnetic island. A continuing increase of magnetic shear can trigger a new reconnection process and create a new island in the under lying arcade below the magnetic island. The new born island rises faster than the preceding island and merges with it to form one island. Before completing the island merging process, the new born island exhibits two phases of rising motion: a first phase with a slower rising speed and a second phase with a faster rising speed. The flare plasma heating occurs mainly due to magnetic reconnection in the current sheet under the new born island. The new born island represents the X-ray plasma ejecta which shows two phases of rising motion observed by Yohkoh [Ohyama and Shibata (1997)]. The first phase with slower new born island rising speed corresponds to the early phase of reconnection of line-tied field in the underlying current sheet and is considered as the preflare phase. In the second phase, the island coalescence takes place, and the underlying current sheet is elongated so that the line-tied arcade field reconnection rate is enhanced. This phase is interpreted as the impulsive phase or the flash phase of flares. The obtained reconnection electric field is large enough to accelerate electrons to an energy level higher than 10 keV, which is necessary for observed hard X-ray emissions. After merging of the islands is completed, magnetic reconnection continues in the current sheet under the integrated island for

  14. Magnetic Reconnection

    NARCIS (Netherlands)

    Schep, T. J.

    1994-01-01

    This lecture deals with the concept of magnetic field lines and with the conservation of magnetic flux. In high temperature fusion devices like tokamaks flux conservation can be violated and reconnection can occur at closed magnetic field lines. Reconnection processes lead to changes in the global t

  15. Dissipation and reconnection in boundary-driven reduced magnetohydrodynamics

    Energy Technology Data Exchange (ETDEWEB)

    Wan, Minping; Rappazzo, Antonio Franco; Matthaeus, William H. [Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Servidio, Sergio [Dipartimento di Fisica, Università della Calabria, I-87036 Cosenza (Italy); Oughton, Sean [Department of Mathematics, University of Waikato, Hamilton 3240 (New Zealand)

    2014-12-10

    We study the statistics of coherent current sheets, the population of X-type critical points, and reconnection rates in a coronal loop geometry, via numerical simulations of reduced magnetohydrodynamic turbulence. Current sheets and sites of reconnection (magnetic X-points) are identified in two-dimensional planes of the three-dimensional simulation domain. The geometry of the identified current sheets—including area, length, and width—and the magnetic dissipation occurring in the current sheets are statistically characterized. We also examine the role of magnetic reconnection, by computing the reconnection rates at the identified X-points and investigating their association with current sheets.

  16. Structure of the dayside reconnection layer in resistive MHD and hybrid models

    Science.gov (United States)

    Lin, Y.; Lee, L. C.

    1993-01-01

    Numerical simulations were performed to investigate the structure of the reconnection layer at the dayside magnetopause. Two typical cases are examined in detail; both are asymmetric in magnetic field and plasma density. In case 1, the guide fields in the magnetosheath and in the magnetosphere are set at zero and thus the tangential magnetic fields on the two sides of the initial current sheet are exactly antiparallel. In case 2, the angle between the tangential magnetic fields on the two sides of the initial current sheet is 145 deg. The results obtained from a resistive MHD model and from a hybrid model are found to be different. In the MHD simulation of case 1, a 2-4 intermediate shock is found to bound the reconnection layer on the magnetosheath side, while an Alfven wave pulse bounds the reconnection layer on the magnetospheric side. In case 2, it is found that a time-dependent intermediate shock (TDIS) bounds the reconnection layer on the magnetosheath side, with a slow expansion wave propagating behind. With the MHD simulations, in the general case in which the tangential magnetic fields on the two sides of the initial current sheet are not exactly antiparallel, a rotational discontinuity across which the tangential magnetic field rotates, a large angle is found to bound the reconnection layer on the magnetosheath side.

  17. Electron cyclotron maser instability (ECMI in strong magnetic guide field reconnection

    Directory of Open Access Journals (Sweden)

    R. A. Treumann

    2017-08-01

    Full Text Available The ECMI model of electromagnetic radiation from electron holes is shown to be applicable to spontaneous magnetic reconnection. We apply it to reconnection in strong current-aligned magnetic guide fields. Such guide fields participate only passively in reconnection, which occurs in the antiparallel components to both sides of the guide-field-aligned current sheets with current carried by kinetic Alfvén waves. Reconnection generates long (the order of hundreds of electron inertial scales electron exhaust regions at the reconnection site X point, which are extended perpendicular to the current and the guide fields. Exhausts contain a strongly density-depleted hot electron component and have properties similar to electron holes. Exhaust electron momentum space distributions are highly deformed, exhibiting steep gradients transverse to both the reconnecting and guide fields. Such properties suggest application of the ECMI mechanism with the fundamental ECMI X-mode emission beneath the nonrelativistic guide field cyclotron frequency in localized source regions. An outline of the mechanism and its prospects is given. Potential applications are the kilometric radiation (AKR in auroral physics, solar radio emissions during flares, planetary emissions and astrophysical scenarios (radiation from stars and compact objects involving the presence of strong magnetic fields and field-aligned currents. Drift of the exhausts along the guide field maps the local field and plasma properties. Escape of radiation from the exhaust and radiation source region still poses a problem. The mechanism can be studied in 2-D particle simulations of strong guide field reconnection which favours 2-D, mapping the deformation of the electron distribution perpendicular to the guide field, and using it in the numerical calculation of the ECMI growth rate. The mechanism suggests also that reconnection in general may become a source of the ECMI with or without guide fields. This is

  18. Progress on study of unusual structure of electrostatic solitary waves associated with magnetic reconnection in the near-Earth magnetotail

    Science.gov (United States)

    Li, Shiyou; Chen, Xiaoqian; Guo, Jianming

    2016-07-01

    The electrostatic solitary waves (ESWs) have been widely observed and studied for many years. In the magnetic reconnection process, ESWs are regarded as one kind of means for the fast energy release by outward propagating electrons along re-connecting magnetic field lines. In this report, we present observation evidences of two kinds of unusual structures of ESWs associated with magnetic reconnection in the near-Earth magnetotail, including the 2-D ESWs and the tri-polar ESWs. First of all, more than 300 of electrostatic solitary waves (ESWs) with large perpendicular component which is bi-polar waveform structure are observed in the boundary layer within magnetic reconnection diffusion region in the near-Earth magnetotail. Such kinds of ESWs are named as 2-D ESWs. Singe-Reconnection-Based-Statistical study of 2-D ESWs is performed. Secondly, more than 200 waveforms with clear tri-polar characteristics are differentiated along the plasma sheet boundary layer near the magnetic reconnection X-line in the near-Earth magnetotail. Within reconnection diffusion region, the tri-polar ESWs are ample and are continuously observed during one burst interval (8.75 seconds) of the Geotail/WFC in the neutral plasma sheet where and thus the tri-polar ESW is suggested to be one kind of steady-going solitary structure. Statistical analysis to the characteristics of tri-polar ESWs will also be carried out. The observation of 2-D ESWs and the tri-polar ESWs presents evidence of complex structure of electron holes within the reconnection diffusion region and is helpful to the understanding of the energy release process of reconnection.

  19. RECONNECTION-DRIVEN DOUBLE LAYERS IN THE STRATIFIED PLASMA OF THE SOLAR TRANSITION REGION: SUPPLY OF HOT PLASMA INTO THE CORONA

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Nagendra [Department of Electrical and Computer Engineering University of Alabama, Huntsville, AL 35899 (United States)

    2015-09-01

    A novel mechanism for the supply of hot plasma into the corona from the chromosphere is suggested here; the mechanism involves collisionless magnetic reconnection (CMR) in the transition region (TR) followed by double layer (DL) formation in the enhanced expansion of the chromospheric cold plasma mixed with CMR-heated hot electrons. It is well known that (i) the CMR produces energetic electrons and (ii) DLs naturally form in expanding dense plasmas containing a minor population of hot electrons. We apply these plasma physics facts to the dynamics of stratified plasma in the TR. In the TR where densities fall below ∼10{sup 16} m{sup −3}, all collisional mean-free paths, electron–ion, ion–neutral, and electron–neutral, become long enough to render plasma collisionless at kinetic scale lengths, making CMR and DL formation possible. The DLs accelerate the chromospheric cold ions to energies comparable to the energy of the hot electrons. When the upflowing energized ions neutralized by the escaping hot electrons thermalize, the resulting hot tenuous plasma supplies an energy flux ∼3 × 10{sup 5} erg cm{sup −2} s{sup −1} = 3 × 10{sup 2} J m{sup −2} s{sup −1} into the corona. The CMR–DL mechanism introduces sudden transitions in the TR as microstructures in both density and energy. The global transition in the TR could be a fractal structure containing such microscopic features. If not impossible, it is difficult to measure such microstructures, but it seems that the coronal heating begins in the nearly collisionless TR by CMR and DL formation.

  20. A Quantitative Model of Energy Release and Heating by Time-dependent, Localized Reconnection in a Flare with a Thermal Loop-top X-ray Source

    CERN Document Server

    Longcope, D W; Carranza-Fulmer, T; Qiu, J; 10.1007/s11207-010-9635-z

    2011-01-01

    We present a quantitative model of the magnetic energy stored and then released through magnetic reconnection for a flare on 26 Feb 2004. This flare, well observed by RHESSI and TRACE, shows evidence of non-thermal electrons only for a brief, early phase. Throughout the main period of energy release there is a super-hot (T>30 MK) plasma emitting thermal bremsstrahlung atop the flare loops. Our model describes the heating and compression of such a source by localized, transient magnetic reconnection. It is a three-dimensional generalization of the Petschek model whereby Alfven-speed retraction following reconnection drives supersonic inflows parallel to the field lines, which form shocks heating, compressing, and confining a loop-top plasma plug. The confining inflows provide longer life than a freely-expanding or conductively-cooling plasma of similar size and temperature. Superposition of successive transient episodes of localized reconnection across a current sheet produces an apparently persistent, localiz...

  1. Current sheets at three-dimensional magnetic nulls: Effect of compressibility

    Science.gov (United States)

    Pontin, D. I.; Bhattacharjee, A.; Galsgaard, K.

    2007-05-01

    The nature of current sheet formation in the vicinity of three-dimensional (3D) magnetic null points is investigated. The particular focus is upon the effect of the compressibility of the plasma on the qualitative and quantitative properties of the current sheet. An initially potential 3D null is subjected to shearing perturbations, as in a previous paper [Pontin et al., Phys. Plasmas 14, 052106 (2007)]. It is found that as the incompressible limit is approached, the collapse of the null point is suppressed and an approximately planar current sheet aligned to the fan plane is present instead. This is the case regardless of whether the spine or fan of the null is sheared. Both the peak current and peak reconnection rate are reduced. The results have a bearing on previous analytical solutions for steady-state reconnection in incompressible plasmas, implying that fan current sheet solutions are dynamically accessible, while spine current sheet solutions are not.

  2. Shocks and Thermal Conduction Fronts in Retracting Reconnected Flux Tubes

    Science.gov (United States)

    Guidoni, S. E.; Longcope, D. W.

    2010-08-01

    We present a model for plasma heating produced by time-dependent, spatially localized reconnection within a flare current sheet separating skewed magnetic fields. The reconnection creates flux tubes of new connectivity which subsequently retract at Alfvénic speeds from the reconnection site. Heating occurs in gas-dynamic shocks (GDSs) which develop inside these tubes. Here we present generalized thin flux tube equations for the dynamics of reconnected flux tubes, including pressure-driven parallel dynamics as well as temperature-dependent, anisotropic viscosity and thermal conductivity. The evolution of tubes embedded in a uniform, skewed magnetic field, following reconnection in a patch, is studied through numerical solutions of these equations, for solar coronal conditions. Even though viscosity and thermal conductivity are negligible in the quiet solar corona, the strong GDSs generated by compressing plasma inside reconnected flux tubes generate large velocity and temperature gradients along the tube, rendering the diffusive processes dominant. They determine the thickness of the shock that evolves up to a steady state value, although this condition may not be reached in the short times involved in a flare. For realistic solar coronal parameters, this steady state shock thickness might be as long as the entire flux tube. For strong shocks at low Prandtl numbers, typical of the solar corona, the GDS consists of an isothermal sub-shock where all the compression and cooling occur, preceded by a thermal front where the temperature increases and most of the heating occurs. We estimate the length of each of these sub-regions and the speed of their propagation.

  3. Thinning and functionalization of few-layer graphene sheets by CF4 plasma treatment

    KAUST Repository

    Shen, Chao

    2012-05-24

    Structural changes of few-layer graphene sheets induced by CF4 plasma treatment are studied by optical microscopy and Raman spectroscopy, together with theoretical simulation. Experimental results suggest a thickness reduction of few-layer graphene sheets subjected to prolonged CF4 plasma treatment while plasma treatment with short time only leads to fluorine functionalization on the surface layer by formation of covalent bonds. Raman spectra reveal an increase in disorder by physical disruption of the graphene lattice as well as functionalization during the plasma treatment. The F/CF3 adsorption and the lattice distortion produced are proved by theoretical simulation using density functional theory, which also predicts p-type doping and Dirac cone splitting in CF4 plasma-treated graphene sheets that may have potential in future graphene-based micro/nanodevices.

  4. Spatial Offsets in Flare-CME Current Sheets

    Science.gov (United States)

    Raymond, John C.; Giordano, Silvio; Ciaravella, Angela

    2017-07-01

    Magnetic reconnection plays an integral part in nearly all models of solar flares and coronal mass ejections (CMEs). The reconnection heats and accelerates the plasma, produces energetic electrons and ions, and changes the magnetic topology to form magnetic flux ropes and to allow CMEs to escape. Structures that appear between flare loops and CME cores in optical, UV, EUV, and X-ray observations have been identified as current sheets and have been interpreted in terms of the nature of the reconnection process and the energetics of the events. Many of these studies have used UV spectral observations of high temperature emission features in the [Fe xviii] and Si xii lines. In this paper, we discuss several surprising cases in which the [Fe xviii] and Si xii emission peaks are spatially offset from each other. We discuss interpretations based on asymmetric reconnection, on a thin reconnection region within a broader streamer-like structure, and on projection effects. Some events seem to be easily interpreted as the projection of a sheet that is extended along the line of sight that is viewed an angle, but a physical interpretation in terms of asymmetric reconnection is also plausible. Other events favor an interpretation as a thin current sheet embedded in a streamer-like structure.

  5. Separatrix regions of magnetic reconnection at the magnetopause

    Directory of Open Access Journals (Sweden)

    T. Lindstedt

    2009-10-01

    Full Text Available Using data from the four Cluster spacecraft we study the separatrix regions of magnetic reconnection sites at the dayside magnetopause under conditions when reconnection is occurring in the magnetopause current layer which separates magnetosheath plasma from the hot magnetospheric plasma sheet. We define the separatrix region as the region between the separatrix – the first field line opened by reconnection – and the reconnection jet (outflow region. We analyze eight separatrix region crossings on the magnetospheric side of the magnetopause and present detailed data for two of the events. We show that characteristic widths of the separatrix regions are of the order of ten ion inertial lengths at the magnetopause. Narrow separatrix regions with widths comparable to a few ion inertial lengths are rare. We show that inside the separatrix region there is a density cavity which sometimes has complex internal structure with multiple density dips. Strong electric fields exist inside the separatrix regions and the electric potential drop across the regions can be up to several kV. On the magnetosheath side of the region there is a density gradient with strong field aligned currents. The observed strong electric fields and currents inside the separatrix region can be important for a local energization of ions and electrons, particularly of ionospheric origin, as well as for magnetosphere-ionosphere coupling.

  6. Laboratory Study of Magnetic Reconnection in 3D Geometry Relevant to Magnetopause and Magnetotail

    Science.gov (United States)

    Ren, Y.; Lu, Q.; Ji, H.; Mao, A.; Wang, X.; E, P.; Wang, Z.; Xiao, Q.; Ding, W.; Zheng, J.

    2015-12-01

    Laboratory Study of Magnetic Reconnection in 3D Geometry Relevant to Magnetopause and Magnetotail Y. Ren1,2, Quaming Lu3, Hantao Ji1,2, Aohua Mao1, Xiaogang Wang1, Peng E1, Zhibin Wang1, Qingmei Xiao1, Weixing Ding4, Jinxing Zheng51 Harbin Institute of Technology, Harbin, China2 Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 3University of Science and Technology of China, Hefei, China 4University of California at Los Angeles, Los Angeles, CA, 90095 5ASIPP, Hefei, China A new magnetic reconnection experiment, Harbin reconnection eXperiment (HRX), is currently being designed as a key part of Space Plasma Environment Research Facility (SPERF) at Harbin Institute of Technology in Harbin, China. HRX aims to provide a unique experimental platform for studying reconnections in 3D geometry relevant to magnetopause and magnetotail to address: the role of electron and ion-scale dynamics in the current sheet; particle and energy transfer from magnetosheath to magnetosphere; particle energization/heating mechanisms during magnetic reconnection; 3D effects in fast reconnection, e.g. the role of 3D magnetic null point. HRX employs a unique set of coils to generate the required 3D magnetic geometry and provides a wide range of plasma parameters. Here, important motivating scientific problems are reviewed and the physics design of HRX is presented, including plasma parameters determined from Vlasov scaling law, reconnection scenarios explored using vacuum magnetic field calculations and numerical simulations of HRX using hybrid and MHD codes. Plasma diagnostics plan and engineering design of important coils will also be briefly presented.

  7. MMS Observations of Large Guide Field Symmetric Reconnection Between Colliding Reconnection Jets at the Center of a Magnetic Flux Rope at the Magnetopause

    Science.gov (United States)

    Oieroset, M.; Phan, T. D.; Haggerty, C.; Shay, M. A.; Eastwood, J. P.; Gershman, D. J.; Drake, J. F.; Fujimoto, M.; Ergun, R. E.; Mozer, F. S.; hide

    2016-01-01

    We report evidence for reconnection between colliding reconnection jets in a compressed current sheet at the center of a magnetic flux rope at Earth's magnetopause. The reconnection involved nearly symmetric Inflow boundary conditions with a strong guide field of two. The thin (2.5 ion-skin depth (d(sub i) width) current sheet (at approximately 12 d(sub i) downstream of the X line) was well resolved by MMS, which revealed large asymmetries in plasma and field structures in the exhaust. Ion perpendicular heating, electron parallel heating, and density compression occurred on one side of the exhaust, while ion parallel heating and density depression were shifted to the other side. The normal electric field and double out-of-plane (bifurcated) currents spanned almost the entire exhaust. These observations are in good agreement with a kinetic simulation for similar boundary conditions, demonstrating in new detail that the structure of large guide field symmetric reconnection is distinctly different from antiparallel reconnection.

  8. Influence of the lower-hybrid drift instability on magnetic reconnection in asymmetric configurations.

    Science.gov (United States)

    Roytershteyn, V; Daughton, W; Karimabadi, H; Mozer, F S

    2012-05-04

    Using fully kinetic 3D simulations of magnetic reconnection in asymmetric antiparallel configurations, we demonstrate that an electromagnetic lower-hybrid drift instability (LHDI) localized near the X line can substantially modify the reconnection mechanism in the regimes with large asymmetry, a moderate ratio of electron to ion temperature, and low plasma β. However, the mode saturates at a small amplitude in the regimes typical of Earth's magnetopause. In these cases, LHDI-driven turbulence is predominantly localized along the separatrices on the low-β side of the current sheet, in agreement with spacecraft observations.

  9. Bi-directional electrons in the near-Earth plasma sheet

    Directory of Open Access Journals (Sweden)

    K. Shiokawa

    Full Text Available We have studied the occurrence characteristics of bi-directional electron pitch angle anisotropy (enhanced flux in field-aligned directions, F^ /F|| > 1.5 at energies of 0.1–30 keV using plasma and magnetic field data from the AMPTE/IRM satellite in the near-Earth plasma sheet. The occurrence rate increases in the tailward direction from XGSM = - 9 RE to - 19 RE . The occurrence rate is also enhanced in the midnight sector, and furthermore, whenever the elevation angle of the magnetic field is large while the magnetic field intensity is small, B ~ 15 nT. From these facts, we conclude that the bi-directional electrons in the central plasma sheet are produced mainly in the vicinity of the neutral sheet and that the contribution from ionospheric electrons is minor. A high occurrence is also found after earthward high-speed ion flows, suggesting Fermi-type field-aligned electron acceleration in the neutral sheet. Occurrence characteristics of bi-directional electrons in the plasma sheet boundary layer are also discussed.

    Key words. Magnetospheric physics (magnetospheric configuration and dynamics; magnetotail; plasma sheet

  10. A Resistive MHD Simulation of the Shear Flow Effects on the Structure of Reconnection Layer

    Institute of Scientific and Technical Information of China (English)

    SUN Xiaoxia; WANG Chunhua; LIN Yu; WANG Xiaogang

    2007-01-01

    By using a one-dimensional resistive magnetohydrodynamic (MHD) model, the Rie-mann problem is solved numerically for the structure of the reconnection layer under a sheared flow along the anti-parallel magnetic field components. The simulation is carried out for general cases with symmetric or asymmetric plasma densities and magnetic fields on the two sides of the initial current sheet, and cases with or without a guide magnetic field, as in various space and fusion plasmas. The generation of MHD discontinuities in the reconnection layer is discussed, including time-dependent intermediate shocks, intermediate shocks, slow shocks, slow expansion waves, and the contact discontinuity. It is shown that the structure of the reconnection layer is significantly affected by the presence of the shear flow. For an initial symmetric current sheet, the symmetry condition is altered due to the shear flow. For cases with an asymmetric initial current sheet, as at the Earth's magnetopause, the strengths of MHD discontinuities change significantly with the shear flow speed. Moreover, the general results for the reconnection layers in the outflow regions on either side of the X line are discussed systematically for the first time.

  11. The formation and evolution of reconnection-driven, slow-mode shocks in a partially ionised plasma

    Science.gov (United States)

    Hillier, A.; Takasao, S.; Nakamura, N.

    2016-06-01

    The role of slow-mode magnetohydrodynamic (MHD) shocks in magnetic reconnection is of great importance for energy conversion and transport, but in many astrophysical plasmas the plasma is not fully ionised. In this paper, we use numerical simulations to investigate the role of collisional coupling between a proton-electron, charge-neutral fluid and a neutral hydrogen fluid for the one-dimensional (1D) Riemann problem initiated in a constant pressure and density background state by a discontinuity in the magnetic field. This system, in the MHD limit, is characterised by two waves. The first is a fast-mode rarefaction wave that drives a flow towards a slow-mode MHD shock wave. The system evolves through four stages: initiation, weak coupling, intermediate coupling, and a quasi-steady state. The initial stages are characterised by an over-pressured neutral region that expands with characteristics of a blast wave. In the later stages, the system tends towards a self-similar solution where the main drift velocity is concentrated in the thin region of the shock front. Because of the nature of the system, the neutral fluid is overpressured by the shock when compared to a purely hydrodynamic shock, which results in the neutral fluid expanding to form the shock precursor. Once it has formed, the thickness of the shock front is proportional to ξ i-1.2 , which is a smaller exponent than would be naively expected from simple scaling arguments. One interesting result is that the shock front is a continuous transition of the physical variables of subsonic velocity upstream of the shock front (a c-shock) to a sharp jump in the physical variables followed by a relaxation to the downstream values for supersonic upstream velocity (a j-shock). The frictional heating that results from the velocity drift across the shock front can amount to ~2 per cent of the reference magnetic energy.

  12. Study of the turbulence in the central plasma sheet using the CLUSTER satellite data

    Science.gov (United States)

    Stepanova, M.; Arancibia Riveros, K.; Bosqued, J.; Antonova, E.

    2008-05-01

    Recent studies are shown that the turbulent processes in the space plasmas are very important. It includes the behavior of the plasma sheet plasma during geomagnetic substorms and storms. Study of the plasma turbulence in the central plasma sheet was made using the CLUSTER satellite mission data. For this studies we used the Cluster Ion Spectrometry experiment (CIS), and fluxgate magnetometer (FGM) data for studying fluctuations of the plasma bulk velocity and geomagnetic field fluctuations for different levels of geomagnetic activity and different locations inside the plasma sheet. Case studies for the orbits during quiet geomagnetic conditions, different phases of geomagnetic substroms and storms showed that the properties of plasma turbulence inside the sheet differ significantly for all afore mentioned cases. Variations in the probability distribution functions, flatness factors, local intermittency measure parameters, and eddy diffusion coefficients indicate that the turbulence increases significantly during substorm growth and expansion phases and decreases slowly to the initial level during the recovery phase. It became even stronger during the storm main phase.

  13. Continuous lobe reconnection in the mid-tail and its relationship to substorms: Cluster observations of continuous lobe reconnection in the mid-magneto tail

    Institute of Scientific and Technical Information of China (English)

    CAO Xin; Q. G. Zong; H. Reme; K. H. Glassmeier; PU Zuyin; ZHANG Hui; FU Suiyan; XIAO Chijie; LIU Zhenxing; J. B. Cao; A. Korth; M. Frazen

    2005-01-01

    When the IMF turns southward, a great amount of magnetic energy is stored in the magnetotail, and the electric field across the magnetotail substantially enhances. As long as magnetic reconnection (MR) in the magnetotail initiates and continues, the magnetic field and plasma in the central plasma sheet are carried away to the near-Earth and down to the tail, the magnetic field and plasma in the lobe region enter the CPS and are involved in MR. We call this process "Continuous Lobe Reconnection (CLR)". In this paper a detailed analysis of Cluster observation of MR through 2001―2003 is made. Plenty of CLR events are found that led to considerable changes of tail configuration, appearance of BBF, as well as large-scale bubbles in which both plasma temperature and number density substantially decrease. It is shown that in general CLR events last for dozens of minutes and have good correspondence to substorm initiation under the condition of continuous southward IMF.

  14. A Modified Porous Titanium Sheet Prepared by Plasma-Activated Sintering for Biomedical Applications

    Directory of Open Access Journals (Sweden)

    Yukimichi Tamaki

    2010-01-01

    Full Text Available This study aimed to develop a contamination-free porous titanium scaffold by a plasma-activated sintering within an originally developed TiN-coated graphite mold. The surface of porous titanium sheet with or without a coated graphite mold was characterized. The cell adhesion property of porous titanium sheet was also evaluated in this study. The peak of TiC was detected on the titanium sheet processed with the graphite mold without a TiN coating. Since the titanium fiber elements were directly in contact with the carbon graphite mold during processing, surface contamination was unavoidable event in this condition. The TiC peak was not detectable on the titanium sheet processed within the TiN-coated carbon graphite mold. This modified plasma-activated sintering with the TiN-coated graphite mold would be useful to fabricate a contamination-free titanium sheet. The number of adherent cells on the modified titanium sheet was greater than that of the bare titanium plate. Stress fiber formation and the extension of the cells were observed on the titanium sheets. This modified titanium sheet is expected to be a new tissue engineering material in orthopedic bone repair.

  15. Reconnection in the Heliosheath: Effects of Plasma Beta on Particle Acceleration and the Shape of Magnetic Islands

    Science.gov (United States)

    Schoeffler, K. M.; Drake, J. F.; Swisdak, M. M.

    2011-12-01

    In the heliosheath it has been predicted that current sheets are compressed and break up into magnetic islands or bubbles. The interaction of particles in these islands via the Fermi process in contracting islands has been predicted to be a source of anomalous cosmic rays (ACRs). The plasma β (the ratio of the plasma pressure to the magnetic pressure) can have a large range of values in this region. We investigate the effects of β on the formation of islands, and of the acceleration of particles as these magnetic islands form. Using a particle-in-cell code, we simulate island growth in multiple interacting Harris current sheets. We produce different values of β by changing the temperature of a background population. We find that for higher β significantly more elongated islands are formed. More modestly elongated islands are suppressed by pressure anisotropy approaching the marginal firehose condition. Measurements from the Voyager spacecrafts are consistent with these long islands. We also find significantly less electron acceleration as β increases, while the ions are mostly unaffected. Scattering of the electrons in high β systems (β > 1) halts the Fermi process while the ions continue to be accelerated.

  16. Frontiers for Laboratory Research of Magnetic Reconnection

    Energy Technology Data Exchange (ETDEWEB)

    Ji, Hantao [Princeton University; Guo, Fan [Los Alamos National Laboratory

    2015-07-16

    Magnetic reconnection occcurs throughout heliophysical and astrophysical plasmas as well as in laboratory fusion plasmas. Two broad categories of reconnection models exist: collisional MHD and collisionless kinetic. Eight major questions with respect to magnetic connection are set down, and past and future devices for studying them in the laboratory are described. Results of some computerized simulations are compared with experiments.

  17. Occurrence and location of concentrated load and generator regions observed by Cluster in the plasma sheet

    Directory of Open Access Journals (Sweden)

    M. Hamrin

    2009-11-01

    Full Text Available Here, and in a companion paper by Hamrin et al. (2009 [Scale size and life time of energy conversion regions observed by Cluster in the plasma sheet], we investigate localized energy conversion regions (ECRs in the Earth's plasma sheet. In total we have studied 151 ECRs within 660 h of plasma sheet data from the summer and fall of 2001 when Cluster was close to apogee at an altitude of about 15–20 RE. Cluster offers appropriate conditions for the investigation of energy conversion by the evaluation of the power density, E·J, where E is the electric field and J the current density. From the sign of the power density, we have identified more than three times as many Concentrated Load Regions (CLRs as Concentrated Generator Regions (CGRs. We also note that the CLRs appear to be stronger. To our knowledge, these are the first in situ observations confirming the general notion of the plasma sheet, on the average, behaving as a load. At the same time the plasma sheet appears to be highly structured, with energy conversion occurring in both directions between the fields and the particles. From our data we also find that the CLRs appear to be located closer to the neutral sheet, while CGRs prefer locations towards the plasma sheet boundary layer (PSBL. For both CLRs and CGRs, E and J in the GSM y (cross-tail direction dominate the total power density, even though the z contribution occasionally can be significant. The prevalence of the y-direction seems to be weaker for the CGRs, possibly related to a higher fluctuation level near the PSBL.

  18. Effects of a moving X-line in a time-dependent reconnection model

    Directory of Open Access Journals (Sweden)

    S. A. Kiehas

    2007-02-01

    Full Text Available In the frame of magnetized plasmas, reconnection appears as an essential process for the description of plasma acceleration and changing magnetic field topology. Under the variety of reconnection regions in our solar system, we focus our research onto the Earth's magnetotail. Under certain conditions a Near Earth Neutral Line (NENL is free to evolve in the current sheet of the magnetotail. Reconnection in this region leads to the formation of Earth- and tailward propagating plasma bulges, which can be detected by the Cluster or Geotail spacecraft. Observations give rise to the assumption that the evolved reconnection line does not provide a steady state behavior, but is propagating towards the tail (e.g., Baker et al., 2002. Based on a time-dependent variant of the Petschek model of magnetic reconnection, we present a method that includes an X-line motion and discuss the effects of such a motion. We focus our main interest on the shock structure and the magnetic field behavior, both for the switch-on and the switch-off phase.

  19. SMALL-SCALE LOCAL PHENOMENA RELATED TO THE MAGNETIC RECONNECTION AND TURBULENCE IN THE PROXIMITY OF THE HELIOPAUSE

    Energy Technology Data Exchange (ETDEWEB)

    Strumik, M.; Czechowski, A.; Grzedzielski, S.; Macek, W. M.; Ratkiewicz, R. [Space Research Centre, Polish Academy of Sciences, Bartycka 18A, 00-716 Warsaw (Poland)

    2013-08-20

    We study processes related to magnetic reconnection and plasma turbulence occurring in the presence of the heliopause (HP) and the heliospheric current sheet. It is shown that the interaction of plasmoids initiated by magnetic reconnection may provide connections between the inner and outer heliosheath and lead to an exchange of particles between the interstellar medium and the solar wind plasma shocked at the heliospheric termination shock. The magnetic reconnection may also cause plasma density and magnetic field compressions in the proximity of the HP. We argue that these phenomena could possibly be detected by the Voyager spacecraft approaching and crossing the HP. These results could clarify the concepts of the ''magnetic highway'' and the ''heliosheath depletion region'' recently proposed to explain recent Voyager 1 observations.

  20. Energy exchanges in reconnection outflows

    Science.gov (United States)

    Lapenta, Giovanni; Goldman, Martin V.; Newman, David L.; Markidis, Stefano

    2017-01-01

    Reconnection outflows are highly energetic directed flows that interact with the ambient plasma or with flows from other reconnection regions. Under these conditions the flow becomes highly unstable and chaotic, as any flow jets interacting with a medium. We report here massively parallel simulations of the two cases of interaction between outflow jets and between a single outflow with an ambient plasma. We find in both case the development of a chaotic magnetic field, subject to secondary reconnection events that further complicate the topology of the field lines. The focus of the present analysis is on the energy balance. We compute each energy channel (electromagnetic, bulk, thermal, for each species) and find where the most energy is exchanged and in what form. The main finding is that the largest energy exchange is not at the reconnection site proper but in the regions where the outflowing jets are destabilized.

  1. Relativistic Magnetic Reconnection in the Laboratory

    CERN Document Server

    Raymond, A; McKelvey, A; Zulick, C; Alexander, N; Batson, T; Bhattacharjee, A; Campbell, P; Chen, H; Chvykov, V; Del Rio, E; Fitzsimmons, P; Fox, W; Hou, B; Maksimchuk, A; Mileham, C; Nees, J; Nilson, P M; Stoeckl, C; Thomas, A G R; Wei, M S; Yanovsky, V; Willingale, L; Krushelnick, K

    2016-01-01

    Magnetic reconnection is a fundamental plasma process involving an exchange of magnetic energy to plasma kinetic energy through changes in the magnetic field topology. In many astrophysical plasmas magnetic reconnection plays a key role in the release of large amounts of energy \\cite{hoshino1}, although making direct measurements is challenging in the case of high-energy astrophysical systems such as pulsar wind emissions \\cite{lyubarsky1}, gamma-ray bursts \\cite{thompson1}, and jets from active galactic nuclei \\cite{liu1}. Therefore, laboratory studies of magnetic reconnection provide an important platform for testing theories and characterising different regimes. Here we present experimental measurements as well as numerical modeling of relativistic magnetic reconnection driven by short-pulse, high-intensity lasers that produce relativistic plasma along with extremely strong magnetic fields. Evidence of magnetic reconnection was identified by the plasma's X-ray emission patterns, changes to the electron ene...

  2. TURBULENT MAGNETOHYDRODYNAMIC RECONNECTION MEDIATED BY THE PLASMOID INSTABILITY

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Yi-Min; Bhattacharjee, A., E-mail: yiminh@princeton.edu [Department of Astrophysical Sciences and Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)

    2016-02-10

    It has been established that the Sweet–Parker current layer in high Lundquist number reconnection is unstable to the super-Alfvénic plasmoid instability. Past two-dimensional magnetohydrodynamic simulations have demonstrated that the plasmoid instability leads to a new regime where the Sweet–Parker current layer changes into a chain of plasmoids connected by secondary current sheets, and the averaged reconnection rate becomes nearly independent of the Lundquist number. In this work, a three-dimensional simulation with a guide field shows that the additional degree of freedom allows plasmoid instabilities to grow at oblique angles, which interact and lead to self-generated turbulent reconnection. The averaged reconnection rate in the self-generated turbulent state is of the order of a hundredth of the characteristic Alfvén speed, which is similar to the two-dimensional result but is an order of magnitude lower than the fastest reconnection rate reported in recent studies of externally driven three-dimensional turbulent reconnection. Kinematic and magnetic energy fluctuations both form elongated eddies along the direction of the local magnetic field, which is a signature of anisotropic magnetohydrodynamic turbulence. Both energy fluctuations satisfy power-law spectra in the inertial range, where the magnetic energy spectral index is in the range from −2.3 to −2.1, while the kinetic energy spectral index is slightly steeper, in the range from −2.5 to −2.3. The anisotropy of turbulence eddies is found to be nearly scale-independent, in contrast with the prediction of the Goldreich–Sridhar theory for anisotropic turbulence in a homogeneous plasma permeated by a uniform magnetic field.

  3. Physical conditions in the reconnection layer in pulsar magnetospheres

    Energy Technology Data Exchange (ETDEWEB)

    Uzdensky, Dmitri A. [Center for Integrated Plasma Studies, Physics Department, University of Colorado, UCB 390, Boulder, CO 80309-0390 (United States); Spitkovsky, Anatoly, E-mail: uzdensky@colorado.edu, E-mail: anatoly@astro.princeton.edu [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

    2014-01-01

    The magnetosphere of a rotating pulsar naturally develops a current sheet (CS) beyond the light cylinder (LC). Magnetic reconnection in this CS inevitably dissipates a nontrivial fraction of the pulsar spin-down power within a few LC radii. We develop a basic physical picture of reconnection in this environment and discuss its implications for the observed pulsed gamma-ray emission. We argue that reconnection proceeds in the plasmoid-dominated regime, via a hierarchical chain of multiple secondary islands/flux ropes. The inter-plasmoid reconnection layers are subject to strong synchrotron cooling, leading to significant plasma compression. Using the conditions of pressure balance across these current layers, the balance between the heating by magnetic energy dissipation and synchrotron cooling, and Ampere's law, we obtain simple estimates for key parameters of the layers—temperature, density, and layer thickness. In the comoving frame of the relativistic pulsar wind just outside of the equatorial CS, these basic parameters are uniquely determined by the strength of the reconnecting upstream magnetic field. For the case of the Crab pulsar, we find them to be of order 10 GeV, 10{sup 13} cm{sup –3}, and 10 cm, respectively. After accounting for the bulk Doppler boosting due to the pulsar wind, the synchrotron and inverse-Compton emission from the reconnecting CS can explain the observed pulsed high-energy (GeV) and very high energy (∼100 GeV) radiation, respectively. Also, we suggest that the rapid relative motions of the secondary plasmoids in the hierarchical chain may contribute to the production of the pulsar radio emission.

  4. Physical Conditions in the Reconnection Layer in Pulsar Magnetospheres

    Science.gov (United States)

    Uzdensky, Dmitri A.; Spitkovsky, Anatoly

    2014-01-01

    The magnetosphere of a rotating pulsar naturally develops a current sheet (CS) beyond the light cylinder (LC). Magnetic reconnection in this CS inevitably dissipates a nontrivial fraction of the pulsar spin-down power within a few LC radii. We develop a basic physical picture of reconnection in this environment and discuss its implications for the observed pulsed gamma-ray emission. We argue that reconnection proceeds in the plasmoid-dominated regime, via a hierarchical chain of multiple secondary islands/flux ropes. The inter-plasmoid reconnection layers are subject to strong synchrotron cooling, leading to significant plasma compression. Using the conditions of pressure balance across these current layers, the balance between the heating by magnetic energy dissipation and synchrotron cooling, and Ampere's law, we obtain simple estimates for key parameters of the layers—temperature, density, and layer thickness. In the comoving frame of the relativistic pulsar wind just outside of the equatorial CS, these basic parameters are uniquely determined by the strength of the reconnecting upstream magnetic field. For the case of the Crab pulsar, we find them to be of order 10 GeV, 1013 cm-3, and 10 cm, respectively. After accounting for the bulk Doppler boosting due to the pulsar wind, the synchrotron and inverse-Compton emission from the reconnecting CS can explain the observed pulsed high-energy (GeV) and very high energy (~100 GeV) radiation, respectively. Also, we suggest that the rapid relative motions of the secondary plasmoids in the hierarchical chain may contribute to the production of the pulsar radio emission.

  5. Reconnection events in Saturn's magnetotail: Dependence of plasmoid occurrence on planetary period oscillation phase

    Science.gov (United States)

    Jackman, C. M.; Provan, G.; Cowley, S. W. H.

    2016-04-01

    During its exploration of Saturn's magnetotail the Cassini magnetometer has detected many in situ examples of magnetic reconnection, in the form of plasmoids, traveling compression regions (TCRs), and dipolarizations. Meanwhile, many magnetospheric phenomena have been shown to be organized with particular regularity by planetary period oscillation systems driven separately from the Northern and Southern Hemispheres of the planet. Here we examine the relationship between the occurrence of plasmoids and TCRs and the magnetic phases of the northern and southern systems. We find a striking degree of organization of the events by both northern and southern phases, with events linked preferentially to intervals in which the magnetospheric plasma and field lines are displaced outward from the planet and the current sheet thinned, both effects being likely to favor the occurrence of reconnection and plasmoid-related mass loss. Little evidence is found for significant visibility effects associated with north-south motions of the plasma sheet.

  6. NUMERICAL STUDIES OF WEAKLY STOCHASTIC MAGNETIC RECONNECTION

    Directory of Open Access Journals (Sweden)

    G. Kowal

    2009-01-01

    Full Text Available We study the e ects of turbulence on magnetic reconnection using three-dimensional numerical simulations.This is the rst attempt to test the model of fast magnetic reconnection proposed by Lazarian & Vishniac (1999, which assumes the presence of weak, small-scale magnetic eld structure near the current sheet. This a ects the rate of reconnection by reducing the transverse scale for reconnection ows and by allowing many independent ux reconnection events to occur simultaneously. We performed a number of simulations to test the dependencies of the reconnection speed, de ned as the ratio of the in ow velocity to the Alfv n speed, on the turbulence power, the injection scale and resistivity. Our results show that turbulence signi cantly a ects the topology of magnetic eld near the di usion region and increases the thickness of the out ow region. We con rm the predictions of the Lazarian & Vishniac model. In particular, we report the growth of the reconnection speed proportional to V 2 l , where Vl is the amplitude of velocity at the injection scale. It depends on the injection scale linj as (linj=L2=3, where L is the size of the system, which is somewhat faster but still roughly consistent with the theoretical expectations. We also show that for 3D reconnection the Ohmic resistivity is important in the local reconnection events only, and the global reconnection rate in the presence of turbulence does not depend on it.

  7. Magnetotail Reconnection and Flux Circulation: Jupiter and Saturn Compared

    Science.gov (United States)

    Jackman, C. M.; Vogt, M. F.; Slavin, J. A.; Cowley, S. W. H.; Boardsen, S. A.

    2011-01-01

    The Jovian magnetosphere has been visited by eight spacecraft, and the magnetometer data have been used to identify dozens of plasmoids and 250 field dipolarizations associated with magnetic reconnection in the tail [e.g. Vogt et al., 2010]. Since the arrival of the Cassini spacecraft at Saturn in 2004, the magnetometer instrument has also been used to identify reconnection signatures. The deepest magnetotail orbits were in 2006, and during this time 34 signatures of plasmoids were identified. In this study we compare the statistical properties of plasmoids at Jupiter and Saturn such as duration, size, location, and recurrence period. Such parameters can be influenced by many factors, including the different Dungey cycle timescales and cross-magnetospheric potential drops at the two planets. We present superposed epoch analyses of plasmoids at the two planets to determine their average properties and to infer their role in the reconfiguration of the nightside of the magnetosphere. We examine the contributions of plasmoids to the magnetic flux transfer cycle at both planets. At Jupiter, there is evidence of an extended interval after reconnection where the field remains northward (analogous to the terrestrial post-plasmoid plasma sheet). At Saturn we see a similar feature, and calculate the amount of flux closed on average in reconnection events, leading us to an estimation of the recurrence rate of plasmoid release.

  8. The Impact of Geometrical Constraints on Collisionless Magnetic Reconnection

    Science.gov (United States)

    Hesse, Michael; Aunai, Nico; Kuznetsova, Masha; Frolov, Rebekah; Black, Carrrie

    2012-01-01

    One of the most often cited features associated with collisionless magnetic reconnection is a Hall-type magnetic field, which leads, in antiparallel geometries, to a quadrupolar magnetic field signature. The combination of this out of plane magnetic field with the reconnection in-plane magnetic field leads to angling of magnetic flux tubes out of the plane defined by the incoming magnetic flux. Because it is propagated by Whistler waves, the quadrupolar field can extend over large distances in relatively short amounts of time - in fact, it will extend to the boundary of any modeling domain. In reality, however, the surrounding plasma and magnetic field geometry, defined, for example, by the overall solar wind flow, will in practice limit the extend over which a flux tube can be angled out of the main plain. This poses the question to what extent geometric constraints limit or control the reconnection process and this is the question investigated in this presentation. The investigation will involve a comparison of calculations, where open boundary conditions are set up to mimic either free or constrained geometries. We will compare momentum transport, the geometry of the reconnection regions, and the acceleration if ions and electrons to provide the current sheet in the outflow jet.

  9. Energy release and conversion by reconnection in the magnetotail

    Directory of Open Access Journals (Sweden)

    J. Birn

    2005-11-01

    Full Text Available Magnetic reconnection is the crucial process in the release of magnetic energy previously stored in the magnetotail in association with substorms. However, energy transfer and dissipation in the vicinity of the reconnection site is only a minor part of the energy conversion. We discuss the energy release, transport, and conversion based on large-scale resistive MHD simulations of magnetotail dynamics and more localized full particle simulations of reconnection. We address in particular, where the energy is released, how it propagates and where and how it is converted from one form into another. We find that Joule (or ohmic dissipation plays only a minor role in the overall energy transfer. Bulk kinetic energy, although locally significant in the outflow from the reconnection site, plays a more important role as mediator or catalyst in the transfer between magnetic and thermal energy. Generator regions with potential auroral consequences are located primarily off the equatorial plane in the boundary regions of the plasma sheet.

  10. Ion Bernstein waves in the magnetic reconnection region

    Science.gov (United States)

    Narita, Y.; Nakamura, R.; Baumjohann, W.; Glassmeier, K.-H.; Motschmann, U.; Comişel, H.

    2016-01-01

    Four-dimensional energy spectra and a diagram for dispersion relations are determined for the first time in a magnetic reconnection region in the magnetotail using data from four-spacecraft measurements by the Cluster mission on a spatial scale of 200 km, about 0.1 ion inertial lengths. The energy spectra are anisotropic with an extension in the perpendicular direction and axially asymmetric with respect to the mean magnetic field. The dispersion diagram in the plasma rest frame is in reasonably good agreement with the ion Bernstein waves at the second and higher harmonics of the proton gyrofrequency. Perpendicular-propagating ion Bernstein waves likely exist in an outflow region of magnetic reconnection, which may contribute to bifurcation of the current sheet in the outflow region.

  11. Dynamic of Current Sheets and Their Associated Particle Energization

    Energy Technology Data Exchange (ETDEWEB)

    Li, Hui [Los Alamos National Laboratory; Guo, Fan [Los Alamos National Laboratory; Makwan, Kirit [Univ. Chicago; Li, Xiaocan [Los Alamos National Laboratory; Zhandrin, Vladimir [Univ. Washington; Daughton, William Scott [Los Alamos National Laboratory

    2015-08-19

    Magnetic reconnection in current sheets has relevance to Earth's magnetosphere, solar flares, high-energy astrophysics (pulsar wind nebula (e.g. Crab Nebula), gamma-ray bursts, black hole jets), and laboratory plasma/fusion. Data are shown for several cases with varying values of configuration energy Ec and β. Several conclusions were drawn: Depending on the “configuration energy”, the formation, shape, and lifetime of current sheets can vary. Plasma condition (configuration, β, driving, etc.) strongly affect the efficiency of particle acceleration. For low β and general “configuration energy”, particle heating is expected. For low β, large and long-lived current sheets, it is possible to produce highly non-thermal particles via collisionless plasmoid reconnection.

  12. Magnetopause Reconnection Impact Parameters from Multiple Spacecraft Magnetic Field Measurements

    Science.gov (United States)

    Wendel, Deirdre E.; Reiff, Patricia H.

    2009-01-01

    We present a novel technique that exploits multiple spacecraft data to determine the impact parameters of the most general form of magnetic reconnection at the magnetopause. The method consists of a superposed epoch of multiple spacecraft magnetometer measurements that yields the instantaneous magnetic spatial gradients near a magnetopause reconnection site. The gradients establish the instantaneous positions of the spacecraft relative to the reconnection site. The analysis is well suited to evaluating the spatial scales of singular field line reconnection, which is characterized by a two-dimensional x-type topology adjacent and perpendicular to a reconnecting singular field line. Application of the method to Cluster data known to lie in the vicinity of a northward IMF reconnection site establishes a field topology consistent with singular field line reconnection and a normal magnetic field component of 20 nT. The corresponding current structure consists of a 130 km sheet possibly embedding a thinner. bifurcated sheet.

  13. Survey of 0. 1- to 16-keV/e plasma sheet ion composition

    Energy Technology Data Exchange (ETDEWEB)

    Lennartsson, W.; Shelley, E.G.

    1986-03-01

    A large statistical survey of the 0.1- to 16-keV/e plasma sheet ion composition has been carried out using data obtained by the Plasma Composition Experiment on ISEE 1 between 10 and 23 R/sub E/ during 1978 and 1979. This survey includes more than 10 times the quantity of data used in earlier studies of the same topic and makes it possible to investigate in finer detail the relationship between the ion composition and the substorm activity. The larger data base also makes it possible for the first time to study the spatial distribution of the principal ion species. As found in previous studies, the ion composition has a large variance at any given value of the AE index, but a number of distinct trends emerge when the data are averaged at each activity level. During quiet conditions the plasma sheet is dominated by ions of solar origin (H/sup +/ and He/sup + +/), as found in earlier studies, and these ions are most numerous during extended periods of very low activity (AE< or approx. =30 ..gamma..). The quiet time density of these ions is particularly large in the flanks of the plasma sheet (GSM Yapprox. +- 10 R/sub E/), where it is about twice as large as it is near the central axis of the plasma sheet (Y = Z = 0). In contrast, the energy of these ions peaks near the central axis.

  14. Observation of reconnection pulses by Cluster and Double Star

    Directory of Open Access Journals (Sweden)

    X. H. Deng

    2005-11-01

    Full Text Available During a reconnection event on 7 August 2004, Cluster and Double Star (TC-1 were near the neutral sheet and simultaneously detected the signatures of the reconnection pulses. AT 22:59 UT tailward flow followed by earthward flow was detected by Cluster at about 15 RE, while earthward plasma flow followed by tailward flow was observed by TC-1 at about 10 RE. During the flow reversal from tailward to earthward, the magnetic field Bz changed sign from mainly negative values to positive, and the X component of the magnetic curvature vector switched sign from the tailward direction to the earthward direction, which indicates that the reconnection site (X-line moved tailward past the Cluster constellation. By using multi-point analysis and observation of energetic electron and ion flux, we study the movement and structure of the current sheet and discuss the braking effect of the earthward flow bursts in the inner magnetosphere.

  15. Early results of microwave transmission experiments through an overly dense rectangular plasma sheet with microparticle injection

    Science.gov (United States)

    Gillman, Eric D.; Amatucci, W. E.

    2014-06-01

    These experiments utilize a linear hollow cathode to create a dense, rectangular plasma sheet to simulate the plasma layer surrounding vehicles traveling at hypersonic velocities within the Earth's atmosphere. Injection of fine dielectric microparticles significantly reduces the electron density and therefore lowers the electron plasma frequency by binding a significant portion of the bulk free electrons to the relatively massive microparticles. Measurements show that microwave transmission through this previously overly dense, impenetrable plasma layer increases with the injection of alumina microparticles approximately 60 μm in diameter. This method of electron depletion is a potential means of mitigating the radio communications blackout experienced by hypersonic vehicles.

  16. Magnetic Reconnection in Different Environments: Similarities and Differences

    Science.gov (United States)

    Hesse, Michael; Aunai, Nicolas; Kuznetsova, Masha; Zenitani, Seiji; Birn, Joachim

    2014-01-01

    Depending on the specific situation, magnetic reconnection may involve symmetric or asymmetric inflow regions. Asymmetric reconnection applies, for example, to reconnection at the Earth's magnetopause, whereas reconnection in the nightside magnetotail tends to involve more symmetric geometries. A combination of review and new results pertaining to magnetic reconnection is being presented. The focus is on three aspects: A basic, MHD-based, analysis of the role magnetic reconnection plays in the transport of energy, followed by an analysis of a kinetic model of time dependent reconnection in a symmetric current sheet, similar to what is typically being encountered in the magnetotail of the Earth. The third element is a review of recent results pertaining to the orientation of the reconnection line in asymmetric geometries, which are typical for the magnetopause of the Earth, as well as likely to occur at other planets.

  17. Oxygen plasma-treated thermoresponsive polymer surfaces for cell sheet engineering.

    Science.gov (United States)

    Shimizu, Kazunori; Fujita, Hideaki; Nagamori, Eiji

    2010-06-01

    Although cell sheet tissue engineering is a potent and promising method for tissue engineering, an increase of mechanical strength of a cell sheet is needed for easy manipulation of it during transplantation or 3D tissue fabrication. Previously, we developed a cell sheet-polymer film complex that had enough mechanical strength that can be manipulated even by tweezers (Fujita et al., 2009. Biotechnol Bioeng 103(2): 370-377). We confirmed the polymer film involving a temperature sensitive polymer and extracellular matrix (ECM) proteins could be removed by lowering temperature after transplantation, and its potential use in regenerative medicine was demonstrated. However, the use of ECM proteins conflicted with high stability in long-term storage and low cost. In the present study, to overcome these drawbacks, we employed the oxygen plasma treatment instead of using the ECM proteins. A cast and dried film of thermoresponsive poly-N-isopropylacrylamide (PNIPAAm) was fabricated and treated with high-intensity oxygen plasma. The cells became possible to adhere to the oxygen plasma-treated PNIPAAm surface, whereas could not to the inherent surface of bulk PNIPAAm without treatment. Characterizations of the treated surface revealed the surface had high stability. The surface roughness, wettability, and composition were changed, depending on the plasma intensity. Interestingly, although bulk PNIPAAm layer had thermoresponsiveness and dissolved below lower critical solution temperature (LCST), it was found that the oxygen plasma-treated PNIPAAm surface lost its thermoresponsiveness and remained insoluble in water below LCST as a thin layer. Skeletal muscle C2C12 cells could be cultured on the oxygen plasma-treated PNIPAAm surface, a skeletal muscle cell sheet with the insoluble thin layer could be released in the medium, and thus the possibility of use of the cell sheet for transplantation was demonstrated.

  18. Magnetic Reconnection in the Solar Chromosphere

    Science.gov (United States)

    Lukin, Vyacheslav S.; Ni, Lei; Murphy, Nicholas Arnold

    2017-08-01

    We report on the most recent efforts to accurately and self-consistently model magnetic reconnection processes in the context of the solar chromosphere. The solar chromosphere is a notoriously complex and highly dynamic boundary layer of the solar atmosphere where local variations in the plasma parameters can be of the order of the mean values. At the same time, the interdependence of the physical processes such as magnetic field evolution, local and global energy transfer between internal and electromagnetic plasma energy, radiation transport, plasma reactivity, and dissipation mechanisms make it a particularly difficult system to self-consistently model and understand. Several recent studies have focused on the micro-physics of multi-fluid magnetic reconnection at magnetic nulls in the weakly ionized plasma environment of the lower chromosphere[1-3]. Here, we extend the previous work by considering a range of spatial scales and magnetic field strengths in a configuration with component magnetic reconnection, i.e., for magnetic reconnection with a guide field. We show that in all cases the non-equilibrium reactivity of the plasma and the dynamic interaction among the plasma processes play important roles in determining the structure of the reconnection region. We also speculate as to the possible observables of chromospheric magnetic reconnection and the likely plasma conditions required for generation of Ellerman and IRIS bombs.[1] Leake, Lukin, Linton, and Meier, “Multi-fluid simulations of chromospheric magnetic reconnection in a weakly ionized reacting plasma,” ApJ 760 (2012).[2] Leake, Lukin, and Linton, “Magnetic reconnection in a weakly ionized plasma,” PoP 20 (2013).[3] Murphy and Lukin, “Asymmetric magnetic reconnection in weakly ionized chromospheric plasmas,” ApJ 805 (2015).[*Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National

  19. In Situ Observations of Ion Scale Current Sheets and Associated Electron Heating in Turbulent Space Plasmas

    Science.gov (United States)

    Chasapis, A.; Retino, A.; Sahraoui, F.; Greco, A.; Vaivads, A.; Khotyaintsev, Y. V.; Sundkvist, D. J.; Canu, P.

    2014-12-01

    We present a statistical study of ion-scale current sheets in turbulent space plasma. The study was performed using in situ measurements from the Earth's magnetosheath downstream of the quasi-parallel shock. Intermittent structures were identified using the Partial Variance of Increments method. We studied the distribution of the identified structures as a function of their magnetic shear angle, the PVI index and the electron heating. The properties of the observed current sheets were different for high (>3) and low (3) structures that accounted for ~20% of the total. Those current sheets have high magnetic shear (>90 degrees) and were observed mostly in close proximity to the bow shock with their numbers reducing towards the magnetopause. Enhancement of the estimated electron temperature within these current sheets suggest that they are important for local electron heating and energy dissipation.

  20. Plasma Sheet Actuator Driven by Repetitive Nanosecond Pulses with a Negative DC Component

    Institute of Scientific and Technical Information of China (English)

    宋慧敏; 张乔根; 李应红; 贾敏; 吴云; 梁华

    2012-01-01

    A type of electrical discharge called sliding discharge was developed to generate plasma aerodynamic actuation for flow control. A three-electrode plasma sheet actuator driven by repetitive nanosecond pulses with a negative DC component was used to generate sliding discharge, which can be called nanosecond-pulse sliding discharge. The phenomenology and behaviour of the plasma sheet actuator were investigated experimentally. Discharge morphology shows that the formation of nanosecond-pulse sliding discharge is dependent on the peak value of the repetitive nanosecond pulses and negative DC component applied on the plasma sheet actuator. Compared to dielectric barrier discharge (DBD), the extension of plasma in nanosecond-pulse sliding discharge is quasi-diffusive, stable, longer and more intensive. Test results of particle image velocimetry demonstrate that the negative DC component applied to a third electrode could significantly modify the topology of the flow induced by nanosecond-pulse DBD. Body force induced by the nanosecond-pulse sliding discharge can be approximately in the order of mN. Both the maximum velocity and the body force induced by sliding discharge increase significantly as compared to single DBD. Therefore, nanosecond-pulse sliding discharge is a preferable plasma aerodynamic actuation generation mode, which is very promising in the field of aerodynamics.

  1. Momentum transport and non-local transport in heat-flux-driven magnetic reconnection in HEDP

    Science.gov (United States)

    Liu, Chang; Fox, Will; Bhattacharjee, Amitava

    2016-10-01

    Strong magnetic fields are readily generated in high-energy-density plasmas and can affect the heat confinement properties of the plasma. Magnetic reconnection can in turn be important as an inverse process, which destroys or reconfigures the magnetic field. Recent theory has demonstrated a novel physics regime for reconnection in high-energy-density plasmas where the magnetic field is advected into the reconnection layer by plasma heat flux via the Nernst effect. In this work we elucidate the physics of the electron dissipation layer in this heat-flux-driven regime. Through fully kinetic simulation and a new generalized Ohm's law, we show that momentum transport due to the heat-flux-viscosity effect provides the dissipation mechanism to allow magnetic field line reconnection. Scaling analysis and simulations show that the characteristic width of the current sheet in this regime is several electron mean-free-paths. These results additionally show a coupling between non-local transport and momentum transport, which in turn affects the dynamics of the magnetic field. This work was supported by the U.S. Department of Energy under Contract No. DE-SC0008655.

  2. Electron Acceleration in Collisionless Magnetic Reconnection

    Institute of Scientific and Technical Information of China (English)

    GUO Jun; LU Quan-Ming; WANG Shui; FU Xiang-Rong

    2005-01-01

    @@ A 21/2-dimensional electromagnetic particle-in-cell (PIC) simulation code is used to investigate the electron acceleration in collisionless magnetic reconnection. The results show that the electrons are accelerated in the diffusion region near the X point, and the acceleration process can be roughly divided into two procedures: firstly the electrons are accelerated in the z direction due to the electric field in the negative z direction. Then the electrons gyrate surrounding the magnetic field with the action of the Lorentz force, through this procedure the electrons reach higher velocity in the x direction and then flow out of the diffusion region. After being accelerated away from the diffusion region, part of electrons is trapped near the O point, and the other part of electrons flows into plasma sheet boundary layer along the magnetic field.

  3. Experimental study of nonlinear interaction of plasma flow with charged thin current sheets: 2. Hall dynamics, mass and momentum transfer

    Directory of Open Access Journals (Sweden)

    S. Savin

    2006-01-01

    Full Text Available Proceeding with the analysis of Amata et al. (2005, we suggest that the general feature for the local transport at a thin magnetopause (MP consists of the penetration of ions from the magnetosheath with gyroradius larger than the MP width, and that, in crossing it, the transverse potential difference at the thin current sheet (TCS is acquired by these ions, providing a field-particle energy exchange without parallel electric fields. It is suggested that a part of the surface charge is self-consistently produced by deflection of ions in the course of inertial drift in the non-uniform electric field at MP. Consideration of the partial moments of ions with different energies demonstrates that the protons having gyroradii of roughly the same size or larger than the MP width carry fluxes normal to MP that are about 20% of the total flow in the plasma jet under MP. This is close to the excess of the ion transverse velocity over the cross-field drift speed in the plasma flow just inside MP (Amata et al., 2005, which conforms to the contribution of the finite-gyroradius inflow across MP. A linkage through the TCS between different plasmas results from the momentum conservation of the higher-energy ions. If the finite-gyroradius penetration occurs along the MP over ~1.5 RE from the observation site, then it can completely account for the formation of the jet under the MP. To provide the downstream acceleration of the flow near the MP via the cross-field drift, the weak magnetic field is suggested to rotate from its nearly parallel direction to the unperturbed flow toward being almost perpendicular to the accelerated flow near the MP. We discuss a deceleration of the higher-energy ions in the MP normal direction due to the interaction with finite-scale electric field bursts in the magnetosheath flow frame, equivalent to collisions, providing a charge separation. These effective collisions, with a nonlinear frequency proxy of the order of the proton

  4. Slipping magnetic reconnection in coronal loops.

    Science.gov (United States)

    Aulanier, Guillaume; Golub, Leon; Deluca, Edward E; Cirtain, Jonathan W; Kano, Ryouhei; Lundquist, Loraine L; Narukage, Noriyuki; Sakao, Taro; Weber, Mark A

    2007-12-07

    Magnetic reconnection of solar coronal loops is the main process that causes solar flares and possibly coronal heating. In the standard model, magnetic field lines break and reconnect instantaneously at places where the field mapping is discontinuous. However, another mode may operate where the magnetic field mapping is continuous but shows steep gradients: The field lines may slip across each other. Soft x-ray observations of fast bidirectional motions of coronal loops, observed by the Hinode spacecraft, support the existence of this slipping magnetic reconnection regime in the Sun's corona. This basic process should be considered when interpreting reconnection, both on the Sun and in laboratory-based plasma experiments.

  5. Hyper-resistive forced magnetic reconnection

    Energy Technology Data Exchange (ETDEWEB)

    Vekstein, G., E-mail: g.vekstein@manchester.ac.uk [Jodrell Bank Centre for Astrophysics, University of Manchester, Manchester M13 9PL (United Kingdom)

    2016-02-15

    We study Taylor's model of forced magnetic reconnection mediated by plasma hyper-resistivity. This includes both linear and nonlinear regimes of the process. It is shown how the onset of plasmoid instability occurs in the strongly nonlinear regime of forced reconnection.

  6. On the plasma-based growth of ‘flowing’ graphene sheets at atmospheric pressure conditions

    Science.gov (United States)

    Tsyganov, D.; Bundaleska, N.; Tatarova, E.; Dias, A.; Henriques, J.; Rego, A.; Ferraria, A.; Abrashev, M. V.; Dias, F. M.; Luhrs, C. C.; Phillips, J.

    2016-02-01

    A theoretical and experimental study on atmospheric pressure microwave plasma-based assembly of free standing graphene sheets is presented. The synthesis method is based on introducing a carbon-containing precursor (C2H5OH) through a microwave (2.45 GHz) argon plasma environment, where decomposition of ethanol molecules takes place and carbon atoms and molecules are created and then converted into solid carbon nuclei in the ‘colder’ nucleation zones. A theoretical model previously developed has been further updated and refined to map the particle and thermal fluxes in the plasma reactor. Considering the nucleation process as a delicate interplay between thermodynamic and kinetic factors, the model is based on a set of non-linear differential equations describing plasma thermodynamics and chemical kinetics. The model predictions were validated by experimental results. Optical emission spectroscopy was applied to detect the plasma emission related to carbon species from the ‘hot’ plasma zone. Raman spectroscopy, scanning electron microscopy (SEM), and x-ray photoelectron spectroscopy (XPS) techniques have been applied to analyze the synthesized nanostructures. The microstructural features of the solid carbon nuclei collected from the colder zones of plasma reactor vary according to their location. A part of the solid carbon was deposited on the discharge tube wall. The solid assembled from the main stream, which was gradually withdrawn from the hot plasma region in the outlet plasma stream directed to a filter, was composed by ‘flowing’ graphene sheets. The influence of additional hydrogen, Ar flow rate and microwave power on the concentration of obtained stable species and carbon-dicarbon was evaluated. The ratio of sp3/sp2 carbons in graphene sheets is presented. A correlation between changes in C2 and C number densities and sp3/sp2 ratio was found.

  7. Laboratory observations of spontaneous magnetic reconnection.

    Science.gov (United States)

    Egedal, J; Fox, W; Katz, N; Porkolab, M; Reim, K; Zhang, E

    2007-01-05

    Detailed measurements of spontaneous magnetic reconnection are presented. The experimental data, which were obtained in the new closed Versatile Toroidal Facility magnetic configuration, document the profile evolution of the plasma density, magnetic flux function, reconnection rate, and the current density during a spontaneous reconnection event in the presence of a strong guide magnetic field. The reconnection process is at first slow, which allows magnetic stress to build in the system while the current channel becomes increasingly narrow and intense. The onset of a fast reconnection event occurs as the width of the current channel approaches the ion-sound-Larmor radius rho s. During the reconnection event magnetically stored energy is channeled into energetic ion outflows and a rapid increase in the electron temperature.

  8. Kink-like mode of a double gradient instability in a compressible plasma current sheet

    Science.gov (United States)

    Korovinskiy, D.B.; Ivanova, V.V.; Erkaev, N.V.; Semenov, V.S.; Ivanov, I.B.; Biernat, H.K.; Zellinger, M.

    2011-01-01

    A linear MHD instability of the electric current sheet, characterized by a small normal magnetic field component, varying along the sheet, is investigated. The tangential magnetic field component is modeled by a hyperbolic function, describing Harris-like variations of the field across the sheet. For this problem, which is formulated in a 3D domain, the conventional compressible ideal MHD equations are applied. By assuming Fourier harmonics along the electric current, the linearized 3D equations are reduced to 2D ones. A finite difference numerical scheme is applied to examine the time evolution of small initial perturbations of the plasma parameters. This work is an extended numerical study of the so called “double gradient instability”, – a possible candidate for the explanation of flapping oscillations in the magnetotail current sheet, which has been analyzed previously in the framework of a simplified analytical approach for an incompressible plasma. The dispersion curve is obtained for the kink-like mode of the instability. It is shown that this curve demonstrates a quantitative agreement with the previous analytical result. The development of the instability is investigated also for various enhanced values of the normal magnetic field component. It is found that the characteristic values of the growth rate of the instability shows a linear dependence on the square root of the parameter, which scales uniformly the normal component of the magnetic field in the current sheet. PMID:22053125

  9. Helicity, Reconnection, and Dynamo Effects

    Energy Technology Data Exchange (ETDEWEB)

    Ji, Hantao

    1998-11-01

    The inter-relationships between magnetic helicity, magnetic reconnection, and dynamo effects are discussed. In laboratory experiments, where two plasmas are driven to merge, the helicity content of each plasma strongly affects the reconnection rate, as well as the shape of the diffusion region. Conversely, magnetic reconnection events also strongly affect the global helicity, resulting in efficient helicity cancellation (but not dissipation) during counter-helicity reconnection and a finite helicity increase or decrease (but less efficiently than dissipation of magnetic energy) during co-helicity reconnection. Close relationships also exist between magnetic helicity and dynamo effects. The turbulent electromotive force along the mean magnetic field (alpha-effect), due to either electrostatic turbulence or the electron diamagnetic effect, transports mean-field helicity across space without dissipation. This has been supported by direct measurements of helicity flux in a laboratory plasma. When the dynamo effect is driven by electromagnetic turbulence, helicity in the turbulent field is converted to mean-field helicity. In all cases, however, dynamo processes conserve total helicity except for a small battery effect, consistent with the observation that the helicity is approximately conserved during magnetic relaxation.

  10. Experimental study of nonlinear interaction of plasma flow with charged thin current sheets: 1. Boundary structure and motion

    Directory of Open Access Journals (Sweden)

    E. Amata

    2006-01-01

    Full Text Available We study plasma transport at a thin magnetopause (MP, described hereafter as a thin current sheet (TCS, observed by Cluster at the southern cusp on 13 February 2001 around 20:01 UT. The Cluster observations generally agree with the predictions of the Gas Dynamic Convection Field (GDCF model in the magnetosheath (MSH up to the MSH boundary layer, where significant differences are seen. We find for the MP a normal roughly along the GSE x-axis, which implies a clear departure from the local average MP normal, a ~90 km thickness and an outward speed of 35 km/s. Two populations are identified in the MSH boundary layer: the first one roughly perpendicular to the MSH magnetic field, which we interpret as the "incident" MSH plasma, the second one mostly parallel to B. Just after the MP crossing a velocity jet is observed with a peak speed of 240 km/s, perpendicular to B, with MA=3 and β>10 (peak value 23. The magnetic field clock angle rotates by 70° across the MP. Ex is the main electric field component on both sides of the MP, displaying a bipolar signature, positive on the MSH side and negative on the opposite side, corresponding to a ~300 V electric potential jump across the TCS. The E×B velocity generally coincides with the perpendicular velocity measured by CIS; however, in the speed jet a difference between the two is observed, which suggests the need for an extra flow source. We propose that the MP TCS can act locally as an obstacle for low-energy ions (<350 eV, being transparent for ions with larger gyroradius. As a result, the penetration of plasma by finite gyroradius is considered as a possible source for the jet. The role of reconnection is briefly discussed. The electrodynamics of the TCS along with mass and momentum transfer across it are further discussed in the companion paper by Savin et al. (2006.

  11. A study of the formation and dynamics of the Earth's plasma sheet using ion composition data

    Energy Technology Data Exchange (ETDEWEB)

    Lennartsson, O.W.

    1994-04-01

    Over two years of data from the Lockheed Plasma Composition Experiment on the ISEE 1 spacecraft, covering ion energies between 100 eV/e and about 16 keV/e, have been analyzed in an attempt to extract new information about three geophysical issues: (1) solar wind penetration of the Earth's magnetic tail; (2) relationship between plasma sheet and tail lobe ion composition; and (3) possible effects of heavy terrestrial ions on plasma sheet stability.

  12. The Inner Workings of Magnetic Reconnection

    Science.gov (United States)

    Hesse, Michael; Zenitani, S.

    2007-01-01

    Magnetic reconnection is arguably the most efficient transport and energy conversion mechanism in almost ideal plasmas. Reconnection controls the overall dynamics in space and astrophysics plasmas, as well as in many laboratory plasma systems. Reconnection operates by means of a localized diffusion region, where deviations from the plasma idealness condition generate electric fields and permit plasma transport even far away from the diffusion region itself. Recent advances in analytic theory and computer modeling have begun to shed light on the internal dynamics of the diffusion region. In particular, we begin to understand the delicate nature of the force balance in the inner diffusion region, where particles can become unmagnetized and where electric field forces are important. This presentation will provide a brief introduction of the reconnection process and its applications. This introduction will be followed by a detailed analysis of the current understanding of dissipation region physics, and by an outlook toward future research.

  13. The Dissipation Mechanism of Magnetic Reconnection

    Science.gov (United States)

    Hesse, Michael

    2008-01-01

    Magnetic reconnection is arguably the most efficient transport and energy conversion mechanism in almost ideal plasmas. Reconnection controls the overall dynamics in space and astrophysics plasmas, as well as in many laboratory plasma systems. Reconnection operates by means of a localized diffusion region, where deviations from the plasma idealness condition generate electric fields and permit plasma transport even far away from the diffusion region itself. Recent advances in analytic theory and computer modeling have begun to shed light on the internal dynamics of the diffusion region. In particular, we begin to understand the delicate nature of the force balance in the inner diffusion region, where particles can become unmagnetized and where electric field forces are important. This presentation will provide a brief introduction of the reconnection process and its applications. This introduction will be followed by a detailed analysis of the current understanding of dissipation region physics, and by an outlook toward future research.

  14. Conceptual design of the 3D magnetic field configuration relevant to the magnetopause reconnection in the SPERF

    Science.gov (United States)

    Mao, Aohua; Ji, Hantao; Ren, Yang; E, Peng; Wang, Zhibin; Xiao, Qingmei; Xiao, Chijie

    2016-10-01

    A new terrella device, the Space Plasma Environment Research Facility (SPERF), is designed and under construction in China, with Asymmetric Reconnection EXperiment (AREX) as one component to study the interaction between the magnetosheath and magnetosphere plasmas. AREX will provide a unique platform for studying asymmetric magnetic reconnection relevant to the magnetopause, via a set of coils for simulating ``solar-wind-side'' magnetosheath field and a dipole field on the ``magnetosphere-side''. Thus it could be able to investigate a range of important issues in the magnetosphere geometry, such as the electron and ion-scale dynamics in the current sheet, particle and energy transfer from magnetosheath to magnetosphere, particle energization/heating during magnetic reconnection, 3D and asymmetric effects in fast reconnection, and so on. The plasma is generated by two flux cores at the ``magnetosheath-side'' and one electron cyclotron resonance source at the ``magnetosphere-side''. Different kinds of coils with specific current driven functions, as well as advanced diagnostics are designed. Motivation, overview of the AREX design and reconnection scenarios will be discussed.

  15. Secondary reconnection, energisation and turbulence in dipolarisation fronts: results of a 3D kinetic simulation campaign

    Science.gov (United States)

    Lapenta, Giovanni; Goldman, Martin; Newman, David; olshevskyi, Vyacheslav; Markidis, Stefano

    2016-04-01

    regions in the fronts. [1] Hamrin, Maria, et al. "The evolution of flux pileup regions in the plasma sheet: Cluster observations." Journal of Geophysical Research: Space Physics 118.10 (2013): 6279-6290. [2] Wu, Mingyu, et al. "In situ observations of multistage electron acceleration driven by magnetic reconnection." Journal of Geophysical Research: Space Physics 120.8 (2015): 6320-6331. [3] Schmid, D., et al. "Two states of magnetotail dipolarization fronts: A statistical study." Journal of Geophysical Research: Space Physics 120.2 (2015): 1096-1108. [4] Lapenta, Giovanni, et al. "Secondary reconnection sites in reconnection-generated flux ropes and reconnection fronts." Nature Physics 11.8 (2015): 690-695.

  16. Laboratory study of ion and electron dynamics during asymmetric magnetic reconnection

    Science.gov (United States)

    Yoo, J.; Jara-Almonte, J.; Yamada, M.; Ji, H.; Fox, W. R., II; Chen, L. J.; Roytershteyn, V.; Na, B.

    2015-12-01

    Magnetic reconnection at the dayside magnetopause has a large density asymmetry across the current sheet. To study effects of the density asymmetry on the ion and electron dynamics, plasmas with a significant (~10) density asymmetry are created in the Magnetic Reconnection Experiment (MRX) [1]. The density asymmetry affects the ion flow pattern by changing the in-plane electrostatic field such that the potential decrease on the high-density side becomes much smaller than that on the low-density side [2]. The ion inflow stagnation point is shifted toward the low-density side and the maximum ion outflow velocity is observed on the low-density side. The density asymmetry also makes the electron temperature profile asymmetric, which has a higher temperature near the low-density-side separatrices. The bulk electron heating is proportional to the total incoming magnetic energy per particle. The electron energization process during asymmetric reconnection is studied via numerical simulations. By comparing 2D simulations with corresponding 3D simulations, we find that the overall energization process does not depend on variations along the third dimension. Where and how electrons are energized during asymmetric reconnection will be discussed by using data from 2D numerical simulations. Finally, the scaling of the reconnection rate and the ion outflow speed given by the Cassak and Shay 2007 [3] is tested by systematically varying the density ratio. The measured ion outflow speed is about 40% of the theoretical values and the measured reconnection rate agrees with the scaling only with the measured density in the exhaust region. [1] M. Yamada et al., Phys. Plasmas 4, 1936 (1997). [2] J. Yoo et al., Phys. Rev. Lett. 113, 095002 (2014). [3] P. Cassak and M. Shay, Phys. Plasmas 14, 102114 (2007).

  17. Constraining reconnection region conditions using imaging and spectroscopic analysis of a coronal jet

    Science.gov (United States)

    Brannon, Sean; Kankelborg, Charles

    2017-08-01

    Coronal jets typically appear as thin, collimated structures in EUV and X-ray wavelengths, and are understood to be initiated by magnetic reconnection in the lower corona or upper chromosphere. Plasma that is heated and accelerated upward into coronal jets may therefore carry indirect information on conditions in the reconnection region and current sheet located at the jet base. On 2017 October 14, the Interface Region Imaging Spectrograph (IRIS) and Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO/AIA) observed a series of jet eruptions originating from NOAA AR 12599. The jet structure has a length-to-width ratio that exceeds 50, and remains remarkably straight throughout its evolution. Several times during the observation bright blobs of plasma are seen to erupt upward, ascending and subsequently descending along the structure. These blobs are cotemporal with footpoint and arcade brightenings, which we believe indicates multiple episodes of reconnection at the structure base. Through imaging and spectroscopic analysis of jet and footpoint plasma we determine a number of properties, including the line-of-sight inclination, the temperature and density structure, and lift-off velocities and accelerations of jet eruptions. We use these properties to constrain the geometry of the jet structure and conditions in reconnection region.

  18. Influence of Spontaneously Generated Turbulence on Magnetic Reconnection

    Science.gov (United States)

    Daughton, William; Roytershteyn, Vadim; Karimabadi, Homa

    2012-10-01

    The 3D dynamics of reconnection is examined for electron-positron plasmas within Harris sheet geometry with a guide field. This configuration is unstable to tearing modes at resonant surfaces across the layer, corresponding to oblique angles relative to 2D models. Vlasov theory predicts a spectrum of oblique modes which can destroy the flux surfaces and produce interacting flux ropes. These structures coalesce to larger scales leading to the continual formation and break-up of new current sheets and the generation of turbulence. The fluctuation spectrum is highly anisotropic and is characterized by two power-laws with a break at k di˜1, where di is the inertial length. In the large 3D simulations, the dissipation rate is reduced by ˜40% relative to small 2D cases which are steady and laminar. In both limits, the reconnection remains fast (i.e. Alfv'enic), is insensitive to the system size and ultimately occurs within inertial-scale current sheets. These results imply that the physics responsible for setting the time scale is not radically altered by the turbulence. However, the results indicate that a larger fraction of the magnetic energy is accessible in 3D and that many more particles are accelerated into the high energy tails due to the turbulence.

  19. Scale size and life time of energy conversion regions observed by Cluster in the plasma sheet

    Directory of Open Access Journals (Sweden)

    M. Hamrin

    2009-11-01

    Full Text Available In this article, and in a companion paper by Hamrin et al. (2009 [Occurrence and location of concentrated load and generator regions observed by Cluster in the plasma sheet], we investigate localized energy conversion regions (ECRs in Earth's plasma sheet. From more than 80 Cluster plasma sheet crossings (660 h data at the altitude of about 15–20 RE in the summer and fall of 2001, we have identified 116 Concentrated Load Regions (CLRs and 35 Concentrated Generator Regions (CGRs. By examining variations in the power density, E·J, where E is the electric field and J is the current density obtained by Cluster, we have estimated typical values of the scale size and life time of the CLRs and the CGRs. We find that a majority of the observed ECRs are rather stationary in space, but varying in time. Assuming that the ECRs are cylindrically shaped and equal in size, we conclude that the typical scale size of the ECRs is 2 RE≲ΔSECR≲5 RE. The ECRs hence occupy a significant portion of the mid altitude plasma sheet. Moreover, the CLRs appear to be somewhat larger than the CGRs. The life time of the ECRs are of the order of 1–10 min, consistent with the large scale magnetotail MHD simulations of Birn and Hesse (2005. The life time of the CGRs is somewhat shorter than for the CLRs. On time scales of 1–10 min, we believe that ECRs rise and vanish in significant regions of the plasma sheet, possibly oscillating between load and generator character. It is probable that at least some of the observed ECRs oscillate energy back and forth in the plasma sheet instead of channeling it to the ionosphere.

  20. Reconnection on the Sun

    Science.gov (United States)

    Kohler, Susanna

    2016-05-01

    , erupting from the solar surface.Snapshots from the SDO side view (left and center) and STEREO overhead view (right). The three rows show the time evolution of the double-loop structure after the initial flare. In the STEREO view, you can see the central footpoints of the loops slip to the left. [Gou et al. 2016]In the SDO observations presented by Chen and collaborators, the pre-flare/CME structures look remarkably like the structures predicted in the breakout model. Sequential heating of loops can be seen as the breakout reconnection starts, followed by anenormous flare and CME as the lower loops erupt outward.Study 2: Slipping ReconnectionA team of scientists from the University of Science and Technology of China, led by Tingyu Gou and Rui Liu, have presented the first stereoscopic observation of slipping reconnection in the Sun, made by the two-spacecraft Solar Terrestrial Relations Observatory (STEREO).In slipping reconnection, magnetic field lines continuously exchange connectivities with their neighbors, causing them to slip through plasma. Observations by STEREO of a flaring double-loop system revealed that the central footpoints the endpoints where the loops are anchored to the solar surface slipped sideways after a flare.The authors model of the double-loop structure at two different times, during which the central footpoint slips from point C to D. Projections onto the XY and YZ planes show STEREOs and SDOs views, respectively. [Gou et al. 2016]The authors reconstructed a 3D model of the loop system using the overhead observations from STEREO and a simultaneous side view from SDO. They speculate that the slipping reconnection was likely triggered by the initial solar flare.Double BonusCheck out the videos belowto watch these processes happen!This first video is from Chen et al. 2016, and shows the SDO view of coronal loops in three wavelengths. If you watch carefully, you can see the sequential brightening of loops signs of the breakout reconnection before the

  1. Plasma heating in a post eruption Current Sheet: a case study based on ultraviolet, soft, and hard X-ray data

    CERN Document Server

    Susino, Roberto; Krucker, Säm

    2013-01-01

    Off-limb observations of the solar corona after Coronal Mass Ejections (CMEs) often show strong, compact, and persistent UV sources behind the eruption. They are primarily observed by the SOHO/UVCS instrument in the "hot" Fe XVIII {\\lambda}974 {\\AA} line and are usually interpreted as a signature of plasma heating due to magnetic reconnection in the post-CME Current Sheet (CS). Nevertheless, the physical process itself and the altitude of the main energy release are currently not fully understood. In this work, we studied the evolution of plasma heating after the CME of 2004 July 28 by comparing UV spectra acquired by UVCS with soft X-ray (SXR) and hard X-ray (HXR)images of the post-flare loops taken by GOES/SXI and RHESSI. The X-ray data show a long-lasting extended source that is rising upwards, toward the high-temperature source detected by UVCS. UVCS data show the presence of significant non-thermal broadening in the CS (signature of turbulent motions) and a strong density gradient across the CS region. T...

  2. Lessons on collisionless reconnection from quantum fluids

    Directory of Open Access Journals (Sweden)

    Yasuhito eNarita

    2014-12-01

    Full Text Available Magnetic reconnection in space plasmas remains a challenge in physics in that the phenomenon is associated with the breakdown of frozen-in magnetic field in a collisionless medium. Such a topology change can also be found in superfluidity, known as the quantum vortex reconnection. We give a plasma physicists' view of superfluidity to obtain insights on essential processes in collisionless reconnection, including discussion of the kinetic and fluid pictures, wave dynamics, and time reversal asymmetry. The most important lesson from the quantum fluid is the scenario that reconnection is controlled by the physics of topological defects on the microscopic scale, and by the physics of turbulence on the macroscopic scale. Quantum vortex reconnection is accompanied by wave emission in the form of Kelvin waves and sound waves, which imprints the time reversal asymmetry.

  3. Magnetohydrodynamic Turbulence and Reconnection in the Magnetotail

    Science.gov (United States)

    El-Alaoui, Mostafa; Richard, Robert L.; Ashour-Abdalla, Maha; Goldstein, Melvyn L.; Walker, Raymond J.

    2011-01-01

    We have used a global MHD simulation with high spatial resolution to investigate the origin and properties of turbulence in the plasma sheet. In this simulation we imposed a steady southward IMF with a magnitude of 5 nT at the upstream simulation boundary for more than three hours followed by ninety minutes of northward IMF of the same magnitude. The solar wind number density was 20 cm-3, the thermal pressure was 20 pPa, and the velocity was 500 km/s in the x direction. The moderately high dynamic pressure confined the magnetotail to the high-grid resolution region. Even for these nominal solar wind parameters and steady driving the plasma sheet became turbulent. The power spectral densities and probability distribution functions computed from the simulations were comparable to those obtained from spacecraft observations. The largest scale vortices were associated with reconnection outflows and, in the southward IMF case, with the diversion of high speed flows in the near-Earth region. Both time and space domain analyses revealed that there were three scales present, the large scale of the driving processes, the intermediate inertial scale and the dissipative scale.

  4. Magnetic Reconnection and Intermittent Turbulence in the Solar Wind

    CERN Document Server

    Osman, K T; Gosling, J T; Greco, A; Servidio, S; Hnat, B; Chapman, S C; Phan, T D

    2014-01-01

    A statistical relationship between magnetic reconnection, current sheets and intermittent turbulence in the solar wind is reported for the first time using in-situ measurements from the Wind spacecraft at 1 AU. We identify intermittency as non-Gaussian fluctuations in increments of the magnetic field vector, $\\mathbf{B}$, that are spatially and temporally non-uniform. The reconnection events and current sheets are found to be concentrated in intervals of intermittent turbulence, identified using the partial variance of increments method: within the most non-Gaussian 1% of fluctuations in $\\mathbf{B}$, we find 87%-92% of reconnection exhausts and $\\sim$9% of current sheets. Also, the likelihood that an identified current sheet will also correspond to a reconnection exhaust increases dramatically as the least intermittent fluctuations are removed from the dataset. Hence, the turbulent solar wind contains a hierarchy of intermittent magnetic field structures that are increasingly linked to current sheets, which ...

  5. A Statistical study of plasma sheet oscillations with kinetic ballooning/interchange instability signatures using THEMIS spacecraft

    Science.gov (United States)

    Jurisic, Mirjana; Panov, Evgeny; Nakamura, Rumi; Baumjohann, Wolfgang

    2016-04-01

    We use THEMIS data from 2010-2012 tail seasons to collect observations of plasma sheet oscillations with kinetic ballooning/interchange instability (BICI) signatures. Over seventy observations with closely located THEMIS probes P3-P5 reveal that BICI-like plasma sheet oscillations may appear at different magnetic local time. For these, we derive background plasma sheet parameters such as BZ, δBZ/δx and plasma beta, and investigate solar wind conditions. We also estimate the proper parameters of BICI-like oscillations such as frequency and amplitude. Based on this, we search for a relation between the background plasma sheet parameters and the proper parameters of BICI-like oscillations.

  6. Magnetic Reconnection in the Earth's Magnetosphere

    Science.gov (United States)

    Tsurutani, B. T.; Lakhina, G. S.

    1997-01-01

    The process of magnetic reconnection plays an important role during the interaction of the solar wind with the Earth's magnetosphere which leads to the exchange of mass, momentum, and energy between these two highly conducting plasmas.

  7. Relationship between Magnetic Helicity Injection and Magnetic Reconnection in Double-Null Startup of the UTST Spherical Tokamak

    Science.gov (United States)

    Watanabe, Takenori; Kamio, Shuji; Cao, Qinghong; Itagaki, Hirotomo; Takemura, Koichiro; Yamasaki, Kotaro; Ishiguchi, Koji; Yamada, Takuma; Inomoto, Michiaki; Ono, Yasushi

    2012-10-01

    Magnetic helicity injection is a useful idea for explaining plasma current drive and startup of various magnetized plasmas such as Spherical Tokamaks (STs). Magnetic reconnection is directly related with the magnetic helicity injection, because it is essential to reorganization of magnetic field lines injected externally. We address how and why helicity injection is related with magnetic reconnection. An ST plasma is produced by using two pairs of external poloidal field coils in the University of Tokyo Spherical Tokamak (UTST) device. In the late phase of the formation, a single ST is connected to the coil flux, which enables magnetic helicity injection from the helicity source (the coil flux) into the helicity sink (the ST plasma). We measured the Y-shaped reconnection region between the ST plasma and the poloidal coil using two dimensional pickup coil arrays in the r-z plane. magnetic reconnection of common flux into private flux causes concentration of current density along the current sheet, forming a high eigen-value area between the helicity source and the helicity sink. We made a parameter scan to study how crucial and effective the plasmoid ejection is for helicity injection and found that the plasmoid motion is a dynamic helicity injection process.

  8. Simulation of the 3-D Evolution of Electron Scale Magnetic Reconnection - Motivated by Laboratory Experiments Predictions for MMS

    Science.gov (United States)

    Buechner, J.; Jain, N.; Sharma, A.

    2013-12-01

    The four s/c of the Magnetospheric Multiscale (MMS) mission, to be launched in 2014, will use the Earth's magnetosphere as a laboratory to study the microphysics of three fundamental plasma processes. One of them is magnetic reconnection, an essentially multi-scale process. While laboratory experiments and past theoretical investigations have shown that important processes necessary to understand magnetic reconnection take place at electron scales the MMS mission for the first time will be able to resolve these scales by in space observations. For the measurement strategy of MMS it is important to make specific predictions of the behavior of current sheets with a thickness of the order of the electron skin depth which play an important role in the evolution of collisionless magnetic reconnection. Since these processes are highly nonlinear and non-local numerical simulation is needed to specify the current sheet evolution. Here we present new results about the nonlinear evolution of electron-scale current sheets starting from the linear stage and using 3-D electron-magnetohydrodynamic (EMHD) simulations. The growth rates of the simulated instabilities compared well with the growth rates obtained from linear theory. Mechanisms and conditions of the formation of flux ropes and of current filamentation will be discussed in comparison with the results of fully kinetic simulations. In 3D the X- and O-point configurations of the magnetic field formed in reconnection planes alternate along the out-of-reconnection-plane direction with the wavelength of the unstable mode. In the presence of multiple reconnection sites, the out-of-plane magnetic field can develop nested structure of quadrupoles in reconnection planes, similar to the 2-D case, but now with variations in the out-of-plane direction. The structures of the electron flow and magnetic field in 3-D simulations will be compared with those in 2-D simulations to discriminate the essentially 3D features. We also discuss

  9. Geotail observations of temperature anisotropy of the two-component protons in the dusk plasma sheet

    Directory of Open Access Journals (Sweden)

    M. N. Nishino

    2007-03-01

    Full Text Available In search for clues towards the understanding of the cold plasma sheet formation under northward IMF, we study the temperature anisotropy of the two-component protons in the plasma sheet near the dusk low-latitude boundary observed by the Geotail spacecraft. The two-component protons result from mixing of the cold component from the solar wind and the hot component of the magnetospheric origin, and may be the most eloquent evidence for the transport process across the magnetopause. The cold component occasionally has a strong anisotropy in the dusk flank, and the sense of the anisotropy depends on the observed locations: the parallel temperature is enhanced in the tail flank while the perpendicular temperature is enhanced on the dayside. The hot component is nearly isotropic in the tail while the perpendicular temperature is enhanced on the dayside. We discuss possible mechanism that can lead to the observed temperature anisotropies.

  10. Distribution of energetic oxygen and hydrogen in the near-Earth plasma sheet

    CERN Document Server

    Kronberg, E A; Haaland, S E; Daly, P W; Delcourt, D C; Luo, H; Kistler, L M; Dandouras, I

    2016-01-01

    The spatial distributions of different ion species are useful indicators for plasma sheet dynamics. In this statistical study based on 7 years of Cluster observations, we establish the spatial distributions of oxygen ions and protons at energies from 274 to 955 keV, depending on geomagnetic and solar wind (SW) conditions. Compared with protons, the distribution of energetic oxygen has stronger dawn-dusk asymmetry in response to changes in the geomagnetic activity. When the interplanetary magnetic field (IMF) is directed southward, the oxygen ions show significant acceleration in the tail plasma sheet. Changes in the SW dynamic pressure ($\\mathit{P}_{dyn}$) affect the oxygen and proton intensities in the same way. The energetic protons show significant intensity increases at the near-Earth duskside during disturbed geomagnetic conditions, enhanced SW $\\mathit{P}_{dyn}$, and southward IMF, implying there location of effective inductive acceleration mechanisms and a strong duskward drift due to the increase of t...

  11. Optical Studies of the Neutral Sheet Physics on MRX

    Science.gov (United States)

    Kuritsyn, A.; Ji, H.; Ren, Y.; Terry, S.; Yamada, M.; Levinton, F.

    2003-04-01

    Recent experiments on MRX have produced a lot of fundamental data on magnetic reconnection [1]. Nevertheless some key questions about the reconnection physics still remain unsolved such as the mechanism of the nonclassical ion heating and resistivity enhancement. To further improve our understanding of the structure of the neutral sheet and microscale processes accompanying reconnection the following non-perturbing optical diagnostics are being implemented: ion dynamics spectroscopy probe (IDSP) and planar laser induced fluorescence (PLIF). The IDSP is an insertable optical probe capable of measuring local ion temperature and flow velocities via Dopler spectroscopy. The PLIF imaging diagnostic is being developed on MRX to obtain the space and time resolved structure of the ion density fluctuations in the reconnection layer. There are some experimental indications and theoretical predictions that lower hybrid frequency electromagnetic fluctuations recently found in the current sheet can play significant role in the ion heating [2,3]. To verify this hypothesis we plan to do a systematic study, employing new diagnostics together with currently used fast Langmuir and magnetic pickup fluctuation probes, of the correlation between the ion temperature rise and fluctuations in the reconnection layer. MRX is jointly supported by DOE, NASA and NSF. [1] M. Yamada et al., Phys. Plasmas 4(5),1936(1997) [2] S. Ichimaru, J. Phys. Soc. Japan 39(5),1373(1975) [3] H. Ji et al., Bull. Am. Phys. Soc. 44,322(2002)

  12. Effect of the initial plasma parameters on the structure of the current sheets developing in two-dimensional magnetic fields with a null line

    Science.gov (United States)

    Ostrovskaya, G. V.; Frank, A. G.; Bogdanov, S. Yu.

    2010-07-01

    The effect of the initial plasma parameters on the structure of the plasma of the current sheets that form in two-dimensional magnetic fields with a null line is studied by holographic interferometry. The evolution of the plasma sheets that develop in an initial low-density plasma, where a gas is mainly ionized by a pulse current passing through the plasma and initiating the formation of a current sheet, has been comprehensively studied for the first time. At the early stage of evolution, the spatial structure of such a plasma sheet differs substantially from the classic current sheets forming in a dense plasma. Nevertheless, extended plasma sheets with similar parameters form eventually irrespective of the initial plasma density.

  13. Plasma sheet ion composition at various levels of geomagnetic and solar activity

    Science.gov (United States)

    Lennartsson, W.

    1987-08-01

    The data obtained in the earth's plasma sheet by the Plasma Composition Experiment on the ISEE-1 spacecraft are briefly reexamined. The data are shown in the form of statistically averaged bulk parameters for the four major ions H(+), He(2+), He(+), and O(+) to illustrate the apparent mixture of solar and terrestrial ions, a mixture that varies with geomagnetic and other conditions. Some major differences in the statistical properties of different ions, which may have a bearing on the physics of the solar wind-magnetosphere interaction, are highlighted.

  14. Sounding of the plasma sheet in the deep geomagnetic tail using energetic particles

    Energy Technology Data Exchange (ETDEWEB)

    Daly, P.W.; Wenzel, K.; Sanderson, T.R.

    1984-10-01

    Energetic ions (E>35 keV) at 90/sup 0/ to the magnetic field line are measured on ISEE-3 in the distant geomagnetic tail and are used as tracers of the particle density during two encounters with the plasma sheet at 210 and 128 earth radii from the earth. Because of the finite gyroradius (2400 km) of these (assumed) protons, different orientation about the magnetic field measure the intensity of different locations, allowing a separation of spatial from temporal variations. Density contour maps of the plasma hseet are constructed, demonstrating the wavy nature of this regime, as well as the existence of density layers within it.

  15. On the problem of Plasma Sheet Boundary Layer identification from plasma moments in Earth's magnetotail

    Directory of Open Access Journals (Sweden)

    E. E. Grigorenko

    2012-09-01

    Full Text Available The problem of identification of the interface region between the lobe and the Plasma Sheet (PS – the Plasma Sheet Boundary Layer (PSBL – using ion moments and magnetic field data often arises in works devoted to statistical studies of various PSBL phenomena. Our experience in the identification of this region based on the analysis of ion velocity distribution functions demonstrated that plasma parameters, such as the ion density and bulk velocity, the plasma beta or the dynamic pressure vary widely depending on the state of magnetotail activity. For example, while field-aligned beams of accelerated ions are often observed propagating along the lobeward edge of the PSBL there are times when no signatures of these beams could be observed. In the last case, a spacecraft moving from the lobe region to the PS registers almost isotropic PS-like ion velocity distribution. Such events may be classified as observations of the outer PS region. In this paper, we attempt to identify ion parameter ranges or their combinations that result in a clear distinction between the lobe, the PSBL and the adjacent PS or the outer PS regions. For this we used 100 crossings of the lobe-PSBL-PS regions by Cluster spacecraft (s/c made in different periods of magnetotail activity. By eye inspection of the ion distribution functions we first identify and separate the lobe, the PSBL and the adjacent PS or outer PS regions and then perform a statistical study of plasma and magnetic field parameters in these regions. We found that the best results in the identification of the lobe-PSBL boundary are reached when one uses plasma moments, namely the ion bulk velocity and density calculated not for the entire energy range, but for the energies higher than 2 keV. In addition, we demonstrate that in many cases the plasma beta fails to correctly identify and separate the PSBL and the adjacent PS or the outer PS regions.

  16. MMS observations of plasma wave and electron energization in the electron diffusion region of asymmetric reconnection with strong guide field

    Science.gov (United States)

    Xiao, Chijie; Zhao, Siqi; Shi, Mijie; Pu, Zuyin; Wang, Xiaogang

    2016-10-01

    Here we report an asymmetric reconnection event with strong guide field observed by Magnetospheric Multiscale Mission (MMS) on the dayside magnetopause. In this event there are multiple wave modes, such as electron Alfvenic mode, broadband waves between the lower-hybrid and electron cyclotron frequencies, exist in the vicinity of the electron diffusion region and the separatrix. And the electron velocity distribution functions show that bi-stream electrons with low energy (processes are investigated and comparison with some 3D numerical simulation results. This work was supported by NSFC (Grants 41274168 and 11375053).

  17. Collisionless reconnection in Jupiter's magnetotail

    Energy Technology Data Exchange (ETDEWEB)

    Zimbardo, G. (Univ. ' della Calabria (Italy))

    1991-04-01

    The authors present the first quantitative study of collisionless reconnection in Jupiter's magnetotail. Recently it has been shown that collisionless reconnection can occur in the Earth's magnetotail quasi-neutral sheet when the electrons are subject to chaotic pitch angle diffusion. This happens when the curvature parameter K{sub e} = B{sub z}/B{sub 0}(L{sub z}/{rho}{sub e0}){sup 1/2} decreases to {approximately} 1.6. For Jupiter's magnetotail, a self-consistent axisymmetric equilibrium model is used to compute the magnetic field and K{sub e}, and it is found that the condition for electron chaotization is satisfied in a region large enough to allow the growth of a tearing instability. The favorite site for reconnection is situated at about 60 R{sub j}, and the growth time is estimated to be about 370 s, i.e., much shorter than the plasma transit time through the chaotization region. The inductive e.m.f. along a 20 R{sub j} X line is estimated to be of order 100 kV - 1 MV, and should accelerate the ions dawnward and the electrons duskward.

  18. Observational Aspects of Magnetic Reconnection at the Earth's Magnetosphere

    Science.gov (United States)

    Souza, Vitor M.; Koga, Daiki; Gonzalez, Walter D.; Cardoso, Flavia R.

    2017-08-01

    Magnetic field reconnection has shown to be the dominant process in the solar wind-Earth's magnetosphere interaction. It enables mass, momentum, and energy exchange between different plasma regimes, and it is regarded as an efficient plasma acceleration and heating mechanism. Reconnection has been observed to occur in laboratory plasmas, at planetary magnetospheres in our Solar System, and the Sun. In this work, we focus on analyzing the characteristics of magnetic reconnection at the Earth's magnetosphere according to spaceborne observations in the vicinity of our planet. Firstly, the locations where magnetic field reconnection are expected to occur within the vast magnetospheric region are addressed, and is shown how they are influenced by changes in the interplanetary magnetic field direction. The main magnetic field and plasma signatures of magnetic reconnection are discussed from both theoretical and observational points of view. Spacecraft observations of ion inertial length scale reconnection are also presented.

  19. Multiscale structures of resistive magnetic reconnection at high magnetic Reynolds numbers

    Science.gov (United States)

    Miyoshi, Takahiro; Kusano, Kanya

    Magnetic reconnection is the most important process of explosive phenomena in space plasmas. The magnetic Reynolds number for the space plasmas are extremely high in general since those plasmas are thought to be collisionless or semi-collisional. However, magnetic reconnection rate becomes low as magnetic Reynolds number increases within the framework of a stationary resistive MHD model. Thus, modern models of magnetic reconnection often include kinetic effects such as the Hall effect to explain realistic explosive magnetic reconnection. It is thought, on the other hand, that the MHD approximation is valid for the plasmas within a very wide range of scales since the scale gap between the macro-and micro-scale is quite large, e.g., in the solar corona, the ratio of the macro to micro will be more than 107 . Such multiscale structures of MHD with wide range of scales, however, have not been clarified so far. Therefore, in this paper, resistive magnetic reconnection at high magnetic Reynolds numbers are investigated using very high-resolution MHD simulations. Simulation results show that the magnetic energy at high magnetic Reynolds numbers is explosively released, while that at not-so-high magnetic Reynolds numbers is steadily dissipated. In the case of high magnetic Reynolds numbers, multiple small scale plasmoids are intermittently created and ejected via secondary tearing modes in a nonlinearly developed thin current sheet. It is revealed that a secondary plasmoid is not only accelerated up to a local magnetosonic speed toward the down-stream region but also perturbs the up-stream region. Thus, complicated multiscale structures appear around the magnetic field reversal layer. Perspective for the high-resolution simulation of extremely high magnetic Reynolds numbers will be also discussed.

  20. Large-volume flux closure during plasmoid-mediated reconnection in coaxial helicity injection

    Science.gov (United States)

    Ebrahimi, F.; Raman, R.

    2016-04-01

    A large-volume flux closure during transient coaxial helicity injection (CHI) in NSTX-U is demonstrated through resistive magnetohydrodynamics (MHD) simulations. Several major improvements, including the improved positioning of the divertor poloidal field coils, are projected to improve the CHI start-up phase in NSTX-U. Simulations in the NSTX-U configuration with constant in time coil currents show that with strong flux shaping the injected open field lines (injector flux) rapidly reconnect and form large volume of closed flux surfaces. This is achieved by driving parallel current in the injector flux coil and oppositely directed currents in the flux shaping coils to form a narrow injector flux footprint and push the injector flux into the vessel. As the helicity and plasma are injected into the device, the oppositely directed field lines in the injector region are forced to reconnect through a local Sweet-Parker type reconnection, or to spontaneously reconnect when the elongated current sheet becomes MHD unstable to form plasmoids. In these simulations for the first time, it is found that the closed flux is over 70% of the initial injector flux used to initiate the discharge. These results could work well for the application of transient CHI in devices that employ super conducting coils to generate and sustain the plasma equilibrium.

  1. Effect of Inductive Coil Geometry and Current Sheet Trajectory of a Conical Theta Pinch Pulsed Inductive Plasma Accelerator

    Science.gov (United States)

    Hallock, Ashley K.; Polzin, Kurt A.; Bonds, Kevin W.; Emsellem, Gregory D.

    2011-01-01

    Results are presented demonstrating the e ect of inductive coil geometry and current sheet trajectory on the exhaust velocity of propellant in conical theta pinch pulsed induc- tive plasma accelerators. The electromagnetic coupling between the inductive coil of the accelerator and a plasma current sheet is simulated, substituting a conical copper frustum for the plasma. The variation of system inductance as a function of plasma position is obtained by displacing the simulated current sheet from the coil while measuring the total inductance of the coil. Four coils of differing geometries were employed, and the total inductance of each coil was measured as a function of the axial displacement of two sep- arate copper frusta both having the same cone angle and length as the coil but with one compressed to a smaller size relative to the coil. The measured relationship between total coil inductance and current sheet position closes a dynamical circuit model that is used to calculate the resulting current sheet velocity for various coil and current sheet con gura- tions. The results of this model, which neglects the pinching contribution to thrust, radial propellant con nement, and plume divergence, indicate that in a conical theta pinch ge- ometry current sheet pinching is detrimental to thruster performance, reducing the kinetic energy of the exhausting propellant by up to 50% (at the upper bound for the parameter range of the study). The decrease in exhaust velocity was larger for coils and simulated current sheets of smaller half cone angles. An upper bound for the pinching contribution to thrust is estimated for typical operating parameters. Measurements of coil inductance for three di erent current sheet pinching conditions are used to estimate the magnetic pressure as a function of current sheet radial compression. The gas-dynamic contribution to axial acceleration is also estimated and shown to not compensate for the decrease in axial electromagnetic acceleration

  2. Cluster and TC-1 observation of magnetic holes in the plasma sheet

    Directory of Open Access Journals (Sweden)

    W. J. Sun

    2012-03-01

    Full Text Available Magnetic holes with relatively small scale sizes, detected by Cluster and TC-1 in the magnetotail plasma sheet, are studied in this paper. It is found that these magnetic holes are spatial structures and they are not magnetic depressions generated by the flapping movement of the magnetotail current sheet. Most of the magnetic holes (93% were observed during intervals with Bz larger than Bx, i.e. they are more likely to occur in a dipolarized magnetic field topology. Our results also suggest that the occurrence of these magnetic holes might have a close relationship with the dipolarization process. The magnetic holes typically have a scale size comparable to the local proton Larmor radius and are accompanied by an electron energy flux enhancement at a 90° pitch angle, which is quite different from the previously observed isotropic electron distributions inside magnetic holes in the plasma sheet. It is also shown that most of the magnetic holes occur in marginally mirror-stable environments. Whether the plasma sheet magnetic holes are generated by the mirror instability related to ions or not, however, is unknown. Comparison of ratios, scale sizes and propagation direction of magnetic holes detected by Cluster and TC-1, suggests that magnetic holes observed in the vicinity of the TC-1 orbit (~7–12 RE are likely to be further developed than those observed by Cluster (~7–18 RE.

  3. The Role of Geometry in Magnetic Reconnection

    Science.gov (United States)

    Hesse, Michael; Aunai, Nicholas; Birn, Joachim; Zenitani, Seiji

    2012-01-01

    Magnetic reconnection is arguably the most effective energy conversion and transport process in plasmas. Reconnection is subject to topological considerations in two ways. First, the process itself involves a change in topology of the combined plasma-magnetic field system. This change in topology transcends that of the magnetic field alone and accounts for flux transport relative to the motion of the plasma in the system under investigation. The second way topology is important to magnetic reconnection is through modifications of the diffUSion/dissipation physics brought about by the structure of the reconnecting system. This presentation will present an overview and summary of both past and recent results pertaining to both aspects.

  4. Magnetic Reconnection in Extreme Astrophysical Environments

    CERN Document Server

    Uzdensky, Dmitri A

    2011-01-01

    Magnetic reconnection is a basic plasma process of dramatic rearrangement of magnetic topology, often leading to a violent release of magnetic energy. It is important in magnetic fusion and in space and solar physics --- areas that have so far provided the context for most of reconnection research. Importantly, these environments consist just of electrons and ions and the dissipated energy always stays with the plasma. In contrast, in this paper I introduce a new direction of research, motivated by several important problems in high-energy astrophysics --- reconnection in high energy density (HED) radiative plasmas, where radiation pressure and radiative cooling become dominant factors in the pressure and energy balance. I identify the key processes distinguishing HED reconnection: special-relativistic effects; radiative effects (radiative cooling, radiation pressure, and Compton resistivity); and, at the most extreme end, QED effects, including pair creation. I then discuss the main astrophysical application...

  5. Morphology and Density Structure of Post-CME Current Sheets

    Science.gov (United States)

    Vrsnak, B.; Poletto, G.; Vujic, E.; Vourlidas, A.

    2009-01-01

    Eruption of a coronal mass ejection (CME) is believed to drag and open the coronal magnetic field, presumably leading to the formation of a large-scale current sheet and field relaxation by magnetic reconnection. This paper analyzes the physical characteristics of ray-like coronal features formed in the aftermath of CMEs, to confirm whether interpreting such phenomena in terms of a reconnecting current sheet is consistent with observations. Methods: The study focuses on UVCS/SOHO and LASCO/SOHO measurements of the ray width, density excess, and coronal velocity field as a function of the radial distance. The morphology of the rays implies that they are produced by Petschek-like reconnection in the large-scale current sheet formed in the wake of CME. The hypothesis is supported by the flow pattern, often showing outflows along the ray, and sometimes also inflows into the ray. The inferred inflow velocities range from 3 to 30 km/s, and are consistent with the narrow opening-angle of rays, which add up to a few degrees. The density of rays is an order of magnitude higher than in the ambient corona. The model results are consistent with the observations, revealing that the main cause of the density excess in rays is a transport of the dense plasma from lower to higher heights by the reconnection outflow.

  6. Statistics of Reconnection-Driven Turbulence

    CERN Document Server

    Kowal, Grzegorz; Lazarian, Alex; Vishniac, Ethan T

    2016-01-01

    Magnetic reconnection is a process that changes magnetic field topology in highly conducting fluids. Within the standard Sweet-Parker model, this process would be too slow to explain observations (e.g. solar flares). In reality, the process must be ubiquitous as astrophysical fluids are magnetized and motions of fluid elements necessarily entail crossing of magnetic frozen-in field lines and magnetic reconnection. In the presence of turbulence, the reconnection is independent of microscopic plasma properties, and may be much faster than previously thought, as proposed in Lazarian & Vishniac (1999) and tested in Kowal et al. (2009, 2012). However, the considered turbulence in the Lazarian-Vishniac model was imposed externally. In this work we consider reconnection-driven magnetized turbulence in realistic three-dimensional geometry initiated by stochastic noise. We demonstrate through numerical simulations that the stochastic reconnection is able to self-generate turbulence through interactions between the...

  7. Plasma-filled rippled wall rectangular backward wave oscillator driven by sheet electron beam

    Indian Academy of Sciences (India)

    A Hadap; J Mondal; K C Mittal; K P Maheshwari

    2011-03-01

    Performance of the backward wave oscillator (BWO) is greatly enhanced with the introduction of plasma. Linear theory of the dispersion relation and the growth rate have been derived and analysed numerically for plasma-filled rippled wall rectangular waveguide driven by sheet electron beam. To see the effect of plasma on the TM01 cold wave structure mode and on the generated frequency, the parameters used are: relativistic factor = 1.5 (i.e. / = 0.741), average waveguide height 0 = 1.445 cm, axial corrugation period 0 = 1.67 cm, and corrugation amplitude = 0.225 cm. The plasma density is varied from zero to 2 × 1012 cm-3. The presence of plasma tends to raise the TM01 mode cut-off frequency (14 GH at 2 × 1012 cm-3 plasma density) relative to the vacuum cut-off frequency (5 GH) which also causes a decrease in the group velocity everywhere, resulting in a flattening of the dispersion relation. With the introduction of plasma, an enhancement in absolute instability was observed.

  8. Responses of properties in the plasma sheet and at the geosynchronous orbit to interplanetary shock

    Institute of Scientific and Technical Information of China (English)

    YAO Li; LIU ZhenXing; ZUO PingBing; ZHANG LingQian; DUAN SuPing

    2009-01-01

    On July 22,2004,the WIND spacecraft detected a typical interplanetary shock. There was sustaining weak southward magnetic field in the preshock region and the southward field was suddenly enhanced across the shock front (i.e.,southward turning). When the shock impinged on the magnetosphere,the magnetospheric plasma convection was abruptly enhanced in the central plasma sheet,which was directly observed by both the TC-1 and Cluster spacecraft located in different regions. Simultaneously,the Cluster spacecraft observed that the dawn-to-dusk electric field was abruptly enhanced. The variations of the magnetic field observed by TC-1,Cluster,GOES-10 and GOES-12 that were distributed in different regions in the plasma sheet and at the geosynchronous orbit are obviously distinct. TC-1 observations showed that the magnetic intensity kept almost unchanged and the elevation angle decreased,but the Cluster spacecraft,which was also in the plasma sheet and was further from the equator,observed that the magnetic field was obviously enhanced. Simultaneously,GOES-12 located near the midnight observed that the magnetic intensity sharply increased and the elevation angle decreased,but GOES-10 located in the dawn side observed that the magnetic field was merely compressed with its three components all sharply increasing. Furthermore,the energetic proton and electron fluxes at nearly all channels observed by five LANL satellites located at different magnetic local times (MLTs) all showed impulsive enhancements due to the compression of the shock. The responses of the energetic particles were much evident on the dayside than those on the nightside. Especially the responses near the midnight were rather weak. In this paper,the possible reasonable physical explanation to above observations is also discussed. All the shock-induced responses are the joint effects of the solar wind dynamic pressure pulse and the magnetic field southward turning.

  9. Resistive Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection

    Science.gov (United States)

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex

    2010-01-01

    Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten-Lan-van Leer method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfv enic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the "diamond-chain" structure due to multiple shock reflections. Under a uniform resistivity, Sweet-Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.

  10. Resistive Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection

    CERN Document Server

    Zenitani, Seiji; Klimas, Alex

    2010-01-01

    Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten--Lan--van Leer (HLL) method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfv\\'{e}nic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the "diamond--chain" structure due to multiple shock reflections. Under a uniform resistivity, Sweet--Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.

  11. Magnetic reconnection in the presence of sheared flow and density asymmetry: Applications to the Earth's magnetopause

    Science.gov (United States)

    La Belle-Hamer, A. L.; Otto, A.; Lee, L. C.

    1995-01-01

    Classical models of magnetic reconnection consist of a small diffusion region bounded by two symmetric slow shocks, across which the plasma is accelerated. Asymmetries often present in space plasmas are sheared plasma flow and dissimilar plasma densities on the two sides of current sheets. In this paper, we investigate magnetic reconnection in the presence of a shear flow and an asymmetric density across the current sheet using two-dimensional magnetohydrodynamic (MHD) simulations. The results demonstrate that magnetic reconnection can occur only for a plasma flow velocity (in the frame of the X line) which is below the Alfven speed in each inflow region. This limits the velocity of the X line to a certain range for a given flow shear and provides an upper limit to the total velocity shear at which reconnection ceases to operate. Depending on the direction of the flow in the adjacent inflow region, the effects from the sheared flow and from the density asymmetry will compete with or enhance each other in respect to the magnitude and location of the currents which bound the outflow regions. The results are applied to the dayside and flank regions of the magnetosphere. For the dayside region where the magnetosheath flow is slow, the magnetic field transition region is thin and the accelerated flow is earthward of the sharp current layer (magnetopause). At the flanks tailward of the X line, shear flow and density asymmetry effects compete making the magnetic field transition layer broad with the high-speed flow contained within the transition region which explains corresponding observations. At the flanks sunward of the X line, shear flow and density asymmetry effects enhance each other and lead to a strong current sheet on the magnetosheath side of the accelerated flow. The total volume affected by magnetic reconnection is much larger than the steady state region. A large bulge region precedes the steady state region. Qualitatively, the bulge and the steady state

  12. Numerical analysis of the current sheet near a magnetic null line

    Energy Technology Data Exchange (ETDEWEB)

    Brushlinskii, K.V.; Zaborov, A.M.; Syrovatskii, S.I.

    1980-03-01

    A mathematical model is constructed for the two-dimensional MHD plasma flow near a magnetic null line in a perturbing electric field. A numerical study is also carried out. This type of flow is the key element of the reconnection of magnetic lines of force and is being studied in connection with the mechanism for solar flares, the magnetospheres of planes, and certain questions in thermonuclear fusion. The results show that during this flow a nearly steady-state current sheet forms with a characteristic two-dimensional configuration. The sheet has four outgrowths corresponding to slow MHD shock waves. The geometric shape of the sheet and the maximum current in it are determined primarily by the plasma conductivity. The dependence of the sheet properties on the gas pressure is very weak. The thermal conditions in the flow, which are related to the heat conduction and radiation, strongly affect the plasma density distribution on the current sheet.

  13. Particle acceleration with anomalous pitch angle scattering in 2D magnetohydrodynamic reconnection simulations

    Science.gov (United States)

    Borissov, A.; Kontar, E. P.; Threlfall, J.; Neukirch, T.

    2017-09-01

    The conversion of magnetic energy into other forms (such as plasma heating, bulk plasma flows, and non-thermal particles) during solar flares is one of the outstanding open problems in solar physics. It is generally accepted that magnetic reconnection plays a crucial role in these conversion processes. In order to achieve the rapid energy release required in solar flares, an anomalous resistivity, which is orders of magnitude higher than the Spitzer resistivity, is often used in magnetohydrodynamic (MHD) simulations of reconnection in the corona. The origin of Spitzer resistivity is based on Coulomb scattering, which becomes negligible at the high energies achieved by accelerated particles. As a result, simulations of particle acceleration in reconnection events are often performed in the absence of any interaction between accelerated particles and any background plasma. This need not be the case for scattering associated with anomalous resistivity caused by turbulence within solar flares, as the higher resistivity implies an elevated scattering rate. We present results of test particle calculations, with and without pitch angle scattering, subject to fields derived from MHD simulations of two-dimensional (2D) X-point reconnection. Scattering rates proportional to the ratio of the anomalous resistivity to the local Spitzer resistivity, as well as at fixed values, are considered. Pitch angle scattering, which is independent of the anomalous resistivity, causes higher maximum energies in comparison to those obtained without scattering. Scattering rates which are dependent on the local anomalous resistivity tend to produce fewer highly energised particles due to weaker scattering in the separatrices, even though scattering in the current sheet may be stronger when compared to resistivity-independent scattering. Strong scattering also causes an increase in the number of particles exiting the computational box in the reconnection outflow region, as opposed to along the

  14. Relative contributions of terrestrial and solar wind ions in the plasma sheet

    Science.gov (United States)

    Lennartsson, W.; Sharp, R. D.

    A major uncertainty concerning the origins of plasma sheet ions is due to the fact that terrestrial H(+) can have similar fluxes and energies as H(+) from the solar wind. The situation is especially ambiguous during magnetically quiet conditions (AE less than 60 gamma) when H(+) typically contributes more than 90 percent of the plasma sheet ion population. In this study that problem is examined using a large data set obtained by the ISEE-1 Plasma Composition Experiment. The data suggest that one component of the H(+) increases in energy with increasing activity, roughly in proportion to 1/4 the energy of the He(++), whereas the other H(+) component has about the same energy at all activity levels, as do the O(+) and the He(+). If it is assumed that the H(+) of solar wind origin on the average has about the same energy-per-nucleon as the He(++), which is presumably almost entirely from the solar wind, then the data imply that as much as 20-30 percent of the H(+) can be of terrestrial origin even during quiet conditions.

  15. Relative contributions of terrestrial and solar wind ions in the plasma sheet

    Energy Technology Data Exchange (ETDEWEB)

    Lennartsson, W.; Sharp, R.D.

    1985-01-01

    A major uncertainty concerning the origins of plasma sheet ions is due to the fact that terrestrial H(+) can have similar fluxes and energies as H(+) from the solar wind. The situation is especially ambiguous during magnetically quiet conditions (AE less than 60 gamma) when H(+) typically contributes more than 90 percent of the plasma sheet ion population. In this study that problem is examined using a large data set obtained by the ISEE-1 Plasma Composition Experiment. The data suggest that one component of the H(+) increases in energy with increasing activity, roughly in proportion to 1/4 the energy of the He(++), whereas the other H(+) component has about the same energy at all activity levels, as do the O(+) and the He(+). If it is assumed that the H(+) of solar wind origin on the average has about the same energy-per-nucleon as the He(++), which is presumably almost entirely from the solar wind, then the data imply that as much as 20-30 percent of the H(+) can be of terrestrial origin even during quiet conditions.

  16. Survey of 0.1- to 16-keV/e plasma sheet ion composition

    Science.gov (United States)

    Lennartsson, W.; Shelley, E. G.

    1986-03-01

    An analysis is performed of all plasma sheet data collected in 1978-79 in order to discern statistical trends in the data. Attention is focused on the bulk parameters of 0.1-16 keV/e plasma sheet ions detected by the Plasma Composition Experiment on the ISEE 1 satellite. The data were collected at 10-23 earth radii, and are averaged for various levels of activity in the AE index. Solar H(+) and He(2+) ions dominate during quiet periods and possess energies similar to those of the solar wind when the quiet period lasts several hours. Increasing AE index values eventually lead to a replacement of the solar ions with terrestrial ions, particularly O(+), which can have an average energy density of 3-4 keV/e at every activity level. The solar ions, however, increase in energy as their density decreases. The O(+) density is highest near the local midnight and becomes the most numerous during highly disturbed conditions. Finally, the O(+) density was observed to increase by a factor of three over the monitoring period, possibly due to enhanced solar EUV radiation.

  17. Observing the reconnection region in a transequatorial loop system

    Institute of Scientific and Technical Information of China (English)

    Rui Liu; Tong-Jiang Wang; Jeongwoo Lee; Guillermo Stenborg; Chang Liu; Sung-Hong Park; Hai-Min Wang

    2011-01-01

    A vertical current sheet is a crucial element in many flare/coronal mass ejection (CME) models.For the first time,Liu et al.reported a vertical current sheet directly imaged during the flare rising phase with the EUV Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO).As a follow-up study,here we present the comprehensive analysis and detailed physical interpretation of the observation.The current sheet formed due to the gradual rise of a transequatorial loop system.As the loop legs approached each other,plasma flew at ~6 km s-1 into a local area where a cusp-shaped flare loop subsequently formed and the current sheet was seen as a bright,collimated structure of global length (≥ 0.25 R(@)) and macroscopic width ((5-10)× 103 km),extending from 50 Mm above the flaring loop to the border of the EIT field of view (FOV).The reconnection rate in terms of the Alfvén Mach number is estimated to be only 0.005-0.009,albeit a halo CME was accelerated from ~ 400 km s- 1 to ~ 1300 km s- 1 within the coronagraph FOV.Drifting pulsating structures at metric frequencies were recorded during the impulsive phase,implying tearing of the current sheet in the high corona.A radio Type Ⅲ burst occurred when the current sheet was clearly seen in EUV,indicative of accelerated electrons beaming upward from the upper tip of the current sheet.A cusp-shaped dimming region was observed to be located above the post-flare arcade during the decay phase in EIT;both the arcade and the dimming expanded with time.With the Coronal Diagnostic Spectrometer (CDS) aboard SOHO,a clear signature of chromospheric evaporation was seen during the decay phase,i.e.,the cusp-shaped dimming region was associated with plasma upflows detected with EUV hot emission lines,while the post-flare loop was associated with downflows detected with cold lines.This event provides a comprehensive view of the reconnection geometry and dynamics in the solar corona.

  18. Plasma sheet stretching accompanied by field aligned energetic ion fluxes observed by the MUADU instrument aboard TC-2

    Institute of Scientific and Technical Information of China (English)

    Lu Li; S.MCKENNA-LAWLOR; S.BARABASH; LIU ZhenXing; CAO JinBin; J.BALAZ; K.KUDELA; T.L.ZHANG; C.M.CARR

    2007-01-01

    The NUADU(NeUtral Atom Detector Unit)instrument aboard TC-2 recorded 4π solid angle images of charged particles(E>180 keV)spiraling around the magnetic field lines in the near-Earth plasma sheet (at~-7 RE,equatorial dawn-to-night side)during a geomagnetic storm(Dst=-219 nT)on August 24,2005.Energetic ion beam events characterized by symmetrical,ring-like,solid angle distributions around ambient magnetic field lines were observed during a 34-minute traversal of the plasma sheet by the TC-2 spacecraft.Also,observations during these multiple crossings of the plasma sheet were monitored by the magnetometer experiment(FGM)aboard the same spacecraft.During each crossing,a whistler-mode chorus enhancement was observed in the anisotropic area by the TC-2 low frequency electromagnetic wave detector(LFEW/TC-2)at a frequency just above that of the local lower hybrid wave.A comparison of the ion pitch angle distribution(PAD)map with the ambient magnetic field shows that an enhancement in the field aligned energetic ion flux was accompanied by tailward stretching of the magnetic field lines in the plasma sheet.In contrast,the perpendicular ion-flux enhancement was accompanied by a signature indicating the corresponding shrinkage of the magnetic field lines in the plasma sheet.Since both parallel ion-flux and perpendicular ion-flux enhancements occurred intermittently,the data were interpreted to imply a dynamical,oscillatory process of the magnetic field line(stretching and shrinking)in the near-Earth plasma sheet,which might have acted to help establish an interaction region in this area which would support continuous aurora-substorm triggering during the ongoing magnetic storm.The whistler-mode chorus may have been produced due to ion gyro-resonance during particle pitch angle diffusion after the plasma sheet compression.

  19. A magnetic reconnection X-line extending more than 390 Earth radii in the solar wind.

    Science.gov (United States)

    Phan, T D; Gosling, J T; Davis, M S; Skoug, R M; Øieroset, M; Lin, R P; Lepping, R P; McComas, D J; Smith, C W; Reme, H; Balogh, A

    2006-01-12

    Magnetic reconnection in a current sheet converts magnetic energy into particle energy, a process that is important in many laboratory, space and astrophysical contexts. It is not known at present whether reconnection is fundamentally a process that can occur over an extended region in space or whether it is patchy and unpredictable in nature. Frequent reports of small-scale flux ropes and flow channels associated with reconnection in the Earth's magnetosphere raise the possibility that reconnection is intrinsically patchy, with each reconnection X-line (the line along which oppositely directed magnetic field lines reconnect) extending at most a few Earth radii (R(E)), even though the associated current sheets span many tens or hundreds of R(E). Here we report three-spacecraft observations of accelerated flow associated with reconnection in a current sheet embedded in the solar wind flow, where the reconnection X-line extended at least 390R(E) (or 2.5 x 10(6) km). Observations of this and 27 similar events imply that reconnection is fundamentally a large-scale process. Patchy reconnection observed in the Earth's magnetosphere is therefore likely to be a geophysical effect associated with fluctuating boundary conditions, rather than a fundamental property of reconnection. Our observations also reveal, surprisingly, that reconnection can operate in a quasi-steady-state manner even when undriven by the external flow.

  20. Implications of RHESSI Flare Observations for Magnetic Reconnection Models

    Science.gov (United States)

    Holman, Gordon D.; Sui, Linhui; Dennis, Brian R.

    2004-01-01

    The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations of the 2002 April 15 solar flare and related flares provide compelling evidence for the formation of a large-scale, reconnecting current sheet in at least some flares. We describe the observed evolution of the April 15 flare in terms of magnetic reconnection models. We argue that the flare most likely evolved through magnetic geometries associated with super-slow reconnection (early rise phase), fast reconnection (impulsive phase), and slow reconnection (gradual phase). We also provide evidence for X-ray brightenings within the evolving current sheet, possibly induced by the tearing mode instability. This work was supported in part by the RHESSI Program and NASA's Sun-Earth Connection Program. This work would not have been possible without the dedicated efforts of the entire RHESSI team.

  1. Three-dimensional magnetic reconnection through a moving magnetic null

    Directory of Open Access Journals (Sweden)

    V. S. Lukin

    2011-11-01

    Full Text Available A computational study of three-dimensional magnetic reconnection between two flux ropes through a moving reconnection site is presented. The configuration is considered in the context of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and oriented to form a single magnetic field null at its center. The initial magnetic field configuration is embedded into a uniform thermal plasma and is unstable to tilting. As the spheromaks tilt, their magnetic fields begin to reconnect at the null, subsequently displacing both the null and the reconnection site. The motion of the reconnection region and the magnetic null are shown to be correlated, with stronger correlation and faster reconnection observed in plasmas with lower thermal to magnetic pressure ratio. It is also shown that ion inertial effects allow for yet faster reconnection, but do not qualitatively change the dynamics of the process. Implications of the coupling between moving magnetic nulls and reconnection sites, as well as of possible mechanisms for fast reconnection through a moving reconnection region, are discussed. The simulations are conducted using both single-fluid and Hall MHD plasma models within the HiFi multi-fluid modeling framework.

  2. Three-dimensional magnetic reconnection through a moving magnetic null

    Science.gov (United States)

    Lukin, V. S.; Linton, M. G.

    2011-11-01

    A computational study of three-dimensional magnetic reconnection between two flux ropes through a moving reconnection site is presented. The configuration is considered in the context of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and oriented to form a single magnetic field null at its center. The initial magnetic field configuration is embedded into a uniform thermal plasma and is unstable to tilting. As the spheromaks tilt, their magnetic fields begin to reconnect at the null, subsequently displacing both the null and the reconnection site. The motion of the reconnection region and the magnetic null are shown to be correlated, with stronger correlation and faster reconnection observed in plasmas with lower thermal to magnetic pressure ratio. It is also shown that ion inertial effects allow for yet faster reconnection, but do not qualitatively change the dynamics of the process. Implications of the coupling between moving magnetic nulls and reconnection sites, as well as of possible mechanisms for fast reconnection through a moving reconnection region, are discussed. The simulations are conducted using both single-fluid and Hall MHD plasma models within the HiFi multi-fluid modeling framework.

  3. Reconnection experiments including 3D magnetic nulls

    Science.gov (United States)

    Le, A.; Egedal, J.; Vrublevskis, A.

    2010-11-01

    A rich collection of magnetic reconnection scenarios is possible in three dimensions depending on the topological and geometric structure of the magnetic field [1]. In recent experiments at the Versatile Toroidal Facility (VTF) three-dimensional effects were essential even in nearly axisymmetric plasmas with a non-vanishing toroidal field [2]. To explore reconnection in 3D geometries including magnetic null points, a new adjustable set of coils will be installed in the vacuum chamber of VTF. The range of vacuum magnetic field topologies attainable in VTF will be explored numerically. Plasma reconnection experiments will be run in these configurations, and measurements will be presented if available. [4pt] [1] CE Parnell, et al., (2009) ``Three-Dimensional Magnetic Reconnection, in Magnetic Coupling between the Interior and the Atmosphere of the Sun,'' eds. S.S. Hasan and R.J. Rutten, Springer-Verlag, Heidelberg, Berlin. [0ex] [2] Katz, N. et al., (2010) Phys. Rev. Lett. 104, 255004.

  4. Magnetic reconnection events in the interplanetary space

    Institute of Scientific and Technical Information of China (English)

    魏奉思; R.Schwenn; 胡强

    1997-01-01

    Magnetic field and plasma measurements in the period of 1975-1981 with 0. 18-h averages from Helios spacecrafts are analyzed. It is discovered that magnetic reconnection phenomena exist in the interplanetary space. By means of the reconstruction of magnetic field configuration in the azimuth angle plane, it is found that the magnetic reconnection event with time scale of the order of day is a significant form of magnetic reconnection phenomena in the interplanetary space, which consists of a mediate body (or a plasma bulk) and two magnetic separator lines. It could originate from coronal mass ejection event or magnetic cloud in the interplanetary space. Numerical simulation has reproduced the basic characteristics of the magnetic reconnection events.

  5. Reconnection of Magnetic Fields

    Science.gov (United States)

    Birn, J.; Priest, E. R.

    2007-01-01

    Preface; Part I. Introduction: 1.1 The Sun E. R. Priest; 1.2 Earth's magnetosphere J. Birn; Part II. Basic Theory of MHD Reconnection: 2.1 Classical theory of two-dimensional reconnection T. G. Forbes; 2.2 Fundamental concepts G. Hornig; 2.3 Three-dimensional reconnection in the absence of magnetic null points G. Hornig; 2.4 Three-dimensional reconnection at magnetic null points D. Pontin; 2.5 Three-dimensional flux tube reconnection M. Linton; Part III. Basic Theory of Collisionless Reconnection: 3.1 Fundamentals of collisionless reconnection J. Drake; 3.2 Diffusion region physics M. Hesse; 3.3 Onset of magnetic reconnection P. Pritchett; 3.4 Hall-MHD reconnection A. Bhattacharjee and J. Dorelli; 3.5 Role of current-aligned instabilities J. Büchner and W. Daughton; 3.6 Nonthermal particle acceleration M. Hoshino; Part IV. Reconnection in the Magnetosphere: 4.1 Reconnection at the magnetopause: concepts and models J. G. Dorelli and A. Bhattacharjee; 4.2 Observations of magnetopause reconnection K.-H. Trattner; 4.3 On the stability of the magnetotail K. Schindler; 4.4 Simulations of reconnection in the magnetotail J. Birn; 4.5 Observations of tail reconnection W. Baumjohann and R. Nakamura; 4.6 Remote sensing of reconnection M. Freeman; Part V. Reconnection in the Sun's Atmosphere: 5.1 Coronal heating E. R. Priest; 5.2 Separator reconnection D. Longcope; 5.3 Pinching of coronal fields V. Titov; 5.4 Numerical experiments on coronal heating K. Galsgaard; 5.5 Solar flares K. Kusano; 5.6 Particle acceleration in flares: theory T. Neukirch; 5.7 Fast particles in flares: observations L. Fletcher; 6. Open problems J. Birn and E. R. Priest; Bibliography; Index.

  6. Piezoresistive Effect in Plasma-Doping of Graphene Sheet for High-Performance Flexible Pressure Sensing Application.

    Science.gov (United States)

    Haniff, M A S M; Hafiz, S M; Huang, N M; Rahman, S A; Wahid, K A A; Syono, M I; Azid, I A

    2017-05-03

    This paper presents a straightforward plasma treatment modification of graphene with an enhanced piezoresistive effect for the realization of a high-performance pressure sensor. The changes in the graphene in terms of its morphology, structure, chemical composition, and electrical properties after the NH3/Ar plasma treatment were investigated in detail. Through a sufficient plasma treatment condition, our studies demonstrated that plasma-treated graphene sheet exhibits a significant increase in sensitivity by one order of magnitude compared to that of the unmodified graphene sheet. The plasma-doping introduced nitrogen (N) atoms inside the graphene structure and was found to play a significant role in enhancing the pressure sensing performance due to the tunneling behavior from the localized defects. The high sensitivity and good robustness demonstrated by the plasma-treated graphene sensor suggest a promising route for simple, low-cost, and ultrahigh resolution flexible sensors.

  7. Concentration of electrostatic solitary waves around magnetic nulls within magnetic reconnection diffusion region: single-event-based statistics

    Science.gov (United States)

    Li, Shiyou; Zhang, Shifeng; Cai, Hong; Yu, Sufang

    2014-12-01

    It is important to study the `concentrated' electrostatic solitary waves/structures (ESWs) associated with the magnetic reconnection. In the literature published as regards this topic, very few studies have reported the observation of such a large number of ESWs in a single magnetic reconnection event. In this work, we report our observation of a large number of ESWs around the magnetic null-pairs within the magnetic reconnection ion diffusion region of Earth's magnetosphere on 10 September 2001. With more than 9,600 cases of ESWs observed around magnetic null-pairs and more than 97,600 cases observed during the ion diffusion region crossing time span, the observation of such a large number of ESWs in the diffusion region has not been reported often in published works. We further perform single-event-based statistical analysis of the characteristics of the ESWs around magnetic null-pairs. Based on the statistical result, we speculate that the two-stream instability originating from the magnetic null and traveling outward along the plasma sheet boundary layer (PSBL) is the candidate mechanism of the large number of observed ESWs. Our observation and analysis in this work suggests that even with the presence of a complex magnetic structure around a magnetic null-pair in the three-dimensional regime, concentrated ESWs can be observed. This single-reconnection-event-based statistical result of ESWs around the magnetic null-pairs can aid in understanding the microdynamics associated with three-dimensional (3D) magnetic reconnection.

  8. An exact collisionless equilibrium for the Force-Free Harris Sheet with low plasma beta

    Energy Technology Data Exchange (ETDEWEB)

    Allanson, O., E-mail: oliver.allanson@st-andrews.ac.uk; Neukirch, T., E-mail: tn3@st-andrews.ac.uk; Wilson, F., E-mail: fw237@st-andrews.ac.uk; Troscheit, S., E-mail: s.troscheit@st-andrews.ac.uk [School of Mathematics and Statistics, University of St Andrews, St. Andrews, KY16 9SS (United Kingdom)

    2015-10-15

    We present a first discussion and analysis of the physical properties of a new exact collisionless equilibrium for a one-dimensional nonlinear force-free magnetic field, namely, the force-free Harris sheet. The solution allows any value of the plasma beta, and crucially below unity, which previous nonlinear force-free collisionless equilibria could not. The distribution function involves infinite series of Hermite polynomials in the canonical momenta, of which the important mathematical properties of convergence and non-negativity have recently been proven. Plots of the distribution function are presented for the plasma beta modestly below unity, and we compare the shape of the distribution function in two of the velocity directions to a Maxwellian distribution.

  9. An exact collisionless equilibrium for the Force-Free Harris Sheet with low plasma beta

    CERN Document Server

    Allanson, O; Wilson, F; Troscheit, S

    2015-01-01

    We present a first discussion and analysis of the physical properties of a new exact collisionless equilibrium for a one-dimensional nonlinear force-free magnetic field, namely the Force-Free Harris Sheet. The solution allows any value of the plasma beta, and crucially below unity, which previous nonlinear force-free collisionless equilibria could not. The distribution function involves infinite series of Hermite Polynomials in the canonical momenta, of which the important mathematical properties of convergence and non-negativity have recently been proven. Plots of the distribution function are presented for the plasma beta modestly below unity, and we compare the shape of the distribution function in two of the velocity directions to a Maxwellian distribution.

  10. Cluster view of the plasma sheet boundary layer and bursty bulk flow connection

    Directory of Open Access Journals (Sweden)

    O. W. Lennartsson

    2009-04-01

    Full Text Available The high-latitude boundaries of the plasma sheet (PSBL are dynamic latitude zones of recurring and transient (minutes to tens of minutes earthward and magnetic field-aligned bursts of plasma, each being more or less confined in longitude as well, whose ionic component is dominated by protons with flux, energies and density that are consistent with a central plasma sheet (CPS source at varying distance (varying rates of energy time dispersion, sometimes as close as the ~19 RE Cluster apogees, or closer still. The arguably most plausible source consists of so called "bursty bulk flows" (BBFs, i.e. proton bulk flow events with large, positive and bursty GSE vx. Known mainly from CPS observations made at GSE x>−30 RE, the BBF type events probably take place much further downtail as well. What makes the BBFs an especially plausible source are (1 their earthward bulk flow, which helps explain the lack of distinctive latitudinal PSBL energy dispersion, and (2 their association with a transient strong increase of the local tail Bz component ("local dipolarization". The enhanced Bz provides intermittent access to higher latitudes for the CPS plasma, resulting in local density reductions in the tail midplane, as illustrated here by proton data from the Cluster CIS CODIF instruments. Another sign of kinship between the PSBL bursts and the BBFs is their similar spatial fine structure. The PSBL bursts have prominent filaments aligned along the magnetic field with transverse flux gradients that are often characterized by local ~10 keV proton gyroradii scale size (or even smaller, as evidenced by Cluster measurements. The same kind of fine structure is also found during Cluster near-apogee traversals of the tail midplane, as illustrated here and implied by recently published statistics on BBFs obtained with Cluster multipoint observations at varying satellite

  11. Turbulent General Magnetic Reconnection

    CERN Document Server

    Eyink, Gregory L

    2014-01-01

    Plasma flows with an MHD-like turbulent inertial range, such as the solar wind, require a generalization of General Magnetic Reconnection (GMR) theory. We introduce the slip-velocity source vector, which gives the rate of development of slip velocity per unit arc length of field line. The slip source vector is the ratio of the curl of the non ideal electric field in the Generalized Ohm's Law and the magnetic field strength. It diverges at magnetic nulls, unifying GMR with magnetic null-point reconnection. Only under restrictive assumptions is the slip velocity related to the gradient of the quasi potential (integral of parallel electric field along field lines). In a turbulent inertial range the curl becomes extremely large while the parallel component is tiny, so that line slippage occurs even while ideal MHD becomes accurate. The resolution of this paradox is that ideal MHD is valid for a turbulent inertial-range only in a weak sense which does not imply magnetic line freezing. The notion of weak solution i...

  12. The island coalescence problem: scaling of reconnection in extended fluid models including higher-order moments

    CERN Document Server

    Ng, Jonathan; Hakim, Ammar; Bhattacharjee, Amitava; Stanier, Adam; Daughton, William; Wang, Liang; Germaschewski, Kai

    2015-01-01

    As modeling of collisionless magnetic reconnection in most space plasmas with realistic parameters is beyond the capability of today's simulations, due to the separation between global and kinetic length scales, it is important to establish scaling relations in model problems so as to extrapolate to realistic scales. Recently, large scale particle-in-cell (PIC) simulations of island coalescence have shown that the time averaged reconnection rate decreases with system size, while fluid systems at such large scales in the Hall regime have not been studied. Here we perform the complementary resistive MHD, Hall MHD and two fluid simulations using a ten-moment model with the same geometry. In contrast to the standard Harris sheet reconnection problem, Hall MHD is insufficient to capture the physics of the reconnection region. Additionally, motivated by the results of a recent set of hybrid simulations which show the importance of ion kinetics in this geometry, we evaluate the efficacy of the ten-moment model in re...

  13. The island coalescence problem: Scaling of reconnection in extended fluid models including higher-order moments

    Energy Technology Data Exchange (ETDEWEB)

    Ng, Jonathan; Huang, Yi-Min; Hakim, Ammar; Bhattacharjee, A. [Center for Heliophysics, Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540 (United States); Stanier, Adam; Daughton, William [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Wang, Liang; Germaschewski, Kai [Space Science Center and Physics Department, University of New Hampshire, Durham, New Hampshire 03824 (United States)

    2015-11-15

    As modeling of collisionless magnetic reconnection in most space plasmas with realistic parameters is beyond the capability of today's simulations, due to the separation between global and kinetic length scales, it is important to establish scaling relations in model problems so as to extrapolate to realistic scales. Recently, large scale particle-in-cell simulations of island coalescence have shown that the time averaged reconnection rate decreases with system size, while fluid systems at such large scales in the Hall regime have not been studied. Here, we perform the complementary resistive magnetohydrodynamic (MHD), Hall MHD, and two fluid simulations using a ten-moment model with the same geometry. In contrast to the standard Harris sheet reconnection problem, Hall MHD is insufficient to capture the physics of the reconnection region. Additionally, motivated by the results of a recent set of hybrid simulations which show the importance of ion kinetics in this geometry, we evaluate the efficacy of the ten-moment model in reproducing such results.

  14. Microfabrication of through holes in polydimethylsiloxane (PDMS) sheets using a laser plasma EUV source (Conference Presentation)

    Science.gov (United States)

    Makimura, Tetsuya; Urai, Hikari; Niino, Hiroyuki

    2017-03-01

    Polydimethylsiloxane (PDMS) is a material used for cell culture substrates / bio-chips and micro total analysis systems / lab-on-chips due to its flexibility, chemical / thermo-dynamic stability, bio-compatibility, transparency and moldability. For further development, it is inevitable to develop a technique to fabricate precise three dimensional structures on micrometer-scale at high aspect ratio. In the previous works, we reported a technique for high-quality micromachining of PDMS without chemical modification, by means of photo direct machining using laser plasma EUV sources. In the present work, we have investigated fabrication of through holes. The EUV radiations around 10 nm were generated by irradiation of Ta targets with Nd:YAG laser light (10 ns, 500 mJ/pulse). The generated EUV radiations were focused using an ellipsoidal mirror. It has a narrower incident angle than those in the previous works in order to form a EUV beam with higher directivity, so that higher aspect structures can be fabricated. The focused EUV beam was incident on PDMS sheets with a thickness of 15 micrometers, through holes in a contact mask placed on top of them. Using a contact mask with holes with a diameter of three micrometers, complete through holes with a diameter of two micrometers are fabricated in the PDMS sheet. Using a contact mask with two micrometer holes, however, ablation holes almost reaches to the back side of the PDMS sheet. The fabricated structures can be explained in terms of geometrical optics. Thus, we have developed a technique for micromachining of PDMS sheets at high aspect ratios.

  15. Clusters of small eruptive flares produced by magnetic reconnection in the sun

    CERN Document Server

    Archontis, V

    2015-01-01

    We report on the formation of small solar flares produced by patchy magnetic reconnection between interacting magnetic loops. A three-dimensional (3D) magnetohydrodynamic (MHD) numerical experiment was performed, where a uniform magnetic flux sheet was injected into a fully developed convective layer. The gradual emergence of the field into the solar atmosphere results in a network of magnetic loops, which interact dynamically forming current layers at their interfaces. The formation and ejection of plasmoids out of the current layers leads to patchy reconnection and the spontaneous formation of several small (size ? 1-2Mm) flares. We find that these flares are short-lived (30 s - 3 min) bursts of energy in the range O(10^25 - 10^27) ergs, which is basically the nanoflare-microflare range. Their persistent formation and co-operative action and evolution leads to recurrent emission of fast EUV/X-ray jets and considerable plasma heating in the active corona.

  16. Spontaneous non-steady magnetic reconnection within the solar environment

    CERN Document Server

    Bettarini, Lapo

    2009-01-01

    This work presents a 2.5-dimensional simulation study of the instability of current-sheets located in a medium with a strong density variation along the current layer. The initial force-free configuration is observed to undergo a two-stage evolution consisting of an abrupt regime transition from a slow to a fast reconnection process leading the system to a final chaotic configuration. Yet, the onset of the fast phase is not determined by the presence of any anomalous enhancement in plasma's local resistivity, but rather is the result of a new mechanism discovered in Lapenta (2008)* and captured only when sufficient resolution is present. Hence, the effects of the global resistivity, the global viscosity and the plasma beta on the overall dynamics are considered. This mechanism allowing the transition from slow to fast reconnection provides a simple but effective model of several processes taking place within the solar atmosphere from the high chromosphere up to the low corona. In fact, the understanding of a ...

  17. Turbulent transport in 2D collisionless guide field reconnection

    CERN Document Server

    Muñoz, P A; Kilian, P

    2016-01-01

    Transport in collisionless plasmas is usually called anomalous, being due to the interaction between the particles and the self-generated turbulence by their collective interactions. Because of its relevance for astrophysical and space plasmas, we explore the excitation of turbulence in current sheets prone to component- or guide-field reconnection, a process not well understood, yet. We analyze the anomalous transport properties by using 2.5D Particle-in-Cell (PiC) code simulations. We split off the mean, slow variation (in contrast to the fast turbulent fluctuations) of the macroscopic observables and determine the main transport terms of the generalized Ohm's law. We verify our findings by comparing with the independently determined slowing-down rate of the macroscopic currents and with the transport terms obtained by the first order correlations of the turbulent fluctuations. We find that the turbulence is most intense in the "low density" separatrix region of guide-field reconnection. It is excited by st...

  18. Multiple harmonic ULF waves in the plasma sheet boundary layer observed by Cluster

    Science.gov (United States)

    Engebretson, M. J.; Kahlstorf, C. R. G.; Posch, J. L.; Keiling, A.; Walsh, A. P.; Denton, R. E.; Broughton, M. C.; Owen, C. J.; FornaçOn, K.-H.; RèMe, H.

    2010-12-01

    The passage of the Cluster satellites in a polar orbit through Earth's magnetotail has provided numerous observations of harmonically related Pc 1-2 ULF wave events, with the fundamental near the local proton cyclotron frequency Ωcp. Broughton et al. (2008) reported observations by Cluster of three such events in the plasma sheet boundary layer, and used the wave telescope technique to determine that their wave vectors k were nearly perpendicular to B. This paper reports the results of a search for such waves throughout the 2003 Cluster tail passage. During the 4 month period of July-October 2003, 35 multiple-harmonic wave events were observed, all in the plasma sheet boundary layer (PSBL). From the first observed event (22 July) to the last (28 October), 13 of Cluster's 42 tail passes had at least one event. The wave events were rather evenly distributed from XGSE = -7 RE out to the Cluster apogee distance of -18 RE, with one event observed at -4 RE. ZGSE for these events ranged from -10 to -3 RE and +3 to +7 RE (i.e., there were no events for ∣Z∣ elevated fluxes of counterstreaming ions with energies ranging from ˜3 to 30 keV, and elevated fluxes of electrons with energies ranging from 0.25 to ˜5 keV. Analysis of plasma parameters suggests that although waves occurred only when the ion beta exceeded 0.1 (somewhat larger than typical for the PSBL), ion particle pressure may be of more physical importance in controlling wave occurrence. Electron distributions were more isotropic in pitch angles than the ion distributions, but some evidence of counterstreaming electrons was detected in 83% of the events. The ions also showed clear signatures of shell-like or ring-like distributions; i.e., with reduced fluxes below the energy of maximum flux. The suprathermal ion fluxes were asymmetric in all events studied, with more ions streaming earthward (for events both north and south of the central plasma sheet). Good agreement between the observed frequency of the

  19. Continuous magnetic reconnection at Earth's magnetopause.

    Science.gov (United States)

    Frey, H U; Phan, T D; Fuselier, S A; Mende, S B

    2003-12-04

    The most important process that allows solar-wind plasma to cross the magnetopause and enter Earth's magnetosphere is the merging between solar-wind and terrestrial magnetic fields of opposite sense-magnetic reconnection. It is at present not known whether reconnection can happen in a continuous fashion or whether it is always intermittent. Solar flares and magnetospheric substorms--two phenomena believed to be initiated by reconnection--are highly burst-like occurrences, raising the possibility that the reconnection process is intrinsically intermittent, storing and releasing magnetic energy in an explosive and uncontrolled manner. Here we show that reconnection at Earth's high-latitude magnetopause is driven directly by the solar wind, and can be continuous and even quasi-steady over an extended period of time. The dayside proton auroral spot in the ionosphere--the remote signature of high-latitude magnetopause reconnection--is present continuously for many hours. We infer that reconnection is not intrinsically intermittent; its steadiness depends on the way that the process is driven.

  20. Magnetic reconnection as an element of turbulence

    Directory of Open Access Journals (Sweden)

    S. Servidio

    2011-10-01

    Full Text Available In this work, recent advances on the study of reconnection in turbulence are reviewed. Using direct numerical simulations of decaying incompressible two-dimensional magnetohydrodynamics (MHD, it was found that in fully developed turbulence complex processes of reconnection locally occur (Servidio et al., 2009, 2010a. In this complex scenario, reconnection is spontaneous but locally driven by the fields, with the boundary conditions provided by the turbulence. Matching classical turbulence analysis with a generalized Sweet-Parker theory, the statistical features of these multiple-reconnection events have been identified. A discussion on the accuracy of our algorithms is provided, highlighting the necessity of adequate spatial resolution. Applications to the study of solar wind discontinuities are reviewed, comparing simulations to spacecraft observations. New results are shown, studying the time evolution of these local reconnection events. A preliminary study on the comparison between MHD and Hall MHD is reported. Our new approach to the study of reconnection as an element of turbulence has broad applications to space plasmas, shedding a new light on the study of magnetic reconnection in nature.

  1. Evolutions of nonsteady state magnetic reconnection

    Energy Technology Data Exchange (ETDEWEB)

    Wan, Weigang [Los Alamos National Laboratory; Lapenta, Giovanni [KATHOLIEKE UNIV

    2008-01-01

    The full evolutions of collisionless non-steady-state magnetic reconnection are studied with full kinetic particle-in-cell simulations. There are different stages of reconnection: the onset or early growing stage when the out-of-plane electric field (Ey) structure is a monopole at the X-point, the bipolar stage when the Ey structure is bipolar and the outer electron diffusion region (EDR) is being elongated over time, and the possible final steady-state stage when E{sub y} is uniform in the reconnection plane. We find the change of reconnection rate is not empowered or dependent on the length of the EDR. During the early growing stage, the EDR is elongated while the reconnection rate is growing. During the later stage, the reconnection rate may significantly decrease but the length of the inner EDR is largely stable. The results indicate that reconnection is not controlled by the downstream physics, but rather by the availability of plasma inflows from upstream. The physical mechanism of the EDR elongation is studied. The Hall current induced by the quadrupole magnetic field (B{sub y}) is discovered to play an important role in this process. The condition of forming an extended electron super-Alfvenic outflow jet structure in nature is discussed. The jet structure could be elongated during the bipolar stage, and remains stable during steady state. The sufficiency of the electron inflow is crucial for the elongation. Open boundary conditions are applied in the outflow direction.

  2. Restructured graphene sheets embedded carbon film by oxygen plasma etching and its tribological properties

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Meiling [Key Laboratory of Education Ministry for Modern Design and Rotor-Bearing System, School of Mechanical Engineering, Xi’an Jiaotong University, Xi’an 710049 (China); Diao, Dongfeng, E-mail: dfdiao@szu.edu.cn [Institute of Nanosurface Science and Engineering (INSE), Shenzhen University, Shenzhen 518060 (China); Yang, Lei [Key Laboratory of Education Ministry for Modern Design and Rotor-Bearing System, School of Mechanical Engineering, Xi’an Jiaotong University, Xi’an 710049 (China); Fan, Xue [Institute of Nanosurface Science and Engineering (INSE), Shenzhen University, Shenzhen 518060 (China)

    2015-12-01

    Highlights: • Oxygen plasma etching was developed to improve tribological properties of GSEC film. • Etching restructured 3 nm top layer with smaller crystallite size and higher sp{sup 3} fraction. • The etched film had smoother surface, enhanced mechanical properties, longer wear life. • High electrical conductivity and strong magnetism were retained after etching. - Abstract: An oxygen plasma etching technique was introduced for improving the tribological properties of the graphene sheets embedded carbon (GSEC) film in electron cyclotron resonance plasma processing system. The nanostructural changing in the film caused by oxygen plasma etching was examined by transmission electron microscope, Raman spectroscopy and X-ray photoelectron spectroscopy, showing that the 3 nm thick top surface layer was restructured with smaller graphene nanocrystallite size as well as higher sp{sup 3} bond fraction. The surface roughness, mechanical behavior and tribological properties of the original GSEC and oxygen plasma treated GSEC films were compared. The results indicated that after the oxygen plasma treatment, the average roughness decreased from 20.8 ± 1.1 nm to 1.9 ± 0.1 nm, the hardness increased from 2.3 ± 0.1 GPa to 2.9 ± 0.1 GPa, the nanoscratch depth decreased from 64.5 ± 5.4 nm to 9.9 ± 0.9 nm, and the wear life increased from 930 ± 390 cycles to more than 15,000 frictional cycles. The origin of the improved tribological behavior was ascribed to the 3 nm thick graphene nanocrystallite film. This finding can be expected for wide applications in nanoscale surface engineering.

  3. Streaming energetic electrons in earth's magnetotail - Evidence for substorm-associated magnetic reconnection

    Science.gov (United States)

    Bieber, J. W.; Stone, E. C.

    1980-01-01

    This letter reports the results of a systematic study of streaming greater than 200 keV electrons observed in the magnetotail with the Caltech Electron/Isotope Spectrometers aboard IMP-7 and IMP-8. A clear statistical association of streaming events with southward magnetic fields, often of steep inclination, and with substorms as evidenced by the AE index is demonstrated. These results support the interpretation that streaming energetic electrons are indicative of substorm-associated magnetic reconnection in the near-earth plasma sheet.

  4. Optimized H{sup -} extraction in an argon-magnesium seeded magnetized sheet plasma

    Energy Technology Data Exchange (ETDEWEB)

    Noguera, Virginia R. [Plasma Physics Laboratory, National Institute of Physics, University of the Philippines, Diliman, Quezon City 1101 (Philippines)], E-mail: virginia.noguera@gmail.com; Blantocas, Gene Q. [Plasma Physics Laboratory, National Institute of Physics, University of the Philippines, Diliman, Quezon City 1101 (Philippines); West Visayas State University, Lapaz, Iloilo City 5000 (Philippines); Ramos, Henry J. [Plasma Physics Laboratory, National Institute of Physics, University of the Philippines, Diliman, Quezon City 1101 (Philippines)

    2008-06-15

    The enhancement and optimization of H{sup -} extraction through argon and magnesium seeding of hydrogen discharges in a magnetized sheet plasma source are reported. The paper first presents the modification of the production chamber into a hexapole multicusp configuration resulting in decreased power requirements, improved plasma confinement and longer filament lifetime. By this, a wider choice of discharge currents for sustained quiescent plasmas is made possible. Second, the method of adding argon to the hydrogen plasma similar to the scheme in Abate and Ramos [Y. Abate, H. Ramos, Rev. Sci. Instr. 71 (10) (2000) 3689] was performed to find the optimum conditions for H{sup -} formation and extraction. Using an E x B probe, H{sup -} yields were investigated at varied argon-hydrogen admixtures, different discharge currents and spatial points relative to the core plasma. The optimum H{sup -} current density extracted at 3.0 cm from the plasma core using 3.0 A plasma current with 10% argon seeding increased by a factor of 2.42 (0.63 A/m{sup 2}) compared to the measurement of Abate and Ramos [Y. Abate, H. Ramos, Rev. Sci. Instr. 71 (10) (2000) 3689]. Third, the argon-hydrogen plasma at the extraction chamber is seeded with magnesium. Mg disk with an effective area of 22 cm{sup 2} is placed at the extraction region's anode biased 175 V with respect to the cathode. With Mg seeding, the optimum H{sup -} current density at the same site and discharge conditions increased by 4.9 times (3.09 A/m{sup 2}). The enhancement effects were analyzed vis-a-vis information gathered from the usual Langmuir probe (electron temperature and density), electron energy distribution function (EEDF) and the ensuing dissociative attachment (DA) reaction rates at different spatial points for various plasma discharges and gas ratios. Investigations on the changes in the effective electron temperature and electron density indicate that the enhancement is due to increased density of low

  5. Dynamo-driven plasmoid formation from a current-sheet instability

    CERN Document Server

    Ebrahimi, F

    2016-01-01

    Axisymmetric current-carrying plasmoids are formed in the presence of nonaxisymmetric fluctuations during nonlinear three-dimensional resistive MHD simulations in a global toroidal geometry. We utilize the helicity injection technique to form an initial poloidal flux in the presence of a toroidal guide field. As helicity is injected, two types of current sheets are formed from 1) the oppositely directed field lines in the injector region (primary reconnecting current sheet), and 2) the poloidal flux compression near the plasma edge (edge current sheet). We first find that nonaxisymmetic fluctuations arising from the current-sheet instability isolated near the plasma edge have tearing parity but can nevertheless grow fast (on the poloidal Alfven time scale). These modes saturate by breaking up the current sheet. Second, for the first time a dynamo poloidal flux amplification is observed at the reconnetion site (in the region of the oppositely directed magnetic field). This fluctuation-induced flux amplificatio...

  6. Test particle acceleration in torsional fan reconnection

    Science.gov (United States)

    Hosseinpour, M.

    2014-12-01

    Magnetic reconnection is understood to be a potential mechanism for particle acceleration in astrophysical and space plasmas, especially in solar flares. Torsional fan reconnection is one of the proposed mechanisms for steady-state three-dimensional (3D) magnetic reconnection. By using the magnetic and electric fields for `torsional fan reconnection', the features of test particle acceleration with input parameters for the solar corona are investigated numerically. We show that torsional fan reconnection is potentially an efficient particle accelerator and a proton can gain up to tens of MeV of kinetic energy within only a few milliseconds. Although the final kinetic energy of the accelerated particle depends on the injection position but there exists only one scenario for the particle's trajectory with different initial positions in which the particle is accelerated on the fan plane. Moreover, adopting either spatially uniform or non-uniform localized plasma resistivity does not much influence the features of trajectory. These results are compared with those of torsional spine reconnection.

  7. Evidence for reconnection at Saturn's magnetopause

    Science.gov (United States)

    McAndrews, H. J.; Owen, C. J.; Thomsen, M. F.; Lavraud, B.; Coates, A. J.; Dougherty, M. K.; Young, D. T.

    2008-04-01

    Observations of Saturn's magnetopause by the Cassini Plasma Spectrometer (CAPS) and magnetometer have revealed clear instances of magnetic reconnection signatures, two of which are described here. Both encounters occurred at the equator in the prenoon sector as Cassini was exiting the magnetosphere. Evidence of heating in the electrons and ions is highly suggestive of energization comparable to that associated with the reconnection process at Earth. In one case, the fields are strongly antiparallel and the magnetic data indicate the presence of a locally open magnetic field. In the other example, magnetic data indicate a locally closed magnetic field compatible with the field lines being locally parallel, but the particle signatures lead to the conclusion of a distant reconnection site poleward of the cusps being active. The reconnection voltage for the first case is calculated to be 48 kV, which is of the same order as previous estimates at Saturn. This is lower than the corotational voltage but is not insignificant.

  8. Anisotropic Equilibrium and Ballooning Mode Analysis in the Tail Plasma Sheet.

    Science.gov (United States)

    Lee, Dae-Young

    This thesis is a theoretical study about the Earth's tail plasma sheet with regard to two aspects: the equilibrium structure for the anisotropic pressure, and the ideal-MHD ballooning stability. By adopting a stretched magnetotail model where ion motions are generally nonadiabatic, and assuming that the anisotropy resides only in the electron pressure tensor, it is shown that the magnetic field lines with rm p_| > p_| are less stretched than the isotropic cases. As the parallel pressure p_| exceeds the perpendicular pressure p_| approaching the conventional marginal firehose limit, rm p_| = p{_ |} + B^2/ mu_0, the magnetic field lines are more and more stretched. It is also shown that the current density is highly enhanced at the same limit, a situation that might be subject to a microscopic instability. However, we also emphasize that such an enhancement in the current density is heavily localized near the z = 0 plane, and thus it is unclear if such a microscopic instability can significantly alter the global configuration of the tail. It is further argued, in terms of the radius of the field curvature versus the particle's gyroradius, that the conventional adiabatic description of electrons may become questionable, very close to the conventional marginal firehose limit. To study the ideal-MHD ballooning mode, we first adopt a hard ionospheric boundary condition where the perturbation is required to vanish at the ionospheric foot points. For such a hard boundary condition, an "untypical" magnetic field configuration is found to be unstable to a ballooning mode that is antisymmetric about the equatorial plane while most of the "typical" tail plasma-sheet configurations are stable against the ideal-MHD ballooning mode. The unstable magnetic field model, however, does not look like the average observation-based model, but rather resembles some of the characteristics of the steady-state magnetic field models by Hau (1989, 1991). In addition, a physical argument is

  9. Influence of the initial parameters of the magnetic field and plasma on the spatial structure of the electric current and electron density in current sheets formed in helium

    Energy Technology Data Exchange (ETDEWEB)

    Ostrovskaya, G. V., E-mail: galya-ostr@mail.ru [Russian Academy of Sciences, Ioffe Physical Technical Institute (Russian Federation); Markov, V. S.; Frank, A. G., E-mail: annfrank@fpl.gpi.ru [Russian Academy of Sciences, Prokhorov General Physics Institute (Russian Federation)

    2016-01-15

    The influence of the initial parameters of the magnetic field and plasma on the spatial structure of the electric current and electron density in current sheets formed in helium plasma in 2D and 3D magnetic configurations with X-type singular lines is studied by the methods of holographic interferometry and magnetic measurements. Significant differences in the structures of plasma and current sheets formed at close parameters of the initial plasma and similar configurations of the initial magnetic fields are revealed.

  10. Generation of Electric Field and Net Charge in Hall Reconnection

    Institute of Scientific and Technical Information of China (English)

    MA Zhi-Wei; FENG Shu-Ling

    2008-01-01

    @@ Generation of Hall electric field and net charge associated with magnetic reconnection is studied under different initial conditions of plasma density and magnetic field. With inclusion of the Hall effects, decoupling of the electron and ion motions leads to the formation of a narrow layer with strong electric field and large net charge density along the separatrix. The asymmetry of the plasma density or magnetic field or both across the current sheet will largely increase the magnitude of the electric field and net charge. The results indicate that the asymmetry of the magnetic field is more effective in producing larger electric field and charge density. The electric field and net charge are always much larger in the low density or/and high magnetic field side than those in the high density or/and low magnetic field side. Both the electric field and net charge density are linearly dependent on the ratios of the plasma density or the square of the magnetic field across the current sheet. For the case with both initial asymmetries of the magnetic field and density, rather large Hall electric field and charge density are generated.

  11. ISEE-3 observations of a viscously-driven plasma sheet: magnetosheath mass and/or momentum transfer?

    Directory of Open Access Journals (Sweden)

    R. T. Mist

    Full Text Available A statistical analysis of data from the ISEE-3 distant tail campaign is presented. We investigate the mechanism driving slow, tailward flows observed in the plasma sheet. The possibility that these slow flows are driven by mass and/or momentum transfer across the distant tail magnetopause is explored. We establish that 40% of these flows could be driven by the transfer of approximately 4% of the magnetosheath momentum flux into the magnetotail. Current understanding of the Kelvin-Helmholtz instability suggests that this figure is consistent with the amount of momentum flux transfer produced by this mechanism. We also consider the possibility that these flows are solely driven by transferring magnetosheath plasma across the magnetopause. We find that there is sufficient mass observed on these field lines for this to be the sole driving mechanism for only 27% of the observed slow flows.

    Key words. Magnetospheric physics (magnetotail boundary layers; plasma convection; plasma sheet

  12. A computational model for He{sup +} ions in a magnetized sheet plasma: comparative analysis between model and experimental data

    Energy Technology Data Exchange (ETDEWEB)

    Blantocas, Gene Q. [West Visayas State Univ., Lapaz, Iloilo City (Philippines); Ramos, Henry J. [Univ. of the Phillippines, College of Science, National Inst. of Physics, Deliman Quezon City (Philippines); Wada, Motoi [Doshisha Univ., Dept. of Engineering, Kyoto (Japan)

    2003-07-01

    An E x B probe was used to extract He{sup +} ions from a magnetized steady sheet plasma. Plasma parameters T{sub e}, n{sub e} and extracted He{sup +} ion current were analyzed vis-a-vis a modified Saha population density equation of the collisional-radiative model. Numerical calculations show that at low discharge currents and in the hot electron region of the sheet plasma, relative densities of He{sup +} ions show some degree of correlation with ion current profiles established experimentally using the E x B probe. Both experimental and computational results indicate a division of the plasma into two distinct regions each with different formation mechanisms of He{sup +} ions. (author)

  13. Ion and electron heating characteristics of magnetic reconnection in a two flux loop merging experiment.

    Science.gov (United States)

    Ono, Y; Tanabe, H; Hayashi, Y; Ii, T; Narushima, Y; Yamada, T; Inomoto, M; Cheng, C Z

    2011-10-28

    Characteristics of the high-power reconnection heating were measured for the first time directly by two-dimensional measurements of ion and electron temperatures. While electrons are heated mainly inside the current sheet by the Ohmic heating power, ions are heated mainly by fast shock or viscosity damping of the reconnection outflow in the two downstream areas. The magnetic reconnection converts the energy of reconnecting magnetic field B(p) mostly to the ion thermal energy, indicating that the reconnection heating energy is proportional to B(p)(2).

  14. Onset and Evolution of Magnetic Reconnection in Line-Tied Systems

    Science.gov (United States)

    Daughton, W. S.; Akcay, C.; Billey, Z.; Finn, J.; Zweibel, E.; Gekelman, W. N.

    2014-12-01

    In space and astrophysical plasmas, current sheets arise spontaneously from the interaction of large-scale flows or magnetic structures. As these current layers approach kinetic scales, they may become unstable to the collisionless tearing instability, resulting in the formation and interaction of magnetic flux ropes. While theoretical treatments of the tearing instability have largely focused on 1D equilibria with periodic boundary conditions, current sheets in nature have a finite spatial extent and are embedded within larger open systems. In many applications, the field boundary conditions are line-tied as in the case of flux ropes on the dayside magnetopause where the ionosphere acts as a conducting surface. To assess the applicability of existing tearing theory to these more realistic configurations, we consider a series of 3D kinetic simulations of initially force-free current layers with line-tied boundary conditions for the fields, and open boundaries for the particles. The geometry and plasma parameters are motivated by a new laboratory experiment on the Large Plasma Device at UCLA. For sufficiently long systems, we demonstrate that key aspects of the theory remain valid, and a threshold condition is derived for the onset of reconnection in line-tied systems. To gain additional insight into the nonlinear evolution, field-line mapping diagnostics are employed to characterize the 3D structure of the magnetic field, the nonlinear reconnection rate and the dominant non-ideal terms in the generalized Ohm's law.

  15. Particle Acceleration and Heating by Turbulent Reconnection

    Science.gov (United States)

    Vlahos, Loukas; Pisokas, Theophilos; Isliker, Heinz; Tsiolis, Vassilis; Anastasiadis, Anastasios

    2016-08-01

    Turbulent flows in the solar wind, large-scale current sheets, multiple current sheets, and shock waves lead to the formation of environments in which a dense network of current sheets is established and sustains “turbulent reconnection.” We constructed a 2D grid on which a number of randomly chosen grid points are acting as scatterers (i.e., magnetic clouds or current sheets). Our goal is to examine how test particles respond inside this large-scale collection of scatterers. We study the energy gain of individual particles, the evolution of their energy distribution, and their escape time distribution. We have developed a new method to estimate the transport coefficients from the dynamics of the interaction of the particles with the scatterers. Replacing the “magnetic clouds” with current sheets, we have proven that the energization processes can be more efficient depending on the strength of the effective electric fields inside the current sheets and their statistical properties. Using the estimated transport coefficients and solving the Fokker-Planck (FP) equation, we can recover the energy distribution of the particles only for the stochastic Fermi process. We have shown that the evolution of the particles inside a turbulent reconnecting volume is not a solution of the FP equation, since the interaction of the particles with the current sheets is “anomalous,” in contrast to the case of the second-order Fermi process.

  16. Origin of low proton-to-electron temperature ratio in the Earth's plasma sheet

    Science.gov (United States)

    Grigorenko, E. E.; Kronberg, E. A.; Daly, P. W.; Ganushkina, N. Yu.; Lavraud, B.; Sauvaud, J.-A.; Zelenyi, L. M.

    2016-10-01

    We study the proton-to-electron temperature ratio (Tp/Te) in the plasma sheet (PS) of the Earth's magnetotail using 5 years of Cluster observations (2001-2005). The PS intervals are searched within a region defined with -19 GSM) under the condition |BX| ≤ 10 nT. One hundred sixty PS crossings are identified. We find an average value of 6.0. However, in many PS intervals Tp/Te varies over a wide range from a few units to several tens of units. In 86 PS intervals the Tp/Te decreases below 3.5. Generally, the decreases of Tp/Te are due to some increase of Te while Tp either decreases or remains unchanged. In the majority of these intervals the Tp/Te drops are observed during magnetotail dipolarizations. A superposed epoch analysis applied to these events shows that the minimum value of Tp/Te is observed after the dipolarization onset during the "turbulent phase" of dipolarization, when a number of transient BZ pulses are reduced, but the value of BZ is still large and an intensification of wave activity is observed. The Tp/Te drops, and associated increases of Te often coincide either with bursts of broadband electrostatic emissions, which may include electron cyclotron harmonics, or with broadband electromagnetic emission in a frequency range from proton plasma frequency (fpp) up to the electron gyrofrequency (fce). These findings show that the wave activity developing in the current sheet after dipolarization onset may play a role in the additional electron heating and the associated Tp/Te decrease.

  17. Fast Collisionless Reconnection Condition and Self-Organization of Solar Coronal Heating

    CERN Document Server

    Uzdensky, Dmitri A

    2007-01-01

    I propose that solar coronal heating is a self-regulating process that keeps the coronal plasma roughly marginally collisionless. The self-regulating mechanism is based on the interplay of two effects. First, plasma density controls coronal energy release via the transition between the slow collisional Sweet--Parker regime and the fast collisionless reconnection regime. This transition takes place when the Sweet--Parker layer becomes thinner than the characteristic collisionless reconnection scale. I present a simple criterion for this transition in terms of the upstream plasma density and magnetic field and the global length of the reconnection layer. Second, coronal energy release by reconnection raises the ambient plasma density via chromospheric evaporation and this, in turn, temporarily inhibits subsequent reconnection involving the newly-reconnected loops. Over time, however, radiative cooling gradually lowers the density again below the critical value and fast reconnection again becomes possible. As a ...

  18. Magnetic reconnection in two-dimensional magnetohydrodynamic turbulence.

    Science.gov (United States)

    Servidio, S; Matthaeus, W H; Shay, M A; Cassak, P A; Dmitruk, P

    2009-03-20

    Systematic analysis of numerical simulations of two-dimensional magnetohydrodynamic turbulence reveals the presence of a large number of X-type neutral points where magnetic reconnection occurs. We examine the statistical properties of this ensemble of reconnection events that are spontaneously generated by turbulence. The associated reconnection rates are distributed over a wide range of values and scales with the geometry of the diffusion region. Locally, these events can be described through a variant of the Sweet-Parker model, in which the parameters are externally controlled by turbulence. This new perspective on reconnection is relevant in space and astrophysical contexts, where plasma is generally in a fully turbulent regime.

  19. Electron self-reinforcing process of magnetic reconnection.

    Science.gov (United States)

    Wan, Weigang; Lapenta, Giovanni

    2008-07-04

    The growth of collisionless magnetic reconnection is discovered to be a nonlinear electron self-reinforcing process. Accelerated by the reconnection electric field, the small portion of energetic electrons in the vicinity of the X point are found to be the cause of the fast reconnection rate. This new mechanism explains that recent simulation results of different reconnection evolutions (i.e., steady state, quasisteady state, or nonsteady state) are essentially determined by the availability of feeding plasma inflows. Simulations are carried out with open boundary conditions.

  20. Long-term variations in the plasma sheet ion composition and substorm occurrence over 23 years

    Science.gov (United States)

    Nosé, Masahito

    2016-12-01

    The Geotail satellite has been operating for almost two solar cycles (~23 years) since its launch in July 1992. The satellite carries the energetic particle and ion composition (EPIC) instrument that measures the energetic ion flux (9.4-212 keV/e) and enables the investigation of long-term variations of the ion composition in the plasma sheet for solar cycles 22-24. From the statistical analysis of the EPIC data, we find that (1) the plasma ion mass ( M) is approximately 1.1 amu during the solar minimum, whereas it increases to 1.5-2.7 amu during the solar maximum; (2) the increases in M seem to have two components: a raising of the baseline levels (~1.5 amu) and a large transient enhancement (~1.8-2.7 amu); (3) the baseline level change of M correlates well with the Mg II index, which is a good proxy for the solar extreme ultraviolet (EUV) or far ultraviolet (FUV) irradiance; and (4) the large transient enhancement of M is caused by strong magnetic storms. We also study the long-term variations of substorm occurrences in 1992-2015 that are evaluated with the number of Pi2 pulsations detected at the Kakioka observatory. The results suggest no clear correlation between the substorm occurrence and the Mg II index. Instead, when the substorms are classified into externally triggered events and non-triggered events, the number of the non-triggered events and the Mg II index are negatively correlated. We interpret these results that the increase in the solar EUV/FUV radiation enhances the supply of ionospheric ions (He+ and O+ ions) into the plasma sheet to increase M, and the large M may suppress spontaneous plasma instabilities initiating substorms and decrease the number of the non-triggered substorms. The present analysis using the unprecedentedly long-term dataset covering ~23 years provides additional observational evidence that heavy ions work to prevent the occurrence of substorms.

  1. Fast Magnetic Reconnection: “Ideal” Tearing and the Hall Effect

    Science.gov (United States)

    Pucci, Fulvia; Velli, Marco; Tenerani, Anna

    2017-08-01

    One of the main questions in magnetic reconnection is the origin of triggering behavior with on/off properties that, once it is activated, accounts for the fast magnetic energy conversion to kinetic and thermal energies at the heart of explosive events in astrophysical and laboratory plasmas. Over the past decade, progress has been made on the initiation of fast reconnection via the plasmoid instability and what has been called “ideal” tearing, which sets in once current sheets thin to a critical inverse aspect ratio {(a/L)}c. As shown by Pucci & Velli, at {(a/L)}c∼ {S}-1/3, the timescale for the instability to develop becomes of the order of the Alfvén time and independent of the Lundquist number (here defined in terms of current sheet length L). However, given the large values of S in natural plasmas, this transition might occur for thicknesses of the inner resistive singular layer that are comparable to the ion inertial length d i . When this occurs, Hall currents produce a three-dimensional quadrupole structure of the magnetic field, and the dispersive waves introduced by the Hall effect accelerate the instability. Here we present a linear study showing how the “ideal” tearing mode critical aspect ratio is modified when Hall effects are taken into account, including more general scaling laws of the growth rates in terms of sheet inverse aspect ratio: the critical inverse aspect ratio is amended to a/L≃ {({di}/L)}0.29{(1/S)}0.19, at which point the instability growth rate becomes Alfvénic and does not depend on either of the (small) parameters {d}i/L,1/S. We discuss the implications of this generalized triggering aspect ratio for recently developed phase diagrams of magnetic reconnection.

  2. Statistical study of electrostatic solitary waves associated with reconnection: Geotail observations

    Science.gov (United States)

    Li, S. Y.; Deng, X. H.; Zhou, M.; Tang, R. X.; Liu, K.; Kojima, H.; Matsumoto, H.

    2009-02-01

    The role of waves in the dynamics of the magnetotail has long been a topic of interest in magnetospheric physics. The characteristics of Electrostatic Solitary Waves (ESWs) associated with reconnection have been studied statistically in the magnetotail by surveying the large amounts data obtained from Waveform Capture (WFC) which is an important component of Plasma Wave Instrument (PWI) on the Geotail spacecraft. About 150 reconnection events with WFC data available are selected, and approximately 10 thousands of ESW waveforms are picked up by hands for statistical study. The ESWs are observed near diffusion region and near the plasma sheet boundary layer (PSBL). Two kinds of waveforms of ESWs are observed: bi-polar and tri-polar pulses. It is found that the pulse width of the ESWs is in the order of 1 5 ms and the peak-to-peak amplitude is in the order of 0.1 5 mV/m. The amplitudes of ESWs are larger in the near-earth tail region than that in deep tail region. ESWs have been observed with or without guide magnetic field . The characteristics of ESWs in different reconnection region and under different strength of guild magnetic field, their possible generation mechanism will be discussed.

  3. Substorm effects on the plasma sheet on composition on March 22, 1979 (CDAW 6)

    Energy Technology Data Exchange (ETDEWEB)

    Lennartsson, W.; Sharp, R.D.; Zwickl, R.D.

    1985-02-01

    Data from the Plasma Composition Experiment on ISSE 1, covering the energy range 0.1--16 keV/e, show that a dramatic change took place in the plasma sheet ion composition in conjunction with the magnetic substorm activity on March 22, 1979. Beginning about 1124 UT the ion population at the ISEE 1 location changed from what appeared to be predominantly ions from the solar wind to a mixture of comparable numbers of solar wind and terrestrial ions. ISEE 1 was inbound in the predawn sector during this time, and the plasma composition experiment provided data from Rapprox. =21 R/sub E/ and LTapprox. =0130, down to Rapprox. =3 R/sub E/ and LTapprox. =0530. Prior to the substorm activity about 90--95% of the ion density was due to H/sup +/ and He/sup + +/ ions, which appeared to be mostly of solar wind origin. The H/sup +/ and He/sup + +/ components, each approximated by a Maxwell-Boltzmann distribution, had a temperature ratio T(He/sup + +/)/T(H/sup +/)approx. =4 and a density ratio n(He/sup + +/)/n(H/sup +/)approx. =1.5--3%. Both values are consistent with measurements made concurrently in the solar wind by the plasma experiment on ISSE 3. The remaining 5--10% of the density was due mainly to O/sup +/ and He/sup +/ ions of ionospheric origin. All four ion populations had broad energy spectra with mean energies of several keV/e.

  4. The evaluation of surface and adhesive bonding properties for cold rolled steel sheet for automotive treated by Ar/O{sub 2} atmospheric pressure plasma

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Chan Joo; Lee, Sang Kon; Kim Byung Min [Pusan National University, Busan (Korea, Republic of); Park, Keun Whan [Sungwoo Hitech Technical Institute, Busan (Korea, Republic of)

    2008-04-15

    Cold rolled steel sheet for automotive was treated by Ar/O{sub 2} atmospheric pressure plasma to improve the adhesive bonding strength. Through the contact angle test and calculation of surface free energy for cold rolled steel sheet, the changes of surface properties were investigated before and after plasma treatment. The contact angle was decreased and surface free energy was increased after plasma treatment. And the change of surface roughness and morphology were observed by AFM(Atomic Force Microscope). The surface roughness of steel sheet was slightly changed. Based on Taguchi method, single lap shear test was performed to investigate the effect of experimental parameter such as plasma power, treatment time and flow rate of O{sub 2} gas. Results shows that the bonding strength of steel sheet treated in Ar/O{sub 2} atmospheric pressure plasma was improved about 20% compared with untreated sheet.

  5. Criticality and turbulence in a resistive magnetohydrodynamic current sheet.

    Science.gov (United States)

    Klimas, Alexander J; Uritsky, Vadim M

    2017-02-01

    Scaling properties of a two-dimensional (2d) plasma physical current-sheet simulation model involving a full set of magnetohydrodynamic (MHD) equations with current-dependent resistivity are investigated. The current sheet supports a spatial magnetic field reversal that is forced through loading of magnetic flux containing plasma at boundaries of the simulation domain. A balance is reached between loading and annihilation of the magnetic flux through reconnection at the current sheet; the transport of magnetic flux from boundaries to current sheet is realized in the form of spatiotemporal avalanches exhibiting power-law statistics of lifetimes and sizes. We identify this dynamics as self-organized criticality (SOC) by verifying an extended set of scaling laws related to both global and local properties of the current sheet (critical susceptibility, finite-size scaling of probability distributions, geometric exponents). The critical exponents obtained from this analysis suggest that the model operates in a slowly driven SOC state similar to the mean-field state of the directed stochastic sandpile model. We also investigate multiscale correlations in the velocity field and find them numerically indistinguishable from certain intermittent turbulence (IT) theories. The results provide clues on physical conditions for SOC behavior in a broad class of plasma systems with propagating instabilities, and suggest that SOC and IT may coexist in driven current sheets which occur ubiquitously in astrophysical and space plasmas.

  6. Criticality and turbulence in a resistive magnetohydrodynamic current sheet

    Science.gov (United States)

    Klimas, Alexander J.; Uritsky, Vadim M.

    2017-02-01

    Scaling properties of a two-dimensional (2d) plasma physical current-sheet simulation model involving a full set of magnetohydrodynamic (MHD) equations with current-dependent resistivity are investigated. The current sheet supports a spatial magnetic field reversal that is forced through loading of magnetic flux containing plasma at boundaries of the simulation domain. A balance is reached between loading and annihilation of the magnetic flux through reconnection at the current sheet; the transport of magnetic flux from boundaries to current sheet is realized in the form of spatiotemporal avalanches exhibiting power-law statistics of lifetimes and sizes. We identify this dynamics as self-organized criticality (SOC) by verifying an extended set of scaling laws related to both global and local properties of the current sheet (critical susceptibility, finite-size scaling of probability distributions, geometric exponents). The critical exponents obtained from this analysis suggest that the model operates in a slowly driven SOC state similar to the mean-field state of the directed stochastic sandpile model. We also investigate multiscale correlations in the velocity field and find them numerically indistinguishable from certain intermittent turbulence (IT) theories. The results provide clues on physical conditions for SOC behavior in a broad class of plasma systems with propagating instabilities, and suggest that SOC and IT may coexist in driven current sheets which occur ubiquitously in astrophysical and space plasmas.

  7. Reconnection outflow generated turbulence in the solar wind

    CERN Document Server

    Vörös, Z; Semenov, V S; Zaqarashvili, T V; Bruno, R; Khodachenko, M

    2014-01-01

    Petschek-type time-dependent reconnection (TDR) and quasi-stationary reconnection (QSR) models are considered to understand reconnection outflow structures and the features of the associated locally generated turbulence in the solar wind. We show that the outflow structures, such as discontinuites, Kelvin-Helmholtz (KH) unstable flux tubes or continuous space filling flows cannot be distinguished from one-point WIND measurements. In both models the reconnection outflows can generate more or less spatially extended turbulent boundary layers (TBDs). The structure of an unique extended reconnection outflow is investigated in detail. The analysis of spectral scalings and break locations show that reconnection outflows can control the local field and plasma conditions which may play in favor of one or another turbulent dissipation mechanisms with their characteristic scales and wavenumbers.

  8. Comment on Lockwood and Davis, "On the longitudinal extent of magnetopause reconnection pulses"

    Science.gov (United States)

    Heikkila, W. J.

    1999-02-01

    Lockwood and Davis (1996) present a concise description of magnetopause reconnection pulses, with the claimed support of three types of observations: (1) flux transfer events (FTE), (2) poleward-moving auroral forms on the dayside, and (3) steps in cusp ion dispersion characteristics. However, there are a number of errors and misconceptions in the paper that make their conclusions untenable. They do not properly take account of the fact that the relevant processes operate in the presence of a plasma. They fail to notice that the source of energy (a dynamo with E · J0) in transient phenomena, since energy (or information) cannot travel faster than the group velocity of waves in the medium (here the Alfvén velocity VA). In short, Lockwood and Davis use the wrong contour in their attempt to evaluate the electromotive force (emf). This criticism goes beyond their article: a dynamo is not included in the usual definition of reconnection, only the reconnection load. Without an explicit source of energy in the assumed model, the idea of magnetic reconnection is improperly posed. Recent research has carried out a superposed epoch analysis of conditions near the dayside magnetopause and has found the dynamo and the load, both within the magnetopause current sheet. Since the magnetopause current is from dawn to dusk, the sign of E · J reflects the sign of the electric field. The electric field reverses, within the magnetopause; this can be discovered by an application of Lenz's law using the concept of erosion of the magnetopause. The net result is plasma transfer across the magnetopause to feed the low latitude boundary layer, at least partly on closed field lines, and viscous interaction as the mechanism by which solar wind plasma couples to the magnetosphere.

  9. Experimental study of the dynamics of a thin current sheet

    Science.gov (United States)

    Gekelman, W.; DeHaas, T.; Van Compernolle, B.; Daughton, W.; Pribyl, P.; Vincena, S.; Hong, D.

    2016-05-01

    Many plasmas in natural settings or in laboratory experiments carry currents. In magnetized plasmas the currents can be narrow field-aligned filaments as small as the electron inertial length ≤ft(\\tfrac{c}{{ω }pe}\\right) in the transverse dimension or fill the entire plasma column. Currents can take the form of sheets, again with the transverse dimension the narrow one. Are laminar sheets of electric current in a magnetized plasma stable? This became an important issue in the 1960s when current-carrying plasmas became key in the quest for thermonuclear fusion. The subject is still under study today. The conditions necessary for the onset for tearing are known, the key issue is that of the final state. Is there a final state? One possibility is a collection of stable tubes of current. On the other hand, is the interaction between the current filaments which are the byproduct endless, or does it go on to become chaotic? The subject of three-dimensional current systems is intriguing, rich in a variety of phenomena on multiple scale sizes and frequencies, and relevant to fusion studies, solar physics, space plasmas and astrophysical phenomena. In this study a long (δz = 11 m) and narrow (δx = 1 cm, δy = 20 cm) current sheet is generated in a background magnetoplasma capable of supporting Alfvén waves. The current is observed to rapidly tear into a series of magnetic islands when viewed in a cross-sectional plane, but they are in essence three-dimensional flux ropes. At the onset of the current, magnetic field line reconnection is observed between the flux ropes. The sheet on the whole is kink-unstable, and after kinking exhibits large-scale, low-frequency (f ≪ f ci ) rotation about the background field with an amplitude that grows with distance from the source of the current. Three-dimensional data of the magnetic and electric fields is acquired throughout the duration of the experiment and the parallel resistivity is derived from it. The parallel

  10. Jet formation in solar atmosphere due to magnetic reconnection

    CERN Document Server

    González-Avilés, J J; Fedun, V

    2016-01-01

    Using numerical simulations, we show that jets with features of type II spicules and cold coronal jets corresponding to temperatures $10^{4}$ K can be formed due to magnetic reconnection in a scenario in presence of magnetic resistivity. For this we model the low chromosphere-corona region using the C7 equilibrium solar atmosphere model and assuming Resistive MHD rules the dynamics of the plasma. The magnetic filed configurations we analyze correspond to two neighboring loops with opposite polarity. The separation of the loops' feet determines the thickness of a current sheet that triggers a magnetic reconnection process, and the further formation of a high speed and sharp structure. We analyze the cases where the magnetic filed strength of the two loops is equal and different. In the first case, with a symmetric configuration the spicules raise vertically whereas in an asymmetric configuration the structure shows an inclination. With a number of simulations carried out under a 2.5D approach, we explore vario...

  11. CO2 laser-micro plasma arc hybrid welding for galvanized steel sheets

    Institute of Scientific and Technical Information of China (English)

    C. H. KIM; Y. N. AHN; J. H. KIM

    2011-01-01

    A laser lap welding process for zinc-coated steel has a well-known unsolved problem-porosity formation. The boiling temperature of coated zinc is lower than the melting temperature of the base metal. which is steel. In the autogenous laser welding,the zinc vapor generates from the lapped surfaces expels the molten pool and the expulsion causes numerous weld defects, such as spatters and blow holes on the weld surface and porosity inside the welds. The laser-arc hybrid welding was suggested as an alternative method for the laser lap welding because the arc can preheat or post-heat the weldment according to the arrangement of the laser beam and the arc. CO2 laser-micro plasma hybrid welding was applied to the lap welding of zinc-coated steel with zero-gap.The relationships among the weld quality and process parameters of the laser-arc arrangement, and the laser-arc interspacing distance and arc current were investigated using a full-factorial experimental design. The effect of laser-arc arrangement is dominant because the leading plasma arc partially melts the upper steel sheets and vaporizes or oxidizes the coated zinc on the lapped surfaces.Compared with the result from the laser-TIG hybrid welding, the heat input from arc can be reduced by 40%.

  12. Fractal Structure of the Heliospheric Plasma Sheet at the Earth's Orbit

    Institute of Scientific and Technical Information of China (English)

    M. V. Eselevich; V. G. Eselevich

    2005-01-01

    An analysis of the data from the Wind and IMP-8 spacecraft revealed that a slow solar wind,flowing in the heliospheric plasma sheet, represents a set of magnetic tubes with plasma of increased density(N > 10cm-3 at the Earth's orbit). They have a fine structure at several spatial scales (fractality), from2°-3° (at the Earth's orbit, it is equivalent to 3.6-5.4 h, or(5.4-8.0) × 106 km) to the minimum about0.025°, i.e. the angular siz.e of the nested tubes is changed nearly by two orders of magnitude. The magnetic tubes at each observed spatial scale are diamagnetic, i.e. their surface sustains a flow of diamagnetic (or drift)current that decreases the magnetic field within the tube itself and increases it outside the tube. Furthermore,the value of β = 8π[N(Te + Tp)]/B2 within the tube exceeds the value of β outside the tube. In many cases total pressure P = N(Te + Tp) + B2/8π is almost constant within and outside the tubes at any one of the aforementioned scales.

  13. Multiple harmonic ULF waves in the plasma sheet boundary layer: Instability analysis

    Science.gov (United States)

    Denton, R. E.; Engebretson, M. J.; Keiling, A.; Walsh, A. P.; Gary, S. P.; DéCréAu, P. M. E.; Cattell, C. A.; RèMe, H.

    2010-12-01

    Multiple-harmonic electromagnetic waves in the ULF band have occasionally been observed in Earth's magnetosphere, both near the magnetic equator in the outer plasmasphere and in the plasma sheet boundary layer (PSBL) in Earth's magnetotail. Observations by the Cluster spacecraft of multiple-harmonic electromagnetic waves with fundamental frequency near the local proton cyclotron frequency, Ωcp, were recently reported in the plasma sheet boundary layer by Broughton et al. (2008). A companion paper surveys the entire magnetotail passage of Cluster during 2003, and reports 35 such events, all in the PSBL, and all associated with elevated fluxes of counterstreaming ions and electrons. In this study we use observed pitch angle distributions of ions and electrons during a wave event observed by Cluster on 9 September 2003 to perform an instability analysis. We use a semiautomatic procedure for developing model distributions composed of bi-Maxwellian components that minimizes the difference between modeled and observed distribution functions. Analysis of wave instability using the WHAMP electromagnetic plasma wave dispersion code and these model distributions reveals an instability near Ωcp and its harmonics. The observed and model ion distributions exhibit both beam-like and ring-like features which might lead to instability. Further instability analysis with simple beam-like and ring-like model distribution functions indicates that the instability is due to the ring-like feature. Our analysis indicates that this instability persists over an enormous range in the effective ion beta (based on a best fit for the observed distribution function using a single Maxwellian distribution), β', but that the character of the instability changes with β'. For β' of order unity (for instance, the observed case with β' ˜ 0.4), the instability is predominantly electromagnetic; the fluctuating magnetic field has components in both the perpendicular and parallel directions, but the

  14. Multiscale Modeling of Solar Coronal Magnetic Reconnection

    Science.gov (United States)

    Antiochos, Spiro K.; Karpen, Judith T.; DeVore, C. Richard

    2010-01-01

    Magnetic reconnection is widely believed to be the primary process by which the magnetic field releases energy to plasma in the Sun's corona. For example, in the breakout model for the initiation of coronal mass ejections/eruptive flares, reconnection is responsible for the catastrophic destabilizing of magnetic force balance in the corona, leading to explosive energy release. A critical requirement for the reconnection is that it have a "switch-on' nature in that the reconnection stays off until a large store of magnetic free energy has built up, and then it turn on abruptly and stay on until most of this free energy has been released. We discuss the implications of this requirement for reconnection in the context of the breakout model for CMEs/flares. We argue that it imposes stringent constraints on the properties of the flux breaking mechanism, which is expected to operate in the corona on kinetic scales. We present numerical simulations demonstrating how the reconnection and the eruption depend on the effective resistivity, i.e., the effective Lundquist number, and propose a model for incorporating kinetic flux-breaking mechanisms into MHO calculation of CMEs/flares.

  15. Ion shell distributions as free energy source for plasma waves on auroral field lines mapping to plasma sheet boundary layer

    Directory of Open Access Journals (Sweden)

    A. Olsson

    2004-06-01

    Full Text Available Ion shell distributions are hollow spherical shells in velocity space that can be formed by many processes and occur in several regions of geospace. They are interesting because they have free energy that can, in principle, be transmitted to ions and electrons. Recently, a technique has been developed to estimate the original free energy available in shell distributions from in-situ data, where some of the energy has already been lost (or consumed. We report a systematic survey of three years of data from the Polar satellite. We present an estimate of the free energy available from ion shell distributions on auroral field lines sampled by the Polar satellite below 6 RE geocentric radius. At these altitudes the type of ion shells that we are especially interested in is most common on auroral field lines close to the polar cap (i.e. field lines mapping to the plasma sheet boundary layer, PSBL. Our analysis shows that ion shell distributions that have lost some of their free energy are commonly found not only in the PSBL, but also on auroral field lines mapping to the boundary plasma sheet (BPS, especially in the evening sector auroral field lines. We suggest that the PSBL ion shell distributions are formed during the so-called Velocity Dispersed Ion Signatures (VDIS events. Furthermore, we find that the partly consumed shells often occur in association with enhanced wave activity and middle-energy electron anisotropies. The maximum downward ion energy flux associated with a shell distribution is often 10mWm-2 and sometimes exceeds 40mWm-2 when mapped to the ionosphere and thus may be enough to power many auroral processes. Earlier simulation studies have shown that ion shell distributions can excite ion Bernstein waves which, in turn, energise electrons in the parallel direction. It is possible that ion shell distributions are the link between the X-line and the auroral wave activity and electron

  16. Reconnection at the Heliopause

    CERN Document Server

    Nickeler, D H; Nickeler, Dieter H.; Fahr, Hans-Joerg

    2005-01-01

    In this MHD-model of the heliosphere, we assume a Parker-type flow, and a Parker-type spiral magnetic field, which is extrapolated further downstream from the termination shock to the heliopause. We raise the question whether the heliopause nose region may be leaky with respect to fields and plasmas due to nonideal plasma dynamics, implying a breakdown of the magnetic barrier. We analyse some simple scenarios to find reconnection rates and circumstances, under which the heliosphere can be an "open" or a "closed" magnetosphere. We do not pretend to offer a complete solution for the heliosphere, on the basis of nonideal MHD theory, but present a prescription to find such a solution on the basis of potential fields including the knowledge of neutral points. As an example we imitate the Parker spiral as a monopole with a superposition of homogeneous asymptotical boundary conditions. We use this toy model for x < -R where R = 100 AU is the distance of the termination shock to describe the situation in the nose ...

  17. Collisionless magnetic reconnection via Alfvén eigenmodes.

    Science.gov (United States)

    Dai, Lei

    2009-06-19

    We propose an analytic approach to the problem of collisionless magnetic reconnection formulated as a process of Alfvén eigenmodes' generation and dissipation. Alfvén eigenmodes are confined by the current sheet in the same way that quantum mechanical waves are confined by the tanh;{2} potential. The dynamical time scale of reconnection is the system scale divided by the eigenvalue propagation velocity of the n = 1 mode. The prediction of the n = 1 mode shows good agreement with the in situ measurement of the reconnection-associated Hall fields.

  18. Plasmoid formation in the elongated current sheet during transient CHI on HIST

    Science.gov (United States)

    Nagata, Masayoshi; Fujita, Akihiro; Matsui, Takahiro; Kikuchi, Yusuke; Fukumoto, Naoyuki; Kanki, Takashi

    2016-10-01

    The Transient-Coaxial Helicity Injection (T-CHI) is a promising candidate for the non-inductive plasma start-up on Spherical Torus (ST). The problem of the flux closure in the T-CHI is important and related to understand the physics of fast magnetic reconnection. The recent MHD simulation (F. Ebrahimi and R. Raman, Phys. Rev. Lett. 114, 205003 (2015)) on T-CHI for NSTX predicts the formation and breakup of an elongated Sweet-Parker (S-P) current sheet and a transient to plasmoid instability. According to this simulation, the reconnection rate based on the plasmoid instability is faster than that by S-P model and becomes nearly independent of the Lundquist number S. In this meeting, we will present that the formation of multiple X-points and plasmoids has been observed in T-CHI start-up plasmas on HIST. The stronger external guide (toroidal) magnetic field makes plasma less compressible, leading to slower reconnection time and longer current sheet. The experimental observation shows that 2/3 plasmoids are generated in the elongated current sheet with the narrow width comparable to the ion skin depth or the ion sound gyro-radius. The small plasmoids develop to a large-scale flux structure due to a current inward diffusion during the decay phase.

  19. Controllable formation of graphene and graphene oxide sheets using photo-catalytic reduction and oxygen plasma treatment

    Science.gov (United States)

    Ostovari, Fatemeh; Abdi, Yaser; Ghasemi, Foad

    2012-12-01

    Au/SiO2/Si interdigital electrodes with thickness of 1 μm were created on silicon substrate. Graphene oxide (GO) sheets hanging from these electrodes were obtained by spin coating of chemically synthesized GO dispersed in water. We used UV-light-induced photo-catalytic activity of titanium oxide nanoparticles to reduce the GO layer. Effects of the photo-induced chemical reduction on the conductivity of the GO were investigated. Also, low power DC plasma was used for oxidation of the sheets. Oxygen bombardment leads to sheets with low electrical conductivity. Measurements show that graphene and GO sheets with the controlled electrical conductivity were obtained by these processes. Scanning electron and atomic force microscopy were used to study the morphology of the TiO2/GO and graphene structures. X-ray diffraction and Raman scattering analysis were used to verify the structural characteristics of the prepared sheets. Analysis showed a gradual increase in the number of C-O bonds on the surface of the graphene layer as a result of increasing the time of plasma bombardment. Based on the Raman spectroscopy, the photo-catalytic activity of TiO2 nanoparticles resulted in a decrease in the number of C-O bonds.

  20. Steady state reconnection at a single 3D magnetic null point

    Science.gov (United States)

    Galsgaard, K.; Pontin, D. I.

    2011-05-01

    Aims: We systematically stress a rotationally symmetric 3D magnetic null point by advecting the opposite footpoints of the spine axis in opposite directions. This stress eventually concentrates in the vicinity of the null point, thereby forming a local current sheet through which magnetic reconnection takes place. The aim is to look for a steady state evolution of the current sheet dynamics, which may provide scaling relations for various characteristic parameters of the system. Methods: The evolution is followed by solving numerically the non-ideal MHD equations in a Cartesian domain. The null point is embedded in an initially constant density and temperature plasma. Results: It is shown that a quasi-steady reconnection process can be set up at a 3D null by continuous shear driving. It appears that a true steady state is unlikely to be realised because the current layer tends to grow until it is restricted by the geometry of the computational domain and the imposed driving profile. However, ratios between characteristic quantities clearly settle after some time to stable values, so that the evolution is quasi-steady. The experiments show a number of scaling relations, but they do not provide a clear consensus for extending to lower magnetic resistivity or faster driving velocities. More investigations are needed to fully clarify the properties of current sheets at magnetic null points.

  1. New types of coating systems for steel sheets by high-rate evaporation in combination with plasma processes

    Energy Technology Data Exchange (ETDEWEB)

    Scheffel, B.; Metzner, C. [Fraunhofer-Institut fuer Elektronenstrahl und Plasmatechnik (FEP), Dresden (Germany); Ehlers, K.D. [Salzgitter AG Stahl und Technologie (Germany); Schuhmacher, B. [Dortmunder Oberflaechencentrum GmbH, Dortmund (Germany); Flossdorf, F.J.; Steinbeck, G. [Verein Deutscher Eisenhuettenleute (VDEh), Duesseldorf (Germany); Steffen, R. [Stahlwerke Bremen GmbH (Germany); Hagler, J. [voestalpine Stahl GmbH, Linz (Austria)

    2002-03-01

    High-rate evaporation in combination with plasma processes is a promising approach to obtain new types of steel sheet coating with improved corrosion resistance and application properties. To estimate the potential for the application of PVD-coatings (physical vapour deposition) different coating systems for steel sheet as well as for hot-dip or electro-galvanized steel sheet were designed. The samples were produced on a laboratory scale using PVD processes with very high deposition rates (in the order of 1 {mu}m s{sup -1}) as well as high-power plasma processes for the pre-treatment. The relationship between the composition, microstructure and properties of the coating systems, in particular concerning corrosion protection, abrasion during forming, phosphating and paint adhesion, were studied. It was found that the corrosion resistance of galvanized steel sheets can be considerably improved by vapour deposition of metal or inorganic films with a thickness of several hundred nanometers. Investigations on vapour deposition of titanium and stainless steel coatings on steel sheets, for applications in a severely corrosive environment, showed that the corrosion resistance in relation to the coating thickness can be significantly enhanced by means of plasma activation during the vapour deposition process. Finally, an outlook on possible industrial applications including an estimation of the process costs will be presented. For certain coating systems the results look promising. Consequently, these particular coating systems will be investigated in more detail by means of using a large-scale in-line deposition plant for metallic strips and sheets. (orig.)

  2. Reconnection Processes in the Chromosphere and Corona

    Science.gov (United States)

    Shibata, Kazunari

    2012-07-01

    Magnetic reconnection is a fundamental key physical process in magnetized plasmas. Recent space solar observations revealed that magnetic reconnection is ubiquitous in the solar chromospheres and corona. Especially recent Hinode observations has found various types of tiny chromospheric jets, such as chromospheric anemone jets (Shibata et al. 2007), penumbral microjets (Katsukawa et al. 2007), light bridge jets from sunspot umbra (Shimizu et al. 2009), etc. It was also found that the corona is full of tiny X-ray jets (Cirtain et al. 2007). Often they are seen as helical spinning jets (Shimojo et al. 2007, Patsourakos et al. 2008, Pariat et al. 2009, Filippov et al. 2009, Kamio et al. 2010) with Alfvenic waves (Nishizuka et al. 2008, Liu et al. 2009) and there are increasing evidence of magnetic reconnection in these tiny jets. We can now say that as spatial resolution of observations become better and better, smaller and smaller flares and jets have been discovered, which implies that the magnetized solar atmosphere consist of fractal structure and dynamics, i.e., fractal reconnection. Bursty radio and hard X-ray emissions from flares also suggest the fractal reconnection and associated particle acceleration. Since magnetohydrodynamics (MHD) does not contain any characteristic length and time scale, it is natural that MHD structure, dynamics, and reconnection, tend to become fractal in ideal MHD plasmas with large magnetic Reynolds number such as in the solar atmosphere. We would discuss recent observations and theories related to fractal reconnection in the chromospheres and corona, and discuss possible implication to chromospheric and coronal heating.

  3. Two-Dimensional MHD Numerical Simulations of Magnetic Reconnection Triggered by A Supernova Shock in Interstellar Medium, Generation of X-Ray Gas in Galaxy

    CERN Document Server

    Tanuma, S; Kudoh, T; Shibata, K; Tanuma, Syuniti; Yokoyama, Takaaki; Kudoh, Takahiro; Shibata, Kazunari

    2001-01-01

    We examine the magnetic reconnection triggered by a supernova (or a point explosion) in interstellar medium, by performing two-dimensional resistive magnetohydrodynamic (MHD) numerical simulations with high spatial resolution. We found that the magnetic reconnection starts long after a supernova shock (fast-mode MHD shock) passes a current sheet. The current sheet evolves as follows: (i) Tearing-mode instability is excited by the supernova shock, and the current sheet becomes thin in its nonlinear stage. (ii) The current-sheet thinning is saturated when the current-sheet thickness becomes comparable to that of Sweet-Parker current sheet. After that, Sweet-Parker type reconnection starts, and the current-sheet length increases. (iii) ``Secondary tearing-mode instability'' occurs in the thin Sweet-Parker current sheet. (iv) As a result, further current-sheet thinning occurs and anomalous resistivity sets in, because gas density decreases in the current sheet. Petschek type reconnection starts and heats interste...

  4. A Model for Patchy Reconnection in Three Dimensions

    CERN Document Server

    Linton, M G

    2005-01-01

    We show, theoretically and via MHD simulations, how a short burst of reconnection localized in three dimensions on a one-dimensional current sheet creates a pair of reconnected flux tubes. We focus on the post-reconnection evolution of these flux tubes, studying their velocities and shapes. We find that slow-mode shocks propagate along these reconnected flux tubes, releasing magnetic energy as in steady-state Petschek reconnection. The geometry of these three-dimensional shocks, however, differs dramatically from the classical two-dimensional geometry. They propagate along the flux tube legs in four isolated fronts, whereas in the two-dimensional Petschek model, they form a continuous, stationary pair of V-shaped fronts. We find that the cross sections of these reconnected flux tubes appear as teardrop shaped bundles of flux propagating away from the reconnection site. Based on this, we argue that the descending coronal voids seen by Yohkoh SXT, LASCO, and TRACE are reconnected flux tubes descending from a fl...

  5. A Model for Patchy Reconnection in Three Dimensions

    Science.gov (United States)

    Linton, M. G.; Longcope, D. W.

    2006-05-01

    We show, theoretically and via MHD simulations, how a short burst of localized reconnection on a current sheet creates a pair of reconnected flux tubes. We focus on the post-reconnection evolution of these flux tubes, studying their velocities and shapes. We find that slow-mode shocks propagate along these reconnected flux tubes, releasing magnetic energy as in steady state Petschek reconnection. The geometry of these three-dimensional shocks, however, differs significantly from the classical two-dimensional geometry. They propagate along the flux tube legs in four isolated fronts, whereas in the two-dimensional Petschek model, they form a continuous, stationary pair of V-shaped fronts. We find that the cross sections of these reconnected flux tubes appear as teardrop-shaped bundles of flux propagating away from the reconnection site. Based on this, we argue that the descending coronal voids seen by Yohkoh SXT, LASCO, and TRACE are reconnected flux tubes descending from a flare site in the high corona, for example after a coronal mass ejection. In this model, these flux tubes would then settle into equilibrium in the low corona, forming an arcade of postflare coronal loops.

  6. Magnetic reconnection in the near Venusian magnetotail.

    Science.gov (United States)

    Zhang, T L; Lu, Q M; Baumjohann, W; Russell, C T; Fedorov, A; Barabash, S; Coates, A J; Du, A M; Cao, J B; Nakamura, R; Teh, W L; Wang, R S; Dou, X K; Wang, S; Glassmeier, K H; Auster, H U; Balikhin, M

    2012-05-04

    Observations with the Venus Express magnetometer and low-energy particle detector revealed magnetic field and plasma behavior in the near-Venus wake that is symptomatic of magnetic reconnection, a process that occurs in Earth's magnetotail but is not expected in the magnetotail of a nonmagnetized planet such as Venus. On 15 May 2006, the plasma flow in this region was toward the planet, and the magnetic field component transverse to the flow was reversed. Magnetic reconnection is a plasma process that changes the topology of the magnetic field and results in energy exchange between the magnetic field and the plasma. Thus, the energetics of the Venus magnetotail resembles that of the terrestrial tail, where energy is stored and later released from the magnetic field to the plasma.

  7. Collisionless Reconnection and Electron Demagnetization

    Science.gov (United States)

    Scudder, J. D.

    Observable, dimensionless properties of the electron diffusion region of collisionless magnetic reconnection are motivated and benchmarked in two and three dimensional Particle In Cell (PIC) simulations as appropriate for measurements with present state of the art spacecraft. The dimensionless quantities of this paper invariably trace their origin to breaking the magnetization of the thermal electrons. Several observable proxies are also motivated for the rate of frozen flux violation and a parameter \\varLambda _{\\varPhi } that when greater than unity is associated with close proximity to the analogue of the saddle point region of 2D reconnection usually called the electron diffusion region. Analogous regions to the electron diffusion region of 2D reconnection with \\varLambda _{\\varPhi } > 1 have been identified in 3D simulations. 10-20 disjoint diffusion regions are identified and the geometrical patterns of their locations illustrated. First examples of associations between local observables based on electron demagnetization and global diagnostics (like squashing) are also presented. A by product of these studies is the development of a single spacecraft determinations of gradient scales in the plasma.

  8. Fast Reconnection of Weak Magnetic Fields

    Science.gov (United States)

    Zweibel, Ellen G.

    1998-01-01

    Fast magnetic reconnection refers to annihilation or topological rearrangement of magnetic fields on a timescale that is independent (or nearly independent) of the plasma resistivity. The resistivity of astrophysical plasmas is so low that reconnection is of little practical interest unless it is fast. Yet, the theory of fast magnetic reconnection is on uncertain ground, as models must avoid the tendency of magnetic fields to pile up at the reconnection layer, slowing down the flow. In this paper it is shown that these problems can be avoided to some extent if the flow is three dimensional. On the other hand, it is shown that in the limited but important case of incompressible stagnation point flows, every flow will amplify most magnetic fields. Although examples of fast magnetic reconnection abound, a weak, disordered magnetic field embedded in stagnation point flow will in general be amplified, and should eventually modify the flow. These results support recent arguments against the operation of turbulent resistivity in highly conducting fluids.

  9. Perspectives on magnetic reconnection

    Science.gov (United States)

    Yamada, Masaaki

    2016-01-01

    Magnetic reconnection is a topological rearrangement of magnetic field that occurs on time scales much faster than the global magnetic diffusion time. Since the field lines break on microscopic scales but energy is stored and the field is driven on macroscopic scales, reconnection is an inherently multi-scale process that often involves both magnetohydrodynamic (MHD) and kinetic phenomena. In this article, we begin with the MHD point of view and then describe the dynamics and energetics of reconnection using a two-fluid formulation. We also focus on the respective roles of global and local processes and how they are coupled. We conclude that the triggers for reconnection are mostly global, that the key energy conversion and dissipation processes are either local or global, and that the presence of a continuum of scales coupled from microscopic to macroscopic may be the most likely path to fast reconnection. PMID:28119547

  10. VINETA II: a linear magnetic reconnection experiment.

    Science.gov (United States)

    Bohlin, H; Von Stechow, A; Rahbarnia, K; Grulke, O; Klinger, T

    2014-02-01

    A linear experiment dedicated to the study of driven magnetic reconnection is presented. The new device (VINETA II) is suitable for investigating both collisional and near collisionless reconnection. Reconnection is achieved by externally driving magnetic field lines towards an X-point, inducing a current in the background plasma which consequently modifies the magnetic field topology. Owing to the open field line configuration of the experiment, the current is limited by the axial sheath boundary conditions. A plasma gun is used as an additional electron source in order to counterbalance the charge separation effects and supply the required current. Two drive methods are used in the device. First, an oscillating current through two parallel conductors drive the reconnection. Second, a stationary X-point topology is formed by the parallel conductors, and the drive is achieved by an oscillating current through a third conductor. In the first setup, the magnetic field of the axial plasma current dominates the field topology near the X-point throughout most of the drive. The second setup allows for the amplitude of the plasma current as well as the motion of the flux to be set independently of the X-point topology of the parallel conductors.

  11. Magnetic reconnection as a chondrule heating mechanism

    Science.gov (United States)

    Lazerson, Samuel A.

    2010-12-01

    The origin of chondrules (sub-millimeter inclusions found in stony meteorites) remains today an open question despite over century of examination. The age of these proto-solar relics shows a well defined cutoff of around 4.5 billion years ago. This places them as the oldest solids in the solar system. Chemical examination indicates that they experienced heating events on the order of 5000 K/hr for periods of around 30 minutes, followed by extending periods of cooling. Additional examination indicates the presence of large magnetic fields during their formation. Most attempts to explain chondrule formation in the proto-solar nebula neglect the existence of a plasma environment, with even less mention of dust being a charge carrier (dusty plasma). Simulations of magnetic reconnection in a dusty plasma are forwarded as a mechanism for chondrule formation in the proto-solar nebula. Here large dust-neutral relative velocities are found in the reconnection region. These flows are associated with the dynamics of reconnection. The high Knudsen number of the dust particles allows for a direct calculation of frictional heating due to collisions with neutrals (allowing for the neglect of boundary layer formation around the particle). Test particle simulations produce heating equivalent to that recorded in the chondrule mineral record. It is shown that magnetic reconnection in a dusty plasma is of fundamental importance to the formation of the most primitive solids in the solar system.

  12. In situ observations of ion scale current sheet and associated electron heating in Earth's magnetosheath turbulence

    Science.gov (United States)

    Chasapis, Alexandros; Retinò, Alessandro; Sahraoui, Fouad; Greco, Antonella; Vaivads, Andris; Sundkvist, David; Canu, Patrick

    2014-05-01

    Magnetic reconnection occurs in thin current sheets that form in turbulent plasmas. Numerical simulations indicate that turbulent reconnection contributes to the dissipation of magnetic field energy and results in particle heating and non-thermal acceleration. Yet in situ measurements are required to determine its importance as a dissipation mechanism at those scales. The Earth's magnetosheath downstream of the quasi-parallel shock is a turbulent near-Earth environment that offers a privileged environment for such a study. Here we present a study of the properties of thin current sheets by using Cluster data. We studied the distribution of the current sheets as a function of their magnetic shear angle, the PVI index and the electron heating. The properties of the observed current sheets were different for high shear (θ > 90 degrees) and low shear current sheets (θ < 90 degrees). These high-shear current sheets account for about ˜ 20% of the total and have an average thickness comparable to the ion inertial length. Enhancement of electron temperature within these current sheets suggest that they are important for local electron heating and energy dissipation.

  13. Magnetic Reconnection: Theoretical and Observational Perspectives: Preface

    Science.gov (United States)

    Lewis, W. S.; Antiochos, S. K,; Drake, J. F.

    2011-01-01

    Magnetic reconnection is a fundamental plasma-physical process by which energy stored in a magnetic field is converted, often explosively, into heat and the kinetic energy of the charged particles that constitute the plasma. It occurs in a variety of astrophysical settings, ranging from the solar corona to pulsar magnetospheres and winds, as well as in laboratory fusion experiments, where it is responsible for sawtooth crashes. First proposed by R.G. Giovanelli in the late I 940s as the mechanism responsible for solar flares, magnetic reconnection was invoked at the beginning of the space age to explain not just solar flares but also the transfer of energy, mass, and momentum from the solar wind to Earth's magnetosphere and the subsequent storage and release of the transferred energy in the magnetotai\\. During the half century or so that has followed the seminal theoretical works by J.W. Dungey, P.A. Sweet, E.N. Parker, and H.E. Petschek, in-situ measurements by Earth-orbiting satellites and remote-sensing observations of the solar corona have provided a growing body of evidence for the occurrence of reconnection at the Sun, in the solar wind, and in the near-Earth space environment. The last thirty years have also seen the development of laboratory reconnection experiments at a number of institutions. In parallel with the efforts of experimentalists in both space and laboratory plasma physics, theorists have investigated, analytically and with the help of increasingly powerful MHD, hybrid, and kinetic numerical simulations, the structure of the diffusion region, the factors controlling the rate, onset, and cessation of reconnection, and the detailed physics that enables the demagnetization of the ions and electrons and the topological reconfiguration of the magnetic field. Moreover, the scope of theoretical reconnection studies has been extended well beyond solar system and laboratory plasmas to include more exotic astrophysical plasma systems whose strong (10

  14. The energetics of relativistic magnetic reconnection: ion-electron repartition and particle distribution hardness

    CERN Document Server

    Melzani, Mickaël; Folini, Doris; Winisdoerffer, Christophe; Favre, Jean M

    2014-01-01

    Collisionless magnetic reconnection is a prime candidate to account for flare-like or steady emission, outflow launching, or plasma heating, in a variety of high-energy astrophysical objects, including ones with relativistic ion-electron plasmas. But the fate of the initial magnetic energy in a reconnection event remains poorly known: what is the amount given to kinetic energy, the ion/electron repartition, and the hardness of the particle distributions? We explore these questions with 2D particle-in-cell simulations of ion-electron plasmas. We find that 45 to 75% of the total initial magnetic energy ends up in kinetic energy, this fraction increasing with the inflow magnetization. Depending on the guide field strength, ions get from 30 to 60% of the total kinetic energy. Particles can be separated into two populations that only weakly mix: (i) particles initially in the current sheet, heated by its initial tearing and subsequent contraction of the islands; and (ii) particles from the background plasma that p...

  15. Shock wave interaction with a thermal layer produced by a plasma sheet actuator

    Science.gov (United States)

    Koroteeva, E.; Znamenskaya, I.; Orlov, D.; Sysoev, N.

    2017-03-01

    This paper explores the phenomena associated with pulsed discharge energy deposition in the near-surface gas layer in front of a shock wave from the flow control perspective. The energy is deposited in 200 ns by a high-current distributed sliding discharge of a ‘plasma sheet’ type. The discharge, covering an area of 100× 30 mm2, is mounted on the top or bottom wall of a shock tube channel. In order to analyse the time scales of the pulsed discharge effect on an unsteady supersonic flow, we consider the propagation of a planar shock wave along the discharge surface area 50–500 μs after the discharge pulse. The processes in the discharge chamber are visualized experimentally using the shadowgraph method and modelled numerically using 2D/3D CFD simulations. The interaction between the planar shock wave and the discharge-induced thermal layer results in the formation of a lambda-shock configuration and the generation of vorticity in the flow behind the shock front. We determine the amount and spatial distribution of the electric energy rapidly transforming into heat by comparing the calculated flow patterns and the experimental shadow images. It is shown that the uniformity of the discharge energy distribution strongly affects the resulting flow dynamics. Regions of turbulent mixing in the near-surface gas are detected when the discharge energy is deposited non-uniformly along the plasma sheet. They account for the increase in the cooling rate of the discharge-induced thermal layer and significantly influence its interaction with an incident shock wave.

  16. Two-dimensional MHD model of the reconnection diffusion region

    Directory of Open Access Journals (Sweden)

    N. V. Erkaev

    2002-01-01

    Full Text Available Magnetic reconnection is an important process providing a fast conversion of magnetic energy into thermal and kinetic plasma energy. In this concern, a key problem is that of the resistive diffusion region where the reconnection process is initiated. In this paper, the diffusion region is associated with a nonuniform conductivity localized to a small region. The nonsteady resistive incompressible MHD equations are solved numerically for the case of symmetric reconnection of antiparallel magnetic fields. A Petschek type steady-state solution is obtained as a result of time relaxation of the reconnection layer structure from an arbitrary initial stage. The structure of the diffusion region is studied for various ratios of maximum and minimum values of the plasma resistivity. The effective length of the diffusion region and the reconnection rate are determined as functions of the length scale and the maximum of the resistivity. For sufficiently small length scale of the resistivity, the reconnection rate is shown to be consistent with Petschek's formula. By increasing the resistivity length scale and decreasing the resistivity maximum, the reconnection layer tends to be wider, and correspondingly, the reconnection rate tends to be more consistent with that of the Parker-Sweet regime.

  17. Modeling the effect of doping on the catalyst-assisted growth and field emission properties of plasma-grown graphene sheet

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, Neha; Sharma, Suresh C.; Sharma, Rinku [Department of Applied Physics, Delhi Technological University (DTU), Shahbad Daulatpur, Bawana Road, Delhi-110042 (India)

    2016-08-15

    A theoretical model describing the effect of doping on the plasma-assisted catalytic growth of graphene sheet has been developed. The model accounts the charging rate of the graphene sheet, kinetics of all the plasma species, including the doping species, and the growth rate of graphene nuclei and graphene sheet due to surface diffusion, and accretion of ions on the catalyst nanoparticle. Using the model, it is observed that nitrogen and boron doping can strongly influence the growth and field emission properties of the graphene sheet. The results of the present investigation indicate that nitrogen doping results in reduced thickness and shortened height of the graphene sheet; however, boron doping increases the thickness and height of the graphene sheet. The time evolutions of the charge on the graphene sheet and hydrocarbon number density for nitrogen and boron doped graphene sheet have also been examined. The field emission properties of the graphene sheet have been proposed on the basis of the results obtained. It is concluded that nitrogen doped graphene sheet exhibits better field emission characteristics as compared to undoped and boron doped graphene sheet. The results of the present investigation are consistent with the existing experimental observations.

  18. A feature of negative hydrogen ion production in the Uramoto-type sheet plasma

    Energy Technology Data Exchange (ETDEWEB)

    Jimbo, Kouichi [Kyoto Univ., Uji (Japan). Inst. of Atomic Energy

    1997-02-01

    It seems that negative hydrogen ions H{sup -} are formed directly from atomic hydrogens H. When the chamber was biased more negative against the anode potential at constant are power, forming a much deeper electrostatic well in the Uramoto-type sheet plasma negative ion source, more negative hydrogen ion currents were extracted. The chamber potential V{sub B} was biased down to -100V in the 150V discharge. The negative ion current J{sup -} was evaluated by the JAERI-probe measurement. J{sup -} increases linearly with the chamber current I{sub B}. The largest J{sup -} value was obtained at absolute value of |V{sub prob,f}|=15V and absolute value of |V{sub B}|=100V; the discharge was not operated for absolute value of |V{sub B}|>100V. We speculate the following collisional (three-body) electron attachment to H as a possible production process for H{sup -}; e+e+H{yields}e+H{sup -}. This process may explain the linear increase of J{sup -} with absolute value of |V{sub prob,f}|. (S.Y.)

  19. Study of kinetic Alfven wave (KAW) in plasma - sheet-boundary- layer

    Energy Technology Data Exchange (ETDEWEB)

    Shukla, Nidhi; Varma, P; Tiwari, M S, E-mail: tiwarims@rediffmail.co, E-mail: poornimavarma@yahoo.co, E-mail: nidhiphy.shukla@gmail.co [Department of Physics and Electronics, Dr. H. S. Gour University, Sagar (M.P.), 470003 (India)

    2010-02-01

    The effect of parallel electric field with general loss-cone distribution function on the dispersion relation and damping rate/growth rate of the kinetic Alfven wave (KAW) is evaluated by kinetic approach. The generation of KAW by the combined effect of parallel electric field and loss-cone distribution indices (J) at a particular range of k{sub p}erpendicular{rho}{sub i} (k{sub p}erpendicular{rho}{sub i} <1 and k{sub p}erpendicular{rho}{sub i} >1) is noticed, where k{sub p}erpendicular is perpendicular wave number and {rho}{sub i} is the ion-gyro radius. Thus the propagation of KAW and loss of the Poynting flux from plasma sheet boundary layer (PSBL) to the ionosphere can be explained on the basis of present investigation. It is found that the present study also shows that the loss-cone distribution index is an important parameter to study KAW in the PSBL.

  20. A Tailward Moving Current Sheet Normal Magnetic Field Front Followed by an Earthward Moving Dipolarization Front

    Science.gov (United States)

    Hwang, K.-J.; Goldstein, M. L.; Moore, T. E.; Walsh, B. M.; Baishev, D. G.; Moiseyev, A. V.; Shevtsov, B. M.; Yumoto, K.

    2014-01-01

    A case study is presented using measurements from the Cluster spacecraft and ground-based magnetometers that show a substorm onset propagating from the inner to outer plasma sheet. On 3 October 2005, Cluster, traversing an ion-scale current sheet at the near-Earth plasma sheet, detected a sudden enhancement of Bz, which was immediately followed by a series of flux rope structures. Both the local Bz enhancement and flux ropes propagated tailward. Approximately 5 min later, another Bz enhancement, followed by a large density decrease, was observed to rapidly propagate earthward. Between the two Bz enhancements, a significant removal of magnetic flux occurred, possibly resulting from the tailward moving Bz enhancement and flux ropes. In our scenario, this flux removal caused the magnetotail to be globally stretched so that the thinnest sheet formed tailward of Cluster. The thinned current sheet facilitated magnetic reconnection that quickly evolved from plasma sheet to lobe and generated the later earthward moving dipolarization front (DF) followed by a reduction in density and entropy. Ground magnetograms located near the meridian of Cluster's magnetic foot points show two-step bay enhancements. The positive bay associated with the first Bz enhancement indicates that the substorm onset signatures propagated from the inner to the outer plasma sheet, consistent with the Cluster observation. The more intense bay features associated with the later DF are consistent with the earthward motion of the front. The event suggests that current disruption signatures that originated in the near-Earth current sheet propagated tailward, triggering or facilitating midtail reconnection, thereby preconditioning the magnetosphere for a later strong substorm enhancement.

  1. Observations of turbulence within reconnection jet in the presence of guide field

    Science.gov (United States)

    Huang, S. Y.; Zhou, M.; Sahraoui, F.; Vaivads, A.; Deng, X. H.; André, M.; He, J. S.; Fu, H. S.; Li, H. M.; Yuan, Z. G.; Wang, D. D.

    2012-06-01

    We present the first comprehensive observations of turbulence properties within high speed reconnection jet in the plasma sheet with moderate guide field. The power spectral density index is about -1.73 in the inertial range, and follows the value of -2.86 in the ion dissipation range. The turbulence is strongly anisotropic in the wave-vector space with the major power having its wave-vector highly oblique to the ambient magnetic field, suggesting that the turbulence is quasi-2D. The measured "dispersion relations" obtained using the k-filtering technique are compared with theory and are found to be consistent with the Alfvén-Whistler mode. In addition, both Probability Distribution Functions and flatness results show that the turbulence in the reconnection jet is intermittent (multifractal) at scales less than the proton gyroradius/inertial lengths. The estimated electric field provided by anomalous resistivity caused by turbulence is about 3 mV/m, which is close to the typical reconnection electric field in the magnetotail.

  2. Field-aligned currents observed by MMS in the near-Earth plasma sheet during large-scale substorm dipolarizations.

    Science.gov (United States)

    Nakamura, Rumi; Nagai, Tsugunobu; Giles, Barbara; Le Contel, Olivier; Stawarz, Julia; Khotyaintsev, Yuri; Artemyev, Anton

    2017-04-01

    During substorms significant energy conversion has been reported to take place at the sharp dipolarization front in the flow braking region where the probability of observing bursty bulk flows (BBFs) significantly drops. On 10 August 2016, MMS traversed the pre-midnight near-Earth plasma sheet when dipolarization disturbances were detected in an extended nightside local time region by Cluster, Geotail, GOES 13, 14 and 15, and the Van Allen Probes. In an expanding plasma sheet during the dipolarization, MMS detected sub-ion scale field-aligned current layers that are propagating both Earthward (equatorward) as well as tailward (outward). These multi-scale multi-point observations enable a unique investigation of both the meso-scale evolution of the disturbances and the detailed kinetic structures of the fronts and boundaries relevant to the dipolarizations.

  3. Reconnection experiments with 3D magnetic nulls

    Science.gov (United States)

    Vrublevskis, A.; Egedal, J.; Le, A.; Montag, P.

    2011-10-01

    Three-dimensional effects have been crucial in explaining experiments at the Versatile Toroidal Facility (VTF) even in nominal axisymmetric plasmas with a non-vanishing toroidal field. In general, depending on the topological and geometric structure of the magnetic field, a rich collection of magnetic reconnection scenarios is possible in three dimensions. The new adjustable set of coils in VTF allows exploring reconnection in 2D and 3D geometries including configurations with magnetic null points. We present results of a numerical and experimental investigation of magnetic field topologies attainable in VTF. This work was supported by NSF CAREER Award 0844620.

  4. ISEE-3 observations of a viscously-driven plasma sheet: magnetosheath mass and/or momentum transfer?

    OpenAIRE

    Mist, R. T.; Owen, C.J.

    2002-01-01

    A statistical analysis of data from the ISEE-3 distant tail campaign is presented. We investigate the mechanism driving slow, tailward flows observed in the plasma sheet. The possibility that these slow flows are driven by mass and/or momentum transfer across the distant tail magnetopause is explored. We establish that 40% of these flows could be driven by the transfer of approximately 4% of the magnetosheath momentum flux into the magnetotail. Current understanding of the Kelvin-Helmholtz in...

  5. ISEE-3 observations of a viscously-driven plasma sheet: magnetosheath mass and/or momentum transfer?

    OpenAIRE

    Mist, R. T.; Owen, C.J.

    2002-01-01

    A statistical analysis of data from the ISEE-3 distant tail campaign is presented. We investigate the mechanism driving slow, tailward flows observed in the plasma sheet. The possibility that these slow flows are driven by mass and/or momentum transfer across the distant tail magnetopause is explored. We establish that 40% of these flows could be driven by the transfer of approximately 4% of the magnetosheath momentum flux into the magnetotail. Current understanding of the Kelvin-Helmh...

  6. Magnetic reconnection: from the Sweet-Parker model to stochastic plasmoid chains

    CERN Document Server

    Loureiro, N F

    2015-01-01

    (abridged) Magnetic reconnection is the topological reconfiguration of the magnetic field in a plasma, accompanied by the violent release of energy and particle acceleration. Reconnection is as ubiquitous as plasmas themselves, with solar flares perhaps the most popular example. Over the last few years, the theoretical understanding of magnetic reconnection in large-scale fluid systems has undergone a major paradigm shift. The steady-state model of reconnection described by the famous Sweet-Parker (SP) theory, which dominated the field for ~50 years, has been replaced with an essentially time-dependent, bursty picture of the reconnection layer, dominated by the continuous formation and ejection of multiple secondary islands (plasmoids). Whereas in the SP model reconnection was predicted to be slow, a major implication of this new paradigm is that reconnection in fluid systems is fast (i.e., independent of the Lundquist number), provided that the system is large enough. This conceptual shift hinges on the real...

  7. Distinct characteristics of asymmetric magnetic reconnections: Observational results from the exhaust region at the dayside magnetopause

    Science.gov (United States)

    Zhang, Y. C.

    2016-01-01

    Magnetic reconnection plays a key role in the conversion of magnetic energy into the thermal and kinetic energy of plasma. On either side of the diffusion region in space plasma, the conditions for the occurrence of reconnections are usually not symmetric. Previous theoretical studies have predicted that reconnections under asymmetric conditions will bear different features compared with those of symmetric reconnections, and numerical simulations have verified these distinct features. However, to date, the features of asymmetric reconnections have not been thoroughly investigated using in situ observations; thus, some results from theoretical studies and simulations have not been tested with observations sufficiently well. Here, spacecraft observations are used in a statistical investigation of asymmetric magnetic reconnection exhaust at the dayside magnetopause. The resulting observational features are consistent with the theoretical predictions. The results presented here advance our understanding of the development of reconnections under asymmetric conditions. PMID:27270685

  8. CHAIN RECONNECTIONS OBSERVED IN SYMPATHETIC ERUPTIONS

    Energy Technology Data Exchange (ETDEWEB)

    Joshi, Navin Chandra; Magara, Tetsuya [School of Space Research, Kyung Hee University, Yongin, Gyeonggi-Do, 446-701 (Korea, Republic of); Schmieder, Brigitte; Aulanier, Guillaume [LESIA, Observatoire de Paris, PSL Research University, CNRS Sarbonne Universités, Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Jansson, F-92195 Meudon (France); Guo, Yang, E-mail: navin@khu.ac.kr, E-mail: njoshi98@gmail.com [School of Astronomy and Space Science, Nanjing University, 210023 Nanjing (China)

    2016-04-01

    The nature of various plausible causal links between sympathetic events is still a controversial issue. In this work, we present multiwavelength observations of sympathetic eruptions, associated flares, and coronal mass ejections (CMEs) occurring on 2013 November 17 in two close active regions. Two filaments, i.e., F1 and F2, are observed in between the active regions. Successive magnetic reconnections, caused for different reasons (flux cancellation, shear, and expansion) have been identified during the whole event. The first reconnection occurred during the first eruption via flux cancellation between the sheared arcades overlying filament F2, creating a flux rope and leading to the first double-ribbon solar flare. During this phase, we observed the eruption of overlying arcades and coronal loops, which leads to the first CME. The second reconnection is believed to occur between the expanding flux rope of F2 and the overlying arcades of filament F1. We suggest that this reconnection destabilized the equilibrium of filament F1, which further facilitated its eruption. The third stage of reconnection occurred in the wake of the erupting filament F1 between the legs of the overlying arcades. This may create a flux rope and the second double-ribbon flare and a second CME. The fourth reconnection was between the expanding arcades of the erupting filament F1 and the nearby ambient field, which produced the bi-directional plasma flows both upward and downward. Observations and a nonlinear force-free field extrapolation confirm the possibility of reconnection and the causal link between the magnetic systems.

  9. Plasma arc brazing - a low energy joining technology for steel sheets; Plasmalichtbogenloeten - eine energiearme Fuegetechnik fuer Feinblechwerkstoffe

    Energy Technology Data Exchange (ETDEWEB)

    Bouaifi, B.; Draugelates, U.; Helmich, A.; Ouaissa, B. [TU Clausthal, Clausthal-Zellerfeld (Germany)

    2001-07-01

    Mild and high strength steel sheets are comparatively difficult to weld. The heat input in the case of conventional welding processes is too high, so that plasma brazing is an attractive alternative and complementary joining process. One characteristic of the process is the independent input of energy and filler material. In addition, the process is practically spatter-free. Plasma brazing reduces joint and panel distortion and is tolerant to surface contamination and metallic surface coatings. The brazed seams are aesthetic in appearance and clear good mechanical properties. (orig.)

  10. Formation of plasmoid chains in magnetic reconnection.

    Science.gov (United States)

    Samtaney, R; Loureiro, N F; Uzdensky, D A; Schekochihin, A A; Cowley, S C

    2009-09-04

    A detailed numerical study of magnetic reconnection in resistive MHD for very large, previously inaccessible, Lundquist numbers (10(4) magnetic-island) chains. The plasmoid number scales as S(3/8) and the instability growth rate in the linear stage as S(1/4), in agreement with the theory by Loureiro et al. [Phys. Plasmas 14, 100703 (2007)]. In the nonlinear regime, plasmoids continue to grow faster than they are ejected and completely disrupt the reconnection layer. These results suggest that high-Lundquist-number reconnection is inherently time-dependent and hence call for a substantial revision of the standard Sweet-Parker quasistationary picture for S>10(4).

  11. Electron-scale measurements of magnetic reconnection in space.

    Science.gov (United States)

    Burch, J L; Torbert, R B; Phan, T D; Chen, L-J; Moore, T E; Ergun, R E; Eastwood, J P; Gershman, D J; Cassak, P A; Argall, M R; Wang, S; Hesse, M; Pollock, C J; Giles, B L; Nakamura, R; Mauk, B H; Fuselier, S A; Russell, C T; Strangeway, R J; Drake, J F; Shay, M A; Khotyaintsev, Yu V; Lindqvist, P-A; Marklund, G; Wilder, F D; Young, D T; Torkar, K; Goldstein, J; Dorelli, J C; Avanov, L A; Oka, M; Baker, D N; Jaynes, A N; Goodrich, K A; Cohen, I J; Turner, D L; Fennell, J F; Blake, J B; Clemmons, J; Goldman, M; Newman, D; Petrinec, S M; Trattner, K J; Lavraud, B; Reiff, P H; Baumjohann, W; Magnes, W; Steller, M; Lewis, W; Saito, Y; Coffey, V; Chandler, M

    2016-06-03

    Magnetic reconnection is a fundamental physical process in plasmas whereby stored magnetic energy is converted into heat and kinetic energy of charged particles. Reconnection occurs in many astrophysical plasma environments and in laboratory plasmas. Using measurements with very high time resolution, NASA's Magnetospheric Multiscale (MMS) mission has found direct evidence for electron demagnetization and acceleration at sites along the sunward boundary of Earth's magnetosphere where the interplanetary magnetic field reconnects with the terrestrial magnetic field. We have (i) observed the conversion of magnetic energy to particle energy; (ii) measured the electric field and current, which together cause the dissipation of magnetic energy; and (iii) identified the electron population that carries the current as a result of demagnetization and acceleration within the reconnection diffusion/dissipation region.

  12. Turbulent transport in 2D collisionless guide field reconnection

    Science.gov (United States)

    Muñoz, P. A.; Büchner, J.; Kilian, P.

    2017-02-01

    Transport in hot and dilute, i.e., collisionless, astrophysical and space, plasmas is called "anomalous." This transport is due to the interaction between the particles and the self-generated turbulence by their collective interactions. The anomalous transport has very different and not well known properties compared to the transport due to binary collisions, dominant in colder and denser plasmas. Because of its relevance for astrophysical and space plasmas, we explore the excitation of turbulence in current sheets prone to component- or guide-field reconnection, a process not well understood yet. This configuration is typical for stellar coronae, and it is created in the laboratory for which a 2.5D geometry applies. In our analysis, in addition to the immediate vicinity of the X-line, we also include regions outside and near the separatrices. We analyze the anomalous transport properties by using 2.5D Particle-in-Cell code simulations. We split off the mean slow variation (in contrast to the fast turbulent fluctuations) of the macroscopic observables and determine the main transport terms of the generalized Ohm's law. We verify our findings by comparing with the independently determined slowing-down rate of the macroscopic currents (due to a net momentum transfer from particles to waves) and with the transport terms obtained by the first order correlations of the turbulent fluctuations. We find that the turbulence is most intense in the "low density" separatrix region of guide-field reconnection. It is excited by streaming instabilities, is mainly electrostatic and "patchy" in space, and so is the associated anomalous transport. Parts of the energy exchange between turbulence and particles are reversible and quasi-periodic. The remaining irreversible anomalous resistivity can be parametrized by an effective collision rate ranging from the local ion-cyclotron to the lower-hybrid frequency. The contributions to the parallel and the perpendicular (to the magnetic

  13. Asymmetric magnetic reconnection with a flow shear and applications to the magnetopause

    Science.gov (United States)

    Doss, C. E.; Komar, C. M.; Cassak, P. A.; Wilder, F. D.; Eriksson, S.; Drake, J. F.

    2015-09-01

    We perform a systematic theoretical and numerical study of antiparallel two-dimensional magnetic reconnection with asymmetries in the plasma density and reconnecting magnetic field strength in addition to a bulk flow shear across the reconnection site in the plane of the reconnecting fields, which commonly occurs at planetary magnetospheres. We analytically predict the speed at which an isolated X line is convected by the flow, the reconnection rate, and the critical flow speed at which reconnection no longer takes place for arbitrary reconnecting magnetic field strengths, densities, and upstream flow speeds, and we confirm the results with two-fluid numerical simulations. The predictions and simulation results counter the prevailing model of reconnection at Earth's dayside magnetopause which says reconnection occurs with a stationary X line for sub-Alfvénic magnetosheath flow, reconnection occurs but the X line convects for magnetosheath flows between the Alfvén speed and double the Alfvén speed, and reconnection does not occur for magnetosheath flows greater than double the Alfvén speed. In particular, we find that X line motion is governed by momentum conservation from the upstream flows, which are weighted differently in asymmetric systems, so the X line convects for generic conditions including sub-Alfvénic upstream speeds. For the reconnection rate, as with symmetric reconnection, it drops with increasing flow shear and there is a cutoff speed above which reconnection is not predominant. However, while the cutoff condition for symmetric reconnection is that the difference in flows on the two sides of the reconnection site is twice the Alfvén speed, we find asymmetries cause the cutoff speed for asymmetric reconnection to be higher than twice the asymmetric form of the Alfvén speed. The stronger the asymmetries, the more the cutoff exceeds double the asymmetric Alfvén speed. This is due to the fact that in asymmetric reconnection, the plasma with the

  14. Global and local disturbances in the magnetotail during reconnection

    Directory of Open Access Journals (Sweden)

    T. V. Laitinen

    2007-05-01

    Full Text Available We examine Cluster observations of a reconnection event at xGSM=−15.7 RE in the magnetotail on 11 October 2001, when Cluster recorded the current sheet for an extended period including the entire duration of the reconnection event. The onset of reconnection is associated with a sudden orientation change of the ambient magnetic field, which is also observed simultaneously by Goes-8 at geostationary orbit. Current sheet oscillations are observed both before reconnection and during it. The speed of the flapping motions is found to increase when the current sheet undergoes the transition from quiet to active state, as suggested by an earlier statistical result and now confirmed within one single event. Within the diffusion region both the tailward and earthward parts of the quadrupolar magnetic Hall structure are recorded as an x-line passes Cluster. We report the first observations of the Hall structure conforming to the kinks in the current sheet. This results in relatively strong fluctuations in Bz, which are shown to be the Hall signature tilted in the yz plane with the current sheet.

  15. Nonthermal Particle Acceleration in Magnetic Reconnection

    Science.gov (United States)

    Guo, Fan; Li, Hui; Zhang, Haocheng; Daughton, William; Liu, Yi-Hsin; Lloyd-Ronning, Nicole

    2017-08-01

    Magnetic reconnection is a leading mechanism for dissipating magnetic energy and accelerating nonthermal particles in Poynting-flux-dominated flows. In this study, we investigate nonthermal particle acceleration during magnetic reconnection in a magnetically dominated plasma using fully kinetic simulations. We have studied the magnetically dominated regime by varying σe = 103-105 and mass ratios. The results demonstrate that reconnection quickly establishes power-law energy distributions for both electrons and ions within several (2-3) light-crossing times. For the cases with periodic boundary conditions, the power-law index is 1 < p < 2 for both electrons and ions. We study particle acceleration in magnetic reconnection via large-scale 3D kinetic simulations to examine several effects that may be important, including pre-existing fluctuations, kink and secondary tearing instabilities, and open boundary conditions. The results show that particle acceleration in reconnection layers is surprisingly robust despite the development of 3D turbulence and instabilities. The main acceleration mechanism is a Fermi-like acceleration through the drift motions of charged particles. We discuss the implication of this study in the context of Poynting-flux dominated jets and pulsar winds, especially the applications for explaining nonthermal high-energy emissions.

  16. Relativistic Reconnection: an Efficient Source of Non-Thermal Particles

    CERN Document Server

    Sironi, Lorenzo

    2014-01-01

    In magnetized astrophysical outflows, the dissipation of field energy into particle energy via magnetic reconnection is often invoked to explain the observed non-thermal signatures. By means of two- and three-dimensional particle-in-cell simulations, we investigate anti-parallel reconnection in magnetically-dominated electron-positron plasmas. Our simulations extend to unprecedentedly long temporal and spatial scales, so we can capture the asymptotic state of the system beyond the initial transients, and without any artificial limitation by the boundary conditions. At late times, the reconnection layer is organized into a chain of large magnetic islands connected by thin X-lines. The plasmoid instability further fragments each X-line into a series of smaller islands, separated by X-points. At the X-points, the particles become unmagnetized and they get accelerated along the reconnection electric field. We provide definitive evidence that the late-time particle spectrum integrated over the whole reconnection r...

  17. Conservation of writhe helicity under anti-parallel reconnection

    CERN Document Server

    Laing, Christian E; Sumners, De Witt L

    2014-01-01

    Reconnection is a fundamental event in many areas of science, from the interaction of vortices in classical and quantum fluids, and magnetic flux tubes in magnetohydrodynamics and plasma physics, to the recombination in polymer physics and DNA biology. By using fundamental results in topological fluid mechanics, the helicity of a flux tube can be calculated in terms of writhe and twist contributions. Here we show that the writhe is conserved under anti-parallel reconnection. Hence, for a pair of interacting flux tubes of equal flux, if the twist of the reconnected tube is the sum of the original twists of the interacting tubes, then helicity is conserved during reconnection. Thus, any deviation from helicity conservation is entirely due to the intrinsic twist inserted or deleted locally at the reconnection site. This result has important implications for helicity and energy considerations in various physical contexts.

  18. Laser-induced fluorescence measurement of the ion-energy-distribution function in a collisionless reconnection experiment.

    Science.gov (United States)

    Stark, A; Fox, W; Egedal, J; Grulke, O; Klinger, T

    2005-12-02

    Observations in space and laboratory plasmas suggest magnetic reconnection as a mechanism for ion heating and formation of non-Maxwellian ion velocity distribution functions (IVDF). Laser-induced fluorescence measurements of the IVDF parallel to the X line of a periodically driven reconnection experiment are presented. A time-resolved analysis yields the evolution of the IVDF within a reconnection cycle. It is shown that reconnection causes a strong increase of the ion temperature, where the strongest increase is found at the maximum reconnection rate. Monte Carlo simulations demonstrate that ion heating is a consequence of the in-plane electric field that forms around the X line in response to reconnection.

  19. A statistical study of the THEMIS satellite data for plasma sheet electrons carrying auroral upward field-aligned currents

    Science.gov (United States)

    Lee, S.; Shiokawa, K.; McFadden, J. P.

    2010-12-01

    The magnetospheric electron precipitation along the upward field-aligned currents without the potential difference causes diffuse aurora, and the magnetospheric electrons accelerated by a field-aligned potential difference cause the intense and bright type of aurora, namely discrete aurora. In this study, we are trying to find out when and where the aurora can be caused with or without electron acceleration. We statistically investigate electron density, temperature, thermal current, and conductivity in the plasma sheet using the data from the electrostatic analyzer (ESA) onboard the THEMIS-D satellite launched in 2007. According to Knight (Planet. Space Sci., 1973) and Lyons (JGR, 1980), the thermal current, jth(∝ nT^(1/2) where n is electron density and T is electron temperature in the plasma sheet), represents the upper limit to field aligned current that can be carried by magnetospheric electrons without field-aligned potential difference. The conductivity, K(∝ nT^(-1/2)), represents the efficiency of the upward field-aligned current (j) that the field-aligned potential difference (V) can produce (j=KV). Therefore, estimating jth and K in the plasma sheet is important in understanding the ability of plasma sheet electrons to carry the field-aligned current which is driven by various magnetospheric processes such as flow shear and azimuthal pressure gradient. Similar study was done by Shiokawa et al. (2000) based on the auroral electron data obtained by the DMSP satellites above the auroral oval and the AMPTE/IRM satellite in the near Earth plasma sheet at 10-18 Re on February-June 1985 and March-June 1986 during the solar minimum. The purpose of our study is to examine auroral electrons with pitch angle information inside 12 Re where Shiokawa et al. (2000) did not investigate well. For preliminary result, we found that in the dawn side inner magnetosphere (source of the region 2 current), electrons can make sufficient thermal current without field

  20. Fragment Driven Magnetic Reconnection

    CERN Document Server

    Galsgaard, K

    2004-01-01

    In this paper, we investigate a simple model where two, initially unconnected, flux systems are forced to interact in response to the imposed boundary driving by solving the non-ideal 3D MHD equations numerically. The reconnection rate of the dynamical process is determined and compared with the corresponding rate for the potential evolution of the magnetic field. This shows that the dynamic reconnection rate is about a factor of two smaller than the potential (perfect, instantaneous) rate for realistic solar driving velocities demonstrating that this three-dimensional magnetic reconnection process is fast. The energy input for a fixed advection distance is found to be independent of the driving velocity. The Joule dissipation associated with the reconnection process is also found to be basically dependent on the advection distance rather than driving velocity. This implies that the timescale for the event determines the effect the heating has on the temperature increase. Finally, the numerical experiments in...

  1. A Catapult (Slingshot) Current Sheet Relaxation Model for Substorm Triggering

    Science.gov (United States)

    Machida, S.; Miyashita, Y.; Ieda, A.

    2010-12-01

    Based on the results of our superposed epoch analysis of Geotail data, we have proposed a catapult (slingshot) current sheet relaxation model in which earthward flows are produced in the central plasma sheet (CPS) due to the catapult (slingshot) current sheet relaxation, together with the rapid enhancement of Poynting flux toward the CPS in the lobe around X ~ -15 Re about 4 min before the substrom onset. These earthward flows are characterized by plasma pressure decrease and large amplitude magnetic field fluctuations. When these flows reach X ~ 12Re in the magnetotail, they give significant disturbances to the inner magnetosphere to initiate some instability such as a ballooning instability or other instabilities, and the substorm starts in the inner magnetosphere. The occurrence of the magnetic reconnection is a natural consequence of the initial convective earthward flows, because the relaxation of a highly stretched catapult current sheet produces a very thin current at its tailward edge being surrounded by intense magnetic fields which were formerly the off-equatorial lobe magnetic fields. Recently, Nishimura et al. [2010] reported that the substorm onset begins when faint poleward discrete arcs collide with equatorward quiet arcs. The region of earthward convective flows correlatively moves earthward prior to the onset. Thus, this region of the earthward convective flows seems to correspond to the faint poleward discrete arcs. Interestingly, our statistical analysis shows that the earthward convective flows are not produced by the magnetic reconnection, but they are attributed to the dominance of the earthward JxB force over the tailward pressure associated with the progress of the plasma sheet thinning.

  2. Observations of slow electron holes at a magnetic reconnection site.

    Science.gov (United States)

    Khotyaintsev, Yu V; Vaivads, A; André, M; Fujimoto, M; Retinò, A; Owen, C J

    2010-10-15

    We report in situ observations of high-frequency electrostatic waves in the vicinity of a reconnection site in the Earth's magnetotail. Two different types of waves are observed inside an ion-scale magnetic flux rope embedded in a reconnecting current sheet. Electron holes (weak double layers) produced by the Buneman instability are observed in the density minimum in the center of the flux rope. Higher frequency broadband electrostatic waves with frequencies extending up to f(pe) are driven by the electron beam and are observed in the denser part of the rope. Our observations demonstrate multiscale coupling during the reconnection: Electron-scale physics is induced by the dynamics of an ion-scale flux rope embedded in a yet larger-scale magnetic reconnection process.

  3. How is the magnetic reconnection derived from magnetohydrodynamics equations?

    CERN Document Server

    Tashiro, Tohru

    2012-01-01

    We clarify how magnetic reconnection can be derived from magnetohydrodynamics (MHD) equations in a way that is easily understandable to university students. The essential mechanism governing the time evolution of the magnetic field is diffusion dynamics. The magnetic field is represented by two components. It is clarified that the diffusion of a component causes a generation of another component that is initially zero and, accordingly, that the magnetic force lines are reconnected. For this reconnection to occur correctly, the initial magnetic field must be directed oppositely in the two regions, e.g., $y>0$ and $y0$ ($y<0$); and must be saturated for $y$ far from the x axis, which would indicate the existence of the current sheet. It will be clear that our comprehension based on diffusion runs parallel to the common qualitative explanation about the magnetic reconnection.

  4. Observations of post-flare supra-arcades: instabilities at the head of