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.

Symmetry breaking bifurcations of a current sheet

International Nuclear Information System (INIS)

Parker, R.D.; Dewar, R.L.; Johnson, J.L.

1988-08-01

Using a time evolution code with periodic boundary conditions, the viscoresistive hydromagnetic equations describing an initially static, planar current sheet with large Lundquist number have been evolved for times long enough to reach a steady state. A cosh 2 x resistivity model was used. For long periodicity lengths, L p , the resistivity gradient drives flows which cause forced reconnection at X point current sheets. Using L p as a bifurcation parameter, two new symmetry breaking bifurcations were found - a transition to an asymmetric island chain with nonzero, positive or negative phase velocity, and a transition to a static state with alternating large and small islands. These states are reached after a complex transient behavior which involves a competition between secondary current sheet instability and coalescence. 31 refs., 6 figs

Analytic modeling of axisymmetric disruption halo currents

International Nuclear Information System (INIS)

Humphreys, D.A.; Kellman, A.G.

1999-01-01

Currents which can flow in plasma facing components during disruptions pose a challenge to the design of next generation tokamaks. Induced toroidal eddy currents and both induced and conducted poloidal ''halo'' currents can produce design-limiting electromagnetic loads. While induction of toroidal and poloidal currents in passive structures is a well-understood phenomenon, the driving terms and scalings for poloidal currents flowing on open field lines during disruptions are less well established. A model of halo current evolution is presented in which the current is induced in the halo by decay of the plasma current and change in enclosed toroidal flux while being convected into the halo from the core by plasma motion. Fundamental physical processes and scalings are described in a simplified analytic version of the model. The peak axisymmetric halo current is found to depend on halo and core plasma characteristics during the current quench, including machine and plasma dimensions, resistivities, safety factor, and vertical stability growth rate. Two extreme regimes in poloidal halo current amplitude are identified depending on the minimum halo safety factor reached during the disruption. A 'type I' disruption is characterized by a minimum safety factor that remains relatively high (typically 2 - 3, comparable to the predisruption safety factor), and a relatively low poloidal halo current. A 'type II' disruption is characterized by a minimum safety factor comparable to unity and a relatively high poloidal halo current. Model predictions for these two regimes are found to agree well with halo current measurements from vertical displacement event disruptions in DIII-D [T. S. Taylor, K. H. Burrell, D. R. Baker, G. L. Jackson, R. J. La Haye, M. A. Mahdavi, R. Prater, T. C. Simonen, and A. D. Turnbull, open-quotes Results from the DIII-D Scientific Research Program,close quotes in Proceedings of the 17th IAEA Fusion Energy Conference, Yokohama, 1998, to be published in

Near-earth Thin Current Sheets and Birkeland Currents during Substorm Growth Phase

International Nuclear Information System (INIS)

Sorin Zaharia; Cheng, C.Z.

2003-01-01

Two important phenomena observed during the magnetospheric substorm growth phase are modeled: the formation of a near-Earth (|X| ∼ 9 R E ) thin cross-tail current sheet, as well as the equatorward shift of the ionospheric Birkeland currents. Our study is performed by solving the 3-D force-balance equation with realistic boundary conditions and pressure distributions. The results show a cross-tail current sheet with large current (J φ ∼ 10 nA/m 2 ) and very high plasma β (β ∼ 40) between 7 and 10 R E . The obtained region-1 and region-2 Birkeland currents, formed on closed field lines due to pressure gradients, move equatorward and become more intense (J parallel max ∼ 3 (micro)A/m 2 ) compared to quiet times. Both results are in agreement with substorm growth phase observations. Our results also predict that the cross-tail current sheet maps into the ionosphere in the transition region between the region-1 and region-2 currents

Study of runaway current generation following disruptions in KSTAR

International Nuclear Information System (INIS)

Chen, Z Y; Kim, W C; Yu, Y W; England, A C; Yoo, J W; Hahn, S H; Yoon, S W; Lee, K D; Oh, Y K; Kwak, J G; Kwon, M

2013-01-01

The high fraction of runaway current conversion following disruptions has an important effect on the first wall for next-generation tokamaks. Because of the potentially severe consequences of a large full current runaway beam on the first wall in an unmitigated disruption, runaway suppression is given a high priority. The behavior of runaway currents both in spontaneous disruptions and in D 2 massive gas injection (MGI) shutdown experiments is investigated in the KSTAR tokamak. The experiments in KSTAR show that the toroidal magnetic field threshold, B T >2 T, for runaway generation is not absolute. A high fraction of runaway current conversion following spontaneous disruptions is observed at a much lower toroidal magnetic field of B T = 1.3 T. A dedicated fast valve for high-pressure gas injection with 39.7 bar is developed for the study of disruptions. A study of runaway current parameters shows that the conversion efficiency of pre-disruptive plasma currents into runaway current can reach over 80% both in spontaneous disruptions and in D 2 MGI shutdown experiments in KSTAR. (paper)

THE ROLE OF FAST MAGNETOSONIC WAVES IN THE RELEASE AND CONVERSION VIA RECONNECTION OF ENERGY STORED BY A CURRENT SHEET

Energy Technology Data Exchange (ETDEWEB)

Longcope, D. W.; Tarr, L. [Department of Physics, Montana State University, Bozeman, MT 59717 (United States)

2012-09-10

Using a simple two-dimensional, zero-{beta} model, we explore the manner by which reconnection at a current sheet releases and dissipates free magnetic energy. We find that only a small fraction (3%-11% depending on current-sheet size) of the energy is stored close enough to the current sheet to be dissipated abruptly by the reconnection process. The remaining energy, stored in the larger-scale field, is converted to kinetic energy in a fast magnetosonic disturbance propagating away from the reconnection site, carrying the initial current and generating reconnection-associated flows (inflow and outflow). Some of this reflects from the lower boundary (the photosphere) and refracts back to the X-point reconnection site. Most of this inward wave energy is reflected back again and continues to bounce between X-point and photosphere until it is gradually dissipated, over many transits. This phase of the energy dissipation process is thus global and lasts far longer than the initial purely local phase. In the process, a significant fraction of the energy (25%-60%) remains as undissipated fast magnetosonic waves propagating away from the reconnection site, primarily upward. This flare-generated wave is initiated by unbalanced Lorentz forces in the reconnection-disrupted current sheet, rather than by dissipation-generated pressure, as some previous models have assumed. Depending on the orientation of the initial current sheet, the wave front is either a rarefaction, with backward-directed flow, or a compression, with forward-directed flow.

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.

Disruption-induced poloidal currents in the tokamak wall

International Nuclear Information System (INIS)

Pustovitov, V.D.

2017-01-01

Highlights: • Induction effects during disruptions and rapid transient events in tokamaks. • Plasma-wall electromagnetic interaction. • Flux-conserving evolution of plasma equilibrium. • Poloidal current induced in the vacuum vessel wall in a tokamak. • Complete analytical derivations and estimates. - Abstract: The poloidal current induced in the tokamak wall during fast transient events is analytically evaluated. The analysis is based on the electromagnetic relations coupled with plasma equilibrium equations. The derived formulas describe the consequences of both thermal and current quenches. In the final form, they give explicit dependence of the wall current on the plasma pressure and current. A comparison with numerical results of Villone et al. [F. Villone, G. Ramogida, G. Rubinacci, Fusion Eng. Des. 93, 57 (2015)] for IGNITOR is performed. Our analysis confirms the importance of the effects described there. The estimates show that the disruption-induced poloidal currents in the wall should be necessarily taken into account in the studies of disruptions and disruption mitigation in ITER.

Disruption-induced poloidal currents in the tokamak wall

Energy Technology Data Exchange (ETDEWEB)

Pustovitov, V.D., E-mail: Pustovitov_VD@nrcki.ru [National Research Centre ‘Kurchatov Institute’, Pl. Kurchatova 1, Moscow 123182 (Russian Federation); National Research Nuclear University MEPhI, Kashirskoe sh. 31, Moscow 115409, Russia (Russian Federation)

2017-04-15

Highlights: • Induction effects during disruptions and rapid transient events in tokamaks. • Plasma-wall electromagnetic interaction. • Flux-conserving evolution of plasma equilibrium. • Poloidal current induced in the vacuum vessel wall in a tokamak. • Complete analytical derivations and estimates. - Abstract: The poloidal current induced in the tokamak wall during fast transient events is analytically evaluated. The analysis is based on the electromagnetic relations coupled with plasma equilibrium equations. The derived formulas describe the consequences of both thermal and current quenches. In the final form, they give explicit dependence of the wall current on the plasma pressure and current. A comparison with numerical results of Villone et al. [F. Villone, G. Ramogida, G. Rubinacci, Fusion Eng. Des. 93, 57 (2015)] for IGNITOR is performed. Our analysis confirms the importance of the effects described there. The estimates show that the disruption-induced poloidal currents in the wall should be necessarily taken into account in the studies of disruptions and disruption mitigation in ITER.

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.

Nonlinear dynamics of thin current sheets

International Nuclear Information System (INIS)

Daughton, William

2002-01-01

Observations indicate that the current sheet in the Earth's geomagnetic tail may compress to a thickness comparable to an ion gyro-radius prior to substorm onset. In recent years, there has been considerable controversy regarding the kinetic stability of these thin structures. In particular, the growth rate of the kink instability and its relevance to magnetotail dynamics is still being debated. In this work, a series of fully kinetic particle-in-cell simulations are performed for a thin Harris sheet. The ion to electron mass ratio is varied between m i /m e =4→400 and careful comparisons are made with a formally exact approach to the linear Vlasov theory. At low mass ratio m i /m e <64, the simulations are in excellent agreement with the linear theory, but at high mass ratio the kink instability is observed to grow more rapidly in the kinetic simulations than predicted by theory. The resolution to this apparent discrepancy involves the lower hybrid instability which is active on the edge of the sheet and rapidly produces nonlinear modifications to the initial equilibrium. The nature of this nonlinear deformation is characterized and a simple model is proposed to explain the physics. After the growth and saturation of the lower hybrid fluctuations, the deformed current sheet is similar in structure to a Harris equilibrium with an additional background population. This may explain the large growth rate of the kink instability at later times, since this type of modification to the Harris sheet has been shown to greatly enhance the growth rate of the kink mode

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 Z_GSM direction. Observations following the substorms show the occurrence of current sheet waves moving predominantly in the −Y_GSM 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.

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.

On the structure of the magnetotail current sheet

International Nuclear Information System (INIS)

Ashour-Abdalla, M.; Peroomian, V.; Richard, R.L.; Zelenyi, L.M.

1993-01-01

Results from modeling ion distribution functions in a two-dimensional reduction of the Tsyganenko magnetic field model have enabled the authors to calculate the full ion pressure tensor inside the model magnetotail. A thin current sheet is formed in the distant tail and the pressure tensor within this sheet has significant off-diagonal terms. These terms resulting from quasiadiabatic ion trajectories create azimuthally asymmetric distribution functions which are capable of maintaining stress-balance. Outside the current sheet the off-diagonal terms disappear and moderate anisotropy builds up with P perpendicular/P parallel ∼ 0.8. Closer to the Earth rapid isotropization of the distribution occurs

Thin current sheets observation by MMS during a near-Earth's magnetotail reconnection event

Science.gov (United States)

Nakamura, R.; Varsani, A.; Nakamura, T.; Genestreti, K.; Plaschke, F.; Baumjohann, W.; Nagai, T.; Burch, J.; Cohen, I. J.; Ergun, R.; Fuselier, S. A.; Giles, B. L.; Le Contel, O.; Lindqvist, P. A.; Magnes, W.; Schwartz, S. J.; Strangeway, R. J.; Torbert, R. B.

2017-12-01

During summer 2017, the four spacecraft of the Magnetospheric Multiscale (MMS) mission traversed the nightside magnetotail current sheet at an apogee of 25 RE. They detected a number of flow reversal events suggestive of the passage of the reconnection current sheet. Due to the mission's unprecedented high-time resolution and spatial separation well below the ion scales, structure of thin current sheets is well resolved both with plasma and field measurements. In this study we examine the detailed structure of thin current sheets during a flow reversal event from tailward flow to Earthward flow, when MMS crossed the center of the current sheet . We investigate the changes in the structure of the thin current sheet relative to the X-point based on multi-point analysis. We determine the motion and strength of the current sheet from curlometer calculations comparing these with currents obtained from the particle data. The observed structures of these current sheets are also compared with simulations.

Solar Energetic Particle Transport Near a Heliospheric Current Sheet

Energy Technology Data Exchange (ETDEWEB)

Battarbee, Markus; Dalla, Silvia [Jeremiah Horrocks Institute, University of Central Lancashire, PR1 2HE (United Kingdom); Marsh, Mike S., E-mail: mbattarbee@uclan.ac.uk [Met Office, Exeter, EX1 3 PB (United Kingdom)

2017-02-10

Solar energetic particles (SEPs), a major component of space weather, propagate through the interplanetary medium strongly guided by the interplanetary magnetic field (IMF). In this work, we analyze the implications that a flat Heliospheric Current Sheet (HCS) has on proton propagation from SEP release sites to the Earth. We simulate proton propagation by integrating fully 3D trajectories near an analytically defined flat current sheet, collecting comprehensive statistics into histograms, fluence maps, and virtual observer time profiles within an energy range of 1–800 MeV. We show that protons experience significant current sheet drift to distant longitudes, causing time profiles to exhibit multiple components, which are a potential source of confusing interpretations of observations. We find that variation of the current sheet thickness within a realistic parameter range has little effect on particle propagation. We show that the IMF configuration strongly affects the deceleration of protons. We show that in our model, the presence of a flat equatorial HCS in the inner heliosphere limits the crossing of protons into the opposite hemisphere.

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.

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.)

Current disruption and its spreading in collisionless magnetic reconnection

International Nuclear Information System (INIS)

Jain, Neeraj; Büchner, Jörg; Dorfman, Seth; Ji, Hantao; Surjalal Sharma, A.

2013-01-01

Recent magnetic reconnection experiments (MRX) [Dorfman et al., Geophys. Res. Lett. 40, 233 (2013)] have disclosed current disruption in the absence of an externally imposed guide field. During current disruption in MRX, both the current density and the total observed out-of-reconnection-plane current drop simultaneous with a rise in out-of-reconnection-plane electric field. Here, we show that current disruption is an intrinsic property of the dynamic formation of an X-point configuration of magnetic field in magnetic reconnection, independent of the model used for plasma description and of the dimensionality (2D or 3D) of reconnection. An analytic expression for the current drop is derived from Ampere's Law. Its predictions are verified by 2D and 3D electron-magnetohydrodynamic (EMHD) simulations. Three dimensional EMHD simulations show that the current disruption due to localized magnetic reconnection spreads along the direction of the electron drift velocity with a speed which depends on the wave number of the perturbation. The implications of these results for MRX are discussed

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

The evolution of the plasma current during tokamak disruptions

International Nuclear Information System (INIS)

Helander, P.; Andersson, F.; Anderson, D.; Lisak, M.; Eriksson, L.G.

2004-01-01

In a tokamak disruption, the ohmic plasma current is partly replaced by a current carried by runaway electrons. This process is analysed by combining the equations for runaway electron generation with Maxwell's equations for the evolution of the electric field. This allows a quantitative understanding to be gained of runaway production in present experiments, and extrapolation to be made to ITER. The runaway current typically becomes more peaked on the magnetic axis than the pre-disruption current. In fact, the central current density can rise although the total current falls, which may have implications for post-disruption plasma stability. Furthermore, it is found that the runaway current easily spreads radially in a filament way due to the high sensitivity of the runaway generation efficiency to plasma parameters. (authors)

Field reversing magnetotail current sheets: earth, Venus, and Comet Giacobini-Zinner

International Nuclear Information System (INIS)

McComas, D.J.

1986-09-01

This dissertation examines the field reversing magnetotail current sheets at the earth, Venus, and Comet Giacobini-Zinner. In the near earth study a new analysis technique is developed to calculate the detailed current density distributions within the cross tail current sheet for the first time. This technique removes the effects of a variable sheet velocity by inverting intersatellite timings between the co-orbiting satellites ISEE-1 and -2. Case studies of three relatively geomagnetically quiet crossings are made; sheet thicknesses and peak current densities are ∼1-5 x 10 4 km and ∼5-50 nA/m 2 . Current density distributions reveal a high density central region, lower density shoulders, and considerable fine structure throughout. In the Venus study another new analysis technique is developed to reconstruct the average tail configuration from a correlation between field magnitude and draping angle in a large statistical data set. In the comet study, high resolution magnetic field and plasma electron data from the ICE traversal of Giacobini-Zinner are combined for the first time to determine the tail/current sheet geometry and calculate certain important but unmeasured local ion and upstream properties. Pressure balance across the tail gives ion temperatures and betas of ∼1.2 x 10 5 K and ∼40 in the center of the current sheet to ∼1 x 10 6 K and ∼3 in the outer lobes. Axial stress balance shows that the velocity shear upstream near the nucleus is >6 (∼1 at ICE), and that a region of strongly enhanced mass loading (ion source rate ∼24 times that upstream from lobes) exists upstream from the current sheet. The integrated downtail mass flux is ∼2.6 x 10 26 H 2 O+/sec, which is only ∼1% of the independently determined total cometary efflux. 79 refs., 37 figs

Disruption, vertical displacement event and halo current characterization for ITER

International Nuclear Information System (INIS)

Wesley, J.; Fujisawa, N.; Ortolani, S.; Putvinski, S.; Rosenbluth, M.N.

1997-01-01

Characteristics, in ITER, of plasma disruptions, vertical displacement events (VDEs) and the conversion of plasma current to runaway electron current in a disruption are presented. In addition to the well known potential of disruptions to produce rapid thermal energy and plasma current quenches and theoretical predictions that show the likelihood of ∼ 50% runaway conversion, an assessment of VDE and halo current characteristics in vertically elongated tokamaks shows that disruptions in ITER will result in VDEs with peak in-vessel halo currents of up to 50% of the predisruption plasma current and with toroidal peaking factors (peak/average current density) of up to 4:1. However, the assessment also shows an inverse correlation between the halo current magnitude and the toroidal peaking factor; hence, ITER VDEs can be expected to have a product of normalized halo current magnitude times toroidal peaking factor of ≤ 75%. (author). 3 refs, 2 figs, 3 tabs

On the role of topological complexity in spontaneous development of current sheets

Energy Technology Data Exchange (ETDEWEB)

Kumar, Sanjay; 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)

2015-08-15

The computations presented in this work aim to asses the importance of field line interlacing on spontaneous development of current sheets. From Parker's magnetostatic theorem, such development of current sheets is inevitable in a topologically complex magnetofluid, with infinite electrical conductivity, at equilibrium. Relevant initial value problems are constructed by superposition of two untwisted component fields, each component field being represented by a pair of global magnetic flux surface. The intensity of field line interlacing is then specified by the relative amplitude of the two superposed fields. The computations are performed by varying this relative amplitude. Also to have a direct visualization of current sheet formation, we follow the evolution of flux surfaces instead of the vector magnetic field. An important finding of this paper is in the demonstration that initial field lines having intense interlacing tend to develop current sheets which are distributed throughout the computational domain with no preference for topologically favorable sites like magnetic nulls or field reversal layers. The onsets of these current sheets are attributed to favorable contortions of magnetic flux surfaces where two oppositely directed parts of the same field line or different field lines come to close proximity. However, for less intensely interlaced field lines, the simulations indicate development of current sheets at sites only where the magnetic topology is favorable. These current sheets originate as two sets of anti-parallel complimentary field lines press onto each other.

Characterization of plasma current quench during disruptions at HL-2A

Science.gov (United States)

Zhu, Jinxia; Zhang, Yipo; Dong, Yunbo; HL-2A Team

2017-05-01

The most essential assumptions of physics for the evaluation of electromagnetic forces on the plasma-facing components due to a disruption-induced eddy current are characteristics of plasma current quenches including the current quench rate or its waveforms. The characteristics of plasma current quenches at HL-2A have been analyzed during spontaneous disruptions. Both linear decay and exponential decay are found in the disruptions with the fastest current quenches. However, there are two stages of current quench in the slow current quench case. The first stage with an exponential decay and the second stage followed by a rapid linear decay. The faster current quench rate corresponds to the faster movement of plasma displacement. The parameter regimes on the current quench time and the current quench rates have been obtained from disruption statistics at HL-2A. There exists no remarkable difference for distributions obtained between the limiter and the divertor configuration. This data from HL-2A provides basic data of the derivation of design criteria for a large-sized machine during the current decay phase of the disruptions.

Hiro and Evans currents in Vertical Disruption Event

Science.gov (United States)

Zakharov, Leonid; Xujing Li Team; Sergei Galkin Team

2014-10-01

The notion of Tokamak Magneto-Hydrodynamics (TMHD), which explicitly reflects the anisotropy of a high temperature tokamak plasma is introduced. The set of TMHD equations is formulated for simulations of macroscopic plasma dynamics and disruptions in tokamaks. Free from the Courant restriction on the time step, this set of equations is appropriate for high performance plasmas and does not require any extension of the MHD plasma model. At the same time, TMHD requires the use of magnetic field aligned numerical grids. The TMHD model was used for creation of theory of the Wall Touching Kink and Vertical Modes (WTKM and WTVM), prediction of Hiro and Evans currents, design of an innovative diagnostics for Hiro current measurements, installed on EAST device. While Hiro currents have explained the toroidal asymmetry in the plasma current measurements in JET disruptions, the Evans currents explain the tile current measurements in tokamaks. The recently developed Vertical Disruption Code (VDE) have demonstrated 5 regimes of VDE and confirmed the generation of both Hiro and Evans currents. The results challenge the 24 years long misinterpretation of the tile currents in tokamaks as ``halo'' currents, which were a product of misuse of equilibrium reconstruction for VDE. This work is supported by US DoE Contract No. DE-AC02-09-CH1146.

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

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

NON-EQUILIBRIUM IONIZATION MODELING OF THE CURRENT SHEET IN A SIMULATED SOLAR ERUPTION

International Nuclear Information System (INIS)

Shen Chengcai; Reeves, Katharine K.; Raymond, John C.; Murphy, Nicholas A.; Ko, Yuan-Kuen; Lin Jun; Mikić, Zoran; Linker, Jon A.

2013-01-01

The current sheet that extends from the top of flare loops and connects to an associated flux rope is a common structure in models of coronal mass ejections (CMEs). To understand the observational properties of CME current sheets, we generated predictions from a flare/CME model to be compared with observations. We use a simulation of a large-scale CME current sheet previously reported by Reeves et al. This simulation includes ohmic and coronal heating, thermal conduction, and radiative cooling in the energy equation. Using the results of this simulation, we perform time-dependent ionization calculations of the flow in a CME current sheet and construct two-dimensional spatial distributions of ionic charge states for multiple chemical elements. We use the filter responses from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory and the predicted intensities of emission lines to compute the count rates for each of the AIA bands. The results show differences in the emission line intensities between equilibrium and non-equilibrium ionization. The current sheet plasma is underionized at low heights and overionized at large heights. At low heights in the current sheet, the intensities of the AIA 94 Å and 131 Å channels are lower for non-equilibrium ionization than for equilibrium ionization. At large heights, these intensities are higher for non-equilibrium ionization than for equilibrium ionization inside the current sheet. The assumption of ionization equilibrium would lead to a significant underestimate of the temperature low in the current sheet and overestimate at larger heights. We also calculate the intensities of ultraviolet lines and predict emission features to be compared with events from the Ultraviolet Coronagraph Spectrometer on the Solar and Heliospheric Observatory, including a low-intensity region around the current sheet corresponding to this model

Nonlinear Dynamics of Non-uniform Current-Vortex Sheets in Magnetohydrodynamic Flows

Science.gov (United States)

Matsuoka, C.; Nishihara, K.; Sano, T.

2017-04-01

A theoretical model is proposed to describe fully nonlinear dynamics of interfaces in two-dimensional MHD flows based on an idea of non-uniform current-vortex sheet. Application of vortex sheet model to MHD flows has a crucial difficulty because of non-conservative nature of magnetic tension. However, it is shown that when a magnetic field is initially parallel to an interface, the concept of vortex sheet can be extended to MHD flows (current-vortex sheet). Two-dimensional MHD flows are then described only by a one-dimensional Lagrange parameter on the sheet. It is also shown that bulk magnetic field and velocity can be calculated from their values on the sheet. The model is tested by MHD Richtmyer-Meshkov instability with sinusoidal vortex sheet strength. Two-dimensional ideal MHD simulations show that the nonlinear dynamics of a shocked interface with density stratification agrees fairly well with that for its corresponding potential flow. Numerical solutions of the model reproduce properly the results of the ideal MHD simulations, such as the roll-up of spike, exponential growth of magnetic field, and its saturation and oscillation. Nonlinear evolution of the interface is found to be determined by the Alfvén and Atwood numbers. Some of their dependence on the sheet dynamics and magnetic field amplification are discussed. It is shown by the model that the magnetic field amplification occurs locally associated with the nonlinear dynamics of the current-vortex sheet. We expect that our model can be applicable to a wide variety of MHD shear flows.

Generalized lower-hybrid drift instabilities in current-sheet equilibrium

International Nuclear Information System (INIS)

Yoon, Peter H.; Lui, Anthony T. Y.; Sitnov, Mikhail I.

2002-01-01

A class of drift instabilities in one-dimensional current-sheet configuration, i.e., classical Harris equilibrium, with frequency ranging from low ion-cyclotron to intermediate lower-hybrid frequencies, are investigated with an emphasis placed on perturbations propagating along the direction of cross-field current flow. Nonlocal two-fluid stability analysis is carried out, and a class of unstable modes with multiple eigenstates, similar to that of the familiar quantum mechanical potential-well problem, are found by numerical means. It is found that the most unstable modes correspond to quasi-electrostatic, short-wavelength perturbations in the lower-hybrid frequency range, with wave functions localized at the edge of the current sheet where the density gradient is maximum. It is also found that there exist quasi-electromagnetic modes located near the center of the current sheet where the current density is maximum, with both kink- and sausage-type polarizations. These modes are low-frequency, long-wavelength perturbations. It turns out that the current-driven modes are low-order eigensolutions while the lower-hybrid-type modes are higher-order states, and there are intermediate solutions between the two extreme cases. Attempts are made to interpret the available simulation results in light of the present eigenmode analysis

Magnetic reconnection and current sheet formation in 3D magnetic configurations

International Nuclear Information System (INIS)

Frank, A.G.

1999-01-01

The problem of magnetic reconnection in three-dimensional (3D) magnetic configurations has been studied experimentally. The research has concentrated on the possibilities of formation of current sheets, which represent crucial objects for a realization of magnetic reconnection phenomena. Different types of 3D magnetic configurations were examined, including configurations with singular lines of the X-type, non-uniform fields containing isolated magnetic null-points and without null-points. It was revealed that formation of quasi-one-dimensional current sheets is the universal process for plasma dynamics in 3D magnetic fields both with null-points and without. At the same time the peculiarities of current sheets, plasma dynamics and magnetic reconnection processes depend essentially on characteristics of 3D magnetic configurations. The result of principal significance obtained was that magnetic reconnection phenomena can take place in a wide range of 3D magnetic configurations as a consequence of their ability to form current sheets. (author)

Current sheet particle acceleration - theory and observations for the geomagnetic tail

International Nuclear Information System (INIS)

Speiser, T.W.

1984-01-01

It has been found that the current sheet in the geomagnetic tail is a source of plasma and energetic particles for the magnetospheric ring current and radiation belts. It is also a seat for instabilities and magnetospheric substorms. Theoretical studies related to the geomagnetic tail are discussed, taking into account Dungey's (1953) original ideas concerning neutral point acceleration, and studies of particle motion in current sheets conducted by many authors. A description of observations concerning the geomagnetic tail is also provided, taking into account plasma sheet populations, and the plasma sheet boundary layer. Some remaining problems are partly related to the location and the behavior of the distant source, the nature of the relative (time-dependent) ionospheric versus solar wind contributions, and the role of the solar wind in the initiation of distant or near-earth neutral lines. 56 references

Tokamak plasma current disruption infrared control system

International Nuclear Information System (INIS)

Kugel, H.W.; Ulrickson, M.

1987-01-01

This patent describes a device for magnetically confining a plasma driven by a plasma current and contained within a toroidal vacuum chamber, the device having an inner toroidal limiter on an inside wall of the vacuum chamber and an arrangement for the rapid prediction and control in real time of a major plasma disruption. The arrangement is described which includes: scanning means sensitive to infrared radiation emanating from within the vacuum chamber, the infrared radiation indicating the temperature along a vertical profile of the inner toroidal limiter. The scanning means is arranged to observe the infrared radiation and to produce in response thereto an electrical scanning output signal representative of a time scan of temperature along the vertical profile; detection means for analyzing the scanning output signal to detect a first peaked temperature excursion occurring along the profile of the inner toroidal limiter, and to produce a detection output signal in repsonse thereto, the detection output signal indicating a real time prediction of a subsequent major plasma disruption; and plasma current reduction means for reducing the plasma current driving the plasma, in response to the detection output signal and in anticipation of a subsequent major plasma disruption

Wave form of current quench during disruptions in tokamaks

International Nuclear Information System (INIS)

Sugihara, Masayoshi; Gribov, Yuri; Shimada, Michiya; Lukash, Victor; Kawano, Yasunori; Yoshino, Ryuji; Miki, Nobuharu; Ohmori, Junji; Khayrutdinov, Rustam

2003-01-01

The time dependence of the current decay during the current quench phase of disruptions, which can significantly influence the electro-magnetic force on the in-vessel components due to the induced eddy currents, is investigated using data obtained in JT-60U experiments in order to derive a relevant physics guideline for the predictive simulations of disruptions in ITER. It is shown that an exponential decay can fit the time dependence of current quench for discharges with large quench rate (fast current quench). On the other hand, for discharges with smaller quench rate (slow current quench), a linear decay can fit the time dependence of current quench better than exponential. (author)

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

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.

Evolution of three-dimensional relativistic current sheets and development of self-generated turbulence

Science.gov (United States)

Takamoto, M.

2018-05-01

In this paper, the temporal evolution of three-dimensional relativistic current sheets in Poynting-dominated plasma is studied for the first time. Over the past few decades, a lot of efforts have been conducted on studying the evolution of current sheets in two-dimensional space, and concluded that sufficiently long current sheets always evolve into the so-called plasmoid chain, which provides a fast reconnection rate independent of its resistivity. However, it is suspected that plasmoid chain can exist only in the case of two-dimensional approximation, and would show transition to turbulence in three-dimensional space. We performed three-dimensional numerical simulation of relativistic current sheet using resistive relativistic magnetohydrodynamic approximation. The results showed that the three-dimensional current sheets evolve not into plasmoid chain but turbulence. The resulting reconnection rate is 0.004, which is much smaller than that of plasmoid chain. The energy conversion from magnetic field to kinetic energy of turbulence is just 0.01 per cent, which is much smaller than typical non-relativistic cases. Using the energy principle, we also showed that the plasmoid is always unstable for a displacement in the opposite direction to its acceleration, probably interchange-type instability, and this always results in seeds of turbulence behind the plasmoids. Finally, the temperature distribution along the sheet is discussed, and it is found that the sheet is less active than plasmoid chain. Our finding can be applied for many high-energy astrophysical phenomena, and can provide a basic model of the general current sheet in Poynting-dominated plasma.

CURRENT SHEET ENERGETICS, FLARE EMISSIONS, AND ENERGY PARTITION IN A SIMULATED SOLAR ERUPTION

International Nuclear Information System (INIS)

Reeves, Katharine K.; Linker, Jon A.; Mikic, Zoran; Forbes, Terry G.

2010-01-01

We investigate coronal energy flow during a simulated coronal mass ejection (CME). We model the CME in the context of the global corona using a 2.5D numerical MHD code in spherical coordinates that includes coronal heating, thermal conduction, and radiative cooling in the energy equation. The simulation domain extends from 1 to 20 R s . To our knowledge, this is the first attempt to apply detailed energy diagnostics in a flare/CME simulation when these important terms are considered in the context of the MHD equations. We find that the energy conservation properties of the code are quite good, conserving energy to within 4% for the entire simulation (more than 6 days of real time). We examine the energy release in the current sheet as the eruption takes place, and find, as expected, that the Poynting flux is the dominant carrier of energy into the current sheet. However, there is a significant flow of energy out of the sides of the current sheet into the upstream region due to thermal conduction along field lines and viscous drag. This energy outflow is spatially partitioned into three separate components, namely, the energy flux flowing out the sides of the current sheet, the energy flowing out the lower tip of the current sheet, and the energy flowing out the upper tip of the current sheet. The energy flow through the lower tip of the current sheet is the energy available for heating of the flare loops. We examine the simulated flare emissions and energetics due to the modeled CME and find reasonable agreement with flare loop morphologies and energy partitioning in observed solar eruptions. The simulation also provides an explanation for coronal dimming during eruptions and predicts that the structures surrounding the current sheet are visible in X-ray observations.

Dissipation of magnetic energy during disruptive current termination

International Nuclear Information System (INIS)

Yamazaki, K.; Schmidt, G.L.

1983-09-01

The magnetic coupling during a disruption between the plasma and the various coil systems on the PDX tokamak has been modeled. Using measured coil currents, the model indicates that dissipation of magnetic energy in the plasma equal to 75 % of the energy stored in the poloidal field of the plasma current does occur and that coupling between the plasma and the coil systems can reduce such dissipation. In the case of PDX ohmic discharges, bolometric measurements of radiation and charge exchange, integrated over a disruption, account for 90 % of the calculated energy dissipation. (author)

Estimation of post disruption plasma temperature for fast current quench Aditya plasma shots

International Nuclear Information System (INIS)

Purohit, S.; Chowdhuri, M.B.; Joisa, Y.S.; Raval, J.V.; Ghosh, J.; Jha, R.

2013-01-01

Characteristics of tokamak current quenches are an important issue for the determination of electromagnetic forces that act on the in-vessel components and vacuum vessel during major disruptions. It is observed that thermal quench is followed by a sharp current decay. Fast current quench disruptive plasma shots were investigated for ADITYA tokamak. The current decay time was determined for the selected shots, which were in the range of 0.8 msec to 2.5 msec. This current decay information was then applied to L/R model, frequently employed for the estimation of the current decay time in tokamak plasmas, considering plasma inductance and plasma resistivity. This methodology was adopted for the estimation of the post disruption plasma temperature using the experimentally observed current decay time for the fast current quench disruptive ADITYA plasma shots. The study reveals that for the identified shots there is a constant increase in the current decay time with the post disruption plasma temperature. The investigations also explore the behavior post disruption plasma temperature and the current decay time as a function of the edge safety factor, Q. Post disruption plasma temperature and the current decay time exhibits a decrease with the increase in the value Q. (author)

Current disruption in toroidal devices

International Nuclear Information System (INIS)

1979-07-01

Attempts at raising the density or the plasma current in a tokamak above certain critical values generally result in termination of the discharge by a disruption. This sudden end of the plasma current and plasma confinement is accompanied by large induced voltages and currents in the outer structures which, in large tokamaks, can only be handled with considerable effort, and which will probably only be tolerable in reactors as rare accidents. Because of its crucial importance for the construction and operation of tokamaks, this phenomenon and its theoretical interpretation were the subject of a three-day symposium organized by the International Atomic Energy Agency and Max-Planck-Institut fuer Plasmaphysik at Garching from February 14 to 16. (orig./HT)

Engineering aspects of disruption current decay

International Nuclear Information System (INIS)

Murray, J.G.

1983-11-01

Engineering features associated with the configuration of a tokamak can affect the amount of energy that produces melting and damage to the limiters or internal wall surfaces as the result of a major disruption. During the current decay period of a major thermal disruption, the energy that can damage a wall or limiter comes from the external magnetic field. By providing a good conducting torus near the plasma and increasing the plasma circuit resistance, this magnetic energy (transferred by way of the plasma circuit) can be minimized. This report addresses engineering design features to reduce the energy deposited on the inner torus surface that produces melting of the structures

Sudden disruption of the cross-tail current in the magnetotail

International Nuclear Information System (INIS)

Ma, Z. W.

2008-01-01

A Hall magnetohydrodynamic simulation is used to study current dynamic processes with realistic magnetotail geometry. The simulation results indicate that sudden disruption of cross-tail current at the near Earth region inside 15R E is triggered by fast magnetic reconnection with the reconnection rate ∼0.15. The cross-tail current density exhibits an impulsive intensification in the late growth phase. The magnitude of the current increases more than one order within a few minutes. After the reconnection onset, the cross-tail current is suddenly disrupted in a few Alfven times, which is in good agreement with that from the satellite observations. Associated with the current disruption, the tail-like geometry becomes a dipolarlike structure with an impulsive enhancement of the magnetic field B z . Large increases of the electric field and Earthward bulk flow in this simulation are observed immediately after the reconnection onset

Asymmetry of the Martian Current Sheet in a Multi-fluid MHD Model

Science.gov (United States)

Panoncillo, S. G.; Egan, H. L.; Dong, C.; Connerney, J. E. P.; Brain, D. A.; Jakosky, B. M.

2017-12-01

The solar wind carries interplanetary magnetic field (IMF) lines toward Mars, where they drape around the planet's conducting ionosphere, creating a current sheet behind the planet where the magnetic field has opposite polarity on either side. In its simplest form, the current sheet is often thought of as symmetric, extending behind the planet along the Mars-Sun line. Observations and model simulations, however, demonstrate that this idealized representation is only an approximation, and the actual scenario is much more complex. The current sheet can have 3D structure, move back and forth, and be situated dawnward or duskward of the Mars-Sun line. In this project, we utilized a library of global plasma model results for Mars consisting of a collection of multi-fluid MHD simulations where solar max/min, sub-solar longitude, and the orbital position of Mars are varied individually. The model includes Martian crustal fields, and was run for identical steady solar wind conditions. This library was created for the purpose of comparing model results to MAVEN data; we looked at the results of this model library to investigate current sheet asymmetries. By altering one variable at a time we were able to measure how these variables influence the location of the current sheet. We found that the current sheet is typically shifted toward the dusk side of the planet, and that modeled asymmetries are especially prevalent during solar min. Previous model studies that lack crustal fields have found that, for a Parker spiral IMF, the current sheet will shift dawnward, while our results typically show the opposite. This could expose certain limitations in the models used, or it could reveal an interaction between the solar wind and the plasma environment of Mars that has not yet been explored. MAVEN data may be compared to the model results to confirm the sense of the modeled asymmetry. These results help us to probe the physics controlling the Martian magnetotail and atmospheric

Shear flow generation and transport barrier formation on rational surface current sheets in tokamaks

International Nuclear Information System (INIS)

Wang Xiaogang; Xiao Chijie; Wang Jiaqi

2009-01-01

Full text: A thin current sheet with a magnetic field component in the same direction can form the electrical field perpendicularly pointing to the sheet, therefore an ExB flow with a strong shear across the current sheet. An electrical potential well is also found on the rational surface of RFP as well as the neutral sheet of the magnetotail with the E-field pointing to the rational (neutral) surface. Theoretically, a current singularity is found to be formed on the rational surface in ideal MHD. It is then very likely that the sheet current on the rational surfaces will generate the electrical potential well in its vicinity so the electrical field pointing to the sheet. It results in an ExB flow with a strong shear in the immediate neighborhood of the rational surface. It may be the cause of the transport barrier often seen near the low (m, n) rational surfaces with MHD signals. (author)

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.

Monitoring dc stray current corrosion at sheet pile structures

NARCIS (Netherlands)

Peelen, W.H.A.; Neeft, E.A.C.; Leegwater, G.; Kanten-Roos, W. van; Courage, W.M.G.

2012-01-01

Steel is discarded by railway owners as a material for underground structures near railway lines, due to uncertainty over increased corrosion by DC stray currents stemming from the traction power system. This paper presents a large scale field test in which stray currents interference of a sheet

Onset of fast "ideal" tearing in thin current sheets: Dependence on the equilibrium current profile

Science.gov (United States)

Pucci, F.; Velli, M.; Tenerani, A.; Del Sarto, D.

2018-03-01

In this paper, we study the scaling relations for the triggering of the fast, or "ideal," tearing instability starting from equilibrium configurations relevant to astrophysical as well as laboratory plasmas that differ from the simple Harris current sheet configuration. We present the linear tearing instability analysis for equilibrium magnetic fields which (a) go to zero at the boundary of the domain and (b) contain a double current sheet system (the latter previously studied as a Cartesian proxy for the m = 1 kink mode in cylindrical plasmas). More generally, we discuss the critical aspect ratio scalings at which the growth rates become independent of the Lundquist number S, in terms of the dependence of the Δ' parameter on the wavenumber k of unstable modes. The scaling Δ'(k) with k at small k is found to categorize different equilibria broadly: the critical aspect ratios may be even smaller than L/a ˜ Sα with α = 1/3 originally found for the Harris current sheet, but there exists a general lower bound α ≥ 1/4.

The Topology and Properties of Mercury's Tail Current Sheet

Science.gov (United States)

Al Asad, M.; Johnson, C.; Philpott, L. C.

2017-12-01

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft orbited Mercury from March 2011 until April 2015, measuring the vector magnetic field inside and outside the magnetosphere. MESSENGER repeatedly encountered the tail current sheet (TCS) on the nightside of the planet. We examined 1s magnetic field data within 20 minutes of the magnetic equator position on 2435 orbit to characterize the shape and properties of Mercury's TCS and investigate its response to solar wind conditions. Identification of the TCS from vector magnetic field data used the following criteria: (1) a rapid rotation in the field direction from anti-sunward in the southern tail lobe to sunward in the northern lobe, accompanied by (2) a decrease in the field magnitude and (3) an increase in field variability. The current sheet was encountered on 606 orbits allowing the probability of encountering the tail current sheet in the equatorial plane to be mapped. Orbits on which the TCS was identified were binned spatially and superposed epoch analysis used to determine the field magnitude at the edge of the TCS, from which its time-averaged 3D shape was extracted. The TCS has an inner edge at 1.5 RM downtail in the midnight plane with a thickness of 0.34 RM, extends to the observation limit of 2.8 RM, decreasing in thickness to 0.28 RM. The thickness of the TCS increases in the dawn/dusk directions to 0.7 RM at 1.8 RM downtail and ± 1.5 RM from the noon-midnight plane and it warps towards the planet in the dawn/dusk directions. No strong correlations were found between the time-averaged shape and position of the TCS and solar wind conditions such as the solar wind ram pressure and the magnetic disturbance index, nor with parameters that control these conditions such as heliocentric distance. However, it is likely that the TCS does respond to these conditions on time scales too short to be characterized with MESSENGER data. In addition to mapping the shape of the

Lower hybrid drift instability in modified Harris current sheet with negative ions

International Nuclear Information System (INIS)

Huang Feng; Chen, Y-H; Shi Guifen; Hu, Z-Q; Yu, M Y

2008-01-01

The lower hybrid drift instability (LHDI) in a Harris current sheet with negative ions is investigated using the kinetic theory. Numerical results show that the negative ions have considerable effect on the LHDI. With increase of the negative-ion concentration, the growth rate of the LHDI increases and its real frequency decreases for any wave length. The Harris current sheet can thus be significantly modified

Toroidal current asymmetry in tokamak disruptions

Science.gov (United States)

Strauss, H. R.

2014-10-01

It was discovered on JET that disruptions were accompanied by toroidal asymmetry of the toroidal plasma current I ϕ. It was found that the toroidal current asymmetry was proportional to the vertical current moment asymmetry with positive sign for an upward vertical displacement event (VDE) and negative sign for a downward VDE. It was observed that greater displacement leads to greater measured I ϕ asymmetry. Here, it is shown that this is essentially a kinematic effect produced by a VDE interacting with three dimensional MHD perturbations. The relation of toroidal current asymmetry and vertical current moment is calculated analytically and is verified by numerical simulations. It is shown analytically that the toroidal variation of the toroidal plasma current is accompanied by an equal and opposite variation of the toroidal current flowing in a thin wall surrounding the plasma. These currents are connected by 3D halo current, which is π/2 radians out of phase with the n = 1 toroidal current variations.

Simulation of auroral current sheet equilibria and associated V-shaped potential structures

International Nuclear Information System (INIS)

Singh, N.; Thiemann, H.; Schunk, R.W.

1983-01-01

Results from numerical simulations of auroral current sheet equilibrium and associated V-shaped potential structures are presented. It is shown that with allowance for both hot magnetospheric ion and cold ionospheric ion populations, the perpendicular potential drop, assiciated with a non-neutral auroral current sheet is critically controlled by the temperature of the 'heated' ionospheric ions. The heating is caused by the wave turbulence excited by the auroral current sheet. In the presence of heated ionospheric ions, a relatively large variation in the temperature of the hot magnetospheric ion population causes a very small variation in the potential drop thetam. The perpendicular potential drop acts to produce a V-shaped double layer with multiple potential steps parallel to the magnetic field when a zero potential boundary condition is imposed at the ionospheric boundary. Outside the V-shaped potential structure, ionospheric return currents develop self-consistently

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.

Study of the generation and suppression of runaway currents in provoked disruptions in J-TEXT

Energy Technology Data Exchange (ETDEWEB)

Chen, Z.Y., E-mail: zychen@mail.hust.edu.cn [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, College of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan, 430074 (China); Chen, Z.P., E-mail: zpchen@mail.hust.edu.cn [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, College of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan, 430074 (China); Zhang, Y.; Jin, W.; Fang, D.; Ba, W.G.; Wang, Z.J.; Zhang, M.; Yang, Z.J.; Ding, Y.H.; Zhuang, G. [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, College of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan, 430074 (China)

2012-05-14

Runaway currents following disruptions have an important effect on the first wall for the next generation tokamak. The behaviors of runaway currents following intentional provoked disruptions have been investigated in the J-TEXT tokamak. It is found that the runaway current generation following provoked disruptions depends on both the toroidal magnetic field and the plasma current. The conversion efficiency of pre-disruptive plasma currents into runaway currents is in the ranges of 30% to 60% in J-TEXT. The runaway currents can be avoided by the intensive gas puffing of H{sub 2} due to the low multiplication factor in J-TEXT. -- Highlights: ► The regime of runaway generation in disruptions in J-TEXT has been established. ► The magnetic field threshold for runaway current generation in disruptions is 2.2 T. ► The conversion efficiency of runaway current is in the ranges of 30% to 60%. ► The runaway currents can be avoided by the intensive gas puffing of H{sub 2}.

Study of the generation and suppression of runaway currents in provoked disruptions in J-TEXT

International Nuclear Information System (INIS)

Chen, Z.Y.; Chen, Z.P.; Zhang, Y.; Jin, W.; Fang, D.; Ba, W.G.; Wang, Z.J.; Zhang, M.; Yang, Z.J.; Ding, Y.H.; Zhuang, G.

2012-01-01

Runaway currents following disruptions have an important effect on the first wall for the next generation tokamak. The behaviors of runaway currents following intentional provoked disruptions have been investigated in the J-TEXT tokamak. It is found that the runaway current generation following provoked disruptions depends on both the toroidal magnetic field and the plasma current. The conversion efficiency of pre-disruptive plasma currents into runaway currents is in the ranges of 30% to 60% in J-TEXT. The runaway currents can be avoided by the intensive gas puffing of H 2 due to the low multiplication factor in J-TEXT. -- Highlights: ► The regime of runaway generation in disruptions in J-TEXT has been established. ► The magnetic field threshold for runaway current generation in disruptions is 2.2 T. ► The conversion efficiency of runaway current is in the ranges of 30% to 60%. ► The runaway currents can be avoided by the intensive gas puffing of H 2 .

Current density distribution during disruptions and sawteeth in a simple model of plasma current in a tokamak

International Nuclear Information System (INIS)

Stefanovskii, A. M.

2011-01-01

The processes that are likely to accompany discharge disruptions and sawteeth in a tokamak are considered in a simple plasma current model. The redistribution of the current density in plasma is supposed to be primarily governed by the onset of the MHD-instability-driven turbulent plasma mixing in a finite region of the current column. For different disruption conditions, the variation in the total plasma current (the appearance of a characteristic spike) is also calculated. It is found that the numerical shape and amplitude of the total current spikes during disruptions approximately coincide with those measured in some tokamak experiments. Under the assumptions adopted in the model, the physical mechanism for the formation of the spikes is determined. The mechanism is attributed to the diffusion of the negative current density at the column edge into the zero-conductivity region. The numerical current density distributions in the plasma during the sawteeth differ from the literature data.

On the magnitude and distribution of halo currents during disruptions on MAST

International Nuclear Information System (INIS)

Counsell, G F; Martin, R; Pinfold, T; Taylor, D

2007-01-01

Recent results from MAST in which all halo current paths are monitored suggest that, during disruptions, the plasma responsible for the generation of halo current acts more as a voltage source than a current source. As a result the resistance of the current path along which the halo current must flow has a profound impact on the magnitude of the current. This may provide opportunities for directing the current away from sensitive components in future devices such as ITER. Analysis of data from over 3800 disruptions shows that the halo currents on MAST are relatively benign, having a peak value less than 25% of the pre-disruption plasma current with a rather symmetric distribution near the centre column (average toroidal peaking factor ∼1.1). The low peaking factor favourably reduces the tilting/bending forces in the region of the centre column, which has limited space for bulky supports

Characteristics of current quenches during disruptions in the J-TEXT tokamak

International Nuclear Information System (INIS)

Zhang, Y; Chen, Z Y; Fang, D; Jin, W; Huang, Y H; Wang, Z J; Yang, Z J; Chen, Z P; Ding, Y H; Zhang, M; Zhuang, G

2012-01-01

Characteristics of tokamak current quenches are an important issue for the determination of electro-magnetic forces that act on the in-vessel components and vacuum vessel during major disruptions. The characteristics of current quenches in spontaneous disruptions in the J-TEXT tokamak have been investigated. It is shown that the waveforms for the fastest current quenches are more accurately fitted by linear current decays than exponential, although neither is a good fit in many slower cases. The minimum current quench time is about 2.4 ms for the J-TEXT tokamak. The maximum instantaneous current quench rate is more than seven times the average current quench rate in J-TEXT. (paper)

Intensity variation of cosmic rays near the heliospheric current sheet

International Nuclear Information System (INIS)

Badruddin, K.S.; Yadav, R.S.; Yadav, N.R.

1985-01-01

Cosmic ray intensity variations near the heliospheric current sheet-both above and below it-have been studied during 1964-76. Superposed epoch analysis of the cosmic ray neutron monitor data with respect to sector boundaries (i.e., heliospheric current sheet crossings) has been performed. In this analysis data from neutron monitors well distributed in latitude over the Earth's surface is used. First, this study has been made during the two solar activity minimum periods 1964-65 and 1975-76, using the data from Thule (cut-off rigidity O GV), Deep River (cut-off rigidity 1.02 GV), Rome (cut-off rigidity 6.32 GV) and Huancayo (cut-off rigidity 13.45 GV) neutron monitors. The data is analyzed from Deep River, Rome and Huancayo neutron monitors, for which data is available for the full period (1964-76), by dividing the periods according to the changes in solar activity, interplanetary magnetic field polarity and coronal holes. All these studies have shown a negative gradient with respect to heliomagnetic latitude (current sheet). These results have been discussed in the light of theoretical and observational evidences. Suggestions have been given to overcome the discrepancy between the observational and theoretical results. Further, possible explanations for these observational results have been suggested. (author)

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.

Hysteresis-controlled instability waves in a scale-free driven current sheet model

Directory of Open Access Journals (Sweden)

V. M. Uritsky

2005-01-01

Full Text Available Magnetospheric dynamics is a complex multiscale process whose statistical features can be successfully reproduced using high-dimensional numerical transport models exhibiting the phenomenon of self-organized criticality (SOC. Along this line of research, a 2-dimensional driven current sheet (DCS model has recently been developed that incorporates an idealized current-driven instability with a resistive MHD plasma system (Klimas et al., 2004a, b. The dynamics of the DCS model is dominated by the scale-free diffusive energy transport characterized by a set of broadband power-law distribution functions similar to those governing the evolution of multiscale precipitation regions of energetic particles in the nighttime sector of aurora (Uritsky et al., 2002b. The scale-free DCS behavior is supported by localized current-driven instabilities that can communicate in an avalanche fashion over arbitrarily long distances thus producing current sheet waves (CSW. In this paper, we derive the analytical expression for CSW speed as a function of plasma parameters controlling local anomalous resistivity dynamics. The obtained relation indicates that the CSW propagation requires sufficiently high initial current densities, and predicts a deceleration of CSWs moving from inner plasma sheet regions toward its northern and southern boundaries. We also show that the shape of time-averaged current density profile in the DCS model is in agreement with steady-state spatial configuration of critical avalanching models as described by the singular diffusion theory of the SOC. Over shorter time scales, SOC dynamics is associated with rather complex spatial patterns and, in particular, can produce bifurcated current sheets often seen in multi-satellite observations.

Spatially Localized Particle Energization by Landau Damping in Current Sheets

Science.gov (United States)

Howes, G. G.; Klein, K. G.; McCubbin, A. J.

2017-12-01

Understanding the mechanisms of particle energization through the removal of energy from turbulent fluctuations in heliospheric plasmas is a grand challenge problem in heliophysics. Under the weakly collisional conditions typical of heliospheric plasma, kinetic mechanisms must be responsible for this energization, but the nature of those mechanisms remains elusive. In recent years, the spatial localization of plasma heating near current sheets in the solar wind and numerical simulations has gained much attention. Here we show, using the innovative and new field-particle correlation technique, that the spatially localized particle energization occurring in a nonlinear gyrokinetic simulation has the velocity space signature of Landau damping, suggesting that this well-known collisionless damping mechanism indeed actively leads to spatially localized heating in the vicinity of current sheets.

On the instability of a quasiequilibrium current sheet and the onset of impulsive bursty reconnection

International Nuclear Information System (INIS)

Skender, Marina; Lapenta, Giovanni

2010-01-01

A two-dimensional reconnecting current sheet is studied numerically in the magnetohydrodynamic approach. Different simulation setups are employed in order to follow the evolution of the formed current sheet in diverse configurations: two types of initial equilibria, Harris and force-free, two types of boundary conditions, periodic and open, with uniform and nonuniform grid set, respectively. All the simulated cases are found to exhibit qualitatively the same behavior in which a current sheet evolves slowly through a series of quasiequilibria; eventually it fragments and enters a phase of fast impulsive bursty reconnection. In order to gain more insight on the nature and characteristics of the instability taking place, physical characteristics of the simulated current sheet are related to its geometrical properties. At the adopted Lundquist number of S=10 4 and Reynolds number R=10 4 , the ratio of the length to width (aspect ratio) of the formed current sheet is observed to increase slowly in time up to a maximum value at which it fragments. Moreover, additional turbulence applied to the system is shown to exhibit the same qualitative steps, but with the sooner onset of the fragmentation and at smaller aspect ratio.

Axisymmetric disruption dynamics including current profile changes in the ASDEX-Upgrade tokamak

International Nuclear Information System (INIS)

Nakamura, Y.; Pautasso, G.; Gruber, O.; Jardin, S.C.

2002-01-01

Axisymmetric MHD simulations have revealed a new driving mechanism that governs the vertical displacement event (VDE) dynamics in tokamak disruptions. A rapid flattening of the plasma current profile during the disruption plays a substantial role in dragging a single null-diverted plasma vertically towards the divertor. As a consequence, the occurrence of downward-going VDEs predominates over the upward-going ones in bottom-diverted discharges. This dragging effect, due to an abrupt change in the current profile, is absent in up-down symmetric limiter discharges. These simulation results are consistent with experiments in ASDEX-Upgrade. Together with the attractive force that arises from passive shell currents induced by the plasma current quench, the dragging effect explains many details of the VDE dynamics over the whole period of the disruptive termination. (author)

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.

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.

Additional acceleration of solar-wind particles in current sheets of the heliosphere

Directory of Open Access Journals (Sweden)

V. Zharkova

2015-04-01

Full Text Available Particles of fast solar wind in the vicinity of the heliospheric current sheet (HCS or in a front of interplanetary coronal mass ejections (ICMEs often reveal very peculiar energy or velocity profiles, density distributions with double or triple peaks, and well-defined streams of electrons occurring around or far away from these events. In order to interpret the parameters of energetic particles (both ions and electrons measured by the WIND spacecraft during the HCS crossings, a comparison of the data was carried out with 3-D particle-in-cell (PIC simulations for the relevant magnetic topology (Zharkova and Khabarova, 2012. The simulations showed that all the observed particle-energy distributions, densities, ion peak velocities, electron pitch angles and directivities can be fitted with the same model if the heliospheric current sheet is in a status of continuous magnetic reconnection. In this paper we present further observations of the solar-wind particles being accelerated to rather higher energies while passing through the HCS and the evidence that this acceleration happens well before the appearance of the corotating interacting region (CIR, which passes through the spacecraft position hours later. We show that the measured particle characteristics (ion velocity, electron pitch angles and the distance at which electrons are turned from the HCS are in agreement with the simulations of additional particle acceleration in a reconnecting HCS with a strong guiding field as measured by WIND. A few examples are also presented showing additional acceleration of solar-wind particles during their passage through current sheets formed in a front of ICMEs. This additional acceleration at the ICME current sheets can explain the anticorrelation of ion and electron fluxes frequently observed around the ICME's leading front. Furthermore, it may provide a plausible explanation of the appearance of bidirectional "strahls" (field-aligned most energetic

Instabilities of collisionless current sheets revisited: The role of anisotropic heating

International Nuclear Information System (INIS)

Muñoz, P. A.; Kilian, P.; Büchner, J.

2014-01-01

In this work, we investigate the influence of the anisotropic heating on the spontaneous instability and evolution of thin Harris-type collisionless current sheets, embedded in antiparallel magnetic fields. In particular, we explore the influence of the macroparticle shape-function using a 2D version of the PIC code ACRONYM. We also investigate the role of the numerical collisionality due to the finite number of macroparticles in PIC codes. It is shown that it is appropriate to choose higher order shape functions of the macroparticles compared to a larger number of macroparticles per cell. This allows to estimate better the anisotropic electron heating due to the collisions of macroparticles in a PIC code. Temperature anisotropies can stabilize the tearing mode instability and trigger additional current sheet instabilities. We found a good agreement between the analytically derived threshold for the stabilization of the anisotropic tearing mode and other instabilities, either spontaneously developing or initially triggered ones. Numerical effects causing anisotropic heating at electron time scales become especially important for higher mass ratios (above m i /m e =180). If numerical effects are carefully taken into account, one can recover the theoretical estimated linear growth rates of the tearing instability of thin isotropic collisionless current sheets, also for higher mass ratios

Electron Cooling and Isotropization during Magnetotail Current Sheet Thinning: Implications for Parallel Electric Fields

Science.gov (United States)

Lu, San; Artemyev, A. V.; Angelopoulos, V.

2017-11-01

Magnetotail current sheet thinning is a distinctive feature of substorm growth phase, during which magnetic energy is stored in the magnetospheric lobes. Investigation of charged particle dynamics in such thinning current sheets is believed to be important for understanding the substorm energy storage and the current sheet destabilization responsible for substorm expansion phase onset. We use Time History of Events and Macroscale Interactions during Substorms (THEMIS) B and C observations in 2008 and 2009 at 18 - 25 RE to show that during magnetotail current sheet thinning, the electron temperature decreases (cooling), and the parallel temperature decreases faster than the perpendicular temperature, leading to a decrease of the initially strong electron temperature anisotropy (isotropization). This isotropization cannot be explained by pure adiabatic cooling or by pitch angle scattering. We use test particle simulations to explore the mechanism responsible for the cooling and isotropization. We find that during the thinning, a fast decrease of a parallel electric field (directed toward the Earth) can speed up the electron parallel cooling, causing it to exceed the rate of perpendicular cooling, and thus lead to isotropization, consistent with observation. If the parallel electric field is too small or does not change fast enough, the electron parallel cooling is slower than the perpendicular cooling, so the parallel electron anisotropy grows, contrary to observation. The same isotropization can also be accomplished by an increasing parallel electric field directed toward the equatorial plane. Our study reveals the existence of a large-scale parallel electric field, which plays an important role in magnetotail particle dynamics during the current sheet thinning process.

Propagation of large amplitude Alfven waves in the solar wind current sheet

International Nuclear Information System (INIS)

Malara, Francesco; Primavera, Leonardo; Veltri, Pierluigi

1996-01-01

The time evolution of Alfvenic perturbations in the Solar Wind current sheet is studied by using numerical simulations of the compressible magnetohydrodynamic (MHD) equations. The simulations show that the interaction between the large amplitude Alfvenic pertubation and the solar wind current sheet decreases the correlation between velocity and magnetic field fluctuations and produces compressive fluctuations. The characteristics of these compressive fluctuations compare rather well with spatial observations. The behavior of the correlation between density and magnetic field intensity fluctuations and of the their spectra are well reproduced so that the physical mechanisms giving rise to these behaviors can be identified

Survey of large-amplitude flapping motions in the midtail current sheet

Directory of Open Access Journals (Sweden)

V. A. Sergeev

2006-08-01

Full Text Available We surveyed fast current sheet crossings (flapping motions over the distance range 10–30 RE in the magnetotail covered by the Geotail spacecraft. Since the local tilts of these dynamic sheets are large and variable in these events, we compare three different methods of evaluating current sheet normals using 4-s/c Cluster data and define the success criteria for the single-spacecraft-based method (MVA to obtain the reliable results. Then, after identifying more than ~1100 fast CS crossings over a 3-year period of Geotail observations in 1997–1999, we address their parameters, spatial distribution and activity dependence. We confirm that over the entire distance covered and LT bins, fast crossings have considerable tilts in the YZ plane (from estimated MVA normals which show a preferential appearance of one (YZ kink-like mode that is responsible for these severe current sheet perturbations. Their occurrence is highly inhomogeneous; it sharply increases with radial distance and has a peak in the tail center (with some duskward shift, resembling the occurrence of the BBFs, although there is no one-to-one local correspondence between these two phenomena. The crossing durations typically spread around 1 min and decrease significantly where the high-speed flows are registered. Based on an AE index superposed epoch study, the flapping motions prefer to appear during the substorm expansion phase, although a considerable number of events without any electrojet and auroral activity were also observed. We also present statistical distributions of other parameters and briefly discuss what could be possible mechanisms to generate the flapping motions.

On the energy release rate in a turbulent current sheet on the Sun

International Nuclear Information System (INIS)

Bardakov, V.M.

1986-01-01

It is shown that turbulent current sheets on the Sun, realizing in the form of the Parker - Sweet flow, are in quasilinear regime of turbulence (or in the regime of instability threshold). The energy release rate in such sheets does not exceed 10 26 erg/s for typical plasma parameters in active regions

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.)

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

Characteristics of disruptive plasma current decay in the HT-2 tokamak

International Nuclear Information System (INIS)

Abe, Mitsushi; Takeuchi, Kazuhiro; Otsuka, Michio

1993-01-01

Motions of plasma current channel and time evolutions of eddy current distribution on the vacuum vessel during disruptive plasma current decay were studied experimentally in the Hitachi tokamak HT-2. The plasmas are vertically elongated and circularly shaped plasmas. A disruptive plasma current decay has three phases. During the first phase, a large displacement of the plasma position without plasma current decay is observed. Rapid plasma current decay is observed during the second phase and the decay rate is roughly constant with time. The eddy current distribution is like that due to the shell effect which creates a poloidal field to reduce the plasma displacement. During the third phase, the plasma current decays exponentially. The second phase is observed in slightly elongated and high plasma current (> 20 kA) circularly shaped plasmas. The plasma current decay rates in the second phase depend on the plasma cross sectional shape, but they do not in the third phase. The magnetic axis moves from the plasma area to the vacuum vessel wall between the second and third phases. (author)

Instabilities of collisionless current sheets: Theory and simulations

International Nuclear Information System (INIS)

Silin, I.; Buechner, J.; Zelenyi, L.

2002-01-01

The problem of Harris current sheet stability is investigated. A linear dispersion relation in the long-wavelength limit is derived for instabilities, propagating in the neutral plane at an arbitrary angle to the magnetic field but symmetric across the sheet. The role of electrostatic perturbations is especially investigated. It appears, that for the tearing-mode instability electrostatic effects are negligible. However, for obliquely propagating modes the modulation of the electrostatic potential φ is essential. In order to verify the theoretical results, the limiting cases of tearing and sausage instabilities are compared to the two-dimensional (2D) Vlasov code simulations. For tearing the agreement between theory and simulations is good for all mass ratios. For sausage-modes, the theory predicts fast stabilization for mass ratios m i /m e ≥10. This is not observed in simulations due to the diminishing of the wavelength for higher mass ratios, which leads beyond the limit of applicability of the theory developed here

Kinky heliospheric current sheet: Cause of CDAW-6 substorms

International Nuclear Information System (INIS)

Tsurutani, B.T.; Russell, C.T.; King, J.H.; Zwickl, R.D.; Lin, R.P.

1984-01-01

Two magnetospheric substorms and the intensification of the second are caused by interplanetary magnetic field and ram pressure changes associated with a kinky heliospheric current sheet (KHCS). The responsible interplanetary features occur in a highly compressed region between a solar flare-associated shock wave and the cold driver gas. The possibity that the interplanetary structure is a ''magnetic cloud'' is ruled out

High-resolution disruption halo current measurements using Langmuir probes in Alcator C-Mod

Science.gov (United States)

Tinguely, R. A.; Granetz, R. S.; Berg, A.; Kuang, A. Q.; Brunner, D.; LaBombard, B.

2018-01-01

Halo currents generated during disruptions on Alcator C-Mod have been measured with Langmuir ‘rail’ probes. These rail probes are embedded in a lower outboard divertor module in a closely-spaced vertical (poloidal) array. The dense array provides detailed resolution of the spatial dependence (~1 cm spacing) of the halo current distribution in the plasma scrape-off region with high time resolution (400 kHz digitization rate). As the plasma limits on the outboard divertor plate, the contact point is clearly discernible in the halo current data (as an inversion of current) and moves vertically down the divertor plate on many disruptions. These data are consistent with filament reconstructions of the plasma boundary, from which the edge safety factor of the disrupting plasma can be calculated. Additionally, the halo current ‘footprint’ on the divertor plate is obtained and related to the halo flux width. The voltage driving halo current and the effective resistance of the plasma region through which the halo current flows to reach the probes are also investigated. Estimations of the sheath resistance and halo region resistivity and temperature are given. This information could prove useful for modeling halo current dynamics.

Axisymmetric MHD simulation of ITB crash and following disruption dynamics of Tokamak plasmas with high bootstrap current

International Nuclear Information System (INIS)

Takei, Nahoko; Tsutsui, Hiroaki; Tsuji-Iio, Shunji; Shimada, Ryuichi; Nakamura, Yukiharu; Kawano, Yasunori; Ozeki, Takahisa; Tobita, Kenji; Sugihara, Masayoshi

2004-01-01

Axisymmetric MHD simulation using the Tokamak Simulation Code demonstrated detailed disruption dynamics triggered by a crash of internal transport barrier in high bootstrap current, high β, reversed shear plasmas. Self-consistent time-evolutions of ohmic current bootstrap current and induced loop voltage profiles inside the disrupting plasma were shown from a view point of disruption characterization and mitigation. In contrast with positive shear plasmas, a particular feature of high bootstrap current reversed shear plasma disruption was computed to be a significant change of plasma current profile, which is normally caused due to resistive diffusion of the electric field induced by the crash of internal transport barrier in a region wider than the internal transport barrier. Discussion based on the simulation results was made on the fastest record of the plasma current quench observed in JT-60U reversed shear plasma disruptions. (author)

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].

Observations of the Formation, Development, and Structure of a Current Sheet in an Eruptive Solar Flare

Energy Technology Data Exchange (ETDEWEB)

Seaton, Daniel B.; Darnel, Jonathan M. [Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, Boulder, CO 80305 (United States); Bartz, Allison E., E-mail: daniel.seaton@noaa.gov [Department of Physics, Grinnell College, Grinnell, IA 50112 (United States)

2017-02-01

We present Atmospheric Imaging Assembly observations of a structure we interpret as a current sheet associated with an X4.9 flare and coronal mass ejection that occurred on 2014 February 25 in NOAA Active Region 11990. We characterize the properties of the current sheet, finding that the sheet remains on the order of a few thousand kilometers thick for much of the duration of the event and that its temperature generally ranged between 8 and 10 MK. We also note the presence of other phenomena believed to be associated with magnetic reconnection in current sheets, including supra-arcade downflows and shrinking loops. We estimate that the rate of reconnection during the event was M{sub A} ≈ 0.004–0.007, a value consistent with model predictions. We conclude with a discussion of the implications of this event for reconnection-based eruption models.

Mutual Inductance Problem for a System Consisting of a Current Sheet and a Thin Metal Plate

Science.gov (United States)

Fulton, J. P.; Wincheski, B.; Nath, S.; Namkung, M.

1993-01-01

Rapid inspection of aircraft structures for flaws is of vital importance to the commercial and defense aircraft industry. In particular, inspecting thin aluminum structures for flaws is the focus of a large scale R&D effort in the nondestructive evaluation (NDE) community. Traditional eddy current methods used today are effective, but require long inspection times. New electromagnetic techniques which monitor the normal component of the magnetic field above a sample due to a sheet of current as the excitation, seem to be promising. This paper is an attempt to understand and analyze the magnetic field distribution due to a current sheet above an aluminum test sample. A simple theoretical model, coupled with a two dimensional finite element model (FEM) and experimental data will be presented in the next few sections. A current sheet above a conducting sample generates eddy currents in the material, while a sensor above the current sheet or in between the two plates monitors the normal component of the magnetic field. A rivet or a surface flaw near a rivet in an aircraft aluminum skin will disturb the magnetic field, which is imaged by the sensor. Initial results showed a strong dependence of the flaw induced normal magnetic field strength on the thickness and conductivity of the current-sheet that could not be accounted for by skin depth attenuation alone. It was believed that the eddy current imaging method explained the dependence of the thickness and conductivity of the flaw induced normal magnetic field. Further investigation, suggested the complexity associated with the mutual inductance of the system needed to be studied. The next section gives an analytical model to better understand the phenomenon.

Prevention of the current-quench phase of a major disruption in a tokamak reactor

International Nuclear Information System (INIS)

Miller, J.B.

1987-01-01

The 2-D Tokamak Simulation Code written by the Princeton Plasma Physics Laboratory was joined to a 3-D eddy-current code, which models periodic torus sectors. The combined system was found to be an efficient and accurate method for modeling the plasma/eddy current interaction during a major disruption. For modeling large highly compartmentalized structures, artificially increasing the self-inductance and limiting the mutual inductance of current elements were necessary to enhance numerical stability. Even with these modifications, a slowly growing instability made the results unreliable after 58 ms. This model was used to demonstrate prevention of the current quench phase of a major disruption in INTOR. The average plasma temperature was reduced to 150 eV over 3 ms. The (outboard) breeding blanket structure was constructed of CuBeNi and was electrically connected between torus sectors. Disruption recovery coils were provided inboard of the inboard shield (linking the toroidal field coils). It was necessary to supply to these coils a total of 500 MW for 0.6 s and to reheat the plasma to full beta in 6 s. The calculation shows a method of recovery from the most severe disruption probable. Determining the severity of the disruption from which recovery would be cost effective is beyond the scope of this study

Chaotic jumps in the generalized first adiabatic invariant in current sheets

International Nuclear Information System (INIS)

Brittnacher, M.J.; Whipple, E.C.

1991-01-01

In attempting to develop a fluidlike model of plasma dynamics in a current sheet, kinetic effects due to chaotic non-adiabatic particle motion must be included in any realistic description. Using drift variables, derived by the Kruskal averaging procedure, to construct distribution functions may provide an approach in which to develop the fluid description. However, the drift motion is influenced by abrupt changes in the value of the generalized first adiabatic invariant J. In this letter, the authors indicate how the changes in J derived from separatrix crossing theory can be incorporated into the drift variable approach to generating distribution functions. In particular, the authors propose a method to determine distribution functions for an ensemble of particles following interactions with the tail current sheet by treating the interaction as a scattering problem characterized by changes in the invariant

Flapping current sheet with superposed waves seen in space and on the ground

Science.gov (United States)

Wang, Guoqiang; Volwerk, Martin; Nakamura, Rumi; Boakes, Peter; Zhang, Tielong; Ge, Yasong; Yoshikawa, Akimasa; Baishev, Dmitry

2015-04-01

A wavy current sheet event observed on 15th of October 2004 between 1235 and 1300 UT has been studied by using Cluster and ground-based magnetometer data. Waves propagating from the tail centre to the duskside flank with a period ~30 s and wavelength ~1 RE, are superimposed on a flapping current sheet, accompanied with a bursty bulk flow (BBF). Three Pi2 pulsations, with onset at ~1236, ~1251 and ~1255 UT, respectively, are observed at the Tixie (TIK) station located near the foot-points of Cluster. The mechanism creating the Pi2 (period ~40 s) onset at ~1236 UT is unclear. The second Pi2 (period ~90 s, onset at ~1251 UT) is associated with a strong field-aligned current, which has a strong transverse component of the magnetic field, observed by Cluster with a time delay ~60 s. We suggest that it is caused by bouncing Alfvén waves between the northern and southern ionosphere which transport the field-aligned current. For the third Pi2 (period ~60 s) there is almost no damping at the first three periods. They occur in conjunction with periodic field-aligned currents one-on-one with 72s delay. We suggest that it is generated by these periodic field-aligned currents. We conclude that the strong field-aligned currents generated in the plasma sheet during flapping with superimposed higher frequency waves can drive Pi2 pulsations on the ground, and periodic field-aligned currents can even control the period of the Pi2s.

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.

Radial expansion of the tail current disruption during substorms: A new approach to the substorm onset region

International Nuclear Information System (INIS)

Ohtani, S.; Kokubun, S.; Russell, C.T.

1992-01-01

The substorm onset region and the radial development of the tail current disruption are examined from a new viewpoint. The reconfiguration of the magnetotail field at substorm onset can be understood in terms of a sudden decrease (disruption) in tail current intensity. The north-south component (B Z ) is very sensitive to whether the spacecraft position is earthward or tailward of the disruption region, while the change in Sun-Earth component (B X ) is most sensitive to the change in tail current intensity near the spacecraft. If the current disruption starts in a localized range of radial distance and expands radially, a distinctive phase relationship between the changes in B X and B Z is expected to be observed. This phase relationship depends on whether the current disruption starts on the earthward side or the tailward side of the spacecraft. Thus it is possible to infer the direction of the radial expansion of the current disruption from magnetic field data of a single spacecraft. This method is applied to ISEE observations of a tail reconfiguration event that occurred on March 6, 1979. The phase relationship indicates that eh disruption region expanded tailward from the earthward side of the spacecraft during the event. This model prediction is consistent with the time lag of magnetic signatures observed by the two ISEE spacecraft. The expansion velocity is estimated at 2 R E /min (∼200 km/s) for this event. Furthermore, it is found that the observed magnetic signatures can be reproduced to a good approximation by a simple geometrical model of the current disruption. The method is used statistically for 13 events selected from the ISEE magnetometer data. It is found that the current disruption usually starts in the near-Earth magnetotail (|X| E ) and often within 15 R E of the Earth

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.

Is the Near-Earth Current Sheet Prior to Reconnection Unstable to Tearing Mode?

International Nuclear Information System (INIS)

Xin-Hua, Wei; Jin-Bin, Cao; Guo-Cheng, Zhou; Hui-Shan, Fu

2010-01-01

The tearing mode instability plays a key role in the triggering process of reconnection. The triggering collisionless tearing mode instability has been theoretically and numerically analyzed by many researchers. However, due to the difficulty in obtaining the observational wave number, it is still unknown whether the tearing mode instability can be excited in an actual plasma sheet prior to reconnection onset. Using the data from four Cluster satellites prior to a magnetospheric reconnection event on 13 September 2002, we utilized the wave telescope technique to obtain the wave number which corresponds to the peak of power spectral density. The wavelength is about 18R E and is consistent with previous theoretic and numerical results. After substituting the wave vector and other necessary parameters of the observed current sheet into the triggering condition of tearing mode instability, we find that the near-Earth current sheet prior to reconnection is unstable to tearing mode. (geophysics, astronomy, and astrophysics)

Modeling Solar Energetic Particle Transport near a Wavy Heliospheric Current Sheet

Science.gov (United States)

Battarbee, Markus; Dalla, Silvia; Marsh, Mike S.

2018-02-01

Understanding the transport of solar energetic particles (SEPs) from acceleration sites at the Sun into interplanetary space and to the Earth is an important question for forecasting space weather. The interplanetary magnetic field (IMF), with two distinct polarities and a complex structure, governs energetic particle transport and drifts. We analyze for the first time the effect of a wavy heliospheric current sheet (HCS) on the propagation of SEPs. We inject protons close to the Sun and propagate them by integrating fully 3D trajectories within the inner heliosphere in the presence of weak scattering. We model the HCS position using fits based on neutral lines of magnetic field source surface maps (SSMs). We map 1 au proton crossings, which show efficient transport in longitude via HCS, depending on the location of the injection region with respect to the HCS. For HCS tilt angles around 30°–40°, we find significant qualitative differences between A+ and A‑ configurations of the IMF, with stronger fluences along the HCS in the former case but with a distribution of particles across a wider range of longitudes and latitudes in the latter. We show how a wavy current sheet leads to longitudinally periodic enhancements in particle fluence. We show that for an A+ IMF configuration, a wavy HCS allows for more proton deceleration than a flat HCS. We find that A‑ IMF configurations result in larger average fluences than A+ IMF configurations, due to a radial drift component at the current sheet.

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.

Disintegration of liquid sheets

Science.gov (United States)

Mansour, Adel; Chigier, Norman

1990-01-01

The development, stability, and disintegration of liquid sheets issuing from a two-dimensional air-assisted nozzle is studied. Detailed measurements of mean drop size and velocity are made using a phase Doppler particle analyzer. Without air flow the liquid sheet converges toward the axis as a result of surface tension forces. With airflow a quasi-two-dimensional expanding spray is formed. The air flow causes small variations in sheet thickness to develop into major disturbances with the result that disruption starts before the formation of the main break-up region. In the two-dimensional variable geometry air-blast atomizer, it is shown that the air flow is responsible for the formation of large, ordered, and small chaotic 'cell' structures.

Distributions of the ion temperature, ion pressure, and electron density over the current sheet surface

International Nuclear Information System (INIS)

Kyrie, N. P.; Markov, V. S.; Frank, A. G.; Vasilkov, D. G.; Voronova, E. V.

2016-01-01

The distributions of the ion temperature, ion pressure, and electron density over the width (the major transverse dimension) of the current sheet have been studied for the first time. The current sheets were formed in discharges in argon and helium in 2D and 3D magnetic configurations. It is found that the temperature of argon ions in both 2D and 3D magnetic configurations is almost uniform over the sheet width and that argon ions are accelerated by the Ampère force. In contrast, the distributions of the electron density and the temperature of helium ions are found to be substantially nonuniform. As a result, in the 2D magnetic configuration, the ion pressure gradient across the sheet width makes a significant contribution (comparable with the Ampère force) to the acceleration of helium ions, whereas in the 3D magnetic configuration, the Ampère force is counterbalanced by the pressure gradient.

Distributions of the ion temperature, ion pressure, and electron density over the current sheet surface

Energy Technology Data Exchange (ETDEWEB)

Kyrie, N. P., E-mail: kyrie@fpl.gpi.ru; Markov, V. S., E-mail: natalya.kyrie@yandex.ru; Frank, A. G.; Vasilkov, D. G.; Voronova, E. V. [Russian Academy of Sciences, Prokhorov General Physics Institute (Russian Federation)

2016-06-15

The distributions of the ion temperature, ion pressure, and electron density over the width (the major transverse dimension) of the current sheet have been studied for the first time. The current sheets were formed in discharges in argon and helium in 2D and 3D magnetic configurations. It is found that the temperature of argon ions in both 2D and 3D magnetic configurations is almost uniform over the sheet width and that argon ions are accelerated by the Ampère force. In contrast, the distributions of the electron density and the temperature of helium ions are found to be substantially nonuniform. As a result, in the 2D magnetic configuration, the ion pressure gradient across the sheet width makes a significant contribution (comparable with the Ampère force) to the acceleration of helium ions, whereas in the 3D magnetic configuration, the Ampère force is counterbalanced by the pressure gradient.

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.

PERISTALTIC PUMPING NEAR POST-CORONAL MASS EJECTION SUPRA-ARCADE CURRENT SHEETS

Energy Technology Data Exchange (ETDEWEB)

Scott, Roger B.; Longcope, Dana W.; McKenzie, David E., E-mail: rscott@physics.montana.edu [Department of Physics, Montana State University, P.O. Box 173840, Bozeman, MT 59717 (United States)

2013-10-10

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

Electromagnetic analysis of ITER generic equatorial port plug designs during three plasma current disruption cases

International Nuclear Information System (INIS)

Guirao, J.; Rodríguez, E.; Ordieres, J.; Cabanas, M.F.; García, C.H. Rojas

2012-01-01

Highlights: ► Electromagnetic transient performance evaluation of the GEPP structure. ► Three different plasma current disruption cases: MD UP LIN36, VDE UP LIN36 and VDE DW LIN36 were analyzed. ► Three DSM-First Wall (FW) designs (horizontal and vertical drawers and monoblock) were compared. - Abstract: Electromagnetic phenomena due to plasma current disruptions are the cause for the main mechanical operation loads over the ITER equatorial level port plug structures. This paper presents a detailed finite element simulation and analysis of the transient electromagnetic effects of three different plasma current disruption cases over three designs of diagnostic shielding module (DSM) structure. The DSMs are contained into and supported by the generic equatorial port plug (GEPP) analyzed structure. The three plasma disruption cases studied were: major disruption upwards linear decay in 36 ms (MD UP LIN36), vertical displacements events, upwards and downwards linear decay in 36 ms (VDE UP LIN36 and VDE DW LIN36). A detailed analysis for GEPP structure and three DSM-first wall (FW) designs (horizontal and vertical drawers and monoblock) is also presented in order to extract the Eddy current distribution on these devices and thus the resultant electromagnetic forces and moments acting on them.

A kinky heliospheric current sheet - Cause of CDAW-6 substorms

Science.gov (United States)

Tsurutani, B. T.; Russell, C. T.; King, J. H.; Zwickl, R. D.; Lin, R. P.

1984-01-01

Two magnetospheric substorms and the intensification of the second are caused by interplanetary magnetic field and ram pressure changes associated with a kinky heliospheric current sheet (KHCS). The responsible interplanetary features occur in a highly compressed region between a solar flare-associated shock wave and the cold driver gas. The possibility that the interplanetary structure is a 'magnetic cloud' is ruled out.

DROPOUTS IN SOLAR ENERGETIC PARTICLES: ASSOCIATED WITH LOCAL TRAPPING BOUNDARIES OR CURRENT SHEETS?

International Nuclear Information System (INIS)

Seripienlert, A.; Ruffolo, D.; Matthaeus, W. H.; Chuychai, P.

2010-01-01

In recent observations by the Advanced Composition Explorer, the intensity of solar energetic particles exhibits sudden, large changes known as dropouts. These have been explained in terms of turbulence or a flux tube structure in the solar wind. Dropouts are believed to indicate filamentary magnetic connection to a localized particle source near the solar surface, and computer simulations of a random-phase model of magnetic turbulence have indicated a spatial association between dropout features and local trapping boundaries (LTBs) defined for a two-dimensional (2D) + slab model of turbulence. Previous observations have shown that dropout features are not well associated with sharp magnetic field changes, as might be expected in the flux tube model. Random-phase turbulence models do not properly treat sharp changes in the magnetic field, such as current sheets, and thus cannot be tested in this way. Here, we explore the properties of a more realistic magnetohydrodynamic (MHD) turbulence model (2D MHD), in which current sheets develop and the current and magnetic field have characteristic non-Gaussian statistical properties. For this model, computer simulations that trace field lines to determine magnetic connection from a localized particle source indicate that sharp particle gradients should frequently be associated with LTBs, sometimes with strong 2D magnetic fluctuations, and infrequently with current sheets. Thus, the 2D MHD + slab model of turbulent fluctuations includes some realistic features of the flux tube view and is consistent with the lack of an observed association between dropouts and intense magnetic fields or currents.

Multiple current sheets in a double auroral oval observed from the MAGION-2 and MAGION-3 satellites

Directory of Open Access Journals (Sweden)

M. Echim

1997-04-01

Full Text Available A case is described of multiple current sheets crossed by the MAGION-2 satellite in the near-midnight quieting auroral oval. The data were obtained by the magnetometer experiment onboard. Results show during a quieting period after a preceding substorm, or during an early growth phase of the next substorm, two double-sheet current bands, POLB and EQUB, located at respectively the polar and equatorial borders of the auroral oval separated by about 500 km in latitude. This is consistent with the double-oval structure during recovery introduced by Elphinstone et al. (1995. Within the POLB, the magnetic field data show simultaneous existence of several narrow parallel bipolar current sheets within the upward current branch (at 69.5–70.3° invariant latitude with an adjacent downward current branch at its polar side at (70.5–71.3°. The EQUB was similarly stratified and located at 61.2–63.5° invariant latitude. The narrow current sheets were separated on average by about 35 km and 15 km, respectively, within the POLB and EQUB. A similar case of double-oval current bands with small-scale structuring of their upward current branches during a quieting period is found in the data from the MAGION-3 satellite. These observations contribute to the double-oval structure of the late recovery phase, and add a small-scale structuring of the upward currents producing the auroral arcs in the double- oval pattern, at least for the cases presented here. Other observations of multiple auroral current sheets and theories of auroral arc multiplicity are briefly discussed. It is suggested that multiple X-lines in the distant tail, and/or leakage of energetic particles and FA currents from a series of plasmoids formed during preceding magnetic activity, could be one cause of highly stratified upward FA currents at the polar edge of the quieting double auroral oval.

Kinetic instabilities of thin current sheets: Results of two-and-one-half-dimensional Vlasov code simulations

International Nuclear Information System (INIS)

Silin, I.; Buechner, J.

2003-01-01

Nonlinear triggering of the instability of thin current sheets is investigated by two-and-one-half- dimensional Vlasov code simulations. A global drift-resonant instability (DRI) is found, which results from the lower-hybrid-drift waves penetrating from the current sheet edges to the center where they resonantly interact with unmagnetized ions. This resonant nonlinear instability grows faster than a Kelvin-Helmholtz instability obtained in previous studies. The DRI is either asymmetric or symmetric mode or a combination of the two, depending on the relative phase of the lower-hybrid-drift waves at the edges of the current sheet. With increasing particle mass ratio the wavenumber of the fastest-growing mode increases as kL z ∼(m i /m e ) 1/2 /2 and the growth rate of the DRI saturates at a finite level

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.;

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.

Glaciological parameters of disruptive event analysis

International Nuclear Information System (INIS)

Bull, C.

1979-01-01

The following disruptive events caused by ice sheets are considered: continental glaciation, erosion, loading and subsidence, deep ground water recharge, flood erosion, isostatic rebound rates, melting, and periodicity of ice ages

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.

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

Resistance and sheet resistance measurements using electron beam induced current

International Nuclear Information System (INIS)

Czerwinski, A.; Pluska, M.; Ratajczak, J.; Szerling, A.; KaPtcki, J.

2006-01-01

A method for measurement of spatially uniform or nonuniform resistance in layers and strips, based on electron beam induced current (EBIC) technique, is described. High electron beam currents are used so that the overall resistance of the measurement circuit affects the EBIC signal. During the evaluation, the electron beam is scanned along the measured object, whose load resistance varies with the distance. The variation is compensated by an adjustable resistance within an external circuit. The method has been experimentally deployed for sheet resistance determination of buried regions of lateral confinements in semiconductor laser heterostructures manufactured by molecular beam epitaxy

Studies of the disruption prevention by ECRH at plasma current rise stage in limiter discharges

International Nuclear Information System (INIS)

Alikaev, V.V.; Borshegovskij, A.A.; Chistyakov, V.V.

1999-01-01

Studies of disruption prevention by means of ECRH in T-10 at the plasma current rise phase in limiter discharges with circular plasma cross-section were performed. Reliable disruption prevention by ECRH at HF power (P HF ) min level equal to 20% of ohmic heating power P OH was demonstrated. m/n=2/1 mode MHD-activity developed before disruption (with characteristic time ∼120 ms) can be considered as disruption precursor and can be used in a feedback system. (author)

Toroidal current asymmetry and boundary conditions in disruptions

Science.gov (United States)

Strauss, Henry

2014-10-01

It was discovered on JET that disruptions were accompanied by toroidal asymmetry of the plasma current. The toroidal current asymmetry ΔIϕ is proportional to the vertical current moment ΔMIZ , with positive sign for an upward vertical displacement event (VDE) and negative sign for a downward VDE. It was claimed that this could only be explained by Hiro current. It is shown that instead it is essentially a kinematic effect produced by the VDE displacement of a 3D magnetic perturbation. This is verified by M3D simulations. The simulation results do not require penetration of plasma into the boundary, as in the Hiro current model. It is shown that the normal velocity perpendicular to the magnetic field vanishes at the wall, in the small Larmor radius limit of electromagnetic sheath boundary conditions. Plasma is absorbed into the wall only via the parallel velocity, which is small, penetrates only an infinitesimal distance into the wall, and does not affect forces exerted by the plasma on the wall. Supported by USDOE and ITER.

Development of tearing instability in a current sheet forming by sheared incompressible flow

Science.gov (United States)

Tolman, Elizabeth A.; Loureiro, Nuno F.; Uzdensky, Dmitri A.

2018-02-01

Sweet-Parker current sheets in high Lundquist number plasmas are unstable to tearing, suggesting they will not form in physical systems. Understanding magnetic reconnection thus requires study of the stability of a current sheet as it forms. Formation can occur due to sheared, sub-Alfvénic incompressible flows which narrow the sheet. Standard tearing theory (Furth et al. Phys. Fluids, vol. 6 (4), 1963, pp. 459-484, Rutherford, Phys. Fluids, vol. 16 (11), 1973, pp. 1903-1908, Coppi et al. Fizika Plazmy, vol. 2, 1976, pp. 961-966) is not immediately applicable to such forming sheets for two reasons: first, because the flow introduces terms not present in the standard calculation; second, because the changing equilibrium introduces time dependence to terms which are constant in the standard calculation, complicating the formulation of an eigenvalue problem. This paper adapts standard tearing mode analysis to confront these challenges. In an initial phase when any perturbations are primarily governed by ideal magnetohydrodynamics, a coordinate transformation reveals that the flow compresses and stretches perturbations. A multiple scale formulation describes how linear tearing mode theory (Furth et al. Phys. Fluids, vol. 6 (4), 1963, pp. 459-484, Coppi et al. Fizika Plazmy, vol. 2, 1976, pp. 961-966) can be applied to an equilibrium changing under flow, showing that the flow affects the separable exponential growth only implicitly, by making the standard scalings time dependent. In the nonlinear Rutherford stage, the coordinate transformation shows that standard theory can be adapted by adding to the stationary rates time dependence and an additional term due to the strengthening equilibrium magnetic field. Overall, this understanding supports the use of flow-free scalings with slight modifications to study tearing in a forming sheet.

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)

Limited Impact of Subglacial Supercooling Freeze-on for Greenland Ice Sheet Stratigraphy

Science.gov (United States)

Dow, Christine F.; Karlsson, Nanna B.; Werder, Mauro A.

2018-02-01

Large units of disrupted radiostratigraphy (UDR) are visible in many radio-echo sounding data sets from the Greenland Ice Sheet. This study investigates whether supercooling freeze-on rates at the bed can cause the observed UDR. We use a subglacial hydrology model to calculate both freezing and melting rates at the base of the ice sheet in a distributed sheet and within basal channels. We find that while supercooling freeze-on is a phenomenon that occurs in many areas of the ice sheet, there is no discernible correlation with the occurrence of UDR. The supercooling freeze-on rates are so low that it would require tens of thousands of years with minimal downstream ice motion to form the hundreds of meters of disrupted radiostratigraphy. Overall, the melt rates at the base of the ice sheet greatly overwhelm the freeze-on rates, which has implications for mass balance calculations of Greenland ice.

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.

Heliospheric current sheet and effects of its interaction with solar cosmic rays

Energy Technology Data Exchange (ETDEWEB)

Malova, H. V., E-mail: hmalova@yandex.ru [Moscow State University, Skobeltsyn Institute of Nuclear Physics (Russian Federation); Popov, V. Yu.; Grigorenko, E. E.; Dunko, A. V.; Petrukovich, A. A. [Russian Academy of Sciences, Space Research Institute (Russian Federation)

2016-08-15

The effects of interaction of solar cosmic rays (SCRs) with the heliospheric current sheet (HCS) in the solar wind are analyzed. A self-consistent kinetic model of the HCS is developed in which ions with quasiadiabatic dynamics can present. The HCS is considered an equilibrium embedded current structure in which two main plasma species with different temperatures (the low-energy background plasma of the solar wind and the higher energy SCR component) contribute to the current. The obtained results are verified by comparing with the results of numerical simulations based on solving equations of motion by the particle tracing method in the given HCS magnetic field with allowance for SCR particles. It is shown that the HCS is a relatively thin multiscale current configuration embedded in a thicker plasma layer. In this case, as a rule, the shear (tangential to the sheet current) component of the magnetic field is present in the HCS. Taking into account high-energy SCR particles in the HCS can lead to a change of its configuration and the formation of a multiscale embedded structure. Parametric family of solutions is considered in which the current balance in the HCS is provided at different SCR temperatures and different densities of the high-energy plasma. The SCR densities are determined at which an appreciable (detectable by satellites) HCS thickening can occur. Possible applications of this modeling to explain experimental observations are discussed.

A statistical study of current-sheet formation above solar active regions based on selforganized criticality

Science.gov (United States)

Dimitropoulou, M.; Isliker, H.; Vlahos, L.; Georgoulis, M.; Anastasiadis, A.; Toutountzi, A.

2013-09-01

We treat flaring solar active regions as physical systems having reached the self-organized critical state. Their evolving magnetic configurations in the low corona may satisfy an instability criterion, related to the excession of a specific threshold in the curl of the magnetic field. This imposed instability criterion implies an almost zero resistivity everywhere in the solar corona, except in regions where magnetic-field discontinuities and. hence, local currents, reach the critical value. In these areas, current-driven instabilities enhance the resistivity by many orders of magnitude forming structures which efficiently accelerate charged particles. Simulating the formation of such structures (thought of as current sheets) via a refined SOC cellular-automaton model provides interesting information regarding their statistical properties. It is shown that the current density in such unstable regions follows power-law scaling. Furthermore, the size distribution of the produced current sheets is best fitted by power laws, whereas their formation probability is investigated against the photospheric magnetic configuration (e.g. Polarity Inversion Lines, Plage). The average fractal dimension of the produced current sheets is deduced depending on the selected critical threshold. The above-mentioned statistical description of intermittent electric field structures can be used by collisional relativistic test particle simulations, aiming to interpret particle acceleration in flaring active regions and in strongly turbulent media in astrophysical plasmas. The above work is supported by the Hellenic National Space Weather Research Network (HNSWRN) via the THALIS Programme.

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.

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.

Numerical simulation on current spike behaviour of JT-60U disruptive plasmas

International Nuclear Information System (INIS)

Takei, N; Nakamura, Y; Tsutsui, H; Yoshino, R; Kawano, Y; Ozeki, T; Tobita, K; Tsuji-Iio, S; Shimada, R; Jardin, S C

2004-01-01

Characteristics and underlying mechanisms for plasma current spikes, which have been frequently observed during the thermal quench of JT-60U disruptions, were investigated through tokamak simulation code simulations including the passive shell effects of the vacuum vessel. Positive shear and reversed shear (PS and RS) plasmas were shown to have various current spike features in the experiments, e.g. an impulsive increase in the plasma current (positive spike) in the majority of thermal quenches, and a sudden decrease (negative spike), that has been excluded from past consideration, as an exception. It was first clarified that the shell effects, which become significant especially at a strong pressure drop due to the thermal quench of high β p plasmas, play an important role in the current spike in accordance with the initial relation of the radial location between the plasma equilibria and the vacuum vessel. As a consequence, a negative current spike may appear at thermal quench when the plasma is positioned further out from the geometric centre of the vacuum vessel. It was also pointed out that a further lowering in the internal inductance, in contradiction to previous interpretation in the past, is a plausible candidate for the mechanism for positive current spikes observed even in RS plasmas. The new interpretation enables us to reason out the whole character of current spikes of JT-60U disruptions

Disruption of myoblast alignment by highly motile rhabdomyosarcoma cell in tissue structure.

Science.gov (United States)

Li, Menglu; Nagamori, Eiji; Kino-Oka, Masahiro

2017-02-01

Rhabdomyosarcoma (RMS) is a highly malignant tumor type of skeletal muscle origin, hallmarked by local invasion. Interaction between invasive tumor cells and normal cells plays a major role in tumor invasion and metastasis. Culturing tumor cells in a three-dimensional (3D) model can translate tumor malignancy relevant cell-cell interaction. To mimic tumor heterogeneity in vitro, a co-culture system consisting of a malignant embryonal rhabdomyosarcoma (ERMS) cell line RD and a normal human skeletal muscle myoblast (HSMM) cell line was established by cell sheet technology. Various ratios of RDs to HSMMs were employed to understand the quantitative effect on intercellular interactions. Disruption of sheet structure was observed in heterogeneous cell sheets having a low ratio of RDs to HSMMs, whereas homogeneous HSMM or RD sheets maintained intact structure. Deeper exploration of dynamic tumor cell behavior inside HSMM sheets revealed that HSMM cell alignment was disrupted by highly motile RDs. This study demonstrated that RMS cells are capable of compromising their surrounding environment through induced decay of HSMMs alignment in a cell-based 3D system. This suggests that muscle disruption might be a major consequence of RMS cell invasion into muscles, which could be a promising target to preventing tumor invasion. Copyright © 2016 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

Analysis of minor disruptions during current flat phase in the HL-1 device

International Nuclear Information System (INIS)

Yan Longwen; Shi Bingren; Zheng Yongzhen; Peng Liling; Huang Keqiang

1991-01-01

The phenomena of minor disruptions during current flat phase have been observed in the HL-1 device for five years. When these phenomena appear the safety factors qa are between 2.5∼4.5, and densities are between 1 x 10 13 cm -3 and 3 x 10 13 cm -3 or greater than 4 x 10 13 cm -3 . Periodic relaxation ocsillations of voltage and soft-X-rays are observed during minor disruptions. Their character and development conditions are carefully analylsed

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)

The most intense current sheets in the high-speed solar wind near 1 AU

Science.gov (United States)

Podesta, John J.

2017-03-01

Electric currents in the solar wind plasma are investigated using 92 ms fluxgate magnetometer data acquired in a high-speed stream near 1 AU. The minimum resolvable scale is roughly 0.18 s in the spacecraft frame or, using Taylor's "frozen turbulence" approximation, one proton inertial length di in the plasma frame. A new way of identifying current sheets is developed that utilizes a proxy for the current density J obtained from the derivatives of the three orthogonal components of the observed magnetic field B. The most intense currents are identified as 5σ events, where σ is the standard deviation of the current density. The observed 5σ events are characterized by an average scale size of approximately 3di along the flow direction of the solar wind, a median separation of around 50di or 100di along the flow direction of the solar wind, and a peak current density on the order of 0.5 pA/cm2. The associated current-carrying structures are consistent with current sheets; however, the planar geometry of these structures cannot be confirmed using single-point, single-spacecraft measurements. If Taylor's hypothesis continues to hold for the energetically dominant fluctuations at kinetic scales 1current-carrying structures in high-speed wind occur at electron scales, although the peak current densities at kinetic and electron scales are predicted to be nearly the same as those found in this study.

Behavior of hard X-ray emission in discharges with current disruptions in the DAMAVAND and TVD tokamaks

International Nuclear Information System (INIS)

Farshi, E.; Amrollahy, R.; Bortnikov, A.V.; Brevnov, N.N.; Gott, Yu.V.; Shurygin, V.A.

2001-01-01

Results are presented from studies of the behavior of hard X-ray emission in discharges with current disruptions in the DAMAVAND and TVD tokamaks. The current disruptions are caused by either an MHD instability or the instability related to the vertical displacement of the plasma column. Experiments were conducted at a fixed value of the safety factor at the plasma boundary (q a ≅ 2.3). Experimental data show that, during a disruption caused by an MHD instability, hard X-ray emission is suppressed by this instability if the amplitude of the magnetic field fluctuations exceeds a certain level. If the disruption is caused by the instability related to the vertical displacement of the plasma column, then hard X-ray emission is observed at the instant of disruption. The experimental results show that the physical processes resulting in the generation and suppression of runaway electron beams are almost identical in large and small tokamaks

A cylindrical current sheet over the South solar pole observed by Ulysses

Science.gov (United States)

Khabarova, Olga; Kislov, Roman; Malova, Helmi; Obridko, Vladimir

2016-04-01

We provide the first evidence for the existence of a quasi-stable cylindrical current sheet over the South solar pole as observed by Ulysses in 2006, near the solar minimum, when it reached maximal heliolatitude of 79.7 degrees at 2.4 AU. It took place inside a fast speed stream from the coronal hole, and the tube was presumably crossed rather far from the center within two degrees of heliolatitude and ~10 degrees of heliolongitude. During the spacecraft passage throughout the structure, the solar wind velocity was approximately twice as little, the solar wind density was 20 times lower than the surrounded plasma values, but the temperature was twice as large in the point closest to the pole. The interplanetary magnetic field (IMF) strongly decreased due to sharp variations in the IMF radial component (RTN) that changed its sign twice, but other components did not show changes out of usual stochastic behavior. Both the behavior of the IMF, rotation of the plasma flow direction and other features indicate the occurrence of cylindrical current sheet. We discuss its solar origin and present modeling that can explain the observations.

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

Electron Acceleration in a Turbulent Current Sheet - Comparison of GCA and HARHA Methods

Czech Academy of Sciences Publication Activity Database

Kramoliš, D.; Varady, Michal; Bárta, Miroslav

2016-01-01

Roč. 40, č. 1 (2016), s. 69-77 ISSN 1845-8319. [Hvar Astrophysical Colloquium /14./. Hvar, 26.09.2016-30.09.2016] R&D Projects: GA ČR(CZ) GA16-18495S Institutional support: RVO:67985815 Keywords : magnetic reconnection * current sheet * electron acceleration Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

Characterization of the plasma current quench during disruptions in the National Spherical Torus Experiment

International Nuclear Information System (INIS)

Gerhardt, S.P.; Menard, J.E.

2008-01-01

A detailed analysis of the plasma current quench in the National Spherical Torus Experiment (M.Ono, et al Nuclear Fusion 40, 557 (2000)) is presented. The fastest current quenches are fit better by a linear waveform than an exponential one. Area-normalized current quench times down to .4 msec/m2 have been observed, compared to the minimum of 1.7 msec/m2 recommendation based on conventional aspect ratio tokamaks; as noted in previous ITPA studies, the difference can be explained by the reduced self-inductance at low aspect ratio and high-elongation. The maximum instantaneous dIp/dt is often many times larger than the mean quench rate, and the plasma current before the disruption is often substantially less than the flat-top value. The poloidal field time-derivative during the disruption, which is directly responsible for driving eddy currents, has been recorded at various locations around the vessel. The Ip quench rate, plasma motion, and magnetic geometry all play important roles in determining the rate of poloidal field change

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

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

Directory of Open Access Journals (Sweden)

G. Lapenta

2000-01-01

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

General formulation for magnetohydrodynamic wave propagation, fire-hose, and mirror instabilities in Harris-type current sheets

International Nuclear Information System (INIS)

Hau, L.-N.; Lai, Y.-T.

2013-01-01

Harris-type current sheets with the magnetic field model of B-vector=B x (z)x-caret+B y (z)y-caret have many important applications to space, astrophysical, and laboratory plasmas for which the temperature or pressure usually exhibits the gyrotropic form of p↔=p ∥ b-caretb-caret+p ⊥ (I↔−b-caretb-caret). Here, p ∥ and p ⊥ are, respectively, to be the pressure component along and perpendicular to the local magnetic field, b-caret=B-vector/B. This study presents the general formulation for magnetohydrodynamic (MHD) wave propagation, fire-hose, and mirror instabilities in general Harris-type current sheets. The wave equations are expressed in terms of the four MHD characteristic speeds of fast, intermediate, slow, and cusp waves, and in the local (k ∥ ,k ⊥ ,z) coordinates. Here, k ∥ and k ⊥ are, respectively, to be the wave vector along and perpendicular to the local magnetic field. The parameter regimes for the existence of discrete and resonant modes are identified, which may become unstable at the local fire-hose and mirror instability thresholds. Numerical solutions for discrete eigenmodes are shown for stable and unstable cases. The results have important implications for the anomalous heating and stability of thin current sheets.

Scientific basis and engineering design to accommodate disruption and halo current loads for the DIII-D tokamak

Energy Technology Data Exchange (ETDEWEB)

Anderson, P.M.; Bozek, A.S.; Hollerbach, M.A.; Humphreys, D.A.; Luxon, J.L.; Reis, E.E.; Schaffer, M.J.

1996-10-01

Plasma disruptions and halo current events apply sudden impulsive forces to the interior structures and vacuum vessel walls of tokamaks. These forces arise when induced toroidal currents and attached poloidal halo currents in plasma facing components interact with the poloidal and toroidal magnetic fields respectively. Increasing understanding of plasma disruptions and halo current events has been developed from experiments on DIII-D and other machines. Although the understanding has improved, these events must be planned for in system design because there is no assurance that these events can be eliminated in the operation of tokamaks. Increased understanding has allowed an improved focus of engineering designs.

Scientific basis and engineering design to accommodate disruption and halo current loads for the DIII-D tokamak

International Nuclear Information System (INIS)

Anderson, P.M.; Bozek, A.S.; Hollerbach, M.A.; Humphreys, D.A.; Luxon, J.L.; Reis, E.E.; Schaffer, M.J.

1996-10-01

Plasma disruptions and halo current events apply sudden impulsive forces to the interior structures and vacuum vessel walls of tokamaks. These forces arise when induced toroidal currents and attached poloidal halo currents in plasma facing components interact with the poloidal and toroidal magnetic fields respectively. Increasing understanding of plasma disruptions and halo current events has been developed from experiments on DIII-D and other machines. Although the understanding has improved, these events must be planned for in system design because there is no assurance that these events can be eliminated in the operation of tokamaks. Increased understanding has allowed an improved focus of engineering designs

Existence of three-dimensional ideal-magnetohydrodynamic equilibria with current sheets

Energy Technology Data Exchange (ETDEWEB)

Loizu, J. [Max-Planck-Institut für Plasmaphysik, D-17491 Greifswald (Germany); Princeton Plasma Physics Laboratory, PO Box 451, Princeton, New Jersey 08543 (United States); Hudson, S. R.; Bhattacharjee, A.; Lazerson, S. [Princeton Plasma Physics Laboratory, PO Box 451, Princeton, New Jersey 08543 (United States); Helander, P. [Max-Planck-Institut für Plasmaphysik, D-17491 Greifswald (Germany)

2015-09-15

We consider the linear and nonlinear ideal plasma response to a boundary perturbation in a screw pinch. We demonstrate that three-dimensional, ideal-MHD equilibria with continuously nested flux-surfaces and with discontinuous rotational-transform across the resonant rational-surfaces are well defined and can be computed both perturbatively and using fully nonlinear equilibrium calculations. This rescues the possibility of constructing MHD equilibria with current sheets and continuous, smooth pressure profiles. The results predict that, even if the plasma acts as a perfectly conducting fluid, a resonant magnetic perturbation can penetrate all the way into the center of a tokamak without being shielded at the resonant surface.

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.

The Svalbard-Barents Sea ice-sheet - Historical, current and future perspectives

Science.gov (United States)

Ingólfsson, Ólafur; Landvik, Jon Y.

2013-03-01

The history of research on the Late Quaternary Svalbard-Barents Sea ice sheet mirrors the developments of ideas and the shifts of paradigms in glacial theory over the past 150 years. Since the onset of scientific research there in the early 19th Century, Svalbard has been a natural laboratory where ideas and concepts have been tested, and played an important (but rarely acknowledged) role in the break-through of the Ice Age theory in the 1870's. The history of how the scientific perception of the Svalbard-Barents sea ice sheet developed in the mid-20th Century also tells a story of how a combination of fairly scattered and often contradictory observational data, and through both deductive and inductive reasoning, could outline a major ice sheet that had left but few tangible fingerprints. Since the 1980's, with increased terrestrial stratigraphical data, ever more marine geological evidence and better chronological control of glacial events, our perception of the Svalbard-Barents Sea ice sheet has changed. The first reconstructions depicted it as a static, concentric, single-domed ice sheet, with ice flowing from an ice divide over the central northern Barents Sea that expanded and declined in response to large-scale, Late Quaternary climate fluctuations, and which was more or less in tune with other major Northern Hemisphere ice sheets. We now increasingly perceive it as a very dynamic, multidomed ice sheet, controlled by climate fluctuations, relative sea-level change, as well as subglacial topography, substrate properties and basal temperature. In this respect, the Svalbard-Barents Sea ice sheet will increasingly hold the key for understanding the dynamics and processes of how marine-based ice sheets build-up and decay.

Current state and future perspectives on coupled ice-sheet - sea-level modelling

Science.gov (United States)

de Boer, Bas; Stocchi, Paolo; Whitehouse, Pippa L.; van de Wal, Roderik S. W.

2017-08-01

The interaction between ice-sheet growth and retreat and sea-level change has been an established field of research for many years. However, recent advances in numerical modelling have shed new light on the precise interaction of marine ice sheets with the change in near-field sea level, and the related stability of the grounding line position. Studies using fully coupled ice-sheet - sea-level models have shown that accounting for gravitationally self-consistent sea-level change will act to slow down the retreat and advance of marine ice-sheet grounding lines. Moreover, by simultaneously solving the 'sea-level equation' and modelling ice-sheet flow, coupled models provide a global field of relative sea-level change that is consistent with dynamic changes in ice-sheet extent. In this paper we present an overview of recent advances, possible caveats, methodologies and challenges involved in coupled ice-sheet - sea-level modelling. We conclude by presenting a first-order comparison between a suite of relative sea-level data and output from a coupled ice-sheet - sea-level model.

Oscillations Excited by Plasmoids Formed During Magnetic Reconnection in a Vertical Gravitationally Stratified Current Sheet

Science.gov (United States)

Jelínek, P.; Karlický, M.; Van Doorsselaere, T.; Bárta, M.

2017-10-01

Using the FLASH code, which solves the full set of the 2D non-ideal (resistive) time-dependent magnetohydrodynamic (MHD) equations, we study processes during the magnetic reconnection in a vertical gravitationally stratified current sheet. We show that during these processes, which correspond to processes in solar flares, plasmoids are formed due to the tearing mode instability of the current sheet. These plasmoids move upward or downward along the vertical current sheet and some of them merge into larger plasmoids. We study the density and temperature structure of these plasmoids and their time evolution in detail. We found that during the merging of two plasmoids, the resulting larger plasmoid starts to oscillate with a period largely determined by L/{c}{{A}}, where L is the size of the plasmoid and c A is the Alfvén speed in the lateral parts of the plasmoid. In our model, L/{c}{{A}} evaluates to ˜ 25 {{s}}. Furthermore, the plasmoid moving downward merges with the underlying flare arcade, which causes oscillations of the arcade. In our model, the period of this arcade oscillation is ˜ 35 {{s}}, which also corresponds to L/{c}{{A}}, but here L means the length of the loop and c A is the average Alfvén speed in the loop. We also show that the merging process of the plasmoid with the flare arcade is a complex process as presented by complex density and temperature structures of the oscillating arcade. Moreover, all these processes are associated with magnetoacoustic waves produced by the motion and merging of plasmoids.

Energetic Particles of keV–MeV Energies Observed near Reconnecting Current Sheets at 1 au

Energy Technology Data Exchange (ETDEWEB)

Khabarova, Olga V. [Heliophysical Laboratory, Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences (IZMIRAN), Moscow (Russian Federation); Zank, Gary P. [Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35805 (United States)

2017-07-01

We provide evidence for particle acceleration up to ∼5 MeV at reconnecting current sheets in the solar wind based on both case studies and a statistical analysis of the energetic ion and electron flux data from the five Advanced Composition Explorer Electron, Proton, and Alpha Monitor (EPAM) detectors. The case study of a typical reconnection exhaust event reveals (i) a small-scale peak of the energetic ion flux observed in the vicinity of the reconnection exhaust and (ii) a long-timescale atypical energetic particle event (AEPE) encompassing the reconnection exhaust. AEPEs associated with reconnecting strong current sheets last for many hours, even days, as confirmed by statistical studies. The case study shows that time-intensity profiles of the ion flux may vary significantly from one EPAM detector to another partially because of the local topology of magnetic fields, but mainly because of the impact of upstream magnetospheric events; therefore, the occurrence of particle acceleration can be hidden. The finding of significant particle energization within a time interval of ±30 hr around reconnection exhausts is supported by a superposed epoch analysis of 126 reconnection exhaust events. We suggest that energetic particles initially accelerated via prolonged magnetic reconnection are trapped and reaccelerated in small- or medium-scale magnetic islands surrounding the reconnecting current sheet, as predicted by the transport theory of Zank et al. Other mechanisms of initial particle acceleration can contribute also.

Three-dimensional equilibria for the extended magnetotail and the generation of field-aligned current sheets

International Nuclear Information System (INIS)

Birn, J.

1989-01-01

Using the magnetotail equilibrium theory and a solution method outlined by Birn (1987), we have constructed self-consistent three-dimensional models for the quiet average magnetotail beyond about 20 R/sub E/ distance but earthward of a potential distant neutral line, which take into account the decrease of the tail flaring with distance. We find that this effect is coupled with the presence of magnetic shear and thus with field-aligned electric currents. These currents have the signature of region 1 currents, toward the Earth on the dawnside and away on the duskside, and contribute about 5 x 10 5 A to the total Birkeland current. They are strongly concentrated near the plasma sheet-lobe boundary and increase toward the flanks of the tail. Associated with the field-aligned currents and the corresponding magnetic field shear there is a bulging effect that tends to deform a circular cross section of the tail near the Earth into one that has bulges in the low-latitude boundary region. We argue that this effect may be the cause for increased interaction with the solar wind in these regions, producing interconnected fields and tailward flowing plasma on magnetospheric-like fields in the low-latitude boundary layer, and deforming this boundary region into the observed dog bone shape of the plasma sheet cross section. copyright American Geophysical Union 1989

Current Sheet Structures Observed by the TESIS EUV Telescope during a Flux Rope Eruption on the Sun

Science.gov (United States)

Reva, A. A.; Ulyanov, A. S.; Kuzin, S. V.

2016-11-01

We use the TESIS EUV telescope to study the current sheet signatures observed during flux rope eruption. The special feature of the TESIS telescope was its ability to image the solar corona up to a distance of 2 {R}⊙ from the Sun’s center in the Fe 171 Å line. The Fe 171 Å line emission illuminates the magnetic field lines, and the TESIS images reveal the coronal magnetic structure at high altitudes. The analyzed coronal mass ejection (CME) had a core with a spiral—flux rope—structure. The spiral shape indicates that the flux rope radius varied along its length. The flux rope had a complex temperature structure: cold legs (70,000 K, observed in He 304 Å line) and a hotter core (0.7 MK, observed in Fe 171 Å line). Such a structure contradicts the common assumption that the CME core is a cold prominence. When the CME impulsively accelerated, a dark double Y-structure appeared below the flux rope. The Y-structure timing, location, and morphology agree with the previously performed MHD simulations of the current sheet. We interpreted the Y-structure as a hot envelope of the current sheet and hot reconnection outflows. The Y-structure had a thickness of 6.0 Mm. Its length increased over time from 79 Mm to more than 411 Mm.

Disruptions in Tokamaks

International Nuclear Information System (INIS)

Bondeson, A.

1987-01-01

This paper discusses major and minor disruptions in Tokamaks. A number of models and numerical simulations of disruptions based on resistive MHD are reviewed. A discussion is given of how disruptive current profiles are correlated with the experimentally known operational limits in density and current. It is argued that the q a =2 limit is connected with stabilization of the m=2/n=1 tearing mode for a approx.< 2.7 by resistive walls and mode rotation. Experimental and theoretical observations indicate that major disruptions usually occur in at least two phases, first a 'predisruption', or loss of confinement in the region 1 < q < 2, leaving the q approx.= 1 region almost unaffected, followed by a final disruption of the central part, interpreted here as a toroidal n = 1 external kink mode. (author)

Current and high-β sheets in CIR streams: statistics and interaction with the HCS and the magnetosphere

Science.gov (United States)

Potapov, A. S.

2018-04-01

Thirty events of CIR streams (corotating interaction regions between fast and slow solar wind) were analyzed in order to study statistically plasma structure within the CIR shear zones and to examine the interaction of the CIRs with the heliospheric current sheet (HCS) and the Earth's magnetosphere. The occurrence of current layers and high-beta plasma sheets in the CIR structure has been estimated. It was found that on average, each of the CIR streams had four current layers in its structure with a current density of more than 0.12 A/m2 and about one and a half high-beta plasma regions with a beta value of more than five. Then we traced how and how often the high-speed stream associated with the CIR can catch up with the heliospheric current sheet (HCS) and connect to it. The interface of each fourth CIR stream coincided in time within an hour with the HCS, but in two thirds of cases, the CIR connection with the HCS was completely absent. One event of the simultaneous observation of the CIR stream in front of the magnetosphere by the ACE satellite in the vicinity of the L1 libration point and the Wind satellite in the remote geomagnetic tail was considered in detail. Measurements of the components of the interplanetary magnetic field and plasma parameters showed that the overall structure of the stream is conserved. Moreover, some details of the fine structure are also transferred through the magnetosphere. In particular, the so-called "magnetic hole" almost does not change its shape when moving from L1 point to a neighborhood of L2 point.

Multispacecraft observations of the electron current sheet, neighboring magnetic islands, and electron acceleration during magnetotail reconnection

Czech Academy of Sciences Publication Activity Database

Chen, L. J.; Bessho, N.; Lefebvre, B.; Vaith, H.; Asnes, A.; Santolík, Ondřej; Fazakerley, A.; Puhl-Quinn, P.; Bhattacharjee, A.; Khotyaintsev, Y.; Daly, P.; Torbert, R.

2009-01-01

Roč. 16, - (2009), 056501/1-056501/12 ISSN 1070-664X Institutional research plan: CEZ:AV0Z30420517 Keywords : magnetotail reconnection * electron current sheet * multispacecraft observations Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.475, year: 2009

The Disruption of Tephra Fall Deposits by Basaltic Lava Flows

Science.gov (United States)

Brown, R. J.; Thordarson, T.; Self, S.; Blake, S.

2010-12-01

Complex physical and stratigraphic relationships between lava and proximal tephra fall deposits around vents of the Roza Member in the Columbia River Basalt Province, (CRBP), USA, illustrate how basaltic lavas can disrupt, dissect (spatially and temporally) and alter tephra fall deposits. Thin pahoehoe lobes and sheet lobes occur intercalated with tephra deposits and provide evidence for synchronous effusive and explosive activity. Tephra that accumulated on the tops of inflating pahoehoe flows became disrupted by tumuli, which dissected the overlying sheet into a series of mounds. During inflation of subjacent tumuli tephra percolated down into the clefts and rubble at the top of the lava, and in some cases came into contact with lava hot enough to thermally alter it. Lava breakouts from the tumuli intruded up through the overlying tephra deposit and fed pahoehoe flows that spread across the surface of the aggrading tephra fall deposit. Non-welded scoria fall deposits were compacted and welded to a depth of ~50 cm underneath thick sheet lobes. These processes, deduced from the field relationships, have resulted in considerable stratigraphic complexity in proximal regions. We also demonstrate that, when the advance of lava and the fallout of tephra are synchronous, the contacts of some tephra sheets can be diachronous across their extent. The net effect is to reduce the usefulness of pyroclastic deposits in reconstructing eruption dynamics.

Resistive instabilities of current sheets in the solar wind

Energy Technology Data Exchange (ETDEWEB)

Dobrowolny, M [CNR, Laboratorio per il Plasma nello Spazio, Frascati, Italy; Trussoni, E [CNR, Laboratorio di Cosmo-Geofisica, Turin, Italy

1979-03-01

Resistive magnetohydrodynamic instabilities are investigated numerically for non-antisymmetric magnetic field profiles similar to those indicated in spacecraft data on solar wind discontinuities. The eigenvalue problem derived for the growth rate of possible instabilities from dimensionless equations for velocity and magnetic field perturbations is solved starting from the outer regions where the plasma is frozen to the magnetic field. For an antisymmetric magnetic profile, calculations show only tearing modes to be present, with instabilities occurring only at long wavelengths, while for a non-antisymmetric magnetic profile resembling the observed solar wind, calculations indicate the presence of rippling modes driven by resistivity gradients, in addition to the tearing modes. Calculations of the scale lengths of variation of the reversing component based on a scaling law relating the maximum growth rate to the magnetic Reynolds number are found to agree with observed solar current sheet scale lengths.

Disruptions in JET

International Nuclear Information System (INIS)

Wesson, J.A.; Gill, R.D.; Hugon, M.

1989-01-01

In JET, both high density and low-q operation are limited by disruptions. The density limit disruptions are caused initially by impurity radiation. This causes a contraction of the plasma temperature profile and leads to an MHD unstable configuration. There is evidence of magnetic island formation resulting in minor disruptions. After several minor disruptions, a major disruption with a rapid energy quench occurs. This event takes place in two stages. In the first stage there is a loss of energy from the central region. In the second stage there is a more rapid drop to a very low temperature, apparently due to a dramatic increase in impurity radiation. The final current decay takes place in the resulting cold plasma. During the growth of the MHD instability the initially rotating mode is brought to rest. This mode locking is believed to be due to an electromagnetic interaction with the vacuum vessel and external magnetic field asymmetries. The low-q disruptions are remarkable for the precision with which they occur at q ψ = 2. These disruptions do not have extended precursors or minor disruptions. The instability grows and locks rapidly. The energy quench and current decay are generally similar to those of the density limit. (author). 43 refs, 35 figs, 3 tabs

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.

Disruption of crystalline structure of Sn3.5Ag induced by electric current

International Nuclear Information System (INIS)

Huang, Han-Chie; Lin, Kwang-Lung; Wu, Albert T.

2016-01-01

This study presented the disruption of the Sn and Ag_3Sn lattice structures of Sn3.5Ag solder induced by electric current at 5–7 × 10"3 A/cm"2 with a high resolution transmission electron microscope investigation and electron diffraction analysis. The electric current stressing induced a high degree of strain on the alloy, as estimated from the X-ray diffraction (XRD) peak shift of the current stressed specimen. The XRD peak intensity of the Sn matrix and the Ag_3Sn intermetallic compound diminished to nearly undetectable after 2 h of current stressing. The electric current stressing gave rise to a high dislocation density of up to 10"1"7/m"2. The grain morphology of the Sn matrix became invisible after prolonged current stressing as a result of the coalescence of dislocations.

Study of current oscillations and hard x-ray emissions in pre-cursor phase of major disruptions in Damavand tokamak

International Nuclear Information System (INIS)

Amrollahi, R.

2002-01-01

We notice that the hard x-ray activity before disruption consists of a series of spikes, uniformly distributed in time domain forming an orderly periodic series of oscillations at a frequency of 6.0 kHz. Disruption starts with an initial fast rise followed by decay. Current decay occurs in two regimes: the first corresponds to slow decay, in which the current is oscillating and reducing down to ∼70% its max value, and the second corresponds to fast decay, in which it totally vanishes abruptly in about 0.2 ms. In the first regime, the loop voltage also oscillates with considerable amplitude. The frequency of oscillations in the first regime is measured to be also about 6.0 kHz. As well, they follow the oscillation phase of hard x-rays. Thus the micro-instabilities driven by runaway electrons, being responsible for the production of hard x-rays bursts and small current oscillations, play a significant role in the disruption. (author)

Stabilization of the (2,1) tearing mode and of the current disruption in the W VII-A stellarator

International Nuclear Information System (INIS)

Bartlett, D.V.; Cannici, G.; Cattanei, G.

1980-01-01

A numerical code based on a Δ'-analysis is applied to calculate the saturated amplitude of tearing modes dependent on the current density profile. The only stellarator effect included is the additional, shearless external rotational transform in the safety factor profile q(r). In this way, the stellarator field shifts the resonant q=2 surface toward the outside, where the current density gradient is smaller, and stabilizes the (2,1) mode as observed experimentally. Also the measured dependence of the (2,1) mode amplitude on electron density and plasma current can be absolutely predicted by the calculations. - In addition to stabilizing the (2,1) tearing mode, the current disruption is suppressed in Ohmically heated W VII-A discharges for approximately >0.15. The experimental findings, together with the calculated island widths, are compared with the predictions of a theoretical model proposed by several authors to explain the current disruption. (author)

Disruption of crystalline structure of Sn3.5Ag induced by electric current

Energy Technology Data Exchange (ETDEWEB)

Huang, Han-Chie; Lin, Kwang-Lung, E-mail: matkllin@mail.ncku.edu.tw [Department of Material Science and Engineering, National Cheng Kung University, Tainan 70101, Taiwan (China); Wu, Albert T. [Department of Chemical and Material Engineering, National Central University, Jhongli 32001, Taiwan (China)

2016-03-21

This study presented the disruption of the Sn and Ag{sub 3}Sn lattice structures of Sn3.5Ag solder induced by electric current at 5–7 × 10{sup 3} A/cm{sup 2} with a high resolution transmission electron microscope investigation and electron diffraction analysis. The electric current stressing induced a high degree of strain on the alloy, as estimated from the X-ray diffraction (XRD) peak shift of the current stressed specimen. The XRD peak intensity of the Sn matrix and the Ag{sub 3}Sn intermetallic compound diminished to nearly undetectable after 2 h of current stressing. The electric current stressing gave rise to a high dislocation density of up to 10{sup 17}/m{sup 2}. The grain morphology of the Sn matrix became invisible after prolonged current stressing as a result of the coalescence of dislocations.

Low edge safety factor operation and passive disruption avoidance in current carrying plasmas by the addition of stellarator rotational transform

Science.gov (United States)

Pandya, M. D.; ArchMiller, M. C.; Cianciosa, M. R.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Knowlton, S. F.; Ma, X.; Massidda, S.; Maurer, D. A.; Roberds, N. A.; Traverso, P. J.

2015-11-01

Low edge safety factor operation at a value less than two ( q (a )=1 /ι̷tot(a )routine on the Compact Toroidal Hybrid device with the addition of sufficient external rotational transform. Presently, the operational space of this current carrying stellarator extends down to q (a )=1.2 without significant n = 1 kink mode activity after the initial plasma current rise phase of the discharge. The disruption dynamics of these low edge safety factor plasmas depend upon the fraction of helical field rotational transform from external stellarator coils to that generated by the plasma current. We observe that with approximately 10% of the total rotational transform supplied by the stellarator coils, low edge q disruptions are passively suppressed and avoided even though q(a) disrupt, the instability precursors measured and implicated as the cause are internal tearing modes with poloidal, m, and toroidal, n, helical mode numbers of m /n =3 /2 and 4/3 observed on external magnetic sensors and m /n =1 /1 activity observed on core soft x-ray emissivity measurements. Even though the edge safety factor passes through and becomes much less than q(a) disruption phenomenology observed.

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

Orientation of Birkeland current sheets in the dayside polar region and its relationship to the IMF

International Nuclear Information System (INIS)

Saflekos, N.A.; Potemra, T.A.

1980-01-01

Vector magnetic field observations made with the three-axes magnetometer on the Triad satellite have been used to study the orientation of magnetic disturbances in the dayside polar region. These measurements were all made over the southern polar region and recorded at McMurdo, Antarctica. These disturbances are transverse to the main geomagnetic field and may be interpreted as being caused by field-aligned Birkeland current sheets consistent with Maxwell's equations. The current sheets in the regions usually associated with the morning and afternoon auroral regions are most often aligned in the geomagnetic east-west direction. The amplitudes of these 'south auroral' currents are larger in the morning than in the afternoon when the interplanetary magnetic field (IMF) is directed toward the sun (B/sub y/ 0) and larger in the afternoon when the IMF is directed away (B/sub y/>0, B/sub x/ 0 the Birkeland current flow in the region of the southern cusp is predominantly away from the ionosphere in contrast to the downward flow into the northern cusp as determined earlier (e.g., McDiarmid et al., 1978b; Iijima et al., 1978). The cusp Birkeland current flow directions appear to reverse for B/sub y/>0 and B/sub x/<0. From a search of the Triad data set, some rare examples of magnetic disturbances with a large north-south (noon-midnight) component have been discovered in the polar cap near noon

Comparison between 3D eddy current patterns in tokamak in-vessel components generated by disruptions

International Nuclear Information System (INIS)

Sakellaris, J.; Crutzen, Y.

1996-01-01

During plasma disruption events in Tokamaks, a large amount of magnetic energy is associated to the transfer of plasma current into eddy currents in the passive structures. In the ITER program two design concepts have been proposed. One approach (ITER CDA design) is based on copper stabilization loops (i.e., twin loops) attached to box-shaped blanket segments, electrically and mechanically separated along the toroidal direction. For another design concept (ITER EDA design) based on lower plasma elongation there is no need for specific stabilization loops. The passive stabilization is obtained by toroidally continuous components (i.e., the plasma facing wall of the blanket segments allows a continuity along the toroidal direction). Consequently, toroidal currents flow, when electromagnetic transients occur. Electromagnetic loads appear in the blanket structures in case of plasma disruptions and/or vertical displacement events either for the ITER CDA design concept or for the ITER EDA design concept. In this paper the influence of the in-vessel design configuration concepts--insulated segments or electrically continuous structures--in terms of magnetic shielding and electric insulation on the magnitude and the flow pattern of the eddy currents is investigated. This investigation will allow a performance evaluation of the two proposed design concepts

Numerical simulation of the plasma current quench following a disruptive energy loss

International Nuclear Information System (INIS)

Strickler, D.J.; Peng, Y.K.M.; Holmes, J.A.; Miller, J.B.; Rothe, K.E.

1983-11-01

The plasma electromagnetic interaction with poloidal field coils and nearby passive conductor loops during the current quench following a disruptive loss of plasma energy is simulated. By solving a differential/algebraic system consisting of a set of circuit equations (including the plasma circuit) coupled to a plasma energy balance equation and an equilibrium condition, the electromagnetic consequences of an abrupt thermal quench are observed. Limiters on the small and large major radium sides of the plasma are assumed to define the plasma cross section. The presence of good conductors near the plasma and a small initial distance (i.e., 5 to 10% of the plasma minor radius) between the plasma edge and an inboard limiter are shown to lead to long current decay times. For a plasma with an initial major radius R/sub o/ = 4.3 m, aspect ratio A = 3.6, and current I/sub P/ = 4.0 MA, introducing nearby passive conductors lengthens the current decay from milliseconds to hundreds of milliseconds

Calculation of voltages and currents induced in the vacuum vessel of ASDEX by plasma disruptions

International Nuclear Information System (INIS)

Preis, H.

1978-01-01

An approximation method is used to analyze the electromagnetic diffusion process induced in the walls of the ASDEX vacuum vessel by plasma disruptions. For this purpose the rotational-symmetric vessel is regarded as N = 82 circular conductors connected in parallel and inductively coupled with one another and with the plasma. The transient currents and voltages occurring in this circuit are calculated with computer programs. From the calculated currents it is possible to determine the time behavior of the distributions of the current density and magnetic force density in the vessel walls. (orig.) [de

Disruptive mood dysregulation disorder: current insights

Directory of Open Access Journals (Sweden)

Baweja R

2016-08-01

Full Text Available Raman Baweja, Susan D Mayes, Usman Hameed, James G Waxmonsky Department of Psychiatry, Penn State University College of Medicine, Hershey, PA, USA Abstract: Disruptive mood dysregulation disorder (DMDD was introduced as a new diagnostic entity under the category of depressive disorders in Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5. It was included in DSM-5 primarily to address concerns about the misdiagnosis and consequent overtreatment of bipolar disorder in children and adolescents. DMDD does provide a home for a large percentage of referred children with severe persistent irritability that did not fit well into any DSM, Fourth Edition (DSM-IV diagnostic category. However, it has been a controversial addition to the DSM-5 due to lack of published validity studies, leading to questions about its validity as a distinct disorder. In this article, the authors discuss the diagnostic criteria, assessment, epidemiology, criticism of the diagnosis, and pathophysiology, as well as treatment and future directions for DMDD. They also review the literature on severe mood dysregulation, as described by the National Institute of Mental Health, as the scientific support for DMDD is based primarily on studies of severe mood dysregulation. Keywords: disruptive mood dysregulation disorder, persistent irritability, temper outbursts 

Understanding disruptions in tokamaksa)

Science.gov (United States)

Zakharov, Leonid E.; Galkin, Sergei A.; Gerasimov, Sergei N.; contributors, JET-EFDA

2012-05-01

This paper describes progress achieved since 2007 in understanding disruptions in tokamaks, when the effect of plasma current sharing with the wall was introduced into theory. As a result, the toroidal asymmetry of the plasma current measurements during vertical disruption event (VDE) on the Joint European Torus was explained. A new kind of plasma equilibria and mode coupling was introduced into theory, which can explain the duration of the external kink 1/1 mode during VDE. The paper presents first results of numerical simulations using a free boundary plasma model, relevant to disruptions.

Compensation of the Persistent Current Multipoles in the LHC Dipoles by making the Coil Protection Sheet from Soft Magnetic Material

CERN Document Server

Völlinger, C

2000-01-01

This note presents a scheme for compensating the persistent current multipole errors of the LHC dipoles by making the coil protection sheets from soft magnetic material of 0.5 mm thickness. The material properties assumed in this study are those of iron sheets with a very low content of impurities (99.99% pure Fe). The non-linearities in the upramp cycle on the b3 multipole component can be reduced by the factor of four (while decreasing the b5 variation by the factor of two. Using sheets of slightly different thicknesses offers a tuning possibility for the series magnet coils and can compensate deviations arising from cables of different suppliers. The calculation method is based on a semi-analytical hysteresis model for hard superconductors and an M(B) - iteration using the method of coupled boundary elements - finite elements (BEM - FEM). It is now possible to compute persistent current multipole errors of geometries with arbitrarily shaped iron yokes and thin layers of soft magnetic material such as tunin...

Disruption model

International Nuclear Information System (INIS)

Murray, J.G.; Bronner, G.

1982-07-01

Calculations of disruption time and energy dissipation have been obtained by simulating the plasma as an electrical conducting loop that varies in resistivity, current density, major radius. The calculations provide results which are in good agreement with experimental observations. It is believed that this approach allows engineering designs for disruptions to be completed in large tokamaks such as INTOR or FED

Sheet Beam Klystron Instability Analysis

International Nuclear Information System (INIS)

Bane, K.

2009-01-01

Using the principle of energy balance we develop a 2D theory for calculating growth rates of instability in a two-cavity model of a sheet beam klystron. An important ingredient is a TE-like mode in the gap that also gives a longitudinal kick to the beam. When compared with a self-consistent particle-in-cell calculation, with sheet beam klystron-type parameters, agreement is quite good up to half the design current, 65 A; at full current, however, other, current-dependent effects come in and the results deviate significantly

Universities with multicultural disrupted past: what meanings current students attribute to them?

Directory of Open Access Journals (Sweden)

Olena Dobosh

2016-09-01

Full Text Available The changing of pre-war borders of Central and Eastern Europe after WW II caused not only belonging of certain territories to definite countries but also the massive forced relocation of population from those territories. The total change of the population in the multicultural cities affected also institutions, such as universities by changing their staff, language, and national profile. Nowadays, when modern universities are facing post-modernity challenges it is extremely difficult to talk about role, mission, and meaning of this institution, especially in the context of disrupted historical tradition. Look at the problem from the different perspective, from inside will show the tendencies of meanings current students of the universities with long but disrupted historical past attribute to their Alma maters. Are they aware of the presence of representatives of different national groups that created university community before WW II? This article will present results of three studies conducted at three universities that changed their national profile after WWII: Vilnius University in Lithuania (formerly a Polish university, Lviv University in Ukraine (formerly a Polish university and Wrocław University in Poland (formerly a German university. Both at Vilnius University and Lviv Universiy 150 university students participated in the study. At Wrocław University 152 university students participated in the study. The present analysis will try to explore the variety of meanings current students of those three universities attribute to their place of study. It will try to show if current students are aware of the university’s complex history and, if they include/exclude historical meanings connected with representatives of the different national group? Also, it will look at the possible differences between meaning attribution and perception of the university past among representatives of these three universities. Lviv, Wrocław, and Vilnius

Lower hybrid drift instability in a current sheet with anisotropic temperature

International Nuclear Information System (INIS)

Huang Feng; Liu Guohong; Yan Fei; Deng Yan; Chen Yinhua; Yu, M Y; Chen Hanshuang

2013-01-01

The effect of the temperature anisotropy on the lower hybrid drift instability (LHDI) in a current sheet is investigated using local kinetic theory. It is found that the ratio r te of the perpendicular to parallel electron temperatures can significantly affect the instability. In fact, a critical value exists r te = r te * , such that when r te >r te * the LHD waves are unstable if the perpendicular wave vector k y is between two threshold values, and when r te te * the LHD mode is stable for any k y . It is also found that r te * increases and the unstable LHD regime shrinks as the parallel wave vector k z increases. That is, sufficiently low perpendicular electron temperature can stabilize the LHDI, especially that of short parallel wavelength. (paper)

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.

Evidence for a current sheet forming in the wake of a coronal mass ejection from multi-viewpoint coronagraph observations

Science.gov (United States)

Patsourakos, S.; Vourlidas, A.

2011-01-01

Context. Ray-like features observed by coronagraphs in the wake of coronal mass ejections (CMEs) are sometimes interpreted as the white light counterparts of current sheets (CSs) produced by the eruption. The 3D geometry of these ray-like features is largely unknown and its knowledge should clarify their association to the CS and place constraints on CME physics and coronal conditions. Aims: If these rays are related to field relaxation behind CMEs, therefore representing current sheets, then they should be aligned to the CME axis. With this study we test these important implications for the first time. Methods: An example of such a post-CME ray was observed by various coronagraphs, including these of the Sun Earth Connection Coronal and Heliospheric investigation (SECCHI) onboard the Solar Terrestrial Relations Observatory (STEREO) twin spacecraft and the Large Angle Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO). The ray was observed in the aftermath of a CME which occurred on 9 April 2008. The twin STEREO spacecraft were separated by about 48° on that day. This significant separation combined with a third “eye” view supplied by LASCO allow for a truly multi-viewpoint observation of the ray and of the CME. We applied 3D forward geometrical modeling to the CME and to the ray as simultaneously viewed by SECCHI-A and B and by SECCHI-A and LASCO, respectively. Results: We found that the ray can be approximated by a rectangular slab, nearly aligned with the CME axis, and much smaller than the CME in both terms of thickness and depth (≈0.05 and 0.15 R⊙ respectively). The ray electron density and temperature were substantially higher than their values in the ambient corona. We found that the ray and CME are significantly displaced from the associated post-CME flaring loops. Conclusions: The properties and location of the ray are fully consistent with the expectations of the standard CME theories for post-CME current

Effect of halo current and its toroidal asymmetry during disruptions in JT-60U

International Nuclear Information System (INIS)

Neyatani, Y.; Yoshino, R.; Ando, T.

1995-01-01

A poloidal halo current due to a vertical displacement event (VDE) is observed in experimentally simulated VDE discharges and density limit disruptions in the JT-60U tokamak. In the case of a clockwise I p and B T discharge, the halo current flows into the vacuum vessel from the inside separatrix and goes back to the plasma from the outside separatrix. A maximum halo current is produced by a change in the poloidal flux generated by plasma current decay. A toroidal asymmetry factor of 2.5 is estimated from the requirements of the fracture of the carbon-fiber composite tiles. The toroidal asymmetry is caused by the poloidal field (PF) that is produced by the toroidal field (TF) ripple, the deformation of the vacuum vessel, the setting error between the vacuum vessel and the TF and PF coils, the low-n mode during current quench, etc. To consider this asymmetry, in JT-60U, one must estimate the total halo current as nearly 26% of the plasma current just before a current quench. 25 refs., 10 figs

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

Disruption modeling in support of ITER

International Nuclear Information System (INIS)

Bandyopadhyay, I.

2015-01-01

Plasma current disruptions and Vertical Displacement Events (VDEs) are one of the major concerns in any tokamak as they lead to large electromagnetic forces to tokamak first wall components and vacuum vessel. Their occurrence also means disruption to steady state operations of tokamaks. Thus future fusion reactors like ITER must ensure that disruptions and VDEs are minimized. However, since there is still finite probability of their occurrence, one must be able to characterize disruptions and VDEs and able to predict, for example, the plasma current quench time and halo current amplitude, which mainly determine the magnitude of the electromagnetic forces. There is a concerted effort globally to understand and predict plasma and halo current evolution during disruption in tokamaks through MHD simulations. Even though Disruption and VDEs are often 3D MHD perturbations in nature, presently they are mostly simulated using 2D axisymmetric MHD codes like the Tokamak Simulation Code (TSC) and DINA. These codes are also extensively benchmarked against experimental data in present day tokamaks to improve these models and their ability to predict these events in ITER. More detailed 3D models like M3D are only recently being developed, but they are yet to be benchmarked against experiments, as also they are massively computationally exhaustive

The use of cell-sheet technique eliminates arrhythmogenicity of skeletal myoblast-based therapy to the heart with enhanced therapeutic effects.

Science.gov (United States)

Narita, Takuya; Shintani, Yasunori; Ikebe, Chiho; Kaneko, Masahiro; Harada, Narumi; Tshuma, Nomathamsanqa; Takahashi, Kunihiko; Campbell, Niall G; Coppen, Steven R; Yashiro, Kenta; Sawa, Yoshiki; Suzuki, Ken

2013-09-20

Clinical application of skeletal myoblast transplantation has been curtailed due to arrhythmogenicity and inconsistent therapeutic benefits observed in previous studies. However, these issues may be solved by the use of a new cell-delivery mode. It is now possible to generate "cell-sheets" using temperature-responsive dishes without artificial scaffolds. This study aimed to validate the safety and efficacy of epicardial placement of myoblast-sheets (myoblast-sheet therapy) in treating heart failure. After coronary artery ligation in rats, the same numbers of syngeneic myoblasts were transplanted by intramyocardial injection or cell-sheet placement. Continuous radio-telemetry monitoring detected increased ventricular arrhythmias, including ventricular tachycardia, after intramyocardial injection compared to the sham-control, while these were abolished in myoblast-sheet therapy. This effect was conjunct with avoidance of islet-like cell-cluster formation that disrupts electrical conduction, and with prevention of increased arrhythmogenic substrates due to exaggerated inflammation. Persistent ectopic donor cells were found in the lung only after intramyocardial injection, strengthening the improved safety of myoblast-sheet therapy. In addition, myoblast-sheet therapy enhanced cardiac function, corresponding to a 9.2-fold increase in donor cell survival, compared to intramyocardial injection. Both methods achieved reduced infarct size, decreased fibrosis, attenuated cardiomyocyte hypertrophy, and increased neovascular formation, in association with myocardial upregulation of a group of relevant molecules. The pattern of these beneficial changes was similar between two methods, but the degree was more substantial after myoblast-sheet therapy. The cell-sheet technique enhanced safety and therapeutic efficacy of myoblast-based therapy, compared to the current method, thereby paving the way for clinical application. Copyright © 2012 Elsevier Ireland Ltd. All rights

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.

Disruption characteristics in PDX with limiter and divertor discharges

International Nuclear Information System (INIS)

Couture, P.; McGuire, K.

1986-09-01

A comparison has been made between the characteristics of disruptions with limiter and divertor configurations in PDX. A large data base on disruptions has been collected over four years of machine operation, and a total of 15,000 discharges are contained in the data file. It was found that divertor discharges have less disruptions during ramp up and flattop of the plasma current. However, for divertor discharges a large number of fast, low current disruptions take place during the current ramp down. These disruptions are probably caused by the deformation of the plasma shape

Development and anisotropy of three-dimensional turbulence in a current sheet

International Nuclear Information System (INIS)

Onofri, M.; Veltri, P.; Malara, F.

2007-01-01

The nonlinear evolution of three-dimensional reconnection instabilities are studied in a current sheet where many resonant surfaces are simultaneously present at different locations of the simulation domain. The nonlinear evolution produces the development of anisotropic magnetohydrodynamic turbulence. The development of the energy spectrum is followed until the energy is transported to the dissipative length scale and the anisotropy of the spectrum is analyzed. The energy cascade is affected by the Alfven effect and it takes place mainly in the direction perpendicular to the local average magnetic field. Anisotropy is also affected by propagation of perturbations across the main magnetic field, due to the growth of a transverse component related to reconnection. The direction of anisotropy varies with the position in space. The spectral index is different both from what is found in homogeneous isotropic turbulence and from the values predicted for magnetohydrodynamic turbulence with a uniform large-scale magnetic field

Observation of negative potential depression on double layer during a phase of current disruption

International Nuclear Information System (INIS)

Fujita, H.; Matsuo, K.; Yagura, S.

1984-01-01

The negative potential depression with a depth of approximately electron temperature is observed on the low potential tail of the double layer just at the moment when the electron current passing through the layer is disrupted. The depression is confirmed to serve as an electron thermal barrier and form an ion hole from phase-space measurements of electrons and ions, respectively. The depth of the depression becomes maximum when the density around the depression becomes most inhomogeneous. (author)

Engineering analysis of TFTR disruption

Energy Technology Data Exchange (ETDEWEB)

Murray, J.G.; Rothe, K.E.; Bronner, G.

1984-09-01

This report covers an engineering approach quantifying the currents, forces, and times, as well as plasma position, for the worst-case disruption based on engineerign circuit assumptions for the plasma. As the plasma moves toward the wall during the current-decay phase of disruption, the wall currents affect the rate of movement and, hence, the decay time. The calculated structure-induced currents differ considerably from those calculated using a presently available criterion, which specifies that the plasma remains stationary in the center of the torus while decaying in 10 ms. This report outlines the method and basis for the engineering calculation used to determine the current and forces as a function of the circuit characteristics. It provides specific calculations for the Tokamak Fusion Test Reactor (TFTR) with variations in parameters such as the thermal decay time, the torus resistance, and plasma temperature during the current decay. The study reviews possible ways to reduce the disruption damage of TFTR by reducing the magnitude of the plasma external field energy that is absorbed by the plasma during the current decay.

Engineering analysis of TFTR disruption

International Nuclear Information System (INIS)

Murray, J.G.; Rothe, K.E.; Bronner, G.

1984-09-01

This report covers an engineering approach quantifying the currents, forces, and times, as well as plasma position, for the worst-case disruption based on engineerign circuit assumptions for the plasma. As the plasma moves toward the wall during the current-decay phase of disruption, the wall currents affect the rate of movement and, hence, the decay time. The calculated structure-induced currents differ considerably from those calculated using a presently available criterion, which specifies that the plasma remains stationary in the center of the torus while decaying in 10 ms. This report outlines the method and basis for the engineering calculation used to determine the current and forces as a function of the circuit characteristics. It provides specific calculations for the Tokamak Fusion Test Reactor (TFTR) with variations in parameters such as the thermal decay time, the torus resistance, and plasma temperature during the current decay. The study reviews possible ways to reduce the disruption damage of TFTR by reducing the magnitude of the plasma external field energy that is absorbed by the plasma during the current decay

SPECTROSCOPIC OBSERVATIONS OF AN EVOLVING FLARE RIBBON SUBSTRUCTURE SUGGESTING ORIGIN IN CURRENT SHEET WAVES

Energy Technology Data Exchange (ETDEWEB)

Brannon, S. R.; Longcope, D. W.; Qiu, J. [Department of Physics, Montana State University, Bozeman, MT 59717 (United States)

2015-09-01

We present imaging and spectroscopic observations from the Interface Region Imaging Spectrograph of the evolution of the flare ribbon in the SOL2014-04-18T13:03 M-class flare event, at high spatial resolution and time cadence. These observations reveal small-scale substructure within the ribbon, which manifests as coherent quasi-periodic oscillations in both position and Doppler velocities. We consider various alternative explanations for these oscillations, including modulation of chromospheric evaporation flows. Among these, we find the best support for some form of wave localized to the coronal current sheet, such as a tearing mode or Kelvin–Helmholtz instability.

Surface currents associated with external kink modes in tokamak plasmas during a major disruption

Science.gov (United States)

Ng, C. S.; Bhattacharjee, A.

2017-10-01

The surface current on the plasma-vacuum interface during a disruption event involving kink instability can play an important role in driving current into the vacuum vessel. However, there have been disagreements over the nature or even the sign of the surface current in recent theoretical calculations based on idealized step-function background plasma profiles. We revisit such calculations by replacing step-function profiles with more realistic profiles characterized by a strong but finite gradient along the radial direction. It is shown that the resulting surface current is no longer a delta-function current density, but a finite and smooth current density profile with an internal structure, concentrated within the region with a strong plasma pressure gradient. Moreover, this current density profile has peaks of both signs, unlike the delta-function case with a sign opposite to, or the same as the plasma current. We show analytically and numerically that such current density can be separated into two parts, with one of them, called the convective current density, describing the transport of the background plasma density by the displacement, and the other part that remains, called the residual current density. It is argued that consideration of both types of current density is important and can resolve past controversies.

Calculation of the electromagnetic forces on the ASDEX upgrade vacuum vessel on disruption of the plasma current

International Nuclear Information System (INIS)

Preis, H.

1986-01-01

This study investigates the magnetic field diffusion through the vacuum vessel of the ASDEX Upgrade tokamak that occurs on sudden disruption of the plasma current. Eddy currents are thereby produced in the vessel wall. Their time behaviour and distribution are determined. Furthermore, the vessel is permeated by various magnetic fields which, together with the eddy currents, exert magnetic forces in the vessel wall. These are also calculated. These numerical analyses are performed for two of the modes of operation envisaged for ASDEX Upgrade: the so-called limiter and single-null magnetic field configurations. (orig.)

Current state and future perspectives on coupled ice-sheet – sea-level modelling

NARCIS (Netherlands)

de Boer, Bas; Stocchi, Paolo; Whitehouse, Pippa L.; van de Wal, Roderik S.W.

2017-01-01

The interaction between ice-sheet growth and retreat and sea-level change has been an established field of research for many years. However, recent advances in numerical modelling have shed new light on the precise interaction of marine ice sheets with the change in near-field sea level, and the

Automatic location of disruption times in JET

Science.gov (United States)

Moreno, R.; Vega, J.; Murari, A.

2014-11-01

The loss of stability and confinement in tokamak plasmas can induce critical events known as disruptions. Disruptions produce strong electromagnetic forces and thermal loads which can damage fundamental components of the devices. Determining the disruption time is extremely important for various disruption studies: theoretical models, physics-driven models, or disruption predictors. In JET, during the experimental campaigns with the JET-C (Carbon Fiber Composite) wall, a common criterion to determine the disruption time consisted of locating the time of the thermal quench. However, with the metallic ITER-like wall (JET-ILW), this criterion is usually not valid. Several thermal quenches may occur previous to the current quench but the temperature recovers. Therefore, a new criterion has to be defined. A possibility is to use the start of the current quench as disruption time. This work describes the implementation of an automatic data processing method to estimate the disruption time according to this new definition. This automatic determination allows both reducing human efforts to locate the disruption times and standardizing the estimates (with the benefit of being less vulnerable to human errors).

Automatic location of disruption times in JET.

Science.gov (United States)

Moreno, R; Vega, J; Murari, A

2014-11-01

The loss of stability and confinement in tokamak plasmas can induce critical events known as disruptions. Disruptions produce strong electromagnetic forces and thermal loads which can damage fundamental components of the devices. Determining the disruption time is extremely important for various disruption studies: theoretical models, physics-driven models, or disruption predictors. In JET, during the experimental campaigns with the JET-C (Carbon Fiber Composite) wall, a common criterion to determine the disruption time consisted of locating the time of the thermal quench. However, with the metallic ITER-like wall (JET-ILW), this criterion is usually not valid. Several thermal quenches may occur previous to the current quench but the temperature recovers. Therefore, a new criterion has to be defined. A possibility is to use the start of the current quench as disruption time. This work describes the implementation of an automatic data processing method to estimate the disruption time according to this new definition. This automatic determination allows both reducing human efforts to locate the disruption times and standardizing the estimates (with the benefit of being less vulnerable to human errors).

Modelling geomagnetically induced currents in midlatitude Central Europe using a thin-sheet approach

Science.gov (United States)

Bailey, Rachel L.; Halbedl, Thomas S.; Schattauer, Ingrid; Römer, Alexander; Achleitner, Georg; Beggan, Ciaran D.; Wesztergom, Viktor; Egli, Ramon; Leonhardt, Roman

2017-06-01

Geomagnetically induced currents (GICs) in power systems, which can lead to transformer damage over the short and the long term, are a result of space weather events and geomagnetic variations. For a long time, only high-latitude areas were considered to be at risk from these currents, but recent studies show that considerable GICs also appear in midlatitude and equatorial countries. In this paper, we present initial results from a GIC model using a thin-sheet approach with detailed surface and subsurface conductivity models to compute the induced geoelectric field. The results are compared to measurements of direct currents in a transformer neutral and show very good agreement for short-period variations such as geomagnetic storms. Long-period signals such as quiet-day diurnal variations are not represented accurately, and we examine the cause of this misfit. The modelling of GICs from regionally varying geoelectric fields is discussed and shown to be an important factor contributing to overall model accuracy. We demonstrate that the Austrian power grid is susceptible to large GICs in the range of tens of amperes, particularly from strong geomagnetic variations in the east-west direction.

On Jovian plasma sheet structure

International Nuclear Information System (INIS)

Khurana, K.K.; Kivelson, M.G.

1989-01-01

The authors evaluate several models of Jovian plasma sheet structure by determining how well they organize several aspects of the observed Voyager 2 magnetic field characteristics as a function of Jovicentric radial distance. It is shown that in the local time sector of the Voyager 2 outbound pass (near 0300 LT) the published hinged-magnetodisc models with wave (i.e., models corrected for finite wave velocity effects) are more successful than the published magnetic anomaly model in predicting locations of current sheet crossings. They also consider the boundary between the plasma sheet and the magnetotail lobe which is expected to vary slowly with radial distance. They use this boundary location as a further test of the models of the magnetotail. They show that the compressional MHD waves have much smaller amplitude in the lobes than in the plasma sheet and use this criterion to refine the identification of the plasma-sheet-lobe boundary. When the locations of crossings into and out of the lobes are examined, it becomes evident that the magnetic-anomaly model yields a flaring plasma sheet with a halfwidth of ∼ 3 R J at a radial distance of 20 R J and ∼ 12 R J at a radial distance of 100 R J . The hinged-magnetodisc models with wave, on the other hand, predict a halfwidth of ∼ 3.5 R J independent of distance beyond 20 R J . New optimized versions of the two models locate both the current sheet crossings and lobe encounters equally successfully. The optimized hinged-magnetodisc model suggests that the wave velocity decreases with increasing radial distance. The optimized magnetic anomaly model yields lower velocity contrast than the model of Vasyliunas and Dessler (1981)

Electrostatic Solitary Waves in the Solar Wind: Evidence for Instability at Solar Wind Current Sheets

Science.gov (United States)

Malaspina, David M.; Newman, David L.; Wilson, Lynn Bruce; Goetz, Keith; Kellogg, Paul J.; Kerstin, Kris

2013-01-01

A strong spatial association between bipolar electrostatic solitary waves (ESWs) and magnetic current sheets (CSs) in the solar wind is reported here for the first time. This association requires that the plasma instabilities (e.g., Buneman, electron two stream) which generate ESWs are preferentially localized to solar wind CSs. Distributions of CS properties (including shear angle, thickness, solar wind speed, and vector magnetic field change) are examined for differences between CSs associated with ESWs and randomly chosen CSs. Possible mechanisms for producing ESW-generating instabilities at solar wind CSs are considered, including magnetic reconnection.

Real-time disruption handling at ASDEX upgrade

International Nuclear Information System (INIS)

Zehetbauer, Th.; Pautasso, G.; Tichmann, C.; Egorov, S.; Lorenz, A.; Mertens, V.; Neu, G.; Raupp, G.; Treutterer, W.; Zasche, D.

2001-01-01

A neural network for prediction of disruptions has been developed at ASDEX Upgrade with the goal to mitigate or avoid these. The novel idea is to compute the remaining time-to-disruption to indicate the stability level of the discharge. The neural network has been specified, trained and then implemented within the real-time plasma control system. The current version of the system terminates the discharge with an impurity pellet when the computed time-to-disruption falls below a threshold of 80 ms. Routine operation shows that disruptions are recognized reliably. Vessel currents and forces are considerably reduced. The system will be enhanced to avoid disruptions with a soft landing initiated in time

Formation and disruption of current paths of anodic porous alumina films by conducting atomic force microscopy

International Nuclear Information System (INIS)

Oyoshi, K.; Nigo, S.; Inoue, J.; Sakai, O.; Kitazawa, H.; Kido, G.

2010-01-01

Anodic porous alumina (APA) films have a honeycomb cell structure of pores and a voltage-induced bi-stable switching effect. We have applied conducting atomic force microscopy (CAFM) as a method to form and to disrupt current paths in the APA films. A bi-polar switching operation was confirmed. We have firstly observed terminals of current paths as spots or areas typically on the center of the triangle formed by three pores. In addition, though a part of the current path showed repetitive switching, most of them were not observed again at the same position after one cycle of switching operations in the present experiments. This suggests that a part of alumina structure and/or composition along the current paths is modified during the switching operations.

Formation and disruption of current paths of anodic porous alumina films by conducting atomic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Oyoshi, K., E-mail: oyoshi.keiji@nims.go.jp [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Nigo, S.; Inoue, J.; Sakai, O.; Kitazawa, H.; Kido, G. [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 (Japan)

2010-11-15

Anodic porous alumina (APA) films have a honeycomb cell structure of pores and a voltage-induced bi-stable switching effect. We have applied conducting atomic force microscopy (CAFM) as a method to form and to disrupt current paths in the APA films. A bi-polar switching operation was confirmed. We have firstly observed terminals of current paths as spots or areas typically on the center of the triangle formed by three pores. In addition, though a part of the current path showed repetitive switching, most of them were not observed again at the same position after one cycle of switching operations in the present experiments. This suggests that a part of alumina structure and/or composition along the current paths is modified during the switching operations.

Disruption Physics and Mitigation on DIII-D

International Nuclear Information System (INIS)

Whyte, D.G.; Humphreys, D.A.; Kellman, A.G.

2005-01-01

The contributions of the DIII-D tokamak toward the understanding and control of disruptions are reviewed. Disruptions are found to be deterministic, and the underlying causes of disruption can therefore be predicted and avoided. With sufficiently rapid detection, possible damage from disruptions can be mitigated using an understanding of disruption phenomenology and plasma physics. Regimes of high β are readily available in DIII-D and provide access to relatively high energy density disruptions, despite DIII-D's moderate magnetic field and size. DIII-D, with all-graphite wall armor and wall conditioning between discharges, has proven highly resilient to the deleterious effects that disruptions can have on plasma operations. Simultaneously, exploitation and adaptation of DIII-D's extensive core and edge plasma diagnostic set have allowed for unique plasma measurements during disruptions. These measurements have tied into the development of several physical models used to understand aspects of disruptions, such as magnetohydrodynamic growth at the disruption onset, radiation energy balance through the thermal quench, and halo currents during the current quench. Based on this fundamental understanding, DIII-D has developed techniques to mitigate the harmful effects of disruptions by radiative dissipation of the plasma energy and extrapolated these techniques for possible use on larger devices like ITER

Electrochemical bisphenol A sensor based on N-doped graphene sheets

International Nuclear Information System (INIS)

Fan Haixia; Li Yan; Wu Dan; Ma Hongmin; Mao Kexia; Fan Dawei; Du Bin; Li He; Wei Qin

2012-01-01

Highlights: ► N-doped graphene sheets have catalytic activity towards the BPA oxidation. ► The biosensor based on N-doped graphene sheets and chitosan. ► This method was proposed for determination of BPA utilizing N-doped graphene sheets. - Abstract: Bisphenol A (BPA), which could disrupt endocrine system and cause cancer, has been considered as an endocrine disruptor. Therefore, it is very important and necessary to develop a sensitive and selective method for detection of BPA. Herein, nitrogen-doped graphene sheets (N-GS) and chitosan (CS) were used to prepare electrochemical BPA sensor. Compared with graphene, N-GS has favorable electron transfer ability and electrocatalytic property, which could enhance the response signal towards BPA. CS also exhibits excellent film forming ability and improves the electrochemical behavior of N-GS modified electrode. The sensor exhibits a sensitive response to BPA in the range of 1.0 × 10 −8 –1.3 × 10 −6 mol L −1 with a low detection limit of 5.0 × 10 −9 mol L −1 under the optimal conditions. Finally, this proposed sensor was successfully employed to determine BPA in water samples with satisfactory results.

NTPR Fact Sheets

Science.gov (United States)

History Documents US Underground Nuclear Test History Reports NTPR Radiation Exposure Reports Enewetak Atoll Cleanup Documents TRAC About Who We Are Our Values History Locations Our Leadership Director Support Center Contact Us FAQ Sheet Links Success Stories Contracts Business Opportunities Current

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

An overview on plasma disruption mitigation and avoidance in tokamak

International Nuclear Information System (INIS)

He Kaihui; Pan Chuanhong; Feng Kaiming

2002-01-01

Plasma disruption, which seems to be unavoidable in Tokamak operation, occurs very fast and uncontrolled. In order to keep Tokamak plasma from disruption and mitigate the disruption frequency, the research on Tokamak plasma major disruption constitutes one of the main topics in plasma physics. The phenomena and processes of the precursor, thermal quench, current quench, VDE, halo current and runaway electrons generation during plasma disruption are analyzed in detail and systematically based on the data obtained from current Tokamaks such as TFTR, JET, JT-60U and ASDEX-U, etc. The methods to mitigate and avoid disruption in Tokamak are also highlighted schematically. Therefore, it is helpful and instructive for plasma disruption research in next generation large Tokamak such as ITER-FEAT

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.

Current-induced nonuniform enhancement of sheet resistance in A r+ -irradiated SrTi O3

Science.gov (United States)

Roy, Debangsu; Frenkel, Yiftach; Davidovitch, Sagi; Persky, Eylon; Haham, Noam; Gabay, Marc; Kalisky, Beena; Klein, Lior

2017-06-01

The sheet resistance Rs of A r+ irradiated SrTi O3 in patterns with a length scale of several microns increases significantly below ˜40 K in connection with driving currents exceeding a certain threshold. The initial lower Rs is recovered upon warming with accelerated recovery around 70 and 160 K. Scanning superconducting quantum interference device microscopy shows local irreversible changes in the spatial distribution of the current with a length scale of several microns. We attribute the observed nonuniform enhancement of Rs to the attraction of the charged single-oxygen and dioxygen vacancies by the crystallographic domain boundaries in SrTi O3 . The boundaries, which are nearly ferroelectric below 40 K, are polarized by the local electrical field associated with the driven current and the clustered vacancies which suppress conductivity in their vicinity and yield a noticeable enhancement in the device resistance when the current path width is on the order of the boundary extension. The temperatures of accelerated conductivity recovery are associated with the energy barriers for the diffusion of the two types of vacancies.

Experimental investigation of possible geomagnetic feedback from energetic (0.1 to 16 keV) terrestrial O(+) ions in the magnetotail current sheet

Science.gov (United States)

Lennartsson, O. W.; Klumpar, D. M.; Shelley, E. G.; Quinn, J. M.

1994-01-01

Data from energetic ion mass spectrometers on the ISEE 1 and AMPTE/CCE spacecraft are combined with geomagnetic and solar indices to investigate, in a statistical fashion, whether energized O(+) ions of terrestrial origin constitute a source of feedback which triggers or amplifies geomagnetic activity as has been suggested in the literature, by contributing a destabilizing mass increase in the magnetotail current sheet. The ISEE 1 data (0.1-16 keV/e) provide in situ observations of the O(+) concentration in the central plasma sheet, inside of 23 R(sub E), during the rising and maximum phases of solar cycle 21, as well as inner magnetosphere data from same period. The CCE data (0.1-17 keV/e) taken during the subsequent solar minimum all within 9 R(sub E). provide a reference for long-term variations in the magnetosphere O(+) content. Statistical correlations between the ion data and the indices, and between different indices. all point in the same direction: there is probably no feedback specific to the O(+) ions, in spite of the fact that they often contribute most of the ion mass density in the tail current sheet.

Runaway electron generation in tokamak disruptions

International Nuclear Information System (INIS)

Helander, P.; Andersson, F.; Fueloep, T.; Smith, H.; Anderson, D.; Lisak, M.; Eriksson, L.-G.

2005-01-01

The time evolution of the plasma current during a tokamak disruption is calculated by solving the equations for runaway electron production simultaneously with the induction equation for the toroidal electric field. The resistive diffusion time in a post-disruption plasma is typically comparable to the runaway avalanche growth time. Accordingly, the toroidal electric field induced after the thermal quench of a disruption diffuses radially through the plasma at the same time as it accelerates runaway electrons, which in turn back-react on the electric field. When these processes are accounted for in a self-consistent way, it is found that (1) the efficiency and time scale of runaway generation agrees with JET experiments; (2) the runaway current profile typically becomes more peaked than the pre-disruption current profile; and (3) can easily become radially filamented. It is also shown that higher runaway electron generation is expected if the thermal quench is sufficiently fast. (author)

A multisatellite case study of the expansion of a substorm current wedge in the near-Earth magnetotail

International Nuclear Information System (INIS)

Lopez, R.E.; Lui, A.T.Y.

1990-01-01

This study presents observations made by four spacecraft (AMPTE CCE, AMPTE IRM, GOES 5, and GOES 6) and two ground stations (San Juan and Tucson) during a substorm that occurred at ∼0830 UT on April 19, 1985. The spacecraft were arrayed in a configuration that allows for the examination of the spatial evolution of the substorm current wedge, CCE was located between the GOES spacecraft in longitude, but at a radial distance of 8.0 R E . IRM was located west of the other three spacecraft in the same sector as Tucson, but at a radial distance of 11.6 R E . The relative times at which the signature of the substorm current wedge was first observed at the GOES spacecraft and the ground stations are consistent with a simple longitudinally expanding current wedge. However, the times at which IRM and CCE observed the current wedge are not consistent with a current wedge that expanded only longitudinally, IRM first observed the signature of the current wedge at about the same time the signature was observed by GOES 6 and Tucson, and CCE observed the current wedge only after both GOES satellites and the ground stations had done so. Moreover, both GOES spacecraft observed signatures consistent with entry into the central plasma sheet before CCE and IRM did, even though we estimate that CCE was slightly closer to the neutral sheet than the geosynchronous spacecraft. The sequence of events suggests that during this substorm the disruption of the cross-tail current sheet, the formation of the substorm current wedge, and the expansion of the plasma sheet began in the near-Earth region, and subsequently spread tailward as well as longitudinally

Simulating the effects of plasma disruption with a 1 MA current pulse in a coaxial test fixture

International Nuclear Information System (INIS)

Praeg, W.F.

1985-01-01

A test fixture for simulating plasma disruptions, comprising two coaxial cylinders, has been designed for use with Argonne's electromagnetic test facility FELIX. A pulsed power supply drives a half cycle sine wave current of 10 0 A through the test fixture generating fields of -1 . The coaxial structure is 140 cm long, has an outer cylinder with an OD of 78 cm and an inner cylinder with an OD of 8.3 cm. It is surrounded by the FELIX solenoid field of 1 T. This proposed upgrade of the FELIX facility should be useful for testing the effect of plasma disruption on First Wall-Blanket-Shield (FWBS) structures; a future upgrade of the solenoid field to 4 T will allow to simulate reactor conditions even better

Simulating the effects of plasma disruption with A 1 MA current pulse in a coaxial test fixture

International Nuclear Information System (INIS)

Praeg, W.F.

1985-01-01

A test fixture for simulating plasma disruptions, comprising two coaxial cylinders, has been designed for use with Argonne's electromagnetic test facility FELIX. A pulsed power supply drives a half cycle sine wave current of 10 0 A through the test fixture generating fields of -1 . The coaxial structure is 140 cm long, has an outer cylinder with an OD of 78 cm and an inner cylinder with an OD of 8.3 cm. It is surrounded by the FELIX solenoid field of 1 T. This proposed upgrade of the FELIX facility should be useful for testing the effect of plasma disruption on First Wall-Blanket-Shield (FWBS) structures; a future upgrade of the solenoid field to 4 T will allow to simulate reactor conditions even better

Disruptions and X ray activity in LH current drive experiments in Petula

International Nuclear Information System (INIS)

Melin, G.; Blanc, P.; Briand, P.; Briffod, G.; Gormezano, C.; Moulin, B.; Parlange, F.; Ryter, F.; Van Houtte, D.

1983-09-01

In this paper, time evolutions of different parameters when discharges occur during RF application in Petula are presented. The profile evolution during the disruption of the electron temperature is noted; and behaviour of the disruption as a function of the RF power is given

Effect of resistivity profile on current decay time of initial phase of current quench in neon-gas-puff inducing disruptions of JT-60U

Energy Technology Data Exchange (ETDEWEB)

Kawakami, S.; Ohno, N. [Graduate School of Engineering, Nagoya University, Nagoya 464-8603 (Japan); Shibata, Y.; Isayama, A.; Kawano, Y. [Japan Atomic Energy Agency, Naka 311-0193 (Japan); Watanabe, K. Y. [Graduate School of Engineering, Nagoya University, Nagoya 464-8603 (Japan); National Institute for Fusion Science, Toki 509-5292 (Japan); Takizuka, T. [Graduate School of Engineering, Osaka University, Suita 565-0871 (Japan); Okamoto, M. [Ishikawa National College of Technology, Ishikawa 929-0392 (Japan)

2013-11-15

According to an early work [Y. Shibata et al., Nucl. Fusion 50, 025015 (2010)] on the behavior of the plasma current decay in the JT-60U disruptive discharges caused by the radiative collapse with a massive neon-gas-puff, the increase of the internal inductance mainly determined the current decay time of plasma current during the initial phase of current quench. To investigate what determines the increase of the internal inductance, we focus attention on the relationship between the electron temperature (or the resistivity) profile and the time evolution of the current density profile and carry out numerical calculations. As a result, we find the reason of the increase of the internal inductance: The current density profile at the start of the current quench is broader than an expected current density profile in the steady state, which is determined by the temperature (or resistivity) profile. The current density profile evolves into peaked one and the internal inductance is increasing.

Linear MHD stability analysis of post-disruption plasmas in ITER

Energy Technology Data Exchange (ETDEWEB)

Aleynikova, K., E-mail: ksenia.aleynikova@gmail.com [EURATOM Association, Max-Planck-Institut für Plasmaphysik (Germany); Huijsmans, G. T. A. [ITER Organization (France); Aleynikov, P. [EURATOM Association, Max-Planck-Institut für Plasmaphysik (Germany)

2016-05-15

Most of the plasma current can be replaced by a runaway electron (RE) current during plasma disruptions in ITER. In this case the post-disruption plasma current profile is likely to be more peaked than the pre-disruption profile. The MHD activity of such plasma will affect the runaway electron generation and confinement and the dynamics of the plasma position evolution (Vertical Displacement Event), limiting the timeframe for runaway electrons and disruption mitigation. In the present paper, we evaluate the influence of the possible RE seed current parameters on the onset of the MHD instabilities. By varying the RE seed current profile, we search for subsequent plasma evolutions with the highest and the lowest MHD activity. This information can be applied to a development of desirable ITER disruption scenario.

Emerging and Disruptive Technologies.

Science.gov (United States)

Kricka, Larry J

2016-08-01

Several emerging or disruptive technologies can be identified that might, at some point in the future, displace established laboratory medicine technologies and practices. These include increased automation in the form of robots, 3-D printing, technology convergence (e.g., plug-in glucose meters for smart phones), new point-of-care technologies (e.g., contact lenses with sensors, digital and wireless enabled pregnancy tests) and testing locations (e.g., Retail Health Clinics, new at-home testing formats), new types of specimens (e.g., cell free DNA), big biology/data (e.g., million genome projects), and new regulations (e.g., for laboratory developed tests). In addition, there are many emerging technologies (e.g., planar arrays, mass spectrometry) that might find even broader application in the future and therefore also disrupt current practice. One interesting source of disruptive technology may prove to be the Qualcomm Tricorder XPrize, currently in its final stages.

On the avalanche generation of runaway electrons during tokamak disruptions

International Nuclear Information System (INIS)

Martín-Solís, J. R.; Loarte, A.; Lehnen, M.

2015-01-01

A simple zero dimensional model for a tokamak disruption is developed to evaluate the avalanche multiplication of a runaway primary seed during the current quench phase of a fast disruptive event. Analytical expressions for the plateau runaway current, the energy of the runaway beam, and the runaway energy distribution function are obtained allowing the identification of the parameters dominating the formation of the runaway current during disruptions. The effect of the electromagnetic coupling to the vessel and the penetration of the external magnetic energy during the disruption current quench as well as of the collisional dissipation of the runaway current at high densities are investigated. Current profile shape effects during the formation of the runaway beam are also addressed by means of an upgraded one-dimensional model

Structural, electronic structure and antibacterial properties of graphene-oxide nano-sheets

Science.gov (United States)

Sharma, Aditya; Varshney, Mayora; Nanda, Sitansu Sekhar; Shin, Hyun Joon; Kim, Namdong; Yi, Dong Kee; Chae, Keun-Hwa; Ok Won, Sung

2018-04-01

Correlation between the structural/electronic structure properties and bio-activity of graphene-based materials need to be thoroughly evaluated before their commercial implementation in the health and environment precincts. To better investigate the local hybridization of sp2/sp3 orbitals of the functional groups of graphene-oxide (GO) and their execution in the antimicrobial mechanism, we exemplify the antibacterial activity of GO sheets towards the Escherichia coli bacteria (E. coli) by applying the field-emission scanning electron microscopy (FESEM), near edge X-ray absorption fine structure (NEXAFS) and scanning transmission X-ray microscope (STXM) techniques. C K-edge and O K-edge NEXAFS spectra have revealed lesser sp2 carbon atoms in the aromatic ring and attachment of functional oxygen groups at GO sheets. Entrapment of E. coli bacteria by GO sheets is evidenced by FESEM investigations and has also been corroborated by nano-scale imaging of bacteria using the STXM. Spectroscopy evidence of functional oxygen moieties with GO sheets and physiochemical entrapment of E. coli bacteria have assisted us to elaborate the mechanism of cellular oxidative stress-induced disruption of bacterial membrane.

CONTROLLING INFLUENCE OF MAGNETIC FIELD ON SOLAR WIND OUTFLOW: AN INVESTIGATION USING CURRENT SHEET SOURCE SURFACE MODEL

Energy Technology Data Exchange (ETDEWEB)

Poduval, B., E-mail: bpoduval@spacescience.org [Space Science Institute, Boulder, CO 80303 (United States)

2016-08-10

This Letter presents the results of an investigation into the controlling influence of large-scale magnetic field of the Sun in determining the solar wind outflow using two magnetostatic coronal models: current sheet source surface (CSSS) and potential field source surface. For this, we made use of the Wang and Sheeley inverse correlation between magnetic flux expansion rate (FTE) and observed solar wind speed (SWS) at 1 au. During the period of study, extended over solar cycle 23 and beginning of solar cycle 24, we found that the coefficients of the fitted quadratic equation representing the FTE–SWS inverse relation exhibited significant temporal variation, implying the changing pattern of the influence of FTE on SWS over time. A particularly noteworthy feature is an anomaly in the behavior of the fitted coefficients during the extended minimum, 2008–2010 (CRs 2073–2092), which is considered due to the particularly complex nature of the solar magnetic field during this period. However, this variation was significant only for the CSSS model, though not a systematic dependence on the phase of the solar cycle. Further, we noticed that the CSSS model demonstrated better solar wind prediction during the period of study, which we attribute to the treatment of volume and sheet currents throughout the corona and the more accurate tracing of footpoint locations resulting from the geometry of the model.

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.

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

Seasonal dependence of large-scale Birkeland currents

International Nuclear Information System (INIS)

Fujii, R.; Iijima, T.; Potemra, T.A.; Sugiura, M.

1981-01-01

The seasonal dependence of large-scale Birkeland currents has been determined from the analysis of vector magnetic field data acquired by the TRIAD satellite in the northern hemisphere. Statistical characteristics of single sheet (i.e., net currents) and double sheet Birkeland currents were determined from 555 TRIAD passes during the summer, and 408 passes during the winter (more complicated multiple-sheet current systems were not included in this study). The average K/sub p/ value for the summer events is 1.9 and for the winter events is 2.0. The principal results include the following: (1) The single sheet Birkeland currents are statistically observed more often than the double sheet currents in the dayside of the auroral zone during any season. The single sheet currents are also observed more often in the summer than in the winter (as much as 2 to 3 times as often depending upon the MLT sector). (2) The intensities of the single and double sheet Birkeland currents on the dayside, from approximately 1000 MLT to 1800 MLT, are larger during the summer (in comparison to winter) by a factor of about 2. (3) The intensities of the double sheet Birkeland currents in the nightside (the dominant system in this local time) do not show a significant difference from summer to winter. (4) The single and double sheet currents in the dayside (between 0600 and 1800 MLT) appear at higher latitudes (by about 1 0 to 3 0 ) during the summer in comparison to the winter. These characterisctis suggest that the Birkeland current intensities are controlled by the ionosphere conductivity in the polar region. The greater occurrence of single sheet Birkeland currents during the summertime supports the suggestion that these currents close via the polar cap when the conductivity there is sufficiently high to permit it

Effect of Temperature and Sheet Temper on Isothermal Solidification Kinetics in Clad Aluminum Brazing Sheet

Science.gov (United States)

Benoit, Michael J.; Whitney, Mark A.; Wells, Mary A.; Winkler, Sooky

2016-09-01

Isothermal solidification (IS) is a phenomenon observed in clad aluminum brazing sheets, wherein the amount of liquid clad metal is reduced by penetration of the liquid clad into the core. The objective of the current investigation is to quantify the rate of IS through the use of a previously derived parameter, the Interface Rate Constant (IRC). The effect of peak temperature and initial sheet temper on IS kinetics were investigated. The results demonstrated that IS is due to the diffusion of silicon (Si) from the liquid clad layer into the solid core. Reduced amounts of liquid clad at long liquid duration times, a roughened sheet surface, and differences in resolidified clad layer morphology between sheet tempers were observed. Increased IS kinetics were predicted at higher temperatures by an IRC model as well as by experimentally determined IRC values; however, the magnitudes of these values are not in good agreement due to deficiencies in the model when applied to alloys. IS kinetics were found to be higher for sheets in the fully annealed condition when compared with work-hardened sheets, due to the influence of core grain boundaries providing high diffusivity pathways for Si diffusion, resulting in more rapid liquid clad penetration.

High performance electrode material for supercapacitors based on α-Co(OH)2 nano-sheets prepared through pulse current cathodic electro-deposition (PC-CED)

Science.gov (United States)

Aghazadeh, Mustafa; Rashidi, Amir; Ganjali, Mohammad Reza

2018-01-01

In this paper, the well-defined nano-sheets of α-Co(OH)2 were prepared through the cathodic electrosynthesis from an additive-free aqueous cobalt nitrate bath. The pulse current cathodic electro-deposition (PC-CED) was used as the means for the controlling the OH- electrogeneration on the cathode surface. The characteristics and electrochemical behavior of the prepared cobalt hydroxide were also assessed through SEM, TEM, XRD, BET, and IR. The results proved the product to be composed of crystalline pure α phase of cobalt hydroxide with sheet-like morphology at nanoscale. Evaluations of the electrochemical behaviour of the α-Co(OH)2 nano-sheets revealed that they are capable to delivering the specific capacitance of 1122 F g-1 at a discharge load of 3 A g-1 and SC retention of 84% after 4000 continues discharging cycles, suggesting the nano-sheets as promising candidates for use in electrochemical supercapacitors. Further, the method used for the preparation of the compounds enjoys the capability of being scaled up. [Figure not available: see fulltext.

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.

Abnormal energy deposition on the wall through plasma disruptions

International Nuclear Information System (INIS)

Yamazaki, K.; Schmidt, G.L.

1984-07-01

The dissipation of plasma kinetic and magnetic energy during sawtooth oscillstions and disruptions in tokamaks is analyzed using Kadomtsev's disruption model and the plasma-circuit equations. New simple scalings of several characteristic times are obtained for sawteeth and for thermal and magnetic energy quenches of disruptions. The abnormal energy deposition on the wall during major or minor disruptions, estimated from this analysis, is compared with bolometric measurements in the PDX tokamak. Especially, magnetic energy dissipation during current termination period is shown to be reduced by the strong coupling of the plasma current with external circuits. These analyses are found to be useful to predict the phenomenological behavior of plasma disruptions in large future tokamaks, and to estimate abnormal heat deposition on the wall during plasma disruptions. (author)

Disruption mitigation studies in DIII-D

International Nuclear Information System (INIS)

Taylor, P.L.; Kellman, A.G.; Evans, T.E.

1999-01-01

Data on the discharge behavior, thermal loads, halo currents, and runaway electrons have been obtained in disruptions on the DIII-D tokamak. These experiments have also evaluated techniques to mitigate the disruptions while minimizing runaway electron production. Experiments injecting cryogenic impurity killer pellets of neon and argon and massive amounts of helium gas have successfully reduced these disruption effects. The halo current generation, scaling, and mitigation are understood and are in good agreement with predictions of a semianalytic model. Results from killer pellet injection have been used to benchmark theoretical models of the pellet ablation and energy loss. Runaway electrons are often generated by the pellets and new runaway generation mechanisms, modifications of the standard Dreicer process, have been found to explain the runaways. Experiments with the massive helium gas puff have also effectively mitigated disruptions without the formation of runaway electrons that can occur with killer pellets

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

Sideways wall force produced during tokamak disruptions

Science.gov (United States)

Strauss, H.; Paccagnella, R.; Breslau, J.; Sugiyama, L.; Jardin, S.

2013-07-01

A critical issue for ITER is to evaluate the forces produced on the surrounding conducting structures during plasma disruptions. We calculate the non-axisymmetric ‘sideways’ wall force Fx, produced in disruptions. Simulations were carried out of disruptions produced by destabilization of n = 1 modes by a vertical displacement event (VDE). The force depends strongly on γτwall, where γ is the mode growth rate and τwall is the wall penetration time, and is largest for γτwall = constant, which depends on initial conditions. Simulations of disruptions caused by a model of massive gas injection were also performed. It was found that the wall force increases approximately offset linearly with the displacement from the magnetic axis produced by a VDE. These results are also obtained with an analytical model. Disruptions are accompanied by toroidal variation of the plasma current Iφ. This is caused by toroidal variation of the halo current, as verified computationally and analytically.

Abnormal energy deposition on the wall through plasma disruptions

International Nuclear Information System (INIS)

Yamazaki, K.; Schmidt, G.L.

1984-01-01

The dissipation of plasma kinetic and magnetic energy during sawtooth oscillations and disruptions in tokamak is analyzed using Kadomtsev's disruption model and the plasma-circuit equations. New simple scalings of several characteristic times are obtained for sawteeth and for thermal and magnetic energy quenches of disruptions. The abnormal energy deposition on the wall during major or minor disruptions, estimated from this analysis, is compared with bolometric measurements in the PDX tokamak. Especially, magnetic energy dissipation during the current termination period is shown to be reduced by the strong coupling of the plasma current with external circuits. These analyses are found to be useful to predict the phenomenological behavior of plasma disruptions in large future tokamaks, and to estimate abnormal heat deposition on the wall during plasma disruptions. (orig.)

Monitoring-induced disruption in skilled typewriting.

Science.gov (United States)

Snyder, Kristy M; Logan, Gordon D

2013-10-01

It is often disruptive to attend to the details of one's expert performance. The current work presents four experiments that utilized a monitor to report protocol to evaluate the sufficiency of three accounts of monitoring-induced disruption. The inhibition hypothesis states that disruption results from costs associated with preparing to withhold inappropriate responses. The dual-task hypothesis states that disruption results from maintaining monitored information in working memory. The implicit-explicit hypothesis states that disruption results from explicitly monitoring details of performance that are normally implicit. The findings suggest that all three hypotheses are sufficient to produce disruption, but inhibition and dual-task costs are not necessary. Experiment 1 showed that monitoring to report was disruptive even when there was no requirement to inhibit. Experiment 2 showed that maintaining information in working memory caused some disruption but much less than monitoring to report. Experiment 4 showed that monitoring to inhibit was more disruptive than monitoring to report, suggesting that monitoring is more disruptive when it is combined with other task requirements, such as inhibition. PsycINFO Database Record (c) 2013 APA, all rights reserved.

Antarctic Circumpolar Current Dynamics and Their Relation to Antarctic Ice Sheet and Perennial Sea-Ice Variability in the Central Drake Passage During the Last Climate Cycle

Science.gov (United States)

Kuhn, G.; Wu, S.; Hass, H. C.; Klages, J. P.; Zheng, X.; Arz, H. W.; Esper, O.; Hillenbrand, C. D.; Lange, C.; Lamy, F.; Lohmann, G.; Müller, J.; McCave, I. N. N.; Nürnberg, D.; Roberts, J.; Tiedemann, R.; Timmermann, A.; Titschack, J.; Zhang, X.

2017-12-01

The evolution of the Antarctic Ice Sheet during the last climate cycle and the interrelation to global atmospheric and ocean circulation remains controversial and plays an important role for our understanding of ice sheet response to modern global warming. The timing and sequence of deglacial warming is relevant for understanding the variability and sensitivity of the Antarctic Ice Sheet to climatic changes, and the continuing rise of atmospheric greenhouse gas concentrations. The Antarctic Ice Sheet is a pivotal component of the global water budget. Freshwater fluxes from the ice sheet may affect the Antarctic Circumpolar Current (ACC), which is strongly impacted by the westerly wind belt in the Southern Hemisphere (SHWW) and constricted to its narrowest extent in the Drake Passage. The flow of ACC water masses through Drake Passage is, therefore, crucial for advancing our understanding of the Southern Ocean's role in global meridional overturning circulation and global climate change. In order to address orbital and millennial-scale variability of the Antarctic ice sheet and the ACC, we applied a multi-proxy approach on a sediment core from the central Drake Passage including grain size, iceberg-rafted debris, mineral dust, bulk chemical and mineralogical composition, and physical properties. In combination with already published and new sediment records from the Drake Passage and Scotia Sea, as well as high-resolution data from Antarctic ice cores (WDC, EDML), we now have evidence that during glacial times a more northerly extent of the perennial sea-ice zone decreased ACC current velocities in the central Drake Passage. During deglaciation the SHWW shifted southwards due to a decreasing temperature gradient between subtropical and polar latitudes caused by sea ice and ice sheet decline. This in turn caused Southern Hemisphere warming, a more vigorous ACC, stronger Southern Ocean ventilation, and warm Circumpolar Deep Water (CDW) upwelling on Antarctic shelves

High-latitude Conic Current Sheets in the Solar Wind

Energy Technology Data Exchange (ETDEWEB)

Khabarova, Olga V.; Obridko, Vladimir N.; Kharshiladze, Alexander F. [Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences (IZMIRAN), Moscow (Russian Federation); Malova, Helmi V. [Scobeltsyn Nuclear Physics Institute of Lomonosov Moscow State University, Moscow (Russian Federation); Kislov, Roman A.; Zelenyi, Lev M. [Space Research Centre of the Polish Academy of Sciences (CBK PAN), Warsaw (Poland); Tokumaru, Munetoshi; Fujiki, Ken’ichi [Institute for Space-Earth Environmental Research, Nagoya University (Japan); Sokół, Justyna M.; Grzedzielski, Stan [Space Research Centre of the Polish Academy of Sciences (CBK), Warsaw (Poland)

2017-02-10

We provide observational evidence for the existence of large-scale cylindrical (or conic-like) current sheets (CCSs) at high heliolatitudes. Long-lived CCSs were detected by Ulysses during its passages over the South Solar Pole in 1994 and 2007. The characteristic scale of these tornado-like structures is several times less than a typical width of coronal holes within which the CCSs are observed. CCS crossings are characterized by a dramatic decrease in the solar wind speed and plasma beta typical for predicted profiles of CCSs. Ulysses crossed the same CCS at different heliolatitudes at 2–3 au several times in 1994, as the CCS was declined from the rotation axis and corotated with the Sun. In 2007, a CCS was detected directly over the South Pole, and its structure was strongly highlighted by the interaction with comet McNaught. Restorations of solar coronal magnetic field lines reveal the occurrence of conic-like magnetic separators over the solar poles in both 1994 and 2007. Such separators exist only during solar minima. Interplanetary scintillation data analysis confirms the presence of long-lived low-speed regions surrounded by the typical polar high-speed solar wind in solar minima. Energetic particle flux enhancements up to several MeV/ nuc are observed at edges of the CCSs. We built simple MHD models of a CCS to illustrate its key features. The CCSs may be formed as a result of nonaxiality of the solar rotation axis and magnetic axis, as predicted by the Fisk–Parker hybrid heliospheric magnetic field model in the modification of Burger and coworkers.

Links between CO2, glaciation and water flow: reconciling the Cenozoic history of the Antarctic Circumpolar Current

International Nuclear Information System (INIS)

Ladant, J.B.; Donnadieu, Y.; Dumas, C.

2014-01-01

The timing of the onset of the Antarctic Circumpolar Current (ACC) is a crucial event of the Cenozoic because of its cooling and isolating effect over Antarctica. It is intimately related to the glaciations occurring throughout the Cenozoic from the Eocene - Oligocene (EO) transition (∼ 34 Ma) to the middle Miocene glaciations (∼ 13.9 Ma). However, the exact timing of the onset remains debated, with evidence for a late Eocene setup contradicting other data pointing to an occurrence closer to the Oligocene - Miocene (OM) boundary. In this study, we show the potential impact of the Antarctic ice sheet on the initiation of a strong proto- ACC at the EO boundary. Our results reveal that the regional cooling effect of the ice sheet increases sea ice formation, which disrupts the meridional density gradient in the Southern Ocean and leads to the onset of a circumpolar current and its progressive strengthening. We also suggest that subsequent variations in atmospheric CO 2 , ice sheet volumes and tectonic reorganizations may have affected the ACC intensity after the Eocene - Oligocene transition. This allows us to build a hypothesis for the Cenozoic evolution of the Antarctic Circumpolar Current that may provide an explanation for the second initiation of the ACC at the Oligocene - Miocene boundary while reconciling evidence supporting both early Oligocene and early Miocene onset of the ACC. (authors)

Practice Oriented Algorithmic Disruption Management in Passenger Railways

NARCIS (Netherlands)

J.C. Wagenaar (Joris)

2016-01-01

markdownabstractHow to deal with a disruption is a question railway companies face on a daily basis. This thesis focusses on the subject how to handle a disruption such that the passenger service is upheld as much as possible. The current mathematical models for disruption management can not yet be

Non-axisymmetric equilibrium reconstruction and suppression of density limit disruptions in a current-carrying stellarator

Science.gov (United States)

Ma, Xinxing; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Knowlton, S. F.; Maurer, D. A.

2017-10-01

Non-axisymmetric equilibrium reconstructions have been routinely performed with the V3FIT code in the Compact Toroidal Hybrid (CTH), a stellarator/tokamak hybrid. In addition to 50 external magnetic measurements, 160 SXR emissivity measurements are incorporated into V3FIT to reconstruct the magnetic flux surface geometry and infer the current distribution within the plasma. Improved reconstructions of current and q profiles provide insight into understanding the physics of density limit disruptions observed in current-carrying discharges in CTH. It is confirmed that the final scenario of the density limit of CTH plasmas is consistent with classic observations in tokamaks: current profile shrinkage leads to growing MHD instabilities (tearing modes) followed by a loss of MHD equilibrium. It is also observed that the density limit at a given current linearly increases with increasing amounts of 3D shaping fields. Consequently, plasmas with densities up to two times the Greenwald limit are attained. Equilibrium reconstructions show that addition of 3D fields effectively moves resonance surfaces towards the edge of the plasma where the current profile gradient is less, providing a stabilizing effect. This work is supported by US Department of Energy Grant No. DE-FG02-00ER54610.

MHD stability, operational limits and disruptions

International Nuclear Information System (INIS)

1999-01-01

The present physics understandings of magnetohydrodynamic (MHD) stability of tokamak plasmas, the threshold conditions for onset of MHD instability, and the resulting operational limits on attainable plasma pressure (beta limit) and density (density limit), and the consequences of plasma disruption and disruption related effects are reviewed and assessed in the context of their application to a future DT burning reactor prototype tokamak experiment such as ITER. The principal considerations covered within the MHD stability and beta limit assessments are (i) magnetostatic equilibrium, ideal MHD stability and the resulting ideal MHD beta limit; (ii) sawtooth oscillations and the coupling of sawtooth activity to other types of MHD instability; (iii) neoclassical island resistive tearing modes and the corresponding limits on beta and energy confinement; (iv) wall stabilization of ideal MHD instabilities and resistive wall instabilities; (v) mode locking effects of non-axisymmetric error fields; (vi) edge localized MHD instabilities (ELMs, etc.); and (vii) MHD instabilities and beta/pressure gradient limits in plasmas with actively modified current and magnetic shear profiles. The principal considerations covered within the density limit assessments are (i) empirical density limits; (ii) edge power balance/radiative density limits in ohmic and L-mode plasmas; and (iii) edge parameter related density limits in H-mode plasmas. The principal considerations covered in the disruption assessments are (i) disruption causes, frequency and MHD instability onset; (ii) disruption thermal and current quench characteristics; (iii) vertical instabilities (VDEs), both before and after disruption, and plasma and in-vessel halo currents; (iv) after disruption runaway electron formation, confinement and loss; (v) fast plasma shutdown (rapid externally initiated dissipation of plasma thermal and magnetic energies); (vi) means for disruption avoidance and disruption effect mitigation; and

Probing alpha-helical and beta-sheet structures of peptides at solid/liquid interfaces with SFG.

Science.gov (United States)

Chen, Xiaoyun; Wang, Jie; Sniadecki, Jason J; Even, Mark A; Chen, Zhan

2005-03-29

We demonstrated that sum frequency generation (SFG) vibrational spectroscopy can distinguish different secondary structures of proteins or peptides adsorbed at solid/liquid interfaces. The SFG spectrum for tachyplesin I at the polystyrene (PS)/solution interface has a fingerprint peak corresponding to the B1/B3 mode of the antiparallel beta-sheet. This peak disappeared upon the addition of dithiothreitol, which can disrupt the beta-sheet structure. The SFG spectrum indicative of the MSI594 alpha-helical structure was observed at the PS/MSI594 solution interface. This research validates SFG as a powerful technique for revealing detailed secondary structures of interfacial proteins and peptides.

A case for change: disruption in academic medicine.

Science.gov (United States)

Kahn, Marc J; Maurer, Ralph; Wartman, Steven A; Sachs, Benjamin P

2014-09-01

Disruptive technologies allow less expensive and more efficient processes to eventually dominate a market sector. The academic health center's tripartite mission of education, clinical care, and research is threatened by decreasing revenues and increasing expenses and is, as a result, ripe for disruption. The authors describe current disruptive technologies that threaten traditional operations at academic health centers and provide a prescription not only to survive, but also to prosper, in the face of disruptive forces.

Studies of the disruption prevention by ECRH at plasma current rise stage in limiter discharges/Possibility of an internal transport barrier producing under dominating electron transport in the T-10 tokamak

International Nuclear Information System (INIS)

Alikaev, V.V.; Borshegovskij, A.A.; Chistyakov, V.V.

2001-01-01

'Studies of the Disruption Prevention by ECRH at Plasma Current Rise Stage in Limiter Discharges' - Studies of disruption prevention by means of ECRH in T-10 at the plasma current rise phase in limiter discharges with circular plasma cross-section were performed. Reliable disruption prevention by ECRH at HF power (P HF ) min level equal to 20% of ohmic heating power P OH was demonstrated. m/n=2/1 mode MHD-activity developed before disruption (with characteristic time ∼ 120 ms) can be considered as disruption precursor and can be used in a feedback system. 'Possibility of an Internal Transport Barrier Producing under Dominating Electron Transport in the T-10 Tokamak' - The reversed shear experiments were carried out on T-10 at the HF power up to 1MW. The reversed shear in the core was produced by on-axis ECCD in direction opposite to the plasma current. There are no obvious signs of Internal Transport Barriers formation under condition when high-k turbulence determines the electron transport. (author)

Simulation of Plasma Disruptions for HL-2M with the DINA Code

International Nuclear Information System (INIS)

Xue Lei; Duan Xu-Ru; Zheng Guo-Yao; Yan Shi-Lei; Liu Yue-Qiang; Dokuka, V. V.; Khayrutdinov, R. R.; Lukash, V. E.

2015-01-01

Plasma disruption is often an unavoidable aspect of tokamak operations. It may cause severe damage to in-vessel components such as the vacuum vessel conductors, the first wall and the divertor target plates. Two types of disruption, the hot-plasma vertical displacement event and the major disruption with a cold-plasma vertical displacement event, are simulated by the DINA code for HL-2M. The time evolutions of the plasma current, the halo current, the magnetic axis, the minor radius, the elongation as well as the electromagnetic force and eddy currents on the vacuum vessel during the thermal quench and the current quench are investigated. By comparing the electromagnetic forces before and after the disruption, we find that the disruption causes great damage to the vacuum vessel conductors. In addition, the hot-plasma vertical displacement event is more dangerous than the major disruption with the cold-plasma vertical displacement event. (paper)

A model for disruption generated runaway electrons

International Nuclear Information System (INIS)

Russo, A.J.; Campbell, R.B.

1993-01-01

One of the possible consequences of disruptions in tokamaks is the generation of runaway electrons which can impact plasma facing components and cause damage, owing to high local energy deposition. This problem becomes more serious as the machine size and plasma current increase. Since large size and high currents are characteristics of proposed future machines, control of runaway generation is an important design consideration. A lumped circuit model for disruption runaway electron generation indicates that impurity concentration and type, as well as plasma motion, can strongly influence runaway behaviour. A comparison of disruption data from several runs on JET and DIII-D with model results demonstrate the effects of impurities, and plasma motion, on runaway number density and energy. The model is also applied to the calculation of runaway currents for ITER. (author). 16 refs, 13 figs

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.

Prediction of density limit disruptions on the J-TEXT tokamak

International Nuclear Information System (INIS)

Wang, S Y; Chen, Z Y; Huang, D W; Tong, R H; Yan, W; Wei, Y N; Ma, T K; Zhang, M; Zhuang, G

2016-01-01

Disruption mitigation is essential for the next generation of tokamaks. The prediction of plasma disruption is the key to disruption mitigation. A neural network combining eight input signals has been developed to predict the density limit disruptions on the J-TEXT tokamak. An optimized training method has been proposed which has improved the prediction performance. The network obtained has been tested on 64 disruption shots and 205 non-disruption shots. A successful alarm rate of 82.8% with a false alarm rate of 12.3% can be achieved at 4.8 ms prior to the current spike of the disruption. It indicates that more physical parameters than the current physical scaling should be considered for predicting the density limit. It was also found that the critical density for disruption can be predicted several tens of milliseconds in advance in most cases. Furthermore, if the network is used for real-time density feedback control, more than 95% of the density limit disruptions can be avoided by setting a proper threshold. (paper)

Ni-Flash-Coated Galvannealed Steel Sheet with Improved Properties

Science.gov (United States)

Pradhan, D.; Dutta, M.; Venugopalan, T.

2016-11-01

In the last several years, automobile industries have increasingly focused on galvannealed (GA) steel sheet due to their superior properties such as weldability, paintability and corrosion protection. To improve the properties further, different coatings on GA have been reported. In this context, an electroplating process (flash coating) of bright and adherent Ni plating was developed on GA steel sheet for covering the GA defects and enhancing the performances such as weldability, frictional behavior, corrosion resistance and phosphatability. For better illustration, a comparative study with bare GA steel sheet has also been carried out. The maximum electroplating current density of 700 A/m2 yielded higher cathode current efficiency of 95-98%. The performances showed that Ni-coated (coating time 5-7 s) GA steel sheet has better spot weldability, lower dynamic coefficient of friction (0.07 in lubrication) and three times more corrosion resistance compared to bare GA steel sheet. Plate-like crystal of phosphate coating with size of 10-25 µm was obtained on the Ni-coated GA. The main phase in the phosphate compound was identified as hopeite (63.4 wt.%) along with other phases such as spencerite (28.3 wt.%) and phosphophyllite (8.3 wt.%).

Influence of pulsed current on deformation mechanism of AZ31B sheets during tension

Energy Technology Data Exchange (ETDEWEB)

Liu, Kai [National Die & Mold CAD Engineering Research Center, Shanghai Jiao Tong University, 1954 Hua Shan Road, Shanghai 200030 (China); Dong, Xianghuai, E-mail: dongxh@sjtu.edu.cn [National Die & Mold CAD Engineering Research Center, Shanghai Jiao Tong University, 1954 Hua Shan Road, Shanghai 200030 (China); Xie, Huanyang [Shanghai Superior Die Technology Co., Ltd, 775 Jinsui Road, Shanghai 201209 (China); Wu, Yunjian; Peng, Fang [National Die & Mold CAD Engineering Research Center, Shanghai Jiao Tong University, 1954 Hua Shan Road, Shanghai 200030 (China)

2016-08-15

The tensile tests of AZ31B sheets were carried out under pulsed current (PC) of different frequencies, and then the deformation mechanism at different conditions was analyzed by X-Ray Diffraction. The results show that PC does not change the initial yield stress, but reduces the work hardening rate and induces softening effect. Furthermore, electroplasticity effect is controlled by thermal activation. When Z (Zener-Hollomon parameter) is high, the effect of PC is limited, causing a relatively weak electroplasticity effect. With the increasing of Z, the effect of PC strengthens. When Z reaches the critical condition, the activated slip systems obviously change because of PC, which induces the change of texture evolution and the discontinuous change of the intensity of electroplasticity. When Z is low, electroplasticity effect reaches a saturate condition and does not change with Z. Moreover, higher frequency contributes to the dislocation annihilation at all the slip systems, and then increasing frequency can strengthen the extra softening effect of PC. - Highlights: • Pulsed current does not change the initial yield stress, but reduce the work hardening rate and cause softening effect. • Increasing frequency can strengthen the softening effect. • The rules of the softening effect at different deformation condition are different. • The influence of current on deformation mechanism was analyzed by XRD.

Disruption simulation for the EAST plasma

International Nuclear Information System (INIS)

Niu Xingping; Wu Bin

2007-01-01

The disruptions due to vertical displacement event for the EAST plasma are simulated in this article by using the TSC program. Meanwhile, the evolutions of the halo current and stress on vacuum vessel are calculated; the disruptions at different initial conditions are compared with each other, and killer pellet injection is simulated for the device fast shutting-down. (authors)

Magnetohydrodynamic simulations of density-limit disruptions in tokamaks

International Nuclear Information System (INIS)

Kleva, R.G.; Drake, J.F.; Denton, R.E.

1990-01-01

Magnetohydrodynamic simulations are presented which demonstrate that density limit disruptions can be triggered by edge radiation which destabilizes a q = 1 kink followed by a q = 2 tearing mode. A bubble of cold plasma is injected from the edge into the center by the q = 1 kink. The q = 2 mode then broadens the current profile and throws the hot plasma to the wall. The MHD simulations presented are the first to successfully reproduce several key features of density limit disruptions including (1) the rapid drop in the central temperature, (2) the rapid expansion of the current profile, (3) the m = 1 cold bubble which is seen to be injected from the edge into the center during density limit disruptions on JET, and (4) disruptions in sawtoothing discharges. (author)

Magneto-hydrodynamics of coupled fluid–sheet interface with mass suction and blowing

International Nuclear Information System (INIS)

Ahmad, R.

2016-01-01

There are large number of studies which prescribe the kinematics of the sheet and ignore the sheet's mechanics. However, the current boundary layer analysis investigates the mechanics of both the electrically conducting fluid and a permeable sheet, which makes it distinct from the other studies in the literature. One of the objectives of the current study is to (i) examine the behaviour of magnetic field effect for both the surface and the electrically conducting fluid (ii) investigate the heat and mass transfer between a permeable sheet and the surrounding electrically conducting fluid across the hydro, thermal and mass boundary layers. Self-similar solutions are obtained by considering the RK45 technique. Analytical solution is also found for the stretching sheet case. The skin friction dual solutions are presented for various types of sheet. The influence of pertinent parameters on the dimensionless velocity, shear stress, temperature, mass concentration, heat and mass transfer rates on the fluid–sheet interface is presented graphically as well as numerically. The obtained results are of potential benefit for studying the electrically conducting flow over various soft surfaces such as synthetic plastics, soft silicone sheet and soft synthetic rubber sheet. These surfaces are easily deformed by thermal fluctuations or thermal stresses. - Highlights: • The momentum equation is modelled for both the surrounding MHD fluid and the sheet with the effects of mass suction and blowing. • The current study further investigates the heat and mass transfer characteristics between a permeable sheet and the surrounding electrically conducting fluid across the thermal and mass boundary layers. • Both the approximated and analytical techniques have been included for the purpose of comparison, and the perfect numerical agreements have been established with the previous studies. • Dual solutions for the skin friction coefficients are found for various categories of

Disruption mitigation on Tore Supra

International Nuclear Information System (INIS)

Martin, G.; Sourd, F.; Saint-Laurent, F.; Bucalossi, J.; Eriksson, L.G.

2004-01-01

During disruptions, the plasma energy is lost on the first wall within 1 ms, forces up to hundred tons are applied to the structures and kA of electrons are accelerated up to 50 MeV (runaway electrons). Already sources of concern in present day tokamaks, extrapolation to ITER shows the necessity of mitigation procedures, to avoid serious damages to in-vessel components. Massive gas injection was proposed, and encouraging tests have been done on Textor and DIII-D. Similar experiments where performed on Tore Supra, with the goal to validate their effect on runaway electrons, observed during the majority of disruptions. 0.1 mole of helium was injected within 5 ms in ohmic plasmas, up to 1.2 MA, either stable, or in a pre-disruptive phase (argon puffing). Beneficial effects where obtained: reduction of the current fall rate and eddy currents, total disappearance of runaway electrons and easy recovery for the next pulse, without noticeable helium pollution of following plasmas. Analysis of the 4 ms period between injection and disruption indicates that to reach these goals, one need to inject enough helium to keep it only partially ionised. It corresponds to 0.1 g for Tore Supra, and extrapolate to hundreds of grams for ITER. (authors)

Disruption mitigation on Tore Supra

International Nuclear Information System (INIS)

Martin, G.; Sourd, F.; Saint-Laurent, F.; Bucalossi, J.; Eriksson, L.G.

2005-01-01

During disruptions, the plasma energy is lost on the first wall within 1 ms, forces up to hundred tons are applied to the structures and kA of electrons are accelerated up to 50 MeV (runaway electrons). Already sources of concern in present day tokamaks, extrapolation to ITER shows the necessity of mitigation procedures, to avoid serious damages to in-vessel components. Massive gas injection was proposed, and encouraging tests have been done on Textor and DIII-D. Similar experiments where performed on Tore Supra, with the goal to validate their effect on runaway electrons, observed during the majority of disruptions. 0.1 mole of helium was injected within 5 ms in ohmic plasmas, up to 1.2 MA, either stable, or in a pre-disruptive phase (argon puffing). Beneficial effects where obtained: reduction of the current fall rate and eddy currents, total disappearance of runaway electrons and easy recovery for the next pulse, without noticeable helium pollution of following plasmas. Analysis of the 4 ms period between injection and disruption indicates that to reach these goals, one need to inject enough helium to keep it only partially ionised. It correspond to 0.1 g for Tore Supra, and extrapolate to hundred's of grams for ITER. (author)

Nonlinear energy transfer and current sheet development in localized Alfvén wavepacket collisions in the strong turbulence limit

Science.gov (United States)

Verniero, J. L.; Howes, G. G.; Klein, K. G.

2018-02-01

In space and astrophysical plasmas, turbulence is responsible for transferring energy from large scales driven by violent events or instabilities, to smaller scales where turbulent energy is ultimately converted into plasma heat by dissipative mechanisms. The nonlinear interaction between counterpropagating Alfvén waves, denoted Alfvén wave collisions, drives this turbulent energy cascade, as recognized by early work with incompressible magnetohydrodynamic (MHD) equations. Recent work employing analytical calculations and nonlinear gyrokinetic simulations of Alfvén wave collisions in an idealized periodic initial state have demonstrated the key properties that strong Alfvén wave collisions mediate effectively the transfer of energy to smaller perpendicular scales and self-consistently generate current sheets. For the more realistic case of the collision between two initially separated Alfvén wavepackets, we use a nonlinear gyrokinetic simulation to show here that these key properties persist: strong Alfvén wavepacket collisions indeed facilitate the perpendicular cascade of energy and give rise to current sheets. Furthermore, the evolution shows that nonlinear interactions occur only while the wavepackets overlap, followed by a clean separation of the wavepackets with straight uniform magnetic fields and the cessation of nonlinear evolution in between collisions, even in the gyrokinetic simulation presented here which resolves dispersive and kinetic effects beyond the reach of the MHD theory.

Ice sheet hydrology - a review

International Nuclear Information System (INIS)

Jansson, Peter; Naeslund, Jens-Ove; Rodhe, Lars

2007-03-01

This report summarizes the theoretical knowledge on water flow in and beneath glaciers and ice sheets and how these theories are applied in models to simulate the hydrology of ice sheets. The purpose is to present the state of knowledge and, perhaps more importantly, identify the gaps in our understanding of ice sheet hydrology. Many general concepts in hydrology and hydraulics are applicable to water flow in glaciers. However, the unique situation of having the liquid phase flowing in conduits of the solid phase of the same material, water, is not a commonly occurring phenomena. This situation means that the heat exchange between the phases and the resulting phase changes also have to be accounted for in the analysis. The fact that the solidus in the pressure-temperature dependent phase diagram of water has a negative slope provides further complications. Ice can thus melt or freeze from both temperature and pressure variations or variations in both. In order to provide details of the current understanding of water flow in conjunction with deforming ice and to provide understanding for the development of ideas and models, emphasis has been put on the mathematical treatments, which are reproduced in detail. Qualitative results corroborating theory or, perhaps more often, questioning the simplifications made in theory, are also given. The overarching problem with our knowledge of glacier hydrology is the gap between the local theories of processes and the general flow of water in glaciers and ice sheets. Water is often channelized in non-stationary conduits through the ice, features which due to their minute size relative to the size of glaciers and ice sheets are difficult to incorporate in spatially larger models. Since the dynamic response of ice sheets to global warming is becoming a key issue in, e.g. sea-level change studies, the problems of the coupling between the hydrology of an ice sheet and its dynamics is steadily gaining interest. New work is emerging

Ice sheet hydrology - a review

Energy Technology Data Exchange (ETDEWEB)

Jansson, Peter; Naeslund, Jens-Ove [Dept. of Physical Geography and Quaternary Geology, Stockholm Univ., Stockholm (Sweden); Rodhe, Lars [Geological Survey of Sweden, Uppsala (Sweden)

2007-03-15

This report summarizes the theoretical knowledge on water flow in and beneath glaciers and ice sheets and how these theories are applied in models to simulate the hydrology of ice sheets. The purpose is to present the state of knowledge and, perhaps more importantly, identify the gaps in our understanding of ice sheet hydrology. Many general concepts in hydrology and hydraulics are applicable to water flow in glaciers. However, the unique situation of having the liquid phase flowing in conduits of the solid phase of the same material, water, is not a commonly occurring phenomena. This situation means that the heat exchange between the phases and the resulting phase changes also have to be accounted for in the analysis. The fact that the solidus in the pressure-temperature dependent phase diagram of water has a negative slope provides further complications. Ice can thus melt or freeze from both temperature and pressure variations or variations in both. In order to provide details of the current understanding of water flow in conjunction with deforming ice and to provide understanding for the development of ideas and models, emphasis has been put on the mathematical treatments, which are reproduced in detail. Qualitative results corroborating theory or, perhaps more often, questioning the simplifications made in theory, are also given. The overarching problem with our knowledge of glacier hydrology is the gap between the local theories of processes and the general flow of water in glaciers and ice sheets. Water is often channelized in non-stationary conduits through the ice, features which due to their minute size relative to the size of glaciers and ice sheets are difficult to incorporate in spatially larger models. Since the dynamic response of ice sheets to global warming is becoming a key issue in, e.g. sea-level change studies, the problems of the coupling between the hydrology of an ice sheet and its dynamics is steadily gaining interest. New work is emerging

Decontamination sheet

International Nuclear Information System (INIS)

Hirose, Emiko; Kanesaki, Ken.

1995-01-01

The decontamination sheet of the present invention is formed by applying an adhesive on one surface of a polymer sheet and releasably appending a plurality of curing sheets. In addition, perforated lines are formed on the sheet, and a decontaminating agent is incorporated in the adhesive. This can reduce the number of curing operation steps when a plurality steps of operations for radiation decontamination equipments are performed, and further, the amount of wastes of the cured sheets, and operator's exposure are reduced, as well as an efficiency of the curing operation can be improved, and propagation of contamination can be prevented. (T.M.)

VDE/disruption EM analysis for ITER in-vessel components

International Nuclear Information System (INIS)

Miki, N.; Ioki, K.; Ilio, F.; Kodama, T.; Chiocchio, S.; Williamson, D.; Roccella, M.; Barabaschi, P.; Sayer, R.S.

1998-01-01

This paper summarises the results of EM analyses for ITER in-vessel components, such as blanket modules, backplate and divertor modules. In the ITER design the following two disruption scenarios are taken into account: centered or radial disruption, and vertical displacement event (VDE). Eddy currents and forces due to plasma disruption were calculated using the 3D shell element code EDDYCUFF and the 3D solid element code EMAS. The plasma motion and current decay used in the EM analysis was supplied by 2-D axisymmetric plasma equilibrium codes, TSC and MAXFEA. (authors)

Simulation of a major tokamak disruption

International Nuclear Information System (INIS)

White, R.B.; Monticello, D.A.; Rosenbluth, M.N.

1977-08-01

It is known that the internal tokamak disruption leads to a current profile which is flattened inside the surface where the safety factor equals unity. It is shown that such a profile can lead to m = 2 magnetic islands which grow to fill a substantial part of the tokamak cross section in a time consistent with the observations of the major disruption

Total magnetic reconnection during a tokamak major disruption

International Nuclear Information System (INIS)

Goetz, J.A.

1990-09-01

Magnetic reconnection has long been considered to be the cause of sawtooth oscillations and major disruptions in tokamak experiments. Experimental confirmation of reconnection models has been hampered by the difficulty of direct measurement of reconnection, which would involve tracing field lines for many transits around the tokamak. Perhaps the most stringent test of reconnection in a tokamak involves measurement of the safety factor q. Reconnection arising from a single helical disturbance with mode numbers m and n should raise q to m/n everywhere inside of the original resonant surface. Total reconnection should also flatten the temperature and current density profiles inside of this surface. Disruptive instabilities have been studied in the Tokapole 2, a poloidal divertor tokamak. When Tokapole 2 is operated in the material limiter configuration, a major disruption results in current termination as in most tokamaks. However, when operated in the magnetic limiter configuration current termination is suppressed and major disruptions appear as giant sawtooth oscillations. The objective of this thesis is to determine if total reconnection is occurring during major disruptions. To accomplish this goal, the poloidal magnetic field has been directly measured in Tokapole 2 with internal magnetic coils. A full two-dimensional measurement over the central current channel has been done. From these measurements, the poloidal magnetic flux function is obtained and the magnetic surfaces are plotted. The flux-surface-averaged safety factor is obtained by integrating the local magnetic field line pitch over the experimentally obtained magnetic surface

The Effects of Disruption on Strategic Management

DEFF Research Database (Denmark)

Drejer, Anders

2017-01-01

There is a lot of interest in Disruption these days even though the concept itself is still under formation. Disruption can be traced back to the idea of disruptive technological change and the late 1990s but has reemerged in the public eye in current years under guises such as Big Data......, Digitalization, Globalization and much more. Furthermore, the effects of disruption are now being felt by organizations and industries all over the world. In this paper, we will try to outline and illustrate some of those effects using the case-study of an international, Danish, SME. The case company has been...... forced to face some challenges caused by disruption and in the process of doing so has changed its strategy process significantly towards a more learning based approach to strategic management. Keywords: disruption; case- study; SME; strategy process....

Nanotechnology for Site Remediation: Fact Sheet

Science.gov (United States)

This fact sheet presents a snapshot of nanotechnology and its current uses in remediation. It presents information to help site project managers understand the potential applications of this group of technologies at their sites.

3D eddy-current distribution in a tokamak first wall during a plasma disruption using 'TRIFOU'

International Nuclear Information System (INIS)

Chaussecourte, P.; Bossavit, A.; Verite, J.C.; Crutzen, Y.R.

1989-01-01

In fusion reactor studies there is a lack of knowledge concerning the electromagnetic-type of phenomena generated by a plasma disruption event (rapid quenching of the plasma current). The induced eddy current distribution in space and time in the passive conducting structural components surrounding the plasma ring needs to be accurately investigated. TRIFOU is a full 3D eddy-current computer program based on a mixed FEM and BIEM technique, using the magnetic field, h, as a state variable, It has already been used in various areas of interest including static or rotating machines, non-destructive testing, induction heating, and research devices such as tokamaks. It can take into account various geometries and a wide range of physical situations (time dependency, physical properties, etc.). The present application is related to the eddy-current situation arising from a strong electromagnetic transient generated in the NET (Next European Torus) first wall segment. With respect to previous numerical simulations, the general 3D approach for the current density shows different eddy current circulations in the front/side shells and in the stiff back plate. The results obtained by TRIFOU are illustrated by means of advanced computer graphic displays and an animation movie. (orig.)

Neutron spatial distribution measurement with 6Li-contained thermoluminescent sheets

International Nuclear Information System (INIS)

Konnai, A.; Odano, N.; Sawamura, H.; Ozasa, N.; Ishikawa, Y.

2006-01-01

We have been developing a thermoluminescent (TL) sheet for photon dosimetry (TL sheet) with thermoluminescent material of LiF:Mg, Cu, P and a co-polymer of ethylene and tetrafluoroethylene. For the purpose of a development of simple method for neutron spatial distribution measurement, TL sheet for neutron detection (NTL sheet) is made by adding 94.7% enriched 6 LiF to TL sheet. TL material in TL sheet is directly excited by ionizing radiation whereas, in the case of neutron detection, TL material in NTL sheet is indirectly excited by neutron capture reaction. That is neutron distribution can be obtained with TL caused by α particle from 6 Li(n, α) 3 H reaction. Responses of NTL sheets to neutrons were examined at the neutron beam irradiation facility for Boron Neutron Capture Therapy (BNCT) in JRR-4 research reactor in Japan Atomic Energy Agency. TL and NTL sheets were exposed to striped and roundly distributed neutron fields. Attenuations of neutron flux in air and water were also observed using NTL sheets. TL sheets were also exposed on the same conditions and compared with NTL sheets. TL intensity ratios of NTL sheet to TL sheet were consistent with the calculated value from 6 Li content. Thermal neutron attenuation observed by NTL sheet also corresponded with the result measured by Au wire radioactivation and TLD chips, which were currently used in BNCT at JRR-4. These results were analyzed with by Monte Carlo simulation. The present results indicated that NTL sheet is applicable to measurement of neutron spatial distribution. (author)

Large patternable metal nanoparticle sheets by photo/e-beam lithography

Science.gov (United States)

Saito, Noboru; Wang, Pangpang; Okamoto, Koichi; Ryuzaki, Sou; Tamada, Kaoru

2017-10-01

Techniques for micro/nano-scale patterning of large metal nanoparticle sheets can potentially be used to realize high-performance photoelectronic devices because the sheets provide greatly enhanced electrical fields around the nanoparticles due to localized surface plasmon resonances. However, no single metal nanoparticle sheet currently exists with sufficient durability for conventional lithographical processes. Here, we report large photo and/or e-beam lithographic patternable metal nanoparticle sheets with improved durability by incorporating molecular cross-linked structures between nanoparticles. The cross-linked structures were easily formed by a one-step chemical reaction; immersing a single nanoparticle sheet consisting of core metals, to which capping molecules ionically bond, in a dithiol ethanol solution. The ligand exchange reaction processes were discussed in detail, and we demonstrated 20 μm wide line and space patterns, and a 170 nm wide line of the silver nanoparticle sheets.

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.

Multi-scale magnetic field intermittence in the plasma sheet

Directory of Open Access Journals (Sweden)

Z. Vörös

2003-09-01

Full Text Available This paper demonstrates that intermittent magnetic field fluctuations in the plasma sheet exhibit transitory, localized, and multi-scale features. We propose a multifractal-based algorithm, which quantifies intermittence on the basis of the statistical distribution of the "strength of burstiness", estimated within a sliding window. Interesting multi-scale phenomena observed by the Cluster spacecraft include large-scale motion of the current sheet and bursty bulk flow associated turbulence, interpreted as a cross-scale coupling (CSC process.Key words. Magnetospheric physics (magnetotail; plasma sheet – Space plasma physics (turbulence

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

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.

Maternal Characteristics Predicting Young Girls’ Disruptive Behavior

Science.gov (United States)

van der Molen, Elsa; Hipwell, Alison E.; Vermeiren, Robert; Loeber, Rolf

2011-01-01

Little is known about the relative predictive utility of maternal characteristics and parenting skills on the development of girls’ disruptive behavior. The current study used five waves of parent and child-report data from the ongoing Pittsburgh Girls Study to examine these relationships in a sample of 1,942 girls from age 7 to 12 years. Multivariate Generalized Estimating Equation (GEE) analyses indicated that European American race, mother’s prenatal nicotine use, maternal depression, maternal conduct problems prior to age 15, and low maternal warmth explained unique variance. Maladaptive parenting partly mediated the effects of maternal depression and maternal conduct problems. Both current and early maternal risk factors have an impact on young girls’ disruptive behavior, providing support for the timing and focus of the prevention of girls’ disruptive behavior. PMID:21391016

Current Sheets in the Corona and the Complexity of Slow Wind

Science.gov (United States)

Antiochos, Spiro

2010-01-01

The origin of the slow solar wind has long been one of the most important problems in solar/heliospheric physics. Two observational constraints make this problem especially challenging. First, the slow wind has the composition of the closed-field corona, unlike the fast wind that originates on open field lines. Second, the slow wind has substantial angular extent, of order 30 degrees, which is much larger than the widths observed for streamer stalks or the widths expected theoretically for a dynamic heliospheric current sheet. We propose that the slow wind originates from an intricate network of narrow (possibly singular) open-field corridors that emanate from the polar coronal hole regions. Using topological arguments, we show that these corridors must be ubiquitous in the solar corona. The total solar eclipse in August 2008, near the lowest point of cycle 23 affords an ideal opportunity to test this theory by using the ultra-high resolution Predictive Science's (PSI) eclipse model for the corona and wind. Analysis of the PSI eclipse model demonstrates that the extent and scales of the open-field corridors can account for both the angular width of the slow wind and its closed-field composition. We discuss the implications of our slow wind theory for the structure of the corona and heliosphere at solar minimum and describe further observational and theoretical tests.

CURRENT SHEET REGULATION OF SOLAR NEAR-RELATIVISTIC ELECTRON INJECTION HISTORIES

Energy Technology Data Exchange (ETDEWEB)

Agueda, N.; Sanahuja, B. [Departament d' Astronomia i Meteorologia, Institut de Ciencies del Cosmos, Universitat de Barcelona (Spain); Vainio, R. [Department of Physics, University of Helsinki (Finland); Dalla, S. [Jeremiah Horrocks Institute, University of Central Lancashire (United Kingdom); Lario, D. [Applied Physics Laboratory, Johns Hopkins University (United States)

2013-03-10

We present a sample of three large near-relativistic (>50 keV) electron events observed in 2001 by both the ACE and the Ulysses spacecraft, when Ulysses was at high-northern latitudes (>60 Degree-Sign ) and close to 2 AU. Despite the large latitudinal distance between the two spacecraft, electrons injected near the Sun reached both heliospheric locations. All three events were associated with large solar flares, strong decametric type II radio bursts and accompanied by wide (>212 Degree-Sign ) and fast (>1400 km s{sup -1}) coronal mass ejections (CMEs). We use advanced interplanetary transport simulations and make use of the directional intensities observed in situ by the spacecraft to infer the electron injection profile close to the Sun and the interplanetary transport conditions at both low and high latitudes. For the three selected events, we find similar interplanetary transport conditions at different heliolatitudes for a given event, with values of the mean free path ranging from 0.04 AU to 0.27 AU. We find differences in the injection profiles inferred for each spacecraft. We investigate the role that sector boundaries of the heliospheric current sheet (HCS) have on determining the characteristics of the electron injection profiles. Extended injection profiles, associated with coronal shocks, are found if the magnetic footpoints of the spacecraft lay in the same magnetic sector as the associated flare, while intermittent sparse injection episodes appear when the spacecraft footpoints are in the opposite sector or a wrap in the HCS bounded the CME structure.

The influence of a conducting wall on disruptions in HBT-EP

International Nuclear Information System (INIS)

Kombargi, R.

1997-01-01

The characteristics of long wavelength magnetohydrodynamic (MHD) disruptive instabilities have been studied in a tokamak device with segmented and movable conducting walls. Coupling between the wall and the plasma was varied by systematically adjusting the radial position, b, of the conducting plates relative to the plasma surface of minor radius a. By pre-selecting the total plasma current ramp rate (dI p /dt), disruptive instabilities driven either by large edge currents or high plasma pressure were studied. Specifically, three types of disruptions caused by both external (to the plasma) and internal instabilities were obtained by changing the plasma-wall separation (b/a) and the temporal evolution of the total plasma current. The properties of these disruptions were examined using a variety of magnetic pickup coils and arrays of soft x-ray detectors. Experiments demonstrated that rapidly developing, low-n kink instabilities were suppressed if the conducting wall was positioned sufficiently near the plasma (b/a p /dt > 0) was maintained. Conducting wall stabilization of fast growing external instabilities was observed in discharges with high edge current and in plasmas with β-values near the ideal MED stability boundary. When the conducting wall was near the plasma surface and as the current profile evolved in time (dI p /dt < 0), slowly growing internal instabilities would also lead to disruptions. Disruption mechanisms for plasmas with b/a=1.52 and b/a=1.07 were compared. Differences in the precursor modes, the speed of the thermal collapse and the chronological sequence of events were found. In summary, the disruptions with an external character were eliminated when the conducting wall was moved from b/a=1.52 to b/a<1.2. Internal disruptions could not be averted even with b/a=1.07

Comparing Sources of Storm-Time Ring Current O+

Science.gov (United States)

Kistler, L. M.

2015-12-01

The first observations of the storm-time ring current composition using AMPTE/CCE data showed that the O+ contribution to the ring current increases significantly during storms. The ring current is predominantly formed from inward transport of the near-earth plasma sheet. Thus the increase of O+ in the ring current implies that the ionospheric contribution to the plasma sheet has increased. The ionospheric plasma that reaches the plasma sheet can come from both the cusp and the nightside aurora. The cusp outflow moves through the lobe and enters the plasma sheet through reconnection at the near-earth neutral line. The nightside auroral outflow has direct access to nightside plasma sheet. Using data from Cluster and the Van Allen Probes spacecraft, we compare the development of storms in cases where there is a clear input of nightside auroral outflow, and in cases where there is a significant cusp input. We find that the cusp input, which enters the tail at ~15-20 Re becomes isotropized when it crosses the neutral sheet, and becomes part of the hot (>1 keV) plasma sheet population as it convects inward. The auroral outflow, which enters the plasma sheet closer to the earth, where the radius of curvature of the field line is larger, does not isotropize or become significantly energized, but remains a predominantly field aligned low energy population in the inner magnetosphere. It is the hot plasma sheet population that gets accelerated to high enough energies in the inner magnetosphere to contribute strongly to the ring current pressure. Thus it appears that O+ that enters the plasma sheet further down the tail has a greater impact on the storm-time ring current than ions that enter closer to the earth.

Energetics of LMFBR core disruptive accidents

International Nuclear Information System (INIS)

Marchaterre, J.F.

1979-01-01

In general, in the design of fast reactor systems, containment design margins are specified by investigating the response of the containment to core disruptive accidents. The results of these analyses are then translated into criteria which the designers must meet. Currently, uniform and agreed upon criteria are lacking, and in this time while they are being developed, the designer should be aware of the considerations which go into the particular criteria he must work with, and participate in their development. This paper gives an overview of the current state of the art in assessing core disruptive accidents and the design implications of this process. (orig.)

Disruption Studies in JT-60U

International Nuclear Information System (INIS)

Kawano, Y.; Yoshino, R.; Neyatani, Y.; Nakamura, Y.; Tokuda, S.; Tamai, H.

2002-01-01

Intensive studies on the physics of disruptions and developments of avoidance/mitigation methods of disruption-related phenomena have being carried out in JT-60U. The characteristics of the disruption sequence were well understood from the observation of the relationship between the heat pulse onto divertor plates during thermal quench and the impurity influx into the plasma, which determined the speed of the following current quench. A fast shutdown was first demonstrated by injecting impurity ice pellets to the plasma and intensively reducing the heat flux on first wall. The halo current and its toroidal asymmetry were precisely measured, and the halo current database was made for ITER in a wide parameter range. It was found that TPF x I h /I p0 was 0.52 at the maximum in a large tokamak like the JT-60U, whereas the higher factor of 0.75 had been observed in medium-sized tokamaks such as Alcator C-Mod and ASDEX-Upgrade. The vertical displacement event (VDE) at the start of the current quench was carefully investigated, and the neutral point where the VDE hardly occurs was discovered. MHD simulations clarified the onset mechanisms of the VDE, in which the eddy current effect of the up-down asymmetric resistive shell was essential. The real-time Z j measurement was improved for avoiding VDEs during slow current quench, and plasma-wall interaction was avoided by a well-optimized plasma equilibrium control. Magnetic fluctuations that were spontaneously generated at the disruption and/or enhanced by the externally applied helical field have been shown to avoid the generation of runaway electrons. Numerical analysis clarified an adequate rate of collisionless loss of runaway electrons in turbulent magnetic fields, which was consistent with the avoidance of runaway electron generation by magnetic fluctuations observed in JT-60U. Once generated, runaway electrons were suppressed when the safety factor at the plasma surface was reduced to 3 or 2

Sleep Disruption in Hematopoietic Cell Transplant Recipients: Prevalence, Severity, and Clinical Management

Science.gov (United States)

Jim, Heather S.L.; Evans, Bryan; Jeong, Jiyeon M.; Gonzalez, Brian D.; Johnston, Laura; Nelson, Ashley M.; Kesler, Shelli; Phillips, Kristin M.; Barata, Anna; Pidala, Joseph; Palesh, Oxana

2014-01-01

Sleep disruption is common among hematopoietic cell transplant (HCT) recipients, with over 50% of patients experiencing sleep disruption pre-transplant, up to 82% experiencing moderate to severe sleep disruption during hospitalization for transplant, and up to 43% in the post-transplant period. These rates of sleep disruption are substantially higher than the general population. Although sleep disruption can be distressing to patients and contribute to diminished quality of life, it is rarely discussed during clinical visits. The goal of the current review is to draw attention to sleep disruption as a clinical problem in HCT in order to facilitate patient education, intervention, and research. The review opens with a discussion of sleep disruption measurement and clinical diagnosis of sleep disorders. An overview of the prevalence, severity, and chronicity of sleep disruption and disorders in patients receiving HCT follows. Current evidence regarding sociodemographic and clinical predictors of sleep disruption and disorders is summarized. The review concludes with suggestions for behavioral and pharmacologic management of sleep disruption and disorders as well as directions for future research. PMID:24747335

Motion and shape of snowplough sheets in coaxial accelerators

International Nuclear Information System (INIS)

Tsagas, N.F.; Mair, G.L.R.; Prinn, A.E.

1978-01-01

A long coaxial accelerator is filled with helium at initial gas pressure between 0.2 and 4 Torr. When connected to a large capacitor at < - 10 kV a discharge is started at one end; the central electrode has negative polarity. The velocity of the plasma sheet, the snowplough, and its shape have been derived from streak photographs for terminal currents between about 100 and 300 kA. The motion of the sheet has been analysed by balancing the electromagnetic driving force against the inertia of the mass of the gas swept up by a plane sheet taken to be impenetrable to gas atoms. The calculated positions and average sheet velocities, which involve simplifying assumptions, have been found to be in good agreement with observations at different positions and pressures. Also the shape of the sheet has been derived by allowing for the sheet's curvature in the linear momentum equation while net radial motions causing variations in profile have, at first, been excluded. The calculated shape of the sheet is very nearly that photographically observed. The axial velocity of a sheet element is evaluated under the assumption that the plasma is azimuthally uniform, free of spikes and that the vessel's wall does not affect the shape. (author)

Multipoint observations of a small substorm

International Nuclear Information System (INIS)

Lopez, R.E.; Luehr, H.; Anderson, B.J.; Newell, P.T.; McEntire, R.W.

1990-01-01

In this paper the authors present multipoint observations of a small substorm which occurred just after 0110 UT on April 25, 1985. The observations were made by spacecraft (AMPTE CCE, AMPTE IRM, DMSP F6, and DMSP F7), ground auroral stations (EISCAT magnetometer cross, Syowa, Narssarssuaq, Great Whale River, and Fort Churchill), and mid-latitude stations (Furstenfeldbruck, Toledo, and Argentine Island). These data provide them with a broad range of observations, including the latitudinal extent of the polar cap, visual identification of substorm aurorae and the magnetic perturbations produced directly beneath them, in situ magnetic field and energetic particle observations of the disruption of the cross-tail current sheet, and observations concerning the spatial expansion of the current disruption region from two radially aligned spacecraft. The DMSP data indicate that the event took place during a period when the polar cap was relatively contracted, yet the disruption of the current sheet was observed by CCE at 8.56 R E . They have been able to infer a considerable amount of detail concerning the structure and westward expansion of the auroral features associated with the event, and they show that those auroral surges were located more than 10 degree equatorward of the boundary between open and closed field lines. Moreover, they present evidence that the current sheet disruption observed by CCE in the neutral sheet was located on field lines which mapped to the westward traveling surge observed directly overhead of the ground station at Syowa. Furthermore, the observations strongly imply that disruption of the cross-tail current began in the near-Earth region and that it had a component of expansion which was radially antisunward

Enzymatic cell disruption of microalgae biomass in biorefinery processes.

Science.gov (United States)

Demuez, Marie; Mahdy, Ahmed; Tomás-Pejó, Elia; González-Fernández, Cristina; Ballesteros, Mercedes

2015-10-01

When employing biotechnological processes for the procurement of biofuels and bio-products from microalgae, one of the most critical steps affecting economy and yields is the "cell disruption" stage. Currently, enzymatic cell disruption has delivered effective and cost competitive results when compared to mechanical and chemical cell disruption methods. However, the introduction of enzymes implies additional associated cost within the overall process. In order to reduce this cost, autolysis of microalgae is proposed as alternative enzymatic cell disruption method. This review aims to provide the state of the art of enzymatic cell disruption treatments employed in biorefinery processes and highlights the use of endopeptidases. During the enzymatic processes of microalgae life cycle, some lytic enzymes involved in cell division and programmed cell death have been proven useful in performing cell lysis. In this context, the role of endopeptidases is emphasized. Mirroring these natural events, an alternative cell disruption approach is proposed and described with the potential to induce the autolysis process using intrinsic cell enzymes. Integrating induced autolysis within biofuel production processes offers a promising approach to reduce overall global costs and energetic input associated with those of current cell disruption methods. A number of options for further inquiry are also discussed. © 2015 Wiley Periodicals, Inc.

Ocean Tide Influences on the Antarctic and Greenland Ice Sheets

Science.gov (United States)

Padman, Laurie; Siegfried, Matthew R.; Fricker, Helen A.

2018-03-01

Ocean tides are the main source of high-frequency variability in the vertical and horizontal motion of ice sheets near their marine margins. Floating ice shelves, which occupy about three quarters of the perimeter of Antarctica and the termini of four outlet glaciers in northern Greenland, rise and fall in synchrony with the ocean tide. Lateral motion of floating and grounded portions of ice sheets near their marine margins can also include a tidal component. These tide-induced signals provide insight into the processes by which the oceans can affect ice sheet mass balance and dynamics. In this review, we summarize in situ and satellite-based measurements of the tidal response of ice shelves and grounded ice, and spatial variability of ocean tide heights and currents around the ice sheets. We review sensitivity of tide heights and currents as ocean geometry responds to variations in sea level, ice shelf thickness, and ice sheet mass and extent. We then describe coupled ice-ocean models and analytical glacier models that quantify the effect of ocean tides on lower-frequency ice sheet mass loss and motion. We suggest new observations and model developments to improve the representation of tides in coupled models that are used to predict future ice sheet mass loss and the associated contribution to sea level change. The most critical need is for new data to improve maps of bathymetry, ice shelf draft, spatial variability of the drag coefficient at the ice-ocean interface, and higher-resolution models with improved representation of tidal energy sinks.

Disruptions and Their Mitigation in TEXTOR

International Nuclear Information System (INIS)

Finken, K.H.; Jaspers, R.; Kraemer-Flecken, A.; Savtchkov, A.; Lehnen, M.; Waidmann, G.

2005-01-01

Disruptions remain a major concern for tokamak devices, particularly for large machines. The critical issues are the induced (halo) currents and the resulting forces, the excessive heating of exposed surfaces by the instantaneous power release, and the possible occurrence of highly energetic runaway electrons. The key topics of the investigations on TEXTOR in the recent years concerned (a) the power deposition pattern recorded by a fast infrared scanner, (b) the runaway generation measured by synchrotron radiation in the infrared spectral region, (c) method development for 'healing' discharges that are going to disrupt, and (d) massive gas puffing for mitigating the adverse effects of disruptions

Spatial variations in the suprathermal ion distributions during substorms in the plasma sheet

International Nuclear Information System (INIS)

Kistler, L.M.; Moebius, E.; Klecker, B.; Gloeckler, G.; Ipavich, F.M.; Hamilton, D.C.

1990-01-01

Using data from AMPTE IRM and AMPTE CCE, the authors have determined the pre- and post-injection suprathermal energy spectra for the ion species H + , O + , He + , and He ++ for six events in which substorm-associated particle injections are observed in both the near-Earth plasma sheet and farther down the tail. They find similar spectral changes in both locations, with the spectra becoming harder with the injection. Post-injection, the flux decreases exponentially with radial distance. Approximately the same gradient is observed in all species. In addition, they find that although the O + /H + and the He ++ /H + ratios increase with energy per charge, the ratios are approximately the same at the same energy per charge at the two spacecraft. The observations are difficult to explain either with a model in which the ions are accelerated at a neutral line and transported toward Earth or with a model in which the ions are accelerated in the near-Earth region by current disruption/diversion and transported down the tail. In either case, the ions would have to be transported throughout the tail without much energization or deenergization in order to explain the energy per charge correlations. Further, earthward transport without energization would not lead to the observed radial gradient. A combination of these acceleration mechanisms, a disturbance that propagates throughout the plasma sheet, or a more global mechanism may explain the observations

Analysis of shot-to-shot variability in post-disruption runaway electron currents for diverted DIII-D discharges

International Nuclear Information System (INIS)

Izzo, V A; Humphreys, D A; Kornbluth, M

2012-01-01

In DIII-D experiments, rapid termination by Ar-pellet injection sometimes produces a post-termination runaway electron (RE) current plateau, but this effect is highly non-reproducible on a shot-to-shot basis, particularly for diverted target plasmas. A set of DIII-D discharges is analyzed with two MHD codes to understand the relationship between the current profile of the target plasma and the amplitude of the RE current plateau. Using the linear stability code GATO, a correlation between the radial profile of the unstable n = 1 mode just after Ar-pellet injection and the observed appearance of an RE plateau is identified. Nonlinear NIMROD simulations with RE test-particle calculations directly predict RE confinement times during the disruption. With one exception, NIMROD predicts better RE confinement for shots in which higher RE currents were observed in DIII-D. But, the variation in confinement is primarily connected to the saturated n = 1 mode amplitude and not its radial profile. Still, both sets of analyses support the hypothesis that RE deconfinement by MHD fluctuations is a major factor in the shot-to-shot variability of RE plateaus, though additional factors such as seed current amplitude cannot be ruled out. (paper)

Study of runaway electron generation process during major disruptions in JET

International Nuclear Information System (INIS)

Plyusnin, V.V.; Riccardo, V.; Alper, B.; Kiptily, V.G.; Popovichev, S.; Helander, P.; Jaspers, R.; Mlynar, J.; Luna, E. de La; Andersson, F.

2005-01-01

The analysis of a large number of JET disruptions has provided further data on the trends of the disruption induced runaway process in large tokamaks. The role of primary runaway electrons generated at the thermal quench has been examined to assess their influence on secondary avalanching, which is recognized as a main source of large runaway currents created during disruptions. The tomographic reconstruction of the soft X-ray emission during the thermal quench has made possible the observation of the magnetic flux geometry evolution and the locating of the most probable zones for generation and confinement of the primary runaway electrons. Runaway currents have been found to increase with toroidal magnetic field and pre-disruption plasma current values. The average conversion efficiency is approximately 40-45% at a wide range of plasma currents. This agrees well with results of numerical simulations, which predict similar conversion rates at an assumed post-disruption plasma electron temperature of 10 eV. The experimental trends and numerical simulations show that runaway electrons might be an issue for ITER and therefore it remains prudent to develop mitigation methods, which suppress runaway generation. (author)

49 CFR 236.338 - Mechanical locking required in accordance with locking sheet and dog chart.

Science.gov (United States)

2010-10-01

... locking sheet and dog chart. 236.338 Section 236.338 Transportation Other Regulations Relating to... in accordance with locking sheet and dog chart. Mechanical locking shall be in accordance with locking sheet and dog chart currently in effect. ...

Disruption studies in DIII-D

International Nuclear Information System (INIS)

Kellman, A.G.; Evans, T.E.; Cuthbertson, J.W.

1996-09-01

Characteristics of disruptions in the DIII-D tokamak including the current decay rate, halo current magnitude and toroidal asymmetry, and heat pulse to the divertor are described. Neon and argon pellet injection is shown to be an effective method for mitigating the halo currents and the heat pulse with a 50% reduction in both quantities achieved. The injection of these impurity pellets frequently gives rise to runaway electrons

Off-balance sheet exposures and banking crises in OECD countries

OpenAIRE

Barrell, R; Davis, P; Liadze, I; Karim, D

2012-01-01

Against the background of the acknowledged importance of off-balance-sheet exposures in the sub prime crisis, we seek to investigate whether this was a new phenomenon or common to earlier crises. Using a logit approach to predicting banking crises in 14 OECD countries we find a significant impact of a proxy for the ratio of banks‟ off-balance-sheet activity to total (off and on balance sheet) activity, as well as capital and liquidity ratios, the current account balance and GDP growth. These ...

RECONNECTION PROPERTIES OF LARGE-SCALE CURRENT SHEETS DURING CORONAL MASS EJECTION ERUPTIONS

Energy Technology Data Exchange (ETDEWEB)

Lynch, B. J.; Kazachenko, M. D. [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States); Edmondson, J. K. [Climate and Space Sciences and Engineering Department, University of Michigan, Ann Arbor, MI 48109 (United States); Guidoni, S. E. [Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2016-07-20

We present a detailed analysis of the properties of magnetic reconnection at large-scale current sheets (CSs) in a high cadence version of the Lynch and Edmondson 2.5D MHD simulation of sympathetic magnetic breakout eruptions from a pseudostreamer source region. We examine the resistive tearing and break-up of the three main CSs into chains of X- and O-type null points and follow the dynamics of magnetic island growth, their merging, transit, and ejection with the reconnection exhaust. For each CS, we quantify the evolution of the length-to-width aspect ratio (up to ∼100:1), Lundquist number (∼10{sup 3}), and reconnection rate (inflow-to-outflow ratios reaching ∼0.40). We examine the statistical and spectral properties of the fluctuations in the CSs resulting from the plasmoid instability, including the distribution of magnetic island area, mass, and flux content. We show that the temporal evolution of the spectral index of the reconnection-generated magnetic energy density fluctuations appear to reflect global properties of the CS evolution. Our results are in excellent agreement with recent, high-resolution reconnection-in-a-box simulations even though our CSs’ formation, growth, and dynamics are intrinsically coupled to the global evolution of sequential sympathetic coronal mass ejection eruptions.

Electromagnetic analysis of transient disruption forces on the ITER shield modules

International Nuclear Information System (INIS)

Kotulski, J.D.; Coats, R.S.; Pasik, M.F.

2007-01-01

There are potential abnormal operating environments where the disruption of the plasma currents inside a tokamak induce eddy currents in the shield modules. These currents interact with the large magnetic fields to produce forces in the modules which could potentially cause mechanical failure in the modules and vacuum vessel. For this reason the design and qualification of the ITER shield modules requires appropriate high-fidelity electromagnetic simulations that capture the physics of these situations. These simulations need to include an accurate representation of the disruption currents as well as an accurate electromagnetic model of the shield modules. The purpose of this presentation is to describe the electromagnetic analysis that has been completed using the OPERA-3D product to characterize the forces on the shield modules allocated to the US. We first describe the electromagnetic model of the system which consists of the disruption currents and the shield modules attached to the vacuum vessel. The disruption currents are represented in OPERA-3D using superposition of a large number of solenoids with independent time variation to account for the spatial and temporal variation of the plasma current and position. In addition, the simplified electromagnetic model of the shield modules will be described and discussed. Once the modeling has been described the simulation results are presented. The force computation are also presented and the results discussed. These forces are then used by a mechanical analysis program to compute stresses and torques on a module during the disruption of the plasma currents. (orig.)

Characterization of plasma current quench at JET

International Nuclear Information System (INIS)

Riccardo, V; Barabaschi, P; Sugihara, M

2005-01-01

Eddy currents generated during the fastest disruption current decays represent the most severe design condition for medium and small size in-vessel components of most tokamaks. Best-fit linear and instantaneous plasma current quench rates have been extracted for a set of recent JET disruptions. Contrary to expectations, the current quench rate spectrum of high and low thermal energy disruptions is not substantially different. For most of the disruptions with the highest instantaneous current quench rate an exponential fit of the early phase of the current decay provides a more accurate estimate of the maximum current decay velocity. However, this fit is only suitable to model the fastest events, for which the current quench is dominated by radiation losses rather than the plasma motion

Relative location of a powerful flare, the heliospheric current sheet and the Earth favourable for the onset of a strong geomagnetic storm

International Nuclear Information System (INIS)

Ivanov, K.G.; Kharshiladze, A.F.; Romashets, E.P.

1992-01-01

Problem of magnetic clouds propagation in regular-nonuniform internal heliosphere is discussed. High dependence of their retardation and consequently intensity of interplanetary and geomagnetic disturbances on mutual location of flares, heliospheric current sheet and the Earth is identified. Eight solar flares, four of which caused strong storms, and another four led to weak disturbances, all of them being in fair agreement with theoretical conclusions, are presented as examples

Inter-machine comparison of the termination phase and energy conversion in tokamak disruptions with runaway current plateau formation and implications for ITER

International Nuclear Information System (INIS)

Martín-Solís, J.R.; Loarte, A.; Hollmann, E.M.; Esposito, B.; Riccardo, V.

2014-01-01

The termination of the current and the loss of runaway electrons following runaway current plateau formation during disruptions have been investigated in the JET, DIII-D and FTU tokamaks. Substantial conversion of magnetic energy into runaway kinetic energy, up to ∼10 times the initial plateau runaway kinetic energy, has been inferred for the slowest current terminations. Both modelling and experiment suggest that, in present devices, the efficiency of conversion into runaway kinetic energy is determined to a great extent by the characteristic runaway loss time, τ diff , and the resistive time of the residual ohmic plasma after the disruption, τ res , increasing with the ratio τ diff /τ res . It is predicted that, in large future devices such as ITER, the generation of runaways by the avalanche mechanism will play an important role, particularly for slow runaway discharge terminations, increasing substantially the amount of energy deposited by the runaways onto the plasma-facing components by the conversion of magnetic energy of the runaway plasma into runaway kinetic energy. Estimates of the power fluxes on the beryllium plasma-facing components during runaway termination in ITER indicate that for runaway currents of up to 2 MA no melting of the components is expected. For larger runaway currents, minimization of the effects of runaway impact on the first wall requires a reduction in the kinetic energy of the runaway beam before termination and, in addition, high plasma density n e and low ohmic plasma resistance (long τ res ) to prevent large conversion of magnetic into runaway kinetic energy during slow current terminations. (paper)

Disruption generated secondary runaway electrons in present day tokamaks

International Nuclear Information System (INIS)

Pankratov, I.M.; Jaspers, R.

2000-01-01

An analysis of the runaway electron secondary generation during disruptions in present day tokamaks (JET, JT-60U, TEXTOR) was made. It was shown that even for tokamaks with the plasma current I approx 100 kA the secondary generation may dominate the runaway production during disruptions. In the same time in tokamaks with I approx 1 MA the runaway electron secondary generation during disruptions may be suppressed

W-Band Sheet Beam Klystron Design

International Nuclear Information System (INIS)

Scheitrum, G.; Caryotakis, G.; Burke, A.; Jensen, A.; Jongewaard, E.; Krasnykh, A.; Neubauer, M.; Phillips, R.; Rauenbuehler, K.

2011-01-01

Sheet beam devices provide important advantages for very high power, narrow bandwidth RF sources like accelerator klystrons (1). Reduced current density and increased surface area result in increased power capabi1ity, reduced magnetic fields for focusing and reduced cathode loading. These advantages are offset by increased complexity, beam formation and transport issues and potential for mode competition in the ovennoded cavities and drift tube. This paper will describe the design issues encountered in developing a 100 kW peak and 2 kW average power sheet beam k1ystron at W-band including beam formation, beam transport, circuit design, circuit fabrication and mode competition.

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.

Disruption of tephra fall deposits caused by lava flows during basaltic eruptions

Science.gov (United States)

Brown, R. J.; Thordarson, T.; Self, S.; Blake, S.

2015-10-01

Observations in the USA, Iceland and Tenerife, Canary Islands reveal how processes occurring during basaltic eruptions can result in complex physical and stratigraphic relationships between lava and proximal tephra fall deposits around vents. Observations illustrate how basaltic lavas can disrupt, dissect (spatially and temporally) and alter sheet-form fall deposits. Complexity arises through synchronous and alternating effusive and explosive activity that results in intercalated lavas and tephra deposits. Tephra deposits can become disrupted into mounds and ridges by lateral and vertical displacement caused by movement (including inflation) of underlying pāhoehoe lavas and clastogenic lavas. Mounds of tephra can be rafted away over distances of 100 s to 1,000 s m from proximal pyroclastic constructs on top of lava flows. Draping of irregular topography by fall deposits and subsequent partial burial of topographic depressions by later lavas can result in apparent complexity of tephra layers. These processes, deduced from field relationships, have resulted in considerable stratigraphic complexity in the studied proximal regions where fallout was synchronous or alternated with inflation of subjacent lava sheets. These mechanisms may lead to diachronous contact relationships between fall deposits and lava flows. Such complexities may remain cryptic due to textural and geochemical quasi-homogeneity within sequences of interbedded basaltic fall deposits and lavas. The net effect of these processes may be to reduce the usefulness of data collected from proximal fall deposits for reconstructing basaltic eruption dynamics.

Integrated disruption avoidance and mitigation in KSTAR

International Nuclear Information System (INIS)

Kim, Jayhyun; Woo, M.H.; Han, H.; In, Y.; Bak, J.G.; Eidietis, N.W.

2014-01-01

The final target of Korea Superconducting Tokamak Advanced Research (KSTAR) aims advanced tokamak operation at plasma current 2 MA and toroidal field 3.5 T. In order to safely achieve the target, disruption counter-measures are unavoidable when considering the disruption risks, inevitably accompanied with high performance discharges, such as electro-magnetic load on conducting structures, collisional damage by run-away electrons, and thermal load on plasma facing components (PFCs). In this reason, the establishment of integrated disruption mitigation system (DMS) has been started for routine mega-ampere class operations of KSTAR since 2013 campaign. The DMS mainly consists of the disruption prediction and its avoidance/mitigation in company with logical/technical integration of them. We present the details of KSTAR DMS and the related experimental results in this article. (author)

A two-fluid study of oblique tearing modes in a force-free current sheet

Energy Technology Data Exchange (ETDEWEB)

Akçay, Cihan, E-mail: akcay@lanl.gov; Daughton, William [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Lukin, Vyacheslav S. [National Science Foundation, Arlington, Virginia 22230 (United States); Liu, Yi-Hsin [NASA Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States)

2016-01-15

Kinetic simulations have demonstrated that three-dimensional reconnection in collisionless regimes proceeds through the formation and interaction of magnetic flux ropes, which are generated due to the growth of tearing instabilities at multiple resonance surfaces. Since kinetic simulations are intrinsically expensive, it is desirable to explore the feasibility of reduced two-fluid models to capture this complex evolution, particularly, in the strong guide field regime, where two-fluid models are better justified. With this goal in mind, this paper compares the evolution of the collisionless tearing instability in a force-free current sheet with a two-fluid model and fully kinetic simulations. Our results indicate that the most unstable modes are oblique for guide fields larger than the reconnecting field, in agreement with the kinetic results. The standard two-fluid tearing theory is extended to address the tearing instability at oblique angles. The resulting theory yields a flat oblique spectrum and underestimates the growth of oblique modes in a similar manner to kinetic theory relative to kinetic simulations.

VOYAGER OBSERVATIONS OF MAGNETIC SECTORS AND HELIOSPHERIC CURRENT SHEET CROSSINGS IN THE OUTER HELIOSPHERE

Energy Technology Data Exchange (ETDEWEB)

Richardson, J. D. [Kavli Center for Astrophysics and Space Science, Massachusetts Institute of Technology, Cambridge, 02139 (United States); Burlaga, L. F. [NASA Goddard Space Flight Center, Code 673, Greenbelt, MD 20771 (United States); Drake, J. F. [Department of Physics and Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742 (United States); Hill, M. E. [Applied Physics Laboratory, The Johns Hopkins University, Laurel, MD 20723 (United States); Opher, M., E-mail: jdr@space.mit.edu, E-mail: lburlagahsp@verizon.net, E-mail: drake@umd.edu, E-mail: Matthew.Hill@jhuapl.edu, E-mail: mopher@bu.edu [Astronomy Department, Boston University, 675 Commonwealth Avenue, Boston, MA 02215 (United States)

2016-11-10

Voyager 1 ( V1 ) has passed through the heliosheath and is in the local interstellar medium. Voyager 2 ( V2 ) has been in the heliosheath since 2007. The role of reconnection in the heliosheath is under debate; compression of the heliospheric current sheets (HCS) in the heliosheath could lead to rapid reconnection and a reconfiguration of the magnetic field topology. This paper compares the expected and actual amounts of time the Voyager spacecraft observe each magnetic sector and the number of HCS crossings. The predicted and observed values generally agree well. One exception is at Voyager 1 in 2008 and 2009, where the distribution of sectors is more equal than expected and the number of HCS crossings is small. Two other exceptions are at V1 in 2011–2012 and at V2 in 2012, when the spacecraft are in the opposite magnetic sector less than expected and see fewer HCS crossings than expected. These features are consistent with those predicted for reconnection, and consequently searches for other reconnection signatures should focus on these times.

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.

Contribution of ASDEX Upgrade to disruption studies for ITER

International Nuclear Information System (INIS)

Pautasso, G.; Reiter, B.; Giannone, L.; Gruber, O.; Herrmann, A.; Kardaun, O.; Maraschek, M.; Mlynek, A.; Schneider, W.; Zhang, Y.; Khayrutdinov, K.K.; Lukash, V.E.; Nakamura, Y.; Sias, G.; Sugihara, M.

2011-01-01

This paper describes the most recent contributions of ASDEX Upgrade to ITER in the field of disruption studies. (1) The ITER specifications for the halo current magnitude are based on data collected from several tokamaks and summarized in the plot of the toroidal peaking factor versus the maximum halo current fraction. Even if the maximum halo current in ASDEX Upgrade reaches 50% of the plasma current, the duration of this maximum lasts a fraction of a ms. (2) Long-lasting asymmetries of the halo current are rare and do not give rise to a large asymmetric component of the mechanical forces on the machine. Differently from JET, these asymmetries are neither locked nor exhibit a stationary harmonic structure. (3) Recent work on disruption prediction has concentrated on the search for a simple function of the most relevant plasma parameters, which is able to discriminate between the safe and pre-disruption phases of a discharge. For this purpose, the disruptions of the last four years have been classified into groups and then discriminant analysis is used to select the most significant variables and to derive the discriminant function. (4) The attainment of the critical density for the collisional suppression of the runaway electrons seems to be technically and physically possible on our medium size tokamak. The CO 2 interferometer and the AXUV diagnostic provide information on the highly 3D impurity transport process during the whole plasma quench.

Petrology of the gabbro and sheeted basaltic intrusives at North Cape, New Zealand

International Nuclear Information System (INIS)

Hopper, D.J.; Smith, I.E.M.

1996-01-01

The North Cape massif consists of a semi-conformable sequence of serpentinite, gabbro, sheeted sill and dike units, and pillow lavas. Although structurally disrupted, they can be interpreted in terms of an idealised ophiolite sequence and represent the most complete sequence in the Northland Ophiolite. Their age is considered to be Late Cretaceous-Paleocene on the basis of microfossils in associated sediments. Early Miocene K-Ar ages from igneous rocks are thought to reflect the time of emplacement as a thrust sheet of oceanic crust and upper mantle. The gabbros are divided into a lower unit characterised by well-developed cumulate layering and an upper unit which is massive; the sheeted sills and dikes are quartz-diorite and microgabbro interleaved with minor pillow lava. Two phases of alteration are observed, a pervasive low-grade greenschist metamorphism attributed to sea-water interaction after formation as oceanic crust, and an overprinting zeolitic alteration which is possibly post-emplacement. Their tholeiitic nature as well as overlapping geochemical compositions suggest that the gabbros and sheeted dikes and sills represent different components of a single magmatic system related by simple fractionation processes. Several lines of evidence suggest that the magmas that formed the North Cape gabbro and sheeted intrusives have subduction-related chemical characteristics. In the gabbro, calcic plagioclase (An 86-92 ) and depleted Zr and Y abundances, and in the sheeted intrusives depleted high field strength element abundances relative to typical MORB, is indicative of a subduction signature. The presence of subduction-related characteristics within the Northland Ophiolite suggests that it may have originated at a back-arc basin rather than a major ocean ridge spreading centre. (author). 64 refs., 12 figs., 7 tabs

Ice sheets on plastically-yielding beds

Science.gov (United States)

Hewitt, Ian

2016-11-01

Many fast flowing regions of ice sheets are underlain by a layer of water-saturated sediments, or till. The rheology of the till has been the subject of some controversy, with laboratory tests suggesting almost perfectly plastic behaviour (stress independent of strain rate), but many models adopting a pseudo-viscous description. In this work, we consider the behaviour of glaciers underlain by a plastic bed. The ice is treated as a viscous gravity current, on a bed that allows unconstrained slip above a critical yield stress. This simplified description allows rapid sliding, and aims to investigate 'worst-case' scenarios of possible ice-sheet disintegration. The plastic bed results in an approximate ice-sheet geometry that is primarily controlled by force balance, whilst ice velocity is determined from mass conservation (rather than the other way around, as standard models would hold). The stability of various states is considered, and particular attention is given to the pace at which transitions between unstable states can occur. Finally, we observe that the strength of basal tills depends strongly on pore pressure, and combine the model with a description of subglacial hydrology. Implications for the present-day ice sheets in Greenland and Antarctica will be discussed. Funding: ERC Marie Curie FP7 Career Integration Grant.

Viewgraphs presented at the ASDEX/DOE workshop on disruptions in divertor tokamaks

Energy Technology Data Exchange (ETDEWEB)

Granetz, R.; Gruber, O.; Zohm, H. [and others

1994-09-01

The emphasis of this year`s ASDEX/DOE workshop was on disruptions in diverted tokamaks. The meeting was held here at MIT on 14--15 March. It is particularly appropriate that MIT hosted the workshop this year, since Alcator C-Mod had just recently completed its very first run campaign, and disruptions are one of the key areas of research in our program. There were a total of 14 speakers, with participants from IPP (Garching), CRPP (Lausanne), Culham, General Atomics, PPPL, Sandia, ORNL, the ITER JCT, and MIT. The subjects addressed included statistical analysis of disruption probabilities in ASDEX, modelling of the vertical axisymmetric plasma motion in DIII-D, impact of disruptions on the design of the ITER divertors, modelling of runaway electrons, and TSC calculations of disruption-induced currents and forces in TPX, etc. One item of particular interest to us was the experimental correlation of halo current magnitude with plasma current on ASDEX-Upgrade. The data indicates at least a linear, and possibly even a quadractic dependence. This has important implications for Alcator C-Mod, since it would predict halo currents of order 1 MA or more at full performance. At the conclusion of the talks, an informal discussion of disruption databases was held, primarily for the purpose of helping us develop a useful one for C-Mod.

Viewgraphs presented at the ASDEX/DOE workshop on disruptions in divertor tokamaks

International Nuclear Information System (INIS)

Granetz, R.; Gruber, O.; Zohm, H.

1994-01-01

The emphasis of this year's ASDEX/DOE workshop was on disruptions in diverted tokamaks. The meeting was held here at MIT on 14--15 March. It is particularly appropriate that MIT hosted the workshop this year, since Alcator C-Mod had just recently completed its very first run campaign, and disruptions are one of the key areas of research in our program. There were a total of 14 speakers, with participants from IPP (Garching), CRPP (Lausanne), Culham, General Atomics, PPPL, Sandia, ORNL, the ITER JCT, and MIT. The subjects addressed included statistical analysis of disruption probabilities in ASDEX, modelling of the vertical axisymmetric plasma motion in DIII-D, impact of disruptions on the design of the ITER divertors, modelling of runaway electrons, and TSC calculations of disruption-induced currents and forces in TPX, etc. One item of particular interest to us was the experimental correlation of halo current magnitude with plasma current on ASDEX-Upgrade. The data indicates at least a linear, and possibly even a quadractic dependence. This has important implications for Alcator C-Mod, since it would predict halo currents of order 1 MA or more at full performance. At the conclusion of the talks, an informal discussion of disruption databases was held, primarily for the purpose of helping us develop a useful one for C-Mod

ASYMMETRIC SUNSPOT ACTIVITY AND THE SOUTHWARD DISPLACEMENT OF THE HELIOSPHERIC CURRENT SHEET

International Nuclear Information System (INIS)

Wang, Y.-M.; Robbrecht, E.

2011-01-01

Observations of the interplanetary magnetic field (IMF) have suggested a statistical tendency for the heliospheric current sheet (HCS) to be shifted a few degrees southward of the heliographic equator during the period 1965-2010, particularly in the years near sunspot minimum. Using potential-field source-surface extrapolations and photospheric flux-transport simulations, we demonstrate that this southward displacement follows from Joy's law and the observed hemispheric asymmetry in the sunspot numbers, with activity being stronger in the southern (northern) hemisphere during the declining (rising) phase of cycles 20-23. The hemispheric asymmetry gives rise to an axisymmetric quadrupole field, whose equatorial zone has the sign of the leading-polarity flux in the dominant hemisphere; during the last four cycles, the polarity of the IMF around the equator thus tended to match that of the north polar field both before and after polar field reversal. However, large fluctuations are introduced by the nonaxisymmetric field components, which depend on the longitudinal distribution of sunspot activity in either hemisphere. Consistent with this model, the HCS showed an average northward displacement during cycle 19, when the 'usual' alternation was reversed and the northern hemisphere became far more active than the southern hemisphere during the declining phase of the cycle. We propose a new method for determining the north-south displacement of the HCS from coronal streamer observations.

Understanding Recent Mass Balance Changes of the Greenland Ice Sheet

Science.gov (United States)

vanderVeen, Cornelius

2003-01-01

The ultimate goal of this project is to better understand the current transfer of mass between the Greenland Ice Sheet, the world's oceans and the atmosphere, and to identify processes controlling the rate of this transfer, to be able to predict with greater confidence future contributions to global sea level rise. During the first year of this project, we focused on establishing longer-term records of change of selected outlet glaciers, reevaluation of mass input to the ice sheet and analysis of climate records derived from ice cores, and modeling meltwater production and runoff from the margins of the ice sheet.

Heat Exchanger Tube to Tube Sheet Joints Corrosion Behavior

Directory of Open Access Journals (Sweden)

M. Iancu

2013-03-01

Full Text Available Paper presents the studies made by the authors above the tube to tube sheet fittings of heat exchanger with fixed covers from hydrofining oil reforming unit. Tube fittings are critical zones for heat exchangers failures. On a device made from material tube and tube sheet at real joints dimensions were establish axial compression force and traction force at which tube is extracted from expanded joint. Were used two shapes joints with two types of fittings surfaces, one with smooth hole of tube sheet and other in which on boring surface we made a groove. From extracted expanded tube zones were made samples for corrosion tests in order to establish the corrosion rate, corrosion potential and corrosion current in working mediums such as hydrofining oil and industrial water at different temperatures. The corrosion rate values and the temperature influence are important to evaluate joints durability and also the results obtained shows that the boring tube sheet shape with a groove on hole tube shape presents a better corrosion behavior then the shape with smooth hole tube sheet.

The Rapid Ice Sheet Change Observatory (RISCO)

Science.gov (United States)

Morin, P.; Howat, I. M.; Ahn, Y.; Porter, C.; McFadden, E. M.

2010-12-01

The recent expansion of observational capacity from space has revealed dramatic, rapid changes in the Earth’s ice cover. These discoveries have fundamentally altered how scientists view ice-sheet change. Instead of just slow changes in snow accumulation and melting over centuries or millennia, important changes can occur in sudden events lasting only months, weeks, or even a single day. Our understanding of these short time- and space-scale processes, which hold important implications for future global sea level rise, has been impeded by the low temporal and spatial resolution, delayed sensor tasking, incomplete coverage, inaccessibility and/or high cost of data available to investigators. New cross-agency partnerships and data access policies provide the opportunity to dramatically improve the resolution of ice sheet observations by an order of magnitude, from timescales of months and distances of 10’s of meters, to days and meters or less. Advances in image processing technology also enable application of currently under-utilized datasets. The infrastructure for systematically gathering, processing, analyzing and distributing these data does not currently exist. Here we present the development of a multi-institutional, multi-platform observatory for rapid ice change with the ultimate objective of helping to elucidate the relevant timescales and processes of ice sheet dynamics and response to climate change. The Rapid Ice Sheet Observatory (RISCO) gathers observations of short time- and space-scale Cryosphere events and makes them easily accessible to investigators, media and general public. As opposed to existing data centers, which are structured to archive and distribute diverse types of raw data to end users with the specialized software and skills to analyze them, RISCO focuses on three types of geo-referenced raster (image) data products in a format immediately viewable with commonly available software. These three products are (1) sequences of images

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.

Disruption mitigation experiment with massive gas injection of HT-7

International Nuclear Information System (INIS)

Zhuang Huidong; Zhang Xiaodong

2013-01-01

Massive gas injection (MGI) is a promising method on disruption mitigation. The working principle of the fast valve for disruption mitigation was introduced. The disruption mitigation experiments by MGI on HT-7 were described. The experiment shows that the impurities radiation is improved by injecting appropriate amount of gas, and the current quench rate is slow down, so the electromagnetic load on the device is mitigated. The experiments show that the fast valve can completely satisfy the requirement of disruption mitigation on HT-7. (authors)

Periodic disruptions in the MT-1 tokamak

International Nuclear Information System (INIS)

Zoletnik, S.

1988-11-01

Disruptive instabilities are common phenomena in toroidal devices, especially in tokamaks. Three types can be distinguished: internal, minor and major disruptions. Periodic minor disruptions in the MT-1 tokamak were measured systematically with values of the limiter safety factor between 4 and 10. The density limit as a function of plasma current and horizontal displacement was investigated. Precursor oscillations always appear before the instability with increasing amplitude but can be observed at the density limit with quasi-stationary amplitude. Phase correlation between precursor oscillations were measured with Mirnov coils and x-ray detectors, and they show good agreement with a simple magnetic island model. (R.P.) 11 refs.; 6 figs

Fatigue analysis of a PWR steam generator tube sheet

International Nuclear Information System (INIS)

Billon, F.; Buchalet, C.; Poudroux, G.

1985-01-01

The fatigue analysis of a PWR steam generator (S.G) tube sheet is threefold. First, the flow, pressure and temperature variations during the design transients are defined for both the primary fluid and the normal and auxiliary feedwater. Second, the flow, velocities, pressure and temperature variations of the secondary fluid at the bottom of the downcomer and above the tube sheet are determined for the transients considered. Finally, the corresponding temperatures and stresses in the tube sheet are calculated and the usage factors determined at various locations in the tube sheet. The currently available standard design transients for the primary fluid and the feedwater are too conservative to be utilized as such in the fatigue analysis of the S.G. tube sheets. Thus, a detailed examination and reappraisal of each operating transient was performed. The revised design conditions are used as inputs to the calculation model TEMPTRON. TEMPTRON determines the mixing conditions between the feedwater and the recirculation fluid from the S.G. feedwater nozzles to the center of the tube sheet via the downcomer. The fluid parameters, flow rate and velocity, temperature and pressure variations, as a function of the time during the transients are obtained. Finally, the usage factors at various locations on the tube sheet are derived using the standard ASME section III method

Characterization of axisymmetric disruption dynamics toward VDE avoidance in tokamaks

International Nuclear Information System (INIS)

Nakamura, Y.; Yoshino, R.; Granetz, R.S.; Pautasso, G.; Gruber, O.; Jardin, S.C.

2003-01-01

Experiments and axisymmetric MHD simulations on tokamak disruptions have explicated the underlying mechanisms of Vertical Displacement Events (VDEs) and a diversity of disruption dynamics. First, the neutral point, which is known as an advantageous vertical plasma position to avoiding VDEs during the plasma current quench, is shown to be fairly insensitive to plasma shape and current profile parameters. Secondly, a rapid flattening of the plasma current profile frequently seen at thermal quench is newly clarified to play a substantial role in dragging a single null-diverted plasma vertically towards the divertor. As a consequence, the occurrence of downward-going VDEs predominates over the upward-going ones in bottom diverted discharges. This dragging effect is absent in up-down symmetric limiter discharges. These simulation results are consistent with experiments. Together with the attractive force that arises from passive shell currents and essentially vanishes at the neutral point, the dragging effect explains many details of the VDE dynamics over the whole period of the disruptive termination. (author)

Spinomotive force induced by a transverse displacement current in a thin metal or doped-semiconductor sheet: Classical and quantum views.

Science.gov (United States)

Hu, Chia-Ren

2004-03-01

We present classical macroscopic, microscopic, and quantum mechanical arguments to show that in a metallic or electron/hole-doped semiconducting sheet thinner than the screening length, a displacement current applied normal to it can induce a spinomotive force along it. The magnitude is weak but clearly detectable. The classical arguments are purely electromagnetic. The quantum argument, based on the Dirac equation, shows that the predicted effect originates from the spin-orbit interaction, but not of the usual kind. That is, it relies on an external electric field, whereas the usual S-O interaction involves the electric field generated by the ions. Because the Dirac equation incorporatesThomas precession, which is due to relativistic kinematics, the quantum prediction is a factor of two smaller than the classical prediction. Replacing the displacement current by a charge current, and one obtains a new source for the spin-Hall effect. Classical macroscopic argument also predicts its existence, but the other two views are controversial.

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.

Neural-net disruption predictor in JT-60U

International Nuclear Information System (INIS)

Yoshino, R.

2003-01-01

The prediction of major disruptions caused by the density limit, the plasma current ramp-down with high internal inductance l i , the low density locked mode and the β-limit has been investigated in JT-60U. The concept of 'stability level', newly proposed in this paper to predict the occurrence of a major disruption, is calculated from nine input parameters every 2 ms by the neural network and the start of a major disruption is predicted when the stability level decreases to a certain level, the 'alarm level'. The neural network is trained in two steps. It is first trained with 12 disruptive and six non-disruptive shots (total of 8011 data points). Second, the target output data for 12 disruptive shots are modified and the network is trained again with additional data points generated by the operator. The 'neural-net disruption predictor' obtained has been tested for 300 disruptive shots (128 945 data points) and 1008 non-disruptive shots (982 800 data points) selected from nine years of operation (1991-1999) of JT-60U. Major disruptions except for those caused by the -limit have been predicted with a prediction success rate of 97-98% at 10 ms prior to the disruption and higher than 90% at 30 ms prior to the disruption while the false alarm rate is 2.1% for non-disruptive shots. This prediction performance has been confirmed for 120 disruptive shots (56 163 data points), caused by the density limit, as well as 1032 non-disruptive shots (1004 611 data points) in the last four years of operation (1999-2002) of JT-60U. A careful selection of the input parameters supplied to the network and the newly developed two-step training of the network have reduced the false alarm rate resulting in a considerable improvement of the prediction success rate. (author)

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.

Magnetic reconnection through the current sheets as the universal process for plasma dynamics in nonuniform magnetic fields

International Nuclear Information System (INIS)

Frank, A.G.; Bogdanov, S.Yu.; Burilina, V.B.; Kyrie, N.P.

1997-01-01

Laboratory experiments are reported, in which we studied the possibilities of the formation of current sheets (CS) in different magnetic configurations, as well as the magnetic reconnection phenomena. In 2D magnetic fields with null-lines the CS formation was shown to be a typical process in both linear and nonlinear regimes. The problem of CS formation is of a fundamental importance in the general case of 3D magnetic configurations. We have revealed experimentally, that the formation of CS occurs in the various 3D configurations, both containing magnetic null-points and without them. At the same time, the CS parameters essentially depend on the local characteristics of the configuration. We may conclude therefore, that the self-organization of CS represents the universal process for the plasma dynamics in the nonuniform magnetic fields. (author)

Numerical Study of the Cascading Energy Conversion of the Reconnecting Current Sheet in Solar Eruptions

Science.gov (United States)

Ye, J.; Lin, J.; Raymond, J. C.; Shen, C.

2017-12-01

In this paper, we present a resistive magnetohydrodynamical study (2D) of the CME eruption based on the Lin & Forbes model (2000) regarding the cascading reconnection by a high-order Godunov scheme code, to better understand the physical mechanisms responsible for the internal structure of the current sheet (CS) and the high reconnection rate. The main improvements of this work include: 1) large enough spatial scale consistent with the stereo LASCO data that yields an observable current sheet 2) A realistic plasma environment (S&G, 1999) adopted rather than an isothermal atmosphere and higher resolution inside CS 3) The upper boundary condition set to be open. The simulation shows a typical acceleration below 2 R⊙, then its speed slightly fluctuated, and the flux rope velocity is estimated to be 100 km/s-250 km/s for a slow CME. The reconnection rates are around 0.02 estimated from inflow and outflow velocities. The dynamic features show a great consistence with the LASCO observations. Looking into the fine structure of CS, magnetic reconnection initializes with a Sweet-Parker stage, and undergoes the time-dependent Petschek/fractural patterns. While the CME continues climbing up, the outflow region becomes turbulent which enhances the reconnection rates furthermore. The local reconnection rates present a simple linear dependence with the length-width ratio of multiple small-scale CSs. The principal X-point is close to the Sun's surface during the entire eruption, causing the energy partition to be unequal. Energy conversion in the vicinity of the principal X-point has also been addressed by simply employing energy equations. And we demonstrate that the dominant energy transfer consists of a conversion of the incoming Poynting flux to enthalpy flux in the sunward direction and bulk kinetic energy in the CME direction. The spectrum of magnetic energy doesn't follow a simple power law after secondary islands appear, and the spectrum index varies from 1.5 to 2

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

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.

Reproductive endocrine-disrupting effects of triclosan: Population exposure, present evidence and potential mechanisms

International Nuclear Information System (INIS)

Wang, Cai-Feng; Tian, Ying

2015-01-01

Triclosan has been used as a broad-spectrum antibacterial agent for over 40 years worldwide. Increasing reports indicate frequent detection and broad exposure to triclosan in the natural environment and the human body. Current laboratory studies in various species provide strong evidence for its disrupting effects on the endocrine system, especially reproductive hormones. Multiple modes of action have been suggested, including disrupting hormone metabolism, displacing hormones from hormone receptors and disrupting steroidogenic enzyme activity. Although epidemiological studies on its effects in humans are mostly negative but conflicting, which is typical of much of the early evidence on the toxicity of EDCs, overall, the evidence suggests that triclosan is an EDC. This article reviews human exposure to triclosan, describes the current evidence regarding its reproductive endocrine-disrupting effects, and discusses potential mechanisms to provide insights for further study on its endocrine-disrupting effects in humans. - Highlights: • Triclosan is widely detected in human urine, blood and breast milk. • Laboratory studies suggest reproductive endocrine-disrupting effects of triclosan. • Laboratory studies suggest estrogenic properties of triclosan. • There are three potential mechanisms regarding the estrogenic effect of triclosan. • Prospective epidemiological studies on vulnerable populations are needed. - This review summarizes current evidence on human exposure to triclosan, and its reproductive endocrine-disrupting effects and potential mechanisms.

The influence of plasma motion on disruption generated runaway electrons

International Nuclear Information System (INIS)

Russo, A.J.

1991-01-01

One of the possible consequences of disruptions is the generation of runaway electrons which can impact plasma facing components and cause damage due to high local energy deposition. This problem becomes more serious as the machine size and plasma current increases. Since large size and high currents are characteristics of proposed future machines, control of runaway generation is an important design consideration. A lumped circuit model for disruption runaway electron generation indicates that control circuitry on strongly influence runaway behavior. A comparison of disruption data from several shots on JET and D3-D with model results, demonstrate the effects of plasma motion on runaway number density and energy. 6 refs., 12 figs

Space Charge Effect in the Sheet and Solid Electron Beam

Science.gov (United States)

Song, Ho Young; Kim, Hyoung Suk; Ahn, Saeyoung

1998-11-01

We analyze the space charge effect of two different types of electron beam ; sheet and solid electron beam. Electron gun simulations are carried out using shadow and control grids for high and low perveance. Rectangular and cylindrical geometries are used for sheet and solid electron beam in planar and disk type cathode. The E-gun code is used to study the limiting current and space charge loading in each geometries.

Study of runaway electron generation during major disruptions in JET

International Nuclear Information System (INIS)

Plyusnin, V.V.; Riccardo, V.; Jaspers, R.; Alper, B.; Kiptily, V.G.; Mlynar, J.; Popovichev, S.; Luna, E. de La; Andersson, F.

2006-01-01

Extensive analysis of disruptions in JET has helped advance the understanding of trends of disruption-generated runaway electrons. Tomographic reconstruction of the soft x-ray emission has made possible a detailed observation of the magnetic flux geometry evolution during disruptions. With the aid of soft and hard x-ray diagnostics runaway electrons have been detected at the very beginning of disruptions. A study of runaway electron parameters has shown that an approximate upper bound for the conversion efficiency of pre-disruptive plasma currents into runaways is about 60% over a wide range of plasma currents in JET. Runaway generation has been simulated with a test particle model in order to verify the results of experimental data analysis and to obtain the background for extrapolation of the existing results onto larger devices such as ITER. It was found that close agreement between the modelling results and experimental data could be achieved if in the calculations the post-disruption plasma electron temperature was assumed equal to 10 eV and if the plasma column geometry evolution is taken into account in calculations. The experimental trends and numerical simulations show that runaway electrons are a critical issue for ITER and, therefore, the development of mitigation methods, which suppress runaway generation, is an essential task

Disruption avoidance by means of electron cyclotron waves

International Nuclear Information System (INIS)

Esposito, B; Granucci, G; Nowak, S; Lazzaro, E; Maraschek, M; Giannone, L; Gude, A; Igochine, V; McDermott, R; Poli, E; Reich, M; Sommer, F; Stober, J; Suttrop, W; Treutterer, W; Zohm, H

2011-01-01

Disruptions are very challenging to ITER operation as they may cause damage to plasma facing components due to direct plasma heating, forces on structural components due to halo and eddy currents and the production of runaway electrons. Electron cyclotron (EC) waves have been demonstrated as a tool for disruption avoidance by a large set of recent experiments performed in ASDEX Upgrade and FTU using various disruption types, plasma operating scenarios and power deposition locations. The technique is based on the stabilization of magnetohydrodynamic (MHD) modes (mainly m/n = 2/1) through the localized injection of EC power on the resonant surface. This paper presents new results obtained in ASDEX Upgrade regarding stable operation above the Greenwald density achieved after avoidance of density limit disruptions by means of ECRH and suitable density feedback control (L-mode ohmic plasmas, I p = 0.6 MA, B t = 2.5 T) and NTM-driven disruptions at high-β limit delayed/avoided by means of both co-current drive (co-ECCD) and pure heating (ECRH) with power ≤1.7 MW (H-mode NBI-heated plasmas, P NBI ∼ 7.5 MW, I p = 1 MA, B t = 2.1 T, q 95 ∼ 3.6). The localized perpendicular injection of ECRH/ECCD onto a resonant surface leads to the delay and/or complete avoidance of disruptions. The experiments indicate the existence of a power threshold for mode stabilization to occur. An analysis of the MHD mode evolution using the generalized Rutherford equation coupled to the frequency and phase evolution equations shows that control of the modes is due to EC heating close to the resonant surface. The ECRH contribution (Δ' H term) is larger than the co-ECCD one in the initial and more important phase when the discharge is 'saved'. Future research and developments of the disruption avoidance technique are also discussed.

Density turbulence and disruption phenomena in TEXTOR

International Nuclear Information System (INIS)

Waidmann, G.; Kuang, G.; Jadoul, M.

1992-01-01

Disruptive processes are observed in tokamak plasmas not only at the operating limits (density limit or q-limit) but can be found under a variety of experimental conditions. Large forces are exerted then on vessel components and support structures. The sudden release of stored plasma energy presents a serious erosion problem for the first wall already in the next generation of large tokamak machines. Strong energy losses from the plasma and an influx of impurities are already present in minor plasma disruptions which do not immediately lead to a plasma current termination. The rapid loss of energy confinement was investigated within the framework of a systematic study on plasma disruption phenomena in TEXTOR. (author) 4 refs., 4 figs

Ice-sheet mass balance and climate change.

Science.gov (United States)

Hanna, Edward; Navarro, Francisco J; Pattyn, Frank; Domingues, Catia M; Fettweis, Xavier; Ivins, Erik R; Nicholls, Robert J; Ritz, Catherine; Smith, Ben; Tulaczyk, Slawek; Whitehouse, Pippa L; Zwally, H Jay

2013-06-06

Since the 2007 Intergovernmental Panel on Climate Change Fourth Assessment Report, new observations of ice-sheet mass balance and improved computer simulations of ice-sheet response to continuing climate change have been published. Whereas Greenland is losing ice mass at an increasing pace, current Antarctic ice loss is likely to be less than some recently published estimates. It remains unclear whether East Antarctica has been gaining or losing ice mass over the past 20 years, and uncertainties in ice-mass change for West Antarctica and the Antarctic Peninsula remain large. We discuss the past six years of progress and examine the key problems that remain.

Total magnetic reconnection during a tokamak major disruption

International Nuclear Information System (INIS)

Goetz, J.A.; Dexter, R.N.; Prager, S.C.

1990-07-01

The safety factor within a tokamak plasma has been measured during a major disruption. During the disruption, the central safety factor jumps from below one to above one, while the total current is unchanged. This implies that total reconnection has occurred. This observation is in contract to the absence of total reconnection observed during a sawtooth oscillation in the same device. 11 refs., 6 figs

Large-scale Modeling of the Greenland Ice Sheet on Long Timescales

DEFF Research Database (Denmark)

Solgaard, Anne Munck

is investigated as well as its early history. The studies are performed using an ice-sheet model in combination with relevant forcing from observed and modeled climate. Changes in ice-sheet geometry influences atmospheric flow (and vice versa) hereby changing the forcing patterns. Changes in the overall climate...... and climate model is included shows, however, that a Föhn effect is activated and hereby increasing temperatures inland and inhibiting further ice-sheet expansion into the interior. This indicates that colder than present temperatures are needed in order for the ice sheet to regrow to the current geometry....... Accordingto this hypothesis, two stages of uplift since the Late Miocene lead to the present-day topography. The results of the ice-sheet simulations show geometries in line with geologicobservations through the period, and it is found that the uplift events enhance the effect of the climatic deterioration...

Mechanical algal disruption for efficient biodiesel extraction

Science.gov (United States)

Krehbiel, Joel David

Biodiesel from algae provides several benefits over current biodiesel feedstocks, but the energy requirements of processing algae into a useable fuel are currently so high as to be prohibitive. One route to improving this is via disruption of the cells prior to lipid extraction, which can significantly increase energy recovery. Unfortunately, several obvious disruption techniques require more energy than can be gained. This dissertation examines the use of microbubbles to improve mechanical disruption of algal cells using experimental, theoretical, and computational methods. New laboratory experiments show that effective ultrasonic disruption of algae is achieved by adding microbubbles to an algal solution. The configuration studied flows the solution through a tube and insonifies a small section with a high-pressure ultrasound wave. Previous biomedical research has shown effective cell membrane damage on animal cells with similar methods, but the present research is the first to extend such study to algal cells. Results indicate that disruption increases with peak negative pressure between 1.90 and 3.07 MPa and with microbubble concentration up to 12.5 x 107 bubbles/ml. Energy estimates of this process suggest that it requires only one-fourth the currently most-efficient laboratory-scale disruption process. Estimates of the radius near each bubble that causes disruption (i.e. the disruption radius) suggest that it increases with peak negative pressure and is near 9--20 microm for all cases tested. It is anticipated that these procedures can be designed for better efficiency and efficacy, which will be facilitated by identifying the root mechanisms of the bubble-induced disruption. We therefore examine whether bubble expansion alone creates sufficient cell deformation for cell rupture. The spherically-symmetric Marmottant model for bubble dynamics allows estimation of the flow regime under experimental conditions. Bubble expansion is modeled as a point source of

An ice sheet model validation framework for the Greenland ice sheet

Science.gov (United States)

Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.; Howat, Ian M.; Neumann, Thomas; Saba, Jack; Tezaur, Irina; Guerber, Jeffrey; Chambers, Don P.; Evans, Katherine J.; Kennedy, Joseph H.; Lenaerts, Jan; Lipscomb, William H.; Perego, Mauro; Salinger, Andrew G.; Tuminaro, Raymond S.; van den Broeke, Michiel R.; Nowicki, Sophie M. J.

2017-01-01

We propose a new ice sheet model validation framework - the Cryospheric Model Comparison Tool (CmCt) - that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013, using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quantitative metrics for use in evaluating the different model simulations against the observations. We find that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin-scale and whole-ice-sheet-scale metrics, we find that simulations using both idealized conceptual models and dynamic, numerical models provide an equally reasonable representation of the ice sheet surface (mean elevation differences of framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate a predictive skill with respect to observed dynamic changes that have occurred on Greenland over the past few decades. An extensible design will allow for continued use of the CmCt as future altimetry, gravimetry, and other remotely sensed data become available for use in ice sheet model validation.

Slow convection of a magnetized plasma and the earth plasma sheet

International Nuclear Information System (INIS)

Hruska, A.

1980-01-01

Stationary convection of an isotropic, infinitely conducting plasma in a magnetic field with non-trivial geometry is discussed under the assumption that the inertial term in the equation of motion may be ignored. The energy gained or lost by a volume element of plasma per unit time does not vary along the field-lines. Simple relations between the components of the current density, depending on the field-line geometry, exist. Similar relations hold for the components of the plasma velocity. The theoretical analysis is applied to the geomagnetically-quiet plasma sheet and a qualitative physical picture of the sheet is suggested. The observed structure of the sheet is compatible with Axford-Hines type of convection perhaps combined with a low-speed flow from a distant neutral point. The magnetic-field-aligned currents are driven by the deformations of the closed field-lines which are enforced by the solar wind. (orig.)

Fuel retention and recovery in natural and MGI disruptions on KSTAR

International Nuclear Information System (INIS)

Yu, Y.W.; Hong, S.H.; Yoon, S.W.; Kim, K.P.; Kim, W.C.; Seo, D.C.

2013-01-01

Fuel retention and recovery are studied during natural and Massive Gas Injection (MGI) induced disruptions in KSTAR with full graphite wall. The amount of released particles in natural disruptions in 15 s after the discharge is ∼5–10 times higher than that of non-disruption shots, but the difference is only ∼ 2 MGI induced disruptions depends on magnetic field (B t ) and MGI amount. The MGI disruption under a low B t and a medium MGI amount shows shorter thermal quench (TQ) and current quench (CQ), thereby higher fuel recovery. High B t plasma requires higher MGI amount for both disruption mitigation and fuel recovery. A high recovery of 4.2 × 10 22 D (∼0.78 monolayers) is obtained by MGI disruption in KSTAR 2011

Suppression of Runaway Electrons by Resonant Magnetic Perturbations in TEXTOR Disruptions

International Nuclear Information System (INIS)

Lehnen, M.; Bozhenkov, S. A.; Abdullaev, S. S.; TEXTOR Team,; Jakubowski, M. W.

2008-01-01

The generation of runaway electrons in the international fusion experiment ITER disruptions can lead to severe damage at plasma facing components. Massive gas injection might inhibit the generation process, but the amount of gas needed can affect, e.g., vacuum systems. Alternatively, magnetic perturbations can suppress runaway generation by increasing the loss rate. In TEXTOR disruptions runaway losses were enhanced by the application of resonant magnetic perturbations with toroidal mode number n=1 and n=2. The disruptions are initiated by fast injection of about 3x10 21 argon atoms, which leads to a reliable generation of runaway electrons. At sufficiently high perturbation levels a reduction of the runaway current, a shortening of the current plateau, and the suppression of high energetic runaways are observed. These findings indicate the suppression of the runaway avalanche during disruptions

Metallurgical Effects of Shunting Current on Resistance Spot-Welded Joints of AA2219 Sheets

Science.gov (United States)

Jafari Vardanjani, M.; Araee, A.; Senkara, J.; Jakubowski, J.; Godek, J.

2016-08-01

Shunting effect is the loss of electrical current via the secondary circuit provided due to the existence of previous nugget in a series of welding spots. This phenomenon influences on metallurgical aspects of resistance spot-welded (RSW) joints in terms of quality and performance. In this paper RSW joints of AA2219 sheets with 1 mm thickness are investigated metallurgically for shunted and single spots. An electro-thermal finite element analysis is performed on the RSW process of shunted spot and temperature distribution and variation are obtained. These predictions are then compared with experimental micrographs. Three values of 5 mm, 20 mm, and infinite (i.e., single spot) are assumed for welding distance. Numerical and experimental results are matching each other in terms of nugget and HAZ geometry as increasing distance raised nugget size and symmetry of HAZ. In addition, important effect of shunting current on nugget thickness, microstructure, and Copper segregation on HAZ grain boundaries were discovered. A quantitative analysis is also performed about the influence of welding distance on important properties including ratio of nugget thickness and diameter ( r t), ratio of HAZ area on shunted and free side of nugget ( r HA), and ratio of equivalent segregated and total amount of Copper, measured in sample ( r Cu) on HAZ. Increasing distance from 5 mm to infinite, indicated a gain of 111.04, -45.55, and -75.15% in r t, r HA, and r Cu, respectively, while obtained ratios for 20 mm welding distance was suitable compared to single spot.

Digital Transformation and Disruption of the Health Care Sector: Internet-Based Observational Study.

Science.gov (United States)

Herrmann, Maximilian; Boehme, Philip; Mondritzki, Thomas; Ehlers, Jan P; Kavadias, Stylianos; Truebel, Hubert

2018-03-27

Digital innovation, introduced across many industries, is a strong force of transformation. Some industries have seen faster transformation, whereas the health care sector only recently came into focus. A context where digital corporations move into health care, payers strive to keep rising costs at bay, and longer-living patients desire continuously improved quality of care points to a digital and value-based transformation with drastic implications for the health care sector. We tried to operationalize the discussion within the health care sector around digital and disruptive innovation to identify what type of technological enablers, business models, and value networks seem to be emerging from different groups of innovators with respect to their digital transformational efforts. From the Forbes 2000 and CBinsights databases, we identified 100 leading technology, life science, and start-up companies active in the health care sector. Further analysis identified projects from these companies within a digital context that were subsequently evaluated using the following criteria: delivery of patient value, presence of a comprehensive and distinctive underlying business model, solutions provided, and customer needs addressed. Our methodological approach recorded more than 400 projects and collaborations. We identified patterns that show established corporations rely more on incremental innovation that supports their current business models, while start-ups engage their flexibility to explore new market segments with notable transformations of established business models. Thereby, start-ups offer higher promises of disruptive innovation. Additionally, start-ups offer more diversified value propositions addressing broader areas of the health care sector. Digital transformation is an opportunity to accelerate health care performance by lowering cost and improving quality of care. At an economic scale, business models can be strengthened and disruptive innovation models

Characterization of axisymmetric disruption dynamics toward VDE avoidance in tokamaks

International Nuclear Information System (INIS)

Nakamura, Y.

2002-01-01

Disruption experiments on Alcator C-Mod and ASDEX-Upgrade tokamaks and axisymmetric MHD simulations using the TSC have explicated the underlying mechanisms of Vertical Displacement Events (VDEs) and a diversity of disruption dynamics. First, the neutral point, which is known as an initial vertical plasma position advantageous to VDE avoidance, is shown to be fairly insensitive to plasma shape and current profile parameters, while the VDE rate significantly depends on those parameters. Secondly, it is clarified that a rapid flattening of the plasma current profile frequently seen at the thermal quench drags a single null-diverted, up-down asymmetric plasma vertically toward divertor, whereas the dragging effect is absent in up-down symmetric limiter discharges. As a consequence, the occurrence of downward-going VDEs predominates over the upward-going ones in bottom-diverted discharges, being consistent with experiments in ASDEX-Upgrade. Together with the attractive force that arises from passive shell currents induced by the current quench and vanishes at the neutral point, the dragging effect explains many details of the VDE dynamics over the whole period of disruptive termination. (author)

Investigating Disruption

DEFF Research Database (Denmark)

Lundgaard, Stine Schmieg; Rosenstand, Claus Andreas Foss

This book shares knowledge collected from 2015 and onward within the Consortium for Digital Disruption anchored at Aalborg University (www.dd.aau.dk). Evidenced by this publication, the field of disruptive innovation research has gone through several stages of operationalizing the theory. In recent...... years, researchers are increasingly looking back towards the origins of the theory in attempts to cure it from its most obvious flaws. This is especially true for the use of the theory in making predictions about future disruptions. In order to continue to develop a valuable theory of disruption, we...... find it useful to first review what the theory of disruptive innovation initially was, how it has developed, and where we are now. A cross section of disruptive innovation literature has been reviewed in order to form a general foundation from which we might better understand the changing world...

Energy flow during disruptions in JET

International Nuclear Information System (INIS)

Paley, J.I.; Andrew, P.; Cowley, S.C.; Fundamenski, W.; Huber, A.

2005-01-01

Disruptions place severe limitations on the materials selected for plasma facing components in fusion devices. In a disruption, the plasma stored thermal and magnetic energy is dissipated leading to predicted power loadings in the current quench of up to 10 MW m -2 in JET. In the thermal quench very high power loads of up to 10 G Wm -2 would be expected if all the power flowed to the steady state strike points, however this is not observed. In this paper the energy balance associated with both events is investigated. The magnetic energy is found to balance well with radiated energy. Circumstantial evidence for limiter interaction during the thermal quench of plasmas in divertor configuration is presented and a possible mechanism for limiter interaction in disruptions resulting from the collapse of an internal transport barrier is discussed

Pulsar glitch dynamics

Science.gov (United States)

Morley, P. D.

2018-01-01

We discuss pulsar glitch dynamics from three different viewpoints: statistical description, neutron star equation of state description and finally an electromagnetic field description. For the latter, the pulsar glitch recovery times are the dissipation time constants of sheet surface currents created in response to the glitch-induced crustal magnetic field disruption. We mathematically derive these glitch time constants (Ohmic time constant and Hall sheet current time constant) from a perturbation analysis of the electromagnetic induction equation. Different crustal channels will carry the sheet surface current and their different electron densities determine the time constants.

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

Chlamydia - CDC Fact Sheet

Science.gov (United States)

... Archive STDs Home Page Bacterial Vaginosis (BV) Chlamydia Gonorrhea Genital Herpes Hepatitis HIV/AIDS & STDs Human Papillomavirus ( ... sheet Pelvic Inflammatory Disease (PID) – CDC fact sheet Gonorrhea – CDC fact sheet STDs Home Page Bacterial Vaginosis ( ...

Understanding Greenland ice sheet hydrology using an integrated multi-scale approach

International Nuclear Information System (INIS)

Rennermalm, A K; Moustafa, S E; Mioduszewski, J; Robinson, D A; Chu, V W; Smith, L C; Forster, R R; Hagedorn, B; Harper, J T; Mote, T L; Shuman, C A; Tedesco, M

2013-01-01

Improved understanding of Greenland ice sheet hydrology is critically important for assessing its impact on current and future ice sheet dynamics and global sea level rise. This has motivated the collection and integration of in situ observations, model development, and remote sensing efforts to quantify meltwater production, as well as its phase changes, transport, and export. Particularly urgent is a better understanding of albedo feedbacks leading to enhanced surface melt, potential positive feedbacks between ice sheet hydrology and dynamics, and meltwater retention in firn. These processes are not isolated, but must be understood as part of a continuum of processes within an integrated system. This letter describes a systems approach to the study of Greenland ice sheet hydrology, emphasizing component interconnections and feedbacks, and highlighting research and observational needs. (letter)

Large-current-controllable carbon nanotube field-effect transistor in electrolyte solution

Science.gov (United States)

Myodo, Miho; Inaba, Masafumi; Ohara, Kazuyoshi; Kato, Ryogo; Kobayashi, Mikinori; Hirano, Yu; Suzuki, Kazuma; Kawarada, Hiroshi

2015-05-01

Large-current-controllable carbon nanotube field-effect transistors (CNT-FETs) were fabricated with mm-long CNT sheets. The sheets, synthesized by remote-plasma-enhanced CVD, contained both single- and double-walled CNTs. Titanium was deposited on the sheet as source and drain electrodes, and an electrolyte solution was used as a gate electrode (solution gate) to apply a gate voltage to the CNTs through electric double layers formed around the CNTs. The drain current came to be well modulated as electrolyte solution penetrated into the sheets, and one of the solution gate CNT-FETs was able to control a large current of over 2.5 A. In addition, we determined the transconductance parameter per tube and compared it with values for other CNT-FETs. The potential of CNT sheets for applications requiring the control of large current is exhibited in this study.

Extensive Holocene ice sheet grounding line retreat and uplift-driven readvance in West Antarctica

Science.gov (United States)

Kingslake, J.; Scherer, R. P.; Albrecht, T.; Coenen, J. J.; Powell, R. D.; Reese, R.; Stansell, N.; Tulaczyk, S. M.; Whitehouse, P. L.

2017-12-01

The West Antarctic Ice Sheet (WAIS) reached its Last Glacial Maximum (LGM) extent 29-14 kyr before present. Numerical models used to project future ice-sheet contributions to sea-level rise exploit reconstructions of post-LGM ice mass loss to tune model parameterizations. Ice-sheet reconstructions are poorly constrained in areas where floating ice shelves or a lack of exposed geology obstruct conventional glacial-geological techniques. In the Weddell and Ross Sea sectors, ice-sheet reconstructions have traditionally assumed progressive grounding line (GL) retreat throughout the Holocene. Contrasting this view, using three distinct lines of evidence, we show that the GL retreated hundreds of kilometers inland of its present position, before glacial isostatic rebound during the Mid to Late Holocene caused the GL to readvance to its current position. Evidence for retreat and readvance during the last glacial termination includes (1) widespread radiocarbon in sediment cores recovered from beneath ice streams along the Siple and Gould Coasts, indicating marine exposure at least 200 km inland of the current GL, (2) ice-penetrating radar observations of relic crevasses and other englacial structures preserved in slow-moving grounded ice, indicating ice-shelf grounding and (3) an ensemble of new ice-sheet simulations showing widespread post-LGM retreat of the GL inland of its current location and later readvance. The model indicates that GL readvance across low slope ice-stream troughs requires uplift-driven grounding of the ice shelf on topographic highs (ice rises). Our findings highlight ice-shelf pinning points and lithospheric response to unloading as drivers of major ice-sheet fluctuations. Full WAIS collapse likely requires GL retreat well beyond its current position in the Ronne and Ross Sectors and linkage via Amundsen Sea sector glaciers.

THREE-DIMENSIONAL GEOMETRY OF A CURRENT SHEET IN THE HIGH SOLAR CORONA: EVIDENCE FOR RECONNECTION IN THE LATE STAGE OF THE CORONAL MASS EJECTIONS

Energy Technology Data Exchange (ETDEWEB)

Kwon, Ryun-Young [College of Science, George Mason University, 4400 University Drive, Fairfax, VA 22030 (United States); Vourlidas, Angelos [The Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723 (United States); Webb, David, E-mail: rkwon@gmu.edu [ISR, Boston College, Chestnut Hill, MA (United States)

2016-07-20

Motivated by the standard flare model, ray-like structures in the wake of coronal mass ejections (CMEs) have been often interpreted as proxies of the reconnecting current sheet connecting the CME with the postflare arcade. We present the three-dimensional properties of a post-CME ray derived from white light images taken from three different viewing perspectives on 2013 September 21. By using a forward modeling method, the direction, cross section, and electron density are determined within the heliocentric distance range of 5–9 R {sub ⊙}. The width and depth of the ray are 0.42 ± 0.08 R {sub ⊙} and 1.24 ± 0.35 R {sub ⊙}, respectively, and the electron density is (2.0 ± 0.5) × 10{sup 4} cm{sup 3}, which seems to be constant with height. Successive blobs moving outward along the ray are observed around 13 hr after the parent CME onset. We model the three-dimensional geometry of the parent CME with the Gradual Cylindrical Shell model and find that the CME and ray are coaxial. We suggest that coaxial post-CME rays, seen in coronagraph images, with successive formation of blobs could be associated with current sheets undergoing magnetic reconnection in the late stage of CMEs.

A mechanism for driving the gross Birkeland current configuration in the auroral oval

International Nuclear Information System (INIS)

Rostoker, G.; Bostrom, R.

1976-01-01

Birkeland (field-aligned) sheet currents flowing into and out of the auroral oval as reported by Zmuda and Armstrong (1974) are integrally associated with convective motion of plasma in the magnetotail. It is demonstrated that these currents can be driven by energy supplied by the braking of this convective motion of the plasma sheet particles as they drift toward the flanks of the magnetosphere. In the ionosphere the sheet currents close as Pedersen currents, resulting in the dissipation of power, while far from the earth the closure currents, which provide the braking force for the plasma, flow in the plasma sheet approximately normal to the neutral sheet out to radial distances of about 80 R/subE/. During periods of moderate magnetospheric activity the Birkeland currents result in a rate of dissipation of convective energy of the order of 10 GW

EGCG Inhibited Lipofuscin Formation Based on Intercepting Amyloidogenic β-Sheet-Rich Structure Conversion.

Directory of Open Access Journals (Sweden)

Shuxian Cai

Full Text Available Lipofuscin (LF is formed during lipid peroxidation and sugar glycosylation by carbonyl-amino crosslinks with biomacrolecules, and accumulates slowly within postmitotic cells. The environmental pollution, modern dietary culture and lifestyle changes have been found to be the major sources of reactive carbonyl compounds in vivo. Irreversible carbonyl-amino crosslinks induced by carbonyl stress are essentially toxiferous for aging-related functional losses in modern society. Results show that (--epigallocatechin gallate (EGCG, the main polyphenol in green tea, can neutralize the carbonyl-amino cross-linking reaction and inhibit LF formation, but the underlying mechanism is unknown.We explored the mechanism of the neutralization process from protein, cell, and animal levels using spectrofluorometry, infrared spectroscopy, conformation antibodies, and electron microscopy. LF demonstrated an amyloidogenic β-sheet-rich with antiparallel structure, which accelerated the carbonyl-amino crosslinks formation and disrupted proteolysis in both PC12 cells and D-galactose (D-gal-induced brain aging mice models. Additionally, EGCG effectively inhibited the formation of the amyloidogenic β-sheet-rich structure of LF, and prevented its conversion into toxic and on-pathway aggregation intermediates, thereby cutting off the carbonyl-amino crosslinks.Our study indicated that the amyloidogenic β-sheet structure of LF may be the core driving force for carbonyl-amino crosslinks further formation, which mediates the formation of amyloid fibrils from native state of biomacrolecules. That EGCG exhibits anti-amyloidogenic β-sheet-rich structure properties to prevent the LF formation represents a novel strategy to impede the development of degenerative processes caused by ageing or stress-induced premature senescence in modern environments.

Disruption of Alfvénic turbulence by magnetic reconnection in a collisionless plasma

Science.gov (United States)

Mallet, Alfred; Schekochihin, Alexander A.; Chandran, Benjamin D. G.

2017-12-01

We calculate the disruption scale \\text{D}$ at which sheet-like structures in dynamically aligned Alfvénic turbulence are destroyed by the onset of magnetic reconnection in a low- collisionless plasma. The scaling of \\text{D}$ depends on the order of the statistics being considered, with more intense structures being disrupted at larger scales. The disruption scale for the structures that dominate the energy spectrum is \\text{D}\\sim L\\bot 1/9(de\\unicode[STIX]{x1D70C}s)4/9$ , where e$ is the electron inertial scale, s$ is the ion sound scale and \\bot $ is the outer scale of the turbulence. When e$ and s/L\\bot $ are sufficiently small, the scale \\text{D}$ is larger than s$ and there is a break in the energy spectrum at \\text{D}$ , rather than at s$ . We propose that the fluctuations produced by the disruption are circularised flux ropes, which may have already been observed in the solar wind. We predict the relationship between the amplitude and radius of these structures and quantify the importance of the disruption process to the cascade in terms of the filling fraction of undisrupted structures and the fractional reduction of the energy contained in them at the ion sound scale s$ . Both of these fractions depend strongly on e$ , with the disrupted structures becoming more important at lower e$ . Finally, we predict that the energy spectrum between \\text{D}$ and s$ is steeper than \\bot -3$ , when this range exists. Such a steep `transition range' is sometimes observed in short intervals of solar-wind turbulence. The onset of collisionless magnetic reconnection may therefore significantly affect the nature of plasma turbulence around the ion gyroscale.

Laminin-521 Promotes Rat Bone Marrow Mesenchymal Stem Cell Sheet Formation on Light-Induced Cell Sheet Technology

Directory of Open Access Journals (Sweden)

Zhiwei Jiang

2017-01-01

Full Text Available Rat bone marrow mesenchymal stem cell sheets (rBMSC sheets are attractive for cell-based tissue engineering. However, methods of culturing rBMSC sheets are critically limited. In order to obtain intact rBMSC sheets, a light-induced cell sheet method was used in this study. TiO2 nanodot films were coated with (TL or without (TN laminin-521. We investigated the effects of laminin-521 on rBMSCs during cell sheet culturing. The fabricated rBMSC sheets were subsequently assessed to study cell sheet viability, reattachment ability, cell sheet thickness, collagen type I deposition, and multilineage potential. The results showed that laminin-521 could promote the formation of rBMSC sheets with good viability under hyperconfluent conditions. Cell sheet thickness increased from an initial 26.7 ± 1.5 μm (day 5 up to 47.7 ± 3.0 μm (day 10. Moreover, rBMSC sheets maintained their potential of osteogenic, adipogenic, and chondrogenic differentiation. This study provides a new strategy to obtain rBMSC sheets using light-induced cell sheet technology.

Disruptions in ITER and strategies for their control and mitigation

Energy Technology Data Exchange (ETDEWEB)

Lehnen, M., E-mail: michael.lehnen@iter.org [ITER Organization, Route de Vinon sur Verdon, 13115 St Paul Lez Durance (France); Aleynikova, K.; Aleynikov, P.B.; Campbell, D.J. [ITER Organization, Route de Vinon sur Verdon, 13115 St Paul Lez Durance (France); Drewelow, P. [Max-Planck-Institut für Plasmaphysik, Greifswald branch, EURATOM Ass., D-17491 Greifswald (Germany); Eidietis, N.W. [General Atomics, P.O. Box 85608, San Diego, CA 92186-5608 (United States); Gasparyan, Yu. [National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Kashirskoe sh. 31, Moscow 115409 (Russian Federation); Granetz, R.S. [MIT Plasma Science and Fusion Center, Cambridge, MA 02139 (United States); Gribov, Y. [ITER Organization, Route de Vinon sur Verdon, 13115 St Paul Lez Durance (France); Hartmann, N. [Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research—Plasma Physics, Association EURATOM-FZJ, Trilateral Euregio Cluster, 52425 Jülich (Germany); Hollmann, E.M. [University of California-San Diego, La Jolla, CA 92093 (United States); Izzo, V.A. [ITER Organization, Route de Vinon sur Verdon, 13115 St Paul Lez Durance (France); Jachmich, S. [Laboratory for Plasma Physics, ERM/KMS, Association EURATOM – Belgian State, B-1000 Brussels (Belgium); Kim, S.-H.; Kočan, M. [ITER Organization, Route de Vinon sur Verdon, 13115 St Paul Lez Durance (France); Koslowski, H.R. [Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research—Plasma Physics, Association EURATOM-FZJ, Trilateral Euregio Cluster, 52425 Jülich (Germany); Kovalenko, D. [SRC RF TRINITI, ul. Pushkovykh, vladenie 12, Troitsk, Moscow 142190 (Russian Federation); Kruezi, U. [CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB (United Kingdom); and others

2015-08-15

The thermal and electromagnetic loads related to disruptions in ITER are substantial and require careful design of tokamak components to ensure they reach the projected lifetime and to ensure that safety relevant components fulfil their function for the worst foreseen scenarios. The disruption load specifications are the basis for the design process of components like the full-W divertor, the blanket modules and the vacuum vessel and will set the boundary conditions for ITER operations. This paper will give a brief overview on the disruption loads and mitigation strategies for ITER and will discuss the physics basis which is continuously refined through the current disruption R&D programs.

Digital Disruption

DEFF Research Database (Denmark)

Rosenstand, Claus Andreas Foss

det digitale domæne ud over det niveau, der kendetegner den nuværende debat, så præsenteres der ny viden om digital disruption. Som noget nyt udlægges Clayton Christens teori om disruptiv innovation med et særligt fokus på små organisationers mulighed for eksponentiel vækst. Specielt udfoldes...... forholdet mellem disruption og den stadig accelererende digitale udvikling i konturerne til ny teoridannelse om digital disruption. Bogens undertitel ”faretruende og fascinerende forandringer” peger på, at der er behov for en nuanceret debat om digital disruption i modsætning til den tone, der er slået an i...... videre kalder et ”disruption-råd”. Faktisk er rådet skrevet ind i 2016 regeringsgrundlaget for VLK-regeringen. Disruption af organisationer er ikke et nyt fænomen; men hastigheden, hvormed det sker, er stadig accelererende. Årsagen er den globale mega-trend: Digitalisering. Og derfor er specielt digital...

Will blockchain disrupt your business?

OpenAIRE

Schmeiss, Jessica

2018-01-01

Blockchain has been praised to be “the technology most likely to change the next decade of business”. The disruptive power of the blockchain technology is yet limited, says HIIG-researcher Jessica Schmeiss. Beyond the hype, there a opportunities for companies to make their current business models more cost-effective and more efficient.

Rapidly cast crystalline thin sheet materials

International Nuclear Information System (INIS)

Warlimont, H.; Emmerich, K.

1986-01-01

The current state and progress of casting thin sheet and ribbons directly from the melt are reviewed. First, the solidification phenomena pertinent to the process are outlined. Subsequently, Fe-Si,l Fe-Si-Al, Fe-Nd-B, Ag-Cu-Ti, alloy steels, Ni superalloys and Si are treated as examples. Finally, the information available on process development is critically assessed

Local charge transport properties of hydrazine reduced monolayer graphene oxide sheets prepared under pressure condition

DEFF Research Database (Denmark)

Ryuzaki, Sou; Meyer, Jakob Abild Stengaard; Petersen, Søren Vermehren

2014-01-01

Charge transport properties of chemically reduced graphene oxide (RGO) sheets prepared by treatment with hydrazine were examined using conductive atomic force microscopy. The current-voltage (I-V) characteristics of monolayer RGO sheets prepared under atmospheric pressure followed an exponentially...

Development of a low energy micro sheet forming machine

Science.gov (United States)

Razali, A. R.; Ann, C. T.; Shariff, H. M.; Kasim, N. I.; Musa, M. A.; Ahmad, A. F.

2017-10-01

It is expected that with the miniaturization of materials being processed, energy consumption is also being `miniaturized' proportionally. The focus of this study was to design a low energy micro-sheet-forming machine for thin sheet metal application and fabricate a low direct current powered micro-sheet-forming machine. A prototype of low energy system for a micro-sheet-forming machine which includes mechanical and electronic elements was developed. The machine was tested for its performance in terms of natural frequency, punching forces, punching speed and capability, energy consumption (single punch and frequency-time based). Based on the experiments, the machine can do 600 stroke per minute and the process is unaffected by the machine's natural frequency. It was also found that sub-Joule of power was required for a single stroke of punching/blanking process. Up to 100micron thick carbon steel shim was successfully tested and punched. It concludes that low power forming machine is feasible to be developed and be used to replace high powered machineries to form micro-products/parts.

Disruption?

DEFF Research Database (Denmark)

2016-01-01

This is a short video on the theme disruption and entrepreneurship. It takes the form of an interview with John Murray......This is a short video on the theme disruption and entrepreneurship. It takes the form of an interview with John Murray...

Development of an ITER prototype disruption mitigation valve

Energy Technology Data Exchange (ETDEWEB)

Czymek, G., E-mail: g.czymek@fz-juelich.de [Institute of Energy and Climate Research – Plasma Physics, Forschungszentrum Jülich GmbH, D52425 Jülich (Germany); Giesen, B., E-mail: ingenieurbuero.giesen@gmx.de [IBG, Sibertstr. 22, D-52525 Heinsberg (Germany); Charl, A.; Panin, A.; Hiller, A.; Nicolai, D.; Neubauer, O.; Koslowski, H.R.; Sandri, N. [Institute of Energy and Climate Research – Plasma Physics, Forschungszentrum Jülich GmbH, D52425 Jülich (Germany)

2015-10-15

Highlights: • An ITER-DMV prototype for 100 bar, D = 80 mm, opening time 3.5 ms, is ready for fabrication. • The vacuum part is sealed against the working gas by stainless steel bellows for 110 bar. • The conical Laval gas outlet allows maximal mass flow rate. • The eddy current drive turn ratio was optimized for low tilting moment. • Polyimide is used for the head sealing, the decelerator and for the bearing of the guide tube. - Abstract: Disruptions in tokamaks seem to be unavoidable. Consequences of disruptions are (i) high heat loads on plasma-facing components, (ii) large forces on the vacuum vessel, and (iii) the generation of runaway electron beams. In ITER, the thermal energy of the plasma needs to be evenly distributed on the first wall in order to prevent melting, forces from vertical displacement events have to be minimized, and the generation of runaway electrons suppressed. Massive gas injection using fast valves is a concept for disruption mitigation which is presently being explored in many tokamaks. Fast disruption mitigation valves based on an electromagnetic eddy current drive have been developed in Jülich since the 1990s and models of various sizes have been built and are in operation in the TEXTOR, MAST, and JET tokamaks. A disruption mitigation valve for ITER is of necessity larger with an estimated injected gas volume of ∼20 kPa m{sup 3}[7] for runaway electron suppression and all materials used have to be resistant to much higher levels of neutron and gamma radiation than in existing tokamaks. During the last 5 years, the concept for an ITER prototype disruption mitigation valve has been developed up to the stage that a fully functional valve could be built and tested. Special emphasis was given to the development and functional testing of some critical items: (i) the injection chamber seal, (ii) the piston seal, (iii) the eddy current drive, and (iv) a braking mechanism to avoid too fast closure of the valve, which could damage

Superfund fact sheet: The remedial program. Fact sheet

International Nuclear Information System (INIS)

1992-09-01

The fact sheet describes what various actions the EPA can take to clean up hazardous wastes sites. Explanations of how the criteria for environmental and public health risk assessment are determined and the role of state and local governments in site remediation are given. The fact sheet is one in a series providing reference information about Superfund issues and is intended for readers with no formal scientific training

Utilization of Superheroes Social Skills to Reduce Disruptive and Aggressive Behavior

Science.gov (United States)

O'Handley, Roderick D.; Radley, Keith C.; Cavell, Hannah J.

2016-01-01

The current pilot study investigated the effectiveness of the Superheroes Social Skills program in decreasing disruptive and aggressive behavior of elementary-age students with high-incidence disabilities. Six students in a self-contained classroom, identified as displaying high rates of disruptive and aggressive behavior toward peers, were…

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.

Quick profile-reorganization driven by helical field perturbation for suppressing tokamak major disruptions

International Nuclear Information System (INIS)

Yamazaki, K.; Kawahata, K.; Ando, R.

1986-09-01

Disruptive behavior of magnetic field configuration leading to tokamak major disruption is found to be controlled by a mild ''mini-disruption'' which is induced by the compact external modular multipole-field coils with m = 3/n = 2 dominant helical field component in the JIPP T-IIU tokamak. This mini-disruption ergodizes the m = 2/n = 1 magnetic island quickly but mildly and then prevents the profile of electron temperature from flattening. This quick profile-reorganization is effective to avoid the two-step disruption (pre- and major disuptions) responsible for the chatastrophic current termination. (author)

Present status of VDEs (Vertical Displacement Events) avoidance studies in tokamak disruptions

International Nuclear Information System (INIS)

Nakamura, Yukiharu

2001-01-01

Present knowledge on the consequences of tokamak disruption and disruption-related effects are reviewed from a viewpoint of disruption mitigation and/or avoidance. The Vertical Displacement Events (VDEs), which are frequently observed in disruptive discharges of elongated tokamaks, are described in detail with an emphasis on the close relationships between the generation of halo currents and runaway electrons. The newly found 'neutral point', at which VDEs hardly occur, is also addressed. Finally, VDE-related issues remaining to be addressed in future works are discussed. (author)

Radiation protecting sheet

International Nuclear Information System (INIS)

Makiguchi, Hiroshi.

1989-01-01

As protection sheets used in radioactivity administration areas, a thermoplastic polyurethane composition sheet with a thickness of less 0.5 mm, solid content (ash) of less than 5% and a shore D hardness of less than 60 is used. A composite sheet with thickness of less than 0.5 mm laminated or coated with such a thermoplastic polyurethane composition as a surface layer and the thermoplastic polyurethane composition sheet applied with secondary fabrication are used. This can satisfy all of the required properties, such as draping property, abrasion resistance, high breaking strength, necking resistance, endurance strength, as well as chemical resistance and easy burnability in burning furnace. Further, by forming uneveness on the surface by means of embossing, etc. safety problems such as slippage during operation and walking can be overcome. (T.M.)

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.

Formation of sheeting joints in Yosemite National Park, California

Science.gov (United States)

Martel, S. J.

2009-04-01

The formation of sheeting joints (i.e., "exfoliation joints"), opening mode fractures subparallel to the Earth's surface, has been a classic unresolved problem in geology. Diverse new observations and analyses support the hypothesis that sheeting joints develop in response to a near-surface tension induced by compressive stresses parallel to a convex slope (hypothesis 1) rather than the conventional explanation that the joints form as a result of removal of overburden by erosion (hypothesis 2). The opening mode displacements across the joints together with the absence of mineral precipitates within the joints mean that sheeting joints open in response to a near-surface tension normal to the surface (N) rather than a pressurized fluid. An absolute tension must arise in the shallow subsurface if a plot of N as a function of depth normal to the surface (z) has a positive slope at the surface (z=0). The differential equations of static equilibrium require that this slope (derivative) equals k2 P22 + k3 P33 - ?g cosβ, where k2 and k3 are the principal curvatures of the surface, P22 and P33 are the respective surface-parallel normal stresses along the principal curvatures, ? is the material density, g is gravitational acceleration, and β is the slope. This derivative will be positive and sheeting joints can open if the surface-parallel stress in at least one direction is sufficiently compressive (negative) and the curvature in that direction is sufficiently convex (negative). Hypotheses 1 and 2 are being tested using geologic mapping and aerial LIDAR data from Yosemite National Park, California. The abundance of sheeting joints on convex ridges there, where erosion is a local minimum, coupled with their scarcity in the adjacent concave valleys, where erosion is a local maximum, is consistent with hypothesis 1 but inconsistent with hypothesis 2. At several sites with sheeting joints, measurements of the current topographic curvatures and the current surface

Spaceborne measurement of Greenland ice sheet changes: the ESA Greenland CCI project

DEFF Research Database (Denmark)

Forsberg, René; Sørensen, Louise Sandberg; Meister, Rakia

The ESA “Greenland_ice_sheet_cci” project is currently making past and present space measurements of Greenland ice sheet changes available for use by scientists, stakeholders and the general public. The data are part of a large set of ECV’s (Essential Climate Variables) made available by the ESA...... Climate Initiative, as a contribution to the global Climate Observing System. The ECV data produced for the Greenlandice sheet include detailed grids of elevation changes and ice flow velocities, as well as line data of grounding lines and calving front locations for major outlet glaciers. The “ice_sheets......_cci” goal is to generate a consistent, validated, long-term and timely set of ECV’s, a.o. to improve the impact of satellite data on climate research and coupled ice sheet/climate models. Special focus is on use of data from ESA missions such as ERS, Envisat and the new Sentinel missions, but in the 2nd...

Deformation Analysis of RC Ties Externally Strengthened with FRP Sheets

Science.gov (United States)

Gribniak, V.; Arnautov, A. K.; Kaklauskas, G.; Jakstaite, R.; Tamulenas, V.; Gudonis, E.

2014-11-01

The current study has two objectives: to validate the ability of the Atena finite-element software to estimate the deformations of reinforced concrete (RC) elements strengthened with fiber-reinforced polymer (FRP) sheets and to assess the effect of FRP-to-concrete bond strength on the results of numerical simulation. It is shown that the bond strength has to be selected according to the overall stiffness of the composite element. The numerical results found are corroborated experimentally by tensile tests of RC elements strengthened with basalt FRP sheets.

Automobile sheet metal part production with incremental sheet forming

Directory of Open Access Journals (Sweden)

İsmail DURGUN

2016-02-01

Full Text Available Nowadays, effect of global warming is increasing drastically so it leads to increased interest on energy efficiency and sustainable production methods. As a result of adverse conditions, national and international project platforms, OEMs (Original Equipment Manufacturers, SMEs (Small and Mid-size Manufacturers perform many studies or improve existing methodologies in scope of advanced manufacturing techniques. In this study, advanced manufacturing and sustainable production method "Incremental Sheet Metal Forming (ISF" was used for sheet metal forming process. A vehicle fender was manufactured with or without die by using different toolpath strategies and die sets. At the end of the study, Results have been investigated under the influence of method and parameters used.Keywords: Template incremental sheet metal, Metal forming

Simulations of tokamak disruptions including self-consistent temperature evolution

International Nuclear Information System (INIS)

Bondeson, A.

1986-01-01

Three-dimensional simulations of tokamaks have been carried out, including self-consistent temperature evolution with a highly anisotropic thermal conductivity. The simulations extend over the transport time-scale and address the question of how disruptive current profiles arise at low-q or high-density operation. Sharply defined disruptive events are triggered by the m/n=2/1 resistive tearing mode, which is mainly affected by local current gradients near the q=2 surface. If the global current gradient between q=2 and q=1 is sufficiently steep, the m=2 mode starts a shock which accelerates towards the q=1 surface, leaving stochastic fields, a flattened temperature profile and turbulent plasma behind it. For slightly weaker global current gradients, a shock may form, but it will dissipate before reaching q=1 and may lead to repetitive minidisruptions which flatten the temperature profile in a region inside the q=2 surface. (author)

The Structure of Childhood Disruptive Behaviors

Science.gov (United States)

Martel, Michelle M.; Gremillion, Monica; Roberts, Bethan; von Eye, Alexander; Nigg, Joel T.

2010-01-01

Attention-deficit/hyperactivity disorder (ADHD) and oppositional defiant disorder (ODD) frequently co-occur. Comorbidity of these 2 childhood disruptive behavior domains has not been satisfactorily explained at either a structural or etiological level. The current study evaluated a bifactor model, which allows for a "g" factor in addition to…

RECONNECTION OUTFLOWS AND CURRENT SHEET OBSERVED WITH HINODE/XRT IN THE 2008 APRIL 9 'CARTWHEEL CME' FLARE

International Nuclear Information System (INIS)

Savage, Sabrina L.; McKenzie, David E.; Longcope, Dana W.; Reeves, Katharine K.; Forbes, Terry G.

2010-01-01

Supra-arcade downflows (SADs) have been observed with Yohkoh/SXT (soft X-rays (SXR)), TRACE (extreme ultraviolet (EUV)), SOHO/LASCO (white light), SOHO/SUMER (EUV spectra), and Hinode/XRT (SXR). Characteristics such as low emissivity and trajectories, which slow as they reach the top of the arcade, are consistent with post-reconnection magnetic flux tubes retracting from a reconnection site high in the corona until they reach a lower-energy magnetic configuration. Viewed from a perpendicular angle, SADs should appear as shrinking loops rather than downflowing voids. We present X-ray Telescope (XRT) observations of supra-arcade downflowing loops (SADLs) following a coronal mass ejection (CME) on 2008 April 9 and show that their speeds and decelerations are consistent with those determined for SADs. We also present evidence for a possible current sheet observed during this flare that extends between the flare arcade and the CME. Additionally, we show a correlation between reconnection outflows observed with XRT and outgoing flows observed with LASCO.

Orientation determination of interfacial beta-sheet structures in situ.

Science.gov (United States)

Nguyen, Khoi Tan; King, John Thomas; Chen, Zhan

2010-07-01

Structural information such as orientations of interfacial proteins and peptides is important for understanding properties and functions of such biological molecules, which play crucial roles in biological applications and processes such as antimicrobial selectivity, membrane protein activity, biocompatibility, and biosensing performance. The alpha-helical and beta-sheet structures are the most widely encountered secondary structures in peptides and proteins. In this paper, for the first time, a method to quantify the orientation of the interfacial beta-sheet structure using a combined attenuated total reflectance Fourier transformation infrared spectroscopic (ATR-FTIR) and sum frequency generation (SFG) vibrational spectroscopic study was developed. As an illustration of the methodology, the orientation of tachyplesin I, a 17 amino acid peptide with an antiparallel beta-sheet, adsorbed to polymer surfaces as well as associated with a lipid bilayer was determined using the regular and chiral SFG spectra, together with polarized ATR-FTIR amide I signals. Both the tilt angle (theta) and the twist angle (psi) of the beta-sheet at interfaces are determined. The developed method in this paper can be used to obtain in situ structural information of beta-sheet components in complex molecules. The combination of this method and the existing methodology that is currently used to investigate alpha-helical structures will greatly broaden the application of optical spectroscopy in physical chemistry, biochemistry, biophysics, and structural biology.

Combustion of available fossil-fuel resources sufficient to eliminate the Antarctic Ice Sheet

Science.gov (United States)

Winkelmann, R.; Levermann, A.; Ridgwell, A.; Caldeira, K.

2015-12-01

The Antarctic Ice Sheet stores water equivalent to 58 meters in global sea-level rise. Here we show in simulations with the Parallel Ice Sheet Model that burning the currently attainable fossil-fuel resources is sufficient to eliminate the ice sheet. With cumulative fossil-fuel emissions of 10 000 GtC, Antarctica is projected to become almost ice-free with an average contribution to sea-level rise exceeding 3 meters per century during the first millennium. Consistent with recent observations and simulations, the West Antarctic Ice Sheet becomes unstable with 600 to 800 GtC of additional carbon emissions. Beyond this additional carbon release, the destabilization of ice basins in both West- and East Antarctica results in a threshold-increase in global sea level. Unabated carbon emissions thus threaten the Antarctic Ice Sheet in its entirety with associated sea-level rise that far exceeds that of all other possible sources.

Geometry of thin liquid sheet flows

Science.gov (United States)

Chubb, Donald L.; Calfo, Frederick D.; Mcconley, Marc W.; Mcmaster, Matthew S.; Afjeh, Abdollah A.

1994-01-01

Incompresible, thin sheet flows have been of research interest for many years. Those studies were mainly concerned with the stability of the flow in a surrounding gas. Squire was the first to carry out a linear, invicid stability analysis of sheet flow in air and compare the results with experiment. Dombrowski and Fraser did an experimental study of the disintegration of sheet flows using several viscous liquids. They also detected the formulation of holes in their sheet flows. Hagerty and Shea carried out an inviscid stability analysis and calculated growth rates with experimental values. They compared their calculated growth rates with experimental values. Taylor studied extensively the stability of thin liquid sheets both theoretically and experimentally. He showed that thin sheets in a vacuum are stable. Brown experimentally investigated thin liquid sheet flows as a method of application of thin films. Clark and Dumbrowski carried out second-order stability analysis for invicid sheet flows. Lin introduced viscosity into the linear stability analysis of thin sheet flows in a vacuum. Mansour and Chigier conducted an experimental study of the breakup of a sheet flow surrounded by high-speed air. Lin et al. did a linear stability analysis that included viscosity and a surrounding gas. Rangel and Sirignano carried out both a linear and nonlinear invisid stability analysis that applies for any density ratio between the sheet liquid and the surrounding gas. Now there is renewed interest in sheet flows because of their possible application as low mass radiating surfaces. The objective of this study is to investigate the fluid dynamics of sheet flows that are of interest for a space radiator system. Analytical expressions that govern the sheet geometry are compared with experimental results. Since a space radiator will operate in a vacuum, the analysis does not include any drag force on the sheet flow.

Reduction of eddy current losses in inductive transmission systems with ferrite sheets.

Science.gov (United States)

Maaß, Matthias; Griessner, Andreas; Steixner, Viktor; Zierhofer, Clemens

2017-01-05

Improvements in eddy current suppression are necessary to meet the demand for increasing miniaturization of inductively driven transmission systems in industrial and biomedical applications. The high magnetic permeability and the simultaneously low electrical conductivity of ferrite materials make them ideal candidates for shielding metallic surfaces. For systems like cochlear implants the transmission of data as well as energy over an inductive link is conducted within a well-defined parameter set. For these systems, the shielding can be of particular importance if the properties of the link can be preserved. In this work, we investigate the effect of single and double-layered substrates consisting of ferrite and/or copper on the inductance and coupling of planar spiral coils. The examined link systems represent realistic configurations for active implantable systems such as cochlear implants. Experimental measurements are complemented with analytical calculations and finite element simulations, which are in good agreement for all measured parameters. The results are then used to study the transfer efficiency of an inductive link in a series-parallel resonant topology as a function of substrate size, the number of coil turns and coil separation. We find that ferrite sheets can be used to shield the system from unwanted metallic surfaces and to retain the inductive link parameters of the unperturbed system, particularly its transfer efficiency. The required size of the ferrite plates is comparable to the size of the coils, which makes the setup suitable for practical implementations. Since the sizes and geometries chosen for the studied inductive links are comparable to those of cochlear implants, our conclusions apply in particular to these systems.

Preparation of Ni(OH)2-graphene sheet-carbon nanotube composite as electrode material for supercapacitors

International Nuclear Information System (INIS)

Liu, Y.F.; Yuan, G.H.; Jiang, Z.H.; Yao, Z.P.; Yue, M.

2015-01-01

Highlights: • CNT is introduced into graphene to prevent restacking by solvothermal reaction. • Ethanol as a low cost and green solvent is used in solvothermal reaction. • Ni(OH) 2 nanosheets were chemically precipitated into GS-CNT to increase the capacitance. - Abstract: Ni(OH) 2 -graphene sheet-carbon nanotube composite was prepared for supercapacitance materials through a simple two-step process involving solvothermal synthesis of graphene sheet-carbon nanotube composite in ethanol and chemical precipitation of Ni(OH) 2 . According to N 2 adsorption/desorption analysis, the Brunauer–Emmett–Teller surface area of graphene sheet-carbon nanotube composite (109.07 m 2 g −1 ) was larger than that of pure graphene sheets (32.06 m 2 g −1 ), indicating that the added carbon nanotubes (15 wt.%) could prevent graphene sheets from restacking in the solvothermal reaction. The results of field emission scanning electron microscopy and transmission electron microscopy showed that Ni(OH) 2 nanosheets were uniformly loaded into the three-dimensional interconnected network of graphene sheet-carbon nanotube composite. The microstructure enhanced the rate capability and utilization of Ni(OH) 2 . The specific capacitance of Ni(OH) 2 -graphene sheet-carbon nanotube composite was 1170.38 F g −1 at a current density of 0.2 A g −1 in the 6 mol L −1 KOH solution, higher than those provided by pure Ni(OH) 2 (953.67 Fg −1 ) and graphene sheets (178.25 F g −1 ). After 20 cycles at each current density (0.2, 0.4, 0.6, 0.8, 1.0 and 1.2 A g −1 ), the capacitance of Ni(OH) 2 -graphene sheet-carbon nanotube composite decreased 26.96% of initial capacitance compared to 74.52% for pure Ni(OH) 2

Disruption avoidance in the SINP-Tokamak by means of electrode-biasing at the plasma edge

Energy Technology Data Exchange (ETDEWEB)

Basu, Debjyoti [Saha Institute of Nuclear Physics, 1/AF-Bidhannagar, Kolkata 700064, WB (India); Instituto de Ciencias Nucleares-UNAM, Mexico D.F. 04510 (Mexico); Pal, Rabindranath [Saha Institute of Nuclear Physics, 1/AF-Bidhannagar, Kolkata 700064, WB (India); Martinell, Julio J. [Instituto de Ciencias Nucleares-UNAM, Mexico D.F. 04510 (Mexico); Ghosh, Joydeep; Chattopadhyay, Prabal K. [Institute for Plasma Research, Gandhinagar (India)

2013-05-15

Control of plasma disruption by a biased edge electrode is reported in SINP-Tokamak. The features that characterize a plasma disruption are reduced with increasing bias potential. The disruption can be completely suppressed with the concomitant stabilization of observed MHD modes that are allegedly precursors of the disruption. An m = 3/n = 1 tearing mode, which apparently causes disruption can be stabilized when a negative biasing potential is applied near the edge. These changes in the disruptive behavior with edge biasing are hypothesized to be due to changes in the current density profile.

Disruption avoidance in the SINP-Tokamak by means of electrode-biasing at the plasma edge

International Nuclear Information System (INIS)

Basu, Debjyoti; Pal, Rabindranath; Martinell, Julio J.; Ghosh, Joydeep; Chattopadhyay, Prabal K.

2013-01-01

Control of plasma disruption by a biased edge electrode is reported in SINP-Tokamak. The features that characterize a plasma disruption are reduced with increasing bias potential. The disruption can be completely suppressed with the concomitant stabilization of observed MHD modes that are allegedly precursors of the disruption. An m = 3/n = 1 tearing mode, which apparently causes disruption can be stabilized when a negative biasing potential is applied near the edge. These changes in the disruptive behavior with edge biasing are hypothesized to be due to changes in the current density profile

Teenage Pregnancy. Highlights: An ERIC/CAPS Fact Sheet.

Science.gov (United States)

Lachance, Laurie L.

This fact sheet addresses the issue of teenage pregnancy. Six factors contributing to the current attention focused on teenage pregnancy and parenthood are listed and teenage pregnancy and birth rates are discussed. Other areas covered include teenage nonuse of contraception, sex education by schools and parents, family planning services, and the…

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

Modeling SOL evolution during disruptions

International Nuclear Information System (INIS)

Rognlien, T.D.; Cohen, R.H.; Crotinger, J.A.

1996-01-01

We present the status of our models and transport simulations of the 2-D evolution of the scrape-off layer (SOL) during tokamak disruptions. This evolution is important for several reasons: It determines how the power from the core plasma is distributed on material surfaces, how impurities from those surfaces or from gas injection migrate back to the core region, and what are the properties of the SOL for carrying halo currents. We simulate this plasma in a time-dependent fashion using the SOL transport code UEDGE. This code models the SOL plasma using fluid equations of plasma density, parallel momentum (along the magnetic field), electron energy, ion energy, and neutral gas density. A multispecies model is used to follow the density of different charge-states of impurities. The parallel transport is classical but with kinetic modifications; these are presently treated by flux limits, but we have initiated more sophisticated models giving the correct long-mean-free path limit. The cross-field transport is anomalous, and one of the results of this work is to determine reasonable values to characterize disruptions. Our primary focus is on the initial thermal quench phase when most of the core energy is lost, but the total current is maintained. The impact of edge currents on the MHD equilibrium will be discussed

Clouds enhance Greenland ice sheet mass loss

Science.gov (United States)

Van Tricht, Kristof; Gorodetskaya, Irina V.; L'Ecuyer, Tristan; Lenaerts, Jan T. M.; Lhermitte, Stef; Noel, Brice; Turner, David D.; van den Broeke, Michiel R.; van Lipzig, Nicole P. M.

2015-04-01

Clouds have a profound influence on both the Arctic and global climate, while they still represent one of the key uncertainties in climate models, limiting the fidelity of future climate projections. The potentially important role of thin liquid-containing clouds over Greenland in enhancing ice sheet melt has recently gained interest, yet current research is spatially and temporally limited, focusing on particular events, and their large scale impact on the surface mass balance remains unknown. We used a combination of satellite remote sensing (CloudSat - CALIPSO), ground-based observations and climate model (RACMO) data to show that liquid-containing clouds warm the Greenland ice sheet 94% of the time. High surface reflectivity (albedo) for shortwave radiation reduces the cloud shortwave cooling effect on the absorbed fluxes, while not influencing the absorption of longwave radiation. Cloud warming over the ice sheet therefore dominates year-round. Only when albedo values drop below ~0.6 in the coastal areas during summer, the cooling effect starts to overcome the warming effect. The year-round excess of energy due to the presence of liquid-containing clouds has an extensive influence on the mass balance of the ice sheet. Simulations using the SNOWPACK snow model showed not only a strong influence of these liquid-containing clouds on melt increase, but also on the increased sublimation mass loss. Simulations with the Community Earth System Climate Model for the end of the 21st century (2080-2099) show that Greenland clouds contain more liquid water path and less ice water path. This implies that cloud radiative forcing will be further enhanced in the future. Our results therefore urge the need for improving cloud microphysics in climate models, to improve future projections of ice sheet mass balance and global sea level rise.

The Properties of Reconnection Current Sheets in GRMHD Simulations of Radiatively Inefficient Accretion Flows

Science.gov (United States)

Ball, David; Özel, Feryal; Psaltis, Dimitrios; Chan, Chi-Kwan; Sironi, Lorenzo

2018-02-01

Non-ideal magnetohydrodynamic (MHD) effects may play a significant role in determining the dynamics, thermal properties, and observational signatures of radiatively inefficient accretion flows onto black holes. In particular, particle acceleration during magnetic reconnection events may influence black hole spectra and flaring properties. We use representative general relativistic magnetohydrodynamic (GRMHD) simulations of black hole accretion flows to identify and explore the structures and properties of current sheets as potential sites of magnetic reconnection. In the case of standard and normal evolution (SANE) disks, we find that in the reconnection sites, the plasma beta ranges from 0.1 to 1000, the magnetization ranges from 10‑4 to 1, and the guide fields are weak compared with the reconnecting fields. In magnetically arrested (MAD) disks, we find typical values for plasma beta from 10‑2 to 103, magnetizations from 10‑3 to 10, and typically stronger guide fields, with strengths comparable to or greater than the reconnecting fields. These are critical parameters that govern the electron energy distribution resulting from magnetic reconnection and can be used in the context of plasma simulations to provide microphysics inputs to global simulations. We also find that ample magnetic energy is available in the reconnection regions to power the fluence of bright X-ray flares observed from the black hole in the center of the Milky Way.

Development of a current sheet in the wake of a fast coronal mass ejection

International Nuclear Information System (INIS)

Ling, A. G.; Webb, D. F.; Burkepile, J. T.; Cliver, E. W.

2014-01-01

A bright ray that developed in the wake of a fast coronal mass ejection (CME) on 2005 September 7 presents a unique opportunity to study the early development and physical characteristics of a reconnecting current sheet (CS). Polarization brightness images from the Mk4 K-Coronameter at the Mauna Loa Solar Observatory are used to determine the structure of the ray along its axis low in the corona as it progressed outward. Coverage of the early development of the ray out to ∼1.3 R ☉ for a period of ∼27 hr after the start of the event enables for the first time in white light a measurement of a CME CS from the top of the arcade to the base of the flux rope. Measured widths of the ray are combined to obtain the kinematics of the upper and lower Y- points described in reconnection flux-rope models such as that of Lin and Forbes. The time dependence of these points are used to derive values for the speed and acceleration of the growth of the CS. We note the appearance of a large structure which increases in size as it expands outward in the early development of the ray and an apparent oscillation with a period of ∼0.5 hr in the position angle of the ray.

Best Management Practice, Fact Sheet 2. Sheet Flow to Open Space

OpenAIRE

Sample, David; Doumar, Lia

2013-01-01

This publication explains what sheet flow to open space is, where and how it is used, their limitations, routine and nonroutine maintenance, expected costs, and a glossary of terms. This fact sheet is one of a 15-part series on urban stormwater management practices.

Combined influence of radiation absorption and Hall current effects on MHD double-diffusive free convective flow past a stretching sheet

Directory of Open Access Journals (Sweden)

G. Sreedevi

2016-03-01

Full Text Available An analysis has been carried out on the influence of radiation absorption, variable viscosity, Hall current of a magnetohydrodynamic free-convective flow and heat and mass transfer over a stretching sheet in the presence of heat generation/absorption. The fluid viscosity is assumed to vary as an inverse linear function of temperature. The boundary-layer equations governing the fluid flow, heat and mass transfer under consideration have been reduced to a system of nonlinear ordinary differential equations by employing a similarity transformation. Using the finite difference scheme, numerical solutions to the transform ordinary differential equations have been obtained and the results are presented graphically. The numerical results obtained are in good agreement with the existing scientific literature.

A high-power millimeter-wave sheet beam free-electron laser amplifier

International Nuclear Information System (INIS)

Cheng, S.; Destler, W.W.; Granatstein, V.L.; Antonsen, T.M.; Levush, B.; Rodgers, J.; Zhang, Z.X.

1996-01-01