Numerical simulations of plasma equilibrium in a one-dimensional current sheet with a nonzero normal magnetic field component

International Nuclear Information System (INIS)

Mingalev, O. V.; Mingalev, I. V.; Malova, Kh. V.; Zelenyi, L. M.

2007-01-01

The force balance in a thin collisionless current sheet in the Earth's magnetotail with a given constant magnetic field component B z across the sheet is numerically studied for the first time in a self-consistent formulation of the problem. The current sheet is produced by oppositely directed plasma flows propagating from the periphery of the sheet toward the neutral plane. A substantially improved version of a macroparticle numerical model is used that makes it possible to simulate on the order of 10 7 macroparticles even with a personal computer and to calculate equilibrium configurations with a sufficiently low discrete noise level in the first-and second-order moments of the distribution function, which determine the stress tensor elements. Quasisteady configurations were calculated numerically for several sets of plasma parameters in some parts of the magnetotail. The force balance in the sheet was checked by calculating the longitudinal and transverse pressures as well as the elements of the full stress tensor. The stress tensor in the current sheet is found to be nondiagonal and to differ appreciably from the gyrotropic stress tensor in the Chew-Goldberger-Low model, although the Chew-Goldberger-Low theory and numerical calculations yield close results for large distances from the region of reversed magnetic field

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.

Nonadiabatic heating of the central plasma sheet at substorm onset

International Nuclear Information System (INIS)

Huang, C.Y.; Frank, L.A.; Rostoker, G.; Fennell, J.; Mitchell, D.G.

1992-01-01

Heating events in the plasma sheet boundary layer and central plasma sheet are found to occur at the onset of expansive phase activity. The main effect is a dramatic increase in plasma temperature, coincident with a partial dipolarization of the magnetic field. Fluxes of energetic particles increase without dispersion during these events which occur at all radial distances up to 23 R E , the apogee of the ISEIE spacecraft. A major difference between these heating events and those observed at geosynchronous distances lies in the heating mechanism which is nonadiabatic beyond 10 R E but may be adiabatic closer to Earth. The energy required to account for the increase in plasma thermal energy is comparable with that required for Joule heating of the ionosphere. The plasma sheet must be considered as a major sink in the energy balance of substorm. The authors estimate lobe magnetic pressures during these events. Changes in lobe pressure are generally not correlated with onsets or intensifications of expansive phase activity

Magnetospheric Multiscale Mission Observations of Magnetic Flux Ropes in the Earth's Plasma Sheet

Science.gov (United States)

Slavin, J. A.; Akhavan-Tafti, M.; Poh, G.; Le, G.; Russell, C. T.; Nakamura, R.; Baumjohann, W.; Torbert, R. B.; Gershman, D. J.; Pollock, C. J.; Giles, B. L.; Moore, T. E.; Burch, J. L.

2017-12-01

A major discovery by the Cluster mission and the previous generation of science missions is the presence of earthward and tailward moving magnetic flux ropes in the Earth's plasma sheet. However, the lack of high-time resolution plasma measurements severely limited progress concerning the formation and evolution of these reconnection generated structures. We use high-time resolution magnetic and electric field and plasma measurements from the Magnetospheric Multiscale mission's first tail season to investigate: 1) the distribution of flux rope diameters relative to the local ion and electron inertial lengths; 2) the internal force balance sustaining these structures; and 3) the magnetic connectivity of the flux ropes to the Earth and/or the interplanetary medium; 4) the specific entropy of earthward moving flux ropes and the possible effect of "buoyancy" on how deep they penetrate into the inner magnetosphere; and 5) evidence for coalescence of adjacent flux ropes and/or the division of existing flux ropes through the formation of secondary X-lines. The results of these initial analyses will be discussed in terms of their implications for reconnection-driven magnetospheric dynamics and substorms.

Fast Fermi acceleration in the plasma sheet boundary layer

International Nuclear Information System (INIS)

Wu, C.S.; Lui, A.T.Y.

1989-01-01

A longstanding question in the field of magnetospheric physics is the source of the energetic particles which are commonly observed along the plasma sheet boundary layer (PSBL). Several models have been suggested for the acceleration of these particles. We suggest a means by which the fast Fermi acceleration mechanism [Wu, 1984] can accelerate electrons at the plasma sheet and perhaps account for some of the observations. We propose the following: A localized hydromagnetic disturbance propagating through the tail lobe region impinges upon the PSBL deforming it and displacing it in towards the central plasma sheet. The boundary layer can then act like a moving magnetic mirror. If the disturbance is propagating nearly perpendicular to the layer then its velocity projected parallel to the layer (and the magnetic field) can be very large resulting in significant acceleration of reflected particles. copyright American Geophysical Union 1989

Electrodynamic forces and plasma conductivity inside the current sheet

International Nuclear Information System (INIS)

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

1985-01-01

The process of accumulation and explosive release of magnetic energy was studied in a current sheet of plasma of a high-current linear discharge. The distribution of current density and of electrodynamic forces were measured and the time evolution of these quantities was determined. The evolution of the plasma conductivity was also obtained. The measured and calculated electrodynamic forces may explain the plasma acceleration up to the velocities about 3x10 4 m/s only near the sheet edges. (D.Gy.)

Plasma sheet behavior during substorms

International Nuclear Information System (INIS)

Hones, E.W. Jr.

1983-01-01

Auroral or magnetic substorms are periods of enhanced auroral and geomagnetic activity lasting one to a few hours that signify increased dissipation of energy from the magnetosphere to the earth. Data acquired during the past decade from satellites in the near-earth sector of the magnetotail have suggested that during a substorm part of the plasma sheet is severed from earth by magnetic reconnection, forming a plasmoid, i.e., a body of plasma and closed magnetic loops, that flows out of the tail into the solar wind, thus returning plasma and energy that have earlier been accumulated from the solar wind. Very recently this picture has been dramatically confirmed by observations, with the ISEE 3 spacecraft in the magnetotail 220 R/sub E/ from earth, of plasmoids passing that location in clear delayed response to substorms. It now appears that plasmoid release is a fundamental process whereby the magnetosphere gives up excess stored energy and plasma, much like comets are seen to do, and that the phenomena of the substorm seen at earth are a by-product of that fundamental process

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.

Statistical study of plasma sheet dynamics using ISEE 1 and 2 energetic particle flux data

International Nuclear Information System (INIS)

Dandouras, J.; Reme, H.; Saint-Marc, A.; Sauvaud, J.A.; Parks, G.K.; Anderson, K.A.; Lin, R.P.

1986-01-01

During magnetospheric substorms, satellites embedded in the plasma sheet often detect transient dropouts of plasma and energetic particle fluxes, a phenomemon generally interpreted as indicating the exit of the satellite into the magnetospheric lobe due to a plasma sheet thinning. In order to determine the large-scale dynamics of the near-earth plasma sheet during substorms, three satellite years of ISEE 1 and 2 energetic particle flux data (1.5 and 6 keV), corresponding to 461 particle flux dropouts, have been analyzed. The principal results show that flux dropouts can be observed anywhere in the nightside plasma sheet, independent of the satellite's geocentric distance (for R>12R/sub E/), magnetic local time (except near the magnetospheric flanks) and estimated distance to the neutral sheet. Furthermore, flux dropouts can be observed for any combination of the AE index value and the satellite's distance to the neutral sheet, which shows that the plasma sheet is dynamic even during weak magnetospheric disturbances. Substorms during which the satellites, though situated in the plasma sheet, did not detect any flux dropout, have also been examined, and it is found that the plasma sheet thickness can locally remain unaffected by substorm development for AE index values up to at least 1000 nT. The predictions of the two major plasma sheet thinning models, i.e., the near-tail X-type magnetic neutral line formation model and the MHD rarefaction wave propagation model, are compared to the experimental results, and it is concluded that neither model can account for all of the observations; plasma sheet dynamics are more complex. Phenomenologically, this study suggests that multiple pinching of the plasma sheet and/or large-amplitude three-dimensional plasma sheet oscillations are important in plasma sheet dynamics

MHD Ballooning Instability in the Plasma Sheet

International Nuclear Information System (INIS)

Cheng, C.Z.; Zaharia, S.

2003-01-01

Based on the ideal-MHD model the stability of ballooning modes is investigated by employing realistic 3D magnetospheric equilibria, in particular for the substorm growth phase. Previous MHD ballooning stability calculations making use of approximations on the plasma compressibility can give rise to erroneous conclusions. Our results show that without making approximations on the plasma compressibility the MHD ballooning modes are unstable for the entire plasma sheet where beta (sub)eq is greater than or equal to 1, and the most unstable modes are located in the strong cross-tail current sheet region in the near-Earth plasma sheet, which maps to the initial brightening location of the breakup arc in the ionosphere. However, the MHD beq threshold is too low in comparison with observations by AMPTE/CCE at X = -(8 - 9)R(sub)E, which show that a low-frequency instability is excited only when beq increases over 50. The difficulty is mitigated by considering the kinetic effects of ion gyrorad ii and trapped electron dynamics, which can greatly increase the stabilizing effects of field line tension and thus enhance the beta(sub)eq threshold [Cheng and Lui, 1998]. The consequence is to reduce the equatorial region of the unstable ballooning modes to the strong cross-tail current sheet region where the free energy associated with the plasma pressure gradient and magnetic field curvature is maximum

Experimental Investigation of the Neutral sheet Profile During Magnetic Reconnection

International Nuclear Information System (INIS)

Trintchouk, F.; Ji, H.; Yamada, M.; Kulsrud, R.; Hsu, S.; Carter, T.

1999-01-01

During magnetic reconnection, a ''neutral sheet'' current is induced, heating the plasma. The resultant plasma thermal pressure forms a stationary equilibrium with the opposing magnetic fields. The reconnection layer profile holds significant clues about the physical mechanisms which control reconnection. On the Magnetic Reconnection Experiment [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)], a quasi steady-state and axisymmetric neutral sheet profile has been measured precisely using a magnetic probe array with spatial resolution equal to one quarter of the ion gyro-radius. It was found that the reconnecting field profile fits well with a Harris-type profile [E. G. Harris, Il Nuovo Cimento 23, 115 (1962)], B(x) approximately tanh(x/delta). This agreement is remarkable since the Harris theory does not take into account reconnection and associated electric fields and dissipation. An explanation for this agreement is presented. The sheet thickness delta is found to be approximately 0.4 times the ion skin depth, which agrees with a generalized Harris theory incorporating non-isothermal electron and ion temperatures and finite electric field. The detailed study of additional local features of the reconnection region is also presented

Impact of the storm-time plasma sheet ion composition on the ring current energy density

Science.gov (United States)

Mouikis, C.; Kistler, L. M.; Petrinec, S. M.; Fuselier, S. A.; Cohen, I.

2017-12-01

The adiabatic inward transport of the night-side near-earth ( 6 Re) hot plasma sheet is the dominant contributor to the ring current pressure during storm times. During storm times, the plasma sheet composition in the 6 - 12 Re tail region changes due to O+ entry from the lobes (from the cusp) and the direct feeding from the night side auroral region. In addition, at substorm onset the plasma sheet O+ ions can be preferentially accelerated. We use MMS and observations during two magnetic storms, 5/8/2016 and 7/16/2017, to monitor the composition changes and energization in the 6 - 12 Re plasma sheet region. For both storms the MMS apogee was in the tail. In addition, we use subsequent Van Allen Probe observations (with apogee in the dawn and dusk respectively) to test if the 6-12 Re plasma sheet, observed by MMS, is a sufficient source of the O+ in the ring current. For this we will compare the phase space density (PSD) of the plasma sheet source population and the PSD of the inner magnetosphere at constant magnetic moment values as used in Kistler et al., [2016].

Ion beam generation at the plasma sheet boundary layer by kinetic Alfven waves

International Nuclear Information System (INIS)

Moghaddam-Taaheri, E.; Goertz, C.K.; Smith, R.A.

1989-01-01

The kinetic Alfven wave, an Alfven wave with a perpendicular wavelength comparable to the ion gyroradius, can diffuse ions both in velocity and coordinate spaces with comparable transport rates. This may lead to the generation of ion beams in the plasma sheet boundary layer (PSBL). To investigate the ion beam generation process numerically, a two-dimensional quasi-linear code was constructed. Assuming that the plasma β (the ratio of plasma pressure to the magnetic pressure) varies from β = 1 to β << 1 across the magnetic field, the dynamics of the ion beam generation in the PSBL was studied. It was found that if your start with an ion distribution function which monotonically decreases with velocity along the magnetic field and a density gradient across the magnetic field, ions diffuse in velocity-coordinate space until nearly a plateau is established along the diffusion path. Depending on the topology of the magnetic field at the lobe side of the simulation system, i.e., open or closed field lines, the ion distribution function may or may not reach a steady state. If the field lines are open there, i.e., if the diffusion extends into the lobe, the double diffusion process may provide a mechanism for continuously transferring the ions from the central plasma sheet to the lobe. The authors comment on the effect of the particle loss on the establishment of the pressure balance in the plasma sheet

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

International Nuclear Information System (INIS)

Catapano, F.; Zimbardo, G.; Artemyev, A. V.; Vasko, I. Y.

2015-01-01

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

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.

Deposition Rate and Energy Enhancements of TiN Thin-Film in a Magnetized Sheet Plasma Source

OpenAIRE

Hamdi Muhyuddin D. Barra; Henry J. Ramos

2011-01-01

Titanium nitride (TiN) has been synthesized using the sheet plasma negative ion source (SPNIS). The parameters used for its effective synthesis has been determined from previous experiments and studies. In this study, further enhancement of the deposition rate of TiN synthesis and advancement of the SPNIS operation is presented. This is primarily achieved by the addition of Sm-Co permanent magnets and a modification of the configuration in the TiN deposition process. The ...

High-beta plasma blobs in the morningside plasma sheet

Directory of Open Access Journals (Sweden)

G. Haerendel

1999-12-01

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

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 9R_E 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

Substorms in the Inner Plasma Sheet

Science.gov (United States)

Le Contel, O.; Perraut, S.; Roux, A.; Pellat, R.; Korth, A.

Thin Current Sheets (TCS) are regularly formed prior to substorm breakup, even in the near-Earth plasma sheet, as close as the geostationary orbit. A self-consistent kinetic theory describing the response of the plasma sheet to an electromagnetic perturbation is given. This perturbation corresponds to an external forcing, for instance caused by the solar wind (not an internal instability). The equilibrium of the configuration of this TCS in the presence of a time varying perturbation is shown to produce a strong parallel thermal anisotropy (T∥ > T⊺) of energetic electrons and ions (E>50keV) as well as an enhanced diamagnetic current carried by low energy ions (Ecurrents tend to enhance the confinement of this current sheet near the magnetic equator. These results are compared with data gathered by GEOS-2 at the geostationary orbit, where the magnetic signatures of TCS, and parallel anisotropies are regularly observed prior to breakup. By ensuring quasi-neutrality everywhere we find, when low frequency electromagnetic perturbations are applied, that although the magnetic field line remains an equipotential to the lowest order in Te/Ti, a field-aligned potential drop exists to the next order in (Te/Ti). Thus the development of a TCS implies the formation of a field-aligned potential drop (~= few hundred volts) to ensure the quasi-neutrality everywhere. For an earthward directed pressure gradient, a field-aligned electric field, directed towards the ionosphere, is obtained, on the western edge of the perturbation (i.e. western edge of the current sheet). Thus field aligned beams of electrons are expected to flow towards the equatorial region on the western edge of the current sheet. We study the stability of these electron beams and show that they are unstable to ``High Frequency'' (HF) waves. These ``HF'' waves are regularly observed at frequencies of the order of the proton gyrofrequency (fH+) just before, or at breakup. The amplitude of these HF waves is so

Complete plasma dropouts at Vela satellites during thinning of the plasma sheet

International Nuclear Information System (INIS)

Lui, A.T.Y.; Hones, E.W. Jr.; Venkatesan, D.; Akasofu, S.; Bame, S.J.

1975-01-01

Five satellite years of Vela data are examined for plasma sheet thinnings. Complete proton disappearances (plasma dropouts) are the main subject here. During such times, the Vela satellite is temporarily in the high-latitude tail lobe. The distribution of such plasma dropouts within the magnetotail suggests that the semithickness of the plasma sheet near midnight seldom reaches less than 1 R/sub E/ during substorms and that the dawn and dusk portions of the plasma sheet remain thicker than the midnight portion. But it is also shown that the plasma sheet occasionally becomes very thin near the dusk magnetopause. No such severe thinnings of the plasma sheet are found near the dawn magnetopause. Plasma dropouts can occur regardless of the sign of the Z component of the IMF, but their frequency of occurrence seems to be greater when the Z component is negative.Three plasma dropouts which occurred in the midnight sector at unusually large distances from the estimated position of the neutral sheet were observed during geomagnetic storms. It is likely that the midnight sector of the plasma sheet can become very thick (approx.18 R/sub E/) at certain times during the main phase of storms. Detailed measurements in the plasma sheet were obtained near the beginning of a geomagnetic storm whose sc triggered a substorm. A compression of the plasma sheet at X/sub SM/approx. =-15 R/sub E/ occurred about 10 min after the sc onset at the earth and about 5 min after the start of plasma sheet thinning associated with the sc-related substorm. If compression-thinning of the plasma sheet initiated this substorm, the triggering action must have occurred earthward of X/sub SM/approx. =-15 R/sub E/

Dispersive O+ conics observed in the plasma-sheet boundary layer with CRRES/LOMICS during a magnetic storm

Directory of Open Access Journals (Sweden)

M. Wüest

1996-06-01

Full Text Available We present initial results from the Low-energy magnetospheric ion composition sensor (LOMICS on the Combined release and radiation effects satellite (CRRES together with electron, magnetic field, and electric field wave data. LOMICS measures all important magnetospheric ion species (H+, He++, He+, O++, O+ simultaneously in the energy range 60 eV to 45 keV, as well as their pitch-angle distributions, within the time resolution afforded by the spacecraft spin period of 30 s. During the geomagnetic storm of 9 July 1991, over a period of 42 min (0734 UT to 0816 UT the LOMICS ion mass spectrometer observed an apparent O+ conic flowing away from the southern hemisphere with a bulk velocity that decreased exponentially with time from 300 km/s to 50 km/s, while its temperature also decreased exponentially from 700 to 5 eV. At the onset of the O+ conic, intense low-frequency electromagnetic wave activity and strong pitch-angle scattering were also observed. At the time of the observations the CRRES spacecraft was inbound at L~7.5 near dusk, magnetic local time (MLT, and at a magnetic latitude of –23°. Our analysis using several CRRES instruments suggests that the spacecraft was skimming along the plasma sheet boundary layer (PSBL when the upward-flowing ion conic arrived. The conic appears to have evolved in time, both slowing and cooling, due to wave-particle interactions. We are unable to conclude whether the conic was causally associated with spatial structures of the PSBL or the central plasma sheet.

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.

Associations of geomagnetic activity with plasma sheet thinning and expansion: A statistical study

International Nuclear Information System (INIS)

Hones, E.W. Jr.; Pytte, T.; West, H.I. Jr.

1984-01-01

Associations of geomagnetic activity in the auroral zone with thinnings and expansions of the magnetotail plasma sheet are examined statistically in this paper. We first identified many plasma sheet thinnings and expansions in plasma and particle data from VELA satellites and from OGO 5 without reference to the ground magnetic data. These events were grouped according to the location of the detecting satellite in the magnetotail. For each such group the times of thinning or expansion were then used as fiducial times in a superposed-epoch analysis of the geomagnetic AL index values that were recorded in 8-hour intervals centered on the event times. The results show that many plasma sheet thinnings and expansions are related to discrete negative bay structures that are the classical signature of substorms. Furthermore, they support earlier findings that plasma sheet thinning and expansion at the VELA orbit (rroughly-equal18 R/sub E/) tend to be associated with the onset of the auroral zone negative bay and the beginning of its subsidence, respectively. Earthward of rroughly-equal13-15 R/sub E/, plasma sheet expansion occurs near the time of the onset of the negative bay, again in agreement with earlier findings. A large fraction of plasma sheet expansions to half thicknesses of > or approx. =6 R/sub E/ at the VELA orbit are associated not with a baylike geomagnetic disturbance but with subsidence of a prolonged interval of disturbance. The study also shows that many plasma sheet expansions are related simply to generally enhanced geomagnetic activity showing no baylike or other distinctive features

Exploration of a possible cause of magnetic reconfiguration/reconnection due to generation, rather than annihilation, of magnetic field in a nun-uniform thin current sheet

Science.gov (United States)

Huang, Y. C.; Lyu, L. H.

2014-12-01

Magnetic reconfiguration/reconnection plays an important role on energy and plasma transport in the space plasma. It is known that magnetic field lines on two sides of a tangential discontinuity can connect to each other only at a neutral point, where the strength of the magnetic field is equal to zero. Thus, the standard reconnection picture with magnetic field lines intersecting at the neutral point is not applicable to the component reconnection events observed at the magnetopause and in the solar corona. In our early study (Yu, Lyu, & Wu, 2011), we have shown that annihilation of magnetic field near a thin current sheet can lead to the formation of normal magnetic field component (normal to the current sheet) to break the frozen-in condition and to accelerate the reconnected plasma flux, even without the presence of a neutral point. In this study, we examine whether or not a generation, rather than annihilation, of magnetic field in a nun-uniform thin current sheet can also lead to reconnection of plasma flux. Our results indicate that a non-uniform enhancement of electric current can yield formation of field-aligned currents. The normal-component magnetic field generated by the field-aligned currents can yield reconnection of plasma flux just outside the current-enhancement region. The particle motion that can lead to non-uniform enhancement of electric currents will be discussed.

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

Science.gov (United States)

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

2015-05-01

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 (Pdyn) 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 Pdyn, and southward IMF, implying there location of effective inductive acceleration mechanisms and a strong duskward drift due to the increase of the magnetic field gradient in the near-Earth tail. Higher losses of energetic ions are observed in the dayside plasma sheet under disturbed geomagnetic conditions and enhanced SW Pdyn. These observations are in agreement with theoretical models.

The plasma sheet boundary and Ksub(p)

International Nuclear Information System (INIS)

Freeman, J.W.

1975-01-01

Freeman and Maguire (1967) first drew attention to the intrusion of energetic plasma from the tail to the geostationary orbit during geomagnetically disturbed times. Vasyliunas (1968) reported a correlation between the inward extension of the inner boundary of the plasma sheet and the Ksub(p) index and pointed out that the plasma sheet could occasionally reach the geostationary orbit distance. More recently McIlwain (1972) using the more refined detectors aboard the ATS-5 geostationary space-craft, has emphasized the correlation between the location of the plasma sheet boundary along the ATS orbit and geomagnetic activity. Using some older but unpublished data from the Suprathermal Ion Detector aboard the ATS-1 geostationary satellite, the relation between the local time occurrence of the plasma sheet at the geostationary orbit (6.6Rsub(E)) and Ksub(p) index is reported and then a relationship for the shift in the plasma sheet radial position is derived. (Auth.)

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.

Polar Plasma at Ganymede: Ionospheric outflow and discovery of the plasma sheet

Science.gov (United States)

Collinson, G.; Paterson, W.; Dorelli, J.; Glocer, A.; Sarantos, M.; Wilson, R. J.; Bard, C.

2017-12-01

On the 27th of June 1996, the NASA Galileo spacecraft made humanities first flyby of Jupiter's largest moon, Ganymede, discovering that it is unique to science in being the only moon known to possess an internally generated magnetic dynamo field. Although Galileo carried a plasma spectrometer, the Plasma Subsystem (PLS), converting its highly complex raw data stream into meaningful plasma moments (density, temperature, velocity) is extremely challenging, and was only ever performed for the second (out of six) Ganymede flybys. Resurrecting the original Galileo PLS data analysis software, we processed the raw PLS data from G01, and for the first time present the properties of plasmas encountered. Dense, cold ions were observed outflowing from the moon's north pole (presumed to be dominated by H+ from the icy surface), with more diffuse, warmer field-aligned outflows in the lobes. Dropouts in plasma density combined with velocity perturbations either side of this suggest that Galileo briefly crossed the cusps onto closed magnetic field lines. PLS observations show that upon entry into the magnetosphere, Galileo crossed through the plasma sheet, observing plasma flows consistent with reconnection-driven convection, highly energized 105 eV ions, and a reversal in the magnetic field. The densities of plasmas flowing upwards from Ganymede's ionosphere were higher on open "lobe" field lines than on closed field lines, suggesting that the ionospheric source of these plasmas may be denser at the poles, there may be additional acceleration mechanisms at play, or the balance of ions were outside the energy range of PLS.

Collisionless current sheet equilibria

Science.gov (United States)

Neukirch, T.; Wilson, F.; Allanson, O.

2018-01-01

Current sheets are important for the structure and dynamics of many plasma systems. In space and astrophysical plasmas they play a crucial role in activity processes, for example by facilitating the release of magnetic energy via processes such as magnetic reconnection. In this contribution we will focus on collisionless plasma systems. A sensible first step in any investigation of physical processes involving current sheets is to find appropriate equilibrium solutions. The theory of collisionless plasma equilibria is well established, but over the past few years there has been a renewed interest in finding equilibrium distribution functions for collisionless current sheets with particular properties, for example for cases where the current density is parallel to the magnetic field (force-free current sheets). This interest is due to a combination of scientific curiosity and potential applications to space and astrophysical plasmas. In this paper we will give an overview of some of the recent developments, discuss their potential applications and address a number of open questions.

ASYMMETRIC MAGNETIC RECONNECTION IN WEAKLY IONIZED CHROMOSPHERIC PLASMAS

International Nuclear Information System (INIS)

Murphy, Nicholas A.; Lukin, Vyacheslav S.

2015-01-01

Realistic models of magnetic reconnection in the solar chromosphere must take into account that the plasma is partially ionized and that plasma conditions within any two magnetic flux bundles undergoing reconnection may not be the same. Asymmetric reconnection in the chromosphere may occur when newly emerged flux interacts with pre-existing, overlying flux. We present 2.5D simulations of asymmetric reconnection in weakly ionized, reacting plasmas where the magnetic field strengths, ion and neutral densities, and temperatures are different in each upstream region. The plasma and neutral components are evolved separately to allow non-equilibrium ionization. As in previous simulations of chromospheric reconnection, the current sheet thins to the scale of the neutral–ion mean free path and the ion and neutral outflows are strongly coupled. However, the ion and neutral inflows are asymmetrically decoupled. In cases with magnetic asymmetry, a net flow of neutrals through the current sheet from the weak-field (high-density) upstream region into the strong-field upstream region results from a neutral pressure gradient. Consequently, neutrals dragged along with the outflow are more likely to originate from the weak-field region. The Hall effect leads to the development of a characteristic quadrupole magnetic field modified by asymmetry, but the X-point geometry expected during Hall reconnection does not occur. All simulations show the development of plasmoids after an initial laminar phase

Plasma parameters, fluctuations and kinetics in a magnetic field line reconnection experiment

International Nuclear Information System (INIS)

Wild, N.C. Jr.

1983-01-01

The processes associated with reconnecting magnetic field lines have been studied in a large experimental laboratory plasma. Detailed time- and space-resolved probe measurements of the plasma density, temperature, potential and electric and magnetic fields are discussed. Plasma currents are seen to modify the vacuum magnetic field topology. A flat neutral sheet develops along the separatrix where magnetic flux is transferred from regions of private to common flux. Forced tearing and magnetic island formation are also observed. Rapid electron heating, density and temperature nonuniformities and plasma potential gradients are all observed. The pressure is found to peak at the two edges of the neutral sheet. The dissipation E.J is determined and analyzed in terms of particle heating and fluid acceleration. A consistent, detailed picture of the energy flow via Poynting's theorem is also described. Significant temporal fluctuations in the magnetic fields and electron velocity distribution are measured and seen to give rise to anomalously high values for the plasma resistivity, the ion viscosity and the cross-field thermal conductivity. Electron temperature fluctuations, double layers associated with partial current disruptions, and whistler wave magnetic turbulence have all been identified and studied during the course of the reconnection event

A triggering of solar flare by magnetosonic waves in a neutral sheet plasma

International Nuclear Information System (INIS)

Sakai, Jun-ichi; Washimi, Haruichi.

1981-09-01

A theoretical model of the triggering of a solar flare by magnetosonic waves in a neutral sheet plasma is discussed. It is shown that the ponderomotive force due to the magnetosonic waves strongly excites the plasma convection flow in the magnetic neutral sheet which in turn enhances the tearing instability. The system of basic equations for the tearing mode including the time-averaged nonlinear effects due to the magnetosonic waves is derived and the boundary value problem is solved. The results show that the growth time of the instability is shortened to about 100 sec for reasonable magnetosonic wave intensity. (author)

Analytical theory of neutral current sheets with a sheared magnetic field in collisionless relativistic plasma

Science.gov (United States)

Kocharovsky, V. V.; Kocharovsky, Vl V.; Martyanov, V. Yu; Nechaev, A. A.

2017-12-01

We derive and describe analytically a new wide class of self-consistent magnetostatic structures with sheared field lines and arbitrary energy distributions of particles. To do so we analyze superpositions of two planar current sheets with orthogonal magnetic fields and cylindrically symmetric momentum distribution functions, such that the magnetic field of one of them is directed along the symmetry axis of the distribution function of the other. These superpositions satisfy the pressure balance equation and allow one to construct configurations with an almost arbitrarily sheared magnetic field. We show that most of previously known current sheet families with sheared magnetic field lines are included in this novel class.

Spatial Evolution of Electrostatic Solitary Waves along Plasma Sheet Boundary Layer Adjacent to the Magnetic Reconnection X-Line

International Nuclear Information System (INIS)

Li Shi-You; Zhang Shi-Feng; Cai Hong; Deng Xiao-Hua

2012-01-01

Analysis on the spatial structure of electrostatic solitary waves (ESWs) along the plasma sheet boundary layer (PSBL) near an on-going magnetic reconnection X-line is performed. Most of the ESWs in the PSBL of R3 region near reconnection X-line are propagating earthwards away from the reconnecting site. An analysis of their spatial structure shows that, when ESWs propagate along the ambient field in the PSBL, outwards from the magnetic reconnection X-line, their amplitude will finally attenuate and thus the electron hole will fade away but their spatial scale remains unchanged. However, the spatial structure of propagating ESWs evolves from 1-D-like to 2-D-like though totally in a 1-D structure. (geophysics, astronomy, and astrophysics)

Vlasov-Maxwell equilibrium solutions for Harris sheet magnetic field with Kappa velocity distribution

International Nuclear Information System (INIS)

Fu, W.-Z.; Hau, L.-N.

2005-01-01

An exact solution of the steady-state, one-dimensional Vlasov-Maxwell equations for a plasma current sheet with oppositely directed magnetic field was found by Harris in 1962. The so-called Harris magnetic field model assumes Maxwellian velocity distributions for oppositely drifting ions and electrons and has been widely used for plasma stability studies. This paper extends Harris solutions by using more general κ distribution functions that incorporate Maxwellian distribution in the limit of κ→∞. A new functional form for the plasma pressure as a function of the magnetic vector potential p(A) is found and the magnetic field is a modified tanh z function. In the extended solutions the effective temperature is no longer spatially uniform like in the Harris model and the thickness of the current layer decreases with decreasing κ

Plasma sheet fast flows and auroral dynamics during substorm: a case study

Directory of Open Access Journals (Sweden)

N. L. Borodkova

2002-03-01

Full Text Available Interball-1 observations of a substorm development in the mid-tail on 16 December 1998 are compared with the auroral dynamics obtained from the Polar UV imager. Using these data, the relationship between plasma flow directions in the tail and the location of the auroral activation is examined. Main attention is given to tailward and earth-ward plasma flows, interpreted as signatures of a Near Earth Neutral Line (NENL. It is unambiguously shown that in the mid-plasma sheet the flows were directed tailward when the auroral bulge developed equatorward of the spacecraft ionospheric footprint. On the contrary, when active auroras moved poleward of the Interball-1 projection, earthward fast flow bursts were observed. This confirms the concept that the NENL (or flow reversal region is the source of auroras forming the poleward edge of the auroral bulge. The observed earthward flow bursts have all typical signatures of Bursty Bulk Flows (BBFs, described by Angelopolous et al. (1992. These BBFs are related to substorm activations starting at the poleward edge of the expanded auroral bulge. We interpret the BBFs as a result of reconnection pulses occurring tail-ward of Interball-1. In addition, some non-typically observed phenomena were detected in the plasma sheet during this substorm: (i tailward/earthward flows were superimposed on a very strong duskward flow, and (ii wavy structures of both magnetic field and plasma density were registered. The latter observation is probably linked to the filamentary structure of the current sheet.Key words. Magnetospheric physics (auroral phenomena; plasma sheet; storms and substorms

Acceleration of O+ from the cusp to the plasma sheet

Science.gov (United States)

Liao, J.; Kistler, L. M.; Mouikis, C. G.; Klecker, B.; Dandouras, I.

2015-02-01

Heavy ions from the ionosphere that are accelerated in the cusp/cleft have been identified as a direct source for the hot plasma in the plasma sheet. However, the details of the acceleration and transport that transforms the originally cold ions into the hot plasma sheet population are not fully understood. The polar orbit of the Cluster satellites covers the main transport path of the O+ from the cusp to the plasma sheet, so Cluster is ideal for tracking its velocity changes. However, because the cusp outflow is dispersed according to its velocity as it is transported to the tail, due to the velocity filter effect, the observed changes in beam velocity over the Cluster orbit may simply be the result of the spacecraft accessing different spatial regions and not necessarily evidence of acceleration. Using the Cluster Ion Spectrometry/Composition Distribution Function instrument onboard Cluster, we compare the distribution function of streaming O+ in the tail lobes with the initial distribution function observed over the cusp and reveal that the observations of energetic streaming O+ in the lobes around -20 RE are predominantly due to the velocity filter effect during nonstorm times. During storm times, the cusp distribution is further accelerated. In the plasma sheet boundary layer, however, the average O+ distribution function is above the upper range of the outflow distributions at the same velocity during both storm and nonstorm times, indicating that acceleration has taken place. Some of the velocity increase is in the direction perpendicular to the magnetic field, indicating that the E × B velocity is enhanced. However, there is also an increase in the parallel direction, which could be due to nonadiabatic acceleration at the boundary or wave heating.

HEATING MECHANISMS IN THE LOW SOLAR ATMOSPHERE THROUGH MAGNETIC RECONNECTION IN CURRENT SHEETS

Energy Technology Data Exchange (ETDEWEB)

Ni, Lei; Lin, Jun [Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011 (China); Roussev, Ilia I. [Division of Geosciences, National Science Foundation Arlington, Virginia (United States); Schmieder, Brigitte, E-mail: leini@ynao.ac.cn [Observatoire de Paris, LESIA, Meudon (France)

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 × 10{sup 4} K) and low temperature (∼10{sup 4} 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 × 10{sup 4} 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 (∼10{sup 4} K) and the high temperature Interface Region Imaging Spectrograph (IRIS) bombs (≳8 × 10{sup 4}) in the future.

Enhancement of the guide field during the current sheet formation in the three-dimensional magnetic configuration with an X line

International Nuclear Information System (INIS)

Frank, Anna; Bugrov, Sergey; Markov, Vladimir

2009-01-01

Results are presented from studies of the formation of current sheets during exciting a current aligned with the X line of the 3D magnetic configuration, in the CS-3D device. Enhancement of the guide field (parallel to the X line) was directly observed for the first time, on the basis of magnetic measurements. After the current sheet formation, the guide field inside the sheet exceeds its initial value, as well as the field outside. It is convincingly demonstrated that an enhancement of the guide field is due to its transportation by plasma flows on the early stage of the sheet formation. The in-plane plasma currents, which produce the excess guide field, are comparable to the total current along the X line that initiates the sheet itself.

Quasi-adiabatic particle acceleration in a magnetic field reversals and the formation of the plasma sheet boundary layer in the earth's magnetotail

International Nuclear Information System (INIS)

Zelenyi, L.M.; Vogin, D.V.; Buechner, J.

1989-01-01

Two types of regularity exist for the particle motion in the two-dimensional magnetic field reversals (MFR) with the strongly curves magnetic field lines - the usual adiabatic and another one which we called 'quasiadiabatic'. Here we consider the acceleration of MFR particles in stationary and homogeneous electric field induced by the motion of MFR through the ambient plasma (i.e. solar wind). Assuming that the time scale of acceleration is slow in comparison with the period of orbital motion we introduce the new longitudinal invariant I κ . This enables to describe the process of acceleration in a closed form and to obtain for the first time the laws governing the quasiadiabatic ion acceleration in the Earth's mangetotail. The similarities and differences in adiabatic and quasiadiabatic acceleration mechanisms are discussed. The obtained results give and important insights to the problem of the particle heating in hte Earth's magnetotail and to the formation of accelerated plasma streams along the edges of the plasma sheet. (author). 17 refs.; 7 figs

Dipole-sheet multipole magnets for accelerators

International Nuclear Information System (INIS)

Walstrom, P.L.

1993-01-01

The dipole-sheet formalism can be used to describe both cylindrical current-sheet multipole magnets and cylindrical-bore magnets made up of permanent magnet blocks. For current sheets, the formalism provides a natural way of finding a finite set of turns that approximate a continuous distribution. The formalism is especially useful In accelerator applications where large-bore, short, high-field-quality magnets that are dominated by fringe fields are needed. A further advantage of the approach is that in systems with either open or cylindrically symmetric magnetic boundaries, analytical expressions for the three-dimensional fields that are suitable for rapid numerical evaluation can be derived. This development is described in some detail. Also, recent developments in higher-order particle-beam optics codes based on the formalism are described briefly

The quiet evening auroral arc and the structure of the growth phase near-Earth plasma sheet

Science.gov (United States)

Coroniti, F. V.; Pritchett, P. L.

2014-03-01

The plasma pressure and current configuration of the near-Earth plasma sheet that creates and sustains the quiet evening auroral arc during the growth phase of magnetospheric substorms is investigated. We propose that the quiet evening arc (QEA) connects to the thin near-Earth current sheet, which forms during the development of the growth phase enhancement of convection. The current sheet's large polarization electric fields are shielded from the ionosphere by an Inverted-V parallel potential drop, thereby producing the electron precipitation responsible for the arc's luminosity. The QEA is located in the plasma sheet region of maximal radial pressure gradient and, in the east-west direction, follows the vanishing of the approximately dawn-dusk-directed gradient or fold in the plasma pressure. In the evening sector, the boundary between the Region1 and Region 2 current systems occurs where the pressure maximizes (approximately radial gradient of the pressure vanishes) and where the approximately radial gradient of the magnetic flux tube volume also vanishes in an inflection region. The proposed intricate balance of plasma sheet pressure and currents may well be very sensitive to disruption by the arrival of equatorward traveling auroral streamers and their associated earthward traveling dipolarization fronts.

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 separations. Altogether, the Cluster observations described here mesh rather well with theories

Generation mechanism of the whistler-mode waves in the plasma sheet prior to magnetic reconnection

Czech Academy of Sciences Publication Activity Database

Wei, X. H.; Cao, J. B.; Zhou, G. C.; Fu, H. S.; Santolík, Ondřej; Reme, H.; Dandouras, I.; Cornilleau, N.; Fazakerley, A.

2013-01-01

Roč. 52, č. 1 (2013), s. 205-210 ISSN 0273-1177 Institutional support: RVO:68378289 Keywords : whistler-mode waves * electron temperature anisotropy * Reconnection * the plasma sheet Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 1.238, year: 2013 http://www.sciencedirect.com/science/article/pii/S0273117713001221

Simultaneous Measurements of Substorm-Related Electron Energization in the Ionosphere and the Plasma Sheet

Science.gov (United States)

Sivadas, N.; Semeter, J.; Nishimura, Y.; Kero, A.

2017-10-01

On 26 March 2008, simultaneous measurements of a large substorm were made using the Poker Flat Incoherent Scatter Radar, Time History of Events and Macroscale Interactions during Substorm (THEMIS) spacecraft, and all sky cameras. After the onset, electron precipitation reached energies ≳100 keV leading to intense D region ionization. Identifying the source of energetic precipitation has been a challenge because of lack of quantitative and magnetically conjugate measurements of loss cone electrons. In this study, we use the maximum entropy inversion technique to invert altitude profiles of ionization measured by the radar to estimate the loss cone energy spectra of primary electrons. By comparing them with magnetically conjugate measurements from THEMIS-D spacecraft in the nightside plasma sheet, we constrain the source location and acceleration mechanism of precipitating electrons of different energy ranges. Our analysis suggests that the observed electrons ≳100 keV are a result of pitch angle scattering of electrons originating from or tailward of the inner plasma sheet at 9RE, possibly through interaction with electromagnetic ion cyclotron waves. The electrons of energy 10-100 keV are produced by pitch angle scattering due to a potential drop of ≲10 kV in the auroral acceleration region (AAR) as well as wave-particle interactions in and tailward of the AAR. This work demonstrates the utility of magnetically conjugate ground- and space-based measurements in constraining the source of energetic electron precipitation. Unlike in situ spacecraft measurements, ground-based incoherent scatter radars combined with an appropriate inversion technique can be used to provide remote and continuous-time estimates of loss cone electrons in the plasma sheet.

Sheet pinch devices

International Nuclear Information System (INIS)

Anderson, O.A.; Baker, W.R.; Ise, J. Jr.; Kunkel, W.B.; Pyle, R.V.; Stone, J.M.

1958-01-01

Three types of sheet-like discharges are being studied at Berkeley. The first of these, which has been given the name 'Triax', consists of a cylindrical plasma sleeve contained between two coaxial conducting cylinders A theoretical analysis of the stability of the cylindrical sheet plasma predicts the existence of a 'sausage-mode' instability which is, however, expected to grow more slowly than in the case of the unstabilized linear pinch (by the ratio of the radial dimensions). The second pinch device employs a disk shaped discharge with radial current guided between flat metal plates, this configuration being identical to that of the flat hydromagnetic capacitor without external magnetic field. A significant feature of these configurations is the absence of a plasma edge, i.e., there are no regions of sharply curved magnetic field lines anywhere in these discharges. The importance of this fact for stability is not yet fully investigated theoretically. As a third configuration a rectangular, flat pinch tube has been constructed, and the behaviour of a flat plasma sheet with edges is being studied experimentally

XUV laser-produced plasma sheet beam and microwave agile mirror

International Nuclear Information System (INIS)

Shen, W.; Scharer, J.E.; Porter, B.; Lam, N.T.

1994-01-01

An excimer-laser (λ = 193 nm) produced plasma in an organic gas (TMAE) has been generated and studied. These studies have determined the ion-electron recombination coefficient and the photon absorption cross-section, of the neutral gas. The dependences of wave transmission, reflection and absorption on plasma density are obtained. A new optical system with an array of cylindrical XUV coated lenses has been implemented to form a plasma sheet to study its usage as agile mirror microwave reflector. The lens system expands the incident laser beam in X direction and compresses it in Y direction to form a sheet beam. The expanded beam then passes through a vacuum chamber filled with TMAE at 50--500 nTorr to produce the plasma sheet. Space-time measurements of the plasma density and temperature as measured by a Langmuir probe are presented. XUV optical measurements of the laser beam as measured by a photodiode are presented. Initial experiments have generated a plasma sheet of 5--10 mm x 11 cm with peak plasma density of 5 x 10 13 cm -3 . A microwave source will be utilized to study the agile mirror character of the plasma sheet. Modeling of the microwave reflection from the plasma profile will also be discussed

Measurement of OH free radical in magnetized sheet plasma crossed with vertical gas-flow by laser-induced fluorescence spectroscopy

International Nuclear Information System (INIS)

Tonegawa, Akira; Takatori, Masahiko; Kobayashi, Yukihiro; Kawamura, Kazutaka; Takayama, Kazuo

1997-01-01

We demonstrated the production of OH free radicals in an argon magnetized sheet plasma crossed with vertical gas-flow mixed with an oxygen gas O 2 and a hydrogen gas H 2 . The density and the rotational-vibrational temperature of the OH free radicals were measured by a laser-induced fluorescence (LIF). The density of OH free radicals increases with increasing O 2 gas-flow, while the high energy part of the electron-energy-distribution-function f e (E) above 8 eV decreases. These results suggest the high energy part of f e (E) is contributed to the dissociation of O 2 and the production of OH free radicals. (author)

MAGNETIC NULL POINTS IN KINETIC SIMULATIONS OF SPACE PLASMAS

International Nuclear Information System (INIS)

Olshevsky, Vyacheslav; Innocenti, Maria Elena; Cazzola, Emanuele; Lapenta, Giovanni; Deca, Jan; Divin, Andrey; Peng, Ivy Bo; Markidis, Stefano

2016-01-01

We present a systematic attempt to study magnetic null points and the associated magnetic energy conversion in kinetic particle-in-cell simulations of various plasma configurations. We address three-dimensional simulations performed with the semi-implicit kinetic electromagnetic code iPic3D in different setups: variations of a Harris current sheet, dipolar and quadrupolar magnetospheres interacting with the solar wind, and a relaxing turbulent configuration with multiple null points. Spiral nulls are more likely created in space plasmas: in all our simulations except lunar magnetic anomaly (LMA) and quadrupolar mini-magnetosphere the number of spiral nulls prevails over the number of radial nulls by a factor of 3–9. We show that often magnetic nulls do not indicate the regions of intensive energy dissipation. Energy dissipation events caused by topological bifurcations at radial nulls are rather rare and short-lived. The so-called X-lines formed by the radial nulls in the Harris current sheet and LMA simulations are rather stable and do not exhibit any energy dissipation. Energy dissipation is more powerful in the vicinity of spiral nulls enclosed by magnetic flux ropes with strong currents at their axes (their cross sections resemble 2D magnetic islands). These null lines reminiscent of Z-pinches efficiently dissipate magnetic energy due to secondary instabilities such as the two-stream or kinking instability, accompanied by changes in magnetic topology. Current enhancements accompanied by spiral nulls may signal magnetic energy conversion sites in the observational data

The Interaction of C-Band Microwaves with Large Plasma Sheets

International Nuclear Information System (INIS)

Ding Liang; Huo Wenqing; Yang Xinjie; Xu Yuemin

2012-01-01

A large plasma sheet 60 cm×60 cm×2 cm in size was generated using a hollow cathode, and measurements were conducted for interactions including transmission, reflection and absorption. With different discharge parameters, plasma sheets can vary and influence microwave strength. Microwave reflection decreases when the discharge current rises, and the opposite occurs in transmission. The C-band microwave is absorbed when it is propagated through large plasma sheets at higher pressure. When plasma density and collision frequency are fitted with incident microwave frequency, a large amount of microwave energy is consumed. Reflection, transmission and absorption all exist simultaneously. Plasma sheets are an attractive alternative to microwave steering at low pressure, and the microwave reflection used in receiving radar can be altered by changing the discharge parameters.

Magnetic vortex growth in the transition layer of a mildly relativistic plasma shock

International Nuclear Information System (INIS)

Murphy, G. C.; Dieckmann, M. E.; Drury, L. O'C.

2010-01-01

A two-dimensional particle simulation models the collision of two electron-ion plasma clouds along a quasiparallel magnetic field. The collision speed is 0.9c and the density ratio, 10. A current sheet forms at the front of the dense cloud, in which the electrons and the magnetic field reach energy equipartition with the ions. A structure composed of a solenoidal and a toroidal magnetic field grows in this sheet. It resembles the cross-section of the torus of a spheromak, which may provide the coherent magnetic fields in gamma-ray burst jets needed for their prompt emissions.

Interaction of a charge with a thin plasma sheet

International Nuclear Information System (INIS)

Bordag, M.

2007-01-01

The interaction of the electromagnetic field with a two-dimensional plasma sheet intended to describe the pi-electrons of a carbon nanotube or a C 60 molecule is investigated. By first integrating out the displacement field of the plasma or the electromagnetic field, different representations for quantities like the Casimir energy are derived which are shown to be consistent with one another. Starting from the covariant gauge for the electromagnetic field, it is shown that the matching conditions to which the presence of the plasma sheet can be reduced are different from the commonly used ones. The difference in the treatments does not show up in the Casimir force between two parallel sheets, but it is present in the Casimir-Polder force between a charge or a neutral atom and a sheet. At once, since the plasma sheet is a regularization of the conductor boundary conditions, this sheds light on the difference in physics found earlier in the realization of conductor boundary conditions as 'thin' or 'thick' boundary conditions in Phys. Rev. D 70, 085010 (2004)

3-D MHD modeling and stability analysis of jet and spheromak plasmas launched into a magnetized plasma

Science.gov (United States)

Fisher, Dustin; Zhang, Yue; Wallace, Ben; Gilmore, Mark; Manchester, Ward; Arge, C. Nick

2016-10-01

The Plasma Bubble Expansion Experiment (PBEX) at the University of New Mexico uses a coaxial plasma gun to launch jet and spheromak magnetic plasma configurations into the Helicon-Cathode (HelCat) plasma device. Plasma structures launched from the gun drag frozen-in magnetic flux into the background magnetic field of the chamber providing a rich set of dynamics to study magnetic turbulence, force-free magnetic spheromaks, and shocks. Preliminary modeling is presented using the highly-developed 3-D, MHD, BATS-R-US code developed at the University of Michigan. BATS-R-US employs an adaptive mesh refinement grid that enables the capture and resolution of shock structures and current sheets, and is particularly suited to model the parameter regime under investigation. CCD images and magnetic field data from the experiment suggest the stabilization of an m =1 kink mode trailing a plasma jet launched into a background magnetic field. Results from a linear stability code investigating the effect of shear-flow as a cause of this stabilization from magnetic tension forces on the jet will be presented. Initial analyses of a possible magnetic Rayleigh Taylor instability seen at the interface between launched spheromaks and their entraining background magnetic field will also be presented. Work supported by the Army Research Office Award No. W911NF1510480.

Dense sheet Z-pinches

International Nuclear Information System (INIS)

Tetsu, Miyamoto

1999-01-01

The steady state and quasi-steady processes of infinite- and finite-width sheet z-pinches are studied. The relations corresponding to the Bennett relation and Pease-Braginskii current of cylindrical fiber z-pinches depend on a geometrical factor in the sheet z-pinches. The finite-width sheet z-pinch is approximated by a segment of infinite-width sheet z-pinch, if it is wide enough, and corresponds to a number of (width/thickness) times fiber z-pinch plasmas of the diameter that equals the sheet thickness. If the sheet current equals this number times the fiber current, the plasma created in the sheet z-pinches is as dense as in the fiber z-pinches. The total energy of plasma and magnetic field per unit mass is approximately equal in both pinches. Quasi-static transient processes are different in several aspects from the fiber z-pinch. No radiation collapse occurs in the sheet z-pinch. The stability is improved in the sheet z-pinches. The fusion criterions and the experimental arrangements to produce the sheet z-pinches are also discussed. (author)

Equilibrium structure of the plasma sheet boundary layer-lobe interface

Science.gov (United States)

Romero, H.; Ganguli, G.; Palmadesso, P.; Dusenbery, P. B.

1990-01-01

Observations are presented which show that plasma parameters vary on a scale length smaller than the ion gyroradius at the interface between the plasma sheet boundary layer and the lobe. The Vlasov equation is used to investigate the properties of such a boundary layer. The existence, at the interface, of a density gradient whose scale length is smaller than the ion gyroradius implies that an electrostatic potential is established in order to maintain quasi-neutrality. Strongly sheared (scale lengths smaller than the ion gyroradius) perpendicular and parallel (to the ambient magnetic field) electron flows develop whose peak velocities are on the order of the electron thermal speed and which carry a net current. The free energy of the sheared flows can give rise to a broadband spectrum of electrostatic instabilities starting near the electron plasma frequency and extending below the lower hybrid frequency.

Interpretation of magnetosonic waves in the boundary regions of the plasma sheet as seen by the ISEE 3 spacecraft

International Nuclear Information System (INIS)

Smith, P.R.; Hopcraft, K.I.; Murphy, N.

1987-01-01

Recent calculations that derive the normal-mode spectrum of an idealized magnetic current sheet are discussed. The Harris neutral-sheet equilibrium is perturbed with an ideal MHD displacement. The longitudinal polarization of the fundamental modes is calculated as a function of the position in the sheet. Using data from the energetic-ion instrument aboard ISEE 3, the thickness of the plasma sheet in the deep geomagnetic tail is estimated. This parameter enables a quantitative comparison between the boundary oscillations reported by Tsurutani and Smith (1984) and the normal mode oscillations derived by Hopcraft and Smith (1985) to be performed. The normal-mode solutions are found to be consistent with observation. Further aspects of the MHD wave spectrum that may lead to an observable variation of the mode character across the boundary of the plasma sheet are pointed out. 12 references

Continuous development of current sheets near and away from magnetic nulls

International Nuclear Information System (INIS)

Kumar, Sanjay; Bhattacharyya, R.

2016-01-01

The presented computations compare the strength of current sheets which develop near and away from the magnetic nulls. To ensure the spontaneous generation of current sheets, the computations are performed congruently with Parker's magnetostatic theorem. The simulations evince current sheets near two dimensional and three dimensional magnetic nulls as well as away from them. An important finding of this work is in the demonstration of comparative scaling of peak current density with numerical resolution, for these different types of current sheets. The results document current sheets near two dimensional magnetic nulls to have larger strength while exhibiting a stronger scaling than the current sheets close to three dimensional magnetic nulls or away from any magnetic null. The comparative scaling points to a scenario where the magnetic topology near a developing current sheet is important for energetics of the subsequent reconnection.

Thermal catastrophe in the plasma sheet boundary layer

International Nuclear Information System (INIS)

Smith, R.A.; Goertz, C.K.; Grossmann, W.

1986-01-01

This letter presents a first step towards a substorm model including particle heating and transport in the plasma sheet boundary layer (PSBL). The heating mechanism discussed is resonant absorption of Alfven waves. For some assumed MHD perturbation incident from the tail lobes onto the plasma sheet, the local heating rate in the PSBL has the form of a resonance function of the one-fluid plasma temperature. Balancing the local heating by convective transport of the heated plasma toward the central plasma sheet, and ''equation of state'' is found for the steady-state PSBL whose solution has the form of a mathematical catastrophe: at a critical value of a parameter containing the incident power flux, the local density, and the convection velocity, the equilibrium temperature jumps discontinuously. Associating this temperature increase with the abrupt onset of the substorm expansion phase, the catastrophe model indicates at least three ways in which the onset may be triggered. Several other consequences related to substorm dynamics are suggested by the simple catastrophe model

Compressional Pc5 type pulsations in the morningside plasma sheet

Directory of Open Access Journals (Sweden)

A. Vaivads

Full Text Available We study compressional pulsations in Pc5 frequency range observed in the dawn-side at distances of about 10 RE , close to the magnetic equator. We use data obtained during two events of conjunctions between Equator-S and Geotail: 1000–1700 UT on 9 March 1998, and 0200–0600 UT on 25 April 1998. In both events, pulsations are observed after substorm activity. The pulsations are antisymmetric with respect to the equatorial plane (even mode, and move eastward with phase velocity close to plasma velocity. The pulsations tend to be pressure balanced. We also discuss possible generation mechanisms of the pulsations.

Key words. Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma sheet

Compressional Pc5 type pulsations in the morningside plasma sheet

Directory of Open Access Journals (Sweden)

A. Vaivads

2001-03-01

Full Text Available We study compressional pulsations in Pc5 frequency range observed in the dawn-side at distances of about 10 RE , close to the magnetic equator. We use data obtained during two events of conjunctions between Equator-S and Geotail: 1000–1700 UT on 9 March 1998, and 0200–0600 UT on 25 April 1998. In both events, pulsations are observed after substorm activity. The pulsations are antisymmetric with respect to the equatorial plane (even mode, and move eastward with phase velocity close to plasma velocity. The pulsations tend to be pressure balanced. We also discuss possible generation mechanisms of the pulsations.Key words. Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma sheet

Composition and plasma properties of the plasma sheet in the Earth's magnetotail

International Nuclear Information System (INIS)

Orsini, S.; Altwegg, K.; Balsiger, H.

1986-01-01

A statistical study of the plasma sheet properties, based on 300 h of data from the ISEE-1 Ion Composition Experiment, yiels a description of H + and He ++ densities and temperatures as functions of magnetospheric substorm activity and geocentric distance. The H + and He ++ temperatures are found to be well correlated, such that a ratio T(He ++ )/T(H + ) = 2.7±0.1 is typical. However, linear-regression analysis typically yields a nonvanishing T(He ++ ) in the limit T(H + ) #-> # 0, a limit that is approached through the addition of cold ionospheric H + to the plasma sheet during active periods. The plasma sheet proton temperature T(H + ) varies inversely with geocentric distance, and the radial gradient of T(H + ) increases with increasing activity index AE. The density ratio N (He ++ )/N(H + ) increases with geocentric distance, irrespective of AE

Effects of the IMF on the plasma sheet

International Nuclear Information System (INIS)

Akasofu, S.-I.; Meng, C.-I.

1986-01-01

It is suggested that the IMF Bsub(z) component controls partially the geometry of the cross-section (y-z plane) of the plasma sheet. Our vacuum superposition model suggests that the cross-section has a dumbbell shape for te IMF Bsub(z) O. It is also suggested that the thinning and subsequent expansion of the plasma sheet during magnetospheric substorms are partially due to a direct effect of the IMF Bsub(z). (author)

Radial evolution of the finite-width plasma sheet in a z-pinch: A parametric analysis based on conservation laws

International Nuclear Information System (INIS)

Sherar, A.G.

1996-01-01

A simple method that allows to estimate the macroscopic variables (width, temperature, density, radial velocity, etc.) of the plasma sheet in the first compression of a z-pinch, is presented. Following the snow-plow model, the radial compression is assumed as a process in which the mass is swept by a sheet of finite width. Very high pressures can be reached inside the sheet due to magnetic compression, higher than the filling gas pressure. A quasi-equilibrium hypothesis for the pressure of the layer is defined. From this assumption the thickness of the dense plasma sheet can be estimated. A set of MHD equations that include a term to compute total energy losses is used. The system of equations is written in the interface reference system in which the internal boundary of the sheet is at rest. In this early stage of the compression, the plasma temperature is mainly due to heavy particles. The results obtained using this model can explain ionic temperatures measured in cold plasmas which cannot be explained from electron-ion collisions. From an analytical study of the formation solution, a well-defined range of validity for each parameter of the model has been found. Based on physical conditions, these ranges of validity give a criterion to understanding the necessary conditions to build and maintain a moving plasma sheet. Using this model, other geometries besides the cylindrical one can be analyzed in the future

Compressional wave events in the dawn plasma sheet observed by Interball-1

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O. Verkhoglyadova

1999-09-01

Full Text Available Compressional waves with periods greater than 2 min (about 10-30 min at low geomagnetic latitudes, namely compressional Pc5 waves, are studied. The data set obtained with magnetometer MIF-M and plasma analyzer instrument CORALL on board the Interball-1 are analyzed. Measurements performed in October 1995 and October 1996 in the dawn plasma sheet at -30 RE ≤ XGSM and |ZGSM| ≤ 10 RE are considered. Anti-phase variations of magnetic field and ion plasma pressures are analyzed by searching for morphological similarities in the two time series. It is found that longitudinal and transverse magnetic field variations with respect to the background magnetic field are of the same order of magnitude. Plasma velocities are processed for each time period of the local dissimilarity in the pressure time series. Velocity disturbances occur mainly transversely to the local field line. The data reveal the rotation of the velocity vector. Because of the field line curvature, there is no fixed position of the rotational plane in the space. These vortices are localized in the regions of anti-phase variations of the magnetic field and plasma pressures, and the vortical flows are associated with the compressional Pc5 wave process. A theoretical model is proposed to explain the main features of the nonlinear wave processes. Our main goal is to study coupling of drift Alfven wave and magnetosonic wave in a warm inhomogeneous plasma. A vortex is the partial solution of the set of the equations when the compression is neglected. A compression effect gives rise to a nonlinear soliton-like solution.Key words. Magnetosphere physics (magnetotail · Space plasma physics (kinetic and MHD theory; non-linear phenomena

Kinetic Simulations of Plasma Energization and Particle Acceleration in Interacting Magnetic Flux Ropes

Science.gov (United States)

Du, S.; Guo, F.; Zank, G. P.; Li, X.; Stanier, A.

2017-12-01

The interaction between magnetic flux ropes has been suggested as a process that leads to efficient plasma energization and particle acceleration (e.g., Drake et al. 2013; Zank et al. 2014). However, the underlying plasma dynamics and acceleration mechanisms are subject to examination of numerical simulations. As a first step of this effort, we carry out 2D fully kinetic simulations using the VPIC code to study the plasma energization and particle acceleration during coalescence of two magnetic flux ropes. Our analysis shows that the reconnection electric field and compression effect are important in plasma energization. The results may help understand the energization process associated with magnetic flux ropes frequently observed in the solar wind near the heliospheric current sheet.

Spatial Distribution and Semiannual Variation of Cold-Dense Plasma Sheet

Science.gov (United States)

Bai, Shichen; Shi, Quanqi; Tian, Anmin; Nowada, Motoharu; Degeling, Alexander W.; Zhou, Xu-Zhi; Zong, Qiu-Gang; Rae, I. Jonathan; Fu, Suiyan; Zhang, Hui; Pu, Zuyin; Fazakerly, Andrew N.

2018-01-01

The cold-dense plasma sheet (CDPS) plays an important role in the entry process of the solar wind plasma into the magnetosphere. Investigating the seasonal variation of CDPS occurrences will help us better understand the long-term variation of plasma exchange between the solar wind and magnetosphere, but any seasonal variation of CDPS occurrences has not yet been reported in the literature. In this paper, we investigate the seasonal variation of the occurrence rate of CDPS using Geotail data from 1996 to 2015 and find a semiannual variation of the CDPS occurrences. Given the higher probability of solar wind entry under stronger northward interplanetary magnetic field (IMF) conditions, 20 years of IMF data (1996-2015) are used to investigate the seasonal variation of IMF Bz under northward IMF conditions. We find a semiannual variation of IMF Bz, which is consistent with the Russell-McPherron (R-M) effect. We therefore suggest that the semiannual variation of CDPS may be related to the R-M effect.

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.

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.

Study of driven magnetic reconnection in a laboratory plasma

International Nuclear Information System (INIS)

Yamada, Masaaki; Ji, H.; Hsu, S.; Carter, T.; Kulsrud, R.; Bretz, N.; Jobes, F.; Ono, Yasushi; Perkins, F.

1998-01-01

The Magnetic Reconnection Experiment (MRX) has been constructed to investigate the fundamental physics of magnetic reconnection in a well controlled laboratory setting. This device creates an environment satisfying the criteria for a magnetohydrodynamic (MHD) plasma (S much-gt 1, ρ i much-lt L). The boundary conditions can be controlled externally, and experiments with fully three-dimensional reconnection are now possible. In the initial experiments, the effects of the third vector component of reconnecting fields have been studied. Two distinctively different shapes of neutral sheet current layers, depending on the third component, are identified during driven magnetic reconnection. Without the third component (anti-parallel or null-helicity reconnection), a thin double-Y shaped diffusion region is identified. A neutral sheet current profile is measured accurately to be as narrow as order ion gyro-radius. In the presence of an appreciable third component (co-helicity reconnection), an O-shaped diffusion region appears and grows into a spheromak configuration

Electron vortex magnetic holes: A nonlinear coherent plasma structure

Energy Technology Data Exchange (ETDEWEB)

Haynes, Christopher T., E-mail: c.t.haynes@qmul.ac.uk; Burgess, David; Sundberg, Torbjorn [School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS (United Kingdom); Camporeale, Enrico [Multiscale Dynamics, Centrum Wiskunde and Informatica (CWI), Amsterdam (Netherlands)

2015-01-15

We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional particle-in-cell simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic holes (EVMHs), have circular cross-section. The magnetic field depression is associated with a diamagnetic azimuthal current provided by a population of trapped electrons in petal-like orbits. The trapped electron population provides a mean azimuthal velocity and since trapping preferentially selects high pitch angles, a perpendicular temperature anisotropy. The structures arise out of initial perturbations in the course of the turbulent evolution of the plasma, and are stable over at least 100 electron gyroperiods. We have verified the model for the EVMH by carrying out test particle and PIC simulations of isolated structures in a uniform plasma. It is found that (quasi-)stable structures can be formed provided that there is some initial perpendicular temperature anisotropy at the structure location. The properties of these structures (scale size, trapped population, etc.) are able to explain the observed properties of magnetic holes in the terrestrial plasma sheet. EVMHs may also contribute to turbulence properties, such as intermittency, at short scale lengths in other astrophysical plasmas.

Three-dimensional earthward fast flow in the near-Earth plasma sheet in a sheared field: comparisons between simulations and observations

Directory of Open Access Journals (Sweden)

K. Kondoh

2009-06-01

Full Text Available Three-dimensional configuration of earthward fast flow in the near-Earth plasma sheet is studied using three-dimensional magnetohydrodynamics (MHD simulations on the basis of the spontaneous fast reconnection model. In this study, the sheared magnetic field in the plasma sheet is newly considered in order to investigate the effects of it to the earthward fast flow, and the results are discussed in comparison with no-shear simulations. The virtual probes located at different positions in our simulation domain in shear/no-shear cases could explain different behavior of fast flows in the real observations.

The lobe to plasma sheet boundary layer transition: Theory and observations

International Nuclear Information System (INIS)

Schriver, D.; Ashour-Abdalla, M.; Treumann, R.; Nakamura, M.; Kistler, L.M.

1990-01-01

The lobe and the plasma sheet boundary layer in the Earth's magnetotail are regions of different plasma conditions and share a common interface. The transition from the lobe to the plasma sheet boundary layer is examined here using AMPTE/IRM data. When the satellite crossed from the lobe to the plasma sheet boundary layer, intense narrow banded wave bursts at 1 kHz were observed an d then broadband electrostatic noise (BEN) immediately followed. Simultaneous with the onset of BEN, high energy earthward streaming proton beams at > 40 keV (> 2,700 km/s) were detected. These results are used as input into a numerical simulation to study ion beam instabilities in the PSBL

Relationship between energetic particles and plasmas in the distant plasma sheet

International Nuclear Information System (INIS)

Sarris, E.T.; Krimigis, S.M.; Lui, A.T.Y.; Ackerson, K.L.; Frank, L.A.; Williams, D.J.

1981-01-01

Measurements of ions from three different instruments on the IMP-7 and 8 spacecraft are combined to yield with differential energy spectra of ions over the entire energy range of approx.100 eV to 4 MeV in the earth's distant (approx.30 to approx.40 R/sub e/) plasma sheet. These spectra, obtained during times of relatively small bulk flow velocities, span the intensity range from approx.10 -5 to 10 5 (cm 2 sec sr keV) -1 , varying smoothly over the entire energy range both when the plasma is cold (approx.1 keV) and hot (approx.9 keV). Overall, the shape of the spectrum resembles a Maxwellian but with a high energy (> or approx. =50 keV) tail described well by a power law (proportionalE -7 ). The high energy tail is displaced in a parallel fashion to higher or lower intensities when the plasma is hot or cold, respectively. The transition between the Maxwellian and the power law occurs at Eapprox. =(g+1)kT. It is found that the energetic particle populations in the plasma sheet appear to be directly related to the mean thermal energies of the corresponding plasmas

Dynamics of particles accelerated by head-on collisions of two magnetized plasma shocks

Science.gov (United States)

Takeuchi, Satoshi

2018-02-01

A kinetic model of the head-on collision of two magnetized plasma shocks is analyzed theoretically and in numerical calculations. When two plasmas with anti-parallel magnetic fields collide, they generate magnetic reconnection and form a motional electric field at the front of the collision region. This field accelerates the particles sandwiched between both shock fronts to extremely high energy. As they accelerate, the particles are bent by the transverse magnetic field crossing the magnetic neutral sheet, and their energy gains are reduced. In the numerical calculations, the dynamics of many test particles were modeled through the relativistic equations of motion. The attainable energy gain was obtained by multiplying three parameters: the propagation speed of the shock, the magnitude of the magnetic field, and the acceleration time of the test particle. This mechanism for generating high-energy particles is applicable over a wide range of spatial scales, from laboratory to interstellar plasmas.

Plasma behavior during energetic electron streaming events: Further evidence for substorm-associated magnetic reconnection

International Nuclear Information System (INIS)

Bieber, J.W.; Stone, E.C.; Hones, E.W. Jr.; Baker, D.N.; Bame, S.J.

1982-01-01

A recent study showed that streaming energetic (>200 keV) electrons in Earth's magnetotail are statistically associated with southward magnetic fields and with enhancements of the AE index. It is shown here that the streaming electrons characteristically are preceded by aapprox.15 minute period of tailward plasma flow and followed by a dropout of the plasma sheet, thus demonstrating a clear statistical association between substorms and the classical signatures of magnetic reconnection and plasmoid formation. Additionally, a brief upward surge of mean electron energy preceded plasma dropout in several of the events studied, providing direct evidence of localized, reconnection-associated heating processes

Magnetic configurations of the tilted current sheets in magnetotail

Directory of Open Access Journals (Sweden)

C. Shen

2008-11-01

Full Text Available In this research, the geometrical structures of tilted current sheet and tail flapping waves have been analysed based on multiple spacecraft measurements and some features of the tilted current sheets have been made clear for the first time. The geometrical features of the tilted current sheet revealed in this investigation are as follows: (1 The magnetic field lines (MFLs in the tilted current sheet are generally plane curves and the osculating planes in which the MFLs lie are about vertical to the equatorial plane, while the normal of the tilted current sheet leans severely to the dawn or dusk side. (2 The tilted current sheet may become very thin, the half thickness of its neutral sheet is generally much less than the minimum radius of the curvature of the MFLs. (3 In the neutral sheet, the field-aligned current density becomes very large and has a maximum value at the center of the current sheet. (4 In some cases, the current density is a bifurcated one, and the two humps of the current density often superpose two peaks in the gradient of magnetic strength, indicating that the magnetic gradient drift current is possibly responsible for the formation of the two humps of the current density in some tilted current sheets. Tilted current sheets often appear along with tail current sheet flapping waves. It is found that, in the tail flapping current sheets, the minimum curvature radius of the MFLs in the current sheet is rather large with values around 1 RE, while the neutral sheet may be very thin, with its half thickness being several tenths of RE. During the flapping waves, the current sheet is tilted substantially, and the maximum tilt angle is generally larger than 45°. The phase velocities of these flapping waves are several tens km/s, while their periods and wavelengths are several tens of minutes, and several earth radii, respectively. These tail flapping events generally last several hours and occur during quiet periods or periods of

One-Dimensional Vlasov-Maxwell Equilibrium for the Force-Free Harris Sheet

International Nuclear Information System (INIS)

Harrison, Michael G.; Neukirch, Thomas

2009-01-01

In this Letter, the first nonlinear force-free Vlasov-Maxwell equilibrium is presented. One component of the equilibrium magnetic field has the same spatial structure as the Harris sheet, but whereas the Harris sheet is kept in force balance by pressure gradients, in the force-free solution presented here force balance is maintained by magnetic shear. Magnetic pressure, plasma pressure and plasma density are constant. The method used to find the equilibrium is based on the analogy of the one-dimensional Vlasov-Maxwell equilibrium problem to the motion of a pseudoparticle in a two-dimensional conservative potential. The force-free solution can be generalized to a complete family of equilibria that describe the transition between the purely pressure-balanced Harris sheet to the force-free Harris sheet

Current sheets in the Earth’s magnetosphere and in laboratory experiments: The magnetic field structure and the Hall effect

International Nuclear Information System (INIS)

Frank, A. G.; Artemyev, A. V.; Zelenyi, L. M.

2016-01-01

The main characteristics of current sheets (CSs) formed in laboratory experiments are compared with the results of satellite observations of CSs in the Earth’s magnetotail. We show that many significant features of the magnetic field structure and the distributions of plasma parameters in laboratory and magnetospheric CSs exhibit a qualitative similarity, despite the enormous differences of scales, absolute values of plasma parameters, magnetic fields, and currents. In addition to a qualitative comparison, we give a number of dimensionless parameters that demonstrate the possibility of laboratory modeling of the processes occurring in the magnetosphere.

Review of recent experiments on magnetic reconnection in laboratory plasmas

International Nuclear Information System (INIS)

Yamada, M.

1995-02-01

The present paper reviews recent laboratory experiments on magnetic reconnection. Examples will be drawn from electron current sheet experiments, merging spheromaks, and from high temperature tokamak plasmas with the Lundquist numbers exceeding 10 7 . These recent laboratory experiments create an environment which satisfies the criteria for MHD plasma and in which the global boundary conditions can be controlled externally. Experiments with fully three dimensional reconnection are now possible. In the most recent TFTR tokamak discharges, Motional Stark effect (MSE) data have verified the existence of a partial reconnection. In the experiment of spheromak merging, a new plasma acceleration parallel to the neutral line has been indicated. Together with the relationship of these observations to the analysis of magnetic reconnection in space and in solar flares, important physics issues such as global boundary conditions, local plasma parameters, merging angle of the field lines, and the 3-D aspects of the reconnection are discussed

Spatial structure of the plasma sheet boundary layer at distances greater than 180 RE as derived from energetic particle measurements on GEOTAIL

Directory of Open Access Journals (Sweden)

T. Yamamoto

Full Text Available We have analyzed the onsets of energetic particle bursts detected by the ICS and STICS sensors of the EPIC instrument on board the GEOTAIL spacecraft in the deep magnetotail (i.e., at distances greater than 180 RE. Such bursts are commonly observed at the plasma-sheet boundary layer (PSBL and are highly collimated along the magnetic field. The bursts display a normal velocity dispersion (i.e., the higher-speed particles are seen first, while the progressively lower speed particles are seen later when observed upon entry of the spacecraft from the magnetotail lobes into the plasma sheet. Upon exit from the plasma sheet a reverse velocity dispersion is observed (i.e., lower-speed particles disappear first and higher-speed particles disappear last. Three major findings are as follows. First, the tailward-jetting energetic particle populations of the distant-tail plasma sheet display an energy layering: the energetic electrons stream along open PSBL field lines with peak fluxes at the lobes. Energetic protons occupy the next layer, and as the spacecraft moves towards the neutral sheet progressively decreasing energies are encountered systematically. These plasma-sheet layers display spatial symmetry, with the plane of symmetry the neutral sheet. Second, if we consider the same energy level of energetic particles, then the H+ layer is confined within that of the energetic electron, the He++ layer is confined within that of the proton, and the oxygen layer is confined within the alpha particle layer. Third, whenever the energetic electrons show higher fluxes inside the plasma sheet as compared to those at the boundary layer, their angular distribution is isotropic irrespective of the Earthward or tailward character of fluxes, suggesting a closed field line topology.

Spatial structure of the plasma sheet boundary layer at distances greater than 180 RE as derived from energetic particle measurements on GEOTAIL

Directory of Open Access Journals (Sweden)

D. V. Sarafopoulos

1997-10-01

Full Text Available We have analyzed the onsets of energetic particle bursts detected by the ICS and STICS sensors of the EPIC instrument on board the GEOTAIL spacecraft in the deep magnetotail (i.e., at distances greater than 180 RE. Such bursts are commonly observed at the plasma-sheet boundary layer (PSBL and are highly collimated along the magnetic field. The bursts display a normal velocity dispersion (i.e., the higher-speed particles are seen first, while the progressively lower speed particles are seen later when observed upon entry of the spacecraft from the magnetotail lobes into the plasma sheet. Upon exit from the plasma sheet a reverse velocity dispersion is observed (i.e., lower-speed particles disappear first and higher-speed particles disappear last. Three major findings are as follows. First, the tailward-jetting energetic particle populations of the distant-tail plasma sheet display an energy layering: the energetic electrons stream along open PSBL field lines with peak fluxes at the lobes. Energetic protons occupy the next layer, and as the spacecraft moves towards the neutral sheet progressively decreasing energies are encountered systematically. These plasma-sheet layers display spatial symmetry, with the plane of symmetry the neutral sheet. Second, if we consider the same energy level of energetic particles, then the H+ layer is confined within that of the energetic electron, the He++ layer is confined within that of the proton, and the oxygen layer is confined within the alpha particle layer. Third, whenever the energetic electrons show higher fluxes inside the plasma sheet as compared to those at the boundary layer, their angular distribution is isotropic irrespective of the Earthward or tailward character of fluxes, suggesting a closed field line topology.

Magnetic reconnection in magnetotail and solar plasmas

International Nuclear Information System (INIS)

Wang Xiaogang.

1991-01-01

The formation of current sheets which dominates the heating of the solar corona and the onset of substorms due to collisionless tearing instability in the magnetotail are investigated in the context of magnetic field line reconnection in space plasmas. In Chapters 2 and 3 of this thesis, the collisionless tearing instability and current disruption of the magnetotail are considered. The linear collisionless tearing instability, with wavelengths of the order of 10 R E , and with a growth rate γ ∼ 10 -2 /sec, is identified as a possible mechanism for the growth phase of a substorm. The linear analysis is carried out in the presence of an equilibrium B y -field, neglected in other theories. The nonlinear theory of collisionless tearing mode is dominated by mode coupling effects. From the evolution equations for electro-magnetic field perturbations, the author derived a nonlinear growth rate by generalizing the boundary layer techniques of linear theory. He finds that the nonlinear growth is of the order of 1 sec, much faster than the linear growth. It is proposed that collisionless tearing modes provide a mechanism for current disruption observed by spacecrafts. The electrical field generated during the nonlinear evolution can cause particle acceleration in the earth-tail direction. His estimates indicate ion energies up to 0.7 MeV and electron energies up to 8.1 MeV, which is not inconsistent with the observations. In the Chapter 4 it is shown that current sheets can be formed in Parker's model of the solar corona in the presence of smooth photospheric flows, despite van Ballegooijen and Field's proof that in an ideal plasma current sheets doe not occur unless the boundary velocity field is discontinuous

Distribution of O+ ions in the plasma sheet and locations of substorm onsets

Science.gov (United States)

Ono, Y.; Christon, S. P.; Frey, H. U.; Lui, A. T. Y.

2010-09-01

We discuss the effect of O+ ions on substorm onsets by examining the relation between the substorm onset location and the distribution of the O+/H+ number density ratio before the onset in the various regions within the plasma sheet (-8 RE > XGSM > -32 RE). We use 9-212 keV/e ion flux data observed by Geotail/Energetic Particles and Ion Composition (EPIC)/Suprathermal Ion Composition Spectrometer (STICS) instrument and the IMAGE/Far Ultra-Violet (FUV) substorm onset list presented by Frey et al. [Frey, H. U., S. B. Mende, V. Angelopoulos, and E. F. Donovan (2004), Substorm onset observations by IMAGE-FUV, J. Geophys. Res., 109, A10304, doi:10.1029/2004JA010607]. The results are summarized as follows. Substorm onsets, which we identify by auroral initial brightenings, are likely to occur in the more dusk-(dawn-)ward region when the O+/H+ number density ratio is high in the dusk (dawn) side. This property is observed only in the near-Earth plasma sheet (at -8 RE > XGSM > -14 RE). The above-mentioned property holds in each of two groups: substorm events due to internal instability of the magnetosphere (i.e., internally triggered substorms) and events due to external changes in the solar wind or the interplanetary magnetic field (i.e., externally triggered substorms). Thus, we conclude that the substorm onset location depends on the density of O+ ions in the near-Earth plasma sheet prior to onset, whether the substorm is triggered internally or externally.

Dust confinement and dust acoustic waves in a magnetized plasma

Science.gov (United States)

Piel, A.

2005-10-01

Systematic laboratory experiments on dust acoustic waves require the confinement of dust particles. Here we report on new experiments in a magnetized plasma region in front of an additional positively biased disk electrode in a background plasma which is generated in argon at 27MHz between a disk and grid electrode. The plasma diffuses through the grid along the magnetic field. The three-dimensional dust distribution is measured with a horizontal sheet of laser light and a CCD camera, which are mounted on a vertical translation stage. Depending on magnetic field and discharge current, cigar or donut-shaped dust clouds are generated, which tend to rotate about the magnetic field direction. Measurements with emissive probes show that the axial confinement of dust particles with diameters between 0.7-2 μm is achieved by a balance of ion-drag force and electric field force. Dust levitation and radial confinement is due to a strong radial electric field. Dust acoustic waves are destabilized by the ion flow or can be stimulated by a periodic bias on the disk electrode. The observed wave dispersion is compared with fluid and kinetic models of the dust acoustic wave.

Kelvin-Helmholtz instability for a bounded plasma flow in a longitudinal magnetic field

International Nuclear Information System (INIS)

Burinskaya, T. M.; Shevelev, M. M.; Rauch, J.-L.

2011-01-01

Kelvin-Helmholtz MHD instability in a plane three-layer plasma is investigated. A general dispersion relation for the case of arbitrarily orientated magnetic fields and flow velocities in the layers is derived, and its solutions for a bounded plasma flow in a longitudinal magnetic field are studied numerically. Analysis of Kelvin-Helmholtz instability for different ion acoustic velocities shows that perturbations with wavelengths on the order of or longer than the flow thickness can grow in an arbitrary direction even at a zero temperature. Oscillations excited at small angles with respect to the magnetic field exist in a limited range of wavenumbers even without allowance for the finite width of the transition region between the flow and the ambient plasma. It is shown that, in a low-temperature plasma, solutions resulting in kink-like deformations of the plasma flow grow at a higher rate than those resulting in quasi-symmetric (sausage-like) deformations. The transverse structure of oscillatory-damped eigenmodes in a low-temperature plasma is analyzed. The results obtained are used to explain mechanisms for the excitation of ultra-low-frequency long-wavelength oscillations propagating along the magnetic field in the plasma sheet boundary layer of the Earth’s magnetotail penetrated by fast plasma flows.

Current sheet characteristics of a parallel-plate electromagnetic plasma accelerator operated in gas-prefilled mode

Science.gov (United States)

Liu, Shuai; Huang, Yizhi; Guo, Haishan; Lin, Tianyu; Huang, Dong; Yang, Lanjun

2018-05-01

The axial characteristics of a current sheet in a parallel-plate electromagnetic plasma accelerator operated in gas-prefilled mode are reported. The accelerator is powered by a fourteen stage pulse forming network. The capacitor and inductor in each stage are 1.5 μF and 300 nH, respectively, and yield a damped oscillation square wave of current with a pulse width of 20.6 μs. Magnetic probes and photodiodes are placed at various axial positions to measure the behavior of the current sheet. Both magnetic probe and photodiode signals reveal a secondary breakdown when the current reverses the direction. An increase in the discharge current amplitude and a decrease in pressure lead to a decrease in the current shedding factor. The current sheet velocity and thickness are nearly constant during the run-down phase under the first half-period of the current. The current sheet thicknesses are typically in the range of 25 mm to 40 mm. The current sheet velocities are in the range of 10 km/s to 45 km/s when the discharge current is between 10 kA and 55 kA and the gas prefill pressure is between 30 Pa and 800 Pa. The experimental velocities are about 75% to 90% of the theoretical velocities calculated with the current shedding factor. One reason for this could be that the idealized snowplow analysis model ignores the surface drag force.

On the possible eigenoscillations of neutral sheets

International Nuclear Information System (INIS)

Almeida, W.A.; Costa, J.M. da; Aruquipa, E.G.; Sudano, J.P.

1974-12-01

A neutral sheet model with hyperbolic tangent equilibrium magnetic field and hyperbolic square secant density profiles is considered. It is shown that the equation for small oscillations takes the form of an eigenvalue oscillation problem. Computed eigenfrequencies of the geomagnetic neutral sheet were found to be in the range of the resonant frequencies of the geomagnetic plasma sheet computed by other authors

Magnetic Reconnection in Strongly Magnetized Regions of the Low Solar Chromosphere

Science.gov (United States)

Ni, Lei; Lukin, Vyacheslav S.; Murphy, Nicholas A.; Lin, Jun

2018-01-01

Magnetic reconnection in strongly magnetized regions around the temperature minimum region of the low solar atmosphere is studied by employing MHD-based simulations of a partially ionized plasma within a reactive 2.5D multi-fluid model. It is shown that in the absence of magnetic nulls in a low β plasma, the ionized and neutral fluid flows are well-coupled throughout the reconnection region. However, non-equilibrium ionization–recombination dynamics play a critical role in determining the structure of the reconnection region, leading to much lower temperature increases and a faster magnetic reconnection rate as compared to simulations that assume plasma to be in ionization–recombination equilibrium. The rate of ionization of the neutral component of the plasma is always faster than recombination within the current sheet region even when the initial plasma β is as high as {β }0=1.46. When the reconnecting magnetic field is in excess of a kilogauss and the plasma β is lower than 0.0145, the initially weakly ionized plasmas can become fully ionized within the reconnection region and the current sheet can be strongly heated to above 2.5× {10}4 K, even as most of the collisionally dissipated magnetic energy is radiated away. The Hall effect increases the reconnection rate slightly, but in the absence of magnetic nulls it does not result in significant asymmetries or change the characteristics of the reconnection current sheet down to meter scales.

Magnetic properties of sheet silicates

International Nuclear Information System (INIS)

Ballet, O.; Coey, J.M.D.

1982-01-01

Susceptibility, magnetisation and Moessbauer measurements are reported for a representative selection of 2:1 layer phyllosilicates. Eight samples from the mica, vermiculite and smectite groups include examples diluted in iron which are paramagnetic at all temperatures, as well as iron-rich silicates which order magnetically below 10 K. Anisotropic susceptibility of crystals of muscovite, biotite and vermiculite is quantitatively explained with a model where the Fe 2+ ions lie in sites of effective trigonal symmetry, the trigonal axis lying normal to the sheets. The ferrous ground state is an orbital singlet. Ferric iron gives an isotropic contribution to the susceptibility. Fe 2+ -Fe 2+ exchange interactions are ferromagnetic with Gapprox. equal to2 K, whereas Fe 3+ -Fe 3+ coupling is antiferromagnetic in the purely ferric minerals. A positive paramagnetic Curie temperature for glauconite may be attributable to Fe 2+ → Fe 3+ charge transfer. Magnetic order was found to set in inhomogeneously for glauconite at 1-7 K. One biotite sample showed an antiferromagnetic transition at Tsub(N) = 7 K marked by a well-defined susceptibility maximum. Its magnetic structure, consisting of ferromagnetic sheets with moments in their planes coupled antiferromagnetically by other, weak interactions, resembles that found earlier for the 1:1 mineral greenalite. (orig.)

Cross-tail velocity component in the plasma sheet fast flows

Directory of Open Access Journals (Sweden)

N. P. Dmitrieva

2008-06-01

Full Text Available The flux transfer in the magnetotail plasma sheet is mainly provided by the tail-aligned fast plasma flows (Bursty Bulk Flows – BBFs. In this paper we study the events with a large cross-tail velocity component, including their occurrence and relationship to the standard BBFs. We found out that a significant part of large Vy events are a subgroup connected with the BBFs propagation. The maximal deviation of the velocity vector from the X direction (about 40–50 degrees, on average is observed near the BBFs' leading front in the sheath, where the fast flow interacts with surrounding plasma. The average variation of the velocity direction in the vicinity of the BBF resembles a plasma vortex. Our results support the model, in which the BBF represents a polarized, bubble-like flux tube, propagating through the plasma sheet.

Magnetic field line reconnection experiments

International Nuclear Information System (INIS)

Gekelman, W.; Stenzel, R.L.; Wild, N.

1982-01-01

A laboratory experiment concerned with the basic physics of magnetic field line reconnection is discussed. Stimulated by important processes in space plasmas and anomalous transport in fusion plasmas the work addresses the following topics: Dynamic magnetic fields in a high beta plasma, magnetic turbulence, plasma dynamics and energy transport. First, the formation of magnetic neutral sheets, tearing and island coalescence are shown. Nonstationary magnetic fluctuations are statistically evaluated displaying the correlation tensor in the #betta#-k domain for mode identification. Then, the plasma properties are analyzed with particular emphasis on transport processes. Although the classical fluid flow across the separatrix can be observed, the fluctuation processes strongly modify the plasma dynamics. Direct measurements of the fluid force density and ion acceleration indicate the presence of an anomalous scattering process characterized by an effective scattering tensor. Turbulence also enhances the plasma resistivity by one to two orders of magnitude. Measurements of the three-dimensional electron distribution function using a novel energy analyzer exhibit the formation of runaway electrons in the current sheet. Associated micro-instabilities are observed. Finally, a macroscopic disruptive instability of the current sheet is observed. Excess magnetic field energy is converted at a double layer into particle kinetic energy and randomized through beam-plasma instabilities. These laboratory results are compared with related observations in space and fusion plasmas. (Auth.)

γ-ray irradiation effect on magnetic properties of electromagnetic Fe-Si sheets

International Nuclear Information System (INIS)

Harara, W.

1994-11-01

The present work investigates the effect of γ-ray irradiation on the relative and differential magnetic permeabilities of electromagnetic steel sheets. The experimental work was carried out using transformer Fe-Si (97-3%) sheets. The sheets have two different forms E and I> The magnetic field dependence on the relative permeability as well as on the differential permeability before and after irradiation were measured. The measurements show that the relative permeability values of the sheets after irradiation in the region of rotation of magnetization domains were decreased whereas the value of their differential permeability around each working point remains unchangeable. (author). 7 refs., 14 figs., 6 tabs

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.

Global dynamics of magnetic reconnection in VINETA II

Energy Technology Data Exchange (ETDEWEB)

Bohlin, Hannes

2014-12-12

Magnetic reconnection is a fundamental plasma process where a change in field line connectivity occurs in a current sheet at the boundary between regions of opposing magnetic fields. In this process, energy stored in the magnetic field is converted into kinetic and thermal energy, which provides a source of plasma heating and energetic particles. Magnetic reconnection plays a key role in many space and laboratory plasma phenomena, e.g. solar flares, Earth's magnetopause dynamics and instabilities in tokamaks. A new linear device (VINETAII) has been designed for the study of the fundamental physical processes involved in magnetic reconnection. The plasma parameters are such that magnetic reconnection occurs in a collision-dominated regime. A plasma gun creates a localized current sheet, and magnetic reconnection is driven by modulating the plasma current and the magnetic field structure. The plasma current is shown to flow in response to a combination of an externally induced electric field and electrostatic fields in the plasma, and is highly affected by axial sheath boundary conditions. Further, the current is changed by an additional axial magnetic field (guide field), and the current sheet geometry was demonstrated to be set by a combination of magnetic mapping and cross-field plasma diffusion. With increasing distance from the plasma gun, magnetic mapping results in an increase of the current sheet length and a decrease of the width. The control parameter is the ratio of the guide field to the reconnection magnetic field strength. Cross-field plasma diffusion leads to a radial expansion of the current sheet at low guide fields. Plasma currents are also observed in the azimuthal plane and were found to originate from a combination of the field-aligned current component and the diamagnetic current generated by steep in-plane pressure gradients in combination with the guide field. The reconnection rate, defined via the inductive electric field, is shown to be

On hot tenuous plasmas, fireballs, and boundary layers in the earth's magnetotail

International Nuclear Information System (INIS)

Frank, L.A.; Ackerson, K.L.; Lepping, R.P.

1976-01-01

Intensive correlative studies of magnetic fields and plasmas within the earth's magnetotail at geocentric radial distances of approx. 23--46 R/sub E/ during March--October 1974 revealed striking new features. The hot tenuous plasmas within the plasma sheet were found to be in a state of almost continual flow and were threaded with northward, or closed, geomagnetic field lines. Proton bulk speeds were in the range 50--500 km s -1 . The magnetic fields are directed northward. These observations demand a strong persistent source of magnetic flux and hot plasmas for the plasma sheet. No characteristic proton bulk flows were evident during crossings of the neutral sheet. Occasionally, the satellite encountered the region of acceleration in the magnetotail, the 'fireball.' This spectacular phenomenon exhibits strong jetting of plasmas in exces of 1000 km s -1 , proton temperatures of approx. 10 7 degreeK (kT approx. 1 keV), disordered magnetic fields, southward magnetic fields during tailward jetting of the plasmas. Earthward plasma flows within the fireball are threaded with closed geomagnetic field lines, and open magnetic field lines are embedded in the tailward jetting plasmas. The magnetosheathlike plasmas within the boundary layers which are positioned contiguous to the plasma sheet display striking evidences of plasma heating, great changes in bulk flow velocities and acceleration of energetic electrons with E > 45 keV. Persistent zones of southward magnetic fields are detected, which are often positioned adjacent to the plasma sheet and within the boundary layer plasmas. Rotations of the magnetic fields from southward to northward, or vice versa, in these boundary layers are accompanied by large enhancements of energetic electron intensities, substantial heating of the low-energy electron distributions, and strong perturbations of the proton velocity distribution functions

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.

Behavior of current sheets at directional magnetic discontinuities in the solar wind at 0.72 AU

Czech Academy of Sciences Publication Activity Database

Zhang, T. L.; Russell, C. T.; Zambelli, W.; Vörös, Zoltán; Wang, C.; Cao, J. B.; Jian l, L. K.; Strangeway, R. J.; Balikhin, M.; Baumjohann, W.; Delva, M.; Volwerk, M.; Glassmeier, K.; H.

2008-01-01

Roč. 35, č. 24 (2008), L24102/1-L24102/5 ISSN 0094-8276 Grant - others:Austrian Wissenschaftfonds(AT) P20131-N16; NNSFC(CN) 40628003; 973 Program(CN) 2006CB806305; NASA (US) NNG06GC62G Institutional research plan: CEZ:AV0Z30420517 Keywords : solar wind * current sheets * magnetic annihilation Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.959, year: 2008

Porcine Dental Epithelial Cells Differentiated in a Cell Sheet Constructed by Magnetic Nanotechnology

Directory of Open Access Journals (Sweden)

Wataru Koto

2017-10-01

Full Text Available Magnetic nanoparticles (MNPs are widely used in medical examinations, treatments, and basic research, including magnetic resonance imaging, drug delivery systems, and tissue engineering. In this study, MNPs with magnetic force were applied to tissue engineering for dental enamel regeneration. The internalization of MNPs into the odontogenic cells was observed by transmission electron microscopy. A combined cell sheet consisting of dental epithelial cells (DECs and dental mesenchymal cells (DMCs (CC sheet was constructed using magnetic force-based tissue engineering technology. The result of the iron staining indicated that MNPs were distributed ubiquitously over the CC sheet. mRNA expression of enamel differentiation and basement membrane markers was examined in the CC sheet. Immunostaining showed Collagen IV expression at the border region between DEC and DMC layers in the CC sheet. These results revealed that epithelial–mesenchymal interactions between DEC and DMC layers were caused by bringing DECs close to DMCs mechanically by magnetic force. Our study suggests that the microenvironment in the CC sheet might be similar to that during the developmental stage of a tooth bud. In conclusion, a CC sheet employing MNPs could be developed as a novel and unique graft for artificially regenerating dental enamel.

Sausage mode instability of thin current sheets as a cause of magnetospheric substorms

Directory of Open Access Journals (Sweden)

J. Büchner

Full Text Available Observations have shown that, prior to substorm explosions, thin current sheets are formed in the plasma sheet of the Earth's magnetotail. This provokes the question, to what extent current-sheet thinning and substorm onsets are physically, maybe even causally, related. To answer this question, one has to understand the plasma stability of thin current sheets. Kinetic effects must be taken into account since particle scales are reached in the course of tail current-sheet thinning. We present the results of theoretical investigations of the stability of thin current sheets and about the most unstable mode of their decay. Our conclusions are based upon a non-local linear dispersion analysis of a cross-magnetic field instability of Harris-type current sheets. We found that a sausage-mode bulk current instability starts after a sheet has thinned down to the ion inertial length. We also present the results of three-dimensional electromagnetic PIC-code simulations carried out for mass ratios up to M_i / m_e=64. They verify the linearly predicted properties of the sausage mode decay of thin current sheets in the parameter range of interest.

Key words. Magnetospheric physics (plasma waves and instabilities; storms and substorms · Space plasma physics (magnetic reconnection

Ion flow ripples in the Earth's plasma sheet

Science.gov (United States)

De Spiegeleer, Alexandre; Hamrin, Maria; Pitkänen, Timo; Norqvist, Patrik; Mann, Ingrid

2016-04-01

For a long time, magnetotail flows were considered rather smooth and laminar, and primarily dominated by a simple convection flow pattern. However, in the early 90's, high speed bursty bulk flows (BBFs) were discovered and found to commonly perturb the underlying convection flows. In addition, there are other disturbances complicating the magnetotail flow pattern. Instabilities such as the Kelvin-Helmholz instability and the kink instability can cause different types of magnetic field oscillations, such as field line resonances. It is expected that ions will follow these oscillations if the typical time and length scales are larger than the gyroperiod and gyroradius of the ions. Though low-velocity sloshing and ripple disturbances of the average magnetotail convection flows have been observed, their connection with magnetic field oscillations is not fully understood. Furthermore, when studying BFFs, these "Ion Flow Ripples" (IFRs) are often neglected, dismissed as noise or can even erroneously be identified as BBFs. It is therefore of utter importance to find out and understand the role of IFRs in magnetotail dynamics. In a statistical investigation, we use several years of Cluster plasma sheet data to study the low-speed flows in the magnetotail. We investigate different types of IFRs, study their occurrence, and discuss their possible causes.

Statistical study of phase relationships between magnetic and plasma thermal pressures in the near-earth magnetosphere using the THEMIS satellites

Science.gov (United States)

Nishi, K.; Kazuo, S.

2017-12-01

The auroral finger-like structures appear in the equatorward part of the auroral oval in the diffuse auroral region, and contribute to the auroral fragmentation into patches during substorm recovery phase. In our previous presentations, we reported the first conjugate observation of auroral finger-like structures using the THEMIS GBO cameras and the THEMIS satellites, which was located at a radial distance of 9 Re in the dawnside plasma sheet. In this conjugate event, we found anti-phase fluctuation of plasma pressure and magnetic pressure with a time scale of 5-20 min in the plasma sheet. This observational fact is consistent with the idea that the finger-like structures are caused by a pressure-driven instability in the balance of plasma and magnetic pressures in the magnetosphere. Then we also searched simultaneous observation events of auroral finger-like structures with the RBSP satellites which have an apogee of 5.8 Re in the inner magnetosphere. Contrary to the first result, the observed variation of plasma and magnetic pressures do not show systematic phase relationship. In order to investigate these phase relationships between plasma and magnetic pressures in the magnetosphere, we statistically analyzed these pressure data using the THEMIS-E satellite for one year in 2011. In the preliminary analysis of pressure variation spectra, we found that out of phase relationship between magnetic and plasma pressures occupied 40 % of the entire period of study. In the presentation, we will discuss these results in the context of relationships between the pressure fluctuations and the magnetospheric instabilities that can cause auroral finger-like structures.

Analysis and comparison of magnetic sheet insulation tests

Science.gov (United States)

Marion-Péra, M. C.; Kedous-Lebouc, A.; Cornut, B.; Brissonneau, P.

1994-05-01

Magnetic circuits of electrical machines are divided into coated sheets in order to limit eddy currents. The surface insulation resistance of magnetic sheets is difficult to evaluate because it depends on parameters like pressure and covers a wide range of values. Two methods of measuring insulation resistance are analyzed: the standardized 'Franklin device' and a tester developed by British Steel Electrical. Their main drawback is poor local repeatability. The Franklin method allows better quality control of industrial process because it measures only one insulating layer at a time. It also gives more accurate images of the distribution of possible defects. Nevertheless, both methods lead to similar classifications of insulation efficiency.

Geotail observations of plasma sheet ion composition over 16 years: On variations of average plasma ion mass and O+ triggering substorm model

Science.gov (United States)

Nosé, M.; Ieda, A.; Christon, S. P.

2009-07-01

We examined long-term variations of ion composition in the plasma sheet, using energetic (9.4-212.1 keV/e) ion flux data obtained by the suprathermal ion composition spectrometer (STICS) sensor of the energetic particle and ion composition (EPIC) instrument on board the Geotail spacecraft. EPIC/STICS observations are available from 17 October 1992 for more than 16 years, covering the declining phase of solar cycle 22, all of solar cycle 23, and the early phase of solar cycle 24. This unprecedented long-term data set revealed that (1) the He+/H+ and O+/H+ flux ratios in the plasma sheet were dependent on the F10.7 index; (2) the F10.7 index dependence is stronger for O+/H+ than He+/H+; (3) the O+/H+ flux ratio is also weakly correlated with the ΣKp index; and (4) the He2+/H+ flux ratio in the plasma sheet appeared to show no long-term trend. From these results, we derived empirical equations related to plasma sheet ion composition and the F10.7 index and estimated that the average plasma ion mass changes from ˜1.1 amu during solar minimum to ˜2.8 amu during solar maximum. In such a case, the Alfvén velocity during solar maximum decreases to ˜60% of the solar minimum value. Thus, physical processes in the plasma sheet are considered to be much different between solar minimum and solar maximum. We also compared long-term variation of the plasma sheet ion composition with that of the substorm occurrence rate, which is evaluated by the number of Pi2 pulsations. No correlation or negative correlation was found between them. This result contradicts the O+ triggering substorm model, in which heavy ions in the plasma sheet increase the growth rate of the linear ion tearing mode and play an important role in localization and initiation of substorms. In contrast, O+ ions in the plasma sheet may prevent occurrence of substorms.

Oscillation of the current sheet velocity in plasma focus discharges

International Nuclear Information System (INIS)

Melzacki, K.; Nardi, V.

1994-01-01

The oscillation of the propagation speed of the plasma focus current sheet has been recorded with schlieren photography. The sheet stuttering in the propagation during the implosion phase has a frequency of about 60 MHz. The effect could be recorded due to application of long exposure time (60 ns) technique. It is not detectable in the subnanosecond pictures. The pictures are taken in black schlieren. The probing range of the electron density gradient, with integration along the path of the 1 J, Q-switched ruby laser beam, has been selected by the size of the stop and aperture within 3 x 10 18 cm -3 and 3 x 10 20 cm -3 . Raising the sensitivity threshold to 2 x 10 19 cm -3 (refraction angle of 4 mrad) has helped to clear the pictures by limiting their image to high gradients of density only. With this technique (and other diagnostic methods) the dynamics of 6 kJ, 16 kV plasma focus discharges in deuterium at 5 torr, with a 10% decrease of the magnetic insulation at the breech has been investigated. The average implosion velocity of the current sheath obtained with this effect, 5 x 10 6 cm/s, is consistent with those measured by the smear effect, and the electric probe. The electron density gradient has been determined at several instants; at the pinch time it is (3 ± 1.5) x 10 20 cm -4 . The data are discussed on the basis of several pictures

Numerical simulation for the magnetic force distribution in electromagnetic forming of small size flat sheet

Science.gov (United States)

Chen, Xiaowei; Wang, Wenping; Wan, Min

2013-12-01

It is essential to calculate magnetic force in the process of studying electromagnetic flat sheet forming. Calculating magnetic force is the basis of analyzing the sheet deformation and optimizing technical parameters. Magnetic force distribution on the sheet can be obtained by numerical simulation of electromagnetic field. In contrast to other computing methods, the method of numerical simulation has some significant advantages, such as higher calculation accuracy, easier using and other advantages. In this paper, in order to study of magnetic force distribution on the small size flat sheet in electromagnetic forming when flat round spiral coil, flat rectangular spiral coil and uniform pressure coil are adopted, the 3D finite element models are established by software ANSYS/EMAG. The magnetic force distribution on the sheet are analyzed when the plane geometries of sheet are equal or less than the coil geometries under fixed discharge impulse. The results showed that when the physical dimensions of sheet are less than the corresponding dimensions of the coil, the variation of induced current channel width on the sheet will cause induced current crowding effect that seriously influence the magnetic force distribution, and the degree of inhomogeneity of magnetic force distribution is increase nearly linearly with the variation of induced current channel width; the small size uniform pressure coil will produce approximately uniform magnetic force distribution on the sheet, but the coil is easy to early failure; the desirable magnetic force distribution can be achieved when the unilateral placed flat rectangular spiral coil is adopted, and this program can be take as preferred one, because the longevity of flat rectangular spiral coil is longer than the working life of small size uniform pressure coil.

Structure of slow shocks in a magnetized plasma with heat conduction

International Nuclear Information System (INIS)

Tsai, C.L.; Tsai, R.H.; Wu, B.H.; Lee, L.C.

2002-01-01

The structure of slow shocks in the presence of a heat conduction parallel to the local magnetic field is simulated from the set of magnetohydrodynamic equations. In this study, a pair of slow shocks is formed through the evolution of a current sheet initiated by the presence of a normal magnetic field. It is found that the slow shock consists of two parts: The isothermal main shock and foreshock. Significant jumps in plasma density, velocity and magnetic field occur across the main shock, but the temperature is found to be continuous across the main shock. The foreshock is featured by a smooth temperature variation and is formed due to the heat flow from downstream to upstream region. The plasma density downstream of the main shock decreases with time, while the downstream temperature increases with time, keeping the downstream pressure constant. It is shown that the jumps in plasma density, pressure, velocity, and magnetic field across the main shock are determined by the set of modified isothermal Rankine-Hugoniot conditions. It is also found that a jump in the temperature gradient is present across the main shock in order to satisfy the energy conservation. The present results can be applied to the heating in the solar corona and solar wind

The spatial structure of magnetospheric plasma disturbance estimated by using magnetic data obtained by SWARM satellites.

Science.gov (United States)

Yokoyama, Y.; Iyemori, T.; Aoyama, T.

2017-12-01

Field-aligned currents with various spatial scales flow into and out from high-latitude ionosphere. The magnetic fluctuations observed by LEO satellites along their orbits having period longer than a few seconds can be regarded as the manifestations of spatial structure of field aligned currents.This has been confirmed by using the initial orbital characteristics of 3 SWARM-satellites. From spectral analysis, we evaluated the spectral indices of these magnetic fluctuations and investigated their dependence on regions, such as magnetic latitude and MLT and so on. We found that the spectral indices take quite different values between the regions lower than the equatorward boundary of the auroral oval (around 63 degrees' in magnetic latitude) and the regions higher than that. On the other hands, we could not find the clear MLT dependence. In general, the FACs are believed to be generated in the magnetiospheric plasma sheet and boundary layer, and they flow along the field lines conserving their currents.The theory of FAC generation [e.g., Hasegawa and Sato ,1978] indicates that the FACs are strongly connected with magnetospheric plasma disturbances. Although the spectral indices above are these of spatial structures of the FACs over the ionosphere, by using the theoretical equation of FAC generation, we evaluate the spectral indices of magnetospheric plasma disturbance in FAC's generation regions. Furthermore, by projecting the area of fluctuations on the equatorial plane of magnetosphere (i.e. plasma sheet), we can estimate the spatial structure of magnetospheric plasma disturbance. In this presentation, we focus on the characteristics of disturbance in midnight region and discuss the relations to the substorm.

A route to explosive large-scale magnetic reconnection in a super-ion-scale current sheet

Directory of Open Access Journals (Sweden)

K. G. Tanaka

2009-01-01

Full Text Available How to trigger magnetic reconnection is one of the most interesting and important problems in space plasma physics. Recently, electron temperature anisotropy (αeo=Te⊥/Te|| at the center of a current sheet and non-local effect of the lower-hybrid drift instability (LHDI that develops at the current sheet edges have attracted attention in this context. In addition to these effects, here we also study the effects of ion temperature anisotropy (αio=Ti⊥/Ti||. Electron anisotropy effects are known to be helpless in a current sheet whose thickness is of ion-scale. In this range of current sheet thickness, the LHDI effects are shown to weaken substantially with a small increase in thickness and the obtained saturation level is too low for a large-scale reconnection to be achieved. Then we investigate whether introduction of electron and ion temperature anisotropies in the initial stage would couple with the LHDI effects to revive quick triggering of large-scale reconnection in a super-ion-scale current sheet. The results are as follows. (1 The initial electron temperature anisotropy is consumed very quickly when a number of minuscule magnetic islands (each lateral length is 1.5~3 times the ion inertial length form. These minuscule islands do not coalesce into a large-scale island to enable large-scale reconnection. (2 The subsequent LHDI effects disturb the current sheet filled with the small islands. This makes the triggering time scale to be accelerated substantially but does not enhance the saturation level of reconnected flux. (3 When the ion temperature anisotropy is added, it survives through the small island formation stage and makes even quicker triggering to happen when the LHDI effects set-in. Furthermore the saturation level is seen to be elevated by a factor of ~2 and large-scale reconnection is achieved only in this case. Comparison with two-dimensional simulations that exclude the LHDI effects confirms that the saturation level

Duality of the magnetic flux tube and electric current descriptions magnetospheric plasma and energy flow

International Nuclear Information System (INIS)

Atkinson, G.

1981-01-01

The duality between electric current and magnetic flux tubes is outlined for the magnetosphere. Magnetic flux tubes are regarded as fluid elements subjected to various stresses. Current closure then becomes the dual of stress balance, and Poynting vector energy flow a dual of J x E dissipation. The stresses acting on a flux tube are magnetic stresses, which correspond to currents at a distance, and plasma stresses, which correspond to local currents. The duality between current and stress is traced for ionospheric ion drag forces, solar wind stresses at the magnetopause, inertial effects, and the effects of energetic plasma on flux tubes. The stress balance and dual current systems are outlined for idealized magnetospheres of increasing complexity. For a simple magnetosphere with no convective flow, the balance stresses are solar wind pressure and neutral sheet plasma pressure. The corresponding current systems are the Chapman-Ferraro magnetopause currents and the magetotail current system. The introduction of convective flow introduces further stresses: ionospheric ion drag. Alfven layer shielding, and an imbalance in day-night magnetic stresses due to transport of flux tubes to the nightside by the solar wind. These stresses balance, and hence the corresponding additional currents (the ionospheric Pedersen current and the electrojets, the partial ring current, and two other current systems from the magnetopause and tail) must form a closed current system and do so by the region I and II field-aligned currents of Iijima and Potemra. The energy flow in the above models is described in terms of both Poynting vectors and the above current systems. Temporal variations examined are (1) an increase in dayside merging and/or nightside reconnection, (2) an increase in the energy density of plasma in the plasma sheet, (3) an increase in ionospheric conductivity, and (4) an increase in solar wind pressure

Thermomechanical processing of plasma sprayed intermetallic sheets

Science.gov (United States)

Hajaligol, Mohammad R.; Scorey, Clive; Sikka, Vinod K.; Deevi, Seetharama C.; Fleischhauer, Grier; Lilly, Jr., A. Clifton; German, Randall M.

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.

Magnetic properties and recrystallization texture of phosphorus-added non-oriented electrical steel sheets

International Nuclear Information System (INIS)

Tanaka, I.; Yashiki, H.

2006-01-01

The effect of phosphorus on magnetic properties and recrystallization texture has been investigated in non-oriented electrical steel sheets to develop low core loss and high permeability core materials. Specimens with different phosphorus contents were cold-rolled to various thicknesses, i.e. with various cold-rolling reductions, and annealed for recrystallization and grain growth. Although magnetic induction of the steel with low phosphorus content dramatically dropped with reducing thickness, i.e. with increasing in cold-rolling reduction, that of the steel with high phosphorus content only slightly decreased. The most effective way to reduce core loss was to reduce thickness of electrical steel sheets. Therefore, phosphorus-added thin gauge non-oriented electrical steel sheets have achieved low core loss and high permeability. The typical magnetic properties of phosphorus-added non-oriented electrical steel sheets 0.27mm in sheet thickness were 16.6W/kg in W 10/400 and 1.73T in B 50 . These excellent magnetic properties were due to the recrystallization texture control. {111} component in recrystallization texture was suppressed by the phosphorus segregation at initial grain boundaries. Accordingly, phosphorus would greatly contribute to the improvement of magnetic properties

SMALL-SCALE MAGNETIC ISLANDS IN THE SOLAR WIND AND THEIR ROLE IN PARTICLE ACCELERATION. I. DYNAMICS OF MAGNETIC ISLANDS NEAR THE HELIOSPHERIC CURRENT SHEET

Energy Technology Data Exchange (ETDEWEB)

Khabarova, O. [Heliophysical Laboratory, Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation RAS (IZMIRAN), Troitsk, Moscow 142190 (Russian Federation); Zank, G. P.; Li, G.; Roux, J. A. le; Webb, G. M.; Dosch, A. [Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35805 (United States); Malandraki, O. E. [IAASARS, National Observatory of Athens, GR-15236 Penteli (Greece)

2015-08-01

Increases of ion fluxes in the keV–MeV range are sometimes observed near the heliospheric current sheet (HCS) during periods when other sources are absent. These resemble solar energetic particle events, but the events are weaker and apparently local. Conventional explanations based on either shock acceleration of charged particles or particle acceleration due to magnetic reconnection at interplanetary current sheets (CSs) are not persuasive. We suggest instead that recurrent magnetic reconnection occurs at the HCS and smaller CSs in the solar wind, a consequence of which is particle energization by the dynamically evolving secondary CSs and magnetic islands. The effectiveness of the trapping and acceleration process associated with magnetic islands depends in part on the topology of the HCS. We show that the HCS possesses ripples superimposed on the large-scale flat or wavy structure. We conjecture that the ripples can efficiently confine plasma and provide tokamak-like conditions that are favorable for the appearance of small-scale magnetic islands that merge and/or contract. Particles trapped in the vicinity of merging islands and experiencing multiple small-scale reconnection events are accelerated by the induced electric field and experience first-order Fermi acceleration in contracting magnetic islands according to the transport theory of Zank et al. We present multi-spacecraft observations of magnetic island merging and particle energization in the absence of other sources, providing support for theory and simulations that show particle energization by reconnection related processes of magnetic island merging and contraction.

Pulsar current sheet C̆erenkov radiation

Science.gov (United States)

Zhang, Fan

2018-04-01

Plasma-filled pulsar magnetospheres contain thin current sheets wherein the charged particles are accelerated by magnetic reconnections to travel at ultra-relativistic speeds. On the other hand, the plasma frequency of the more regular force-free regions of the magnetosphere rests almost precisely on the upper limit of radio frequencies, with the cyclotron frequency being far higher due to the strong magnetic field. This combination produces a peculiar situation, whereby radio-frequency waves can travel at subluminal speeds without becoming evanescent. The conditions are thus conducive to C̆erenkov radiation originating from current sheets, which could plausibly serve as a coherent radio emission mechanism. In this paper we aim to provide a portrait of the relevant processes involved, and show that this mechanism can possibly account for some of the most salient features of the observed radio signals.

Observations and modeling of magnetized plasma jets and bubbles launched into a transverse B-field

Science.gov (United States)

Fisher, Dustin M.; Zhang, Yue; Wallace, Ben; Gilmore, Mark; Manchester, Ward B., IV; van der Holst, Bart; Rogers, Barrett N.; Hsu, Scott C.

2017-10-01

Hot, dense, plasma structures launched from a coaxial plasma gun on the HelCat dual-source plasma device at the University of New Mexico drag frozen-in magnetic flux into the chamber's background magnetic field providing a rich set of dynamics to study magnetic turbulence, force-free magnetic spheromaks, shocks, as well as CME-like dynamics possibly relevant to the solar corona. Vector magnetic field data from an eleven-tipped B-dot rake probe and images from an ultra-fast camera will be presented in comparison with ongoing MHD modeling using the 3-D MHD BATS-R-US code developed at the University of Michigan. BATS-R-US employs an adaptive mesh refinement grid (AMR) that enables the capture and resolution of shock structures and current sheets and is uniquely suited for flux-rope expansion modeling. Recent experiments show a possible magnetic Rayleigh-Taylor (MRT) instability that appears asymmetrically at the interface between launched spheromaks (bubbles) and their entraining background magnetic field. Efforts to understand this instability using in situ measurements, new chamber boundary conditions, and ultra-fast camera data will be presented. Work supported by the Army Research Office Award No. W911NF1510480.

Gas isotope separation method using plasma sheet

International Nuclear Information System (INIS)

Takayama, K.; Takagi, K.; Fukvi, R.

1988-03-01

A high frequency electric field is applied to a plasma sheet with a frequency equal to the cyclotronic frequency of the ions to be separated. Because of resonance the cyclotronic radius of the isotope has increased and the electric charge is eliminated by collision with a separator and the isotope is separated in neutral particles [fr

Theoretical modeling of the plasma-assisted catalytic growth and field emission properties of graphene sheet

International Nuclear Information System (INIS)

Sharma, Suresh C.; Gupta, Neha

2015-01-01

A theoretical modeling for the catalyst-assisted growth of graphene sheet in the presence of plasma has been investigated. It is observed that the plasma parameters can strongly affect the growth and field emission properties of graphene sheet. The model developed accounts for the charging rate of the graphene sheet; number density of electrons, ions, and neutral atoms; various elementary processes on the surface of the catalyst nanoparticle; surface diffusion and accretion of ions; and formation of carbon-clusters and large graphene islands. In our investigation, it is found that the thickness of the graphene sheet decreases with the plasma parameters, number density of hydrogen ions and RF power, and consequently, the field emission of electrons from the graphene sheet surface increases. The time evolution of the height of graphene sheet with ion density and sticking coefficient of carbon species has also been examined. Some of our theoretical results are in compliance with the experimental observations

Lamination sheet of AA BST magnet

CERN Multimedia

CERN PhotoLab

1979-01-01

The AA had 2 types of bending magnets: BLG (window-frame, long and narrow)and BST (H-type, short and wide). The BST had a very wide aperture, 0.564 m of "good field". To demonstrate the size, the petite AA secretary, Val Mansfield, poses with a lamination sheet. See also 7811105, 7906163, 8006050.

Energized Oxygen : Speiser Current Sheet Bifurcation

Science.gov (United States)

George, D. E.; Jahn, J. M.

2017-12-01

A single population of energized Oxygen (O+) is shown to produce a cross-tail bifurcated current sheet in 2.5D PIC simulations of the magnetotail without the influence of magnetic reconnection. Treatment of oxygen in simulations of space plasmas, specifically a magnetotail current sheet, has been limited to thermal energies despite observations of and mechanisms which explain energized ions. We performed simulations of a homogeneous oxygen background, that has been energized in a physically appropriate manner, to study the behavior of current sheets and magnetic reconnection, specifically their bifurcation. This work uses a 2.5D explicit Particle-In-a-Cell (PIC) code to investigate the dynamics of energized heavy ions as they stream Dawn-to-Dusk in the magnetotail current sheet. We present a simulation study dealing with the response of a current sheet system to energized oxygen ions. We establish a, well known and studied, 2-species GEM Challenge Harris current sheet as a starting point. This system is known to eventually evolve and produce magnetic reconnection upon thinning of the current sheet. We added a uniform distribution of thermal O+ to the background. This 3-species system is also known to eventually evolve and produce magnetic reconnection. We add one additional variable to the system by providing an initial duskward velocity to energize the O+. We also traced individual particle motion within the PIC simulation. Three main results are shown. First, energized dawn- dusk streaming ions are clearly seen to exhibit sustained Speiser motion. Second, a single population of heavy ions clearly produces a stable bifurcated current sheet. Third, magnetic reconnection is not required to produce the bifurcated current sheet. Finally a bifurcated current sheet is compatible with the Harris current sheet model. This work is the first step in a series of investigations aimed at studying the effects of energized heavy ions on magnetic reconnection. This work differs

Electron-inertia effects on driven magnetic field reconnection

International Nuclear Information System (INIS)

Al-Salti, N.; Shivamoggi, B.K.

2003-01-01

Electron-inertia effects on the magnetic field reconnection induced by perturbing the boundaries of a slab of plasma with a magnetic neutral surface inside are considered. Energetics of the tearing mode dynamics with electron inertia which controls the linearized collisionless magnetohydrodynamics (MHD) are considered with a view to clarify the role of the plasma pressure in this process. Cases with the boundaries perturbed at rates slow or fast compared with the hydromagnetic evolution rate are considered separately. When the boundaries are perturbed at a rate slow compared with the hydromagnetic evolution rate and fast compared with the resistive diffusion rate, the plasma response for early times is according to ideal MHD. A current sheet formation takes place at the magnetic neutral surface for large times in the ideal MHD stage and plasma becomes motionless. The subsequent evolution of the current sheet is found to be divided into two distinct stages: (i) the electron-inertia stage for small times (when the current sheet is very narrow); (ii) the resistive-diffusion stage for large times. The current sheet mainly undergoes exponential damping in the electron-inertia regime while the bulk of the diffusion happens in the resistivity regime. For large times of the resistive-diffusion stage when plasma flow is present, the current sheet completely disappears and the magnetic field reconnection takes place. When the boundaries are perturbed at a rate fast compared even with the hydromagnetic evolution rate, there is no time for the development of a current sheet and the magnetic field reconnection has been found not to take place

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.

Electron Dynamics in a Subproton-Gyroscale Magnetic Hole

Science.gov (United States)

Gershman, Daniel J.; Dorelli, John C.; Vinas, Adolfo F.; Avanov, Levon A.; Gliese, Ulrik B.; Barrie, Alexander C.; Coffey, Victoria; Chandler, Michael; Dickson, Charles; MacDonald, Elizabeth A.;

Evolution of the MHD sheet pinch

International Nuclear Information System (INIS)

Matthaeus, W.H.; Montgomery, D.

1979-01-01

A magnetohydrodynamic (MHD) problem of recurrent interest for both astrophysical and laboratory plasmas is the evolution of the unstable sheet pinch, a current sheet across which a dc magnetic field reverses sign. The evolution of such a sheet pinch is followed with a spectral-method, incompressible, two-dimensional, MHD turbulence code. Spectral diagnostics are employed, as are contour plots of vector potential (magnetic field lines), electric current density, and velocity stream function (velocity streamlines). The nonlinear effect which seems most important is seen to be current filamentation: the concentration of the current density onto sets of small measure near a mgnetic X point. A great deal of turbulence is apparent in the current distribution, which, for high Reynolds numbers, requires large spatial grids (greater than or equal to (64) 2 ). 11 figures, 1 table

Magnetic Detachment and Plume Control in Escaping Magnetized Plasma

International Nuclear Information System (INIS)

Schmit, P.F.; Fisch, N.J.

2008-01-01

The model of two-fluid, axisymmetric, ambipolar magnetized plasma detachment from thruster guide fields is extended to include plasmas with non-zero injection angular velocity profiles. Certain plasma injection angular velocity profiles are shown to narrow the plasma plume, thereby increasing exhaust efficiency. As an example, we consider a magnetic guide field arising from a simple current ring and demonstrate plasma injection schemes that more than double the fraction of useful exhaust aperture area, more than halve the exhaust plume angle, and enhance magnetized plasma detachment

Ion and electron Kappa distribution functions in the plasma sheet.

Science.gov (United States)

Moya, P. S.; Stepanova, M. V.; Espinoza, C.; Antonova, E. E.; Valdivia, J. A.

2017-12-01

We present a study of ion and electron flux spectra in the Earth's plasma sheet using kappa distribution functions. Satellite data from the THEMIS mission were collected for thousands of crossings through the plasma sheet, between 7 and 35 Re and during the years 2008-2009. The events were separated according to the geomagnetic activity at the time. Our results show the distribution of the kappa index and characteristic energies across the plasma sheet and its evolution with distance to Earth for quiet times and for the substorm expansion and recovery phases. For the ions, it is observed that the kappa values tend to decrease outwards and that this effect is more significant in the dusk sector, where the smallest values are found for distances beyond 15 Re. The main effect of the substorms appears as an enhancement of this behavior. The electrons show a much more homogeneous distribution in quiet times, with a mild tendency for larger kappa values at larger distances. During substorms, the kappa values tend to equalize and appear very homogenous during expansion. However, they exhibit a significant increase in the dusk sector during the recovery substorm phase. Finally, we observe that the characteristic energy of the particles during substorms increases and concentrate at distances less than 15 Re.

Electron precipitation morphology and plasma sheet dynamics: ground and magnetotail studies of the magnetospheric substorm

International Nuclear Information System (INIS)

Pytte, T.

1976-12-01

The main results of some recent studies of the magnetospheric substorm are summarised and discussed in view of the fundamental role of magnetospheric convection. The substorm growth phase is described in terms of a temporary imbalance between the rates of magnetic field-line merging on the dayside, and reconnection on the nightside, of the magnetosphere following a southward turning of the interplanetary magnetic field. Some new understanding of the possible causal relationship between growth-phase and expansion-phase phenomena is provided through studies of multiple-onset substorms, during which substorm expansions are observed to occur at intervals of 10-15 min. Detailed observations have revealed new features of the radial and azimuthal dynamics of these substorms that are not consistent with recent models proposed by Akasofu and by Rostoker and his co-workers. It is shown that the behaviour of the near-earth plasma sheet early in a substorm cannot be inferred from measurements at larger distances (e.g., in the Vela satellite orbits), and that the triggering of a substorm expansion may well be directly related to pre-substorm thinning of the near-earth plasma sheet, even though the most significant thinning in the tailward region may occur at the onset, and therefore appears to be an effect rather than a cause of triggering. Initial results from studies of a new type of magnetospheric activity, characterised by strong auroral-zone bay activity but no other indications of substorm expansions, are shown to be consistent with current models of the growth and expansion phases of substorms and of substorm triggering. (JIW)

Electron energization in the geomagnetic tail current sheet

International Nuclear Information System (INIS)

Lyons, L.R.

1984-01-01

Electron motion in the distant tail current sheet is evaluated and found to violate the guiding center approximation at energies > or approx. =100 eV. Most electrons within the energy range approx.10 -1 -10 2 keV that enter the current sheet become trapped within the magnetic field reversal region. These electrons then convect earthward and gain energy from the cross-tail electric field. If the energy spectrum of electrons entering the current sheet is similar to that of electrons from the boundary layer surrounding the magnetotail, the energy gain from the electric field produces electron energy spectra comparable to those observed in the earth's plasma sheet. Thus current sheet interactions can be a significant source of particles and energy for plasma sheet electrons as well as for plasma sheet ions. A small fraction of electrons within the current sheet has its pitch angles scattered so as to be ejected from the current sheet within the atmospheric loss cone. These electrons can account for the electron precipitation near the high-latitude boundary of energetic electrons, which is approximately isotropic in pitch angle up to at least several hundred keV. Current sheet interaction should cause approximately isotropic auroral precipitation up to several hundred keV energies, which extends to significantly lower latitudes for ions than for electrons in agreement with low-altitude satellite observations. Electron precipitation associated with diffuse aurora generally has a transition at 1-10 keV to anisotropic pitch angle distributions. Such electron precipitation cannot be explained by current sheet interactions, but it can be explained by pitch angle diffusion driven by plasma turbulence

Dynamics of Magnetized Plasma Jets and Bubbles Launched into a Background Magnetized Plasma

Science.gov (United States)

Wallace, B.; Zhang, Y.; Fisher, D. M.; Gilmore, M.

2016-10-01

The propagation of dense magnetized plasma, either collimated with mainly azimuthal B-field (jet) or toroidal with closed B-field (bubble), in a background plasma occurs in a number of solar and astrophysical cases. Such cases include coronal mass ejections moving in the background solar wind and extragalactic radio lobes expanding into the extragalactic medium. Understanding the detailed MHD behavior is crucial for correctly modeling these events. In order to further the understanding of such systems, we are investigating the injection of dense magnetized jets and bubbles into a lower density background magnetized plasma using a coaxial plasma gun and a background helicon or cathode plasma. In both jet and bubble cases, the MHD dynamics are found to be very different when launched into background plasma or magnetic field, as compared to vacuum. In the jet case, it is found that the inherent kink instability is stabilized by velocity shear developed due to added magnetic tension from the background field. In the bubble case, rather than directly relaxing to a minimum energy Taylor state (spheromak) as in vacuum, there is an expansion asymmetry and the bubble becomes Rayleigh-Taylor unstable on one side. Recent results will be presented. Work supported by the Army Research Office Award No. W911NF1510480.

Survey of 0.1- to 16-keV/e plasma sheet ion composition

International Nuclear Information System (INIS)

Lennartsson, W.; Shelley, E.G.

1986-01-01

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 + and He ++ ), as found in earlier studies, and these ions are most numerous during extended periods of very low activity (AE< or approx. =30 γ). 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

The plasma sheet and boundary layers under northward IMF: A multi-point and multi-instrument perspective

Czech Academy of Sciences Publication Activity Database

Taylor, M. G. G. T.; Lavraud, B.; Escoubet, C. P.; Milan, S.E.; Nykyri, K.; Dunlop, M. W.; Davies, J.A.; Friedel, R.H.W.; Frey, H.; Bogdanova, Y.V.; Asnes, A.; Laakso, H.; Trávníček, Pavel M.; Masson, A.; Opgenoorth, H.; Vallat, C.; Fazakerley, A. N.; Lahiff, A.; Owen, C. J.; Pitout, F.; Pu, Y.; Shen, C.; Zong, Q.-G.; Rème, H.; Scudder, J. D.; Zhang, T. L.

2008-01-01

Roč. 41, č. 10 (2008), s. 1619-1629 ISSN 0273-1177 Institutional research plan: CEZ:AV0Z10030501 Keywords : plasma sheet * magnetopshere * cold dense plasma sheet Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 0.860, year: 2008

Penetration of magnetic field in ferromagnetic transformer sheet

Energy Technology Data Exchange (ETDEWEB)

Sikora, R; Ziolkowski, M

1981-01-12

The paper deals with the penetration of magnetic field in a ferromagnetic transformer sheet. The flux-density distribution is computed using Galerkin's procedure. The different boundary conditions and the nonlinear B/H characteristic is taken into account.

The formation of solar prominences by thermal instability in a current sheet

International Nuclear Information System (INIS)

Smith, E.A.; Priest, E.R.

1977-01-01

The energy balance equation for the upper chromosphere or lower corona contains a radiative loss term which is destabilizing, because of slight decrease in temperature from the equilibrium value causes more radiation and hence a cooling of the plasma; also a slight increase in temperature has the effect of heating the plasma. In spite of this tendency towards thermal instability, most of the solar atmosphere is remarkably stable, since thermal conduction is very efficient at equalizing any temperature irregularity which may arise. However, the effectiveness of thermal conduction in transporting heat is decreased considerably in a current sheet or a magnetic flux tube, since heat can be conducted quickly only along the magnetic field lines. This paper presents a simple model for the thermal equilibrium and stability of a current sheet. It is found that, when its length exceeds a certain maximum value, no equilibrium is possible and the plasma in the sheet cools. The results may be relevant for the formation of a quiescent prominence. (Auth.)

On the structure of the tail magnetic field

International Nuclear Information System (INIS)

Candidi, M.; Orsini, S.; Stokholm, M.; Elphic, R.C.

1990-01-01

The authors present a study comparing the magnetic field configuration in the magnetotail lobes with that in the plasma sheet boundary layer. The results indicate a systematic enhancement of the By component of the plasma sheet boundary layer field over that of the lobe. The value of such enhancement increases with distance from the midnight meridian plane and has the same sense in the northern and southern plasma sheet boundary layer. Such a By enhancement corresponds to a smaller rate of flaring of the magnetic field lines in the lobe with respect to the plasma sheet boundary layer. This observation is interpreted as a signature of field-aligned currents at the boundary. The direction of the field-aligned currents agrees with the nightside region 1 current system, which is the most poleward system in the nightside polar ionosphere at low altitude

Dust in flowing magnetized plasma

International Nuclear Information System (INIS)

Pandey, Birendra P.; Samarian, Alex A.; Vladimirov, Sergey V.

2009-01-01

Plasma flows occur in almost every laboratory device and interactions of flowing plasmas with near-wall impurities and/or dust significantly affects the efficiency and lifetime of such devices. The charged dust inside the magnetized flowing plasma moves primarily under the influence of the plasma drag and electric forces. Here, the charge on the dust, plasma potential, and plasma density are calculated self-consistently. The electrons are assumed non-Boltzmannian and the effect of electron magnetization and electron-atom collisions on the dust charge is calculated in a self-consistent fashion. For various plasma magnetization parameters viz. the ratio of the electron and ion cyclotron frequencies to their respective collision frequencies, plasma-atom and ionization frequencies, the evolution of the plasma potential and density in the flow region is investigated. The variation of the dust charge profile is shown to be a sensitive function of plasma parameters. (author)

Relation between current sheets and vortex sheets in stationary incompressible MHD

Directory of Open Access Journals (Sweden)

D. H. Nickeler

2012-03-01

Full Text Available Magnetohydrodynamic configurations with strong localized current concentrations and vortices play an important role in the dissipation of energy in space and astrophysical plasma. Within this work we investigate the relation between current sheets and vortex sheets in incompressible, stationary equilibria. For this approach it is helpful that the similar mathematical structure of magnetohydrostatics and stationary incompressible hydrodynamics allows us to transform static equilibria into stationary ones. The main control function for such a transformation is the profile of the Alfvén-Mach number MA, which is always constant along magnetic field lines, but can change from one field line to another. In the case of a global constant MA, vortices and electric current concentrations are parallel. More interesting is the nonlinear case, where MA varies perpendicular to the field lines. This is a typical situation at boundary layers like the magnetopause, heliopause, the solar wind flowing around helmet streamers and at the boundary of solar coronal holes. The corresponding current and vortex sheets show in some cases also an alignment, but not in every case. For special density distributions in 2-D, it is possible to have current but no vortex sheets. In 2-D, vortex sheets of field aligned-flows can also exist without strong current sheets, taking the limit of small Alfvén Mach numbers into account. The current sheet can vanish if the Alfvén Mach number is (almost constant and the density gradient is large across some boundary layer. It should be emphasized that the used theory is not only valid for small Alfvén Mach numbers MA MA ≲ 1. Connection to other theoretical approaches and observations and physical effects in space plasmas are presented. Differences in the various aspects of theoretical investigations of current sheets and vortex sheets are given.

Sheet Fluorescence and Annular Analysis of Ultracold Neutral Plasmas

International Nuclear Information System (INIS)

Castro, J.; Gao, H.; Killian, T. C.

2009-01-01

Annular analysis of fluorescence imaging measurements on Ultracold Neutral Plasmas (UNPs) is demonstrated. Spatially-resolved fluorescence imaging of the strontium ions produces a spectrum that is Doppler-broadened due to the thermal ion velocity and shifted due to the ion expansion velocity. The fluorescence excitation beam is spatially narrowed into a sheet, allowing for localized analysis of ion temperatures within a volume of the plasma with small density variation. Annular analysis of fluorescence images permits an enhanced signal-to-noise ratio compared to previous fluorescence measurements done in strontium UNPs. Using this technique and analysis, plasma ion temperatures are measured and shown to display characteristics of plasmas with strong coupling such as disorder induced heating and kinetic energy oscillations.

Energization of the Ring Current through Convection of Substorm Enhancements of the Plasma Sheet Source.

Science.gov (United States)

Menz, A.; Kistler, L. M.; Mouikis, C.; Spence, H. E.; Henderson, M. G.; Matsui, H.

2017-12-01

It has been shown that electric field strength and night-side plasma sheet density are the two best predictors of the adiabatic energy gain of the ring current during geomagnetic storms (Liemohn and Khazanov, 2005). While H+ dominates the ring current during quiet times, O+ can contribute substantially during geomagnetic storms. Substorm activity provides a mechanism to enhance the energy density of O+ in the plasma sheet during geomagnetic storms, which is then convected adiabatically into the inner-magnetosphere. Using the Van Allen Probes data in the the plasma sheet source region (defined as L>5.5 during storms) and the inner magnetosphere, along with LANL-GEO data to identify substorm injection times, we show that adiabatic convection of O+ enhancements in the source region can explain the observed enhancements in the inner magnetosphere. We use the UNH-IMEF electric field model to calculate drift times from the source region to the inner magnetosphere to test whether enhancements in the inner-magnetosphere can be explained by dipolarization driven enhancements in the plasma sheet source hours before.

Pressure changes in the plasma sheet during substorm injections

International Nuclear Information System (INIS)

Kistler, L.M.; Moebuis, E.; Baumjohann, W.; Paschmann, G.; Hamilton, D.C.

1992-01-01

The authors have determined the particle pressure and total pressure as a function of radial distance in the plasma sheet for periods before and after the onset of substorm-associated ion enhancements over the radial range 7-19 R E . They have chosen events occurring during times of increasing magnetospheric activity, as determined by an increasing AE index, in which a sudden increase, or injection, of energetic particle flux is observed. During these events the particle energy of maximum contribution to the pressure increases from about 12 to about 27 keV. In addition, the particle pressure increases, and the magnetic pressure decreases, with the total pressure only changing slightly. For radial distances of less than 10 R E the total pressure tends to increase with the injection, while outside 10 R E it tends to decrease or remain the same. Because the fraction of the pressure due to particles has increased and higher energies are contributing to the pressure, a radial gradient is evident in the postinjection, but not preinjection, flux measurements. These observations show that the simulations appearance of energetic particles and changes in the magnetic field results naturally from pressure balance and does not necessarily indicate that the local changing field is accelerating the particles. The changes in the total pressure outside 10 R E are consistent with previous measurements of pressure changes at substorm onset and can be understood in terms of the unloading of energy in the magnetotail and the resulting change in the magnetic field configuration

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 R_E. 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.

TURBULENT DYNAMICS IN SOLAR FLARE SHEET STRUCTURES MEASURED WITH LOCAL CORRELATION TRACKING

Energy Technology Data Exchange (ETDEWEB)

McKenzie, D. E., E-mail: mckenzie@physics.montana.edu [Department of Physics, Montana State University, P.O. Box 173840, Bozeman, MT 59717-3840 (United States)

2013-03-20

High-resolution observations of the Sun's corona in extreme ultraviolet and soft X-rays have revealed a new world of complexity in the sheet-like structures connecting coronal mass ejections (CMEs) to the post-eruption flare arcades. This article presents initial findings from an exploration of dynamic flows in two flares observed with Hinode/XRT and SDO/AIA. The flows are observed in the hot ({approx}> 10 MK) plasma above the post-eruption arcades and measured with local correlation tracking. The observations demonstrate significant shears in velocity, giving the appearance of vortices and stagnations. Plasma diagnostics indicate that the plasma {beta} exceeds unity in at least one of the studied events, suggesting that the coronal magnetic fields may be significantly affected by the turbulent flows. Although reconnection models of eruptive flares tend to predict a macroscopic current sheet in the region between the CME and the flare arcade, it is not yet clear whether the observed sheet-like structures are identifiable as the current sheets or 'thermal halos' surrounding the current sheets. Regardless, the relationship between the turbulent motions and the embedded magnetic field is likely to be complicated, involving dynamic fluid processes that produce small length scales in the current sheet. Such processes may be crucial for triggering, accelerating, and/or prolonging reconnection in the corona.

Magnetic Field Measurements In Magnetized Plasmas Using Zeeman Broadening Diagnostics

Science.gov (United States)

Haque, Showera; Wallace, Matthew; Presura, Radu; Neill, Paul

2017-10-01

The Zeeman effect has been used to measure the magnetic field in high energy density plasmas. This method is limited when plasma conditions are such that the line broadening due to the high plasma density and temperature surpasses the Zeeman splitting. We have measured magnetic fields in magnetized laser plasmas under conditions where the Zeeman splitting was not spectrally resolved. The magnetic field strength was determined from the difference in widths of two doublet components, using an idea proposed by Tessarin et al. (2011). Time-gated spectra with one-dimensional space-resolution were obtained at the Nevada Terawatt Facility for laser plasmas created by 20 J, 1 ns Leopard laser pulses, and expanding in the azimuthal magnetic field produced by the 0.6 MA Zebra pulsed power generator. We explore the response of the Al III 4s 2S1/2 - 4p 2P1 / 2 , 3 / 2 doublet components to the external magnetic field spatially along the plasma. Radial magnetic field and electron density profiles were measured within the plasma plume. This work was supported by the DOE/OFES Grant DE-SC0008829 and DOE/NNSA contract DE-FC52-06NA27616.

On tenuous plasmas, fireballs, and boundary layers in the earth's magnetotail

Science.gov (United States)

Frank, L. A.; Ackerson, K. L.; Lepping, R. P.

1976-01-01

The plasma instrumentation (the Lepedea) and the magnetometer aboard IMP 8 performed correlative measurements of magnetic fields and plasmas within the geomagnetic tail at geocentric radial distances of about 23-46 R-E during March-October 1974. The hot tenuous plasmas within the plasma sheet were found to be in a state of almost continuous flow and were threaded with northward, or closed geomagnetic lines. The satellite encountered a region of acceleration in the magnetotail, the 'fireball' which exhibits strong jetting of plasmas in excess of 1000 km/s, proton temperatures of about 10 to the 7th K, disordered magnetic fields, southward magnetic fields during tailward jetting of plasmas, and northward magnetic fields for fast plasma flows toward earth. In addition, the magnetosheath plasmas within the boundary layers which are contiguous to the plasma sheet display evidence of plasma heating, great changes in bulk flow velocities, and acceleration of energetic electrons with an energy of greater than 45 keV.

Current sheets and pressure anisotropy in the reconnection exhaust

International Nuclear Information System (INIS)

Le, A.; Karimabadi, H.; Roytershteyn, V.; Egedal, J.; Ng, J.; Scudder, J.; Daughton, W.; Liu, Y.-H.

2014-01-01

A particle-in-cell simulation shows that the exhaust during anti-parallel reconnection in the collisionless regime contains a current sheet extending 100 inertial lengths from the X line. The current sheet is supported by electron pressure anisotropy near the X line and ion anisotropy farther downstream. Field-aligned electron currents flowing outside the magnetic separatrices feed the exhaust current sheet and generate the out-of-plane, or Hall, magnetic field. Existing models based on different mechanisms for each particle species provide good estimates for the levels of pressure anisotropy. The ion anisotropy, which is strong enough to reach the firehose instability threshold, is also important for overall force balance. It reduces the outflow speed of the plasma

Current sheets and pressure anisotropy in the reconnection exhaust

Energy Technology Data Exchange (ETDEWEB)

Le, A.; Karimabadi, H.; Roytershteyn, V. [SciberQuest, Inc., Del Mar, California 92014 (United States); Egedal, J. [University of Wisconsin–Madison, Madison, Wisconsin 53706 (United States); Ng, J. [PPPL, Princeton University, Princeton, New Jersey 08543 (United States); Scudder, J. [University of Iowa, Iowa City, Iowa 52242 (United States); Daughton, W.; Liu, Y.-H. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2014-01-15

A particle-in-cell simulation shows that the exhaust during anti-parallel reconnection in the collisionless regime contains a current sheet extending 100 inertial lengths from the X line. The current sheet is supported by electron pressure anisotropy near the X line and ion anisotropy farther downstream. Field-aligned electron currents flowing outside the magnetic separatrices feed the exhaust current sheet and generate the out-of-plane, or Hall, magnetic field. Existing models based on different mechanisms for each particle species provide good estimates for the levels of pressure anisotropy. The ion anisotropy, which is strong enough to reach the firehose instability threshold, is also important for overall force balance. It reduces the outflow speed of the plasma.

Nonlinear equilibrium structure of thin currents sheets: influence of electron pressure anisotropy

Directory of Open Access Journals (Sweden)

L. M. Zelenyi

2004-01-01

Full Text Available Thin current sheets represent important and puzzling sites of magnetic energy storage and subsequent fast release. Such structures are observed in planetary magnetospheres, solar atmosphere and are expected to be widespread in nature. The thin current sheet structure resembles a collapsing MHD solution with a plane singularity. Being potential sites of effective energy accumulation, these structures have received a good deal of attention during the last decade, especially after the launch of the multiprobe CLUSTER mission which is capable of resolving their 3D features. Many theoretical models of thin current sheet dynamics, including the well-known current sheet bifurcation, have been developed recently. A self-consistent 1D analytical model of thin current sheets in which the tension of the magnetic field lines is balanced by the ion inertia rather than by the plasma pressure gradients was developed earlier. The influence of the anisotropic electron population and of the corresponding electrostatic field that acts to restore quasi-neutrality of the plasma is taken into account. It is assumed that the electron motion is fluid-like in the direction perpendicular to the magnetic field and fast enough to support quasi-equilibrium Boltzmann distribution along the field lines. Electrostatic effects lead to an interesting feature of the current density profile inside the current sheet, i.e. a narrow sharp peak of electron current in the very center of the sheet due to fast curvature drift of the particles in this region. The corresponding magnetic field profile becomes much steeper near the neutral plane although the total cross-tail current is in all cases dominated by the ion contribution. The dependence of electrostatic effects on the ion to electron temperature ratio, the curvature of the magnetic field lines, and the average electron magnetic moment is also analyzed. The implications of these effects on the fine structure of thin current sheets

Geothermal Heat Flux Underneath Ice Sheets Estimated From Magnetic Satellite Data

DEFF Research Database (Denmark)

Fox Maule, Cathrine; Purucker, M.E.; Olsen, Nils

The geothermal heat flux is an important factor in the dynamics of ice sheets, and it is one of the important parameters in the thermal budgets of subglacial lakes. We have used satellite magnetic data to estimate the geothermal heat flux underneath the ice sheets in Antarctica and Greenland...

Magnetic Field Effects on Plasma Plumes

Science.gov (United States)

Ebersohn, F.; Shebalin, J.; Girimaji, S.; Staack, D.

2012-01-01

Here, we will discuss our numerical studies of plasma jets and loops, of basic interest for plasma propulsion and plasma astrophysics. Space plasma propulsion systems require strong guiding magnetic fields known as magnetic nozzles to control plasma flow and produce thrust. Propulsion methods currently being developed that require magnetic nozzles include the VAriable Specific Impulse Magnetoplasma Rocket (VASIMR) [1] and magnetoplasmadynamic thrusters. Magnetic nozzles are functionally similar to de Laval nozzles, but are inherently more complex due to electromagnetic field interactions. The two crucial physical phenomenon are thrust production and plasma detachment. Thrust production encompasses the energy conversion within the nozzle and momentum transfer to a spacecraft. Plasma detachment through magnetic reconnection addresses the problem of the fluid separating efficiently from the magnetic field lines to produce maximum thrust. Plasma jets similar to those of VASIMR will be studied with particular interest in dual jet configurations, which begin as a plasma loops between two nozzles. This research strives to fulfill a need for computational study of these systems and should culminate with a greater understanding of the crucial physics of magnetic nozzles with dual jet plasma thrusters, as well as astrophysics problems such as magnetic reconnection and dynamics of coronal loops.[2] To study this problem a novel, hybrid kinetic theory and single fluid magnetohydrodynamic (MHD) solver known as the Magneto-Gas Kinetic Method is used.[3] The solver is comprised of a "hydrodynamic" portion based on the Gas Kinetic Method and a "magnetic" portion that accounts for the electromagnetic behaviour of the fluid through source terms based on the resistive MHD equations. This method is being further developed to include additional physics such as the Hall effect. Here, we will discuss the current level of code development, as well as numerical simulation results

Magnetized relativistic electron-ion plasma expansion

Science.gov (United States)

Benkhelifa, El-Amine; Djebli, Mourad

2016-03-01

The dynamics of relativistic laser-produced plasma expansion across a transverse magnetic field is investigated. Based on a one dimensional two-fluid model that includes pressure, enthalpy, and rest mass energy, the expansion is studied in the limit of λD (Debye length) ≤RL (Larmor radius) for magnetized electrons and ions. Numerical investigation conducted for a quasi-neutral plasma showed that the σ parameter describing the initial plasma magnetization, and the plasma β parameter, which is the ratio of kinetic to magnetic pressure are the key parameters governing the expansion dynamics. For σ ≪ 1, ion's front shows oscillations associated to the break-down of quasi-neutrality. This is due to the strong constraining effect and confinement of the magnetic field, which acts as a retarding medium slowing the plasma expansion.

Large-scale flows, sheet plumes and strong magnetic fields in a rapidly rotating spherical dynamo

Science.gov (United States)

Takahashi, F.

2011-12-01

Mechanisms of magnetic field intensification by flows of an electrically conducting fluid in a rapidly rotating spherical shell is investigated. Bearing dynamos of the Eartn and planets in mind, the Ekman number is set at 10-5. A strong dipolar solution with magnetic energy 55 times larger than the kinetic energy of thermal convection is obtained. In a regime of small viscosity and inertia with the strong magnetic field, convection structure consists of a few large-scale retrograde flows in the azimuthal direction and sporadic thin sheet-like plumes. The magnetic field is amplified through stretching of magnetic lines, which occurs typically through three types of flow: the retrograde azimuthal flow near the outer boundary, the downwelling flow of the sheet plume, and the prograde azimuthal flow near the rim of the tangent cylinder induced by the downwelling flow. It is found that either structure of current loops or current sheets is accompanied in each flow structure. Current loops emerge as a result of stretching the magnetic lines along the magnetic field, wheres the current sheets are formed to counterbalance the Coriolis force. Convection structure and processes of magnetic field generation found in the present model are distinct from those in models at larger/smaller Ekman number.

Streaming sausage, kink and tearing instabilities in a current sheet with applications to the earth's magnetotail

Science.gov (United States)

Lee, L. C.; Wang, S.; Wei, C. Q.; Tsurutani, B. T.

1988-01-01

This paper investigates the growth rates and eigenmode structures of the streaming sausage, kink, and tearing instabilities in a current sheet with a super-Alfvenic flow. The growth rates and eigenmode structures are first considered in the ideal incompressible limit by using a four-layer model, as well as a more realistic case in which all plasma parameters and the magnetic field vary continuously along the direction perpendicular to the magnetic field and plasma flow. An initial-value method is applied to obtain the growth rate and eigenmode profiles of the fastest growing mode, which is either the sausage mode or kink mode. It is shown that, in the earth's magnetotail, where super-Alfvenic plasma flows are observed in the plasma sheet and the ratio between the plasma and magnetic pressures far away from the current layer is about 0.1-0.3 in the lobes, the streaming sausage and streaming tearing instabilities, but not kink modes, are likely to occur.

Controlling magnetism of MoS2 sheets by embedding transition-metal atoms and applying strain.

Science.gov (United States)

Zhou, Yungang; Su, Qiulei; Wang, Zhiguo; Deng, Huiqiu; Zu, Xiaotao

2013-11-14

Prompted by recent experimental achievement of transition metal (TM) atoms substituted in MoS2 nanostructures during growth or saturating existing vacancies (Sun et al., ACS Nano, 2013, 7, 3506; Deepak et al., J. Am. Chem. Soc., 2007, 129, 12549), we explored, via density functional theory, the magnetic properties of a series of 3d TM atoms substituted in a MoS2 sheet, and found that Mn, Fe, Co, Ni, Cu and Zn substitutions can induce magnetism in the MoS2 sheet. The localizing unpaired 3d electrons of TM atoms respond to the introduction of a magnetic moment. Depending on the species of TM atoms, the substituted MoS2 sheet can be a metal, semiconductor or half-metal. Remarkably, the applied elastic strain can be used to control the strength of the spin-splitting of TM-3d orbitals, leading to an effective manipulation of the magnetism of the TM-substituted MoS2 sheet. We found that the magnetic moment of the Mn- and Fe-substituted MoS2 sheets can monotonously increase with the increase of tensile strain, while the magnetic moment of Co-, Ni-, Cu- and Zn-substituted MoS2 sheets initially increases and then decreases with the increase of tensile strain. An instructive mechanism was proposed to qualitatively explain the variation of magnetism with elastic strain. The finding of the magnetoelastic effect here is technologically important for the fabrication of strain-driven spin devices on MoS2 nanostructures, which allows us to go beyond the current scope limited to the spin devices within graphene and BN-based nanostructures.

Stationary quenching wave in magnetized plasma

International Nuclear Information System (INIS)

Alikhanov, S.G.; Glushkov, I.S.

1976-01-01

The interaction of a magnetized hot plasma (ωsub(e)tau sub(e)>>1) with cold plasma or a gas leads to the appearanci of a cooling wave. The transition layer between hot and cold plasma is the main source of radiation losses which should be compensated by a heat flow from the hot region. A stationary state is considered, equations are written in the system in which temperature and magnetic field profiles are steady, and the plasma flux with magnetic field passes through the cooling wave. Calculations, have been carried out on a computer. The dependence of the magnetized plasma flux velocity Vsub(r) on the ratio p/Hsub(r) is shown, where p is the pressure, Hsub(r) is the magnetic field in the hot reqion. The dependence of the characteristic dimension of the cooling wave on the magnetic field is determined for the hot plasma region. A considerable fraction of the rediation losses is shown to fall to the region of (ωsub(e)tausub(e)< or approximately)1

Electron Surfing Acceleration in Magnetic Reconnection

OpenAIRE

Hoshino, Masahiro

2005-01-01

We discuss that energetic electrons are generated near the X-type magnetic reconnection region due to a surfing acceleration mechanism. In a thin plasma sheet, the polarization electric fields pointing towards the neutral sheet are induced around the boundary between the lobe and plasma sheet in association with the Hall electric current. By using a particle-in-cell simulation, we demonstrate that the polarization electric fields are strongly enhanced in an externally driven reconnection syst...

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.

Coronal Heating Topology: The Interplay of Current Sheets and Magnetic Field Lines

Energy Technology Data Exchange (ETDEWEB)

Rappazzo, A. F.; Velli, M. [Department of Earth, Planetary, and Space Sciences, UCLA, Los Angeles, CA 90095 (United States); Matthaeus, W. H. [Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Ruffolo, D. [Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400 (Thailand); Servidio, S., E-mail: rappazzo@ucla.edu [Dipartimento di Fisica, Università della Calabria, Cosenza I-87036 (Italy)

2017-07-20

The magnetic topology and field line random walk (FLRW) properties of a nanoflare-heated and magnetically confined corona are investigated in the reduced magnetohydrodynamic regime. Field lines originating from current sheets form coherent structures, called current sheet connected (CSC) regions, which extend around them. CSC FLRW is strongly anisotropic, with preferential diffusion along the current sheets’ in-plane length. CSC FLRW properties remain similar to those of the entire ensemble but exhibit enhanced mean square displacements and separations due to the stronger magnetic field intensities in CSC regions. The implications for particle acceleration and heat transport in the solar corona and wind, and for solar moss formation are discussed.

Experimental observations of the tearing of an electron current sheet

International Nuclear Information System (INIS)

Gekelman, W.; Pfister, H.

1988-01-01

A neutral magnetic sheet, in which the current is carried mainly by the electrons, is set up in a laboratory plasma. By forcing the current through a thin slot, the ratio of the length to height t of the sheet may be varied; the current is observed to tear when tapprox. >30. The structure of the magnetic islands and their associated currents is fully three dimensional, although a linear two-dimensional theory gives a very good estimate of the tearing mode growth time. Tearing is accompanied by the generation of significant Hall currents, and magnetic disturbances are observed to propagate at the whistler wave speed

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 +, 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 Ri in the night sector has the good response to the Kp index These observations indicate that Kp plays a key role in determining the position of

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

Generation of sheet currents by high frequency fast MHD waves

Energy Technology Data Exchange (ETDEWEB)

Núñez, Manuel, E-mail: mnjmhd@am.uva.es

2016-07-01

The evolution of fast magnetosonic waves of high frequency propagating into an axisymmetric equilibrium plasma is studied. By using the methods of weakly nonlinear geometrical optics, it is shown that the perturbation travels in the equatorial plane while satisfying a transport equation which enables us to predict the time and location of formation of shock waves. For plasmas of large magnetic Prandtl number, this would result into the creation of sheet currents which may give rise to magnetic reconnection and destruction of the original equilibrium. - Highlights: • Regular solutions of quasilinear hyperbolic systems may evolve into shocks. • The shock location is found for high frequency fast MHD waves. • The result is applied to static axisymmetric equilibria. • The previous process may lead to the formation of sheet currents and destruction of the equilibrium.

Super-high magnetic fields in spatially inhomogeneous plasma

International Nuclear Information System (INIS)

Nastoyashchiy, Anatoly F.

2012-01-01

The new phenomenon of a spontaneous magnetic field in spatially inhomogeneous plasma is found. The criteria for instability are determined, and both the linear and nonlinear stages of the magnetic field growth are considered; it is shown that the magnetic field can reach a considerable magnitude, namely, its pressure can be comparable with the plasma pressure. Especially large magnetic fields can arise in hot plasma with a high electron density, for example, in laser-heated plasma. In steady-state plasma, the magnetic field can be self-sustaining. The considered magnetic fields may play an important role in thermal insulation of the plasma. (author)

Radiation dominated relativistic current sheets

International Nuclear Information System (INIS)

Jaroschek, C.H.

2008-01-01

Relativistic Current Sheets (RCS) feature plasma instabilities considered as potential key to magnetic energy dissipation and non-thermal particle generation in Poynting flux dominated plasma flows. We show in a series of kinetic plasma simulations that the physical nature of non-linear RCS evolution changes in the presence of incoherent radiation losses: In the ultra-relativistic regime (i.e. magnetization parameter sigma = 104 defined as the ratio of magnetic to plasma rest frame energy density) the combination of non-linear RCS dynamics and synchrotron emission introduces a temperature anisotropy triggering the growth of the Relativistic Tearing Mode (RTM). As direct consequence the RTM prevails over the Relativistic Drift Kink (RDK) Mode as competitive RCS instability. This is in contrast to the previously studied situation of weakly relativistic RCS (sigma ∼ 1) where the RDK is dominant and most of the plasma is thermalized. The simulations witness the typical life cycle of ultra-relativistic RCS evolving from a violent radiation induced collapse towards a radiation quiescent state in rather classical Sweet-Parker topology. Such a transition towards Sweet-Parker configuration in the late non-linear evolution has immediate consequences for the efficiency of magnetic energy dissipation and non-thermal particle generation. Ceasing dissipation rates directly affect our present understanding of non-linear RCS evolution in conventional striped wind scenarios. (author)

Magnetic reconnection in nontoroidal plasmas

International Nuclear Information System (INIS)

Boozer, Allen H.

2005-01-01

Magnetic reconnection is a major issue in solar and astrophysical plasmas. The mathematical result that the evolution of a magnetic field with only point nulls is always locally ideal limits the nature of reconnection in nontoroidal plasmas. Here it is shown that the exponentially increasing separation of neighboring magnetic field lines, which is generic, tends to produce rapid magnetic reconnection if the length of the field lines is greater than about 20 times the exponentiation, or Lyapunov, length

Latitudinal distribution of the Jovian plasma sheet ions observed by Juno JADE-I

Science.gov (United States)

Kim, T. K. H.; Valek, P. W.; McComas, D. J.; Allegrini, F.; Bagenal, F.; Bolton, S. J.; Connerney, J. E. P.; Ebert, R. W.; Levin, S.; Louarn, P.; Pollock, C. J.; Ranquist, D. A.; Szalay, J.; Thomsen, M. F.; Wilson, R. J.

2017-12-01

The Jovian plasma sheet is a region where the centrifugal force dominates the heavy ion plasma. Properties of the plasma sheet ions near the equatorial plane have been studied with in-situ measurements from the Pioneer, Voyager, and Galileo spacecraft. However, the ion properties for the off-equator regions are not well known due to the limited measurements. Juno is the first polar orbiting spacecraft that can investigate the high latitude region of the Jovian magnetosphere. With Juno's unique trajectory, we will investigate the latitudinal distribution of the Jovian plasma sheet ions using measurements from the Jovian Auroral Distributions Experiment Ion sensor (JADE-I). JADE-I measures an ion's energy-per-charge (E/Q) from 0.01 keV/q to 46.2 keV/q with an electrostatic analyzer (ESA) and a mass-per-charge (M/Q) up to 64 amu/q with a carbon-foil-based time-of-flight (TOF) mass spectrometer. We have shown that the ambiguity between and (both have M/Q of 16) can be resolved in JADE-I using a semi-empirical simulation tool based on carbon foil effects (i.e., charge state modification, angular scattering, and energy loss) from incident ions passing through the TOF mass spectrometer. Based on the simulation results, we have developed an Ion Composition Analysis Tool (ICAT) that determines ion composition at each energy step of JADE-I (total of 64 steps). The velocity distribution for each ion species can be obtained from the ion composition as a function of each energy step. Since there is an ambipolar electric field due to mobile electrons and equatorially confined heavy ions, we expect to see acceleration along the field line. This study will show the species separated velocity distribution at various latitudes to investigate how the plasma sheet ions evolve along the field line.

Identification of Y-shaped and O-shaped diffusion regions during magnetic reconnection in a laboratory plasma

International Nuclear Information System (INIS)

Yamada, Masaaki; Ji, H.; Hsu, S.; Carter, T.; Kulsrud, R.; Ono, Yasushi; Perkins, F.

1997-01-01

Two strikingly different shapes of diffusion regions are identified during magnetic reconnection in a magnetohydrodynamic laboratory plasma. The shapes depend on the third vector component of the reconnecting magnetic fields. Without the third component (anti-parallel or null-helicity reconnection), a thin double-Y shaped diffusion region is identified. In this case, the neutral sheet current profile is accurately measured to be as narrow as the order of the ion gyro-radius. In the presence of an appreciable third component (co-helicity reconnection), an O-shaped diffusion region appears and grows into a spheromak configuration

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.

Laser-plasma interactions in magnetized environment

Science.gov (United States)

Shi, Yuan; Qin, Hong; Fisch, Nathaniel J.

2018-05-01

Propagation and scattering of lasers present new phenomena and applications when the plasma medium becomes strongly magnetized. With mega-Gauss magnetic fields, scattering of optical lasers already becomes manifestly anisotropic. Special angles exist where coherent laser scattering is either enhanced or suppressed, as we demonstrate using a cold-fluid model. Consequently, by aiming laser beams at special angles, one may be able to optimize laser-plasma coupling in magnetized implosion experiments. In addition, magnetized scattering can be exploited to improve the performance of plasma-based laser pulse amplifiers. Using the magnetic field as an extra control variable, it is possible to produce optical pulses of higher intensity, as well as compress UV and soft x-ray pulses beyond the reach of other methods. In even stronger giga-Gauss magnetic fields, laser-plasma interaction enters a relativistic-quantum regime. Using quantum electrodynamics, we compute a modified wave dispersion relation, which enables correct interpretation of Faraday rotation measurements of strong magnetic fields.

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.

Plasma behavior and plasma-wall interaction in magnetic fusion divices

International Nuclear Information System (INIS)

Ohtsuka, Hideo

1984-10-01

To study the fundamental behavior of plasma in magnetic field is the main subject in the early stage of the magnetic fusion research. At the next stage, it is necessary to overcome some actual problems in order to attain reactor grade plasmas. One of them is to control impurities in the plasma. In these points of view, we carried out several experiments or theoretical analyses. Firstly, anomalous loss mechanisms in magnetic field were investigated in a toroidal multipole device JFT-1 and the role of motions of charged particles in the magnetic field was exhibited. Various measurements of plasma in the scrape-off layer were made in a divertor tokamak JFT-2a and in an ordinary tokamak JFT-2. The former study demonstrated the first successful divertor operation of the tokamak device and the latter one clarified the mechanism of arcing on the tokamak first wall. As to arcing, a new theory which describes the retrograde motion, the well known strange motion of arcs in a magnetic field, was proposed. Good agreement with the experimental results was shown. Finally, by considering a zero-dimensional sputtering model a self-consistent relation between light and metal impurities in tokamak plasmas was obtained. It was shown that the relation well describes some fundamental aspects of the plasma-wall interaction. As a conclusion, the importance of simple behavior of charged particles in magnetic fields was pointed out not only for the plasma confinement but also for the plasma-wall interaction. (author)

Current disruptions in the near-earth neutral sheet region

International Nuclear Information System (INIS)

Liu, A.T.Y.; Anderson, B.J.; Takahashi, K.; Zanetti, L.J.; McEntire, R.W.; Potemra, T.A.; Lopez, R.E.; Klumpar, D.M.; Greene, E.M.; Strangeway, R.

1992-01-01

Observations from the Charge Composition Explorer in 1985 and 1986 revealed fifteen current disruption events in which the magnetic field fluctuations were large and their onsets coincided well with ground onsets of substorm expansion or intensification. Over the disruption interval, the local magnetic field can change by as much as a factor of ∼7. In general, the stronger the current buildup and the closer the neutral sheet, the larger the resultant field change. There is also a tendency for a larger subsequent enhancement in the AE index with a stronger current buildup prior to current disruption. For events with good pitch angle coverage and extended observation in the neutral sheet region the authors find that the particle pressure increases toward the disruption onset and decreases afterward. Just prior to disruption, either the total particle pressure is isotropic, or the perpendicular component (P perpendicular ) dominates the parallel component (P parallel ), the plasma beta is seen to be as high as ∼70, and the observed plasma pressure gradient at the neutral sheet is large along the tail axis. The deduced local current density associated with pressure gradient is ∼27-80 n/Am 2 and is ∼85-105 mA/m when integrated over the sheet thickness. They infer from these results that just prior to the onset of current disruption, (1) an extremely thin current sheet requiring P parallel > P perpendicular for stress balance does not develop at these distances, (2) the thermal ion orbits are in the chaotic or Speiser regime while the thermal electrons are in the adiabatic regime and, in one case, exhibit peaked fluxes perpendicular to the magnetic field, thus implying no electron orbit chaotization to possibly initiate ion tearing instability, and (3) the neutral sheet is in the unstable regime specified by the cross-field current instability

Experimental and numerical studies of sheet electron beam propagation through a planar wiggler magnet

International Nuclear Information System (INIS)

Zhang, Ze Xiang; Granatstein, V.L.; Destler, W.W.; Rodgers, J.; Cheng, S.; Antonsen, T.M. Jr.; Levush, B.; Bidwell, S.W.

1993-01-01

Detailed experimental studies on sheet relativistic electron beam propagation through a long planar wiggler are reported and compared with numerical simulations. The planar wiggler has 56 periods with a period of 9.6 mm. Typically, the wiggler field peak amplitude is 5 kG. The experimental efforts have been focused on control of the deviation of the beam toward the side edge of the planar wiggler along the wide transverse direction. It is found that a suitably tapered magnetic field configuration at the wiggler entrance can considerably reduce the rate of the deviation. The effects of the following techniques on beam transport efficiency are also discussed: side focusing, beam transverse velocity tuning at the wiggler entrance, and beam spread limiting. High beam transport efficiency (almost 100%) of a 15 A beam has been obtained in some cases. The results are relevant to development of a free electron laser amplifier for application to stabilizing and heating of plasma in magnetic fusion research

Anomalous resistivity due to kink modes in a thin current sheet

International Nuclear Information System (INIS)

Moritaka, Toseo; Horiuchi, Ritoku; Ohtani, Hiroaki

2007-01-01

The roles of microscopic plasma instabilities on the violation of the frozen-in constraint are investigated by examining the force balance equation based on explicit electromagnetic particle simulation for a thin current sheet. Wave-particle interactions associated with lower hybrid drift instability and drift kink instability (DKI) contribute to the wavy electric force term at the periphery of the current sheet and the wavy magnetic force term at the neutral sheet, respectively. In the linear growing phase of DKI, the wavy magnetic force term balances with the electric force term due to the dc electric field at the neutral sheet. It is concluded that the growth of DKI can create anomalous resistivity and result in the violation of the frozen-in constraint as well as the diffusion of current density

Magnetic fields and uniformity of radio frequency power deposition in low-frequency inductively coupled plasmas with crossed internal oscillating currents

International Nuclear Information System (INIS)

Tsakadze, E.L.; Ostrikov, K.; Tsakadze, Z.L.; Vladimirov, S.V.; Xu, S.

2004-01-01

Radial and axial distributions of magnetic fields in a low-frequency (∼460 kHz) inductively coupled plasma source with two internal crossed planar rf current sheets are reported. The internal antenna configuration comprises two orthogonal sets of eight alternately reconnected parallel and equidistant copper litz wires in quartz enclosures and generates three magnetic (H z , H r , and H φ ) and two electric (E φ and E r ) field components at the fundamental frequency. The measurements have been performed in rarefied and dense plasmas generated in the electrostatic (E) and electromagnetic (H) discharge modes using two miniature magnetic probes. It is shown that the radial uniformity and depth of the rf power deposition can be improved as compared with conventional sources of inductively coupled plasmas with external flat spiral ('pancake') antennas. Relatively deeper rf power deposition in the plasma source results in more uniform profiles of the optical emission intensity, which indicates on the improvement of the plasma uniformity over large chamber volumes. The results of the numerical modeling of the radial magnetic field profiles are found in a reasonable agreement with the experimental data

Structure of intermediate shocks and slow shocks in a magnetized plasma with heat conduction

International Nuclear Information System (INIS)

Tsai, C.L.; Wu, B.H.; Lee, L.C.

2005-01-01

The structure of slow shocks and intermediate shocks in the presence of a heat conduction parallel to the local magnetic field is simulated from the set of magnetohydrodynamic equations. This study is an extension of an earlier work [C. L. Tsai, R. H. Tsai, B. H. Wu, and L. C. Lee, Phys. Plasmas 9, 1185 (2002)], in which the effects of heat conduction are examined for the case that the tangential magnetic fields on the two side of initial current sheet are exactly antiparallel (B y =0). For the B y =0 case, a pair of slow shocks is formed as the result of evolution of the initial current sheet, and each slow shock consists of two parts: the isothermal main shock and the foreshock. In the present paper, cases with B y ≠0 are also considered, in which the evolution process leads to the presence of an additional pair of time-dependent intermediate shocks (TDISs). Across the main shock of the slow shock, jumps in plasma density, velocity, and magnetic field are significant, but the temperature is continuous. The plasma density downstream of the main shock decreases with time, while the downstream temperature increases with time, keeping the downstream pressure constant. The foreshock is featured by a smooth temperature variation and is formed due to the heat flow from downstream to upstream region. In contrast to the earlier study, the foreshock is found to reach a steady state with a constant width in the slow shock frame. In cases with B y ≠0, the plasma density and pressure increase and the magnetic field decreases across TDIS. The TDIS initially can be embedded in the slow shock's foreshock structure, and then moves out of the foreshock region. With an increasing B y , the propagation speed of foreshock leading edge tends to decrease and the foreshock reaches its steady state at an earlier time. Both the pressure and temperature downstreams of the main shock decrease with increasing B y . The results can be applied to the shock heating in the solar corona and

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 R_E 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 R_E≲ΔS_ECR≲5 R_E. 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.

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

Energy Technology Data Exchange (ETDEWEB)

Werner, Gregory R.; Uzdensky, Dmitri A., E-mail: Greg.Werner@colorado.edu [Center for Integrated Plasma Studies, Physics Department, University of Colorado, 390 UCB, Boulder, CO 80309 (United States)

2017-07-10

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.

Experimental results of a sheet-beam, high power, FEL amplifier with application to magnetic fusion research

Energy Technology Data Exchange (ETDEWEB)

Cheng, S.; Destler, W.W.; Granatstein, V.L. [Univ. of Maryland, College Park, MD (United States)] [and others

1995-12-31

The experimental study of sheet-beam FELs as candidate millimeter-wave sources for heating magnetic fusion plasmas has achieved a major milestone. In a proof-of-principle, pulsed experiment, saturated FEL amplifier operation was achieved with 250 kW of output power at 86 GHz. Input microwave power was 1 kW, beam voltage was 450 kV and beam current was 17 A. The planar wiggler had a peak value of 3.8 kG, a period of 0.96 cm and was 71 cm long. The linear gain of 30 dB, saturated gain of 24 dB and saturated efficiency of 3% all are in good agreement with theoretical prediction. Follow-on work would include development of a thermionic sheet-beam electron-gun compatible with CW FEL operation, adding a section of tapered wiggler to increase the output power to levels in excess of 1 megawatt, and increasing the FEL frequency.

Frequency-dependent absorbance of broadband terahertz wave in dense plasma sheet

Science.gov (United States)

Peng, Yan; Qi, Binbin; Jiang, Xiankai; Zhu, Zhi; Zhao, Hongwei; Zhu, Yiming

2018-05-01

Due to the ability of accurate fingerprinting and low-ionization for different substances, terahertz (THz) technology has a lot of crucial applications in material analysis, information transfer, and safety inspection, etc. However, the spectral characteristic of atmospheric gas and ionized gas has not been widely investigated, which is important for the remote sensing application. Here, in this paper, we investigate the absorbance of broadband terahertz wave in dense plasma sheet generated by femtosecond laser pulses. It was found that as the terahertz wave transmits through the plasma sheet formed, respectively, in carbon dioxide, oxygen, argon and nitrogen, spectrum presents completely different and frequency-dependent absorbance. The reasons for these absorption peaks are related to the molecular polarity, electric charge, intermolecular and intramolecular interactions, and collisional absorption of gas molecules. These results have significant implications for the remote sensing of gas medium.

Analysis of 16 plasma vortex events in the geomagnetic tail

International Nuclear Information System (INIS)

Birn, J.; Hones, E.W. Jr.; Bame, S.J.; Russel, C.T.

1985-01-01

The analysis of 16 plasma vortex occurrences in the magnetotail plasma sheet of Hones et al. (1983) is extended. We used two- and three-dimensional plasma measurements and three-dimensional magnetic field measurements to study phase relations, energy propagation, and polarization properties. The results point toward an interpretation as a slow strongly damped MHD eigenmode which is generated by tailward traveling perturbations at the low-latitude interface between plasma sheet and magnetosheath

Localized fast flow disturbance observed in the plasma sheet and in the ionosphere

Directory of Open Access Journals (Sweden)

R. Nakamura

2005-02-01

Full Text Available An isolated plasma sheet flow burst took place at 22:02 UT, 1 September 2002, when the Cluster footpoint was located within the area covered by the Magnetometers-Ionospheric Radars-All-sky Cameras Large Experiment (MIRACLE. The event was associated with a clear but weak ionospheric disturbance and took place during a steady southward IMF interval, about 1h preceding a major substorm onset. Multipoint observations, both in space and from the ground, allow us to discuss the temporal and spatial scale of the disturbance both in the magnetosphere and ionosphere. Based on measurements from four Cluster spacecraft it is inferred that Cluster observed the dusk side part of a localized flow channel in the plasma sheet with a flow shear at the front, suggesting a field-aligned current out from the ionosphere. In the ionosphere the equivalent current pattern and possible field-aligned current location show a pattern similar to the auroral streamers previously obtained during an active period, except for its spatial scale and amplitude. It is inferred that the footpoint of Cluster was located in the region of an upward field-aligned current, consistent with the magnetospheric observations. The entire disturbance in the ionosphere lasted about 10min, consistent with the time scale of the current sheet disturbance in the magnetosphere. The plasma sheet bulk flow, on the other hand, had a time scale of about 2min, corresponding to the time scale of an equatorward excursion of the enhanced electrojet. These observations confirm that localized enhanced convection in the magnetosphere and associated changes in the current sheet structure produce a signature with consistent temporal and spatial scale at the conjugate ionosphere.

Magnetic stresses in ideal MHD plasmas

DEFF Research Database (Denmark)

Jensen, V.O.

1995-01-01

The concept of magnetic stresses in ideal MHD plasma theory is reviewed and revisited with the aim of demonstrating its advantages as a basis for calculating and understanding plasma equilibria. Expressions are derived for the various stresses that transmit forces in a magnetized plasma...... and it is shown that the resulting magnetic forces on a finite volume element can be obtained by integrating the magnetic stresses over the surface of the element. The concept is used to rederive and discuss the equilibrium conditions for axisymmetric toroidal plasmas, including the virial theorem...... and the Shafranov shift. The method had pedagogical merits as it simplifies the calculations, improves the physical understanding and facilitates an assessment of the approximations made in the calculations....

Auroral electrojet dynamics during magnetic storms, connection with plasma precipitation and large-scale structure of the magnetospheric magnetic field

Directory of Open Access Journals (Sweden)

Y. I. Feldstein

1999-04-01

magnetospheric magnetic field paraboloid model the influence of the ring current and magnetospheric tail plasma sheet currents on large-scale magnetosphere structure is considered.Key words. Ionosphere (particle precipitation · Magnetospheric physics (current systems; magnetospheric configuration and dynamics.

A magnetic neutral sheet as cause of the flare productivity of a delta sunspot group

International Nuclear Information System (INIS)

Seehafer, N.

1985-01-01

Flare observations in the solar activity complex HR 16862, 16863, 16864 at the end of May 1980 are compared with the structure of force-free magnetic fields calculated from photospheric magnetograph measurements. A series of homologous flares connected with a delta configuration in HR 16864 was possibly caused by a magnetic neutral sheet. The delta configuration consisted of the large preceding spot of HR 16864 and a small satellite of opposite polarity. All magnetic flux from the satellite is connected to the main spot, and at the outer edge of the satellite, away from the main spot, a magnetic neutral sheet is found. This agrees with the observation that all penumbra was situated between parent spot and satellite, which is typical of such delta configurations. It is suggested that the flare productivity of these configurations is generally caused by magnetic neutral sheets at the penumbra-free outer boundary of the satellites. (author)

Magnetic field in expanding quark-gluon plasma

Science.gov (United States)

Stewart, Evan; Tuchin, Kirill

2018-04-01

Intense electromagnetic fields are created in the quark-gluon plasma by the external ultrarelativistic valence charges. The time evolution and the strength of this field are strongly affected by the electrical conductivity of the plasma. Yet, it has recently been observed that the effect of the magnetic field on the plasma flow is small. We compute the effect of plasma flow on magnetic field and demonstrate that it is less than 10%. These observations indicate that the plasma hydrodynamics and the dynamics of electromagnetic field decouple. Thus, it is a very good approximation, on the one hand, to study QGP in the background electromagnetic field generated by external sources and, on the other hand, to investigate the dynamics of magnetic field in the background plasma. We also argue that the wake induced by the magnetic field in plasma is negligible.

Influence of electrical sheet width on dynamic magnetic properties

CERN Document Server

Chevalier, T; Cornut, B

2000-01-01

Effects of the width of electrical steel sheets on dynamic magnetic properties are investigated by solving diffusion equation on the cross-section of the sheet. Linear and non-linear cases are studied, and are compared with measurement on Epstein frame. For the first one an analytical solution is found, while for the second, a 2D finite element simulation is achieved. The influence of width is highlighted for a width thickness ratio lower than 10. It is shown that the behaviour modification in such cases is conditioned by the excitation signal waveform, amplitude and also frequency.

Investigation of magnetic drift on transport of plasma across magnetic field

International Nuclear Information System (INIS)

Hazarika, Parismita; Chakraborty, Monojit; Das, Bidyut; Bandyopadhyay, Mainak

2015-01-01

When a metallic body is inserted inside plasma chamber it is always associated with sheath which depends on plasma and wall condition. The effect of sheath formed in the magnetic drift and magnetic field direction on cross field plasma transport has been investigated in a double Plasma device (DPD). The drifts exist inside the chamber in the transverse magnetic field (TMF) region in a direction perpendicular to both magnetic field direction and axis of the DPD chamber. The sheath are formed in the magnetic drift direction in the experimental chamber is due to the insertion of two metallic plates in these directions and in the magnetic field direction sheath is formed at the surface of the TMF channels. These metallic plates are inserted in order to obstruct the magnetic drift so that we can minimised the loss of plasma along drift direction and density in the target region is expected to increase due to the obstruction. It ultimately improves the negative ion formation parameters. The formation of sheath in the transverse magnetic field region is studied by applying electric field both parallel and antiparallel to drift direction. Data are acquired by Langmuir probe in source and target region of our chamber. (author)

Microstructure evolution of a dissimilar junction interface between an Al sheet and a Ni-coated Cu sheet joined by magnetic pulse welding

Energy Technology Data Exchange (ETDEWEB)

Itoi, Takaomi, E-mail: itoi@faculty.chiba-u.jp [Department of Mechanical Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan); Mohamad, Azizan Bin; Suzuki, Ryo [Department of Mechanical Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan); Okagawa, Keigo [Department of Electrical and Electronics Engineering, Tokyo Metropolitan College of Industrial Technology, 1-10-40 Higashi ohi, Shinagawa-ku, Tokyo 140-0011 (Japan)

2016-08-15

An Al sheet and a Ni-coated Cu sheet were lap joined by using magnetic pulse welding (MPW). Tensile tests were performed on the joined sheets, and a good lap joint was achieved at a discharge energy of > 0.9 kJ. The weld interface exhibited a wavy morphology and an intermediate layer along the weld interface. Microstructure observations of the intermediate layer revealed that the Ni coating region consisted of a Ni–Al binary amorphous alloy and that the Al sheet region contained very fine Al nanograins. Ni fragments indicative of unmelted residual Ni from the coating were also observed in parts of the intermediate layer. Formation of these features can be attributed to localize melting and a subsequent high rate cooling of molten Al and Ni confined to the interface during the MPW process. In the absence of an oxide film, atomic-scale bonding was also achieved between the intermediate layer and the sheet surfaces after the collision. MPW utilises impact energy, which affects the sheet surfaces. From the obtained results, good lap joint is attributed to an increased contact area, the anchor effect, work hardening, the absence of an oxide film, and suppressed formation of intermetallic compounds at the interface. - Highlights: •Good lap joint of an Al sheet and a Ni-coated Cu sheet was achieved by using magnetic pulse welding. •A Ni–Al binary amorphous alloy was formed as an intermediate layer at weld interface. •Atomic-scale bonding was achieved between the intermediate layer and the sheet surfaces.

Magnetic-flutter-induced pedestal plasma transport

International Nuclear Information System (INIS)

Callen, J.D.; Hegna, C.C.; Cole, A.J.

2013-01-01

Plasma toroidal rotation can limit reconnection of externally applied resonant magnetic perturbation (RMP) fields δB on rational magnetic flux surfaces. Hence it causes the induced radial perturbations δB ρ to be small there, thereby inhibiting magnetic island formation and stochasticity at the top of pedestals in high (H-mode) confinement tokamak plasmas. However, the δB ρ s induced by RMPs increase away from rational surfaces and are shown to induce significant sinusoidal radial motion (flutter) of magnetic field lines with a radial extent that varies linearly with δB ρ and inversely with distance from the rational surface because of the magnetic shear. This produces a radial electron thermal diffusivity that is (1/2)(δB ρ /B 0 ) 2 times a kinetically derived, electron-collision-induced, magnetic-shear-reduced, effective parallel electron thermal diffusivity in the absence of magnetic stochasticity. These low collisionality flutter-induced transport processes and thin magnetic island effects are shown to be highly peaked in the vicinity of rational surfaces at the top of low collisionality pedestals. However, the smaller but finite level of magnetic-flutter-induced electron heat transport midway between rational surfaces is the primary factor that determines the electron temperature difference between rational surfaces at the pedestal top. The magnetic-flutter-induced non-ambipolar electron density transport can be large enough to push the plasma toward an electron density transport root. Requiring ambipolar density transport is shown to determine the radial electric field, the plasma toroidal rotation (via radial force balance), a reduced electron thermal diffusivity and increased ambipolar density transport in the pedestal. At high collisionality the various flutter effects are less strongly peaked at rational surfaces and generally less significant. They are thus less likely to exhibit flutter-induced resonant behaviour and transition toward an

Magnetic-flutter-induced pedestal plasma transport

Science.gov (United States)

Callen, J. D.; Hegna, C. C.; Cole, A. J.

2013-11-01

Plasma toroidal rotation can limit reconnection of externally applied resonant magnetic perturbation (RMP) fields δB on rational magnetic flux surfaces. Hence it causes the induced radial perturbations δBρ to be small there, thereby inhibiting magnetic island formation and stochasticity at the top of pedestals in high (H-mode) confinement tokamak plasmas. However, the δBρs induced by RMPs increase away from rational surfaces and are shown to induce significant sinusoidal radial motion (flutter) of magnetic field lines with a radial extent that varies linearly with δBρ and inversely with distance from the rational surface because of the magnetic shear. This produces a radial electron thermal diffusivity that is (1/2)(δBρ/B0)2 times a kinetically derived, electron-collision-induced, magnetic-shear-reduced, effective parallel electron thermal diffusivity in the absence of magnetic stochasticity. These low collisionality flutter-induced transport processes and thin magnetic island effects are shown to be highly peaked in the vicinity of rational surfaces at the top of low collisionality pedestals. However, the smaller but finite level of magnetic-flutter-induced electron heat transport midway between rational surfaces is the primary factor that determines the electron temperature difference between rational surfaces at the pedestal top. The magnetic-flutter-induced non-ambipolar electron density transport can be large enough to push the plasma toward an electron density transport root. Requiring ambipolar density transport is shown to determine the radial electric field, the plasma toroidal rotation (via radial force balance), a reduced electron thermal diffusivity and increased ambipolar density transport in the pedestal. At high collisionality the various flutter effects are less strongly peaked at rational surfaces and generally less significant. They are thus less likely to exhibit flutter-induced resonant behaviour and transition toward an electron

Particle-in-cell simulations of collisionless magnetic reconnection with a non-uniform guide field

International Nuclear Information System (INIS)

Wilson, F.; Neukirch, T.; Harrison, M. G.; Hesse, M.; Stark, C. R.

2016-01-01

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.

Bone tissue engineering with human mesenchymal stem cell sheets constructed using magnetite nanoparticles and magnetic force.

Science.gov (United States)

Shimizu, Kazunori; Ito, Akira; Yoshida, Tatsuro; Yamada, Yoichi; Ueda, Minoru; Honda, Hiroyuki

2007-08-01

An in vitro reconstruction of three-dimensional (3D) tissues without the use of scaffolds may be an alternative strategy for tissue engineering. We have developed a novel tissue engineering strategy, termed magnetic force-based tissue engineering (Mag-TE), in which magnetite cationic liposomes (MCLs) with a positive charge at the liposomal surface, and magnetic force were used to construct 3D tissue without scaffolds. In this study, human mesenchymal stem cells (MSCs) magnetically labeled with MCLs were seeded onto an ultra-low attachment culture surface, and a magnet (4000 G) was placed on the reverse side. The MSCs formed multilayered sheet-like structures after a 24-h culture period. MSCs in the sheets constructed by Mag-TE maintained an in vitro ability to differentiate into osteoblasts, adipocytes, or chondrocytes after a 21-day culture period using each induction medium. Using an electromagnet, MSC sheets constructed by Mag-TE were harvested and transplanted into the bone defect in the crania of nude rats. Histological observation revealed that new bone surrounded by osteoblast-like cells was formed in the defect area 14 days after transplantation with MSC sheets, whereas no bone formation was observed in control rats without the transplant. These results indicated that Mag-TE could be used for the transplantation of MSC sheets using magnetite nanoparticles and magnetic force, providing novel methodology for bone tissue engineering.

Generation of electromagnetic waves and Alfven waves during coalescence of magnetic islands in pair plasmas

International Nuclear Information System (INIS)

Sakai, J.I.; Haruki, T.; Kazimura, Y.

2000-01-01

It is shown by using a 2-D fully relativistic electromagnetic particle-in-cell (PIC) code that the tearing instability in a current sheet of pair plasmas is caused by Landau resonances of both electrons and positrons. Strong magnetic flux can be generated during coalescence of magnetic islands in the nonlinear phase of the tearing instability. The magnetic flux produced in an O-type magnetic island is caused from the counter-streaming instability found by Kazimura et al. (1998). It is also shown that charge separation with a quadrupole-like structure is generated from the localized strong magnetic flux. During the decay of the quadrupole-like charge structure as well as the magnetic flux, there appear wave emission with high-frequency electromagnetic waves and Alfven waves as well as Langmuir waves. We also show by using a 3-D PIC code that current filaments associated with the O-type magnetic islands become unstable against the kink instability during the coalescence of current filaments. (orig.)

Ion motion in the current sheet with sheared magnetic field – Part 2: Non-adiabatic effects

Directory of Open Access Journals (Sweden)

A. V. Artemyev

2013-10-01

Full Text Available We investigate dynamics of charged particles in current sheets with the sheared magnetic field. In our previouspaper (Artemyev et al., 2013 we studied the particle motion in such magnetic field configurations on the basis of the quasi-adiabatic theory and conservation of the quasi-adiabatic invariant. In this paper we concentrate on violation of the adiabaticity due to jumps of this invariant and the corresponding effects of stochastization of a particle motion. We compare effects of geometrical and dynamical jumps, which occur due to the presence of the separatrix in the phase plane of charged particle motion. We show that due to the presence of the magnetic field shear, the average value of dynamical jumps is not equal to zero. This effect results in the decrease of the time interval necessary for stochastization of trapped particle motion. We investigate also the effect of the magnetic field shear on transient trajectories, which cross the current sheet boundaries. Presence of the magnetic field shear leads to the asymmetry of reflection and transition of particles in the current sheet. We discuss the possible influence of single-particle effects revealed in this paper on the current sheet structure and dynamics.

Steady state magnetic field configurations for the earth's magnetotail

International Nuclear Information System (INIS)

Hau, L.N.; Wolf, R.A.; Voigt, G.H.; Wu, C.C.

1989-01-01

The authors present a two-dimensional, force-balanced magnetic field model in which flux tubes have constant pVγ throughout an extended region of the nightside plasma sheet, between approximately 36 R E geocentric distance and the region of the inner edge of the plasma sheet. They have thus demonstrated the theoretical existence of a steady state magnetic field configuration that is force-balanced and also consistent with slow, lossless, adiabatic, earthward convection within the limit of the ideal MHD (isotropic pressure, perfect conductivity). The numerical solution was constructed for a two-dimensional magnetosphere with a rectangular magnetopause and nonflaring tail. The primary characteristics of the steady state convection solution are (1) a pressure maximum just tailward of the inner edge of the plasma sheet and (2) a deep, broad minimum in equatorial magnetic field strength B ze , also just tailward of the inner edge. The results are consistent with Erickson's (1985) convection time sequences, which exhibited analogous pressure peaks and B ze minima. Observations do not indicate the existence of a B ze minimum, on the average. They suggest that the configurations with such deep minima in B ze may be tearing-mode unstable, thus leading to substorm onset in the inner plasma sheet

Automatic plasma control in magnetic traps

International Nuclear Information System (INIS)

Samojlenko, Y.; Chuyanov, V.

1984-01-01

Hot plasma is essentially in thermodynamic non-steady state. Automatic plasma control basically means monitoring deviations from steady state and producing a suitable magnetic or electric field which brings the plasma back to its original state. Briefly described are two systems of automatic plasma control: control with a magnetic field using a negative impedance circuit, and control using an electric field. It appears that systems of automatic plasma stabilization will be an indispensable component of the fusion reactor and its possibilities will in many ways determine the reactor economy. (Ha)

Nonlinear magnetic electron tripolar vortices in streaming plasmas.

Science.gov (United States)

Vranjes, J; Marić, G; Shukla, P K

2000-06-01

Magnetic electron modes in nonuniform magnetized and unmagnetized streaming plasmas, with characteristic frequencies between the ion and electron plasma frequencies and at spatial scales of the order of the collisionless skin depth, are studied. Two coupled equations, for the perturbed (in the case of magnetized plasma) or self-generated (for the unmagnetized plasma case) magnetic field, and the temperature, are solved in the strongly nonlinear regime and stationary traveling solutions in the form of tripolar vortices are found.

Turbulent transport in magnetized plasmas

CERN Document Server

Horton, Wendell

2012-01-01

This book explains how magnetized plasmas self-organize in states of electromagnetic turbulence that transports particles and energy out of the core plasma faster than anticipated by the fusion scientists designing magnetic confinement systems in the 20th century. It describes theory, experiments and simulations in a unified and up-to-date presentation of the issues of achieving nuclear fusion power.

Formation of fast shocks by magnetic reconnection in the solar corona

International Nuclear Information System (INIS)

Hsieh, M. H.; Tsai, C. L.; Ma, Z. W.; Lee, L. C.

2009-01-01

Reconnections of magnetic fields over the solar surface are expected to generate abundant magnetohydrodynamic (MHD) discontinuities and shocks, including slow shocks and rotational discontinuities. However, the generation of fast shocks by magnetic reconnection process is relatively not well studied. In this paper, magnetic reconnection in a current sheet is studied based on two-dimensional resistive MHD numerical simulations. Magnetic reconnections in the current sheet lead to the formation of plasma jets and plasma bulges. It is further found that the plasma bulges, the leading part of plasma jets, in turn lead to the generation of fast shocks on flanks of the bulges. The simulation results show that during the magnetic reconnection process, the plasma forms a series of structures: plasma jets, plasma bulges, and fast shocks. As time increases, the bulges spread out along the current sheet (±z direction) and the fast shocks move just ahead of the bulges. The effects of initial parameters ρ s /ρ m , β ∞ , and t rec on the fast shock generation are also examined, where ρ s /ρ m is the ratio of plasma densities on two sides of the initial current sheet, β ∞ =P ∞ /(B ∞ 2 /2μ 0 ), P ∞ is the plasma pressure and B ∞ is the magnetic field magnitude far from the current sheet, and t rec is the reconnection duration. In the asymmetric case with ρ s /ρ m =2, β ∞ =0.01 and t rec =1000, the maximum Alfven Mach number of fast shocks (M A1max ) is M A1max congruent with 1.1, where M A1 =V n1 /V A1 , and V n1 and V A1 are, respectively, the normal upstream fluid velocity and the upstream Alfven speed in the fast shocks frame. As the density ratio ρ s /ρ m (=1-8) and plasma beta β ∞ (=0.0001-1) increase, M A1max varies slightly. For the case with a large plasma beta β ∞ (=5), the fast shock is very weak. As the reconnection duration t rec increases, the bulges lead to generation of fast shocks with a higher M A1max . The present results can be

Effects of 3D Magnetic Perturbations on Toroidal Plasmas

International Nuclear Information System (INIS)

Callen, J.D.

2010-01-01

Full text: To lowest order tokamaks are two-dimensional (2D) axisymmetric magnetic systems. But small 3D magnetic perturbations (both externally applied and from plasma instabilities) have many interesting and useful effects on tokamak (and quasi-symmetric stellarator) plasmas. Plasma transport equations that include these effects, especially on diamagnetic-level toroidal plasma rotation, have recently been developed. The 3D magnetic perturbations and their plasma effects can be classified according to their toroidal mode number n: low n (1 to 5) resonant (q = m/n in plasma) and non-resonant fields, medium n (due to toroidal field ripple), and high n (due to microturbulence). This paper concentrates on low and medium n perturbations. Low n non-resonant magnetic fields induce a neoclassical toroidal viscosity (NTV) that damps toroidal plasma rotation throughout the plasma toward an offset flow in the counter-I p direction; recent tokamak experiments have confirmed and exploited these predictions by applying external low n non-resonant magnetic perturbations. Medium n perturbations have similar effects plus possible ripple trapping and resultant edge ion losses. A low n resonant magnetic field induces a toroidal plasma torque in the vicinity of the rational surface; when large enough it can stop plasma rotation there and lead to a locked mode, which often causes a plasma disruption. Externally applied 3D magnetic perturbations usually have many components; in the plasma their lowest n components are amplified by plasma responses, particularly at high beta. Low n plasma instabilities (e.g., NTMs, RWMs) cause additional 3D magnetic perturbations in tokamak plasmas; tearing modes can bifurcate the topology and form magnetic islands. Finally, multiple resonant magnetic perturbations (RMPs) can cause local magnetic stochasticity and influence H-mode edge pedestal transport. These various effects of 3D magnetic perturbations can be used to control the toroidal plasma

Optimal Magnetic Field Shielding Method by Metallic Sheets in Wireless Power Transfer System

Directory of Open Access Journals (Sweden)

Feng Wen

2016-09-01

Full Text Available To meet the regulations established to limit human exposure to time-varying electromagnetic fields (EMFs such as the International Committee on Non-Ionizing Radiation Protection (ICNIRP guidelines, thin metallic sheets are often used to shield magnetic field leakage in high power applications of wireless power transfer (WPT systems based on magnetic field coupling. However, the metals in the vicinity of the WPT coils cause the decrease of self and mutual inductances and increase of effective series resistance; as such, the electric performance including transmission power and the efficiency of the system is affected. With the research objective of further investigating excellent shielding effectiveness associated with system performance, the utilization of the optimal magnetic field shielding method by metallic sheets in magnetic field coupling WPT is carried out in this paper. The circuit and 3D Finite Element Analysis (FEA models are combined to predict the magnetic field distribution and electrical performance. Simulation and experiment results show that the method is very effective by obtaining the largest possible coupling coefficient of the WPT coils within the allowable range and then reducing the value nearest to and no smaller than the critical coupling coefficient via geometric unbroken metallic sheets. The optimal magnetic field shielding method which considers the system efficiency, transmission power, transmission distance, and system size is also achieved using the analytic hierarchy process (AHP. The results can benefit WPT by helping to achieve efficient energy transfer and safe use in metal shielded equipment.

Extraction of volume produced H- or D- ions from a sheet plasma, 2

International Nuclear Information System (INIS)

Uramoto, Joshin.

1984-02-01

A development to large area H - or D - ion source is tried by using three extraction electrodes: The first electrode bias voltage is set near the wall potential (floating), the second electrode is set near 13 % of main extraction voltage and the third electrode is the main acceleration electrode. An ion current of 13 mA (3.3 mA/cm 2 ) for H - or 11 mA (2.8 mA/ cm 2 ) for D - at 3 KeV is extracted from 9 apertures of 6 mm phi in 4 cm 2 outside of the sheet plasma (14 cm wide and 1.0 cm thick) under a pressure of 7.7 x 10 -4 H2 or D2 gas and a weak magnetic field 50 gauss. Then, it is noted that the corresponding electron current is suppressed below 1/10 of the H - or D - ion current. (author)

Convective growth of broadband turbulence in the plasma sheet boundary layer

International Nuclear Information System (INIS)

Dusenbery, P.B.

1987-01-01

Convective growth of slow and fast beam acoustic waves in the plasma sheet boundary layer (PSBL) is investigated. It has been shown previously that a could ion population must be present in order to excite beam acoustic waves in the PSBL. However, growth rates are significantly enhanced when warm plasma sheet boundary layer ions are present. Net wave growth along a ray path is determined by convective growth. This quantity is calculated for particle distribution models consistent with the PSBL where the intensity of broadband turbulence is observed to peak. Total number density dependence on beam acoustic convective growth is evaluated, and it is found that even for low density conditions of ∼0.01 cm -3 , a measurable level of broadband turbulence is expected. Relative drift effects between cold and warm ion populations are also considered. In particular, it is found that slow mode convective growth can be enhanced when slowly streaming cold ions are present, compared to fast ion streams

Plasma diffusion due to magnetic field fluctuations

International Nuclear Information System (INIS)

Okuda, H.; Lee, W.W.; Lin, A.T.

1979-01-01

Plasma diffusion due to magnetic field fluctuations has been studied in two dimensions for a plasma near thermal equilibrium and when the fluctuations are suprathermal. It is found that near thermal equilibrium electron diffusion varies as B -2 when the collisionless skin depth is greater than the thermal electron gyroradius and is generally smaller than the diffusion due to collisions or electrostatic fluctuations for a low-β plasma. When the suprathermal magnetic fluctuation exists because of macroscopic plasma currents, electron diffusion is enhanced due to the coalescence of current filaments and magnetic islands. Magnetic field energy is found to condense to the longest wavelength available in the system and stays there longer than the electron diffusion time scale

Intermittent magnetic reconnection in TS-3 merging experiment

International Nuclear Information System (INIS)

Ono, Y.; Hayashi, Y.; Ii, T.; Tanabe, H.; Ito, S.; Kuwahata, A.; Ito, T.; Kamino, Y.; Yamada, T.; Inomoto, M.

2011-01-01

Ejection of current sheet with plasma mass causes impulsive and intermittent magnetic reconnection in the TS-3 spherical tokamak (ST) merging experiment. Under high guide toroidal field, the sheet resistivity is almost classical due to the sheet thickness much longer than the ion gyroradius. Large inflow flux and low current-sheet resistivity result in flux and plasma pileup followed by rapid growth of the current sheet. When the pileup exceeds a critical limit, the sheet is ejected mechanically from the squeezed X-point area. The reconnection (outflow) speed is slow during the flux/plasma pileup and is fast during the ejection, suggesting that intermittent reconnection similar to the solar flare increases the averaged reconnection speed. These transient effects enable the merging tokamaks to have the fast reconnection as well as the high-power reconnection heating, even when their current-sheet resistivity is low under high guide field.

Lazer-produced plasma in a strong magnetic field

International Nuclear Information System (INIS)

Kaitmazov, S.D.; Shklovskij, E.I.

1978-01-01

Investigations on interaction of laser plasma with the magnetic field in the range of 100-300 kOe are surveyed. Problems associated with the effect of the field on the optical breakdown threshold in gases, the geometry (kinetics) of laser plasma and its radiation are mainly considered. It is noted that the magnetic field may reduce the o tical breakdown threshold in gases, promote the spreading of plasma predominantly in the direction of tice magnetic field, and also affect (increase in the visible range) the radiation intensity of the laser plasma. The effect of the magnetic field on the temperature of the laser plasma is not completely understood yet, but the very fact of existence of this dependence is important; it enables one to search for conditions under which the magnetic field would promote the increase at the temperature of laser plasma

Parametric analysis of a magnetized cylindrical plasma

International Nuclear Information System (INIS)

Ahedo, Eduardo

2009-01-01

The relevant macroscopic model, the spatial structure, and the parametric regimes of a low-pressure plasma confined by a cylinder and an axial magnetic field is discussed for the small-Debye length limit, making use of asymptotic techniques. The plasma response is fully characterized by three-dimensionless parameters, related to the electron gyroradius, and the electron and ion collision mean-free-paths. There are the unmagnetized regime, the main magnetized regime, and, for a low electron-collisionality plasma, an intermediate-magnetization regime. In the magnetized regimes, electron azimuthal inertia is shown to be a dominant phenomenon in part of the quasineutral plasma region and to set up before ion radial inertia. In the main magnetized regime, the plasma structure consists of a bulk diffusive region, a thin layer governed by electron inertia, a thinner sublayer controlled by ion inertia, and the non-neutral Debye sheath. The solution of the main inertial layer yields that the electron azimuthal energy near the wall is larger than the electron thermal energy, making electron resistivity effects non-negligible. The electron Boltzmann relation is satisfied only in the very vicinity of the Debye sheath edge. Ion collisionality effects are irrelevant in the magnetized regime. Simple scaling laws for plasma production and particle and energy fluxes to the wall are derived.

Electron magnetic reconnection without ion coupling in Earth's turbulent magnetosheath

Science.gov (United States)

Phan, T. D.; Eastwood, J. P.; Shay, M. A.; Drake, J. F.; Sonnerup, B. U. Ö.; Fujimoto, M.; Cassak, P. A.; Øieroset, M.; Burch, J. L.; Torbert, R. B.; Rager, A. C.; Dorelli, J. C.; Gershman, D. J.; Pollock, C.; Pyakurel, P. S.; Haggerty, C. C.; Khotyaintsev, Y.; Lavraud, B.; Saito, Y.; Oka, M.; Ergun, R. E.; Retino, A.; Le Contel, O.; Argall, M. R.; Giles, B. L.; Moore, T. E.; Wilder, F. D.; Strangeway, R. J.; Russell, C. T.; Lindqvist, P. A.; Magnes, W.

2018-05-01

Magnetic reconnection in current sheets is a magnetic-to-particle energy conversion process that is fundamental to many space and laboratory plasma systems. In the standard model of reconnection, this process occurs in a minuscule electron-scale diffusion region1,2. On larger scales, ions couple to the newly reconnected magnetic-field lines and are ejected away from the diffusion region in the form of bi-directional ion jets at the ion Alfvén speed3-5. Much of the energy conversion occurs in spatially extended ion exhausts downstream of the diffusion region6. In turbulent plasmas, which contain a large number of small-scale current sheets, reconnection has long been suggested to have a major role in the dissipation of turbulent energy at kinetic scales7-11. However, evidence for reconnection plasma jetting in small-scale turbulent plasmas has so far been lacking. Here we report observations made in Earth's turbulent magnetosheath region (downstream of the bow shock) of an electron-scale current sheet in which diverging bi-directional super-ion-Alfvénic electron jets, parallel electric fields and enhanced magnetic-to-particle energy conversion were detected. Contrary to the standard model of reconnection, the thin reconnecting current sheet was not embedded in a wider ion-scale current layer and no ion jets were detected. Observations of this and other similar, but unidirectional, electron jet events without signatures of ion reconnection reveal a form of reconnection that can drive turbulent energy transfer and dissipation in electron-scale current sheets without ion coupling.

Relevance of southward magnetic fields in the neutral sheet to anisotropic distribution of energetic electrons and substorm activity

International Nuclear Information System (INIS)

Lui, A.T.Y.; Meng, C.

1979-01-01

The implications of southward magnetic fields at the magnetotail neutral sheet to the development of streaming anisotropy of energetic electrons and magnetospheric substorm activity are examined. Magnetic field and energetic particle measurements from the Imp 6 spacecraft, the AE index, and global auroral images from DMSP spacecraft are utilized in this study. Criteria are developed to identify events of southward magnetic fields at the neutral sheet which imply the presence of X-type magnetic neutral lines. Several features of the observations suggest that the southward magnetic fields and the implied X-type neutral lines are associated with magnetic bubbles in the neutral sheet region. It is found that the signatures of magnetic bubbles are sometimes detected in association with tailward streaming and flux enhancement of energetic electrons (47 keV< E<350keV). A cigar-shaped anisotropy in the energetic electron distribution is frequently but not always observed before the onset of tailward streaming of energetic electrons. The tailward streaming is magnetic field-aligned and occurs in the form of bursts, suggestic electrons. The tailward streaming is magnetic field-aligned and occurs in the form of bursts, suggesting that the generating process is activated somewhat quasi-periodically and is not in a steady state. Signatures of magnetic bubbles are also detected without any substantial enhancement or detectable tailward streaming of energetic electrons. By comparing Imp 6 observations with the AW index and global auroral images from DMSP spacecraft. It is found that signatures of magnetic bubbles in the neutral sheet are observed during substorms as well as during quiet geomagnetic conditions, indicating that magnetic bubbles are intrinsic features of the neutral sheet in the magnetotail regardless of substorm activity

Modeling the effect of doping on the catalyst-assisted growth and field emission properties of plasma-grown graphene sheet

International Nuclear Information System (INIS)

Gupta, Neha; Sharma, Suresh C.; Sharma, Rinku

2016-01-01

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.

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.

Static current-sheet models of quiescent prominences

Science.gov (United States)

Wu, F.; Low, B. C.

1986-12-01

A particular class of theoretical models idealize the prominence to be a discrete flat electric-current sheet suspended vertically in a potential magnetic field. The weight of the prominence is supported by the Lorentz force in the current sheet. These models can be extended to have curved electric-current sheets and to vary three-dimensionally. The equation for force balance is 1 over 4 pi (del times B) times Bdel p- p9 z=zero. Using Cartesian coordinates we take, for simplicity, a uniform gravity with constant acceleration g in the direction -z. If we are interested not in the detailed internal structure of the prominence, but in the global magnetic configuration around the prominence, we may take prominence plasma to be cold. Consideration is given to how such equilibrium states can be constructed. To simplify the mathematical problem, suppose there is no electric current in the atmosphere except for the discrete currents in the cold prominence sheet. Let us take the plane z =0 to be the base of the atmosphere and restrict our attention to the domain z greater than 0. The task we have is to solve for a magnetic field which is everywhere potential except on some free surface S, subject to suit able to boundary conditions. The surface S is determined by requiring that it possesses a discrete electric current density such that the Lorentz force on it is everywhere vertically upward to balance the weight of the material m(S). Since the magnetic field is potential in the external atmosphere, the latter is decoupled from the magnetic field and its plane parallel hydrostatic pressure and density can be prescribed.

Wave turbulence in magnetized plasmas

Directory of Open Access Journals (Sweden)

S. Galtier

2009-02-01

Full Text Available The paper reviews the recent progress on wave turbulence for magnetized plasmas (MHD, Hall MHD and electron MHD in the incompressible and compressible cases. The emphasis is made on homogeneous and anisotropic turbulence which usually provides the best theoretical framework to investigate space and laboratory plasmas. The solar wind and the coronal heating problems are presented as two examples of application of anisotropic wave turbulence. The most important results of wave turbulence are reported and discussed in the context of natural and simulated magnetized plasmas. Important issues and possible spurious interpretations are also discussed.

Mass ablation and magnetic flux losses through a magnetized plasma-liner wall interface

Science.gov (United States)

García-Rubio, F.; Sanz, J.

2017-07-01

The understanding of energy and magnetic flux losses in a magnetized plasma medium confined by a cold wall is of great interest in the success of magnetized liner inertial fusion (MagLIF). In a MagLIF scheme, the fuel is magnetized and subsonically compressed by a cylindrical liner. Magnetic flux conservation is degraded by the presence of gradient-driven transport processes such as thermoelectric effects (Nernst) and magnetic field diffusion. In previous publications [Velikovich et al., Phys. Plasmas 22, 042702 (2015)], the evolution of a hot magnetized plasma in contact with a cold solid wall (liner) was studied using the classical collisional Braginskii's plasma transport equations in one dimension. The Nernst term degraded the magnetic flux conservation, while both thermal energy and magnetic flux losses were reduced with the electron Hall parameter ωeτe with a power-law asymptotic scaling (ωeτe)-1/2. In the analysis made in the present paper, we consider a similar situation, but with the liner being treated differently. Instead of a cold solid wall acting as a heat sink, we model the liner as a cold dense plasma with low thermal conduction (that could represent the cryogenic fuel layer added on the inner surface of the liner in a high-gain MagLIF configuration). Mass ablation comes into play, which adds notably differences to the previous analysis. The direction of the plasma motion is inverted, but the Nernst term still convects the magnetic field towards the liner. Magnetization suppresses the Nernst velocity and improves the magnetic flux conservation. Thermal energy in the hot plasma is lost in heating the ablated material. When the electron Hall parameter is large, mass ablation scales as (ωeτe)-3/10, while both the energy and magnetic flux losses are reduced with a power-law asymptotic scaling (ωeτe)-7/10.

Experimental investigation of magnetically confined plasma loops

International Nuclear Information System (INIS)

Tenfelde, Jan

2012-01-01

Arch-shaped magnetic flux tubes generated in a pulsed-power plasma experiment were investigated with a variety of diagnostics concerning their expansion properties. Specifically, the expansion velocity was of interest, which is observed as constant for a wide range of experimental parameters. An MHD transport mechanism is investigated as possible cause of a uniform arch cross section: Axial transport of poloidal magnetic flux along the plasma may cause a pinch force leading to a uniform diameter along the arch. Despite numerous experimental findings at a very similar experimental setup, no indication for the relevance of this process could be found. Instead, magnetic probe data showed that the plasma current in the apex region is constant. A constant expansion velocity was observed for considerably different experimental conditions. This included different plasma source designs with fundamentally different toroidal magnetic field topology and variation of the working gas, which lead to plasma densities lower by an order of magnitude. Inside the current channel of the arch, Alfven velocities were estimated. To this end, plasma density profiles obtained from interferometry were inverted to obtain local densities, which were in turn verified by means of Stark broadening of hydrogen Balmer lines. Furthermore, measurements of multiple components of the magnetic field of the plasma arch were performed. An estimate for the conductivity was obtained from Spitzer's formula for fully ionized plasma using electron temperatures obtained from elementary optical emission spectroscopy. From the presented data of ccd imaging, magnetic field probes, and to lesser extent, interferometry, the underlying assumption of residual plasma (and considerable plasma currents through it) below the actual arch structure is very plausible. Rough estimates of the electric field strength along the arch and results of the magnetic field measurements showed, that the detected expansion

Experimental investigation of magnetically confined plasma loops

Energy Technology Data Exchange (ETDEWEB)

Tenfelde, Jan

2012-12-11

Arch-shaped magnetic flux tubes generated in a pulsed-power plasma experiment were investigated with a variety of diagnostics concerning their expansion properties. Specifically, the expansion velocity was of interest, which is observed as constant for a wide range of experimental parameters. An MHD transport mechanism is investigated as possible cause of a uniform arch cross section: Axial transport of poloidal magnetic flux along the plasma may cause a pinch force leading to a uniform diameter along the arch. Despite numerous experimental findings at a very similar experimental setup, no indication for the relevance of this process could be found. Instead, magnetic probe data showed that the plasma current in the apex region is constant. A constant expansion velocity was observed for considerably different experimental conditions. This included different plasma source designs with fundamentally different toroidal magnetic field topology and variation of the working gas, which lead to plasma densities lower by an order of magnitude. Inside the current channel of the arch, Alfven velocities were estimated. To this end, plasma density profiles obtained from interferometry were inverted to obtain local densities, which were in turn verified by means of Stark broadening of hydrogen Balmer lines. Furthermore, measurements of multiple components of the magnetic field of the plasma arch were performed. An estimate for the conductivity was obtained from Spitzer's formula for fully ionized plasma using electron temperatures obtained from elementary optical emission spectroscopy. From the presented data of ccd imaging, magnetic field probes, and to lesser extent, interferometry, the underlying assumption of residual plasma (and considerable plasma currents through it) below the actual arch structure is very plausible. Rough estimates of the electric field strength along the arch and results of the magnetic field measurements showed, that the detected expansion

Three Dimensional Double Layers in Magnetized Plasmas

DEFF Research Database (Denmark)

Jovanovic, D.; Lynov, Jens-Peter; Michelsen, Poul

1982-01-01

Experimental results are presented which demonstrate the formation of fully three dimensional double layers in a magnetized plasma. The measurements are performed in a magnetized stationary plasma column with radius 1.5 cm. Double layers are produced by introducing an electron beam with radius 0.......4 cm along the magnetic field from one end of the column. The voltage drop across the double layer is found to be determined by the energy of the incoming electron beam. In general we find that the width of the double layer along the external magnetic field is determined by plasma density and beam...

Experimental investigation of coaxial-gun-formed plasmas injected into a background transverse magnetic field or plasma

Science.gov (United States)

Zhang, Yue; Fisher, Dustin M.; Gilmore, Mark; Hsu, Scott C.; Lynn, Alan G.

2018-05-01

Injection of coaxial-gun-formed magnetized plasmas into a background transverse vacuum magnetic field or into a background magnetized plasma has been studied in the helicon-cathode (HelCat) linear plasma device at the University of New Mexico [M. Gilmore et al., J. Plasma Phys. 81, 345810104 (2015)]. A magnetized plasma jet launched into a background transverse magnetic field shows emergent kink stabilization of the jet due to the formation of a sheared flow in the jet above the kink stabilization threshold 0.1kVA [Y. Zhang et al., Phys. Plasmas 24, 110702 (2017)]. Injection of a spheromak-like plasma into a transverse background magnetic field led to the observation of finger-like structures on the side with a stronger magnetic field null between the spheromak and the background field. The finger-like structures are consistent with magneto-Rayleigh-Taylor instability. Jets or spheromaks launched into a background, low-β magnetized plasma show similar behavior as above, respectively, in both cases.

Magnetized whirls in plasma focus discharges

International Nuclear Information System (INIS)

Witalis, E.

1979-05-01

The plasma focus is briefly described with emphasis on its capabilities as a neutron source. The filamentary whirl structures observed in the discharge plasma are described. Starting with a simple, early and particularly well established case of vorticity imparted by a rotational electric field to the plasma in MHD generators, a general derivation is then outlined proving that such magnetically induced rotation is a general feature for the normally Hall-conducting magnetized plasma. Physical interpretations of the effect are given and objections to it are critically reviewed as is also a theory proposing radiation cooling as the cause of plasma filamentation. A more detailed derivation based essentially on the consistent description of the motion and the field generation of the charged plasma particles yields a theoretical model where the specific features of magnetically compressed plasmas are found. In particular, the ion collisionless skin depth is obtained as the key length parameter. This length is identified as roughly the whirl radius. In conjunction with a generalized Bennett relation theoretical whirl properties are predicted and found to agree with observations. Mechanisms that relate the whirls to nuclear fusion reaction conditions are tentatively indicated. (author)

A review on ion–ion plasmas created in weakly magnetized electronegative plasmas

International Nuclear Information System (INIS)

Aanesland, A; Bredin, J; Chabert, P

2014-01-01

Ion–Ion plasmas are electronegative plasmas where the electron density is several orders of magnitude lower than the negative ion density. These plasmas have been scarcely observed and investigated since the 1960s and are formed as a transient state of pulsed plasmas or in separate regions in magnetized plasmas. In this review we focus on the latter case of continuous formation of ion–ion plasmas created at the periphery of magnetized plasma columns or downstream localized magnetic barriers. We bring together and review experimental results already published elsewhere and complement them with new results to illustrate the physics important in ion–ion plasma formation and highlight in particular unanswered questions. We show that with a good design the density in the ion–ion region is dropping only by a factor of 2–3 from the initial plasma density. These plasmas can therefore be well suited for various ion source applications when both fluxes or beams of positive and negative ions are desired, and when electrons can cause harmful effects. (paper)

Ion Motion in a Plasma Interacting with Strong Magnetic Fields

International Nuclear Information System (INIS)

Weingarten, A.; Grabowski, C.; Chakrabarti, N.; Maron, Y.; Fruchtmant, A.

1999-01-01

The interaction of a plasma with strong magnetic fields takes place in many laboratory experiments and astrophysical plasmas. Applying a strong magnetic field to the plasma may result in plasma displacement, magnetization, or the formation of instabilities. Important phenomena in plasma, such as the energy transport and the momentum balance, take a different form in each case. We study this interaction in a plasma that carries a short-duration (80-ns) current pulse, generating a magnetic field of up to 17 kG. The evolution of the magnetic field, plasma density, ion velocities, and electric fields are determined before and during the current pulse. The dependence of the plasma limiting current on the plasma density and composition are studied and compared to theoretical models based on the different phenomena. When the plasma collisionality is low, three typical velocities should be taken into consideration: the proton and heavier-ion Alfven velocities (v A p and v A h , respectively) and the EMHD magnetic-field penetration velocity into the plasma (v EMHD ). If both Alfven velocities are larger than v EMHD the plasma is pushed ahead of the magnetic piston and the magnetic field energy is dissipated into ion kinetic energy. If v EMHD is the largest of three velocities, the plasma become magnetized and the ions acquire a small axial momentum only. Different ion species may drift in different directions along the current lines. In this case, the magnetic field energy is probably dissipated into electron thermal energy. When vs > V EMHD > vi, as in the case of one of our experiments, ion mass separation occurs. The protons are pushed ahead of the piston while the heavier-ions become magnetized. Since the plasma electrons are unmagnetized they cannot cross the piston, and the heavy ions are probably charge-neutralized by electrons originating from the cathode that are 'born' magnetized

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.

Magnetic Reconnection

International Nuclear Information System (INIS)

Yamada, Masaaki; Kulsrud, Russell; Ji, Hantao

2009-01-01

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-fluid 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 briefly discussed.

Production of field-reversed plasma with a magnetized coaxial plasma gun

International Nuclear Information System (INIS)

Turner, W.C.; Granneman, E.H.A.; Hartman, C.W.; Prono, D.S.; Taska, J.; Smith, A.C. Jr.

1981-01-01

Experimental data are presented on the production of field-reversed deuterium plasma by a modified coaxial plasma gun. The coaxial gun is constructed with solenoid coils along the inner and outer electrodes that, together with an external guide field solenoid, form a magnetic cusp at the gun muzzle. The net flux inside the inner electrode is arranged to be opposite the external guide field and is the source of field-reversed flux trapped by the plasma. The electrode length is 145 cm, the diameter of the inner (outer) electrode is 15 cm (32 cm). The gun discharge is driven with a 232-μF 40-kV capacitor bank. Acceleration of plasma through the magnetic cusp at the gun muzzle results in entrainment of field-reversed flux that is detected by magnetic probes 75 cm from the gun muzzle. Field-reversed plasma has been produced for a variety of experimental conditions. In one typical case, the guide magnetic field was B 0 =4.8 kG and the change in axial magnetic field ΔB/sub z/ normalized to B 0 was ΔB/sub z/ /B 0 =-3.1. Total field-reversed flux (poloidal flux) obtained by integrating ΔB/sub z/ profiles is in the range 2 x 10 3 kG cm 2 . Measurement of the orthogonal field component indicates a sizable toroidal field peaked off axis at rapprox. =10 cm with a magnitude of roughly one-half the poloidal field component that is measured on magnetic axis. Reconnection of the poloidal field lines has not been established for the data reported in the paper and will be addressed in future experiments which attempt to trap and confine the field-reversed plasma in a magnetic mirror

Plasma sprayed Nd-Fe-B permanent magnets

International Nuclear Information System (INIS)

Willson, M.; Bauser, S.; Liu, S.; Huang, M.

2003-01-01

This study demonstrated that the plasma spray deposition method is an alternative process for producing Nd-Fe-B magnets in addition to the two existing principal processes: the powder metallurgy process for producing sintered Nd-Fe-B magnets and the melt spinning process for bonded Nd-Fe-B magnets. Plasma spray is a potentially better process for producing magnetic parts with complicated shape, large area, thin thickness, small dimension, or unusual geometry. High intrinsic coercivity greater than 15 kOe was readily obtained for Nd 16 Dy 1 Fe 76 B 7 even in the as-deposited condition when the substrate was preheated. The plasma spray process contains only three steps: melting, crushing, and plasma spray, which is much simpler than the powder metallurgy and melt spinning processes. Without preheating the substrate, the coercivity was usually very low (∼0.1 kOe) in the as-deposited condition and it increased to 10 to >15 kOe after anneal. Evidence of magnetocrystalline anisotropy was observed in plasma sprayed Nd 15 Dy 1 Fe 77 B 7 magnets when the substrate was not preheated. It is believed that a crystal texture was developed during the plasma spray as a result of the existence of a temperature gradient in the solidifying melt

Experimental investigation of coaxial-gun-formed plasmas injected into a background transverse magnetic field or plasma

OpenAIRE

Zhang, Yue; Fisher, Dustin M.; Gilmore, Mark; Hsu, Scott C.; Lynn, Alan G.

2017-01-01

Injection of coaxial-gun-formed magnetized plasmas into a background transverse vacuum magnetic field or into a background magnetized plasma has been studied in the helicon-cathode (HelCat) linear plasma device at the University of New Mexico [M. Gilmore et al., J. Plasma Phys.81, 345810104 (2015)]. Magnetized plasma jet launched into a background transverse magnetic field shows emergent kink stabilization of the jet due to the formation of a sheared flow in the jet above the kink-stabilizati...

Spatial Offsets in Flare-CME Current Sheets

Energy Technology Data Exchange (ETDEWEB)

Raymond, John C. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Giordano, Silvio [INAF-Osservatorio Astrofisico di Torino, via Osservatorio 20, I-10025 Pino Torinese (Italy); Ciaravella, Angela, E-mail: jraymond@cfa.harvard.edu [INAF-Osservatorio Astronomico di Palermo, P.za Parlamento 1, I-90134 Palermo (Italy)

2017-07-10

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.

Dispersion functions for weakly relativistic magnetized plasmas in inhomogeneous magnetic field

International Nuclear Information System (INIS)

Gaelzer, R.; Schneider, R.S.; Ziebell, L.F.

1995-01-01

The study of wave propagation and absorption inhomogeneous plasmas can be made by using a formulation in which the dielectric properties of the plasma are described by an effective dielectric tensor which incorporates inhomogeneity effects, inserted into a dispersion relation which is formally the same as that of an homogeneous plasma. We have recently utilized this formalism in the study of electron cyclotron absorption in inhomogeneous media, both in the case of homogeneous magnetic field and in the case of inhomogeneous magnetic field. In the present paper we resume the study of the case with inhomogeneous magnetic field, in order to introduce a generalized dispersion function useful for the case of a Maxwellian plasma, and discuss some of its properties. (author). 10 refs

Effects of 3D magnetic perturbations on toroidal plasmas

International Nuclear Information System (INIS)

Callen, J.D.

2011-01-01

Small three-dimensional (3D) magnetic field perturbations have many interesting and possibly useful effects on tokamak and quasi-symmetric stellarator plasmas. Plasma transport equations that include these effects, most notably on diamagnetic-level toroidal plasma flows, have recently been developed. The 3D field perturbations and their plasma effects can be classified according to their toroidal mode number n: low n (say 1-5) resonant (with field line pitch, q = m/n) and non-resonant fields, medium n (∼20, due to toroidal field ripple) and high n (due to microturbulence). Low n non-resonant fields induce a neoclassical toroidal viscosity (NTV) that damps toroidal rotation throughout the plasma towards an offset rotation in the counter-current direction. Recent tokamak experiments have generally confirmed and exploited these predictions by applying external low n non-resonant magnetic perturbations. Medium n toroidal field ripple produces similar effects plus possible ripple-trapping NTV effects and ion direct losses in the edge. A low n (e.g. n = 1) resonant field is mostly shielded by the toroidally rotating plasma at and inside the resonant (rational) surface. If it is large enough it can stop plasma rotation at the rational surface, facilitate magnetic reconnection there and lead to a growing stationary magnetic island (locked mode), which often causes a plasma disruption. Externally applied 3D magnetic perturbations usually have many components. In the plasma their lowest n (e.g. n = 1) externally resonant components can be amplified by kink-type plasma responses, particularly at high β. Low n plasma instabilities (e.g. resistive wall modes, neoclassical tearing modes) cause additional 3D magnetic perturbations in tokamak plasmas. Tearing modes in their nonlinear (Rutherford) regime bifurcate the topology and form magnetic islands. Finally, multiple resonant magnetic perturbations (RMPs) can, if not shielded by plasma rotation effects, cause local magnetic

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

Science.gov (United States)

Daldorff, L. K. S.; Klimchuk, J. A.; Knizhnik, K. J.

2016-12-01

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 behaviour 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.

Plasma membrane isolation using immobilized concanavalin A magnetic beads.

Science.gov (United States)

Lee, Yu-Chen; Srajer Gajdosik, Martina; Josic, Djuro; Lin, Sue-Hwa

2012-01-01

Isolation of highly purified plasma membranes is the key step in constructing the plasma membrane proteome. Traditional plasma membrane isolation method takes advantage of the differential density of organelles. While differential centrifugation methods are sufficient to enrich for plasma membranes, the procedure is lengthy and results in low recovery of the membrane fraction. Importantly, there is significant contamination of the plasma membranes with other organelles. The traditional agarose affinity matrix is suitable for isolating proteins but has limitation in separating organelles due to the density of agarose. Immobilization of affinity ligands to magnetic beads allows separation of affinity matrix from organelles through magnets and could be developed for the isolation of organelles. We have developed a simple method for isolating plasma membranes using lectin concanavalin A (ConA) magnetic beads. ConA is immobilized onto magnetic beads by binding biotinylated ConA to streptavidin magnetic beads. The ConA magnetic beads are used to bind glycosylated proteins present in the membranes. The bound membranes are solubilized from the magnetic beads with a detergent containing the competing sugar alpha methyl mannoside. In this study, we describe the procedure of isolating rat liver plasma membranes using sucrose density gradient centrifugation as described by Neville. We then further purify the membrane fraction by using ConA magnetic beads. After this purification step, main liver plasma membrane proteins, especially the highly glycosylated ones and proteins containing transmembrane domains could be identified by LC-ESI-MS/MS. While not described here, the magnetic bead method can also be used to isolate plasma membranes from cell lysates. This membrane purification method should expedite the cataloging of plasma membrane proteome.

Hall magnetohydrodynamic effects for current sheet flapping oscillations related to the magnetic double gradient mechanism

International Nuclear Information System (INIS)

Erkaev, N. V.; Semenov, V. S.; Biernat, H. K.

2010-01-01

Hall magnetohydrodynamic model is investigated for current sheet flapping oscillations, which implies a gradient of the normal magnetic field component. For the initial undisturbed current sheet structure, the normal magnetic field component is assumed to have a weak linear variation. The profile of the electric current velocity is described by hyperbolic functions with a maximum at the center of the current sheet. In the framework of this model, eigenfrequencies are calculated as functions of the wave number for the ''kink'' and ''sausage'' flapping wave modes. Because of the Hall effects, the flapping eigenfrequency is larger for the waves propagating along the electric current, and it is smaller for the opposite wave propagation with respect to the current. The asymmetry of the flapping wave propagation, caused by Hall effects, is pronounced stronger for thinner current sheets. This is due to the Doppler effect related to the electric current velocity.

Tomography of a simply magnetized toroidal plasma

Science.gov (United States)

Ruggero, BARNI; Stefano, CALDIROLA; Luca, FATTORINI; Claudia, RICCARDI

2018-02-01

Optical emission spectroscopy is a passive diagnostic technique, which does not perturb the plasma state. In particular, in a hydrogen plasma, Balmer-alpha (H α ) emission can be easily measured in the visible range along a line of sight from outside the plasma vessel. Other emission lines in the visible spectral range from hydrogen atoms and molecules can be exploited too, in order to gather complementary pieces of information on the plasma state. Tomography allows us to capture bi-dimensional structures. We propose to adopt an emission spectroscopy tomography for studying the transverse profiles of magnetized plasmas when Abel inversion is not exploitable. An experimental campaign was carried out at the Thorello device, a simple magnetized torus. The characteristics of the profile extraction method, which we implemented for this purpose are discussed, together with a few results concerning the plasma profiles in a simply magnetized torus configuration.

Interaction between laser-produced plasma and guiding magnetic field

International Nuclear Information System (INIS)

Hasegawa, Jun; Takahashi, Kazumasa; Ikeda, Shunsuke; Nakajima, Mitsuo; Horioka, Kazuhiko

2013-01-01

Transportation properties of laser-produced plasma through a guiding magnetic field were examined. A drifting dense plasma produced by a KrF laser was injected into an axisymmetric magnetic field induced by permanent ring magnets. The plasma ion flux in the guiding magnetic field was measured by a Faraday cup at various distances from the laser target. Numerical analyses based on a collective focusing model were performed to simulate plasma particle trajectories and then compared with the experimental results. (author)

Optimization of the Magnetic Field Structure for Sustained Plasma Gun Helicity Injection for Magnetic Turbulence Studies at the Bryn Mawr Plasma Laboratory

Science.gov (United States)

Cartagena-Sanchez, C. A.; Schaffner, D. A.; Johnson, H. K.; Fahim, L. E.

2017-10-01

A long-pulsed magnetic coaxial plasma gun is being implemented and characterized at the Bryn Mawr Plasma Laboratory (BMPL). A cold cathode discharged between the cylindrical electrodes generates and launches plasma into a 24cm diameter, 2m long chamber. Three separately pulsed magnetic coils are carefully positioned to generate radial magnetic field between the electrodes at the gun edge in order to provide stuffing field. Magnetic helicity is continuously injected into the flux-conserving vacuum chamber in a process akin to sustained slow-formation of spheromaks. The aim of this source, however, is to supply long pulses of turbulent magnetized plasma for measurement rather than for sustained spheromak production. The work shown here details the optimization of the magnetic field structure for this sustained helicity injection.

A new multi-line cusp magnetic field plasma device (MPD) with variable magnetic field

Science.gov (United States)

Patel, A. D.; Sharma, M.; Ramasubramanian, N.; Ganesh, R.; Chattopadhyay, P. K.

2018-04-01

A new multi-line cusp magnetic field plasma device consisting of electromagnets with core material has been constructed with a capability to experimentally control the relative volume fractions of magnetized to unmagnetized plasma volume as well as accurate control on the gradient length scales of mean density and temperature profiles. Argon plasma has been produced using a hot tungsten cathode over a wide range of pressures 5 × 10-5 -1 × 10-3 mbar, achieving plasma densities ranging from 109 to 1011 cm-3 and the electron temperature in the range 1-8 eV. The radial profiles of plasma parameters measured along the non-cusp region (in between two consecutive magnets) show a finite region with uniform and quiescent plasma, where the magnetic field is very low such that the ions are unmagnetized. Beyond that region, both plasma species are magnetized and the profiles show gradients both in temperature and density. The electrostatic fluctuation measured using a Langmuir probe radially along the non-cusp region shows less than 1% (δIisat/Iisat physics parameter space relevant to both laboratory multi-scale plasmas and astrophysical plasmas.

On the linear stability of sheared and magnetized jets without current sheets - relativistic case

Science.gov (United States)

Kim, Jinho; Balsara, Dinshaw S.; Lyutikov, Maxim; Komissarov, Serguei S.

2018-03-01

In our prior series of papers, we studied the non-relativistic and relativistic linear stability analysis of magnetized jets that do not have current sheets. In this paper, we extend our analysis to relativistic jets with a velocity shear and a similar current sheet free structure. The jets that we study are realistic because we include a velocity shear, a current sheet free magnetic structure, a relativistic velocity and a realistic thermal pressure so as to achieve overall pressure balance in the unperturbed jet. In order to parametrize the velocity shear, we apply a parabolic profile to the jets' 4-velocity. We find that the velocity shear significantly improves the stability of relativistic magnetized jets. This fact is completely consistent with our prior stability analysis of non-relativistic, sheared jets. The velocity shear mainly plays a role in stabilizing the short wavelength unstable modes for the pinch as well as the kink instability modes. In addition, it also stabilizes the long wavelength fundamental pinch instability mode. We also visualize the pressure fluctuations of each unstable mode to provide a better physical understanding of the enhanced stabilization by the velocity shear. Our overall conclusion is that combining velocity shear with a strong and realistic magnetic field makes relativistic jets even more stable.

Pressure balance inconsistency exhibited in a statistical model of magnetospheric plasma

Science.gov (United States)

Garner, T. W.; Wolf, R. A.; Spiro, R. W.; Thomsen, M. F.; Korth, H.

2003-08-01

While quantitative theories of plasma flow from the magnetotail to the inner magnetosphere typically assume adiabatic convection, it has long been understood that these convection models tend to overestimate the plasma pressure in the inner magnetosphere. This phenomenon is called the pressure crisis or the pressure balance inconsistency. In order to analyze it in a new and more detailed manner we utilize an empirical model of the proton and electron distribution functions in the near-Earth plasma sheet (-50 RE attributed to gradient/curvature drift for large isotropic energy invariants but not for small invariants. The tailward gradient of the distribution function indicates a violation of the adiabatic drift condition in the plasma sheet. It also confirms the existence of a "number crisis" in addition to the pressure crisis. In addition, plasma sheet pressure gradients, when crossed with the gradient of flux tube volume computed from the [1989] magnetic field model, indicate Region 1 currents on the dawn and dusk sides of the outer plasma sheet.

Plasma sprayed samarium--cobalt permanent magnets

International Nuclear Information System (INIS)

Willson, M.C.; Janowiecki, R.J.

1975-01-01

Samarium--cobalt permanent magnets were fabricated by arc plasma spraying. This process involves the injection of relatively coarse powder particles into a high-temperature gas for melting and spraying onto a substrate. The technique is being investigated as an economical method for fabricating cobalt--rare earth magnets for advanced traveling wave tubes and cross-field amplifiers. Plasma spraying permits deposition of material at high rates over large areas with optional direct bonding to the substrate, and offers the ability to fabricate magnets in a variety of shapes and sizes. Isotropic magnets were produced with high coercivity and good reproducibility in magnetic properties. Post-spray thermal treatments were used to enhance the magnetic properties of sprayed deposits. Samarium--cobalt magnets, sprayed from samarium-rich powder and subjected to post-spray heat treatment, displayed energy products in excess of 9 million gauss-oersteds and coercive forces of approximately 6000 oersteds. Bar magnet arrays were constructed by depositing magnets on ceramic substrates. (auth)

Plasma sprayed samarium--cobalt permanent magnets

International Nuclear Information System (INIS)

Willson, M.C.; Janowiecki, R.J.

1975-01-01

Samarium--Co permanent magnets were fabricated by arc plasma spraying. This process involves the injection of relatively coarse powder particles into a high temperature gas for melting and spraying onto a substrate. The technique is being investigated as an economical method for fabricating Co--rare earth magnets for advanced traveling wave tubes and cross-field amplifiers. Plasma spraying permits deposition of material at high rates over large areas with optional direct bonding to the substrate, and offers the ability to fabricate magnets in a variety of shapes and sizes. Isotropic magnets were produced with high coercivity and good reproducibility in magnetic properties. Post-spray thermal treatments were used to enhance the magnetic properties of sprayed deposits. Samarium--Co magnets, sprayed from Sm-rich powder and subjected to post-spray heat treatment, displayed energy products in excess of 9 million G-Oe and coercive forces of approximately 6000 Oe. Bar magnet arrays were constructed by depositing magnets on ceramic substrates

Current-Sheet Formation and Reconnection at a Magnetic X Line in Particle-in-Cell Simulations

Science.gov (United States)

Black, C.; Antiochos, S. K.; Hesse, M.; Karpen, J. T.; Kuznetsova, M. M.; Zenitani, S.

2011-01-01

The integration of kinetic effects into macroscopic numerical models is currently of great interest to the heliophysics community, particularly in the context of magnetic reconnection. Reconnection governs the large-scale energy release and topological rearrangement of magnetic fields in a wide variety of laboratory, heliophysical, and astrophysical systems. We are examining the formation and reconnection of current sheets in a simple, two-dimensional X-line configuration using high-resolution particle-in-cell (PIC) simulations. The initial minimum-energy, potential magnetic field is perturbed by excess thermal pressure introduced into the particle distribution function far from the X line. Subsequently, the relaxation of this added stress leads self-consistently to the development of a current sheet that reconnects for imposed stress of sufficient strength. We compare the time-dependent evolution and final state of our PIC simulations with macroscopic magnetohydrodynamic simulations assuming both uniform and localized electrical resistivities (C. R. DeVore et al., this meeting), as well as with force-free magnetic-field equilibria in which the amount of reconnection across the X line can be constrained to be zero (ideal evolution) or optimal (minimum final magnetic energy). We will discuss implications of our results for understanding magnetic-reconnection onset and cessation at kinetic scales in dynamically formed current sheets, such as those occurring in the solar corona and terrestrial magnetotail.

A MODEL FOR THE ELECTRICALLY CHARGED CURRENT SHEET OF A PULSAR

Energy Technology Data Exchange (ETDEWEB)

DeVore, C. R.; Antiochos, S. K.; Black, C. E. [Heliophysics Science Division, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States); Harding, A. K.; Kalapotharakos, C.; Kazanas, D.; Timokhin, A. N., E-mail: c.richard.devore@nasa.gov [Astrophysics Science Division, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States)

2015-03-10

Global-scale solutions for the magnetosphere of a pulsar consist of a region of low-lying, closed magnetic field near the star, bounded by opposite-polarity regions of open magnetic field along which the pulsar wind flows into space. Separating these open-field regions is a magnetic discontinuity—an electric current sheet—consisting of generally nonneutral plasma. We have developed a self-consistent model for the internal equilibrium structure of the sheet by generalizing the charge-neutral Vlasov/Maxwell equilibria of Harris and Hoh to allow for net electric charge. The resulting equations for the electromagnetic field are solved analytically and numerically. Our results show that the internal thermal pressure needed to establish equilibrium force balance, and the associated effective current-sheet thickness and magnetization, can differ by orders of magnitude from the Harris/Hoh charge-neutral limit. The new model provides a starting point for kinetic or fluid investigations of instabilities that can cause magnetic reconnection and flaring in pulsar magnetospheres.

Wakefield generation in magnetized plasmas

International Nuclear Information System (INIS)

Holkundkar, Amol; Brodin, Gert; Marklund, Mattias

2011-01-01

We consider wakefield generation in plasmas by electromagnetic pulses propagating perpendicular to a strong magnetic field, in the regime where the electron cyclotron frequency is equal to or larger than the plasma frequency. Particle-in-cell simulations reveal that for moderate magnetic field strengths previous results are reproduced, and the wakefield wave number spectrum has a clear peak at the inverse skin depth. However, when the cyclotron frequency is significantly larger than the plasma frequency, the wakefield spectrum becomes broadband, and simultaneously the loss rate of the driving pulse is much enhanced. A set of equations for the scalar and vector potentials reproducing these results are derived, using only the assumption of a weakly nonlinear interaction.

Lasers plasmas and magnetic field

International Nuclear Information System (INIS)

Albertazzi, Bruno

2014-01-01

We studied the coupling between a laser produced plasmas and a magnetic field in two cases: 1) in the context of Inertial Fusion Confinement (ICF), we first studied how magnetic fields are self generated during the interaction between a target and a laser, then 2) to progress in the understanding of the large-scale shaping of astrophysical jets, we studied the influence of an externally applied magnetic field on the dynamics of a laser-produced plasma expanding into vacuum. The first part of this thesis is thus dedicated to a numerical and experimental study of the self generated magnetic fields that are produced following the irradiation of a solid target by a high power laser (having pulse duration in the nanosecond and picosecond regimes). These fields play an important role in the frame of ICF since they influence the dynamics of the electrons produced during the laser-matter interaction, and thus condition the success of ICF experiments. The second part of this thesis is a numerical and experimental study of the influence of an externally applied magnetic field on the morphology of a laser produced plasma freely otherwise expanding into vacuum. This work aims at better understanding the observed large-scale collimation of astrophysical jets which cannot be understood in the frame of existing models. We notably show that a purely axial magnetic field can force an initially isotropic laboratory flow, scaled to be representative of a flow emerging from a Young Star Object, in a re-collimation shock, from which emerges a narrow, well collimated jet. We also show that the plasma heating induced at the re-collimation point could explain the 'puzzling' observations of stationary X ray emission zones embedded within astrophysical jets. (author) [fr

Neutral sheet crossings in the distant magnetotail

International Nuclear Information System (INIS)

Heikkila, W.J.; Slavin, J.A.; Smith, E.J.; Baker, D.N.; Zwickl, R.D.

1985-01-01

We have analyzed the magnetic field data from ISEE-3 in the distant magnetotail for 18 crossings of the cross-tail current sheet (or so-called natural sheet) to determine the direction of the normal component B/sub z/. The crossings occurred near the middle of the aberrated magnetotail (0 0.4 nT), consistent with closed field lines connected to the earth. In 3 cases B/sub z/ was very close to zero; in several instances there was structure in B/sub y/, suggesting localized currents with x or z directions. One may have been a magnetopause crossing. The strong preponderance of northward B/sub z/ favors a model of the magnetotail which is dominated by boundary layer plasma, flowing tailward on closed magnetic field lines, which requires the existence of an electric field in the sense from dusk to dawn. 37 refs., 15 figs., 1 tab

Exponential Frequency Spectrum in Magnetized Plasmas

International Nuclear Information System (INIS)

Pace, D. C.; Shi, M.; Maggs, J. E.; Morales, G. J.; Carter, T. A.

2008-01-01

Measurements of a magnetized plasma with a controlled electron temperature gradient show the development of a broadband spectrum of density and temperature fluctuations having an exponential frequency dependence at frequencies below the ion cyclotron frequency. The origin of the exponential frequency behavior is traced to temporal pulses of Lorentzian shape. Similar exponential frequency spectra are also found in limiter-edge plasma turbulence associated with blob transport. This finding suggests a universal feature of magnetized plasma turbulence leading to nondiffusive, cross-field transport, namely, the presence of Lorentzian shaped pulses

Experimental investigation of plasma relaxation using a compact coaxial magnetized plasma gun in a background plasma

Science.gov (United States)

Zhang, Yue; Lynn, Alan; Gilmore, Mark; Hsu, Scott; University of New Mexico Collaboration; Los Alamos National Laboratory Collaboration

2013-10-01

A compact coaxial plasma gun is employed for experimental studies of plasma relaxation in a low density background plasma. Experiments are being conducted in the linear HelCat device at UNM. These studies will advance the knowledge of basic plasma physics in the areas of magnetic relaxation and space and astrophysical plasmas, including the evolution of active galactic jets/radio lobes within the intergalactic medium. The gun is powered by a 120pF ignitron-switched capacitor bank which is operated in a range of 5-10 kV and ~100 kA. Multiple diagnostics are employed to investigate plasma relaxation process. Magnetized Argon plasma bubbles with velocities ~1.2Cs and densities ~1020 m-3 have been achieved. Different distinct regimes of operation with qualitatively different dynamics are identified by fast CCD camera images, with the parameter determining the operation regime. Additionally, a B-dot probe array is employed to measure the spatial toroidal and poloidal magnetic flux evolution to identify detached plasma bubble configurations. Experimental data and analysis will be presented.

Transient, Small-Scale Field-Aligned Currents in the Plasma Sheet Boundary Layer During Storm Time Substorms

Science.gov (United States)

Nakamura, R.; Sergeev, V. A.; Baumjohann, W.; Plaschke, F.; Magnes, W.; Fischer, D.; Varsani, A.; Schmid, D.; Nakamura, T. K. M.; Russell, C. T.;

Observation of enhanced electric field in an RF-plugged sheet plasma in the RFC-XX-M open-ended machine

International Nuclear Information System (INIS)

Oda, T.; Takiyama, K.; Kadota, K.

1987-12-01

We report nonperturbing observation of the electric field in the sheet plasma for RF end-plugging on the RFC XX-M open-ended machine by using the Stark effect with a combined technique of beam-probe and laser-induced fluorescence. Under the optimum condition for the RF plugging, enhanced electric field is found in the sheet plasma by about 2.5 times with respect to the electric field when no plasma is produced. The field spatial profile is also measured, which is discussed in connection with the electrostatic eigenmode. (author)

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).

Confinement of laser plasma expansion with strong external magnetic field

Science.gov (United States)

Tang, Hui-bo; Hu, Guang-yue; Liang, Yi-han; Tao, Tao; Wang, Yu-lin; Hu, Peng; Zhao, Bin; Zheng, Jian

2018-05-01

The evolutions of laser ablation plasma, expanding in strong (∼10 T) transverse external magnetic field, were investigated in experiments and simulations. The experimental results show that the magnetic field pressure causes the plasma decelerate and accumulate at the plasma-field interface, and then form a low-density plasma bubble. The saturation size of the plasma bubble has a scaling law on laser energy and magnetic field intensity. Magnetohydrodynamic simulation results support the observation and find that the scaling law (V max ∝ E p /B 2, where V max is the maximum volume of the plasma bubble, E p is the absorbed laser energy, and B is the magnetic field intensity) is effective in a broad laser energy range from several joules to kilo-joules, since the plasma is always in the state of magnetic field frozen while expanding. About 15% absorbed laser energy converts into magnetic field energy stored in compressed and curved magnetic field lines. The duration that the plasma bubble comes to maximum size has another scaling law t max ∝ E p 1/2/B 2. The plasma expanding dynamics in external magnetic field have a similar character with that in underdense gas, which indicates that the external magnetic field may be a feasible approach to replace the gas filled in hohlraum to suppress the wall plasma expansion and mitigate the stimulated scattering process in indirect drive ignition.

Ferromagnetic nuclear resonance investigation of the surface magnetization in iron sheets

International Nuclear Information System (INIS)

Varga, L.; Tompa, K.

1977-09-01

The role of the domain structure and domain properties in ferromagnetic nuclear resonance (FNR) experiments is reconsidered. Using the FNR signal intensity as a measure of surface domain wall volume, it is found that the behaviour of the surface magnetization differs from that of the bulk magnetization of iron sheets. Namely, a critical field below which the FNR signal remains unchanqed is observed in the surface magnetization. This lag of surface domain wall annihilation is sensitive to the given surface conditions and in particular to the rolling deformation. Considering the small skin depth, FNR as a surface testing method is discussed. (D.P.)

Repetitive formation and decay of current sheets in magnetic loops: An origin of diverse magnetic structures

Energy Technology Data Exchange (ETDEWEB)

Kumar, Dinesh; Bhattacharyya, R. [Udaipur Solar Observatory, Physical Research Laboratory, Dewali, Bari Road, Udaipur 313001 (India); Smolarkiewicz, P. K. [European Centre for Medium-Range Weather Forecasts, Reading RG2 9AX (United Kingdom)

2015-01-15

In this work, evolution of an incompressible, thermally homogeneous, infinitely conducting, viscous magnetofluid is numerically explored as the fluid undergoes repeated events of magnetic reconnection. The initial magnetic field is constructed by a superposition of two linear force-free fields and has similar morphology as the magnetic loops observed in the solar corona. The results are presented for computations with three distinct sets of footpoint geometries. To onset reconnection, we rely on numerical model magnetic diffusivity, in the spirit of implicit large eddy simulation. It is generally expected that in a high Lundquist number fluid, repeated magnetic reconnections are ubiquitous and hence can lead to a host of magnetic structures with considerable observational importance. In particular, the simulations presented here illustrate formations of magnetic islands, rotating magnetic helices and rising flux ropes—depending on the initial footpoint geometry but through the common process of repeated magnetic reconnections. Further, we observe the development of extended current sheets in two case studies, where the footpoint reconnections generate favorable dynamics.

Repetitive formation and decay of current sheets in magnetic loops: An origin of diverse magnetic structures

International Nuclear Information System (INIS)

Kumar, Dinesh; Bhattacharyya, R.; Smolarkiewicz, P. K.

2015-01-01

In this work, evolution of an incompressible, thermally homogeneous, infinitely conducting, viscous magnetofluid is numerically explored as the fluid undergoes repeated events of magnetic reconnection. The initial magnetic field is constructed by a superposition of two linear force-free fields and has similar morphology as the magnetic loops observed in the solar corona. The results are presented for computations with three distinct sets of footpoint geometries. To onset reconnection, we rely on numerical model magnetic diffusivity, in the spirit of implicit large eddy simulation. It is generally expected that in a high Lundquist number fluid, repeated magnetic reconnections are ubiquitous and hence can lead to a host of magnetic structures with considerable observational importance. In particular, the simulations presented here illustrate formations of magnetic islands, rotating magnetic helices and rising flux ropes—depending on the initial footpoint geometry but through the common process of repeated magnetic reconnections. Further, we observe the development of extended current sheets in two case studies, where the footpoint reconnections generate favorable dynamics

Simulating Magnetized Laboratory Plasmas with Smoothed Particle Hydrodynamics

Energy Technology Data Exchange (ETDEWEB)

Johnson, Jeffrey N. [Univ. of California, Davis, CA (United States)

2009-01-01

The creation of plasmas in the laboratory continues to generate excitement in the physics community. Despite the best efforts of the intrepid plasma diagnostics community, the dynamics of these plasmas remains a difficult challenge to both the theorist and the experimentalist. This dissertation describes the simulation of strongly magnetized laboratory plasmas with Smoothed Particle Hydrodynamics (SPH), a method born of astrophysics but gaining broad support in the engineering community. We describe the mathematical formulation that best characterizes a strongly magnetized plasma under our circumstances of interest, and we review the SPH method and its application to astrophysical plasmas based on research by Phillips [1], Buerve [2], and Price and Monaghan [3]. Some modifications and extensions to this method are necessary to simulate terrestrial plasmas, such as a treatment of magnetic diffusion based on work by Brookshaw [4] and by Atluri [5]; we describe these changes as we turn our attention toward laboratory experiments. Test problems that verify the method are provided throughout the discussion. Finally, we apply our method to the compression of a magnetized plasma performed by the Compact Toroid Injection eXperiment (CTIX) [6] and show that the experimental results support our computed predictions.

Multi-instrument observations of the ionospheric counterpart of a bursty bulk flow in the near-Earth plasma sheet

Directory of Open Access Journals (Sweden)

A. Grocott

2004-04-01

Full Text Available On 07 September 2001 the Cluster spacecraft observed a "bursty bulk flow" event in the near-Earth central plasma sheet. This paper presents a detailed study of the coincident ground-based observations and attempts to place them within a simple physical framework. The event in question occurs at ~22:30 UT, some 10min after a southward turning of the IMF. IMAGE and SAMNET magnetometer measurements of the ground magnetic field reveal perturbations of a few tens of nT and small amplitude Pi2 pulsations. CUTLASS radar observations of ionospheric plasma convection show enhanced flows out of the polar cap near midnight, accompanied by an elevated transpolar voltage. Optical data from the IMAGE satellite also show that there is a transient, localised ~1 kR brightening in the UV aurora. These observations are consistent with the earthward transport of plasma in the tail, but also indicate the absence of a typical "large-scale" substorm current wedge. An analysis of the field-aligned current system implied by the radar measurements does suggest the existence of a small-scale current "wedgelet", but one which lacks the global scale and high conductivities observed during substorm expansions.

Key words. Ionosphere (auroral ionosphere; ionospheremagnetosphere interactions; plasma convection

Magnetic pressure effects in a plasma-liner interface

Science.gov (United States)

García-Rubio, F.; Sanz, J.

2018-04-01

A theoretical analysis of magnetic pressure effects in a magnetized liner inertial fusion-like plasma is presented. In previous publications [F. García-Rubio and J. Sanz, Phys. Plasmas 24, 072710 (2017)], the evolution of a hot magnetized plasma in contact with a cold unmagnetized plasma, aiming to represent the hot spot and liner, respectively, was investigated in planar geometry. The analysis was made in a double limit low Mach and high thermal to magnetic pressure ratio β. In this paper, the analysis is extended to an arbitrary pressure ratio. Nernst, Ettingshausen, and Joule effects come into play in the energy balance. The region close to the liner is governed by thermal conduction, while the Joule dissipation becomes predominant far from it when the pressure ratio is low. Mass ablation, thermal energy, and magnetic flux losses are reduced with plasma magnetization, characterized by the electron Hall parameter ω e τ e , until β values of order unity are reached. From this point forward, increasing the electron Hall parameter no longer improves the magnetic flux conservation, and mass ablation is enhanced due to the magnetic pressure gradients. A thoughtful simplification of the problem that allows to reduce the order of the system of governing equations while still retaining the finite β effects is presented and compared to the exact case.

Spin and magnetization effects in plasmas

International Nuclear Information System (INIS)

Brodin, G; Marklund, M; Zamanian, J; Stefan, M

2011-01-01

Quantum effects in plasmas are of interest for a diverse set of systems, and have thus as a field been revived and attracted a lot of attention from a wide community over the past decade. In models of quantum plasmas, the effects studied mostly are due to the quantum particle dispersion and tunnelling. Such effects can be of importance in dense systems and on short length scales. There are also a number of effects related to spin and statistics. However, up to recently the magnetization effect in plasmas due to the intrinsic electron spin has been largely ignored. The magnetization dynamics of e.g. solids has many important applications, such as components for memory storage, but has also been discussed in more 'proper' plasma environments, such as fusion plasmas. Furthermore, also from a basic science point-of-view the effects of intrinsic spin and gyromagnetic effects are of considerable interest. Here we give a short review of a number of different models for treating magnetization effects in plasmas, with a focus on recent results. In particular, the transition between kinetic models and fluid models is discussed. We also give a number of examples of applications of such theories, as well as an outlook for possible future work.

Iron Abundances in Lunar Impact Basin Melt Sheets From Orbital Magnetic Field Data

Science.gov (United States)

Oliveira, Joana S.; Wieczorek, Mark A.; Kletetschka, Gunther

2017-12-01

Magnetic field data acquired from orbit shows that the Moon possesses many magnetic anomalies. Though most of these are not associated with known geologic structures, some are found within large impact basins within the interior peak ring. The primary magnetic carrier in lunar rocks is metallic iron, but indigenous lunar rocks are metal poor and cannot account easily for the observed field strengths. The projectiles that formed the largest impact basins must have contained a significant quantity of metallic iron, and a portion of this iron would have been retained on the Moon's surface within the impact melt sheet. Here we use orbital magnetic field data to invert for the magnetization within large impact basins using the assumption that the crust is unidirectionally magnetized. We develop a technique based on laboratory thermoremanent magnetization acquisition to quantify the relationship between the strength of the magnetic field at the time the rock cooled and the abundance of metal in the rock. If we assume that the magnetized portion of the impact melt sheet is 1 km thick, we find average abundances of metallic iron ranging from 0.11% to 0.45 wt %, with an uncertainty of a factor of about 3. This abundance is consistent with the metallic iron abundances in sampled lunar impact melts and the abundance of projectile contamination in terrestrial impact melts. These results help constrain the composition of the projectile, the impact process, and the time evolution of the lunar dynamo.

Auroral electrojets and boundaries of plasma domains in the magnetosphere during magnetically disturbed intervals

Directory of Open Access Journals (Sweden)

Y. I. Feldstein

2006-09-01

Full Text Available We investigate variations in the location and intensity of the auroral electrojets during magnetic storms and substorms using a numerical method for estimating the equivalent ionospheric currents based on data from meridian chains of magnetic observatories. Special attention was paid to the complex structure of the electrojets and their interrelationship with diffuse and discrete particle precipitation and field-aligned currents in the dusk sector. During magnetospheric substorms the eastward electrojet (EE location in the evening sector changes with local time from cusp latitudes (Φ~77° during early afternoon to latitudes of diffuse auroral precipitation (Φ~65° equatorward of the auroral oval before midnight. During the main phase of an intense magnetic storm the eastward currents in the noon-early evening sector adjoin to the cusp at Φ~65° and in the pre-midnight sector are located at subauroral latitude Φ~57°. The westward electrojet (WE is located along the auroral oval from evening through night to the morning sector and adjoins to the polar electrojet (PE located at cusp latitudes in the dayside sector. The integrated values of the eastward (westward equivalent ionospheric current during the intense substorm are ~0.5 MA (~1.5 MA, whereas they are 0.7 MA (3.0 MA during the storm main phase maximum. The latitudes of auroral particle precipitation in the dusk sector are identical with those of both electrojets. The EE in the evening sector is accompanied by particle precipitation mainly from the Alfvén layer but also from the near-Earth part of the central plasma sheet. In the lower-latitude part of the EE the field-aligned currents (FACs flow into the ionosphere (Region 2 FAC, and at its higher-latitude part the FACs flow out of the ionosphere (Region 1 FAC. During intense disturbances, in addition to the Region 2 FAC and the Region 1 FAC, a Region 3 FAC with the downward current was identified. This FAC is accompanied by diffuse

Estimates on the mean current in a sphere of plasma

International Nuclear Information System (INIS)

Nunez, Manuel

2003-01-01

Several turbulent dynamo models predict the concentration of the magnetic field in chaotic plasmas in sheets with the field vector pointing alternatively in opposite directions, which should produce strong current sheets. It is proved that if the plasma is contained in a rigid sphere with perfectly conducting boundary the geometry of these sheets must be balanced so that the mean current remains essentially bounded by the Coulomb gauged mean vector potential of the field. This magnitude remains regular even for the sharp field variations expected in a chaotic flow. For resistive plasmas the same arguments imply that the contribution to the total current of the regions near the boundary compensates the current of the central part of the sphere

Plasma heating in a variable magnetic field

Energy Technology Data Exchange (ETDEWEB)

Kichigin, G. N., E-mail: king@iszf.irk.ru [Russian Academy of Sciences, Institute of Solar-Terrestrial Physics (Russian Federation)

2013-05-15

The problem of particle acceleration in a periodically variable magnetic field that either takes a zero value or passes through zero is considered. It is shown that, each time the field [0]passes through zero, the particle energy increases abruptly. This process can be regarded as heating in the course of which plasma particles acquire significant energy within one field period. This mechanism of plasma heating takes place in the absence of collisions between plasma particles and is analogous to the mechanism of magnetic pumping in collisional plasma considered by Alfven.

MAGNETOHYDRODYNAMICS STUDY OF THREE-DIMENSIONAL FAST MAGNETIC RECONNECTION FOR INTERMITTENT SNAKE-LIKE DOWNFLOWS IN SOLAR FLARES

International Nuclear Information System (INIS)

Shimizu, T.; Kondo, K.; Ugai, M.; Shibata, K.

2009-01-01

Three-dimensional instability of the spontaneous fast magnetic reconnection is studied with magnetohydrodynamics (MHD) simulation, where the two-dimensional model of the spontaneous fast magnetic reconnection is destabilized in three dimensions. In two-dimensional models, every plasma condition is assumed to be uniform in the sheet current direction. In that case, it is well known that the two-dimensional fast magnetic reconnection can be caused by current-driven anomalous resistivity, when an initial resistive disturbance is locally put in a one-dimensional current sheet. In this paper, it is studied whether the two-dimensional fast magnetic reconnection can be destabilized or not when the initial resistive disturbance is three dimensional, i.e., that which has weak fluctuations in the sheet current direction. According to our study, the two-dimensional fast magnetic reconnection is developed to the three-dimensional intermittent fast magnetic reconnection which is strongly localized in the sheet current direction. The resulting fast magnetic reconnection repeats to randomly eject three-dimensional magnetic loops which are very similar to the intermittent downflows observed in solar flares. In fact, in some observations of solar flares, the current sheet seems to be approximately one dimensional, but the fast magnetic reconnection is strongly localized in the sheet current direction, i.e., fully three dimensional. In addition, the observed plasma downflows as snake-like curves. It is shown that those observed features are consistent with our numerical MHD study.

Magnetic reconnection in the low solar chromosphere with a more realistic radiative cooling model

Science.gov (United States)

Ni, Lei; Lukin, Vyacheslav S.; Murphy, Nicholas A.; Lin, Jun

2018-04-01

Magnetic reconnection is the most likely mechanism responsible for the high temperature events that are observed in strongly magnetized locations around the temperature minimum in the low solar chromosphere. This work improves upon our previous work [Ni et al., Astrophys. J. 852, 95 (2018)] by using a more realistic radiative cooling model computed from the OPACITY project and the CHIANTI database. We find that the rate of ionization of the neutral component of the plasma is still faster than recombination within the current sheet region. For low β plasmas, the ionized and neutral fluid flows are well-coupled throughout the reconnection region resembling the single-fluid Sweet-Parker model dynamics. Decoupling of the ion and neutral inflows appears in the higher β case with β0=1.46 , which leads to a reconnection rate about three times faster than the rate predicted by the Sweet-Parker model. In all cases, the plasma temperature increases with time inside the current sheet, and the maximum value is above 2 ×104 K when the reconnection magnetic field strength is greater than 500 G. While the more realistic radiative cooling model does not result in qualitative changes of the characteristics of magnetic reconnection, it is necessary for studying the variations of the plasma temperature and ionization fraction inside current sheets in strongly magnetized regions of the low solar atmosphere. It is also important for studying energy conversion during the magnetic reconnection process when the hydrogen-dominated plasma approaches full ionization.

Latitude-energy structure of multiple ion beamlets in Polar/TIMAS data in plasma sheet boundary layer and boundary plasma sheet below 6 RE radial distance: basic properties and statistical analysis

Directory of Open Access Journals (Sweden)

P. Janhunen

2005-03-01

Full Text Available Velocity dispersed ion signatures (VDIS occurring at the plasma sheet boundary layer (PSBL are a well reported feature. Theory has, however, predicted the existence of multiple ion beamlets, similar to VDIS, in the boundary plasma sheet (BPS, i.e. at latitudes below the PSBL. In this study we show evidence for the multiple ion beamlets in Polar/TIMAS ion data and basic properties of the ion beamlets will be presented. Statistics of the occurrence frequency of ion multiple beamlets show that they are most common in the midnight MLT sector and for altitudes above 4 RE, while at low altitude (≤3 RE, single beamlets at PSBL (VDIS are more common. Distribution functions of ion beamlets in velocity space have recently been shown to correspond to 3-dimensional hollow spheres, containing a large amount of free energy. We also study correlation with ~100 Hz waves and electron anisotropies and consider the possibility that ion beamlets correspond to stable auroral arcs.

Injection of a coaxial-gun-produced magnetized plasma into a background helicon plasma

Science.gov (United States)

Zhang, Yue; Lynn, Alan; Gilmore, Mark; Hsu, Scott

2014-10-01

A compact coaxial plasma gun is employed for experimental investigation of plasma bubble relaxation into a lower density background plasma. Experiments are being conducted in the linear device HelCat at UNM. The gun is powered by a 120-uF ignitron-switched capacitor bank, which is operated in a range of 5 to 10 kV and 100 kA. Multiple diagnostics are employed to investigate the plasma relaxation process. Magnetized argon plasma bubbles with velocities 1.2Cs, densities 1020 m-3 and electron temperature 13eV have been achieved. The background helicon plasma has density 1013 m-3, magnetic field from 200 to 500 Gauss and electron temperature 1eV. Several distinct operational regimes with qualitatively different dynamics are identified by fast CCD camera images. Additionally a B-dot probe array has been employed to measure the spatial toroidal and poloidal magnetic flux evolution to identify plasma bubble configurations. Experimental data and analysis will be presented.

Magnetic microstructure and magnetic properties of spark plasma sintered NdFeB magnets

Energy Technology Data Exchange (ETDEWEB)

Huang, Y.L., E-mail: hyl1019_lin@163.com [School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063 (China); Wang, Y.; Hou, Y.H.; Wang, Y.L.; Wu, Y.; Ma, S.C. [School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063 (China); Liu, Z.W.; Zeng, D.C. [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Tian, Y.; Xia, W.X. [Key Laboratory of Magnetic Materials and Devices, Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China); Zhong, Z.C., E-mail: zzhong2014@sina.com [School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063 (China)

2016-02-01

Nanocrystalline NdFeB magnets were prepared by spark plasma sintering (SPS) technique using melt-spun ribbons as starting materials. A distinct two-zone structure with coarse grain zone and fine grain zone was formed in the SPSed magnets. Multi-domain particle in coarse grain zone and exchange interaction domain for fine grain zone were observed. Intergranular non-magnetic phase was favorable to improve the coercivity due to the enhancement of domain wall pinning effects and increased exchange-decouple. The remanent polarization of 0.83 T, coercivity of 1516 kA/m, and maximum energy product of 118 kJ/m{sup 3} are obtained for an isotropic magnet. - Highlights: • Nanocrystalline NdFeB magnets were prepared by spark plasma sintering technique. • Multi-domain particle and exchange interaction domain were observed. • Magnetic microstructure and their relation to the properties were investigated.

Effects of assistant anode on planar inductively coupled magnetized argon plasma in plasma immersion ion implantation

International Nuclear Information System (INIS)

Tang, Deli; Chu, Paul K.

2003-01-01

The enhancement of planar radio frequency (RF) inductively coupled argon plasma is studied in the presence of an assistant anode and an external magnetic field at low pressure. The influence of the assistant anode and magnetic field on the efficiency of RF power absorption and plasma parameters is investigated. An external axial magnetic field is coupled into the plasma discharge region by an external electromagnetic coil outside the discharge chamber and an assistant cylindrical anode is inserted into the discharge chamber to enhance the plasma discharge. The plasma parameters and density profile are measured by an electrostatic Langmuir probe at different magnetic fields and anode voltages. The RF power absorption by the plasma can be effectively enhanced by the external magnetic field compared with the nonmagnetized discharge. The plasma density can be further increased by the application of a voltage to the assistant anode. Owing to the effective power absorption and enhanced plasma discharge by the assistant anode in a longitudinal magnetic field, the plasma density can be enhanced by more than a factor of two. Meanwhile, the nonuniformity of the plasma density is less than 10% and it can be achieved in a process chamber with a diameter of 600 mm

Current filaments in turbulent magnetized plasmas

DEFF Research Database (Denmark)

Martines, E.; Vianello, N.; Sundkvist, D.

2009-01-01

gradient region of a fusion plasma confined in reversed field pinch configuration and in a density gradient region in the Earth magnetosphere are measured and compared, showing that in both environments they can be attributed to drift-Alfvén vortices. Current structures associated with reconnection events......Direct measurements of current density perturbations associated with non-linear phenomena in magnetized plasmas can be carried out using in situ magnetic measurements. In this paper we report such measurements for three different kinds of phenomena. Current density fluctuations in the edge density...... measured in a reversed field pinch plasma and in the magnetosheath are detected and compared. Evidence of current filaments occurring during ELMs in an H-mode tokamak plasma is displayed....

A possible mechanism of the enhancement and maintenance of the shear magnetic field component in the current sheet of the Earth’s magnetotail

International Nuclear Information System (INIS)

Grigorenko, E. E.; Malova, H. V.; Malykhin, A. Yu.; Zelenyi, L. M.

2015-01-01

The influence of the shear magnetic field component, which is directed along the electric current in the current sheet (CS) of the Earth’s magnetotail and enhanced near the neutral plane of the CS, on the nonadiabatic dynamics of ions interacting with the CS is studied. The results of simulation of the nonadiabatic ion motion in the prescribed magnetic configuration similar to that observed in the magnetotail CS by the CLUSTER spacecraft demonstrated that, in the presence of some initial shear magnetic field, the north-south asymmetry in the ion reflection/refraction in the CS is observed. This asymmetry leads to the formation of an additional current system formed by the oppositely directed electric currents flowing in the northern and southern parts of the plasma sheet in the planes tangential to the CS plane and in the direction perpendicular to the direction of the electric current in the CS. The formation of this current system perhaps is responsible for the enhancement and further maintenance of the shear magnetic field near the neutral plane of the CS. The CS structure and ion dynamics observed in 17 intervals of the CS crossings by the CLUSTER spacecraft is analyzed. In these intervals, the shear magnetic field was increased near the neutral plane of the CS, so that the bell-shaped spatial distribution of this field across the CS plane was observed. The results of the present analysis confirm the suggested scenario of the enhancement of the shear magnetic field near the neutral plane of the CS due to the peculiarities of the nonadiabatic ion dynamics

A possible mechanism of the enhancement and maintenance of the shear magnetic field component in the current sheet of the Earth’s magnetotail

Energy Technology Data Exchange (ETDEWEB)

Grigorenko, E. E., E-mail: elenagrigorenko2003@yahoo.com; Malova, H. V., E-mail: hmalova@yandex.ru [Russian Academy of Sciences, Space Research Institute (Russian Federation); Malykhin, A. Yu., E-mail: anmaurdreg@gmail.com [Moscow Institute of Physics and Technology (Russian Federation); Zelenyi, L. M., E-mail: lzelenyi@iki.rssi.ru [Russian Academy of Sciences, Space Research Institute (Russian Federation)

2015-01-15

The influence of the shear magnetic field component, which is directed along the electric current in the current sheet (CS) of the Earth’s magnetotail and enhanced near the neutral plane of the CS, on the nonadiabatic dynamics of ions interacting with the CS is studied. The results of simulation of the nonadiabatic ion motion in the prescribed magnetic configuration similar to that observed in the magnetotail CS by the CLUSTER spacecraft demonstrated that, in the presence of some initial shear magnetic field, the north-south asymmetry in the ion reflection/refraction in the CS is observed. This asymmetry leads to the formation of an additional current system formed by the oppositely directed electric currents flowing in the northern and southern parts of the plasma sheet in the planes tangential to the CS plane and in the direction perpendicular to the direction of the electric current in the CS. The formation of this current system perhaps is responsible for the enhancement and further maintenance of the shear magnetic field near the neutral plane of the CS. The CS structure and ion dynamics observed in 17 intervals of the CS crossings by the CLUSTER spacecraft is analyzed. In these intervals, the shear magnetic field was increased near the neutral plane of the CS, so that the bell-shaped spatial distribution of this field across the CS plane was observed. The results of the present analysis confirm the suggested scenario of the enhancement of the shear magnetic field near the neutral plane of the CS due to the peculiarities of the nonadiabatic ion dynamics.

Towards intrinsic magnetism of graphene sheets with irregular zigzag edges.

Science.gov (United States)

Chen, Lianlian; Guo, Liwei; Li, Zhilin; Zhang, Han; Lin, Jingjing; Huang, Jiao; Jin, Shifeng; Chen, Xiaolong

2013-01-01

The magnetism of graphene has remained divergent and controversial due to absence of reliable experimental results. Here we show the intrinsic magnetism of graphene edge states revealed based on unidirectional aligned graphene sheets derived from completely carbonized SiC crystals. It is found that ferromagnetism, antiferromagnetism and diamagnetism along with a probable superconductivity exist in the graphene with irregular zigzag edges. A phase diagram is constructed to show the evolution of the magnetism. The ferromagnetic ordering curie-temperature of the fundamental magnetic order unit (FMOU) is 820 ± 80 K. The antiferromagnetic ordering Neel temperature of the FMOUs belonging to different sublattices is about 54 ± 2 K. The diamagnetism is similar to that of graphite and can be well described by the Kotosonov's equation. Our experimental results provide new evidences to clarify the controversial experimental phenomena observed in graphene and contribute to a deeper insight into the nature of magnetism in graphene based system.

Self-similar compression of a magnetized plasma filled liner

International Nuclear Information System (INIS)

Felber, F.S.; Liberman, M.A.; Velikovich, A.L.

1985-01-01

New analytic, one-dimensional, self-similar solutions of magnetohydrodynamic equations describing the compression of a magnetized plasma by a thin cylindrical liner are presented. The solutions include several features that have not been included in an earlier self-similar solution of the equations of ideal magnetohydrodynamics. These features are the effects of finite plasma electrical conductivity, induction heating, thermal conductivity and related thermogalvanomagnetic effects, plasma turbulence, and plasma boundary effects. These solutions have been motivated by recent suggestions for production of ultrahigh magnetic fields by new methods. The methods involve radially imploding plasmas in which axial magnetic fields have been entrained. These methods may be capable of producing controlled magnetic fields up to approx. = 100 MG. Specific methods of implosion suggested were by ablative radial acceleration of a liner by a laser and by a gas-puff Z pinch. The model presented here addresses the first of these methods. The solutions derived here are used to estimate magnetic flux losses out of the compression volume, and to indicate conditions under which an impulsively-accelerated, plasma-filled liner may compress an axial magnetic field to large magnitude

Dipolar vortex structures in magnetized rotating plasma

International Nuclear Information System (INIS)

Liu Jixing

1990-01-01

Dipolar solitary vortices of both electrostatic and electromagnetic character in low-β, in homogeneous rotating plasma confined in a constant external magnetic field were systematically presented. The main stimulus to this investigation is the expectation to apply this coherent structure as a candidate constituent of plasma turbulance to understand the anomalous transport phenomena in confined plasma. The electrostatic vortices have similar structure and properties as the Rossby vortices in rotating fluids, the electromagnetic vortices obtained here have no analogy in hydrodynamics and hence are intrinsic to magnetized plasma. It is valuably remarked that the intrinsic electromagnetic vortices presented here have no discontinuity of perturbed magnetic field δB and parallel current j(parallel) on the border of vortex core. The existence region of the new type of vortex is found much narrower than the Rossby type one. (M.T.)

Emergent kink stability of a magnetized plasma jet injected into a transverse background magnetic field

Science.gov (United States)

Zhang, Yue; Gilmore, Mark; Hsu, Scott C.; Fisher, Dustin M.; Lynn, Alan G.

2017-11-01

We report experimental results on the injection of a magnetized plasma jet into a transverse background magnetic field in the HelCat linear plasma device at the University of New Mexico [M. Gilmore et al., J. Plasma Phys. 81(1), 345810104 (2015)]. After the plasma jet leaves the plasma-gun muzzle, a tension force arising from an increasing curvature of the background magnetic field induces in the jet a sheared axial-flow gradient above the theoretical kink-stabilization threshold. We observe that this emergent sheared axial flow stabilizes the n = 1 kink mode in the jet, whereas a kink instability is observed in the jet when there is no background magnetic field present.

The role of current sheet formation in driven plasmoid reconnection in laser-produced plasma bubbles

Science.gov (United States)

Lezhnin, Kirill; Fox, William; Bhattacharjee, Amitava

2017-10-01

We conduct a multiparametric study of driven magnetic reconnection relevant to recent experiments on colliding magnetized laser produced plasmas using the PIC code PSC. Varying the background plasma density, plasma resistivity, and plasma bubble geometry, the results demonstrate a variety of reconnection behavior and show the coupling between magnetic reconnection and global fluid evolution of the system. We consider both collision of two radially expanding bubbles where reconnection is driven through an X-point, and collision of two parallel fields where reconnection must be initiated by the tearing instability. Under various conditions, we observe transitions between fast, collisionless reconnection to a Sweet-Parker-like slow reconnection to complete stalling of the reconnection. By varying plasma resistivity, we observe the transition between fast and slow reconnection at Lundquist number S 103 . The transition from plasmoid reconnection to a single X-point reconnection also happens around S 103 . We find that the criterion δ /di < 1 is necessary for fast reconnection onset. Finally, at sufficiently high background density, magnetic reconnection can be suppressed, leading to bouncing motion of the magnetized plasma bubbles.

Progress In Magnetized Target Fusion Driven by Plasma Liners

Science.gov (United States)

Thio, Francis Y. C.; Kirkpatrick, Ronald C.; Knapp, Charles E.; Cassibry, Jason; Eskridge, Richard; Lee, Michael; Smith, James; Martin, Adam; Wu, S. T.; Schmidt, George;

Development of the apparatus for measuring magnetic properties of electrical steel sheets in arbitrary directions under compressive stress normal to their surface

Science.gov (United States)

Maeda, Yoshitaka; Urata, Shinya; Nakai, Hideo; Takeuchi, Yuuya; Yun, Kyyoul; Yanase, Shunji; Okazaki, Yasuo

2017-05-01

In designing motors, one must grasp the magnetic properties of electrical steel sheets considering actual conditions in motors. Especially important is grasping the stress dependence of magnetic power loss. This paper describes a newly developed apparatus to measure two-dimensional (2-D) magnetic properties (properties under the arbitrary alternating and the rotating flux conditions) of electrical steel sheets under compressive stress normal to the sheet surface. The apparatus has a 2-D magnetic excitation circuit to generate magnetic fields in arbitrary directions in the evaluation area. It also has a pressing unit to apply compressive stress normal to the sheet surface. During measurement, it is important to apply uniform stress throughout the evaluation area. Therefore, we have developed a new flux density sensor using needle probe method. It is composed of thin copper foils sputtered on electrical steel sheets. By using this sensor, the stress can be applied to the surface of the specimen without influence of this sensor. This paper described the details of newly developed apparatus with this sensor, and measurement results of iron loss by using are shown.

Periodical plasma structures controlled by external magnetic field

Science.gov (United States)

Schweigert, I. V.; Keidar, M.

2017-11-01

The plasma of Hall thruster type in external magnetic field is studied in 2D3V kinetic simulations using PIC MCC method. The periodical structure with maxima of electron and ion densities is formed and becomes more pronounced with increase of magnetic field incidence angle in the plasma. These ridges of electron and ion densities are aligned with the magnetic field vector and shifted relative each other. This leads to formation of two-dimensional double-layers structure in cylindrical plasma chamber. Depending on Larmor radius and Debye length up to nineteen potential steps appear across the oblique magnetic field. The electrical current gathered on the wall is associated with the electron and ion density ridges.

MHD waveguides in space plasma

International Nuclear Information System (INIS)

Mazur, N. G.; Fedorov, E. N.; Pilipenko, V. A.

2010-01-01

The waveguide properties of two characteristic formations in the Earth's magnetotail-the plasma sheet and the current (neutral) sheet-are considered. The question of how the domains of existence of different types of MHD waveguide modes (fast and slow, body and surface) in the (k, ω) plane and their dispersion properties depend on the waveguide parameters is studied. Investigation of the dispersion relation in a number of particular (limiting) cases makes it possible to obtain a fairly complete qualitative pattern of all the branches of the dispersion curve. Accounting for the finite size of perturbations across the wave propagation direction reveals new additional effects such as a change in the critical waveguide frequencies, the excitation of longitudinal current at the boundaries of the sheets, and a change in the symmetry of the fundamental mode. Knowledge of the waveguide properties of the plasma and current sheets can explain the occurrence of preferred frequencies in the low-frequency fluctuation spectra in the magnetotail. In satellite observations, the type of waveguide mode can be determined from the spectral properties, as well as from the phase relationships between plasma oscillations and magnetic field oscillations that are presented in this paper.

Plasma target output from a magnetically augmented, gas-injected, washer-stack plasma gun

International Nuclear Information System (INIS)

Osher, J.E.

1982-01-01

This article describes a new washer-stack gun design developed for the application of plasma target production for the startup of neutral-beam trapping in a fusion research magnetic confinement system. The gun is a Mo anode type that is D 2 injected and has an auxiliary pulsed magnet for control of plasma-flux mapping. One of the principal features of 2--10-ms duration pulses for gun operation in a suitable magnetic field is the formation of an arc column along magnetic field lines from the gun's central cathode electrode to the vacuum chamber walls (at common anode potential). The primary power output from a 5.0-cm-i.d. gun is typically carried along this arc column by a stream of approximately 2000 A of 50--250-eV electrons. This primary stream of relatively low-density energetic electrons efficiently ionizes the injected gas, forming a quasi-dc source of denser secondary plasma of approx.10 13 /cm 3 at a few eV, which is able to flow or diffuse away along a somewhat larger column of magnetic field lines. In plasma-target production tests on a test stand, a gun operated at a D 2 gas flow of 22 Torr ls -1 yielded 250 A of equivalent plasma flow

Production of a large, quiescent, magnetized plasma

Science.gov (United States)

Landt, D. L.; Ajmera, R. C.

1976-01-01

An experimental device is described which produces a large homogeneous quiescent magnetized plasma. In this device, the plasma is created in an evacuated brass cylinder by ionizing collisions between electrons emitted from a large-diameter electron gun and argon atoms in the chamber. Typical experimentally measured values of the electron temperature and density are presented which were obtained with a glass-insulated planar Langmuir probe. It is noted that the present device facilitates the study of phenomena such as waves and diffusion in magnetized plasmas.

Transport of plasma across a braided magnetic field

International Nuclear Information System (INIS)

Stix, T.H.

1976-10-01

Transport rates are calculated for a plasma immersed in a region through which magnetic lines of force meander in a stochastic fashion and in which the magnetic surfaces are destroyed. Such a magnetic condition, termed magnetic braiding, may be brought about by asymmetric magnetic perturbations, perhaps quite weak, which typically produce overlap of two sets of magnetic islands. Plasma transport is calculated for this environment, using both a fluid and a kinetic drift model. The latter gives an appreciably higher rate, namely, a fast-particle diffusion coefficient equal to ( 1 / 2 )D/sub M/ [absolute value of v/sub ''/], where D/sub M/ is the coefficient of spatial diffusion for the magnetic lines of force. Correction terms, due to polarization-associated E/sub ''/ fields, are small unless components of the braiding field resonate with ion-acoustic or drift waves. Insertion of a Bhatnager--Gross--Krook collision term shows the diffusion rate is unaffected by weak collisions. Diffusion due to magnetic braiding is of interest for tokamaks, particularly with respect to enhanced electron heat transport, enhanced current penetration, plasma disruption, and internal sawtooth oscillations

Electro-Magnetic Fields and Plasma in the Cosmos

International Nuclear Information System (INIS)

Scott, Donald E.

2006-01-01

It is becoming widely recognized that a majority of baryons in the cosmos are in the plasma state. But, fundamental disagreements about the properties and behavior of electro-magnetic fields in these plasmas exist between the science of modern astronomy and the experimentally verified laws of electrical engineering and physics. Some astronomers claim that magnetic fields can be open-ended - that they begin on or beneath the Sun's surface and extend outward to infinity. Astrophysicists have claimed that galactic magnetic fields begin and end on molecular clouds. Electrical engineers, most physicists, and the pioneers in electromagnetic field theory disagree - magnetic fields have no beginning or end. Since these two viewpoints are mutually exclusive, both cannot be correct; one must be completely false. Many astrophysicists claim that magnetic fields are 'frozen into' electric plasma. We also examine the basis for this claim. It has been shown to be incorrect in the laboratory. The hypothetical 'magnetic merging' mechanism is also reviewed in light of both theoretical and experimental investigations. The cause of large-scale filamentation in the cosmos is also simply revealed by experimental results obtained in plasma laboratories

Neutrino (antineutrino) effective charge in a magnetized electron-positron plasma

International Nuclear Information System (INIS)

Serbeto, A.; Rios, L.A.; Mendonca, J.T.; Shukla, P.K.

2004-01-01

Using dynamical techniques of the plasma physics, the neutrino (antineutrino) effective charge in a magnetized dense electron-positron plasma is determined here. It shown that its value, which is determined by the plasma collective processes, depends mainly on the propagation direction of plasma waves and neutrinos against the external magnetic field direction. The direction dependence of the effective charge occurs due to the fact that the magnetic field breaks the plasma isotropy. The present theory gives a unified picture of the problem which is valid for an external magnetic field below the Landau-Schwinger critical value. Comparison with some of the results from the quantum field theory has been made

Magnetic Probe to Study Plasma Jets for Magneto-Inertial Fusion

Energy Technology Data Exchange (ETDEWEB)

Martens, Daniel [Los Alamos National Laboratory; Hsu, Scott C. [Los Alamos National Laboratory

2012-08-16

A probe has been constructed to measure the magnetic field of a plasma jet generated by a pulsed plasma rail-gun. The probe consists of two sets of three orthogonally-oriented commercial chip inductors to measure the three-dimensional magnetic field vector at two separate positions in order to give information about the magnetic field evolution within the jet. The strength and evolution of the magnetic field is one of many factors important in evaluating the use of supersonic plasma jets for forming imploding spherical plasma liners as a standoff driver for magneto-inertial fusion.

Temporally asymmetric laser pulse for magnetic-field generation in plasmas

Energy Technology Data Exchange (ETDEWEB)

Singh, Mamta; Gopal, Krishna; Gupta, Devki Nandan, E-mail: dngupta@physics.du.ac.in

2016-04-01

Of particular interest in this article, the case study of an asymmetric laser pulse interaction with a plasma for magnetic field enhancement has been investigated. The strong ponderomotive force due to the short leading edge of the propagating laser pulse drives a large nonlinear current, producing a stronger quasistatic magnetic field. An analytical expression for the magnetic field is derived and the strength of the magnetic field is estimated for the current laser-plasma parameters. The theoretical results are validated through the particle-in-cell (PIC) simulations and are in very close agreement with the simulation based estimations. This kind of magnetic field can be useful in the plasma based accelerators as well as in the laser-fusion based experiments. - Highlights: • We employ an asymmetric laser pulse to enhance the magnetic field strength in a plasma. • Short leading front of the pulse drives a strong ponderomotive force. • An analytical expression for the magnetic field is derived. • The strength of the magnetic field is estimated for the current laser–plasma parameters.

Temporally asymmetric laser pulse for magnetic-field generation in plasmas

International Nuclear Information System (INIS)

Singh, Mamta; Gopal, Krishna; Gupta, Devki Nandan

2016-01-01

Of particular interest in this article, the case study of an asymmetric laser pulse interaction with a plasma for magnetic field enhancement has been investigated. The strong ponderomotive force due to the short leading edge of the propagating laser pulse drives a large nonlinear current, producing a stronger quasistatic magnetic field. An analytical expression for the magnetic field is derived and the strength of the magnetic field is estimated for the current laser-plasma parameters. The theoretical results are validated through the particle-in-cell (PIC) simulations and are in very close agreement with the simulation based estimations. This kind of magnetic field can be useful in the plasma based accelerators as well as in the laser-fusion based experiments. - Highlights: • We employ an asymmetric laser pulse to enhance the magnetic field strength in a plasma. • Short leading front of the pulse drives a strong ponderomotive force. • An analytical expression for the magnetic field is derived. • The strength of the magnetic field is estimated for the current laser–plasma parameters.

Magnetic monopole plasma oscillations and the survival of Galactic magnetic fields

International Nuclear Information System (INIS)

Parker, E.N.

1987-01-01

This paper explores the general nature of magnetic-monopole plasma oscillations as a theoretical possibility for the observed Galactic magnetic field in the presence of a high abundance of magnetic monopoles. The modification of the hydromagnetic induction equation by the monopole oscillations produces the half-velocity effect, in which the magnetic field is transported bodily with a velocity midway between the motion of the conducting fluid and the monopole plasma. Observational studies of the magnetic field in the Galaxy, and in other galaxies, exclude the half-velocity effect, indicating that the magnetic fields is not associated with monopole oscillations. In any case the phase mixing would destroy the oscillations in less than 100 Myr. The conclusion is that magnetic monopole oscillations do not play a significant role in the galactic magnetic fields. Hence the existence of galactic magnetic fields places a low limit on the monopole flux, so that their detection - if they exist at all - requires a collecting area at least as large as a football field. 47 references

Formation of magnetized plasma stream in the CTCC-I experiment

Energy Technology Data Exchange (ETDEWEB)

Ikegami, K.; Ozaki, A.; Uyama, T.; Satomi, N.; Watenabe, K. (Osaka Univ., Suita (Japan). Faculty of Engineering)

1981-10-01

Magnetized plasma stream with the kinetic energy of more than 500 eV was produced successfully using a coaxial plasma gun with the subsidiary coils for providing the radial magnetic field at its muzzle. It was injected into the drift tube and the characteristics were investigated experimentally using the streak photographs, magnetic probes and flux loops. It was confirmed that this plasma stream had really both toroidal and poloidal magnetic fields.

Magnetic tearing in plasma focus

International Nuclear Information System (INIS)

Sharkawy, W.

1994-01-01

A plasma focus device used is Mather type filled with hydrogen gas at pressure between 0.1 and 1 torr. When connected to a large capacitor ≤10 KV a discharge is started with peak current 100 KA. Under the influence of the radial electric field E r , due to the potential between electrodes, and B φ the plasma will drift in the axial direction with velocity cE r /B φ . An induced axial magnetic field B z has been detected which due to sheath velocity. A propagation of magnetosonic wave has been observed with velocity ≅10 3 m sec -1 . Such a wave might be excited when the magnetic pressure is much greater than the plasma kinetic pressure B 2 /8π>nKT. Assuming (MHD) to be stable, Tearing model was driven which generally has smaller growth rates than (MHD) modes. Using the designed theoretical model and the plasma parameters the electron energy dΦ/dt=Ba 2 /τ R was calculated to be 2.22 KeV, which is comparable with that detected from X-ray measurements. (author)

Nernst Effect in Magnetized Plasmas

OpenAIRE

Joglekar, Archis S.; Thomas, Alexander G. R.; Ridgers, Christopher P.; Kingham, Robert J.

2015-01-01

We present nanosecond timescale Vlasov-Fokker-Planck-Maxwell modeling of magnetized plasma transport and dynamics in a hohlraum with an applied external magnetic field, under conditions similar to recent experiments. Self-consistent modeling of the kinetic electron momentum equation allows for a complete treatment of the heat flow equation and Ohm's Law, including Nernst advection of magnetic fields. In addition to showing the prevalence of non-local behavior, we demonstrate that effects such...

Magnetic Properties and Structure of Non-Oriented Electrical Steel Sheets after Different Shape Processing

Czech Academy of Sciences Publication Activity Database

Bulín, Tomáš; Švábenská, Eva; Hapla, Miroslav; Ondrůšek, Č.; Schneeweiss, Oldřich

2017-01-01

Roč. 131, č. 4 (2017), s. 819-821 ISSN 0587-4246. [CSMAG 2016 - Czech and Slovak Conference on Magnetism /16./. Košice, 13.06.2016-17.06.2016] R&D Projects: GA TA ČR(CZ) TE02000232 Institutional support: RVO:68081723 Keywords : Magnetic properties * Silicon steel * Steel sheet Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 0.469, year: 2016

Interaction of counter-streaming plasma flows in dipole magnetic field

OpenAIRE

Shaikhislamov, I F; Posukh, V G; Melekhov, A V; Prokopov, P A; Boyarintsev, E L; Zakharov, Yu P; Ponomarenko, A G

2017-01-01

Transient interaction of counter-streaming super-sonic plasma flows in dipole magnetic dipole is studied in laboratory experiment. First quasi-stationary flow is produced by teta-pinch and forms a magnetosphere around the magnetic dipole while laser beams focused at the surface of the dipole cover launch second explosive plasma expanding from inner dipole region outward. Laser plasma is energetic enough to disrupt magnetic field and to sweep through the background plasma for large distances. ...

Transient and intermittent magnetic reconnections in TS-3/UTST merging startup experiments

International Nuclear Information System (INIS)

Ono, Y.; Imazawa, R.; Imanaka, H.; Hayamizu, T.; Inomoto, M.; Sato, M.; Kawamori, E.; Ejiri, A.; Takase, Y.; Asai, T.; Takahashi, T.

2007-01-01

The high-power reconnection heating has been developed in the TS-3 merging experiments, leading us to a new pulsed high-beta spherical tokamak (ST) formation. Two ST plasmas were produced inductively by two or four PF coils without using any central solenoid (CS) coil and were merged together for MW-GW reconnection heating. The magnetic reconnection transformed the magnetic energy of reconnecting magnetic field through the outflow kinetic energy finally to the ion thermal energy, increasing the plasma beta of ST up to 0.5. A new finding is that ejection of current sheet (or plasmoid) causes high-speed merging/ reconnection as well as high-power heating. In the high-q ST merging, the sheet resistivity was almost classical due to the sheet thickness much longer than ion gyroradius. Large inflow flux and low current-sheet dissipation resulted in flux pileup followed by rapid growth of the current sheet. When the flux pileup exceeded a critical limit, the sheet was ejected mechanically from the squeezed X-point area. The reconnection (outflow) speed was slow during the flux pileup and was fast during the ejection, indicating that intermittent reconnection similar to the solar flare increased the averaged reconnection speed. These transient effects enable us to have the fast reconnection as well as the high-power reconnection heating, even if the merging high-q tokamaks have low current-sheet resistivity. (author)

Local thermodynamics of a magnetized, anisotropic plasma

International Nuclear Information System (INIS)

Hazeltine, R. D.; Mahajan, S. M.; Morrison, P. J.

2013-01-01

An expression for the internal energy of a fluid element in a weakly coupled, magnetized, anisotropic plasma is derived from first principles. The result is a function of entropy, particle density and magnetic field, and as such plays the role of a thermodynamic potential: it determines in principle all thermodynamic properties of the fluid element. In particular it provides equations of state for the magnetized plasma. The derivation uses familiar fluid equations, a few elements of kinetic theory, the MHD version of Faraday's law, and certain familiar stability and regularity conditions.

Formation of magnetized plasma stream in the CTCC-I experiment

International Nuclear Information System (INIS)

Ikegami, Kazunori; Ozaki, Atsuhiko; Uyama, Tadao; Satomi, Norio; Watanabe, Kenji

1981-01-01

Magnetized plasma stream with the kinetic energy of more than 500 eV was produced successfully using a coaxial plasma gun with the subsidiary coils for providing the radial magnetic field at its muzzle. It was injected into the drift tube and the characteristics were investigated experimentally using the streak photographs, magnetic probes and flux loops. It was confirmed that this plasma stream had really both toroidal and poloidal magnetic fields. (author)

Nonlinear Electrostatic Wave Equations for Magnetized Plasmas

DEFF Research Database (Denmark)

Dysthe, K.B.; Mjølhus, E.; Pécseli, Hans

1984-01-01

The lowest order kinetic effects are included in the equations for nonlinear electrostatic electron waves in a magnetized plasma. The modifications of the authors' previous analysis based on a fluid model are discussed.......The lowest order kinetic effects are included in the equations for nonlinear electrostatic electron waves in a magnetized plasma. The modifications of the authors' previous analysis based on a fluid model are discussed....

Current Sheets in Pulsar Magnetospheres and Winds: Particle Acceleration and Pulsed Gamma Ray Emission

Science.gov (United States)

Arons, Jonathan

The research proposed addresses understanding of the origin of non-thermal energy in the Universe, a subject beginning with the discovery of Cosmic Rays and continues, including the study of relativistic compact objects - neutron stars and black holes. Observed Rotation Powered Pulsars (RPPs) have rotational energy loss implying they have TeraGauss magnetic fields and electric potentials as large as 40 PetaVolts. The rotational energy lost is reprocessed into particles which manifest themselves in high energy gamma ray photon emission (GeV to TeV). Observations of pulsars from the FERMI Gamma Ray Observatory, launched into orbit in 2008, have revealed 130 of these stars (and still counting), thus demonstrating the presence of efficient cosmic accelerators within the strongly magnetized regions surrounding the rotating neutron stars. Understanding the physics of these and other Cosmic Accelerators is a major goal of astrophysical research. A new model for particle acceleration in the current sheets separating the closed and open field line regions of pulsars' magnetospheres, and separating regions of opposite magnetization in the relativistic winds emerging from those magnetopsheres, will be developed. The currents established in recent global models of the magnetosphere will be used as input to a magnetic field aligned acceleration model that takes account of the current carrying particles' inertia, generalizing models of the terrestrial aurora to the relativistic regime. The results will be applied to the spectacular new results from the FERMI gamma ray observatory on gamma ray pulsars, to probe the physics of the generation of the relativistic wind that carries rotational energy away from the compact stars, illuminating the whole problem of how compact objects can energize their surroundings. The work to be performed if this proposal is funded involves extending and developing concepts from plasma physics on dissipation of magnetic energy in thin sheets of

Development of the apparatus for measuring magnetic properties of electrical steel sheets in arbitrary directions under compressive stress normal to their surface

Directory of Open Access Journals (Sweden)

Yoshitaka Maeda

2017-05-01

Full Text Available In designing motors, one must grasp the magnetic properties of electrical steel sheets considering actual conditions in motors. Especially important is grasping the stress dependence of magnetic power loss. This paper describes a newly developed apparatus to measure two-dimensional (2-D magnetic properties (properties under the arbitrary alternating and the rotating flux conditions of electrical steel sheets under compressive stress normal to the sheet surface. The apparatus has a 2-D magnetic excitation circuit to generate magnetic fields in arbitrary directions in the evaluation area. It also has a pressing unit to apply compressive stress normal to the sheet surface. During measurement, it is important to apply uniform stress throughout the evaluation area. Therefore, we have developed a new flux density sensor using needle probe method. It is composed of thin copper foils sputtered on electrical steel sheets. By using this sensor, the stress can be applied to the surface of the specimen without influence of this sensor. This paper described the details of newly developed apparatus with this sensor, and measurement results of iron loss by using are shown.

Magnetic Field Analysis of Plasma Guide in Galathea Trimyx

Directory of Open Access Journals (Sweden)

Jin Xianji

2016-01-01

Full Text Available You Galathea Trimyx is a kind of small size, multipole magnetic confinement devices in controlled thermonuclear fusion. Plasma guide is one of important part in Galathea Trimyx which is responsible for transporting fast and slow plasma bunches ejected from plasma gun. The distribution and uniformity of magnetic field in completed plasma guide is analyzed in detail, including in x -axis direction and in z-axis direction. On the basis, the motion of plasma in the guide is discussed.

Relativistic degenerate electron plasma in an intense magnetic field

International Nuclear Information System (INIS)

Delsante, A.E.; Frankel, N.E.

1978-01-01

The dielectric response function for a dense, ultra-degenerate relativistic electron plasma in an intense uniform magnetic field is presented. Dispersion relations for plasma oscillations parallel and perpendicular to the magnetic field are obtained

SO-FDTD analysis of anisotropic magnetized plasma

International Nuclear Information System (INIS)

Yang Hongwei; Nanjing Univ. of Science and Technology, Nanjing; Yuan Hong; Chen Rushan; Yang Yang

2007-01-01

A novel finite-difference time-domain (FDTD) method, called shift operator FDTD (SO-FDTD) method is developed for anisotropic magnetized dispersive media. The recursive relation between operators is used. In this paper, some expressions containing the dielectric constants of magnetized dispersive media are written as rational polynomial function. The SO-FDTD formulation for anisotropic magnetized plasma is derived. The high efficiency and effectiveness of the method are confirmed by computing the reflection and transmission through a magnetized plasma layer, with the direction of the propagation parallel to the direction of the biasing field. A comparison with frequency domain analytic results is included. The CPU time was several times shorter than that of the JEC method. (authors)

Solar wind and substorm excitation of the wavy current sheet

Directory of Open Access Journals (Sweden)

C. Forsyth

2009-06-01

Full Text Available Following a solar wind pressure pulse on 3 August 2001, GOES 8, GOES 10, Cluster and Polar observed dipolarizations of the magnetic field, accompanied by an eastward expansion of the aurora observed by IMAGE, indicating the occurrence of two substorms. Prior to the first substorm, the motion of the plasma sheet with respect to Cluster was in the ZGSM direction. Observations following the substorms show the occurrence of current sheet waves moving predominantly in the −YGSM direction. Following the second substorm, the current sheet waves caused multiple current sheet crossings of the Cluster spacecraft, previously studied by Zhang et al. (2002. We further this study to show that the velocity of the current sheet waves was similar to the expansion velocity of the substorm aurora and the expansion of the dipolarization regions in the magnetotail. Furthermore, we compare these results with the current sheet wave models of Golovchanskaya and Maltsev (2005 and Erkaev et al. (2008. We find that the Erkaev et al. (2008 model gives the best fit to the observations.

Observations of dusty plasmas with magnetized dust grains

Science.gov (United States)

Luo, Q.-Z.; D'Angelo, N.

2000-11-01

We report a newly observed phenomenon in a dusty plasma device of the \\mbox{Q-machine} type. At low plasma densities the time required by the plasma to return to its no-dust conditions, after the dust dispenser is turned off, can be as long as many tens of seconds or longer. A tentative interpretation of this observation in terms of magnetized dust grains is advanced. It appears that an important loss mechanism of fine dust grains is by ion drag along the magnetic field lines. The effect of ion drag is somewhat counteracted by the -µ∇B force present when the magnetic field has a mirror geometry.

Toward laboratory torsional spine magnetic reconnection

Science.gov (United States)

Chesny, David L.; Orange, N. Brice; Oluseyi, Hakeem M.; Valletta, David R.

2017-12-01

Magnetic reconnection is a fundamental energy conversion mechanism in nature. Major attempts to study this process in controlled settings on Earth have largely been limited to reproducing approximately two-dimensional (2-D) reconnection dynamics. Other experiments describing reconnection near three-dimensional null points are non-driven, and do not induce any of the 3-D modes of spine fan, torsional fan or torsional spine reconnection. In order to study these important 3-D modes observed in astrophysical plasmas (e.g. the solar atmosphere), laboratory set-ups must be designed to induce driven reconnection about an isolated magnetic null point. As such, we consider the limited range of fundamental resistive magnetohydrodynamic (MHD) and kinetic parameters of dynamic laboratory plasmas that are necessary to induce the torsional spine reconnection (TSR) mode characterized by a driven rotational slippage of field lines - a feature that has yet to be achieved in operational laboratory magnetic reconnection experiments. Leveraging existing reconnection models, we show that within a 3$ apparatus, TSR can be achieved in dense plasma regimes ( 24~\\text{m}-3$ ) in magnetic fields of -1~\\text{T}$ . We find that MHD and kinetic parameters predict reconnection in thin current sheets on time scales of . While these plasma regimes may not explicitly replicate the plasma parameters of observed astrophysical phenomena, studying the dynamics of the TSR mode within achievable set-ups signifies an important step in understanding the fundamentals of driven 3-D magnetic reconnection and the self-organization of current sheets. Explicit control of this reconnection mode may have implications for understanding particle acceleration in astrophysical environments, and may even have practical applications to fields such as spacecraft propulsion.

Langmuir probe characteristic in a current - carrying magnetized plasma

International Nuclear Information System (INIS)

Stanojevic, M.; Cercek, M.; Gyergyek, T.

1995-01-01

Experimental investigation of the Langmuir probe characteristic is a magnetized plasma with an electron current along the magnetic field direction shows that the standard procedure for determination of the electron temperature and plasma density, which is applicable in a current - free magnetized plasma, gives erroneous results for these plasma parameters. However, more precise values of the plasma parameters can be calculated from the ion saturation currents and electron temperatures obtained with that procedure for two opposite orientations of the one - sided planar probe collecting surface with respect to the direction of the electron drift. With the existing theoretical models only the order of magnitude of the electron drift velocity can be accurately determined from the measured electron saturation currents for the two probe orientations. (author)

Apparatus for magnetic and electrostatic confinement of plasma

Science.gov (United States)

Rostoker, Norman; Binderbauer, Michl

2013-06-11

An apparatus and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions ions are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.

Relaxed plasmas in external magnetic fields

International Nuclear Information System (INIS)

Spies, G.O.; Li, J.

1991-08-01

The well-known theory of relaxed plasmas (Taylor states) is extended to external magnetic fields whose field lines intersect the conducting toroidal boundary. Application to an axially symmetric, large-aspect-ratio torus with circular cross section shows that the maximum pinch ratio, and hence the phenomenon of current saturation, is independent of the external field. The relaxed state is explicitly given for an external octupole field. In this case, field reversal is inhibited near parts of the boundary if the octupole generates magnetic x-points within the plasma. (orig.)

INDUCTION HEATING OF NON-MAGNETIC SHEET METALS IN THE FIELD OF A FLAT CIRCULAR MULTITURN SOLENOID

Directory of Open Access Journals (Sweden)

Y. Batygin

2016-06-01

Full Text Available The theoretical analysis of electromagnetic processes in the system for induction heating presented by a flat circular multiturn solenoid positioned above a plane of thin sheet non-magnetic metal has been conducted. The calculated dependences for the current induced in a metal sheet blank and ratio of transformation determined have been obtained. The maximal value of the transformation ratio with regard to spreading the eddy-currents over the whole area of the sheet metal has been determined.

Parametric instabilities in magnetized bi-ion and dusty plasmas

Indian Academy of Sciences (India)

-ion or dusty plasma with parametric pumping of the magnetic field is analysed. The equation of motion governing the perturbed plasma is derived and parametrically excited transverse modes propagating along the magnetic field are found.

Predicting Pulsar Scintillation from Refractive Plasma Sheets

Science.gov (United States)

Simard, Dana; Pen, Ue-Li

2018-05-01

The dynamic and secondary spectra of many pulsars show evidence for long-lived, aligned images of the pulsar that are stationary on a thin scattering sheet. One explanation for this phenomenon considers the effects of wave crests along sheets in the ionized interstellar medium, such as those due to Alfvén waves propagating along current sheets. If these sheets are closely aligned to our line-of-sight to the pulsar, high bending angles arise at the wave crests and a selection effect causes alignment of images produced at different crests, similar to grazing reflection off of a lake. Using geometric optics, we develop a simple parameterized model of these corrugated sheets that can be constrained with a single observation and that makes observable predictions for variations in the scintillation of the pulsar over time and frequency. This model reveals qualitative differences between lensing from overdense and underdense corrugated sheets: Only if the sheet is overdense compared to the surrounding interstellar medium can the lensed images be brighter than the line-of-sight image to the pulsar, and the faint lensed images are closer to the pulsar at higher frequencies if the sheet is underdense, but at lower frequencies if the sheet is overdense.

Nonlinear electron transport in magnetized laser plasmas

International Nuclear Information System (INIS)

Kho, T.H.; Haines, M.G.

1986-01-01

Electron transport in a magnetized plasma heated by inverse bremsstrahlung is studied numerically using a nonlinear Fokker--Planck model with self-consistent E and B fields. The numerical scheme is described. Nonlocal transport is found to alter many of the transport coefficients derived from linear transport theory, in particular, the Nernst and Righi--Leduc effects, in addition to the perpendicular heat flux q/sub perpendicular/, are substantially reduced near critical surface. The magnetic field, however, remains strongly coupled to the nonlinear q/sub perpendicular/ and, as has been found in hydrosimulations, convective amplification of the magnetic field occurs in the overdense plasma

Three-dimensional simulation study of compact toroid injection into magnetized plasmas

International Nuclear Information System (INIS)

Yoshio Suzuki; Tomohiko Watanabe; Tetsuya Sato; Takaya Hayashi

1999-01-01

Three-dimensional dynamics of a compact toroid (CT), which is injected into a magnetized target plasma modeling a part of a fusion device is investigated by using magnetohydrodynamic numerical simulations. It is found that the injected CT penetrates into the device region, suffering from a tilting instability. In this process, magnetic reconnection between the CT magnetic field and the device magnetic field takes place, which disrupts the magnetic configuration of the CT. As a result, the high density plasma confined in the CT magnetic field is locally supplied in the device region. Furthermore, the authors examine the penetration depth of the CT high density plasma. And it is revealed that the CT high density plasma is decelerated by the device magnetic field through the compressional heating

Low energy plasma observations at synchronous orbit

International Nuclear Information System (INIS)

Reasoner, D.L.; Lennartsson, W.

1977-08-01

The University of California at San Diego Auroral Particles Experiment on the ATS-6 Satellite in synchronous orbit has detected a low-energy plasma population which is separate and distinct from both the ring current and plasma sheet populations. These observations suggest that this plasma is the outer zone of the plasmasphere. During magnetically active periods, this low energy plasma is often observed flowing sunward. In the dusk sector, enhanced plasma flow is often observed for 1-2 hours prior to the onset of a substorm-associated particle injection. (author)

Effects of a nonuniform open magnetic field on the plasma presheath

International Nuclear Information System (INIS)

Sato, Kunihiro; Miyawaki, Fujio

1991-01-01

Effects of a nonuniform magnetic field on the plasma presheath is numerically investigated using the plasma equation for a collisionless plasma with a finite-temperature particle source. The present calculation confirms that analytical solutions previously published by the authors are available over a wide range of mirror ratio. Potential drop in the presheath, which considerably depends on both the magnetic strength profile and the spatial distribution of the particle source, is remarkably increased by applying an expanding magnetic field when plasma particles are generated in the inner part of the plasma. An effect of a nonuniform magnetic field on sheath formation is also discussed by using the calculated ion distribution function. If the plasma equation has no singularity at the sheath edge, its solution satisfies the generalized Bohm criterion with the inequality sign in the expanding magnetic field. (author)

Reduced energy conservation law for magnetized plasma

International Nuclear Information System (INIS)

Sosenko, P.P.; Decyk, V.K.

1994-01-01

A global energy conservation law for a magnetized plasma is studied within the context of a quasiparticle description. A reduced energy conservation law is derived for low-frequency, as compared to the gyromagnetic frequency, plasma motions with regard to both non-uniform mean flows and fluctuations in the plasma. The mean value of plasma energy is calculated and sufficient stability conditions for non-equilibrium plasmas are derived. (orig.)

PHYSICAL BASES OF SYSTEMS CREATION FOR MAGNETIC-IMPULSIVE ATTRACTION OF THIN-WALLED SHEET METALS

Directory of Open Access Journals (Sweden)

Y. Batygin

2009-01-01

Full Text Available The work is dedicated to the physical base of systems creating for the thin-walled sheet metals magnetic pulse attraction. Some practical realization models of the author’s suggestions are represented.

Three dimensional simulation study of spheromak injection into magnetized plasmas

International Nuclear Information System (INIS)

Suzuki, Y.; Watanabe, T.H.; Sato, T.; Hayashi, T.

2000-01-01

The three dimensional dynamics of a spheromak-like compact toroid (SCT) plasmoid, which is injected into a magnetized target plasma region, is investigated by using MHD numerical simulations. It is found that the process of SCT penetration into this region is much more complicated than that which has been analysed so far by using a conducting sphere (CS) model. The injected SCT suffers from a tilting instability, which grows with a similar timescale to that of the SCT penetration. The instability is accompanied by magnetic reconnection between the SCT magnetic field and the target magnetic field, which disrupts the magnetic configuration of the SCT. Magnetic reconnection plays a role in supplying the high density plasma, initially confined in the SCT magnetic field, to the target region. The penetration depth of the SCT high density plasma is also examined. It is shown to be shorter than that estimated from the CS model. The SCT high density plasma is decelerated mainly by the Lorentz force of the target magnetic field, which includes not only the magnetic pressure force but also the magnetic tension force. Furthermore, by comparing the SCT plasmoid injection with the bare plasmoid injection, magnetic reconnection is considered to relax the magnetic tension force, i.e. the deceleration of the SCT plasmoid. (author)

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.

Growth of carbon fibres, sheets and tubes on diamond films under high power plasma etching conditions

Energy Technology Data Exchange (ETDEWEB)

Villalpando, I. [Centro de Investigacion de los Recursos Naturales, Antigua Normal Rural, Salaices, Lopez, Chihuahua (Mexico); John, P.; Wilson, J. I. B., E-mail: isaelav@hotmail.com [School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh, EH14-4AS (United Kingdom)

2017-11-01

The application of diamond as a plasma facing material for fusion reactors can be limited by unknown reactions between diamond and the chamber materials transported by the plasma. Transformation of diamond to other structures can cause problems such as contamination of the plasma with loose particles or retention of gases. We have seen that diamond thin films are eroded under hydrogen plasma etching, but if silicon is present the growth of various carbon structures on diamond films is observed. We have produced carbon with different morphologies on diamond films including fibres, sheets with flower-like shapes and tubes and proposed growth mechanisms based on the results of scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Sample surfaces contain silicon and are oxidised having COO and CO groups as seen by XP S analysis. Raman analyses revealed a spectrum typical for graphite combined with that from diamond that remains on the surface after hydrogen bombardment. The results of this sturdy show the experimental conditions in which carbon fibres, sheets and tubes are produced under high-power hydrogen etching of diamond films and open the possibility to other applications such as catalysts, sensors and the production of electrodes. (Author)

Growth of carbon fibres, sheets and tubes on diamond films under high power plasma etching conditions

International Nuclear Information System (INIS)

Villalpando, I.; John, P.; Wilson, J. I. B.

2017-01-01

The application of diamond as a plasma facing material for fusion reactors can be limited by unknown reactions between diamond and the chamber materials transported by the plasma. Transformation of diamond to other structures can cause problems such as contamination of the plasma with loose particles or retention of gases. We have seen that diamond thin films are eroded under hydrogen plasma etching, but if silicon is present the growth of various carbon structures on diamond films is observed. We have produced carbon with different morphologies on diamond films including fibres, sheets with flower-like shapes and tubes and proposed growth mechanisms based on the results of scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Sample surfaces contain silicon and are oxidised having COO and CO groups as seen by XP S analysis. Raman analyses revealed a spectrum typical for graphite combined with that from diamond that remains on the surface after hydrogen bombardment. The results of this sturdy show the experimental conditions in which carbon fibres, sheets and tubes are produced under high-power hydrogen etching of diamond films and open the possibility to other applications such as catalysts, sensors and the production of electrodes. (Author)

Dynamics of a rarefied plasma in a magnetic field

Energy Technology Data Exchange (ETDEWEB)

Sagdeyev, R S; Kadomtsev, B B; Rudakov, L I; Vedyonov, A A

1958-07-01

The nature of the motion and properties of high temperature plasma in a magnetic field is of particular interest for the problem of producing controlled thermonuclear reactions. The most general theoretical approach to such problems lies in the description of the plasma by the Boltzmann and Maxwell equations that connect the self-consistent electric and magnetic fields with the ion and electron distribution functions. The exact equations for the motion of plasma in an electromagnetic field can only be solved in certain simple cases especially because the fields are influenced by the collective motion of all the particles. For a certain class of problems it is possible to work out a procedure for decreasing the number of variables and thus simplify the characteristic equations. In this work the following cases are considered and equations derived: equations for the macroscopic motion of the plasma; hydrodynamics of a low pressure plasma; instability of plasma in a magnetic field with an anisotropic ion velocity distribution; stability of a pinched cylindrical plasma using the kinetic equation; non-linear one-dimensional motion of a rarefied plasma.

Magnetic confinement of laser produced LiH plasma in LITE

International Nuclear Information System (INIS)

Ard, W.B.; Stufflebeam, J.H.; Tomlinson, R.G.

1976-01-01

In the LITE experiment, a hot, dense plasma produced by laser heating of an approximately 100 μ dia LiH particle is used to fill a minimum-B baseball coil mirror magnetic containment field. The confined laser produced plasma subsequently serves as the target for an energetic neutral hydrogen beam in experiments to investigate the target plasma buildup approach for creating and sustaining an equilibrium, steady state mirror fusion plasma. In the experiments, the LiH particle is positioned in vacuum at the laser beam focus by a feedback particle suspension system and heated by two sided irradiation with the focused dual beam, 50 j, 7 nsec output of a Q-switched Nd-glass laser. The energy density of the laser produced plasma is initially much greater than that of the surrounding magnetic field and the plasma expands, converting its internal energy into expansion kinetic energy and displacement of the magnetic field. As the energy density falls below that of the magnetic field, the expansion is stopped and the plasma becomes trapped, making the transition to a low beta, mirror confined plasma. This report is concerned with the properties and behavior of the plasma in the confinement stage

Dual-function magnetic structure for toroidal plasma devices

International Nuclear Information System (INIS)

Brown, R.L.

1978-01-01

This invention relates to a support system wherein the iron core and yoke of the plasma current system of a tokamak plasma containment device is redesigned to support the forces of the magnet coils. The containment rings, which occupy very valuable space around the magnet coils, are utilized to serve as yokes for the core such that the conventional yoke is eliminated. The overall result is an improved aspect ratio, reduction in structure, smaller overall size, and improved access to the plasma ring

Plasma flow in a curved magnetic field

International Nuclear Information System (INIS)

Lindberg, L.

1977-09-01

A beam of collisionless plasma is injected along a longitudinal magnetic field into a region of curved magnetic field. Two unpredicted phenomena are observed: The beam becomes deflected in the direction opposite to that in which the field is curved, and it contracts to a flat slab in the plane of curvature of the magnetic field. The phenomenon is of a general character and can be expected to occur in a very wide range of densities. The lower density limit is set by the condition for self-polarization, nm sub(i)/epsilon 0 B 2 >> 1 or, which is equivalent, c 2 /v 2 sub(A) >> 1, where c is the velocity of light, and v sup(A) the Alfven velocity. The upper limit is presumably set by the requirement ωsub(e)tau(e) >> 1. The phenomenon is likely to be of importance e.g. for injection of plasma into magnetic bottles and in space and solar physics. The paper illustrates the comlexity of plasma flow phenomena and the importance of close contact between experimental and theoretical work. (author)

Numerical Simulation on a Possible Formation Mechanism of Interplanetary Magnetic Cloud Boundaries

Science.gov (United States)

Fan, Quan-Lin; Wei, Feng-Si; Feng, Xue-Shang

2003-08-01

The formation mechanism of the interplanetary magnetic cloud (MC) boundaries is numerically investigated by simulating the interactions between an MC of some initial momentum and a local interplanetary current sheet. The compressible 2.5D MHD equations are solved. Results show that the magnetic reconnection process is a possible formation mechanism when an MC interacts with a surrounding current sheet. A number of interesting features are found. For instance, the front boundary of the MCs is a magnetic reconnection boundary that could be caused by a driven reconnection ahead of the cloud, and the tail boundary might be caused by the driving of the entrained flow as a result of the Bernoulli principle. Analysis of the magnetic field and plasma data demonstrates that at these two boundaries appear large value of the plasma parameter β, clear increase of plasma temperature and density, distinct decrease of magnetic magnitude, and a transition of magnetic field direction of about 180 degrees. The outcome of the present simulation agrees qualitatively with the observational results on MC boundary inferred from IMP-8, etc. The project supported by National Natural Science Foundation of China under Grant Nos. 40104006, 49925412, and 49990450

Properties of plasma sheath with ion temperature in magnetic fusion devices

International Nuclear Information System (INIS)

Liu Jinyuan; Wang Feng; Sun Jizhong

2011-01-01

The plasma sheath properties in a strong magnetic field are investigated in this work using a steady state two-fluid model. The motion of ions is affected heavily by the strong magnetic field in fusion devices; meanwhile, the effect of ion temperature cannot be neglected for the plasma in such devices. A criterion for the plasma sheath in a strong magnetic field, which differs from the well-known Bohm criterion for low temperature plasma sheath, is established theoretically with a fluid model. The fluid model is then solved numerically to obtain detailed sheath information under different ion temperatures, plasma densities, and magnetic field strengths.

Effect of current sheets on the solar wind magnetic field power spectrum from the Ulysses observation: from Kraichnan to Kolmogorov scaling.

Science.gov (United States)

Li, G; Miao, B; Hu, Q; Qin, G

2011-03-25

The MHD turbulence theory developed by Iroshnikov and Kraichnan predicts a k(-1.5) power spectrum. Solar wind observations, however, often show a k(-5/3) Kolmogorov scaling. Based on 3 years worth of Ulysses magnetic field data where over 28,000 current sheets are identified, we propose that the current sheet is the cause of the Kolmogorov scaling. We show that for 5 longest current-sheet-free periods the magnetic field power spectra are all described by the Iroshnikov-Kraichnan scaling. In comparison, for 5 periods that have the most number of current sheets, the power spectra all exhibit Kolmogorov scaling. The implication of our results is discussed.

Electron cyclotron instabilities of finite pressure inhomogeneous plasma in crossed fields

International Nuclear Information System (INIS)

Kirochkin, Yu.A.; Pokroev, A.G.; Stepanov, K.N.

1979-01-01

The stability of inhomogeneous plasma sheet with β<=1 in crossed electric and magnetic fields is investigated. The differential equation describing potential oscillations is obtained. Using the local approximation the sheet is shown to be unstable against the excitation of short wavelength electron cyclotron oscillations. The validity criterion of this method for a given type of waves is derived

Microstructural evolution in warm-rolled and cold-rolled strip cast 6.5 wt% Si steel thin sheets and its influence on magnetic properties

Energy Technology Data Exchange (ETDEWEB)

Wang, Xianglong, E-mail: 215454278@qq.com; Liu, Zhenyu, E-mail: zyliu@mail.neu.edu.cn; Li, Haoze; Wang, Guodong

2017-07-01

Highlights: • The experimental materials used in the study are based on strip casting. • Magnetic properties between warm rolled and cold rolled sheets are investigated. • Cold rolled 6.5% Si sheet has better magnetic properties than warm rolled sheet. • The γ and λ-fiber recrystallization textures can be optimized after cold rolling. • Cold rolling should be more suitable for fabricating 6.5% Si steel thin sheets. - Abstract: 6.5 wt% Si steel thin sheets were usually fabricated by warm rolling. In our previous work, 6.5 wt% Si steel thin sheets with good magnetic properties had been successfully fabricated by cold rolling based on strip casting. In the present work, the main purposes were to find out the influences of warm rolling and cold rolling on microstructures and magnetic properties of the thin sheets with the thickness of 0.2 mm, and to confirm which rolling method was more suitable for fabricating 6.5 wt% Si steel thin sheets. The results showed that the cold rolled sheet could obtain good surface quality and flatness, while the warm rolled sheet could not. The intensity of γ-fiber rolling texture (<1 1 1>//ND) of cold rolled specimen was weaker than that of the warm rolled specimen, especially for the {1 1 1}<1 1 2> component at surface layer and {1 1 1}<1 1 0> component at center layer. After the same annealing treatment, the cold rolled specimen, which had higher stored energy and weaker intensity of γ-fiber rolling texture, could obtain smaller recrystallization grain size, weaker intensity of γ-fiber recrystallization texture and stronger intensity of λ-fiber recrystallization texture. Therefore, due to the good surface quality, smaller recrystallization grain size and optimum recrystallization texture, the cold rolled specimen possessed improved magnetic properties, and cold rolling should be more suitable for fabricating 6.5 wt% Si steel thin sheets.

Characteristics of an elongated plasma column produced by magnetically coupled hollow cathode plasma source

Science.gov (United States)

Bhuva, M. P.; Karkari, S. K.; Kumar, Sunil

2018-03-01

An elongated plasma column in the presence of an axial magnetic field has been formed using a cylindrical hollow cathode (HC) and a constricted anode (CA). The plasma characteristics of the central line have been found to vary with the magnetic field strength and the axial distance from the source. It is believed that the primary electrons constituting the discharge current are steered by the axial magnetic field to undertake ionizing collisions along the plasma column. The current carrying electrons from the HC reach the anode by cross-field diffusion towards the central line. The above observation has been substantiated using a phenomenological model which links the observed characteristics of the source with the plasma column. The experimental results are found to be in qualitative agreement with the model.

Lithology and chronology of ice-sheet fluctuations (magnetic susceptibility of cores from the western Ross Sea)

Science.gov (United States)

Jennings, Anne E.

1993-01-01

The goals of the marine geology part of WAIS include reconstructing the chronology and areal extent of ice-sheet fluctuations and understanding the climatic and oceanographic influences on ice-sheet history. As an initial step toward attaining these goals, down-core volume magnetic susceptibility (MS) logs of piston cores from three N-S transects in the western Ross Sea are compared. The core transects are within separate petrographic provinces based on analyses of till composition. The provinces are thought to reflect the previous locations of ice streams on the shelf during the last glaciation. Magnetic susceptibility is a function of magnetic mineral composition, sediment texture, and sediment density. It is applied in the western Ross Sea for two purposes: (1) to determine whether MS data differentiates the three transects (i.e., flow lines), and thus can be used to make paleodrainage reconstructions of the late Wisconsinan ice sheet; and (2) to determine whether the MS data can aid in distinguishing basal till diamictons from diamictons of glacial-marine origin and thus, aid paleoenvironmental interpretations. A comparison of the combined data of cores in each transect is presented.

Electromagnetic Calculation and Plasma Leakage Rate Analysis of the Magnetically Confined Plasma Rocket