Science.gov

Sample records for collisionless current sheets

  1. The model of a collisionless current sheet in a homogeneous gravity field

    NASA Astrophysics Data System (ADS)

    Veselovsky, Igor S.; Kislov, Roman A.; Malova, Helmi V.; Khabarova, Olga V.

    2016-10-01

    The self-consistent 1D kinetic Harris-like model of a collisionless current sheet is developed for the case of the current sheet experiencing the impact of an external uniform gravity field. The ambipolar Pannekoek-Rosseland electric field appears in the system as a result of the additional drift motion of ions and electrons. This produces separation of charges, which is responsible for corresponding changes of the current sheet form. The presence of gravitation leads to formation of asymmetric distributions of the magnetic field as well as the plasma and the current density changes. Our estimations show that gravity-forced disruptions of the current sheet profile may occur in the Mercurial magnetosphere and, most probable, in the Io plasma torus near the Jupiter. Also, the model can be applied to magnetospheres of exoplanets.

  2. Metastability of collisionless current sheets. Hannes Alfven Lecture on behalf of Albert Galeev

    NASA Astrophysics Data System (ADS)

    Zelenyi, L.; Galeev, A.

    2009-04-01

    Complicated magnetic configurations containing numerous magnetic field reversals are widespread in nature. Each of such reversals is supported by corresponding current sheet (CS) which could often have very small thickness comparable to ion skin depth. Since the beginning of Space Age "in situ" investigations of current sheets in the Earth's magnetosphere (magnetopause and magnetotail) acquired one of the highest priorities in national space programs and became one of the cornerstones of various international activities, like ISTP, IACG, and ILWS, which appeared to be very effective. Intense theoretical efforts were undertaken by theorists all over the world to develop both equilibrium models of current sheets and analyze its stability and further nonlinear evolution. Lack of collisions and smallness of many characteristic scales in comparison with ion Larmor radius made an application of straightforward MHD approach dramatically questionable. Professor Alfven was one of the first who suggested in 1968 simple but very physical self-consistent particle model of CS. One of the most intriguing features of current sheets in collisionless plasma is their ability to accumulate tremendous amounts of magnetic energy (1015 J for magnetospheric substorms , 1024 J for solar flare associated sheets) and then suddenly sometimes almost explosively release them. We will demonstrate in this talk that such METASTABILITY is a principal intrinsic feature of current sheets in hot plasma. Very intense theoretical debates of 80-ies and late 90-ies resulted in some consensus that current sheets with the small component of magnetic field normal to their plane become overstable for spontaneous reconnection (i.e. versus the development of ion tearing mode). Analysis of INTERBALL and especially 4- point CLUSTER data have shown that real current sheets observed in the Earth's magnetotail very rarely resemble simplistic HARRIS current sheets which have been used for an early stability

  3. Three dimensional instabilities of an electron scale current sheet in collisionless magnetic reconnection

    SciTech Connect

    Jain, Neeraj; Büchner, Jörg

    2014-06-15

    In collisionless magnetic reconnection, electron current sheets (ECS) with thickness of the order of an electron inertial length form embedded inside ion current sheets with thickness of the order of an ion inertial length. These ECS's are susceptible to a variety of instabilities which have the potential to affect the reconnection rate and/or the structure of reconnection. We carry out a three dimensional linear eigen mode stability analysis of electron shear flow driven instabilities of an electron scale current sheet using an electron-magnetohydrodynamic plasma model. The linear growth rate of the fastest unstable mode was found to drop with the thickness of the ECS. We show how the nature of the instability depends on the thickness of the ECS. As long as the half-thickness of the ECS is close to the electron inertial length, the fastest instability is that of a translational symmetric two-dimensional (no variations along flow direction) tearing mode. For an ECS half thickness sufficiently larger or smaller than the electron inertial length, the fastest mode is not a tearing mode any more and may have finite variations along the flow direction. Therefore, the generation of plasmoids in a nonlinear evolution of ECS is likely only when the half-thickness is close to an electron inertial length.

  4. The evolution of the ion diffusion region during collisionless magnetic reconnection in a force-free current sheet

    SciTech Connect

    Zhou, Fushun; Huang, Can Lu, Quanming; Wang, Shui; Xie, Jinlin

    2015-09-15

    Two-dimensional particle-in-cell simulation is performed to investigate magnetic reconnection in a force-free current sheet. The results show that the evolution of the ion diffusion region has two different phases. In the first phase, the electrons flow toward the X line along one pair of separatrices and away from the X line along the other pair of separatrices. Therefore, in the ion diffusion region, a distorted quadrupole structure of the out-of-plane magnetic field is formed, which is similar to that of a typical guide field reconnection in the Harris current sheet. In the second phase, the electrons move toward the X line along the separatrices and then flow away from the X line at the inner side of the separatrices. In the ion diffusion region, the out-of-plane magnetic field exhibits a characteristic quadrupole pattern with a good symmetry, which is similar to that of antiparallel reconnection in the Harris current sheet.

  5. An exact collisionless equilibrium for the Force-Free Harris Sheet with low plasma beta

    SciTech Connect

    Allanson, O. Neukirch, T. Wilson, F. Troscheit, S.

    2015-10-15

    We present a first discussion and analysis of the physical properties of a new exact collisionless equilibrium for a one-dimensional nonlinear force-free magnetic field, namely, the force-free Harris sheet. The solution allows any value of the plasma beta, and crucially below unity, which previous nonlinear force-free collisionless equilibria could not. The distribution function involves infinite series of Hermite polynomials in the canonical momenta, of which the important mathematical properties of convergence and non-negativity have recently been proven. Plots of the distribution function are presented for the plasma beta modestly below unity, and we compare the shape of the distribution function in two of the velocity directions to a Maxwellian distribution.

  6. Current sheets and pressure anisotropy in the reconnection exhaust

    SciTech Connect

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

    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.

  7. Dynamic of Current Sheets and Their Associated Particle Energization

    SciTech Connect

    Li, Hui; Guo, Fan; Makwan, Kirit; Li, Xiaocan; Zhandrin, Vladimir; Daughton, William Scott

    2015-08-19

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

  8. Marginal stability of thin current sheets in the Earth's magnetotail

    NASA Astrophysics Data System (ADS)

    Zelenyi, Lev; Artemiev, Anton; Malova, Helmi; Popov, Victor

    2008-02-01

    Experimental findings of the last decade shed new light on the physics of the magnetotail plasma system, e.g. investigation of very thin current sheets, and motivated a number of theoretical studies. An example of such theoretical investigations is the analytical 1D collisionless self-consistent model of thin current sheet [Zelenyi L.M., Malova, H.V., Popov, V.Yu., Delcourt, D., Sharma, A.S. 2004. Nonlinear equilibrium structure of thin currents sheets: influence of electron pressure anisotropy. Nonlinear Processes in Geophysics 11, 1-9]. The principal characteristic of this model is its anisotropy (typical features of thin current sheet). Because anisotropic current sheets have larger free energy than Harris' ones, we decided to revisit the classical problem of their stability. The linear tearing instability, as the most natural mechanism for the spontaneous reconnection of magnetic field lines, is investigated in the frame of our anisotropic model. We search for regions in the parameter space of the current sheet where the system could become unstable. The main region of instability is concentrated near Bn~0.1B0 and its width depends on the parameters of the system. This result conforms with an earlier work by Galeev and Zeleny [1976. Tearing instability in plasma configurations. Zhurnal Eksperimental'noi i Teoreticheskoi Fiziki, 70(6), 2133-2151(in Russian)], which suggested that tearing mode could develop in a limited region of Bn values (however, these gaps were erroneously ascribed to Harris equilibrium). Therefore, the current investigation of the stability of anisotropic current sheets in the magnetotail could help to extend the previous results about the stability of Harris-like current sheets with magnetized electrons, and have implications for the physics of substorm initiation.

  9. Suppression of collisionless magnetic reconnection in asymmetric current sheets

    NASA Astrophysics Data System (ADS)

    Liu, Yi-Hsin; Hesse, Michael

    2016-06-01

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

  10. Suppression of Collisionless Magnetic Reconnection in Asymmetric Current Sheets

    NASA Technical Reports Server (NTRS)

    Liu, Yi-Hsin; Hesse, Michael

    2016-01-01

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

  11. Influence of the dissipation mechanism on collisionless magnetic reconnection in symmetric and asymmetric current layers

    SciTech Connect

    Aunai, Nicolas; Hesse, Michael; Black, Carrie; Evans, Rebekah; Kuznetsova, Maria

    2013-04-15

    Numerical studies implementing different versions of the collisionless Ohm's law have shown a reconnection rate insensitive to the nature of the non-ideal mechanism occurring at the X line, as soon as the Hall effect is operating. Consequently, the dissipation mechanism occurring in the vicinity of the reconnection site in collisionless systems is usually thought not to have a dynamical role beyond the violation of the frozen-in condition. The interpretation of recent studies has, however, led to the opposite conclusion that the electron scale dissipative processes play an important dynamical role in preventing an elongation of the electron layer from throttling the reconnection rate. This work re-visits this topic with a new approach. Instead of focusing on the extensively studied symmetric configuration, we aim to investigate whether the macroscopic properties of collisionless reconnection are affected by the dissipation physics in asymmetric configurations, for which the effect of the Hall physics is substantially modified. Because it includes all the physical scales a priori important for collisionless reconnection (Hall and ion kinetic physics) and also because it allows one to change the nature of the non-ideal electron scale physics, we use a (two dimensional) hybrid model. The effects of numerical, resistive, and hyper-resistive dissipation are studied. In a first part, we perform simulations of symmetric reconnection with different non-ideal electron physics. We show that the model captures the already known properties of collisionless reconnection. In a second part, we focus on an asymmetric configuration where the magnetic field strength and the density are both asymmetric. Our results show that contrary to symmetric reconnection, the asymmetric model evolution strongly depends on the nature of the mechanism which breaks the field line connectivity. The dissipation occurring at the X line plays an important role in preventing the electron current layer

  12. Dissipation in Turbulent Plasma due to Reconnection in Thin Current Sheets

    SciTech Connect

    Sundkvist, David; Bale, Stuart D.; Retino, Alessandro; Vaivads, Andris

    2007-07-13

    We present in situ measurements in a space plasma showing that thin current sheets the size of an ion inertial length exist and are abundant in strong and intermittent plasma turbulence. Many of these current sheets exhibit the microphysical signatures of reconnection. The spatial scale where intermittency occurs corresponds to the observed structures. The reconnecting current sheets represent a type of dissipation mechanism, with observed dissipation rates comparable to or even dominating over collisionless damping rates of waves at ion inertial length scales (x100), and can have far reaching implications for small-scale dissipation in all turbulent plasmas.

  13. Reconnection in thin current sheets

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  14. Modeling Harris Current Sheets with Themis Observations

    NASA Technical Reports Server (NTRS)

    Kepko, L.; Angelopoulos, V.; McPherron, R. L.; Apatenkov, S.; Glassmeier, K.-H.

    2010-01-01

    Current sheets are ubiquitous in nature. occurring in such varied locations as the solar atmosphere. the heliosphere, and the Earth's magnetosphere. The simplest current sheet is the one-dimensional Harris neutral sheet, with the lobe field strength and scale-height the only free parameters. Despite its simplicity, confirmation of the Harris sheet as a reasonable description of the Earth's current sheet has remained elusive. In early 2009 the orbits of the 5 THEMIS probes fortuitously aligned such that profiles of the Earth's current sheet could be modeled in a time dependent manner. For the few hours of alignment we have calculated the time history of the current sheet parameters (scale height and current) in the near-Earth region. during both quiet and active times. For one particular substorm. we further demonstrate good quantitative agreement with the diversion of cross tail current inferred from the Harris modeling with the ionospheric current inferred from ground magnetometer data.

  15. Ohm's law for a current sheet

    NASA Technical Reports Server (NTRS)

    Lyons, L. R.; Speiser, T. W.

    1985-01-01

    The paper derives an Ohm's law for single-particle motion in a current sheet, where the magnetic field reverses in direction across the sheet. The result is considerably different from the resistive Ohm's law often used in MHD studies of the geomagnetic tail. Single-particle analysis is extended to obtain a self-consistency relation for a current sheet which agrees with previous results. The results are applicable to the concept of reconnection in that the electric field parallel to the current is obtained for a one-dimensional current sheet with constant normal magnetic field. Dissipated energy goes directly into accelerating particles within the current sheet.

  16. Theory of a Stationary Current-Free Double Layer in a Collisionless Plasma

    SciTech Connect

    Ahedo, Eduardo; Martinez Sanchez, Manuel

    2009-09-25

    Current-free double layers can develop in a collisionless, inertia-controlled plasma with two electron populations, expanding in a convergent-divergent nozzle. The double layer characteristics depend on whether they develop at the nozzle divergent side, convergent side, or throat. The divergent-geometry double layer describes faithfully the Hairapetian-Stenzel experiment [Phys. Rev. Lett. 65, 175 (1990)], whereas the two other types correspond with those studied in self-similar expansions and wall-collection models of similar plasmas.

  17. MHD bending waves in a current sheet

    NASA Technical Reports Server (NTRS)

    Musielak, Z. E.; Suess, S. T.

    1986-01-01

    Transverse MHD bending waves are considered in an isothermal and compressible two-dimensional current sheet of finite thickness in which the magnetic field changes direction and strength. The general form of the wave equation is obtained. It is shown that rotation of the magnetic field across the current sheet prevents the existence of singular points so that continuous spectrum solutions and the concomitant wave decay disappear. Instead, normal modes exist and closed integral solution for arbitrary current sheet structure are found. The results are discussed in terms of small-scale waves on the heliospheric current sheet.

  18. A Semianalytical Ion Current Model for Radio Frequency Driven Collisionless Sheaths

    NASA Technical Reports Server (NTRS)

    Bose, Deepak; Govindan, T. R.; Meyyappan, M.; Arnold, Jim (Technical Monitor)

    2001-01-01

    We propose a semianalytical ion dynamics model for a collisionless radio frequency biased sheath. The model uses bulk plasma conditions and electrode boundary condition to predict ion impact energy distribution and electrical properties of the sheath. The proposed model accounts for ion inertia and ion current modulation at bias frequencies that are of the same order of magnitude as the ion plasma frequency. A relaxation equation for ion current oscillations is derived which is coupled with a damped potential equation in order to model ion inertia effects. We find that inclusion of ion current modulation in the sheath model shows marked improvements in the predictions of sheath electrical properties and ion energy distribution function.

  19. Reconnection properties in collisionless plasma with open boundary conditions

    SciTech Connect

    Sun, H. E.; Ma, Z. W.; Huang, J.

    2014-07-15

    Collisionless magnetic reconnection in a Harris current sheet with different initial thicknesses is investigated using a 21/2 -D Darwin particle-in-cell simulation with the magnetosonic open boundary condition. It is found that the thicknesses of the ion dissipation region and the reconnection current sheet, when the reconnection rate E{sub r} reaches its first peak, are independent of the initial thickness of the current sheet; while the peak reconnection rate depends on it. The peak reconnection rate increases with decrease of the current sheet thickness as E{sub r}∼a{sup −1/2}, where a is the initial current sheet half-thickness.

  20. Experimental Study of Lower-hybrid Drift Turbulence in a Reconnecting Current Sheet

    SciTech Connect

    Carter, T. A.; Yamada, M.; Ji, H.; Kulsrud, R. M.; Trintchouck, F.

    2002-06-18

    The role of turbulence in the process of magnetic reconnection has been the subject of a great deal of study and debate in the theoretical literature. At issue in this debate is whether turbulence is essential for fast magnetic reconnection to occur in collisionless current sheets. Some theories claim it is necessary in order to provide anomalous resistivity, while others present a laminar fast reconnection mechanism based on the Hall term in the generalized Ohm's law. In this work, a thorough study of electrostatic potential fluctuations in the current sheet of the Magnetic Reconnection Experiment (MRX) [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)] was performed in order to ascertain the importance of turbulence in a laboratory reconnection experiment. Using amplified floating Langmuir probes, broadband fluctuations in the lower hybrid frequency range (fLH approximately 5-15 MHz) were measured which arise with the formation of the current sheet in MRX. The frequency spectrum, spatial amplitude profile, and spatial correlation characteristics of the measured turbulence were examined carefully, finding consistency with theories of the lower-hybrid drift instability (LHDI). The LHDI and its role in magnetic reconnection has been studied theoretically for decades, but this work represents the first detection and detailed study of the LHDI in a laboratory current sheet. The observation of the LHDI in MRX has provided the unique opportunity to uncover the role of this instability in collisionless reconnection. It was found that: (1) the LHDI fluctuations are confined to the low-beta edge of current sheets in MRX; (2) the LHDI amplitude does not correlate well in time or space with the reconnection electric field, which is directly related to the rate of reconnection; and (3) significant LHDI amplitude persists in high collisionality current sheets where the reconnection rate is classical. These findings suggest that the measured LHDI fluctuations do not play an

  1. Structure of the Magnetotail Current Sheet

    NASA Technical Reports Server (NTRS)

    Larson, Douglas J.; Kaufmann, Richard L.

    1996-01-01

    An orbit tracing technique was used to generate current sheets for three magnetotail models. Groups of ions were followed to calculate the resulting cross-tail current. Several groups then were combined to produce a current sheet. The goal is a model in which the ions and associated electrons carry the electric current distribution needed to generate the magnetic field B in which ion orbits were traced. The region -20 R(E) less than x less than -14 R(E) in geocentric solar magnetospheric coordinates was studied. Emphasis was placed on identifying the categories of ion orbits which contribute most to the cross-tail current and on gaining physical insight into the manner by which the ions carry the observed current distribution. Ions that were trapped near z = 0, ions that magnetically mirrored throughout the current sheet, and ions that mirrored near the Earth all were needed. The current sheet structure was determined primarily by ion magnetization currents. Electrons of the observed energies carried relatively little cross-tail current in these quiet time current sheets. Distribution functions were generated and integrated to evaluate fluid parameters. An earlier model in which B depended only on z produced a consistent current sheet, but it did not provide a realistic representation of the Earth's middle magnetotail. In the present study, B changed substantially in the x and z directions but only weakly in the y direction within our region of interest. Plasmas with three characteristic particle energies were used with each of the magnetic field models. A plasma was found for each model in which the density, average energy, cross-tail current, and bulk flow velocity agreed well with satellite observations.

  2. RADIATING CURRENT SHEETS IN THE SOLAR CHROMOSPHERE

    SciTech Connect

    Goodman, Michael L.; Judge, Philip G. E-mail: judge@ucar.edu

    2012-05-20

    An MHD model of a hydrogen plasma with flow, an energy equation, NLTE ionization and radiative cooling, and an Ohm's law with anisotropic electrical conduction and thermoelectric effects is used to self-consistently generate atmospheric layers over a 50 km height range. A subset of these solutions contains current sheets and has properties similar to those of the lower and middle chromosphere. The magnetic field profiles are found to be close to Harris sheet profiles, with maximum field strengths {approx}25-150 G. The radiative flux F{sub R} emitted by individual sheets is {approx}4.9 Multiplication-Sign 10{sup 5}-4.5 Multiplication-Sign 10{sup 6} erg cm{sup -2} s{sup -1}, to be compared with the observed chromospheric emission rate of {approx}10{sup 7} erg cm{sup -2} s{sup -1}. Essentially all emission is from regions with thicknesses {approx}0.5-13 km containing the neutral sheet. About half of F{sub R} comes from sub-regions with thicknesses 10 times smaller. A resolution {approx}< 5-130 m is needed to resolve the properties of the sheets. The sheets have total H densities {approx}10{sup 13}-10{sup 15} cm{sup -3}. The ionization fraction in the sheets is {approx}2-20 times larger, and the temperature is {approx}2000-3000 K higher than in the surrounding plasma. The Joule heating flux F{sub J} exceeds F{sub R} by {approx}4%-34%, the difference being balanced in the energy equation mainly by a negative compressive heating flux. Proton Pedersen current dissipation generates {approx}62%-77% of the positive contribution to F{sub J} . The remainder of this contribution is due to electron current dissipation near the neutral sheet where the plasma is weakly magnetized.

  3. The Jovian magnetotail and its current sheet

    NASA Technical Reports Server (NTRS)

    Behannon, K. W.; Burlaga, L. F.; Ness, N. F.

    1980-01-01

    Analyses of Voyager magnetic field measurements have extended the understanding of the structural and temporal characteristics of Jupiter's magnetic tail. The magnitude of the magnetic field in the lobes of the tail is found to decrease with Jovicentric distance approximately as r to he-1.4, compared with the power law exponent of -1.7 found for the rate of decrease along the Pioneer 10 outbound trajectory. Voyager observations of magnetic field component variations with Jovicentric distance in the tail do not support the uniform radial plasma outflow model derived from Pioneer data. Voyager 2 has shown that the azimuthal current sheet which surrounds Jupiter in the inner and middle magnetosphere extends tailward (in the anti-Sun direction) to a distance of at least 100 R sub J. In the tail this current sheet consists of a plasma sheet and embedded neutral sheet. In the region of the tail where the sheet is observed, the variation of the magnetic field as a result of the sheet structure and its 10 hr periodic motion is the dominant variation seen.

  4. Charged particle dynamics in turbulent current sheets

    NASA Astrophysics Data System (ADS)

    Artemyev, A. V.; Vainchtein, D. L.; Neishtadt, A. I.; Zelenyi, L. M.

    2016-05-01

    We study dynamics of charged particle in current sheets with magnetic fluctuations. We use the adiabatic theory to describe the nonperturbed charged particle motion and show that magnetic field fluctuations destroy the adiabatic invariant. We demonstrate that the evolution of particle adiabatic invariant's distribution is described by a diffusion equation and derive analytical estimates of the rate of adiabatic invariant's diffusion. This rate is proportional to power density of magnetic field fluctuations. We compare analytical estimates with numerical simulations. We show that adiabatic invariant diffusion results in transient particles trapping in the current sheet. For magnetic field fluctuation amplitude a few times larger than a normal magnetic field component, more than 50% of transient particles become trapped. We discuss the possible consequences of destruction of adiabaticity of the charged particle motion on the state of the current sheets.

  5. On ballooning instability in current sheets

    NASA Astrophysics Data System (ADS)

    Leonovich, Anatoliy; Kozlov, Daniil

    2015-06-01

    The problem of instability of the magnetotail current sheet to azimuthally small-scale Alfvén and slow magnetosonic (SMS) waves is solved. The solutions describe unstable oscillations in the presence of a current sheet and correspond to the region of stretched closed field lines of the magnetotail. The spectra of eigen-frequencies of several basic harmonics of standing Alfvén and SMS waves are found in the local and WKB approximation, which are compared. It is shown that the oscillation properties obtained in these approximations differ radically. In the local approximation, the Alfvén waves are stable in the entire range of magnetic shells. SMS waves go into the aperiodic instability regime (the regime of the "ballooning" instability), on magnetic shells crossing the current sheet. In the WKB approximation, both the Alfvén and SMS oscillations go into an unstable regime with a non-zero real part of their eigen-frequency, on magnetic shells crossing the current sheet. The structure of azimuthally small-scale Alfvén waves across magnetic shells is determined.

  6. The current-voltage relationship in auroral current sheets

    NASA Technical Reports Server (NTRS)

    Weimer, D. R.; Gurnett, D. A.; Goertz, C. K.; Menietti, J. D.; Burch, J. L.

    1987-01-01

    The current-voltage relation within narrow auroral current sheets is examined through the use of high-resolution data from the high altitude Dynamics Explorer 1 satellite. The north-south perpendicular electric field and the east-west magnetic field are shown for three cases in which there are large amplitude, oppositely directed paired electric fields and narrow current sheets. These data are shown to indicate that there is a linear Ohm's law relationship between the current density and the parallel potential drop within the narrow current sheets. This linear relationship had previously been verified for large-scale auroral formations greater than 20 km wide at the ionosphere. The evidence shown here extends our knowledge down to the scale size of discrete auroral arcs.

  7. Formation of current sheets in magnetic reconnection

    SciTech Connect

    Boozer, Allen H.

    2014-07-15

    An ideal evolution of magnetic fields in three spatial dimensions tends to cause neighboring field lines to increase their separation exponentially with distance ℓ along the lines, δ(ℓ)=δ(0)e{sup σ(ℓ)}. The non-ideal effects required to break magnetic field line connections scale as e{sup −σ}, so the breaking of connections is inevitable for σ sufficiently large—even though the current density need nowhere be large. When the changes in field line connections occur rapidly compared to an Alfvén transit time, the constancy of j{sub ||}/B along the magnetic field required for a force-free equilibrium is broken in the region where the change occurs, and an Alfvénic relaxation of j{sub ||}/B occurs. Independent of the original spatial distribution of j{sub ||}/B, the evolution is into a sheet current, which is stretched by a factor e{sup σ} in width and contracted by a factor e{sup σ} in thickness with the current density j{sub ||} increasing as e{sup σ}. The dissipation of these sheet currents and their associated vorticity sheets appears to be the mechanism for transferring energy from a reconnecting magnetic field to a plasma. Harris sheets, which are used in models of magnetic reconnection, are shown to break up in the direction of current flow when they have a finite width and are in a plasma in force equilibrium. The dependence of the longterm nature of magnetic reconnection in systems driven by footpoint motion can be studied in a model that allows qualitative variation in the nature of that motion: slow or fast motion compared to the Alfvén transit time and the neighboring footpoints either exponentially separating in time or not.

  8. Thin current sheets in the presence of a guiding magnetic field in Earth's magnetosphere

    NASA Astrophysics Data System (ADS)

    Malova, H. V.; Popov, V. Y.; Mingalev, O. V.; Mingalev, I. V.; Mel'nik, M. N.; Artemyev, A. V.; Petrukovich, A. A.; Delcourt, D. C.; Shen, C.; Zelenyi, L. M.

    2012-04-01

    A self-consistent theory of relatively thin anisotropic current sheets (TCS) in collisionless plasma is developed, taking into account the presence of a guiding field By (all notations are used in the GSM coordinate system). TCS configurations with a finite value of guiding field By are often observed in Earth's magnetotail and are typical for Earth's magnetopause. A characteristic signature of such configurations is the existence of a magnetic field component along the direction of TCS current. A general case is considered in this paper with global sheared magnetic field By = const. Analytical and numerical (particle-in-cell) models for such plasma equilibria are analyzed and compared with each other as well as with Cluster observations. It is shown that, in contrast to the case with By = 0, the character of “particle-current sheet” interaction is drastically changed in the case of a global magnetic shear. Specifically, serpentine-like parts of ion trajectories in the neutral plane become more tortuous, leading to a thicker current sheet. The reflection coefficient of particles coming from northern and southern sources also becomes asymmetric and depends upon the value of the By component. As a result, the degree of asymmetry of magnetic field, plasma, and current density profiles appears characteristic of current sheets with a constant By. In addition, in the presence of nonzero guiding field, the curvature current of electrons in the center of the current sheet decreases, yielding an effective thickening of the sheet. Implications of these results for current sheets in Earth's magnetosphere are discussed.

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

    NASA Astrophysics Data System (ADS)

    Howes, Gregory G.

    2016-08-01

    Turbulence profoundly affects particle transport and plasma heating in many astrophysical plasma environments, from galaxy clusters to the solar corona and solar wind to Earth's magnetosphere. Both fluid and kinetic simulations of plasma turbulence ubiquitously generate coherent structures, in the form of current sheets, at small scales, and the locations of these current sheets appear to be associated with enhanced rates of dissipation of the turbulent energy. Therefore, illuminating the origin and nature of these current sheets is critical to identifying the dominant physical mechanisms of dissipation, a primary aim at the forefront of plasma turbulence research. Here, we present evidence from nonlinear gyrokinetic simulations that strong nonlinear interactions between counterpropagating Alfvén waves, or strong Alfvén wave collisions, are a natural mechanism for the generation of current sheets in plasma turbulence. Furthermore, we conceptually explain this current sheet development in terms of the nonlinear dynamics of Alfvén wave collisions, showing that these current sheets arise through constructive interference among the initial Alfvén waves and nonlinearly generated modes. The properties of current sheets generated by strong Alfvén wave collisions are compared to published observations of current sheets in the Earth's magnetosheath and the solar wind, and the nature of these current sheets leads to the expectation that Landau damping of the constituent Alfvén waves plays a dominant role in the damping of turbulently generated current sheets.

  10. Collisionless current generation in the center of the tokamak plasma by an isotropic source of {alpha}-particles

    SciTech Connect

    Ilgisonis, V. I.; Sorokina, E. A.; Yurchenko, E. I.

    2010-01-15

    The density of the noninductive current generated due to collisionless motion of {alpha}-particles in the tokamak magnetic field is calculated. The analysis is based on fully three-dimensional calculations of charged particle trajectories without simplifying assumptions typical for drift and neoclassical approaches. The current is calculated over the entire cross section of the plasma column, including the magnetic axis. It is shown that the current density is not a function of a magnetic surface and is strongly polarized over the poloidal angle. The current density distribution in the tokamak poloidal cross section is obtained, and the current density as a function of the safety factor, the tokamak aspect ratio, and the ratio of the particle Larmor radius on the axis to the tokamak minor radius is determined. It is shown that, when the source of {alpha}-particles is spatially nonuniform, the current density in the center of the tokamak is nonzero due to asymmetry of the phase-space boundary between trapped and passing particles. The current density scaling in the tokamak center differs from the known approximations for the bootstrap current and is sensitive to the spatial distribution of {alpha}-particles.

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

    DOE PAGESBeta

    Akçay, Cihan; Daughton, William; Lukin, Vyacheslav S.; Liu, Yi-Hsin

    2016-01-01

    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. Because 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 indicatemore » 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. As a results this theory yields a flat oblique spectrum and underestimates the growth of oblique modes in a similar manner to kinetic theory relative to kinetic simulations.« less

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

    SciTech Connect

    Akçay, Cihan; Daughton, William; Lukin, Vyacheslav S.; Liu, Yi-Hsin

    2016-01-01

    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. Because 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. As a results this theory yields a flat oblique spectrum and underestimates the growth of oblique modes in a similar manner to kinetic theory relative to kinetic simulations.

  13. Effects of electron pressure anisotropy on current sheet configuration

    NASA Astrophysics Data System (ADS)

    Artemyev, A. V.; Vasko, I. Y.; Angelopoulos, V.; Runov, A.

    2016-09-01

    Recent spacecraft observations in the Earth's magnetosphere have demonstrated that the magnetotail current sheet can be supported by currents of anisotropic electron population. Strong electron currents are responsible for the formation of very thin (intense) current sheets playing the crucial role in stability of the Earth's magnetotail. We explore the properties of such thin current sheets with hot isotropic ions and cold anisotropic electrons. Decoupling of the motions of ions and electrons results in the generation of a polarization electric field. The distribution of the corresponding scalar potential is derived from the electron pressure balance and the quasi-neutrality condition. We find that electron pressure anisotropy is partially balanced by a field-aligned component of this polarization electric field. We propose a 2D model that describes a thin current sheet supported by currents of anisotropic electrons embedded in an ion-dominated current sheet. Current density profiles in our model agree well with THEMIS observations in the Earth's magnetotail.

  14. Current sheet interaction and particle acceleration in the Jovian magnetosphere

    NASA Astrophysics Data System (ADS)

    Cheng, A. F.

    1990-04-01

    The thin, rapidly rotating current sheet in Jupiter's magnetodisk can energize heavy ions by hundreds of keV. If the magnetic field lines are azimuthally swept back, energetic ions undergoing nonadiabatic current sheet interactions will step radially outward and be centrifugally energized. Estimated energization times can be comparable to the Jovian rotation period. Nonadiabatic interactions with the rotating Jovian current sheet may be an important energization mechanism for heavy ions, but are not effective for energizing electrons or light ions like protons.

  15. Spatial variation of cosmic rays near the heliospheric current sheet

    NASA Technical Reports Server (NTRS)

    Jokipii, J. R.; Kota, J.

    1985-01-01

    A quantitative comparison between theoretical predictions and observations of the intensity of galactic cosmic rays near the interplanetary current sheet is reported. Comparison of model calculations is made with a statistical analysis of observations of galactic cosmic rays at Earth and the simultaneous position of the current sheet. An ensemble of different current sheet inclinations is used, in order to make the analysis of the computations approximate the method used to analyses the data.

  16. A comparison of coronal and interplanetary current sheet inclinations

    NASA Technical Reports Server (NTRS)

    Behannon, K. W.; Burlaga, L. F.; Hundhausen, A. J.

    1983-01-01

    The HAO white light K-coronameter observations show that the inclination of the heliospheric current sheet at the base of the corona can be both large (nearly vertical with respect to the solar equator) or small during Cararington rotations 1660 - 1666 and even on a single solar rotation. Voyager 1 and 2 magnetic field observations of crossing of the heliospheric current sheet at distances from the Sun of 1.4 and 2.8 AU. Two cases are considered, one in which the corresponding coronameter data indicate a nearly vertical (north-south) current sheet and another in which a nearly horizontal, near equatorial current sheet is indicated. For the crossings of the vertical current sheet, a variance analysis based on hour averages of the magnetic field data gave a minimum variance direction consistent with a steep inclination. The horizontal current sheet was observed by Voyager as a region of mixed polarity and low speeds lasting several days, consistent with multiple crossings of a horizontal but irregular and fluctuating current sheet at 1.4 AU. However, variance analysis of individual current sheet crossings in this interval using 1.92 see averages did not give minimum variance directions consistent with a horizontal current sheet.

  17. Basic mechanisms controlling the sweeping efficiency of propagating current sheets

    NASA Astrophysics Data System (ADS)

    Berkery, J. W.; Choueiri, E. Y.

    2006-02-01

    The basic mechanisms controlling the sweeping efficiency of propagating current sheets are investigated through experiments and analytical modelling. The sweeping efficiency of a current sheet in a parallel plate gas-fed pulsed plasma accelerator is defined as the ratio of the current sheet mass to the total available propellant mass. Permeability of neutrals through the sheet, and leakage of mass out of the sheet and into a cathode wake, decrease the sweeping efficiency. The sweeping efficiency of current sheets in argon, neon, helium and hydrogen propellants at different initial pressures was determined through measurements of sheet velocity with high speed photography and of sheet mass with laser interferometry. The mechanism that controls the sweeping efficiency of propagating current sheets was found to be an interplay of two processes: the flux of mass entering the sheet and the leakage of mass at the cathode, with the former dependent on the degree of permeability and the latter dependent on the level of ion current as determined by the ion Hall parameter.

  18. Bashful Ballerina: Southward shifted Heliospheric Current Sheet

    NASA Astrophysics Data System (ADS)

    Mursula, K.; Hiltula, T.

    It is known since long (Rosenberg and Coleman, 1969) that one of the two sectors of the interplanetary magnetic field (IMF) observed at the Earth's orbit dominates at high heliographic latitudes during solar minimum times, reflecting the poloidal structure of the global solar magnetic field at these times. Here we find that while this latitudinal variation of the dominant IMF sector around the solar equator is valid for both solar hemispheres during the last four solar minima covered by direct observations, it is systematically more strongly developed in the northern heliographic hemisphere. This implies that the average heliospheric current sheet is shifted or coned southward during solar minimum times, suggesting that the temporary southward shift of the heliosheet found earlier by Ulysses observations in 1995 is a persistent pattern. This also implies that the open solar magnetic field is north-south asymmetric at these times, suggesting that the solar dynamo has an asymmetric component. Accordingly, the Sun with the heliosheet is like a bashful ballerina who is repeatedly trying to push her excessively high flaring skirt downward. However, the effective shift at 1 AU is only a few degrees, allowing the Rosenberg-Coleman rule to be valid, on an average, in both hemispheres during solar minima.

  19. Bashful ballerina: Southward shifted heliospheric current sheet

    NASA Astrophysics Data System (ADS)

    Mursula, K.; Hiltula, T.

    2003-11-01

    It is known since long [Rosenberg and Coleman, 1969] that one of the two sectors of the interplanetary magnetic field (IMF) observed at the Earth's orbit dominates at high heliographic latitudes during solar minimum times, reflecting the poloidal structure of the global solar magnetic field at these times. Here we find that while this latitudinal variation of the dominant IMF sector around the solar equator is valid for both solar hemispheres during the last four solar minima covered by direct observations, it is systematically more strongly developed in the northern heliographic hemisphere. This implies that the average heliospheric current sheet is shifted or coned southward during solar minimum times, suggesting that the temporary southward shift of the heliosheet found earlier by Ulysses observations in 1995 is a persistent pattern. This also implies that the open solar magnetic field is north-south asymmetric at these times, suggesting that the solar dynamo has an asymmetric component. Accordingly, the Sun with the heliosheet is like a bashful ballerina who is repeatedly trying to push her excessively high flaring skirt downward. However, the effective shift at 1 AU is only a few degrees, allowing the Rosenberg-Coleman rule to be valid, on an average, in both hemispheres during solar minima.

  20. Current status of liquid sheet radiator research

    NASA Technical Reports Server (NTRS)

    Chubb, Donald L.; Calfo, Frederick D.; Mcmaster, Matthew S.

    1993-01-01

    Initial research on the external flow, low mass liquid sheet radiator (LSR), has been concentrated on understanding its fluid mechanics. The surface tension forces acting at the edges of the sheet produce a triangular planform for the radiating surface of width, W, and length, L. It has been experimentally verified that (exp L)/W agrees with the theoretical result, L/W = (We/8)exp 1/2, where We is the Weber number. Instability can cause holes to form in regions of large curvature such as where the edge cylinders join the sheet of thickness, tau. The W/tau limit that will cause hole formation with subsequent destruction of the sheet has yet to be reached experimentally. Although experimental measurements of sheet emissivity have not yet been performed because of limited program scope, calculations of the emissivity and sheet lifetime is determined by evaporation losses were made for two silicon based oils; Dow Corning 705 and Me(sub 2). Emissivities greater than 0.75 are calculated for tau greater than or equal to 200 microns for both oils. Lifetimes for Me(sub 2) are much longer than lifetimes for 705. Therefore, Me(sub 2) is the more attractive working fluid for higher temperatures (T greater than or equal to 400 K).

  1. High beta plasma in the dynamic Jovian current sheet

    NASA Technical Reports Server (NTRS)

    Walker, R. J.; Kivelson, M. G.; Schardt, A. W.

    1978-01-01

    The equatorial current sheet, which Pioneer 10 repeatedly encountered on its outbound pass through the Jovian magnetosphere, frequently was associated with intense fluxes of energetic protons. Simultaneous observations of the changes in the energetic proton flux and in the magnetic-field magnitude demonstrate that the current sheet is embedded in a high-beta plasma in which high-energy (above 60 keV) ions frequently are the dominant constituents. Large differences in the plasma temperature and the thickness of this plasma sheet between encounters only 10 hours apart indicate that the Jovian plasma sheet is very dynamic on a time scale of hours. Occasional observations of significant temporal variations in the magnetic field and particle populations during periods within the plasma sheet may represent in situ observations of Jovian magnetic disturbances. Comparison with previous observations suggests that low-energy (not more than 5 keV) plasma contributes less than 3% to the current-sheet energy density.

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

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

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

  3. Magnetorotational instability, current relaxation, and current-vortex sheet

    SciTech Connect

    Silveira, F. E. M.; Galvão, R. M. O.

    2013-08-15

    The conjugate effect of current relaxation and of current-vortex sheet formation on the magnetorotational instability is explored in a conducting fluid. It is found that the relative amplification of the magnetic viscosity from marginal stability to the instability determined by the maximum growth rate is around 924% when resistive effects dominate, while the corresponding quantity is around 220% in the ideal limit. This shows that the conjugate influence is much more efficient to amplify the magnetic viscosity than just the effect due to the standard magnetic tension. It is also found that the magnitude of the magnetic viscosity is effectively enhanced by the conjugate influence. The results presented here may contribute to the understanding of the various processes that play a significant role in the mechanism of anomalous viscosity observed in Keplerian disks. It is argued that the new effect shall be relevant in thin accretion disks. It is also mentioned that the proposed formulation may be of interest for some theories of magnetic reconnection. Possible extensions of this work are suggested.

  4. Proton Temperature Anisotropy and Magnetic Reconnection in the Solar Wind: Effects of Kinetic Instabilities on Current Sheet Stability

    NASA Astrophysics Data System (ADS)

    Matteini, L.; Landi, S.; Velli, M.; Matthaeus, W. H.

    2013-02-01

    We investigate the role of kinetic instabilities driven by a proton anisotropy on the onset of magnetic reconnection by means of two-dimensional hybrid simulations. The collisionless tearing of a current sheet is studied in the presence of a proton temperature anisotropy in the surrounding plasma. Our results confirm that anisotropic protons within the current sheet region can significantly enhance/stabilize the tearing instability of the current. Moreover, fluctuations associated with linear instabilities excited by large proton temperature anisotropies can significantly influence the stability of the plasma and perturb the current sheets, triggering the tearing instability. We find that such a complex coupling leads to a faster tearing evolution in the T_\\perp >T_\\Vert regime when an ion-cyclotron instability is generated by the anisotropic proton distribution functions. On the contrary, in the presence of the opposite anisotropy, fire-hose fluctuations excited by the unstable background protons with T_\\Vert are not able to efficiently destabilize current sheets, which remain stable for a long time after fire-hose saturation. We discuss possible influences of this novel coupling on the solar wind and heliospheric plasma dynamics.

  5. PROTON TEMPERATURE ANISOTROPY AND MAGNETIC RECONNECTION IN THE SOLAR WIND: EFFECTS OF KINETIC INSTABILITIES ON CURRENT SHEET STABILITY

    SciTech Connect

    Matteini, L.; Landi, S.; Velli, M.; Matthaeus, W. H.

    2013-02-15

    We investigate the role of kinetic instabilities driven by a proton anisotropy on the onset of magnetic reconnection by means of two-dimensional hybrid simulations. The collisionless tearing of a current sheet is studied in the presence of a proton temperature anisotropy in the surrounding plasma. Our results confirm that anisotropic protons within the current sheet region can significantly enhance/stabilize the tearing instability of the current. Moreover, fluctuations associated with linear instabilities excited by large proton temperature anisotropies can significantly influence the stability of the plasma and perturb the current sheets, triggering the tearing instability. We find that such a complex coupling leads to a faster tearing evolution in the T{sub Up-Tack} > T{sub ||} regime when an ion-cyclotron instability is generated by the anisotropic proton distribution functions. On the contrary, in the presence of the opposite anisotropy, fire-hose fluctuations excited by the unstable background protons with T{sub ||} < T{sub Up-Tack} are not able to efficiently destabilize current sheets, which remain stable for a long time after fire-hose saturation. We discuss possible influences of this novel coupling on the solar wind and heliospheric plasma dynamics.

  6. Explosive magnetic reconnection caused by an X-shaped current-vortex layer in a collisionless plasma

    SciTech Connect

    Hirota, M.; Hattori, Y.; Morrison, P. J.

    2015-05-15

    A mechanism for explosive magnetic reconnection is investigated by analyzing the nonlinear evolution of a collisionless tearing mode in a two-fluid model that includes the effects of electron inertia and temperature. These effects cooperatively enable a fast reconnection by forming an X-shaped current-vortex layer centered at the reconnection point. A high-resolution simulation of this model for an unprecedentedly small electron skin depth d{sub e} and ion-sound gyroradius ρ{sub s}, satisfying d{sub e}=ρ{sub s}, shows an explosive tendency for nonlinear growth of the tearing mode, where it is newly found that the explosive widening of the X-shaped layer occurs locally around the reconnection point with the length of the X shape being shorter than the domain length and the wavelength of the linear tearing mode. The reason for the onset of this locally enhanced reconnection is explained theoretically by developing a novel nonlinear and nonequilibrium inner solution that models the local X-shaped layer, and then matching it to an outer solution that is approximated by a linear tearing eigenmode with a shorter wavelength than the domain length. This theoretical model proves that the local reconnection can release the magnetic energy more efficiently than the global one and the estimated scaling of the explosive growth rate agrees well with the simulation results.

  7. Eruptive Current Sheets Trailing SOHO/LASCO CMEs

    NASA Astrophysics Data System (ADS)

    Webb, David F.

    2015-04-01

    Current sheets are important signatures of magnetic reconnection during the eruption of solar magnetic structures. Many models of eruptive flare/Coronal Mass Ejections (CMEs) involve formation of a current sheet connecting the ejecting CME flux rope with the post-eruption magnetic loop arcade. Current sheets have been interpreted in white light images as narrow rays trailing the outward-moving CME, in ultraviolet spectra as narrow, bright hot features, and with different manifestations in other wavebands. This study continues that of Webb et al. (2003), who analyzed SMM white light CMEs having candidate magnetic disconnection features at the base of the CME. About half of those were followed by coaxial, bright rays suggestive of newly formed current sheets, and Webb et al. (2003) presented detailed results of analysis of those structures. In this work we extend the study of white light eruptive current sheets to the more sensitive and extensive SOHO/LASCO coronagraph data on CMEs. We comprehensively examined all LASCO CMEs during two periods that we identify with the minimum and maximum activity of solar cycle 23. We identified ~130 ray/current sheets during these periods, nearly all of which trailed CMEs with concave-outward backs. The occurrence rate of the ray/current sheets is 6-7% of all CMEs, irrespective of the solar cycle. We analyze the rays for durations, speeds, alignments, and motions and compare the observational results with some model predictions.

  8. Dynamic Response of Magnetic Reconnection Due to Current Sheet Variability

    NASA Astrophysics Data System (ADS)

    George, D. E.; Jahn, J. M.; Burch, J. L.; Hesse, M.; Pollock, C. J.

    2014-12-01

    Magnetic reconnection is a process which regulates the interaction between regions of magnetized plasma. While many factors have an impact on the evolution of this process, there still remains a lack of understanding of the key behaviors involved in the triggering of fast reconnection. Despite an abundance of in-situ measurements, indicating the high degree of variability in the thickness, density and composition along the current sheet, no simulation studies exist which account for such current sheet variations. 2D and 3D simulations have a periodic boundary in the dimension along the current sheet and so tend to neglect these variations in the current sheet originating external to the modeled reconnection region. Here we focus on the effects on reconnection due to the variability in the thickness and density of the current sheet. Using 2.5D kinetic simulations of 2-species plasma, we isolate and explore the dynamic effects on reconnection associated with variations in the current sheet originating externally to the reconnection region. While periodic boundary conditions are still used, in the direction along the current sheet, a step-change perturbation in thickness or density of the current sheet is introduced once a stable reconnection rate is reached. The dynamic response of the overall system, after introducing the perturbation, is then evaluated, with a focus on the reconnection rate. When the reconnection rate is slowed significantly over time, loading of the inflow region occurs (a build-up of plasma and magnetic energy/pressure. This state is indicated by an asymptotic behavior in the reconnection rate over time. If a sudden variation in the current sheet is introduced under these conditions, a resultant triggering of fast reconnection may occur, which could lead to an episode of fast reconnection, saw-tooth-crash condition or even act as a trigger for sub-storms.

  9. Prediction of the heliospheric current sheet tilt: 1992-1996

    SciTech Connect

    Suess, S.T. ); McComas, D.J. ); Hoeksema, J.T. )

    1993-02-05

    Heliospheric current sheet tilt evolves systematically over the solar cycle. Here the authors show that this evolution is different than the sunspot cycle and that tilt for the period 1992-1996 can be predicted using persistence. That is, the tilt over the coming cycle will be the same as for the past cycle. The Ulysses spacecraft has passed Jupiter and is moving out of the plane of the ecliptic, so they use the prediction of the changing heliospheric current sheet tilt to predict that Ulysses will pass beyond the envelope, or maximum latitude, of the heliospheric current sheet in November 1993. 10 refs., 6 figs.

  10. Eigenmodes of quasi-static magnetic islands in current sheet

    SciTech Connect

    Li Yi; Cai Xiaohui; Chai Lihui; Wang Shui; Zheng Huinan; Shen Chao

    2011-12-15

    As observation have shown, magnetic islands often appear before and/or after the onset of magnetic reconnections in the current sheets, and they also appear in the current sheets in the solar corona, Earth's magnetotail, and Earth's magnetopause. Thus, the existence of magnetic islands can affect the initial conditions in magnetic reconnection. In this paper, we propose a model of quasi-static magnetic island eigenmodes in the current sheet. This model analytically describes the magnetic field structures in the quasi-static case, which will provide a possible approach to reconstructing the magnetic structures in the current sheet via observation data. This model is self-consistent in the kinetic theory. Also, the distribution function of charged particles in the magnetic island can be calculated.

  11. Development of bifurcated current sheets in solar wind reconnection exhausts

    NASA Astrophysics Data System (ADS)

    Mistry, R.; Eastwood, J. P.; Phan, T. D.; Hietala, H.

    2015-12-01

    Petschek-type reconnection is expected to result in bifurcations of reconnection current sheets. In contrast, Hall reconnection simulations show smooth changes in the reconnecting magnetic field. Here we study three solar wind reconnection events where different spacecraft sample oppositely directed reconnection exhausts from a common reconnection site. The spacecraft's relative separations and measurements of the exhaust width are used to geometrically calculate each spacecraft's distance from the X line. We find that in all cases spacecraft farthest from the X line observe clearly bifurcated reconnection current sheets, while spacecraft nearer to the X line do not. These observations suggest that clear bifurcations of reconnection current sheets occur at large distances from the X line (~1000 ion skin depths) and that Petschek-type signatures are less developed close to the reconnection site. This may imply that fully developed bifurcations of reconnection current sheets are unlikely to be observed in the near-Earth magnetotail.

  12. Structure of the Jovian Magnetodisk Current Sheet: Initial Galileo Observations

    NASA Technical Reports Server (NTRS)

    Russell, C. T.; Huddleston, D. E.; Khurana, K. K.; Kivelson, M. G.

    2001-01-01

    The ten-degree tilt of the Jovian magnetic dipole causes the magnetic equator to move back and forth across Jupiter's rotational equator and tile Galileo orbit that lies therein. Beyond about 24 Jovian radii, the equatorial current sheet thins and tile magnetic structure changes from quasi-dipolar into magnetodisk-like with two regions of nearly radial but antiparallel magnetic field separated by a strong current layer. The magnetic field at the center of the current sheet is very weak in this region. Herein we examine tile current sheet at radial distances from 24 55 Jovian radii. We find that the magnetic structure very much resembles tile structure seen at planetary magnetopause and tail current sheet crossings. Tile magnetic field variation is mainly linear with little rotation of the field direction, At times there is almost no small-scale structure present and the normal component of the magnetic field is almost constant through the current sheet. At other times there are strong small-scale structures present in both the southward and northward directions. This small-scale structure appears to grow with radial distance and may provide the seeds for tile explosive reconnection observed at even greater radial distances oil tile nightside. Beyond about 40 Jovian radii, the thin current sheet also appears to be almost constantly in oscillatory motion with periods of about 10 min. The amplitude of these oscillations also appears to grow with radial distance. The source of these fluctuations may be dynamical events in tile more distant magnetodisk.

  13. Reversible collisionless magnetic reconnection

    SciTech Connect

    Ishizawa, A.; Watanabe, T.-H.

    2013-10-15

    Reversible magnetic reconnection is demonstrated for the first time by means of gyrokinetic numerical simulations of a collisionless magnetized plasma. Growth of a current-driven instability in a sheared magnetic field is accompanied by magnetic reconnection due to electron inertia effects. Following the instability growth, the collisionless reconnection is accelerated with development of a cross-shaped structure of current density, and then all field lines are reconnected. The fully reconnected state is followed by the secondary reconnection resulting in a weakly turbulent state. A time-reversed simulation starting from the turbulent state manifests that the collisionless reconnection process proceeds inversely leading to the initial state. During the reversed reconnection, the kinetic energy is reconverted into the original magnetic field energy. In order to understand the stability of reversed process, an external perturbation is added to the fully reconnected state, and it is found that the accelerated reconnection is reversible when the deviation of the E × B streamlines due to the perturbation is comparable with or smaller than a current layer width.

  14. Visco-resistive tearing in thin current sheets.

    NASA Astrophysics Data System (ADS)

    Velli, M. M. C.; Tenerani, A.; Rappazzo, A. F.; Pucci, F.

    2014-12-01

    How fast magnetic energy release is triggered and occurs in high Lundquist (S) and high Reynolds number ( R ) plasmas such as that of the solar corona is a fundamental problem for understanding phenomena ranging from coronal heating to flares and CMEs. Diffusion or collisional reconnection driven by macroscopic flows in quasi-steady Sweet-Parker (SP) current sheets are processes far too slow to fit observational data. Spontaneous reconnection, driven by the onset of the tearing instability inside current sheets, provides an alternative paradigm to SP reconnection. Nevertheless, as long as macroscopic current layers are considered, the growth of such an instability is also a slow process. Recently it has been shown that SP current sheets are rapidly unstable in high S plasmas, indeed have a growth rate diverging with increasing S. It has been suggested that such instabilities are triggered during the nonlinear stage of the primary tearing instability of a macroscopic layer. The formation of plasmoids in this presumed SP sheet speeds up the reconnection rate to ideal values. Recently, we have suggested that SP sheets can not be realized in quasi-ideal plasmas, and that the plasmoid instability is triggered on a much larger scale (i.e. with current sheets having a much larger ration of thickness to length than SP). Here we present a linear parametric study of the tearing instability for a Harris current sheet, while taking into account both viscosity and current sheets of variable aspect ratios. The present study shows that an explosive growth of the reconnection rate may be reached during the linear stage, once a critical width of the current layer is reached. In the absence of a strong guide field this depends on viscosity and a range of critical aspect ratios can be found for different values of S, R, or S and Prandtl number.

  15. Asymmetric Magnetic Reconnection in Coronal Mass Ejection Current Sheets

    NASA Astrophysics Data System (ADS)

    Pope, Crystal; Miralles, M. P.; Murphy, N. A.

    2012-01-01

    Flux rope models of coronal mass ejections (CMEs) predict the formation ofan elongated current sheet in the wake behind the rising plasmoid. These current sheets have been seen to drift or tilt over time by instruments including SOHO/LASCO and Hinode/XRT. We measure this in multiple observations including the 2008 April 9 "Cartwheel CME" and find an average drift that is far more than can be accounted for via the effects of solar rotation. The observed drift could be due to different parts of the current sheet actively reconnecting at different times (e.g., Savage et al. 2010), macroscopic effects from the rising flux rope pulling the plasma sheet along with it, or asymmetry in the magnetic reconnection process itself. These drift rates are compared with resistive magnetohydrodynamic (MHD) simulations of line-tied reconnection between magnetic fields of different strengths. The observed drift rates are comparable to predictions made by the simulations.

  16. Thin current sheet embedded within a thicker plasma sheet: Self-consistent kinetic theory

    NASA Astrophysics Data System (ADS)

    Sitnov, M. I.; Zelenyi, L. M.; Malova, H. V.; Sharma, A. S.

    2000-06-01

    A self-consistent theory of thin current sheets, where the magnetic field line tension is balanced by the ion inertia rather than by the pressure gradient, is presented. Assuming that ions are the main current carriers and their dynamics is quasi-adiabatic, the Maxwell-Vlasov equations are reduced to the nonlocal analogue of the Grad-Shafranov equation using a new set of integrals of motion, namely, the particle energy and the sheet invariant of the quasi-adiabatic motion. It is shown that for a drifting Maxwellian distribution of ions outside the sheet the equilibrium equation can be reduced in the limits of strong and weak anisotropy to universal equations that determine families of equilibria with similar profiles of the magnetic field. In the region Bn/B0sheet and close to its central plane, the ion drift velocity outside the sheet, and the ion thermal velocity, respectively) the thickness of such similar profiles is of the order of (vT/vD)1/3ρ0, where ρ0 is the thermal ion gyroradius outside the sheet. In the limit of weak anisotropy (vT/vD>>1) the self-consistent current sheet equilibrium may also exist with no indications of the catastrophe reported earlier by Burkhart et al. [1992a]. On the contrary, it is found that in this limit the magnetic field profiles again become similar to each other with the characteristic thickness ~ρ0. The profiles of plasma and current densities as well as the components of the pressure tensor are calculated for arbitrary ion anisotropy outside the sheet. It is shown that the thin current sheet for the equilibrium considered here is usually embedded into a much thicker plasma sheet. Moreover, in the case of weak anisotropy the perturbation of the plasma density inside the sheet is shown to be proportional to the parameter vD/vT, and as a result the electrostatic effects should be small, consistent with observations. This model of the thin current sheet

  17. Kinetic models of current sheets with a sheared magnetic field

    SciTech Connect

    Mingalev, O. V.; Mingalev, I. V.; Mel'nik, M. N.; Artemyev, A. V.; Malova, H. V.; Popov, V. Yu.; Chao, Shen; Zelenyi, L. M.

    2012-04-15

    Thin current sheets, whose existence in the Earth's magnetotail is confirmed by numerous spacecraft measurements, are studied analytically and numerically. The thickness of such sheets is on the order of the ion Larmor radius, and the normal component of the magnetic field (B{sub z}) in the sheet is almost constant, while the tangential (B{sub x}) and shear (B{sub y}) components depend on the transverse coordinate z. The current density in the sheet also has two self-consistent components (j{sub x} and j{sub y}, respectively), and the magnetic field lines are deformed and do not lie in a single plane. To study such quasi-one-dimensional current configurations, two kinetic models are used, in particular, a numerical model based on the particle-in-cell method and an analytical model. The calculated results show that two different modes of the self-consistent shear magnetic field B{sub y} and, accordingly, two thin current sheet configurations can exist for the same input parameters. For the mode with an antisymmetric z profile of the B{sub y} component, the magnetic field lines within the sheet are twisted, whereas the profiles of the plasma density, current density component j{sub y}, and magnetic field component B{sub x} differ slightly from those in the case of a shearless magnetic field (B{sub y} = 0). For the symmetric B{sub y} mode, the magnetic field lines lie in a curved surface. In this case, the plasma density in the sheet varies slightly and the current sheet is two times thicker. Analysis of the dependence of the current sheet structure on the flow anisotropy shows that the sheet thickness decreases significantly with decreasing ratio between the thermal and drift plasma velocities, which is caused by the dynamics of quasi-adiabatic ions. It is shown that the results of the analytical and numerical models are in good agreement. The problems of application of these models to describe current sheets at the magnetopause and near magnetic reconnection regions

  18. Phenomenological Model of Current Sheet Canting in Pulsed Electromagnetic Accelerators

    NASA Technical Reports Server (NTRS)

    Markusic, Thomas; Choueiri, E. Y.

    2003-01-01

    The phenomenon of current sheet canting in pulsed electromagnetic accelerators is the departure of the plasma sheet (that carries the current) from a plane that is perpendicular to the electrodes to one that is skewed, or tipped. Review of pulsed electromagnetic accelerator literature reveals that current sheet canting is a ubiquitous phenomenon - occurring in all of the standard accelerator geometries. Developing an understanding of current sheet canting is important because it can detract from the propellant sweeping capabilities of current sheets and, hence, negatively impact the overall efficiency of pulsed electromagnetic accelerators. In the present study, it is postulated that depletion of plasma near the anode, which results from axial density gradient induced diamagnetic drift, occurs during the early stages of the discharge, creating a density gradient normal to the anode, with a characteristic length on the order of the ion skin depth. Rapid penetration of the magnetic field through this region ensues, due to the Hall effect, leading to a canted current front ahead of the initial current conduction channel. In this model, once the current sheet reaches appreciable speeds, entrainment of stationary propellant replenishes plasma in the anode region, inhibiting further Hall-convective transport of the magnetic field; however, the previously established tilted current sheet remains at a fairly constant canting angle for the remainder of the discharge cycle, exerting a transverse J x B force which drives plasma toward the cathode and accumulates it there. This proposed sequence of events has been incorporated into a phenomenological model. The model predicts that canting can be reduced by using low atomic mass propellants with high propellant loading number density; the model results are shown to give qualitative agreement with experimentally measured canting angle mass dependence trends.

  19. Vlasov simulations of collisionless magnetic reconnection without background density

    NASA Astrophysics Data System (ADS)

    Schmitz, H.; Grauer, R.

    2008-02-01

    A standard starting point for the simulation of collisionless reconnection is the Harris equilibrium which is made up of a current sheet that separates two regions of opposing magnetic field. Magnetohydrodynamic simulations of collisionless reconnection usually include a homogeneous background density for reasons of numerical stability. While, in some cases, this is a realistic assumption, the background density may introduce new effects both due to the more involved structure of the distribution function or due to the fact that the Alfvèn speed remains finite far away from the current sheet. We present a fully kinetic Vlasov simulation of the perturbed Harris equilibrium using a Vlasov code. Parameters are chosen to match the Geospace Environment Modeling (GEM) Magnetic Reconnection Challenge but excluding the background density. This allows to compare with earlier simulations [Schmitz H, Grauer R. Kinetic Vlasov simulations of collisionless magnetic reconnection. Phys Plasmas 2006;13:092309] which include the background density. It is found that the absence of a background density causes the reconnection rate to be higher. On the other hand, the time until the onset of reconnection is hardly affected. Again the off diagonal elements of the pressure tensor are found to be important on the X-line but with modified importance for the individual terms.

  20. Dynamics of charged current sheets at high-latitude magnetopause

    NASA Astrophysics Data System (ADS)

    Savin, S.; Amata, E.; Zelenyi, L.; Dunlop, M.; Andre, M.; Song, P.; Blecki, J.; Buechner, J.; Rauch, J. L.; Skalsky, A.

    E. Amata (2), L. Zelenyi (1), M. Dunlop (3), M. Andre (4), P. Song (5), J. Blecki (6), J. Buechner (7), J.L Rauch, J.G. Trotignon (8), G. Consolini, F. Marcucci (2), B. Nikutowski (7), A. Skalsky, S. Romanov, E. Panov (1) (2) IFSI, Roma, Italy, (3) RAL, UK, (4) IRFU, Uppsala, Sweden, (5) U. Mass. Lowell, USA, (6) SRC, Warsaw, Poland, (7) MPAe, Germany, (8) LPCE, Orleans, France; We study dynamics of thin current sheets over polar cusps from data of Interball-1 and Cluster. At the high-beta magnetopause current sheet width often reaches ion gyroradius scales, that leads to their Hall dynamics in the presence of local surface charges. Respective perpendicular electric fields provide the means for momentum coupling through the current sheets and are able to accelerate ions with gyroradius of the order or larger than the sheet width. At borders of large diamagnetic cavities this mechanism is able to support mass exchange and accelerate/ heat incoming magnetosheath particles. At larger scales the inhomogeneous electric fields at the current sheet borders can accelerate incident plasma downtail along magnetopause via inertial drift. It serves to move external plasma away for dynamic equilibrium supporting. Farther away from magnetopause similar nonlinear electric field wave trains, selfconsistently produced by interaction of reflected from the obstacle waves with magnetosheath fluctuations, destroy the incident flux into accelerated magnetosonic jets and decelerated Alfvenic flows and generate small-scale current sheets due to different sign of electron and ion inertial drift in the nonlinear electric field bursts. We suggest that this direct kinetic energy transformation creates current sheets with anomalous statistics of field rotation angles in the turbulent boundary layer in front of magnetopause, which have been attributed earlier to an intermittent turbulence. We compare measured spectra with a model of nonlinear system with intermittent chaotic behavior. Work was

  1. On spontaneous formation of current sheets: Untwisted magnetic fields

    SciTech Connect

    Bhattacharyya, R.; Low, B. C.; Smolarkiewicz, P. K.

    2010-11-15

    This is a study of the spontaneous formation of electric current sheets in an incompressible viscous fluid with perfect electrical conductivity, governed by the magnetohydrodynamic Navier-Stokes equations. Numerical solutions to two initial value problems are presented for a three-dimensional, periodic, untwisted magnetic field evolving, with no change in magnetic topology under the frozen-in condition and at characteristic fluid Reynolds numbers of the order of 500, from a nonequilibrium initial state with the fluid at rest. The evolution converts magnetic free energy into kinetic energy to be all dissipated away by viscosity so that the field settles into a minimum-energy, static equilibrium. The solutions demonstrate that, as a consequence of the frozen-in condition, current sheets must form during the evolution despite the geometric simplicity of the prescribed initial fields. In addition to the current sheets associated with magnetic neutral points and field reversal layers, other sheets not associated with such magnetic features are also in evidence. These current sheets form on magnetic flux surfaces. This property is used to achieve a high degree of the frozen-in condition in the simulations, by describing the magnetic field entirely in terms of the advection of its flux surfaces and integrating the resulting governing equations with a customized version of a general-purpose high-resolution (viz., nonoscillatory) hydrodynamical simulation code EULAG [J. M. Prusa et al., Comput. Fluids 37, 1193 (2008)]. Incompressibility imposes the additional global constraint that the flux surfaces must evolve with no change in the spatial volumes they enclose. In this approach, current sheet formation is demonstrated graphically by the progressive pressing together of suitably selected flux surfaces until their separation has diminished below the minimal resolved distance on a fixed grid. The frozen-in condition then fails in the simulation as the field reconnects through

  2. Mercury's Tail Current Sheet from MESSENGER Magnetic Field Measurements

    NASA Astrophysics Data System (ADS)

    Al Asad, M.; Johnson, C. L.; Philpott, L. C.; Anderson, B. J.; Korth, H.; Slavin, J. A.; Solomon, S. C.

    2014-12-01

    We have estimated the spatial variations in the position and average thickness of Mercury's magnetospheric tail current sheet from orbital magnetic field data collected by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. We have investigated the changes in these average properties with varying solar wind conditions and magnetospheric activity. The time-averaged thickness of the current sheet was obtained from superposed epoch analysis (SEA) of the 1-s-averaged vector magnetic field data within ± 10 min of the identified magnetic equator position at different down-tail distances. The average thickness was then estimated from a given SEA by identifying the time interval during which the field completed a rotation from the sunward to the anti-sunward direction, or vice versa, accompanied by a depression in the field magnitude. We have found that the current sheet has a thickness of ~0.8 RM (where RM is Mercury's radius, or 2440 km) close to the planet (~ 1.1 RM) and thins to ~0.2 RM in the far tail region (~2.8 RM). We examined individual orbits to catalogue the existence and number of current sheet crossings encountered on each orbit. These data allow us to (1) determine whether the thickness obtained from the SEA is an actual thickness or an apparent thickness controlled by rapid motions of the current sheet, and (2) estimate the statistical likelihood of observing the current sheet as a function of down-tail distance. For example, some magnetically quiet orbits that cross the magnetic equator at down-tail distances greater than 2 RM do not record a current sheet crossing and appear to cross closed field lines in the vicinity of the magnetic equator, even though they lie in a region in which the tail current sheet is usually observed. This result suggests that the inner (near-planet) edge of the current sheet is not stationary but may move anti-sunward (or sunward) under quiet (or active) magnetospheric conditions.

  3. Current Sheet Properties and Dynamics During Sympathetic Breakout Eruptions

    NASA Astrophysics Data System (ADS)

    Lynch, B. J.; Edmondson, J. K.

    2013-12-01

    We present the continued analysis of the high-resolution 2.5D MHD simulations of sympathetic magnetic breakout eruptions from a pseudostreamer source region. We examine the generation of X- and O-type null points during the current sheet tearing and track the magnetic island formation and evolution during periods of reconnection. The magnetic breakout eruption scenario forms an overlying 'breakout' current sheet that evolves slowly and removes restraining flux from above the sheared field core that will eventually become the center of the erupting flux rope-like structure. The runaway expansion from the expansion-breakout reconnection positive feedback enables the formation of the second, vertical/radial current sheet underneath the rising sheared field core as in the standard CHSKP eruptive flare scenario. We will examine the flux transfer rates through the breakout and flare current sheets and compare the properties of the field and plasma inflows into the current sheets and the reconnection jet outflows into the flare loops and flux rope ejecta.

  4. Experimental study of the dynamics of a thin current sheet

    NASA Astrophysics Data System (ADS)

    Gekelman, W.; DeHaas, T.; Van Compernolle, B.; Daughton, W.; Pribyl, P.; Vincena, S.; Hong, D.

    2016-05-01

    Many plasmas in natural settings or in laboratory experiments carry currents. In magnetized plasmas the currents can be narrow field-aligned filaments as small as the electron inertial length ≤ft(\\tfrac{c}{{ω }pe}\\right) in the transverse dimension or fill the entire plasma column. Currents can take the form of sheets, again with the transverse dimension the narrow one. Are laminar sheets of electric current in a magnetized plasma stable? This became an important issue in the 1960s when current-carrying plasmas became key in the quest for thermonuclear fusion. The subject is still under study today. The conditions necessary for the onset for tearing are known, the key issue is that of the final state. Is there a final state? One possibility is a collection of stable tubes of current. On the other hand, is the interaction between the current filaments which are the byproduct endless, or does it go on to become chaotic? The subject of three-dimensional current systems is intriguing, rich in a variety of phenomena on multiple scale sizes and frequencies, and relevant to fusion studies, solar physics, space plasmas and astrophysical phenomena. In this study a long (δz = 11 m) and narrow (δx = 1 cm, δy = 20 cm) current sheet is generated in a background magnetoplasma capable of supporting Alfvén waves. The current is observed to rapidly tear into a series of magnetic islands when viewed in a cross-sectional plane, but they are in essence three-dimensional flux ropes. At the onset of the current, magnetic field line reconnection is observed between the flux ropes. The sheet on the whole is kink-unstable, and after kinking exhibits large-scale, low-frequency (f ≪ f ci ) rotation about the background field with an amplitude that grows with distance from the source of the current. Three-dimensional data of the magnetic and electric fields is acquired throughout the duration of the experiment and the parallel resistivity is derived from it. The parallel

  5. What causes the warp in the heliospheric current sheet

    NASA Technical Reports Server (NTRS)

    Wilcox, J. M.; Scherrer, P. H.

    1981-01-01

    A comparative discussion of the warp in the heliospheric current sheet is presented. Pioneer 10 and 11 data of the interplanetary magnetic field compared with earlier data (Helios 1 and 2) show a good agreement on the phenomenon of the warp; however, the interpretations differ. One theory (Thomas and Smith, 1980) proposes that fast solar wind streams associated with interaction regions may move the current sheet higher to heliospheric latitudes, thus causing the warp; while the earlier theory (1976) adequately explained the phenomenon by using the observed photospheric magnetic field and the Zeeman effect but omitted the solar wind dynamical considerations as part of the computations. It is shown that the Helios data of the polarity of the interplanetary magnetic field are in good agreement with the computed location of the current sheet, confirming the earlier theory.

  6. Energy dynamics and current sheet structure in fluid and kinetic simulations of decaying magnetohydrodynamic turbulence

    SciTech Connect

    Makwana, K. D. Cattaneo, F.; Zhdankin, V.; Li, H.; Daughton, W.

    2015-04-15

    Simulations of decaying magnetohydrodynamic (MHD) turbulence are performed with a fluid and a kinetic code. The initial condition is an ensemble of long-wavelength, counter-propagating, shear-Alfvén waves, which interact and rapidly generate strong MHD turbulence. The total energy is conserved and the rate of turbulent energy decay is very similar in both codes, although the fluid code has numerical dissipation, whereas the kinetic code has kinetic dissipation. The inertial range power spectrum index is similar in both the codes. The fluid code shows a perpendicular wavenumber spectral slope of k{sub ⊥}{sup −1.3}. The kinetic code shows a spectral slope of k{sub ⊥}{sup −1.5} for smaller simulation domain, and k{sub ⊥}{sup −1.3} for larger domain. We estimate that collisionless damping mechanisms in the kinetic code can account for the dissipation of the observed nonlinear energy cascade. Current sheets are geometrically characterized. Their lengths and widths are in good agreement between the two codes. The length scales linearly with the driving scale of the turbulence. In the fluid code, their thickness is determined by the grid resolution as there is no explicit diffusivity. In the kinetic code, their thickness is very close to the skin-depth, irrespective of the grid resolution. This work shows that kinetic codes can reproduce the MHD inertial range dynamics at large scales, while at the same time capturing important kinetic physics at small scales.

  7. Particle dynamics and current-free double layers in an expanding, collisionless, two-electron-population plasma

    NASA Technical Reports Server (NTRS)

    Hairapetian, G.; Stenzel, R. L.

    1991-01-01

    The expansion of a two-electron-population, collisionless plasma into vacuum has been examined in detail. Plasma density, plasma potential, electric field, and particle disribution functions have been measured in situ. It is demonstrated that the presence of a low-pressure (P not less than 2 x 10 to the -5th torr) background neutral gas modifies the expansion of the plasma. A new plasma source creating dense, pulsed discharge plasma with a low background pressure (P not greater than 2 x 10 to the -6th torr) has been developed to perform in situ measurements of the temporal and spatial plasma evolution during its expansion into vacuum.

  8. Warping of Saturn's magnetospheric and magnetotail current sheets

    NASA Astrophysics Data System (ADS)

    Arridge, C. S.; Khurana, K. K.; Russell, C. T.; Southwood, D. J.; Achilleos, N.; Dougherty, M. K.; Coates, A. J.; Leinweber, H. K.

    2008-08-01

    The magnetotails of Jupiter and Earth are known to be hinged so that their orientation is controlled by the magnetic field of the planet at small distances and asymptotically approach the direction of the flow of the solar wind at large distances. In this paper we present Cassini observations showing that Saturn's magnetosphere is also similarly hinged. Furthermore, we find that Saturn's magnetosphere is not only hinged in the tail but also on the dayside, in contrast to the Jovian and terrestrial magnetospheres. Over the midnight, dawn, and noon local time sectors we find that the current sheet is displaced above Saturn's rotational equator, and thus the current sheet adopts the shape of a bowl or basin. We present a model to describe the warped current sheet geometry and show that in order to properly describe the magnetic field in the magnetosphere, this hinging must be incorporated. We discuss the impact on plasma observations made in Saturn's equatorial plane, the influence on Titan's magnetospheric interaction, and the effect of periodicities on the mean current sheet structure.

  9. Trigger of Fast Reconnection via Collapsing Current Sheets

    NASA Astrophysics Data System (ADS)

    Tenerani, A.; Velli, M.; Rappazzo, A. F.; Pucci, F.

    2015-12-01

    It has been widely believed that reconnection is the underlying mechanism of many explosive processes observed both in astrophysical and laboratory plasmas. However, both the questions of how magnetic reconnection is triggered in high Lundquist (S) and Reynolds (R) number plasmas, and how it can then occur on fast, ideal, time-scales remain open. Indeed, it has been argued that fast reconnection rates could be achieved once kinetic scales are reached, or, alternatively, by the onset of the so-called plasmoid instability within Sweet-Parker current sheets. However, it has been shown recently that a tearing mode instability (the "ideal tearing") can grow on an ideal, i.e., S-independent, timescale once the width a of a current sheet becomes thin enough with respect to its macroscopic length L, a/L ~ S-1/3. This suggests that current sheet thinning down to such a threshold aspect ratio —much larger, for S>>1, than the Sweet-Parker one that scales as a/L ~ S-1/2— might provide the trigger for fast reconnection even within the fluid plasma framework. Here we discuss the transition to fast reconnection by studying with visco-resistive MHD simulations the onset and evolution of the tearing instability within a single collapsing current sheet. We indeed show that the transition to a fast tearing mode instability takes place when an inverse aspect ratio of the order of the threshold a/L ~ S-1/3 is reached, and that the secondary current sheets forming nonlinearly become the source of a succession of recursive tearing instabilities. The latter is reminiscent of the fractal reconnection model of flares, which we modify in the light of the "ideal tearing" scenario.

  10. 3-D Particle Simulation of Current Sheet Instabilities

    NASA Astrophysics Data System (ADS)

    Wang, Zhenyu; Lin, Yu; Wang, Xueyi; Tummel, Kurt; Chen, Liu

    2015-11-01

    The electrostatic (ES) and electromagnetic (EM) instabilities of a Harris current sheet are investigated using a 3-D linearized (δf) gyrokinetic (GK) electron and fully kinetic (FK) ion (GeFi) particle simulation code. The equilibrium magnetic field consists of an asymptotic anti-parallel Bx 0 and a guide field BG. The ES simulations show the excitation of lower-hybrid drift instability (LHDI) at the current sheet edge. The growth rate of the 3-D LHDI is scanned through the (kx ,ky) space. The most unstable modes are found to be at k∥ = 0 for smaller ky. As ky increases, the growth rate shows two peaks at k∥ ≠ 0 , consistent with analytical GK theory. The eigenmode structure and growth rate of LHDI obtained from the GeFi simulation agree well with those obtained from the FK PIC simulation. Decreasing BG, the asymptotic βe 0, or background density can destabilize the LHDI. In the EM simulation, tearing mode instability is dominant in the cases with ky kx , there exist two unstable modes: a kink-like (LHDI) mode at the current sheet edge and a sausage-like mode at the sheet center. The results are compared with the GK eigenmode theory and the FK simulation.

  11. A Catapult (Slingshot) Current Sheet Relaxation Model for Substorm Triggering

    NASA Astrophysics Data System (ADS)

    Machida, S.; Miyashita, Y.; Ieda, A.

    2010-12-01

    Based on the results of our superposed epoch analysis of Geotail data, we have proposed a catapult (slingshot) current sheet relaxation model in which earthward flows are produced in the central plasma sheet (CPS) due to the catapult (slingshot) current sheet relaxation, together with the rapid enhancement of Poynting flux toward the CPS in the lobe around X ~ -15 Re about 4 min before the substrom onset. These earthward flows are characterized by plasma pressure decrease and large amplitude magnetic field fluctuations. When these flows reach X ~ 12Re in the magnetotail, they give significant disturbances to the inner magnetosphere to initiate some instability such as a ballooning instability or other instabilities, and the substorm starts in the inner magnetosphere. The occurrence of the magnetic reconnection is a natural consequence of the initial convective earthward flows, because the relaxation of a highly stretched catapult current sheet produces a very thin current at its tailward edge being surrounded by intense magnetic fields which were formerly the off-equatorial lobe magnetic fields. Recently, Nishimura et al. [2010] reported that the substorm onset begins when faint poleward discrete arcs collide with equatorward quiet arcs. The region of earthward convective flows correlatively moves earthward prior to the onset. Thus, this region of the earthward convective flows seems to correspond to the faint poleward discrete arcs. Interestingly, our statistical analysis shows that the earthward convective flows are not produced by the magnetic reconnection, but they are attributed to the dominance of the earthward JxB force over the tailward pressure associated with the progress of the plasma sheet thinning.

  12. Current sheet formation in a sheared magnetic field

    NASA Astrophysics Data System (ADS)

    Zhou, Yao; Huang, Yi-Min; Qin, Hong; Bhattacharjee, Amitava

    2015-11-01

    Recently a variational integrator for ideal magnetohydrodynamics in Lagrangian labeling has been developed using discrete exterior calculus. Its built-in frozen-in equation makes it optimal for studying current sheet formation. We use this scheme to study the Hahm-Kulsrud-Taylor problem, which considers the response of a 2D plasma magnetized by a sheared field under mirrored sinusoidal boundary perturbations. The equilibrium solutions are found to not converge with increasing spatial resolution, which suggests that there exists no smooth equilibrium that preserves the topology of the initial field exactly. Unlike previous studies that examine the current density output, we identify a singular current sheet from the converged part of the fluid mapping. This research was supported by the U.S. Department of Energy under Contract No. DE-AC02-09CH11466.

  13. Quasilinear saturation of forced current sheet tearing modes

    NASA Technical Reports Server (NTRS)

    Liewer, Paulett C.; Payne, David G.

    1990-01-01

    Numerical studies of tearing modes in a nearly singular forced current sheet equilibrium (Liewer and Payne, 1990) show that the modes saturate quasilinearly when the width of the magnetic island formed by the reconnection is on the order of several times the linear mode width which scales as approximately (kS) exp -2/5, where S is the Lundquist number and k is the wavenumber. The modes saturate quasilinearly by flattening the current profile, converting magnetic energy into plasma energy. The longer wavelength modes, which saturate at higher levels, release the most energy. These modes may, nonlinearly, play a role in coronal heating when sharp current sheets form as a result of global magnetic stresses.

  14. Dynamic Harris current sheet thickness from Cluster current density and plasma measurements

    NASA Technical Reports Server (NTRS)

    Thompson, S. M.; Kivelson, M. G.; Khurana, K. K.; McPherron, R. L.; Weygand, J. M.; Balogh, A.; Reme, H.; Kistler, L. M.

    2005-01-01

    We use the first accurate measurements of current densities in the plasma sheet to calculate the half-thickness and position of the current sheet as a function of time. Our technique assumes a Harris current sheet model, which is parameterized by lobe magnetic field B(o), current sheet half-thickness h, and current sheet position z(sub o). Cluster measurements of magnetic field, current density, and plasma pressure are used to infer the three parameters as a function of time. We find that most long timescale (6-12 hours) current sheet crossings observed by Cluster cannot be described by a static Harris current sheet with a single set of parameters B(sub o), h, and z(sub o). Noting the presence of high-frequency fluctuations that appear to be superimposed on lower frequency variations, we average over running 6-min intervals and use the smoothed data to infer the parameters h(t) and z(sub o)(t), constrained by the pressure balance lobe magnetic field B(sub o)(t). Whereas this approach has been used in previous studies, the spatial gnuhen& now provided by the Cluster magnetometers were unavailable or not well constrained in earlier studies. We place the calculated hdf&cknessa in a magnetospheric context by examining the change in thickness with substorm phase for three case study events and 21 events in a superposed epoch analysis. We find that the inferred half-thickness in many cases reflects the nominal changes experienced by the plasma sheet during substorms (i.e., thinning during growth phase, thickening following substorm onset). We conclude with an analysis of the relative contribution of (Delta)B(sub z)/(Delta)X to the cross-tail current density during substorms. We find that (Delta)B(sub z)/(Delta)X can contribute a significant portion of the cross-tail c m n t around substorm onset.

  15. Current Sheets in the Heliosheath: Voyager 1, 2009

    NASA Technical Reports Server (NTRS)

    Burlaga, L. F.; Ness, N. F.

    2011-01-01

    We identified all of the current sheets for which we have relatively complete and accurate magnetic field (B) data from Voyager 1 (V1) from days of year (DOYs) 1 to 331, 2009, which were obtained deep in the heliosheath between 108.5 and 111.8 AU. Three types of current sheets were found: (1) 15 proton boundary layers (PBLs), (2) 10 and 3 magnetic holes and magnetic humps, respectively, and (3) 3 sector boundaries. The magnetic field strength changes across PBL, and the profile B(t) is linearly related to the hyperbolic tangent function, but the direction of B does not change. For each of the three sector boundaries, B rotated in a plane normal to the minimum variance direction, and the component of B along the minimum variance direction was zero within the uncertainties, indicating that the sector boundaries were tangential discontinuities. The structure of the sector boundaries was not as simple as that for PBLs. The average thickness of magnetic holes and humps (approx.30 RL) was twice that of the PBLs (approx.15 RL). The average thickness of the current sheets associated with sector boundaries was close to the thickness of the PBLs. Our observations are consistent with the hypothesis that magnetic holes and humps are solitons, which are initiated by the mirror mode instability, and evolve by nonlinear kinetic plasma processes to pressure balanced structures maintained by magnetization currents and proton drift currents in the gradients of B.

  16. Spontaneous magnetic reconnection. Collisionless reconnection and its potential astrophysical relevance

    NASA Astrophysics Data System (ADS)

    Treumann, R. A.; Baumjohann, W.

    2015-10-01

    The present review concerns the relevance of collisionless reconnection in the astrophysical context. Emphasis is put on recent developments in theory obtained from collisionless numerical simulations in two and three dimensions. It is stressed that magnetic reconnection is a universal process of particular importance under collisionless conditions, when both collisional and anomalous dissipation are irrelevant. While collisional (resistive) reconnection is a slow, diffusive process, collisionless reconnection is spontaneous. On any astrophysical time scale, it is explosive. It sets on when electric current widths become comparable to the leptonic inertial length in the so-called lepton (electron/positron) "diffusion region", where leptons de-magnetise. Here, the magnetic field contacts its oppositely directed partner and annihilates. Spontaneous reconnection breaks the original magnetic symmetry, violently releases the stored free energy of the electric current, and causes plasma heating and particle acceleration. Ultimately, the released energy is provided by mechanical motion of either the two colliding magnetised plasmas that generate the current sheet or the internal turbulence cascading down to lepton-scale current filaments. Spontaneous reconnection in such extended current sheets that separate two colliding plasmas results in the generation of many reconnection sites (tearing modes) distributed over the current surface, each consisting of lepton exhausts and jets which are separated by plasmoids. Volume-filling factors of reconnection sites are estimated to be as large as {<}10^{-5} per current sheet. Lepton currents inside exhausts may be strong enough to excite Buneman and, for large thermal pressure anisotropy, also Weibel instabilities. They bifurcate and break off into many small-scale current filaments and magnetic flux ropes exhibiting turbulent magnetic power spectra of very flat power-law shape W_b∝ k^{-α } in wavenumber k with power becoming as

  17. CURRENT SHEETS FORMATION IN TANGLED CORONAL MAGNETIC FIELDS

    SciTech Connect

    Rappazzo, A. F.; Parker, E. N. E-mail: parker@oddjob.uchicago.edu

    2013-08-10

    We investigate the dynamical evolution of magnetic fields in closed regions of solar and stellar coronae. To understand under which conditions current sheets form, we examine dissipative and ideal reduced magnetohydrodynamic models in Cartesian geometry, where two magnetic field components are present: the strong guide field B{sub 0}, extended along the axial direction, and the dynamical orthogonal field b. Magnetic field lines thread the system along the axial direction that spans the length L and are line-tied at the top and bottom plates. The magnetic field b initially has only large scales, with its gradient (current) length scale of the order of l{sub b}. We identify the magnetic intensity threshold b/B{sub 0} {approx} l{sub b}/L. For values of b below this threshold, field-line tension inhibits the formation of current sheets, while above the threshold they form quickly on fast ideal timescales. In the ideal case, above the magnetic threshold, we show that current sheets thickness decreases in time until it becomes smaller than the grid resolution, with the analyticity strip width {delta} decreasing at least exponentially, after which the simulations become underresolved.

  18. Giacobini-Zinner magnetotail: Tail configuration and current sheet

    SciTech Connect

    McComas, D.J.; Gosling, J.T.; Bame, S.J.; Slavin, J.A.; Smith, E.J.; Steinberg, J.L.

    1987-02-01

    The high-resolution plasma electron and magnetic field data sets from the ICE tail traversal of comet Giacobini-Zinner have been combined to make a detailed study of the draped Giacobini-Zinner magnetotail in general, and its field-reversing current sheet in particular. The goemetry of the magnetotail at the time of the ICE crossing is determined and is shown to be consistent with a circular tail cross section rotated 10.5 in the normal sense of aberration and 9.9/sup 0/ above the ecliptic plane, bisected by a cross-tail current sheet which is rotated 43/sup 0/ out of the ecliptic about the solar wind velocity vector. MHD continuity, momentum, and energy equations are combined with the plasma and field observations to determine unmeasured plasma properties at ICE and upstream at the average point along each stream-line where the cometary ions are picked up. The ion temperature, beta, and flow speed at ICE range from 1--1.5 x 10/sup 6/ K, 1--4, and --20 to --30 km s/sup -1/, respectively, in the draped lobes to --1.2 x 10/sup 5/ K, up to --40, and ----20 km s/sup -1/ in the current sheet. Upstream at the average pickup locations, the flow velocity, ion temperature, density, and ion source rates range from ----75 km s/sup -1/, --4. x 10/sup 6/ K, --20 cm/sup -3/, and --1.5 cm/sup -3/ s/sup -1/ in the regions upstream from the lobes to ---12 km s/sup -1/, --1 x 10/sup 5/ K, 200--600 cm/sup -3/, and --3.6 cm/sup -3/ s/sup -1/ in the prime mass-loading region upstream from the current sheet.

  19. Morphology and Density Structure of Post-CME Current Sheets

    NASA Technical Reports Server (NTRS)

    Vrsnak, B.; Poletto, G.; Vujic, E.; Vourlidas, A.

    2009-01-01

    Eruption of a coronal mass ejection (CME) is believed to drag and open the coronal magnetic field, presumably leading to the formation of a large-scale current sheet and field relaxation by magnetic reconnection. This paper analyzes the physical characteristics of ray-like coronal features formed in the aftermath of CMEs, to confirm whether interpreting such phenomena in terms of a reconnecting current sheet is consistent with observations. Methods: The study focuses on UVCS/SOHO and LASCO/SOHO measurements of the ray width, density excess, and coronal velocity field as a function of the radial distance. The morphology of the rays implies that they are produced by Petschek-like reconnection in the large-scale current sheet formed in the wake of CME. The hypothesis is supported by the flow pattern, often showing outflows along the ray, and sometimes also inflows into the ray. The inferred inflow velocities range from 3 to 30 km/s, and are consistent with the narrow opening-angle of rays, which add up to a few degrees. The density of rays is an order of magnitude higher than in the ambient corona. The model results are consistent with the observations, revealing that the main cause of the density excess in rays is a transport of the dense plasma from lower to higher heights by the reconnection outflow.

  20. The role of entropy in collisionless evolution

    NASA Astrophysics Data System (ADS)

    Barnes, Eric

    2011-04-01

    Understanding the path to mechanical equilibria for collisionless systems is a topic with a rich history. We are investigating the part that entropy plays in determining the outcome of collisionless evolution. I will discuss some previous work that lays a foundation for our current studies. With that framework in place, I will explain a modification to the entropy maximization procedure and compare the results to previous ideas. It is possible that entropy maxima are not achievable, and we argue that entropy production rates can influence collisionless system evolution. This work has been supported by NASA ATP grant NNX07AG86G.

  1. Heliospheric current sheet and its interaction with solar cosmic rays

    NASA Astrophysics Data System (ADS)

    Malova, Helmi; Popov, Victor; Grigorenko, Elena; Dunko, Andrey; Petrukovich, Anatoly

    2016-04-01

    We investigated effects resulting from the interaction of solar cosmic rays (SCR) with the heliospheric current sheet (HCS) in the solar wind. Self-consistent kinetic model of the HCS is developed, where ions demonstrate quasi-adiabatic dynamics. HCS is considered as the equilibrium embedded current structure, where the two main kinds of plasma with different temperatures give the main contribution to the current (low-energy background plasma and SCR). It is shown that HCS is a relatively thin multiscale configuration of the current sheet, embedded in a thicker plasma layer. The taking into account of SCR particles in HCS could lead to a change of its structure and to enhancement of its properties such as the embedding and multi-scaling. Parametric family of solutions is considered where the current balance in HCS is provided at different temperatures of SCR and different concentrations of high-energy plasma. Concentrations of SCR are determined which may contribute to the thickening of the HCS that can be observed in satellite studies. The possibility to apply this modeling for the explanation of experimental observations is considered.

  2. The Effects of Ion Kinetic Instabilities on the Three-Dimensional Reconnection of Ion-Scale Current Sheets in the Solar Wind

    NASA Astrophysics Data System (ADS)

    Burgess, D.; Gingell, P.; Matteini, L.

    2014-12-01

    Solar wind plasmas have been observed to host a population of magnetic discontinuities associated with turbulent fluctuations and solar atmospheric processes. These thin current sheets, which may be subject to a tearing instability, can heat the plasma and accelerate particles via magnetic reconnection, and indeed have observed correlations with energetic particles. Further correlations of observations of thin, ion-scale current sheets with local temperature anisotropies invite an exploration of the role of ion kinetic instabilities in their evolution and associated heating processes, particularly when coupled with a turbulent medium such as the solar wind. Recent work has demonstrated that proton temperature anisotropy plays an important role in the growth and evolution of the two-dimensional, collisionless tearing instability, for example via the growth of background ion cyclotron and fire hose instabilities. Here, we present results of a three-dimensional extension of this investigation using three-dimensional hybrid simulations of current sheets in Harris equilibrium. We demonstrate the emergence of persistent three-dimensional structures and instabilities which significantly alter the development of the tearing instability, including i) patchy reconnection sites formed by break up of initially two-dimensional x-lines, and ii) narrow-band kink of the current sheet in the current-carrying direction by the growth of a drift-kink instability. We discuss the relative growth rates of tearing and drift-kink instabilities for a range of background and current sheet temperature anisotropies and guide fields, quantify local ion heating, and present potential observational signatures. We also examine the character of turbulence generated by the interaction of multiple ion-scale current sheets in three-dimensions.

  3. Energy dynamics and current sheet structure in fluid and kinetic simulations of decaying magnetohydrodynamic turbulence

    DOE PAGESBeta

    Makwana, K. D.; Zhdankin, V.; Li, H.; Daughton, W.; Cattaneo, F.

    2015-04-10

    We performed simulations of decaying magnetohydrodynamic (MHD) turbulence with a fluid and a kinetic code. The initial condition is an ensemble of long-wavelength, counter-propagating, shear-Alfvén waves, which interact and rapidly generate strong MHD turbulence. The total energy is conserved and the rate of turbulent energy decay is very similar in both codes, although the fluid code has numerical dissipation, whereas the kinetic code has kinetic dissipation. The inertial range power spectrum index is similar in both the codes. The fluid code shows a perpendicular wavenumber spectral slope of k-1.3⊥k⊥-1.3. The kinetic code shows a spectral slope of k-1.5⊥k⊥-1.5 for smallermore » simulation domain, and k-1.3⊥k⊥-1.3 for larger domain. We then estimate that collisionless damping mechanisms in the kinetic code can account for the dissipation of the observed nonlinear energy cascade. Current sheets are geometrically characterized. Their lengths and widths are in good agreement between the two codes. The length scales linearly with the driving scale of the turbulence. In the fluid code, their thickness is determined by the grid resolution as there is no explicit diffusivity. In the kinetic code, their thickness is very close to the skin-depth, irrespective of the grid resolution. Finally, this work shows that kinetic codes can reproduce the MHD inertial range dynamics at large scales, while at the same time capturing important kinetic physics at small scales.« less

  4. Energy dynamics and current sheet structure in fluid and kinetic simulations of decaying magnetohydrodynamic turbulence

    SciTech Connect

    Makwana, K. D.; Zhdankin, V.; Li, H.; Daughton, W.; Cattaneo, F.

    2015-04-10

    We performed simulations of decaying magnetohydrodynamic (MHD) turbulence with a fluid and a kinetic code. The initial condition is an ensemble of long-wavelength, counter-propagating, shear-Alfvén waves, which interact and rapidly generate strong MHD turbulence. The total energy is conserved and the rate of turbulent energy decay is very similar in both codes, although the fluid code has numerical dissipation, whereas the kinetic code has kinetic dissipation. The inertial range power spectrum index is similar in both the codes. The fluid code shows a perpendicular wavenumber spectral slope of k-1.3⊥k⊥-1.3. The kinetic code shows a spectral slope of k-1.5⊥k⊥-1.5 for smaller simulation domain, and k-1.3⊥k⊥-1.3 for larger domain. We then estimate that collisionless damping mechanisms in the kinetic code can account for the dissipation of the observed nonlinear energy cascade. Current sheets are geometrically characterized. Their lengths and widths are in good agreement between the two codes. The length scales linearly with the driving scale of the turbulence. In the fluid code, their thickness is determined by the grid resolution as there is no explicit diffusivity. In the kinetic code, their thickness is very close to the skin-depth, irrespective of the grid resolution. Finally, this work shows that kinetic codes can reproduce the MHD inertial range dynamics at large scales, while at the same time capturing important kinetic physics at small scales.

  5. A new stationary analytical model of the heliospheric current sheet and the plasma sheet

    NASA Astrophysics Data System (ADS)

    Kislov, Roman A.; Khabarova, Olga V.; Malova, Helmi V.

    2015-10-01

    We develop a single-fluid 2-D analytical model of the axially symmetric thin heliospheric current sheet (HCS) embedded into the heliospheric plasma sheet (HPS). A HCS-HPS system has a shape of a relatively thin plasma disk limited by separatrices that also represent current sheets, which is in agreement with Ulysses observations in the aphelion, when it crossed the HCS perpendicular to its plane. Our model employs a differential rotation of the solar photosphere that leads to unipolar induction in the corona. Three components of the interplanetary magnetic field (IMF), the solar wind speed, and the thermal pressure are taken into account. Solar corona conditions and a HCS-HPS system state are tied by boundary conditions and the "frozen-in" equation. The model allows finding spatial distributions of the magnetic field, the speed within the HPS, and electric currents within the HCS. An angular plasma speed is low within the HPS due to the angular momentum conservation (there is no significant corotation with the Sun), which is consistent with observations. We found that the HPS thickness L decreases with distance r, becoming a constant far from the Sun (L ~2.5 solar radii (R0) at 1 AU). Above the separatrices and at large heliocentric distances, the solar wind behavior obeys Parker's model, but the magnetic field spiral form may be different from Parker's one inside the HPS. At r ≤ 245 R0, the IMF spiral may undergo a turn simultaneously with a change of the poloidal current direction (from sunward to antisunward).

  6. Kinetic scale current sheet observed at the magnetopause

    NASA Astrophysics Data System (ADS)

    Norgren, Cecilia; Graham, Daniel; Khotyaintsev, Yuri; André, Mats; Vaivads, Andris

    2016-04-01

    Kinetic scale current sheets associated with sharp plasma boundaries are often formed in plasmas. Studying the processes responsible for plasma transport and acceleration operating within these thin boundaries require high-resolution data. We present an event observed by the Magnetospheric Multiscale (MMS) mission as the spacecraft cross a reconnection diffusion region at the magnetopause. We investigate the kinetic structure of the reconnection layer including particle distribution functions and waves and find what terms in the generalized Ohm's law balances the observed electric field.

  7. Ultraviolet emission of current sheets on the sun

    NASA Astrophysics Data System (ADS)

    Kuznetsov, V. D.

    1981-04-01

    Calculations are presented for the ultraviolet flux densities expected from a current sheet radiating in the lines of ions, at temperatures lower than 100,000 K. An opportunity for flare prediction is seen in the development of enhanced ultraviolet emission from preflare processes, which would be observable several hours prior to the flare. The higher the energy of the flare, (1) the stronger the preflare region ultraviolet and radio emission will be, and (2) the farther toward the shortwave part of the radio spectrum the preflare situation will be observed.

  8. Generation of sheet currents by high frequency fast MHD waves

    NASA Astrophysics Data System (ADS)

    Núñez, Manuel

    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.

  9. Continuous development of current sheets near and away from magnetic nulls

    NASA Astrophysics Data System (ADS)

    Kumar, Sanjay; Bhattacharyya, R.

    2016-04-01

    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.

  10. High current density sheet-like electron beam generator

    NASA Astrophysics Data System (ADS)

    Chow-Miller, Cora; Korevaar, Eric; Schuster, John

    Sheet electron beams are very desirable for coupling to the evanescent waves in small millimeter wave slow-wave circuits to achieve higher powers. In particular, they are critical for operation of the free-electron-laser-like Orotron. The program was a systematic effort to establish a solid technology base for such a sheet-like electron emitter system that will facilitate the detailed studies of beam propagation stability. Specifically, the effort involved the design and test of a novel electron gun using Lanthanum hexaboride (LaB6) as the thermionic cathode material. Three sets of experiments were performed to measure beam propagation as a function of collector current, beam voltage, and heating power. The design demonstrated its reliability by delivering 386.5 hours of operation throughout the weeks of experimentation. In addition, the cathode survived two venting and pump down cycles without being poisoned or losing its emission characteristics. A current density of 10.7 A/sq cm. was measured while operating at 50 W of ohmic heating power. Preliminary results indicate that the nearby presence of a metal plate can stabilize the beam.

  11. Reconnection in photospheric-chromospheric current sheet and coronal heating

    SciTech Connect

    Kumar, P.; Kumar, N.; Uddin, W.

    2011-02-15

    It has been observed by various ground and space based solar missions that magnetic reconnection occurs frequently in the photosphere-chromosphere region as well as in the solar corona. The purpose of this article is to examine the process of reconnection in thin current sheet formed between two oppositely directed magnetic flux tubes in photospheric-chromospheric region. Using the data of different atmospheric models for the solar photosphere and chromosphere, we have estimated the rate of magnetic reconnection in terms of Alfvenic Mach number, growth rate of tearing mode, island length scales, and energy dissipation rate necessary to heat the chromospheric plasma. It is found that magnetic Reynolds number for the current sheet in the chromosphere varies from 1.14 Multiplication-Sign 10{sup 3} to 7.14 Multiplication-Sign 10{sup 6} which indicates that the field lines in the photosphere and chromosphere reconnect with speed, that is, 0.00034 to 0.0297 times the Alfven speed. Frequency of the MHD waves generated in the chromosphere reconnection region is of the order of 100 Hz, so these high-frequency waves may be the sources of coronal heating and solar wind acceleration.

  12. New insights from modeling the wavy heliospheric current sheet

    NASA Astrophysics Data System (ADS)

    Raath, Jan-Louis; Toit Strauss, Du; Potgieter, Marius

    2016-07-01

    The solar modulation of cosmic rays has increasingly been studied by utilizing numerical modulation models based on the solution of an appropriate set of stochastic differential equations (SDEs). We apply such a SDE-based model to study the modulation effects of the wavy heliospheric current sheet (HCS), in particular as its waviness increases with solar activity up to extreme maximum conditions. The SDE-model allows for more in-depth studies because of its numerical stability as well as its ability to trace pseudo-particles so that insightful trajectories of how they respond to the wavy heliospheric current sheet can be computed and displayed. We present valuable insights into how the geometry of the wavy HCS can affect the modulation of cosmic rays, especially at the highest levels of solar activity. This enables us to show, from a modeling perspective, why a certain choice for the HCS profile is more suited than another at these high activity levels. We also discuss the concept of an effective HCS tilt angle and emphasize its importance by illustrating how it can be employed effectively in interpreting modulation results pertaining to drifts along the wavy HCS.

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

    SciTech Connect

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

    2015-05-01

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

  14. Collisionless magnetic reconnection under anisotropic MHD approximation

    NASA Astrophysics Data System (ADS)

    Hirabayashi, Kota; Hoshino, Masahiro

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

  15. Earth magnetotail current sheet near and beyond the Lunar orbit

    NASA Astrophysics Data System (ADS)

    Vasko, I.; Petrukovich, A. A.; Artemyev, A.; Nakamura, R.; Zelenyi, L. M.

    2015-12-01

    We analyze the structure of the Earth magnetotail current sheet (CS) in middle, -50 REcurrent sheet thickness L, current density amplitude j0 and velocity vD=j0/e n0 (n0 is the plasma density). We analyze dawn-dusk distributions of the CS parameters: L is about 3000 km at the dusk flank and grows up to 12000 km toward the dawn flank; j0 grows toward the dusk flank by a factor of 2-3; the most intense CSs (with higher vD) are observed near the midnight. We show that ion-scale CSs with the thickness of several ion thermal gyroradii (say less than seven) are observed in middle and distant tail regions in more than 50% of crossings. For observed CSs electrons provide likely the dominant contribution to the current density. We divide the subset into intense and weak CSs (using parameter vD). The weak CSs have thickness of about 20 ion thermal gyroradii and Bz of about 1.5 nT. The intense CSs have thickness of about 3-7 thermal gyroradii and much smaller Bz implying a more stretched field line configuration. For intense CSs velocity vD is larger for larger amplitudes of ion bulk velocity vx that is likely due to larger contribution of Speiser ions. Intense CSs may be responsible for the Bursty Bulk Flow generation in the middle and distant tail regions.

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

    SciTech Connect

    Sorin Zaharia; C.Z. Cheng

    2003-04-30

    Two important phenomena observed during the magnetospheric substorm growth phase are modeled: the formation of a near-Earth (|X| {approx} 9 R{sub 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{sub {phi}} {approx} 10 nA/m{sup 2}) and very high plasma {beta} ({beta} {approx} 40) between 7 and 10 R{sub 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{sub {parallel}max} {approx} 3 {micro}A/m{sup 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.

  17. Plume Contribution to the Plasma Sheet and Ring Current

    NASA Astrophysics Data System (ADS)

    Moore, T. E.; Fok, M. H.; Delcourt, D. C.; Slinker, S. P.; Fedder, J. A.

    2007-05-01

    We investigate the fate of plasmaspheric plumes to assess the resultant enhancement of plasma sheet and ring current pressure and compare with that for steady polar wind outflows. We use test particle motions in LFM global circulation model fields. The inner magnetosphere is simulated with the CRCM model of Fok and Wolf, including the Ober plasmasphere model. Global circulation is stimulated by a period of southward IMF embedded in a longer interval of northward IMF. This leads to the production of a realistic plasmaspheric plume, enhancing the plasma density on the dayside. Large numbers of test particles are launched with the properties of plasmaspheric ions on the L=8 shell, and weighted by densities as specified by the Ober model, as it responds to enhanced convection. Particles are tracked until they are lost from the system downstream or into the atmosphere, using the full equations of motion as implemented in the Delcourt code. Results are compared with earlier computations for polar wind outflows from the region above 55 deg. latitude. The plume produces an enhanced cloud of polar wind like plasma that flows through the polar caps and lobes, entering the plasma sheet reconnection region and splitting into earthward and tailward flows. We assess the magnitude and duration of the resultant pressure enhancement.

  18. Catapult current sheet relaxation model confirmed by THEMIS observations

    NASA Astrophysics Data System (ADS)

    Machida, S.; Miyashita, Y.; Ieda, A.; Nose, M.; Angelopoulos, V.; McFadden, J. P.

    2014-12-01

    In this study, we show the result of superposed epoch analysis on the THEMIS probe data during the period from November, 2007 to April, 2009 by setting the origin of time axis to the substorm onset determined by Nishimura with THEMIS all sky imager (THEMS/ASI) data (http://www.atmos.ucla.edu/~toshi/files/paper/Toshi_THEMIS_GBO_list_distribution.xls). We confirmed the presence of earthward flows which can be associated with north-south auroral streamers during the substorm growth phase. At around X = -12 Earth radii (Re), the northward magnetic field and its elevation angle decreased markedly approximately 4 min before substorm onset. A northward magnetic-field increase associated with pre-onset earthward flows was found at around X = -17Re. This variation indicates the occurrence of the local depolarization. Interestingly, in the region earthwards of X = -18Re, earthward flows in the central plasma sheet (CPS) reduced significantly about 3min before substorm onset. However, the earthward flows enhanced again at t = -60 sec in the region around X = -14 Re, and they moved toward the Earth. At t = 0, the dipolarization of the magnetic field started at X ~ -10 Re, and simultaneously the magnetic reconnection started at X ~ -20 Re. Synthesizing these results, we can confirm the validity of our catapult current sheet relaxation model.

  19. Substorm onset: Current sheet avalanche and stop layer

    NASA Astrophysics Data System (ADS)

    Haerendel, Gerhard

    2015-03-01

    A new scenario is presented for the onset of a substorm and the nature of the breakup arc. There are two main components, current sheet avalanche and stop layer. The first refers to an earthward flow of plasma and magnetic flux from the central current sheet of the tail, triggered spontaneously or by some unknown interaction with an auroral streamer or a suddenly appearing eastward flow at the end of the growth phase. The second offers a mechanism to stop the flow abruptly at the interface between magnetosphere and tail and extract momentum and energy to be partially processed locally and partially transmitted as Poynting flux toward the ionosphere. The stop layer has a width of the order of the ion inertial length. The different dynamics of the ions entering freely and the magnetized electrons create an electric polarization field which stops the ion flow and drives a Hall current by which flow momentum is transferred to the magnetic field. A simple formalism is used to describe the operation of the process and to enable quantitative conclusions. An important conclusion is that by necessity the stop layer is also highly structured in longitude. This offers a natural explanation for the coarse ray structure of the breakup arc as manifestation of elementary paths of energy and momentum transport. The currents aligned with the rays are balanced between upward and downward directions. While the avalanche is invoked for explaining the spontaneous substorm onset at the inner edge of the tail, the expansion of the breakup arc for many minutes is taken as evidence for a continued formation of new stop layers by arrival of flow bursts from the near-Earth neutral line. This is in line with earlier conclusions about the nature of the breakup arc. Small-scale structure, propagation speed, and energy flux are quantitatively consistent with observations. However, the balanced small-scale currents cannot constitute the substorm current wedge. The source of the latter must be

  20. Particle distributions in collisionless magnetic reconnection: An implicit Particle-In-Cell (PIC) description

    SciTech Connect

    Hewett, D.W.; Francis, G.E.; Max, C.E.

    1990-06-29

    Evidence from magnetospheric and solar flare research supports the belief that collisionless magnetic reconnection can proceed on the Alfven-wave crossing timescale. Reconnection behavior that occurs this rapidly in collisionless plasmas is not well understood because underlying mechanisms depend on the details of the ion and electron distributions in the vicinity of the emerging X-points. We use the direct implicit Particle-In-Cell (PIC) code AVANTI to study the details of these distributions as they evolve in the self-consistent E and B fields of magnetic reconnection. We first consider a simple neutral sheet model. We observe rapid movement of the current-carrying electrons away from the emerging X-point. Later in time an oscillation of the trapped magnetic flux is found, superimposed upon continued linear growth due to plasma inflow at the ion sound speed. The addition of a current-aligned and a normal B field widen the scope of our studies.

  1. A new fast reconnection model in a collisionless regime

    SciTech Connect

    Tsiklauri, David

    2008-11-15

    Based on the first principles [i.e., (i) by balancing the magnetic field advection with the term containing electron pressure tensor nongyrotropic components in the generalized Ohm's law; (ii) using the conservation of mass; and (iii) assuming that the weak magnetic field region width, where electron meandering motion supports electron pressure tensor off-diagonal (nongyrotropic) components, is of the order of electron Larmor radius] a simple model of magnetic reconnection in a collisionless regime is formulated. The model is general, resembling its collisional Sweet-Parker analog in that it is not specific to any initial configuration, e.g., Harris-type tearing unstable current sheet, X-point collapse or otherwise. In addition to its importance from the fundamental point of view, the collisionless reconnection model offers a much faster reconnection rate [M{sub c{sup '}}{sub less}=(c/{omega}{sub pe}){sup 2}/(r{sub L,e}L)] than Sweet-Parker's classical one (M{sub sp}=S{sup -1/2}). The width of the diffusion region (current sheet) in the collisionless regime is found to be {delta}{sub c{sup '}}{sub less}=(c/{omega}{sub pe}){sup 2}/r{sub L,e}, which is independent of the global reconnection scale L and is only prescribed by microphysics (electron inertial length, c/{omega}{sub pe}, and electron Larmor radius, r{sub L,e}). Amongst other issues, the fastness of the reconnection rate alleviates, e.g., the problem of interpretation of solar flares by means of reconnection, as for the typical solar coronal parameters the obtained collisionless reconnection time can be a few minutes, as opposed to Sweet-Parker's equivalent value of less than a day. The new theoretical reconnection rate is compared to the Magnetic Reconnection Experiment device experimental data by Yamada et al. [Phys. Plasmas 13, 052119 (2006)] and Ji et al. [Geophys. Res. Lett. 35, 13106 (2008)], and a good agreement is obtained.

  2. The peculiarities of formation of thin current sheet in the Earth's magnetotail

    NASA Astrophysics Data System (ADS)

    Kropotkin, Alexey; Artemyev, Anton; Malova, Helmi; Domrin, Vladimir

    We investigate the process of self-consistent thinning of magnetotail current sheet in the presence of the evolving magnetic field normal component Bz, which usually decreases during the substorm growth phase. Using PIC codes to describe plasma processes with ions becoming demagnetized and electrons being considered as the cold neutralizing background, we show that the appearance of the self-consistent electric field component inside CS can lead to the current sheet thinning and to the appearance of an extremely thin current sheet with thickness close to the ion gyroradius. Due to particle [ExB] drift during the current sheet evolution, the enhanced trapping of ions near the current sheet central plane takes place. It is shown that the density of quasi-trapped particles around current sheet at the final stage depends on both the value of the initial magnetic field normal component Bz, and the speed of the Bz decrease. If the initial magnetic field normal component is less than about 0.14 of the tangential field at the edges, the trapped plasma density near the current sheet is small. As a result, the above mentioned extremely thin current sheet is formed. In the opposite case, when the initial normal component related to the tangential field is larger than 0.14, the density of trapped particles is much higher, which produces effective thickening of the current sheet. In both cases transient (Speiser) ions are the main current carriers, but in the second case local diamagnetic currents of the trapped plasma perturb the сurrent sheet profile making it thicker. Also trapped particles can be responsible for intense negative currents at the current sheet edges. During the Bz decrease, an additional effect of ion polarization drifts in the Y direction can compete with these negative diamagnetic fields of quasi-trapped ions. Therefore the ion dynamics is probably the general mechanism which contributes to the formation of thin current sheet and its fine structure.

  3. THEMIS two‐point measurements of the cross‐tail current density: A thick bifurcated current sheet in the near‐Earth plasma sheet

    PubMed Central

    2015-01-01

    Abstract The basic properties of the near‐Earth current sheet from 8 RE to 12 RE were determined based on Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations from 2007 to 2013. Ampere's law was used to estimate the current density when the locations of two spacecraft were suitable for the calculation. A total of 3838 current density observations were obtained to study the vertical profile. For typical solar wind conditions, the current density near (off) the central plane of the current sheet ranged from 1 to 2 nA/m2 (1 to 8 nA/m2). All the high current densities appeared off the central plane of the current sheet, indicating the formation of a bifurcated current sheet structure when the current density increased above 2 nA/m2. The median profile also showed a bifurcated structure, in which the half thickness was about 3 RE. The distance between the peak of the current density and the central plane of the current sheet was 0.5 to 1 RE. High current densities above 4 nA/m2 were observed in some cases that occurred preferentially during substorms, but they also occurred in quiet times. In contrast to the commonly accepted picture, these high current densities can form without a high solar wind dynamic pressure. In addition, these high current densities can appear in two magnetic configurations: tail‐like and dipolar structures. At least two mechanisms, magnetic flux depletion and new current system formation during the expansion phase, other than plasma sheet compression are responsible for the formation of the bifurcated current sheets. PMID:27722039

  4. Analogies between Jovian magnetodisk and heliospheric current sheet

    NASA Astrophysics Data System (ADS)

    Kislov, Roman; Khabarova, Olga; Malova, Helmi

    Recently due to the development of spatial missions the famous model by E. Parker [1] faced with some problems, such as the effect of magnetic flux excess and the existence of latitude component of magnetic field [2]. Thus the incomplete knowledge about large scale current system of heliospheric current sheet (HCS) motivated us to construct and investigate the self-consistent axisymmetric stationary MHD model of HCS and to compare it with earlier presented model of Jupiterian magnetodisk [3]. Both HCS and magnetodisk have inner plasma sources (i.e. the Sun in case of HCS and satellite Io in case of Jupiter); also they depend on the centrifugal force at small distances and on corotation processes. They both have strong radial component of current density, thin elongated structure etc. Thus in the frame of the MHD model we have calculated for HCS the parallel currents (analogous to Jovian Birkeland currents) and we obtained the latitude component of the magnetic field. The results of the model allowed us to explain the magnetic flux excess by the existence of the self-consistent HCS magnetic field. The decrease of radial magnetic field from the distance from the Sun as the power -5/3 obtained by numerical calculations is in good agreement with experimental data. Generally this model can be applied for the quiet period of the low solar activity when the perturbation of HCS structure named “ballerina skirt” does not play any role. References: 1. Parker E. N., Astrophys. J., V. 128, 664, pp. 664-676, 1958. 2. Khabarova O. V., Астрономический журнал, V. 90, №11, pp. 919-935, 2013. 3. Kislov R.A. et al., Bull. MSU, Physics and Astron., 2013

  5. Current sheet thinning, reconnection onset, and auroral morphology during geomagnetic substorms

    NASA Astrophysics Data System (ADS)

    Otto, A.; Hsieh, M. S.

    2015-12-01

    Geomagnetic substorms represent a fundamental energy release mechanism for the terrestrial magnetosphere. Specifically, the evolution of thin currents sheets during the substorm growth phase plays a key role for substorms because such current sheets present a much lower threshold for the onset of tearing modes and magnetic reconnection than the usually thick magnetotail current sheet. Here we examine and compare two basic processes for current sheet thinning in the Earth's magnetotail: Current sheet thinning (1) through closed magnetic flux depletion (MFD) in the near Earth magnetotail caused by divergent flux transport to replace closed flux on the dayside and (2) through accumulation of open flux magnetic flux in the tail lobes also caused by dayside reconnection. Both processes are expected to operate during any period of enhanced dayside reconnection. It is demonstrated that closed magnetic flux depletion (MFD) in the near Earth magnetotail and the increase of open lobe magnetic flux can lead to the evolution of two separate thin current sheets in the near Earth and the mid tail regions of the magnetosphere. While the auroral morphology associated with MFD and near Earth current sheet formation is well consistent with typical substorm growth observation, midtail current sheet formation through lobe flux increase shows only a minor influence on the auroral ionosphere. We discuss the physics of the dual current sheet formation and local and auroral properties of magnetic reconnection in either current sheet. It is suggested that only reconnection onset in the near Earth current sheet may be consistent with substorm expansion because the flux tube entropy depletion of mid tail reconnection appears insufficient to cause geosynchronous particle injection and dipolarization. Therefore reconnection in the mid tail current sheet is more likely associated with bursty bulk flows or dipolarization fronts which stop short of geosynchronous distances.

  6. Hybrid modeling of the formation and structure of thin current sheets in the magnetotail

    SciTech Connect

    Hesse, M.; Winske, D.; Birn, J.

    1996-07-01

    Hybrid simulations are used to investigate the formation of a thin current sheet inside the plasma sheet of a magnetotail-like configuration. The initial equilibrium is subjected to a driving electric field qualitatively similar to what would be expected from solar wind driving. As a result, we find the formation of a raw current sheet, with a thickness of approximately the ion inertial length. The current density inside the current sheet region is supplied largely by the electrons. Ion acceleration in the cross-tail direction is absent due since the driving electric field fails to penetrate into the equatorial region.

  7. Collisionless shocks in the heliosphere: A tutorial review

    NASA Technical Reports Server (NTRS)

    Stone, Robert G. (Editor); Tsurutani, Bruce T. (Editor)

    1985-01-01

    An update is presented on current knowledge of collisionless shocks in the heliosphere. The individual papers address: a quarter century of collisionless shock research, some macroscopic properties of shock waves in the heliosphere, microinstabilities and anomalous transport, and acceleration of energetic particles.

  8. Growth-phase thinning of the near-Earth current sheet during the CDAW 6 substorm

    NASA Technical Reports Server (NTRS)

    Sanny, Jeff; Mcpherron, R. L.; Russell, C. T.; Baker, D. N.; Pulkkinen, T. I.; Nishida, A.

    1994-01-01

    The thinning of the near-Earth current sheet during the growth phase of the Coordinated Data Analysis Workshop (CDAW) 6 magnetospheric substorm is studied. The expansion onset of the substorm occurred at 1054 UT, March 22, 1979. During the growth phase, two spacecraft, International Sun Earth Explorer (ISEE) 1 and ISEE 2, were within the current sheet approximately 13 R(sub E) from the Earth and obtained simultaneous high-resolution magnetic data at two points in the current sheet. Plasma data were also provided by the ISEE spacecraft and solar wind data by IMP 8. To facilitate the analysis, the GSM magnetic field data are transformed to a 'neutral sheet coordinate system' in which the new x axis is parallel to the average magnetic field above and below the neutral sheet and the new y axis lies in the GSM equatorial plane. A model based on the assumption that the current sheet is a time-invariant structure fails to predict neutral sheet crossing times. Consequently, the Harris sheet model, which allows one to remove the restriction of time invariancy, is used instead. It is found that during the growth phase, a model parameter corresponding to the thickness of the current sheet decreased exponentially from about 5 R(sub E) to 1 R(sub E) with a time constant of about 14 min. In addition, the ISEE 1 and ISEE 2 neutral sheet crossings after expansion onset indicate that the neutral sheet was moving upward at 7 km/s relative to the spacecraft. Since both crossings occurred in approximately 80 s, the current sheet thickness is estimated to be about 500 km. These results demonstrate that the near-Earth current sheet undergoes dramatic thinning during the substorm growth phase and expansion onset.

  9. Heliospheric current sheet in the distant solar wind plasma

    NASA Astrophysics Data System (ADS)

    Borovikov, S.; Pogorelov, N. V.; Zank, G. P.; Kryukov, I. A.

    2007-12-01

    Since Voyager 1 plasma instrument is not operational, understanding the data obtained by its magnetometer is of great importance for heliospheric community. One of the main difficulties one encounters when modeling the interplanetary magnetic field (IMF) in the solar wind (SW) is the necessity of a very fine resolution of the heliospheric current sheet (HCS). The angle between the Sun's rotation and magnetic-dipole axes is never zero, varying from about 8-9 degrees during solar minima to 90 degrees at solar maxima. As a result of Sun's rotation, the distance between two consecutive crossings of the ecliptic plane by the HCS becomes as small as about 3 AU in the supersonic SW and necessarily smaller in the inner heliosheath. As shown by Pogorelov (2006), charge exchange of the SW plasma with the interstellar medium neutrals can affect the HCS behavior qualitatively. This study is an attempt to investigate the HCS evolution in the SW from its origin at the inner boundary of the computational region out into the heliosheath. Comparison is made of the ideal MHD and MHD-neutral solutions.

  10. Modeling the heliospheric current sheet: Solar cycle variations

    NASA Astrophysics Data System (ADS)

    Riley, Pete; Linker, J. A.; Mikić, Z.

    2002-07-01

    In this report we employ an empirically driven, three-dimensional MHD model to explore the evolution of the heliospheric current sheet (HCS) during the course of the solar cycle. We compare our results with a simpler ``constant-speed'' approach for mapping the HCS outward into the solar wind to demonstrate that dynamic effects can substantially deform the HCS in the inner heliosphere (<~5 AU). We find that these deformations are most pronounced at solar minimum and become less significant at solar maximum, when interaction regions are less effective. Although solar maximum is typically associated with transient, rather than corotating, processes, we show that even under such conditions, the HCS can maintain its structure over the course of several solar rotations. While the HCS may almost always be topologically equivalent to a ``ballerina skirt,'' we discuss an interval approaching the maximum of solar cycle 23 (Carrington rotations 1960 and 1961) when the shape would be better described as ``conch shell''-like. We use Ulysses magnetic field measurements to support the model results.

  11. Solar wind eddies and the heliospheric current sheet

    NASA Technical Reports Server (NTRS)

    Suess, S. T.; Mccomas, D. J.; Bame, S. J.; Goldstein, B. E.

    1995-01-01

    Ulysses has collected data between 1 and 5 AU during, and just following solar maximum, when the heliospheric current sheet (HCS) can be thought of as reaching its maximum tilt and being subject to the maximum amount of turbulence in the solar wind. The Ulysses solar wind plasma instrument measures the vector velocity and can be used to estimate the flow speed and direction in turbulent 'eddies' in the solar wind that are a fraction of an astronomical unit in size and last (have either a turnover or dynamical interaction time of) several hours to more than a day. Here, in a simple exercise, these solar wind eddies at the HCS are characterized using Ulysses data. This character is then used to define a model flow field with eddies that is imposed on an ideal HCS to estimate how the HCS will be deformed by the flow. This model inherently results in the complexity of the HCS increasing with heliocentric distance, but the result is a measure of the degree to which the observed change in complexity is a measure of the importance of solar wind flows in deforming the HCS. By comparison with randomly selected intervals not located on the HCS, it appears that eddies on the HCS are similar to those elsewhere at this time during the solar cycle, as is the resultant deformation of the interplanetary magnetic field (IMF). The IMF deformation is analogous to what is often termed the 'random walk' of interplanetary magnetic field lines.

  12. Statistical Analysis of Current Sheets in Three-dimensional Magnetohydrodynamic Turbulence

    NASA Astrophysics Data System (ADS)

    Zhdankin, Vladimir; Uzdensky, Dmitri A.; Perez, Jean C.; Boldyrev, Stanislav

    2013-07-01

    We develop a framework for studying the statistical properties of current sheets in numerical simulations of magnetohydrodynamic (MHD) turbulence with a strong guide field, as modeled by reduced MHD. We describe an algorithm that identifies current sheets in a simulation snapshot and then determines their geometrical properties (including length, width, and thickness) and intensities (peak current density and total energy dissipation rate). We then apply this procedure to simulations of reduced MHD and perform a statistical analysis on the obtained population of current sheets. We evaluate the role of reconnection by separately studying the populations of current sheets which contain magnetic X-points and those which do not. We find that the statistical properties of the two populations are different in general. We compare the scaling of these properties to phenomenological predictions obtained for the inertial range of MHD turbulence. Finally, we test whether the reconnecting current sheets are consistent with the Sweet-Parker model.

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

    SciTech Connect

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

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  15. Dielectric and permeability effects in collisionless plasmas. [in collisionless plasmas

    NASA Technical Reports Server (NTRS)

    Cole, K. D.

    1984-01-01

    Using the unabridged Maxwell equations (including vectors D, E and H) new effects in collisionless plasmas are uncovered. In a steady state, it is found that spatially varying energy density of the electric field (E perpendicular) orthogonal to B produces electric current leading, under certain conditions, to the relationship P perpendicular + B(2)/8 pi-epsilon E perpendicular(2)/8 pi = constant, where epsilon is the dielectric constant of the plasma for fields orthogonal to B. In steady state quasi-two-dimensional flows in plasmas, a general relationship between the components of electric field parallel and perpendicular to B is found. These effects are significant in geophysical and astrophysical plasmas. The general conditions for a steady state in collisionless plasma are deduced. With time variations in a plasma, slow compared to ion-gyroperiod, there is a general current, (j-asterisk), which includes the well-known polarization current, given by J-asterisk = d/dt (E x M) + (P x B) x B B(-2) where M and P are the magnetization and polarization vectors respectively.

  16. A hybrid-Vlasov model based on the current advance method for the simulation of collisionless magnetized plasma

    SciTech Connect

    Valentini, F. . E-mail: valentin@fis.unical.it; Travnicek, P.; Califano, F.; Hellinger, P.; Mangeney, A.

    2007-07-01

    We present a numerical scheme for the integration of the Vlasov-Maxwell system of equations for a non-relativistic plasma, in the hybrid approximation, where the Vlasov equation is solved for the ion distribution function and the electrons are treated as a fluid. In the Ohm equation for the electric field, effects of electron inertia have been retained, in order to include the small scale dynamics up to characteristic lengths of the order of the electron skin depth. The low frequency approximation is used by neglecting the time derivative of the electric field, i.e. the displacement current in the Ampere equation. The numerical algorithm consists in coupling the splitting method proposed by Cheng and Knorr in 1976 [C.Z. Cheng, G. Knorr, J. Comput. Phys. 22 (1976) 330-351.] and the current advance method (CAM) introduced by Matthews in 1994 [A.P. Matthews, J. Comput. Phys. 112 (1994) 102-116.] In its present version, the code solves the Vlasov-Maxwell equations in a five-dimensional phase space (2-D in the physical space and 3-D in the velocity space) and it is implemented in a parallel version to exploit the computational power of the modern massively parallel supercomputers. The structure of the algorithm and the coupling between the splitting method and the CAM method (extended to the hybrid case) is discussed in detail. Furthermore, in order to test the hybrid-Vlasov code, the numerical results on propagation and damping of linear ion-acoustic modes and time evolution of linear elliptically polarized Alfven waves (including the so-called whistler regime) are compared to the analytical solutions. Finally, the numerical results of the hybrid-Vlasov code on the parametric instability of Alfven waves are compared with those obtained using a two-fluid approach.

  17. Galactic Cosmic Ray Modulation near the Heliospheric Current Sheet

    NASA Astrophysics Data System (ADS)

    Thomas, S. R.; Owens, M. J.; Lockwood, M.; Scott, C. J.

    2014-07-01

    Galactic cosmic rays (GCRs) are modulated by the heliospheric magnetic field (HMF) both over decadal time scales (due to long-term, global HMF variations), and over time scales of a few hours (associated with solar wind structures such as coronal mass ejections or the heliospheric current sheet, HCS). Due to the close association between the HCS, the streamer belt, and the band of slow solar wind, HCS crossings are often associated with corotating interaction regions where fast solar wind catches up and compresses slow solar wind ahead of it. However, not all HCS crossings are associated with strong compressions. In this study we categorize HCS crossings in two ways: Firstly, using the change in magnetic polarity, as either away-to-toward (AT) or toward-to-away (TA) magnetic field directions relative to the Sun and, secondly, using the strength of the associated solar wind compression, determined from the observed plasma density enhancement. For each category, we use superposed epoch analyses to show differences in both solar wind parameters and GCR flux inferred from neutron monitors. For strong-compression HCS crossings, we observe a peak in neutron counts preceding the HCS crossing, followed by a large drop after the crossing, attributable to the so-called `snow-plough' effect. For weak-compression HCS crossings, where magnetic field polarity effects are more readily observable, we instead observe that the neutron counts have a tendency to peak in the away magnetic field sector. By splitting the data by the dominant polarity at each solar polar region, we find that the increase in GCR flux prior to the HCS crossing is primarily from strong compressions in cycles with negative north polar fields due to GCR drift effects. Finally, we report on unexpected differences in GCR behavior between TA weak compressions during opposing polarity cycles.

  18. Electron Force Balance in Steady Collisionless-Driven Reconnection

    SciTech Connect

    Li Bin; Horiuchi, Ritoku

    2008-11-21

    Steady collisionless-driven reconnection in an open system is investigated by means of full-particle simulations. A long thin electron current sheet extends towards the outflow direction when the system relaxes to a steady state. Although the pressure tensor term along the reconnection electric field contributes to the violation of the electron frozen-in condition, a new force balance in the inflow direction is realized between the Lorentz and electrostatic forces, which is quite different from that in Harris equilibrium. The strong electrostatic field is generated through the combined effect of the Hall term and a driving inflow. This new force balance is more evident in the three-dimensional case due to the growth of an instability along the reconnection electric field. It is also found that the normalized charge density is in proportion to the square of the electron Alfven velocity averaged over the electron dissipation region.

  19. A Trigger Mechanism of Magnetic Reconnection and Particle Acceleration during Thinning of the Current Sheet

    NASA Astrophysics Data System (ADS)

    Saito, S.; Sakai, J. I.

    2006-11-01

    One of the trigger mechanisms of magnetic reconnection in the compressing current sheet is studied by using a two-dimensional full particle-in-cell code modified from the TRISTAN code. In the compressed current sheet, the electrons are heated preferentially perpendicular to the magnetic field due to adiabatic heating. The thinning and anisotropy T⊥/T|| of electrons in the current sheet vigorously enhance the tearing instability with several small-scale magnetic islands. The generated magnetic islands successively coalesce and the magnetic energy is converted into plasma kinetic energy. Through the coalescence, high-energy electrons are quasi-periodically produced. At almost the same time, some ions are accelerated by the magnetosonic shock waves generated around the current sheet. The acceleration sites for the ions move the outside of the current sheet. At the final stage, all magnetic islands merge into a large one whose width is about 10 times larger than the compressed sheet width. The thinning of the current sheet leads to the generation of large-scale magnetic islands and converts the magnetic field energy into kinetic energy of the plasma. The dynamical evolution of current sheets can be applied to solar flares.

  20. Current Sheet Formation in a Conical Theta Pinch Faraday Accelerator with Radio-frequency Assisted Discharge

    NASA Technical Reports Server (NTRS)

    Polzin, Kurt A.; Hallock, Ashley K.; Choueiri, Edgar Y.

    2008-01-01

    Data from an inductive conical theta pinch accelerator are presented to gain insight into the process of inductive current sheet formation in the presence of a preionized background gas produced by a steady-state RF-discharge. The presence of a preionized plasma has been previously shown to allow for current sheet formation at lower discharge voltages and energies than those found in other pulsed inductive accelerator concepts, leading to greater accelerator efficiencies at lower power levels. Time-resolved magnetic probe measurements are obtained for different background pressures and pulse energies to characterize the effects of these parameters on current sheet formation. Indices are defined that describe time-resolved current sheet characteristics, such as the total current owing in the current sheet, the time-integrated total current ('strength'), and current sheet velocity. It is found that for a given electric field strength, maximums in total current, strength, and velocity occur for one particular background pressure. At other pressures, these current sheet indices are considerably smaller. The trends observed in these indices are explained in terms of the principles behind Townsend breakdown that lead to a dependence on the ratio of the electric field to the background pressure. Time-integrated photographic data are also obtained at the same experimental conditions, and qualitatively they compare quite favorably with the time-resolved magnetic field data.

  1. Radial profile of magnetic field in earth magnetotail current sheet

    NASA Astrophysics Data System (ADS)

    Rong, Zhaojin; Wan, Weixing; Shen, Chao; Petrukovich, Anatoli; Zhang, Tielong; Baumjohann, Wolfgang; Dunlop, Malcolm; Zhang, Yongcun

    2014-05-01

    Knowing the magnetic field distribution in the magnetotail current sheet (CS) is essential for exploring magnetotail dynamics. In this study, using a joint dataset of Cluster/TC-1, the radial profile of the magnetic field in the magnetotail CS with radial distances covering 8 100 nT for active times) and solar wind parameters are statistically surveyed. Our new findings demonstrate that, independent of the activity state, the field strength and Bz component (GSM coordinates) start the monotonous increase prominently as r decreases down to ~11.5RE, which means the dipole field starts to make a significant contribution from there. At least in the surveyed radial range, the Bz component is found to be weaker in the midnight sector and at the dusk flank than that at the dawn flank, displaying a dawn-dusk asymmetry. The occurrence rate of negative Bz during active times also exhibites a similar asymmetric distribution, which implies active dynamics may occur more frequently at midnight and dusk flank. In contrast to quiet intervals, several features can be seen during active times: (1) a local Bz minimum between 10.55 nPa), which may support the dawn-dusk squeezeing effect presented in the case study of Miyashita et al. [2010]. The CS By is generally correlated with the interplanetary magnetic field (IMF) By component, but the correlation is better with higher penetration coefficient (the ratio of CS By to IMF By) when IMF Bz is positive. The implications of the present results are

  2. Radial distribution of magnetic field in earth magnetotail current sheet

    NASA Astrophysics Data System (ADS)

    Rong, Z. J.; Wan, W. X.; Shen, C.; Petrukovich, A. A.; Baumjohann, W.; Dunlop, M. W.; Zhang, Y. C.

    2014-11-01

    Knowing the magnetic field distribution in the magnetotail current sheet (CS) is essential for exploring magnetotail dynamics. In this study, using a joint dataset of Cluster/TC-1, the radial profile of the magnetic field in the magnetotail CS with radial distances covering 8100 nT for active times) and solar wind parameters are statistically surveyed. Our new findings demonstrate that, independent of the activity state, the field strength and Bz component (GSM coordinates) start the monotonic increase prominently as r decreases down to ~11.5RE, which means the dipole field starts to make a significant contribution from there. At least in the surveyed radial range, the Bz component is found to be weaker in the midnight and dusk sectors than that in the dawn sector, displaying a dawn-dusk asymmetry. The occurrence rate of negative Bz in active times also exhibits a similar asymmetric distribution, which implies active dynamics may occur more frequently at midnight and dusk flank. In comparison with that in quiet intervals, several features can be seen in active times: (1) a local Bz minimum between 10.55 nPa), which may support the dawn-dusk squeezing effect as presented by Miyashita et al. (2010). The CS By is generally correlated with the interplanetary magnetic field (IMF) By component, and the correlation quality is found to be better with higher penetration coefficient (the ratio of CS By to IMF By) when IMF Bz is positive. The implications of the present results are discussed.

  3. Nonlinear evolution of three-dimensional instabilities of thin and thick electron scale current sheets: Plasmoid formation and current filamentation

    SciTech Connect

    Jain, Neeraj; Büchner, Jörg

    2014-07-15

    Nonlinear evolution of three dimensional electron shear flow instabilities of an electron current sheet (ECS) is studied using electron-magnetohydrodynamic simulations. The dependence of the evolution on current sheet thickness is examined. For thin current sheets (half thickness =d{sub e}=c/ω{sub pe}), tearing mode instability dominates. In its nonlinear evolution, it leads to the formation of oblique current channels. Magnetic field lines form 3-D magnetic spirals. Even in the absence of initial guide field, the out-of-reconnection-plane magnetic field generated by the tearing instability itself may play the role of guide field in the growth of secondary finite-guide-field instabilities. For thicker current sheets (half thickness ∼5 d{sub e}), both tearing and non-tearing modes grow. Due to the non-tearing mode, current sheet becomes corrugated in the beginning of the evolution. In this case, tearing mode lets the magnetic field reconnect in the corrugated ECS. Later thick ECS develops filamentary structures and turbulence in which reconnection occurs. This evolution of thick ECS provides an example of reconnection in self-generated turbulence. The power spectra for both the thin and thick current sheets are anisotropic with respect to the electron flow direction. The cascade towards shorter scales occurs preferentially in the direction perpendicular to the electron flow.

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

    SciTech Connect

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

    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.

  5. Flapping current sheet motions in magnetotail excited by non-adiabatic ions: case study

    NASA Astrophysics Data System (ADS)

    Wei, X., Jr.

    2015-12-01

    The current sheet is a crucial region of the magnetotail, where energy reserve and release take place. The origin of the up-down motions of the current sheet, referred to as flapping motions, is among the most fundamental issues of magnetotail dynamics. Observational evidences suggest that the flapping motion is a kind of internal excited kink-like waves, but its particular propagating features such as the low phase speeds and the propagating direction from the tail center toward flanks do not match any local generation mechanisms previously established so far. Here we report observations of the current sheet flapping motions induced by non-adiabatic ions in the magnetic field configurations with a finite guiding component, whose population present periodic hemispherical asymmetries. Three type of current sheet flapping event in this paper will be discussed. This current sheet flapping phenomenon implies that the excitation mechanism of the current sheet flapping motions is a self-circulation process between the non-adiabatic ion population and the current sheet equilibrium itself.

  6. The current sheet tiled and non-adiabatic ions effect on the flapping motion in magnetotail

    NASA Astrophysics Data System (ADS)

    Wei, XinHua

    2016-04-01

    The current sheet is a crucial region of the magnetotail, where energy reserve and release take place. The origin of the up-down motions of the current sheet, referred to as flapping motions, is among the most fundamental issues of magnetotail dynamics. Observational evidences suggest that the flapping motion is a kind of internal excited kink-like waves, but its particular propagating features such as the low phase speeds and the propagating direction from the tail center toward flanks do not match any local generation mechanisms previously established so far. Here we report observations of the current sheet flapping motions induced by non-adiabatic ions in the magnetic field configurations with a finite guiding component, whose population present periodic hemispherical asymmetries. These flapping motion current sheet cases often observed tiled. The current sheet flapping phenomenon implies that the excitation mechanism of the current sheet flapping motions is a self-circulation process between the non-adiabatic ion population and the current sheet equilibrium itself.

  7. A coronal magnetic field model with horizontal volume and sheet currents

    NASA Technical Reports Server (NTRS)

    Zhao, Xuepu; Hoeksema, J. Todd

    1994-01-01

    When globally mapping the observed photospheric magnetic field into the corona, the interaction of the solar wind and magnetic field has been treated either by imposing source surface boundary conditions that tacitly require volume currents outside the source surface or by limiting the interaction to thin current sheets between oppositely directed field regions. Yet observations and numerical Magnetohydrodynamic (MHD) calculations suggest the presence of non-force-free volume currents throughout the corona as well as thin current sheets in the neighborhoods of the interfaces between closed and open field lines or between oppositely directed open field lines surrounding coronal helmet-streamer structures. This work presents a model including both horizontal volume currents and streamer sheet currents. The present model builds on the magnetostatic equilibria developed by Bogdan and Low and the current-sheet modeling technique developed by Schatten. The calculation uses synoptic charts of the line-of-sight component of the photospheric magnetic field measured at the Wilcox Solar Observatory. Comparison of an MHD model with the calculated model results for the case of a dipole field and comparison of eclipse observations with calculations for CR 1647 (near solar minimum) show that this horizontal current-current-sheet model reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces coro nal helmet structures better than the current-sheet model.

  8. Study of instability of the nonelectroneutral current sheets in quasilinear approximation

    NASA Astrophysics Data System (ADS)

    Lyahov, V. V.; Neshchadim, V. M.

    2016-10-01

    The techniques of investigation of low-frequency instabilities of the current sheet in quasi-linear approximation with due regard to the effect of plasma polarization is described. This makes it possible to study the mechanism of the reverse impact of the developing instability modes of nonelectroneutral current sheet on the background distribution function. Evolution equations of the equilibrium distribution function of the plasma current sheet and the perturbation of the electromagnetic field are derived. Algorithms for solution of evolution equations are developed. A dispersion curve for the plasma wave with damping decrement propagating along the magnetic field is derived.

  9. Differential measurement of cosmic-ray gradient with respect to interplanetary current sheet

    NASA Technical Reports Server (NTRS)

    Christon, S. P.; Cummings, A. C.; Stone, E. C.; Behannon, K. W.; Burlaga, L. F.

    1985-01-01

    Simultaneous magnetic field and charged particle measurements from the Voyager spacecraft at heliographic latitude separations from 10 deg. to 21 deg. are used to determine the latitude gradient of the galactic cosmic ray flux with respect to the interplanetary current sheet. By comparing the ratio of cosmic ray flux at Voyager 1 to that a Voyager 2 during periods when both spacecraft are first nort and then south of the interplanetary current sheet, we find an estimate of the latitudinal gradient with respect to the current sheet of approximately -0.15 + or 0.05% deg under restricted interplanetary conditions.

  10. Magnetic Reconnection Onset via Disruption of a Forming Current Sheet by the Plasmoid Instability

    NASA Astrophysics Data System (ADS)

    Loureiro, Nuno; Uzdensky, Dmitri

    The recent realization that Sweet-Parker reconnection current sheets are violently unstable to the secondary tearing (plasmoid) instability implies that such current sheets are unlikely to be realized in real systems. This suggests that, in order to understand the onset of magnetic reconnection, one needs to consider the growth of the tearing instability in a current layer as it is just being formed. We present such an analysis in the context of nonlinear resistive MHD for a generic time-dependent equilibrium representing a gradually forming current sheet. It is shown that, under most conditions, the longest-wavelength mode dominates, resulting in just one or two big plasmoids produced in the immediate aftermath of current sheet formation. Specific examples pertaining to solar flares and to parasitic modes of the magnetorotational instability are provided.

  11. RECONNECTION OF QUASI-SINGULAR CURRENT SHEETS: THE ''IDEAL'' TEARING MODE

    SciTech Connect

    Pucci, Fulvia; Velli, Marco E-mail: mvelli@jpl.nasa.gov

    2014-01-10

    A strong indication that fast reconnection regimes exist within resistive magnetohydrodynamics was given by the proof that the Sweet-Parker current sheet, maintained by a flow field with an appropriate inflow-outflow structure, could be unstable to a reconnecting instability which grows without bound as the Lundquist number, S, tends to infinity. The requirement of a minimum value for S in order for the plasmoid instability to kick in does little to resolve the paradoxical nature of the result. Here we argue against the realizability of Sweet-Parker current sheets in astrophysical plasmas with very large S by showing that an ''ideal'' tearing mode takes over before current sheets reach such a thickness. While the Sweet-Parker current sheet thickness scales as ∼S {sup –1/2}, the tearing mode becomes effectively ideal when a current sheet collapses to a thickness of the order of ∼S {sup –1/3}, up to 100 times thicker than S {sup –1/2}, when (as happens in many astrophysical environments) S is as large as 10{sup 12}. Such a sheet, while still diffusing over a very long time, is unstable to a tearing mode with multiple x-points: here we detail the characteristics of the instability and discuss how it may help solve the flare trigger problem and effectively initiate the turbulent disruption of the sheet.

  12. Reconnection of Quasi-singular Current Sheets: The "Ideal" Tearing Mode

    NASA Astrophysics Data System (ADS)

    Pucci, Fulvia; Velli, Marco

    2014-01-01

    A strong indication that fast reconnection regimes exist within resistive magnetohydrodynamics was given by the proof that the Sweet-Parker current sheet, maintained by a flow field with an appropriate inflow-outflow structure, could be unstable to a reconnecting instability which grows without bound as the Lundquist number, S, tends to infinity. The requirement of a minimum value for S in order for the plasmoid instability to kick in does little to resolve the paradoxical nature of the result. Here we argue against the realizability of Sweet-Parker current sheets in astrophysical plasmas with very large S by showing that an "ideal" tearing mode takes over before current sheets reach such a thickness. While the Sweet-Parker current sheet thickness scales as ~S -1/2, the tearing mode becomes effectively ideal when a current sheet collapses to a thickness of the order of ~S -1/3, up to 100 times thicker than S -1/2, when (as happens in many astrophysical environments) S is as large as 1012. Such a sheet, while still diffusing over a very long time, is unstable to a tearing mode with multiple x-points: here we detail the characteristics of the instability and discuss how it may help solve the flare trigger problem and effectively initiate the turbulent disruption of the sheet.

  13. Spontaneous formation of electric current sheets and the origin of solar flares

    NASA Technical Reports Server (NTRS)

    Low, B. C.; Wolfson, R.

    1988-01-01

    It is demonstrated that the continuous boundary motion of a sheared magnetic field in a tenuous plasma with an infinite electrical conductivity can induce the formation of multiple electric current sheets in the interior plasma. In response to specific footpoint displacements, the quadrupolar magnetic field considered is shown to require the formation of multiple electric current sheets as it achieves a force-free state. Some of the current sheets are found to be of finite length, running along separatrix lines of force which separate lobes of magnetic flux. It is suggested that current sheets in the form of infinitely thin magnetic shear layers may be unstable to resistive tearing, a process which may have application to solar flares.

  14. Structure and evolution of the current sheet by multi-spacecraft observations

    SciTech Connect

    Zhou, X.Y.; Russell, C.T.; Gosling, J.

    1997-12-31

    On April 22, 1979, from 0840 to 1018 UT, ISEE 1, ISEE 2 and IMP 8 were all in or near the magnetotail current sheet at 17 Re, 16 Re and 35 Re respectively while ISEE 3 monitored the solar wind 206 Re upstream of the Earth. A global perspective of the four spacecraft observations and of the ground magnetic records is presented in this paper. The hyperbolic tangent current sheet model of Harris has been used to calculate the current sheet thickness and to analyze the plasma distribution in the vertical direction. It is found that during this event the current sheet thickness varied from 2.5 Re to 1.5 Re for northward IMF but thinned abruptly to 0.5 Re when the IMF turned southward.

  15. Formation and Properties of Magnetic Island Plasmoids in Large-Scale Current Sheets During CME Eruptions

    NASA Astrophysics Data System (ADS)

    Lynch, Benjamin J.; Edmondson, Justin K

    2014-06-01

    We present the continued analysis of the high-resolution 2.5D MHD simulations of sympathetic magnetic breakout eruptions from a pseudostreamer source region. We examine the generation of X- and O-type null points during the current sheet tearing and their evolution as reconnection progresses. There are three large-scale current sheets that we investigate in detail over the course of the simulation. We examine the properties of reconnection occurring within these current sheets including evolution of the current sheet lengths, Lundquist number, and reconnection rates. We also quantify the statistical and spectral properties of the fluctuations in the current sheets resulting from the resistive tearing and magnetic island plasmoid formation including the distribution of magnetic island width, flux content, and mass. We show that the temporal evolution of the spectral index of the magnetic energy density in our current sheets appears to reflect the transition from the linear to non-linear phase of the instability. Our results are in excellent agreement with recent dedicated reconnection simulations even though our current sheets’ formation, growth, and dynamics are both dictated by and in turn, govern the global evolution of sequential, sympathetic CME eruptions.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

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

    SciTech Connect

    Reeves, Katharine K.; Linker, Jon A.; Mikic, Zoran; Forbes, Terry G. E-mail: linkerj@predsci.co E-mail: terry.forbes@unh.ed

    2010-10-01

    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{sub 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.

  18. An Observational Research on Magnetic Reconnection Current Sheet Occurred in Two Solar Eruptions

    NASA Astrophysics Data System (ADS)

    Cai, Q. W.; Wu, N.; Lin, J.

    2015-11-01

    The coronal magnetic configuration is severely stretched by the disruption in the process of coronal mass ejection (CME), pushing the magnetic fields of opposite polarity to approach one another, and creating a magnetic neutral region (current sheet) behind CME. Magnetic reconnection taking place inside the current sheet converts the magnetic energy into heat and kinetic energy of the plasma, and the kinetic energy of energetic particles. The role of the current sheet in this process is two-fold: the region where reconnection occurs, and connecting the flare to the associated CME. We studied the events of 2003 January 3 and 2003 November 4, respectively. Development of the current sheet was observed in both cases. We investigated the dynamic features of the two events, as well as physical properties of the current sheet, on the basis of analyzing the observational data from LASCO (Large Angle and Spectrometric Coronagraph) and UVCS (Ultraviolet Coronagraph Spectrometer) on board SOHO (Solar and Heliospheric Observatory), and the Hα data from BBSO (Big Bear Solar Observatory) and YNAO (Yunnan Observatories). The existence of ions with high ionization state, such as Fe^{+17} and Si^{+11}, indicated a high temperature up to 3×10^{6}-5×10^{6} K. Direct measurements showed that the apparent thickness of the current sheet varies from 1.3×10^{4} to 1.1×10^{5} km, which increases first and then decreases with time. Using the CHIANTI code (v.7.1), we further calculated the averages of the electron temperature and the corresponding emission measure in the current sheet of the 2003 January 3 event, which were about 3.86× 10^{6} K and 6.1× 10^{24} cm^{-5}, respectively. We also noticed that the current sheet twisted forth and back in a quasi-periodical fashion during the event on 2003 November 4 by analyzing the data from SOHO/UVCS.

  19. A Theoretical Model of a Thinning Current Sheet in the Low-β Plasmas

    NASA Astrophysics Data System (ADS)

    Takeshige, Satoshi; Takasao, Shinsuke; Shibata, Kazunari

    2015-07-01

    Magnetic reconnection is an important physical process in various explosive phenomena in the universe. In previous studies, it was found that fast reconnection takes place when the thickness of a current sheet becomes on the order of a microscopic length such as the ion Larmor radius or the ion inertial length. In this study, we investigated the pinching process of a current sheet by the Lorentz force in a low-β plasma using one-dimensional magnetohydrodynamics (MHD) simulations. It is known that there is an exact self-similar solution for this problem that neglects gas pressure. We compared the non-linear MHD dynamics with the analytic self-similar solution. From the MHD simulations, we found that with the gas pressure included the implosion process deviates from the analytic self-similar solution as t\\to {t}0, where t0 is the explosion time when the thickness of a current sheet of the analytic solution becomes 0. We also found that a pair of MHD fast-mode shocks is generated and propagates after the formation of the pinched current sheet as t\\to {t}0. On the basis of the Rankine-Hugoniot relations, we derived the scaling law of the physical quantities with respect to the initial plasma beta in the pinched current sheet. Our study could help us estimate the physical quantities in the pinched current sheet formed in a low-β plasma.

  20. The Helium Abundance at Quiescent Current Sheets and the Slow Solar Wind

    NASA Technical Reports Server (NTRS)

    Suess, Steven T.; Ko, Y.-K.; VonSteiger, R.

    2008-01-01

    Ulysses MAG data were used to identify current sheets during sunspot minimum years of 1994-1997 and 2004-2006. The purpose of limiting the dates was to focus attention on 'quiescent current sheets' with as little influence from ICMEs as possible. SWOOPS data were then used in a superposed epoch analysis to study Helium abundance in the vicinity of the current sheet, similar to the study done by Borrini et al. (1981). That earlier study found a narrow (ca. 2 day) minimum in He/H around the current sheet that is extremely variable from one year to the next in the period 1971-1978. A similar result is found here for data at all latitudes and distances in 2004-2006. Conversely, data from 1994-1997 produce a deep minimum several times wider (ca. 10 days). The reason for this is found to be that low He/H is more closely associated with slow wind than the current sheet per se. There are thus apparently at least two sources of slow wind, one associated with very low He/H of 0-0.02 and one associated with moderate abundance of 0.03-0.05. The large variability is a consequence of the relatively small number of current sheet encounters around solar minimum and the random distribution of low He/H intervals, lasting less than 1 day to more than 7 days, throughout slow wind.

  1. Fast magnetic reconnection in thin current sheets: effects of different current profiles and electron inertia in Ohm's law.

    NASA Astrophysics Data System (ADS)

    Pucci, Fulvia; Del Sarto, Daniele; Tenerani, Anna; Velli, Marco

    2015-04-01

    By examining sheets with thicknesses scaling as different powers of the Lundquist number S, we previously showed (Pucci and Velli, 2014) that the growth rate of the tearing mode increases as current sheets thin and, once the inverse aspect ratio reaches a scaling a/L = S-1/3, the time-scale for the instability to develop becomes of the order of the Alfvén time. That means that a fast instability sets in well before Sweet-Parker type current sheets can form. In addition, such an instability produces many islands in the sheet, leading to fast nonlinear evolution and most probably a turbulent disruption of the sheet itself. This has fundamental implications for magnetically driven reconnection throughout the corona, and in particular for coronal heating and the triggering of coronal mass ejections. Here we extend the study of reconnection instabilities to magnetic fields of grater complexity, displaying different current structures such as, for example, multiple or asymmetric current layers. We also consider the possibility of a Δ' dependence on wave-number k-p for different values of p, studying analogies and variations of the trigger scaling relation a/L ~ S-1/3 with respect to the Harris current sheet equilibrium. At large Lundquist numbers in typical Heliospheric plasmas kinetic effects become more important in Ohm's law: we consider the effects of electron skin depth reconnection, showing that we can define a trigger relation similar to the resistive case. The results are important to the transition to fast reconnection in the solar corona, solar wind, magnetosphere as well as laboratory plasmas. F. Pucci and M. Velli, "Reconnection of quasi-singular current sheets: the 'ideal" tearing mode" ApJ 780:L19, 2014.

  2. Excitation of an electrostatic wave by a cold electron current sheet of finite thickness

    NASA Technical Reports Server (NTRS)

    Hwang, K. S.; Fontheim, E. G.; Ong, R. S. B.

    1983-01-01

    Calculations for the threshold of current-driven instabilities and the growth rates of ion acoustic and electrostatic ion cyclotron instabilities in a magnetized plasma driven a current sheet with a finite width are presented. Maxwellian equations are employed to model the velocity distributions of electrons and ions in a direction perpendicular to the sheet. A dispersion relation is defined for the regions of instability, and boundary conditions are characterized in order to obtain a set of eigenvalue equations. Thresholds are delineated for various regions, including ducted mode solutions where only ion-acoustic waves are excited in areas where the frequency range significantly exceeds the ion cyclotron frequency. When a constant electron drift velocity is present, a thick current sheet is more unstable than a thin one. Fewer modes become unstable with a thinner sheet.

  3. Numerical simulation of current sheet formation in a quasiseparatrix layer using adaptive mesh refinement

    SciTech Connect

    Effenberger, Frederic; Thust, Kay; Grauer, Rainer; Dreher, Juergen; Arnold, Lukas

    2011-03-15

    The formation of a thin current sheet in a magnetic quasiseparatrix layer (QSL) is investigated by means of numerical simulation using a simplified ideal, low-{beta}, MHD model. The initial configuration and driving boundary conditions are relevant to phenomena observed in the solar corona and were studied earlier by Aulanier et al. [Astron. Astrophys. 444, 961 (2005)]. In extension to that work, we use the technique of adaptive mesh refinement (AMR) to significantly enhance the local spatial resolution of the current sheet during its formation, which enables us to follow the evolution into a later stage. Our simulations are in good agreement with the results of Aulanier et al. up to the calculated time in that work. In a later phase, we observe a basically unarrested collapse of the sheet to length scales that are more than one order of magnitude smaller than those reported earlier. The current density attains correspondingly larger maximum values within the sheet. During this thinning process, which is finally limited by lack of resolution even in the AMR studies, the current sheet moves upward, following a global expansion of the magnetic structure during the quasistatic evolution. The sheet is locally one-dimensional and the plasma flow in its vicinity, when transformed into a comoving frame, qualitatively resembles a stagnation point flow. In conclusion, our simulations support the idea that extremely high current densities are generated in the vicinities of QSLs as a response to external perturbations, with no sign of saturation.

  4. Generalized magnetotail equilibria: Effects of the dipole field, thin current sheets, and magnetic flux accumulation

    NASA Astrophysics Data System (ADS)

    Sitnov, M. I.; Merkin, V. G.

    2016-08-01

    Generalizations of the class of quasi-1-D solutions of the 2-D Grad-Shafranov equation, first considered by Schindler in 1972, are investigated. It is shown that the effect of the dipole field, treated as a perturbation, can be included into the original 1972 class solution by modification of the boundary conditions. Some of the solutions imply the formation of singularly thin current sheets. Equilibrium solutions for such sheets resolving their singular current structure on the scales comparable to the thermal ion gyroradius can be obtained assuming anisotropic and nongyrotropic plasma distributions. It is shown that one class of such equilibria with the dipole-like boundary perturbation describes bifurcation of the near-Earth current sheet. Another class of weakly anisotropic equilibria with thin current sheets embedded into a thicker plasma sheet helps explain the formation of thin current sheets in a relatively distant tail, where such sheets can provide ion Landau dissipation for spontaneous magnetic reconnection. The free energy for spontaneous reconnection can be provided due to accumulation of the magnetic flux at the tailward end of the closed field line region. The corresponding hump in the normal magnetic field profile Bz(x,z = 0) creates a nonzero gradient along the tail. The resulting gradient of the equatorial magnetic field pressure is shown to be balanced by the pressure gradient and the magnetic tension force due to the higher-order correction of the latter in the asymptotic expansion of the tail equilibrium in the ratio of the characteristic tail current sheet variations across and along the tail.

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

    SciTech Connect

    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 approx.1-5 x 10/sup 4/ km and approx.5-50 nA/m/sup 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 approx.1.2 x 10/sup 5/ K and approx.40 in the center of the current sheet to approx.1 x 10/sup 6/ K and approx.3 in the outer lobes. Axial stress balance shows that the velocity shear upstream near the nucleus is >6 (approx.1 at ICE), and that a region of strongly enhanced mass loading (ion source rate approx.24 times that upstream from lobes) exists upstream from the current sheet. The integrated downtail mass flux is approx.2.6 x 10/sup 26/ H/sub 2/O+/sec, which is only approx.1% of the independently determined total cometary efflux. 79 refs., 37 figs.

  6. Graphene electron cannon: High-current edge emission from aligned graphene sheets

    SciTech Connect

    Liu, Jianlong; Li, Nannan; Guo, Jing; Fang, Yong; Deng, Jiang; Zeng, Baoqing; Wang, Wenzhong; Li, Jiangnan; Hao, Chenchun

    2014-01-13

    High-current field emitters are made by graphene paper consist of aligned graphene sheets. Field emission luminance pattern shows that their electron beams can be controlled by rolling the graphene paper from sheet to cylinder. These specific electron beams would be useful to vacuum devices and electron beam lithograph. To get high-current emission, the graphene paper is rolled to array and form graphene cannon. Due to aligned emission array, graphene cannon have high emission current. Besides high emission current, the graphene cannon is also tolerable with excellent emission stability. With good field emission properties, these aligned graphene emitters bring application insight.

  7. Self-organization in space plasma: formation of magnetic shear in current sheets

    NASA Astrophysics Data System (ADS)

    Zelenyi, Lev; Delcourt, Dominique; Mingalev, Oleg; Malova, Helmi; Popov, Victor; Grigorenko, Elena; Petrukovich, Anatoli

    2016-07-01

    Thin current sheets are plasma structures that usually appear near reconnection regions. The presence of the shear magnetic field is characteristic for these structures. Self-consistent kinetic model of magnetotail thin current sheet (TCS) is used to understand the mechanisms of self-organization of sheared thin current sheets in a space plasma. It is shown that these configurations appear as a result of self-consistent evolution of some initial magnetic perturbation at current sheet center. Two general shapes of shear TCS components are found as a function of the transverse coordinate: symmetric and antisymmetric. We show that TCS formation goes together with the emergence of field-aligned currents in the center of the current sheet, as a result of north-south asymmetry of quasi-adiabatic ion motions. Ion drift currents can also contribute to the magnetic shear evolution, but their role is much less significant, their contribution depending upon the normal component Bz and the amplitude of the initial perturbation in TCS. Parametric maps illustrating different types of TCS equilibria are presented.

  8. Nonlinear Collisionless Magnetic Reconnection

    SciTech Connect

    Grasso, D.; Tassi, E.; Borgogno, D.; Pegoraro, F.

    2008-10-15

    We review some recent results that have been obtained in the investigation of collisionless reconnection in two and three dimensional magnetic configurations with a strong guide field in regimes of interest for laboratory plasmas. First, we adopt a two-field plasma model where two distinct regimes, laminar and turbulent, can be identified. Then, we show that these regimes may combine when we consider a more general four-field model, where perturbation of the magnetic and velocity fields are allowed also along the ignorable coordinate.

  9. A Tailward Moving Current Sheet Normal Magnetic Field Front Followed by an Earthward Moving Dipolarization Front

    NASA Technical Reports Server (NTRS)

    Hwang, K.-J.; Goldstein, M. L.; Moore, T. E.; Walsh, B. M.; Baishev, D. G.; Moiseyev, A. V.; Shevtsov, B. M.; Yumoto, K.

    2014-01-01

    A case study is presented using measurements from the Cluster spacecraft and ground-based magnetometers that show a substorm onset propagating from the inner to outer plasma sheet. On 3 October 2005, Cluster, traversing an ion-scale current sheet at the near-Earth plasma sheet, detected a sudden enhancement of Bz, which was immediately followed by a series of flux rope structures. Both the local Bz enhancement and flux ropes propagated tailward. Approximately 5 min later, another Bz enhancement, followed by a large density decrease, was observed to rapidly propagate earthward. Between the two Bz enhancements, a significant removal of magnetic flux occurred, possibly resulting from the tailward moving Bz enhancement and flux ropes. In our scenario, this flux removal caused the magnetotail to be globally stretched so that the thinnest sheet formed tailward of Cluster. The thinned current sheet facilitated magnetic reconnection that quickly evolved from plasma sheet to lobe and generated the later earthward moving dipolarization front (DF) followed by a reduction in density and entropy. Ground magnetograms located near the meridian of Cluster's magnetic foot points show two-step bay enhancements. The positive bay associated with the first Bz enhancement indicates that the substorm onset signatures propagated from the inner to the outer plasma sheet, consistent with the Cluster observation. The more intense bay features associated with the later DF are consistent with the earthward motion of the front. The event suggests that current disruption signatures that originated in the near-Earth current sheet propagated tailward, triggering or facilitating midtail reconnection, thereby preconditioning the magnetosphere for a later strong substorm enhancement.

  10. Plasmoid instability in a large post-CME current sheet system

    NASA Astrophysics Data System (ADS)

    Guo, L.; Bhattacharjee, A.; Huang, Y.; CenterIntegrated Computation; Analysis of Reconnection; Turbulence

    2011-12-01

    Solar flares and CME that cause violent space weather change have been studied for years. The standard model suggests that there is a current sheet connecting the CME and the site of the post-CME flare after the eruption, but understanding of the detailed physical mechanism of dynamical processes in the current sheet remains incomplete. Recently, the secondary plasmoid instabilities of large scale current sheet in high Lundquist number environment such as solar corona and the change of magnetic topology in such a current sheet system has become a subject of great interest (Bhattacharjee et al. 2009). In our work, we study a post-CME current sheet via both observation and simulation. We use SOHO/LASCO observations of a fast halo CME as well as a slow CME. After the fast halo CME event on January 8, 2002, we observe a long, thin current sheet which connects the CME to a flare site on the surface of the sun. In this current sheet we identify over 60 bright plasmoid-like blobs in 39 hours. In the slow CME event on June 25, 2005, we observe 32 such blobs in 18 hours after the formation of the current sheet. We simulate both cases using high-Lundquist-number resistive MHD simulations of the model of Lin & Forbes (2000), and demonstrate that the distribution of plasmoid size in both cases appears to conform well to a distribution function that is independent of the Lundquist number and predicted by theory. The average observed plasmoid speed in both cases is a fraction of the typical Alfven speed, qualitatively consistent with the simulations. Thus, we propose that these observations can be plausibly accounted for by the plasmoid instability of the large-scale current sheet. The observed bright blobs are probably evidence of large-scale plasmoids, and their behavior appears to be qualitatively consistent with high-Lundquist-number MHD simulations.
    observation case summary

  11. Linear evolution of current sheets in sheared force-free magnetic fields with discontinuous connectivity

    NASA Technical Reports Server (NTRS)

    Wolfson, Richard

    1990-01-01

    Thin current sheets arising in tenuous, magnetized solar coronal plasmas may constitute an important mechanism for energy buildups and subsequent energy releases; they could arise from the continuous-and-random motion of magnetic footprints associated with photospheric velocity fields. A model is presented for study of the quasi-static evolution of current sheets due to shearing of the footpoints, in a highly idealized geometry that incorporates an abrupt jump in field-line connectivity. The model highlights that formation of thin current layers and allows large shearing motions prior to violation of the linear approximation. Excess energy comparable to that released by solar flares can be stored in a sheared field.

  12. Observations of current sheets associated with solar wind reconnection exhausts passing through the near lunar wake

    NASA Astrophysics Data System (ADS)

    Xu, Xiaojun; Wong, Hon-Cheng; Ma, Yonghui; Wang, Yi; Zuo, Pingbing; Zhou, Meng; Deng, Xiaohua

    2015-11-01

    Two reconnection exhausts were detected by one of the dual ARTEMIS orbiters in the solar wind near the Moon. Almost meanwhile, the other ARTEMIS orbiter encountered the two corresponding current sheets at the relatively marginal and central locations in the near lunar wake. Due to the Moon's direct absorption, the current density of the current sheet disappears within the wake. As a result, the wake magnetic field around the current sheets is changed. It is found that the variations of the magnetic field in the wake are primarily governed by two factors: diamagnetic current system at the wake boundary and the dropout of M direction currents (jM) within the wake. Instead of being almost unaltered as commonly assumed in the study of lunar wake, the magnetic field of the current sheets becomes potential with almost zero current density. With respect to the solar wind magnetic field, this potential magnetic field is weaker in the center and has an X line-like configuration with significant normal components in the marginal portions of the wake. Our result may be applicable to nonconducting or weakly conducting contexts widely existing in the universe.

  13. Magnetic Field Relaxation and Current Sheets in an Ideal Plasma

    NASA Astrophysics Data System (ADS)

    Candelaresi, S.; Pontin, D. I.; Hornig, G.

    2015-08-01

    We investigate the existence of magnetohydrostatic equilibria for topologically complex magnetic fields. The approach employed is to perform ideal numerical relaxation experiments. We use a newly developed Lagrangian relaxation scheme that exactly preserves the magnetic field topology during the relaxation. Our configurations include both twisted and sheared fields, of which some fall into the category for which Parker predicted no force-free equilibrium. The first class of field considered contains no magnetic null points, and field lines connect between two perfectly conducting plates. In these cases, we observe only resolved current layers of finite thickness. In further numerical experiments, we confirm that magnetic null points are loci of singular currents.

  14. MAGNETIC FIELD RELAXATION AND CURRENT SHEETS IN AN IDEAL PLASMA

    SciTech Connect

    Candelaresi, S.; Pontin, D. I.; Hornig, G.

    2015-08-01

    We investigate the existence of magnetohydrostatic equilibria for topologically complex magnetic fields. The approach employed is to perform ideal numerical relaxation experiments. We use a newly developed Lagrangian relaxation scheme that exactly preserves the magnetic field topology during the relaxation. Our configurations include both twisted and sheared fields, of which some fall into the category for which Parker predicted no force-free equilibrium. The first class of field considered contains no magnetic null points, and field lines connect between two perfectly conducting plates. In these cases, we observe only resolved current layers of finite thickness. In further numerical experiments, we confirm that magnetic null points are loci of singular currents.

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

    PubMed Central

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

    2011-01-01

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

  16. Current sheet formation in a sheared force-free-magnetic field. [in sun

    NASA Technical Reports Server (NTRS)

    Wolfson, Richard

    1989-01-01

    This paper presents the results of a study showing how continuous shearing motion of magnetic footpoints in a tenuous, infinitely conducting plasma can lead to the development of current sheets, despite the absence of such sheets or even of neutral points in the initial state. The calculations discussed here verify the earlier suggestion by Low and Wolfson (1988) that extended current sheets should form due to the shearing of a force-free quadrupolar magnetic field. More generally, this work augments earlier studies suggesting that the appearance of discontinuities - current sheets - may be a necessary consequence of the topological invariance imposed on the magnetic field geometry of an ideal MHD system by virtue of its infinite conductivity. In the context of solar physics, the work shows how the gradual and continuous motion of magnetic footpoints at the solar photosphere may lead to the buildup of magnetic energy that can then be released explosively when finite conductivity effects become important and lead to the rapid dissipation of current sheets. Such energy release may be important in solar flares, coronal mass ejections, and other eruptive events.

  17. RICHTMYER-MESHKOV-TYPE INSTABILITY OF A CURRENT SHEET IN A RELATIVISTICALLY MAGNETIZED PLASMA

    SciTech Connect

    Inoue, Tsuyoshi

    2012-11-20

    The linear stability of a current sheet that is subject to an impulsive acceleration due to shock passage with the effect of a guide magnetic field is studied. We find that a current sheet embedded in relativistically magnetized plasma always shows a Richtmyer-Meshkov-type instability, while the stability depends on the density structure in the Newtonian limit. The growth of the instability is expected to generate turbulence around the current sheet, which can induce the so-called turbulent reconnection, the rate of which is essentially free from plasma resistivity. Thus, the instability can be applied as a triggering mechanism for rapid magnetic energy release in a variety of high-energy astrophysical phenomena such as pulsar wind nebulae, gamma-ray bursts, and active galactic nuclei, where the shock wave is thought to play a crucial role.

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

    NASA Astrophysics Data System (ADS)

    Nickeler, D.; Wiegelmann, T.

    2011-12-01

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

  19. Kinetic models of two-dimensional plane and axially symmetric current sheets: Group theory approach

    SciTech Connect

    Vasko, I. Y.; Artemyev, A. V.; Popov, V. Y.; Malova, H. V.

    2013-02-15

    In this paper, we present new class of solutions of Grad-Shafranov-like (GS-like) equations, describing kinetic plane and axially symmetric 2D current sheets. We show that these equations admit symmetry groups only for Maxwellian and {kappa}-distributions of charged particles. The admissible symmetry groups are used to reduce GS-like equations to ordinary differential equations for invariant solutions. We derive asymptotes of invariant solutions, while invariant solutions are found analytically for the {kappa}-distribution with {kappa}=7/2. We discuss the difference of obtained solutions from equilibria widely used in other studies. We show that {kappa} regulates the decrease rate of plasma characteristics along the current sheet and determines the spatial distribution of magnetic field components. The presented class of plane and axially symmetric (disk-like) current sheets includes solutions with the inclined neutral plane.

  20. Reconnection and scale-free avalanching in a driven current-sheet model

    NASA Astrophysics Data System (ADS)

    Klimas, Alex J.; Uritsky, Vadim M.; Vassiliadis, Dimitris; Baker, Daniel N.

    2004-02-01

    [2002], through a study of Polar UVI auroral image sequences, have produced a set of scale-free probability distributions for several characteristic properties of the evolving bright emission regions in the nightside auroral oval. These distributions almost certainly reflect the dynamics of the plasma sheet. A scale-free avalanching process involving reconnection and/or current diversion over an exceptionally broad range of spatiotemporal scales is implied. The most straightforward, and at present sole, explanation for this behavior is that the plasma sheet dynamics is in the neighborhood of self-organized criticality (SOC). However, the auroral images provide only an indirect measure of the plasma sheet dynamics. Confirmation of this state in the plasma sheet would require multispatiotemporal-scale in situ plasma sheet studies that, with the advent of multispacecraft missions, are now possible. To suggest specific tests for such studies, a numerical current-sheet model has been constructed and analyzed to develop the properties and requirements of SOC in a plasma physical setting. The model incorporates the anomalous resistivity of a current-driven kinetic instability into a two-dimensional resistive MHD system. The disparate scales of these two systems enable multiscale behavior in the intervening range. Several novel features in the model's behavior are enabled through the assumption of hysteresis in the kinetic instability threshold. Under steady loading of plasma containing a reversed magnetic field topology, an irregular loading-unloading cycle is established in which unloading is due primarily to annihilation at the field reversal. Following a loading interval during which the current-sheet supporting the field reversal thins and intensifies, an unloading event originates at a localized reconnection site that then becomes the source of waves of unstable current sheets. These current sheets propagate away from the reconnection site, each leaving a trail of

  1. Response of Saturn's Current Sheet Structure to Changes in the Solar Wind Dynamic Pressure and IMF

    NASA Astrophysics Data System (ADS)

    Hansen, K. C.; Jia, X.; Gombosi, T. I.

    2010-12-01

    Using our global MHD model of Saturn’s magnetosphere, we investigate the location, shape and motion of Saturn’s current sheet under a variety of situations. Our global MHD model self consistently treats the entire magnetosphere and includes magnetospheric plasma sources from a major disk-like source from Enceladus and the rings and a secondary toroidal plasma source from Titan. The model produces solutions which are not constrained to be symmetric therefore the results are quite useful in trying to extend previous models that have been generated using Cassini data. Because we can carefully control the inputs to our MHD model, we do not have to worry about separating variations due to local time, varying upstream conditions, spacecraft motion or changes in the mass loading rate that often make interpreting the data complicated. We will present results for both steady state, as well as time varying solar wind conditions. Simulations with constant solar wind conditions allow us to study the effect that upsteam dynamic pressure has on both the shape and size of the current sheet. In addition, we will present results from simulations that include sudden changes in the solar wind dynamics pressure as well as the IMF direction. These simulations will allow us to study the current sheet response and to look for features such as current sheet flapping. Our previous studies have shown that the current sheet in our model does in fact reproduce the “bowl-like” behavior expect at most local times. However, at dusk, the current sheet is often quite warped. We will examine the cause of this warping and under what conditions it occurs.

  2. Neoclassical tearing mode saturation in periodic current sheets

    SciTech Connect

    Militello, F.

    2008-04-15

    The saturation of Neoclassical Tearing Mode islands in a periodic slab configuration is investigated. Several theoretical models, all based on a generalization of Rutherford's procedure, that aim at reducing the complete system to a single equation of the magnetic island width, are compared against numerical simulations. When the effects of the bootstrap current and of the second derivative of the equilibrium current profile are included, the numerical saturation levels are well matched with the predictions of this equation in a wide region of the stability diagram. However, the numerical results diverge from the standard theory when evaluating the threshold for nonlinear destabilization, since the theoretical value appears to be strongly conservative. In other words, the standard generalization of Rutherford's equation is not able to capture the minimum value of the linear stability parameter and of the island width such that below them the Neoclassical Tearing Mode is always suppressed. To correct this discrepancy, a new theoretical model in which the transverse propagation of the island affects the bootstrap current term is proposed.

  3. Collisionless parallel shocks

    NASA Technical Reports Server (NTRS)

    Khabibrakhmanov, I. KH.; Galeev, A. A.; Galinskii, V. L.

    1993-01-01

    Consideration is given to a collisionless parallel shock based on solitary-type solutions of the modified derivative nonlinear Schroedinger equation (MDNLS) for parallel Alfven waves. The standard derivative nonlinear Schroedinger equation is generalized in order to include the possible anisotropy of the plasma distribution and higher-order Korteweg-de Vies-type dispersion. Stationary solutions of MDNLS are discussed. The anisotropic nature of 'adiabatic' reflections leads to the asymmetric particle distribution in the upstream as well as in the downstream regions of the shock. As a result, nonzero heat flux appears near the front of the shock. It is shown that this causes the stochastic behavior of the nonlinear waves, which can significantly contribute to the shock thermalization.

  4. The stability of steady magnetohydrodynamic flows with current-vortex sheets

    NASA Astrophysics Data System (ADS)

    Ilin, K. I.; Trakhinin, Y. L.; Vladimirov, V. A.

    2003-07-01

    The stability of steady magnetohydrodynamic flows of an inviscid incompressible fluid with current-vortex sheets to small three-dimensional perturbations is studied. The energy method of Frieman and Rotenberg is extended to the case of steady flows with surfaces of tangential discontinuities across which the tangent velocity or the tangent magnetic field or both of them have jump discontinuities. Sufficient conditions for linear stability of some classes of steady flows with parallel velocity and magnetic field are obtained. Also, a sufficient condition for instability of a tubular current-vortex sheet is given.

  5. Current Sheet and Reconnection Inflow-Outflow Observations During Solar Eruptions

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina; Holman, Gordon; Reeves, Kathy R.; Seaton, Daniel B.; McKenzie, David E.; Su, Yang

    2011-01-01

    Magnetic reconnection is widely accepted as a dominant source of energy during solar flares; however, observations of it have been indirect and/or incomplete. Using the suite of instruments available spanning wavelength space, we will provide observations and measurements of both the inputs and outputs predicted from reconnection in the form of inflows preceding outflows (i.e. supra-arcade downflows, supra-arcade downflowing loops, upflows, and disconnection events). We will also present evidence for current sheets through which reconnection is expected to occur and discuss current sheet motion during flare progression.

  6. Investigation of Thickness and Electrical Resistivity of the Current Sheets in Solar Eruptions

    NASA Technical Reports Server (NTRS)

    Lin, J.; Li, J.; Ko, Y.-K.; Raymond, J. C.

    2009-01-01

    A discussion of the thickness of current sheets in solar eruptions led Lin et al. in 2007 to estimate very large values for the effective resistivity. This paper addresses some questions raised by that paper. The limb synoptic map technique is applied to find the current sheet thickness to be between 5.OE4 and 4.6E5 km, increasing with both time and altitude. The possibility that large apparent values result from projection effects is examined and rejected. Theoretical scaling laws corroborate this conclusion.

  7. Laboratory Observation of Resistive Electron Tearing in a Two-Fluid Reconnecting Current Sheet.

    PubMed

    Jara-Almonte, Jonathan; Ji, Hantao; Yamada, Masaaki; Yoo, Jongsoo; Fox, William

    2016-08-26

    The spontaneous formation of plasmoids via the resistive electron tearing of a reconnecting current sheet is observed in the laboratory. These experiments are performed during driven, antiparallel reconnection in the two-fluid regime within the Magnetic Reconnection Experiment. It is found that plasmoids are present even at a very low Lundquist number, and the number of plasmoids scales with both the current sheet aspect ratio and the Lundquist number. The reconnection electric field increases when plasmoids are formed, leading to an enhanced reconnection rate. PMID:27610861

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

    NASA Technical Reports Server (NTRS)

    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.

  9. Confinement of pure ion plasma in a cylindrical current sheet

    NASA Astrophysics Data System (ADS)

    Paul, Stephen F.; Chao, Edward H.; Davidson, Ronald C.; Phillips, Cynthia K.

    1999-12-01

    A novel method for containing a pure ion plasma at thermonuclear densities and temperatures has been modeled. The method combines the confinement principles of a Penning-Malmberg trap and a pulsed theta-pinch. A conventional Penning trap can confine a uniform-density plasma of about 5×1011cm-3 with a 30-Tesla magnetic field. However, if the axial field is ramped, a much higher local ion density can be obtained. Starting with a 107cm-3 trapped deuterium plasma at the Brillouin limit (B=0.6 Tesla), the field is ramped to 30 Tesla. Because the plasma is comprised of particles of only one sign of charge, transport losses are very low, i.e., the conductivity is high. As a result, the ramped field does not penetrate the plasma and a diamagnetic surface current is generated, with the ions being accelerated to relativistic velocities. To counteract the inward j×B forces from this induced current, additional ions are injected into the plasma along the axis to increase the density (and mutual electrostatic repulsion) of the target plasma. In the absence of the higher magnetic field in the center, the ions drift outward until a balance is established between the outward driving forces (centrifugal, electrostatic, pressure gradient) and the inward j×B force. An equilibrium calculation using a relativistic, 1-D, cold-fluid model shows that a plasma can be trapped in a hollow, 49-cm diameter, 0.2-cm thick cylinder with a density exceeding 4×1014cm-3.

  10. Modeling of different scenarios of thin current sheet equilibria in the Earth's magnetotail

    NASA Astrophysics Data System (ADS)

    Ul'kin, A. A.; Malova, H. V.; Popov, V. Yu.; Zelenyi, L. M.

    2015-02-01

    The Earth's magnetosphere is an open dynamic system permanently interacting with the solar wind, i.e., the plasma flow from the Sun. Some plasma processes in the magnetosphere are of spontaneous explosive character, while others develop rather slowly as compared to the characteristic times of plasma particle motion in it. The large-scale current sheet in the magnetotail can be in an almost equilibrium state both in quiet periods and during geomagnetic perturbations, and its variations can be considered quasistatic. Thus, under some conditions, the magnetotail current sheet can be described as an equilibrium plasma system. Its state depends on various parameters, in particular, on those determining the dynamics of charged particles. Knowing the main governing parameters, one can study the structure and properties of the current sheet equilibrium. This work is devoted to the self-consistent modeling of the equilibrium thin current sheet (TCS) of the Earth's magnetotail, the thickness of which is comparable with the ion gyroradius. The main objective of this work is to examine how the TCS structure depends on the parameters characterizing the particle dynamics and magnetic field geometry. A numerical hybrid self-consistent TCS model in which the tension of magnetic field lines is counterbalanced by the inertia of ions moving through the sheet is constructed. The ion dynamics is considered in the quasi-adiabatic approximation, while the electron motion, in the conductive fluid approximation. Depending on the values of the adiabaticity parameter κ (which determines the character of plasma particle motion) and the dimensionless normal component of the magnetic field b z , the following two scenarios are considered: (A) the adiabaticity parameter is proportional to the particle energy and b z = const and (B) the particle energy is fixed and the adiabaticity parameter is proportional to b z . The structure of the current sheet and particle dynamics in it are studied as

  11. Modeling of different scenarios of thin current sheet equilibria in the Earth’s magnetotail

    SciTech Connect

    Ul’kin, A. A.; Malova, H. V. Popov, V. Yu.; Zelenyi, L. M.

    2015-02-15

    The Earth’s magnetosphere is an open dynamic system permanently interacting with the solar wind, i.e., the plasma flow from the Sun. Some plasma processes in the magnetosphere are of spontaneous explosive character, while others develop rather slowly as compared to the characteristic times of plasma particle motion in it. The large-scale current sheet in the magnetotail can be in an almost equilibrium state both in quiet periods and during geomagnetic perturbations, and its variations can be considered quasistatic. Thus, under some conditions, the magnetotail current sheet can be described as an equilibrium plasma system. Its state depends on various parameters, in particular, on those determining the dynamics of charged particles. Knowing the main governing parameters, one can study the structure and properties of the current sheet equilibrium. This work is devoted to the self-consistent modeling of the equilibrium thin current sheet (TCS) of the Earth’s magnetotail, the thickness of which is comparable with the ion gyroradius. The main objective of this work is to examine how the TCS structure depends on the parameters characterizing the particle dynamics and magnetic field geometry. A numerical hybrid self-consistent TCS model in which the tension of magnetic field lines is counterbalanced by the inertia of ions moving through the sheet is constructed. The ion dynamics is considered in the quasi-adiabatic approximation, while the electron motion, in the conductive fluid approximation. Depending on the values of the adiabaticity parameter κ (which determines the character of plasma particle motion) and the dimensionless normal component of the magnetic field b{sub z}, the following two scenarios are considered: (A) the adiabaticity parameter is proportional to the particle energy and b{sub z} = const and (B) the particle energy is fixed and the adiabaticity parameter is proportional to b{sub z}. The structure of the current sheet and particle dynamics in it

  12. Fe, O, and C Charge States Associated with Quiescent Versus Active Current Sheets in the Solar Wind

    NASA Technical Reports Server (NTRS)

    Suess, S. T.; Ko, Y.-K.; vonSteiger, R.

    2008-01-01

    Ulysses MAG data were used to locate the heliospheric current sheet in data from 1991 through 2006. The purpose was to characterize typical charge states for Fe, O, and C in the vicinity of the current sheet and provide insight into the physical sources for these charge states in the corona. A study of He/H around the current sheets has led to a clear distinction between quiescent current sheets at times of low solar activity and active current sheets associated with magnetic clouds (and, presumably, ICMES). It has been shown that high ionization state Fe is produced in the corona in current sheets associated with CMEs through spectroscopic observations of the corona and through in situ detection at Ulysses. Here we show that the ionization state of Fe is typically only enhanced around active current sheets while the ionization states of O and C are commonly enhanced around both quiescent and active current sheets. This is consistent with UV coronal spectroscopy, which has shown that reconnection in current sheets behind CMEs leads to high temperatures not typically seen above quiet streamers.

  13. Laboratory Investigations of Current Sheets at the Electron Skin Depth Scale

    NASA Astrophysics Data System (ADS)

    Vincena, S.; Gekelman, W.

    2005-12-01

    Laboratory Investigations of Current Sheets at the Electron Skin Depth Scale. Theoretical investigations, in situ spacecraft and rocket missions, and laboratory studies form an essential triad for understanding the variety of current sheet phenomena found in space plasmas. In the Large Plasma Device (LAPD) at UCLA, the formation dynamics, equilibrium state, and wave-mediated disruptions of current sheets can be studied with great spatial and temporal resolution using a variety of probes as well as non-invasive laser induced fluorescence and other optical diagnostics. The LAPD is aptly suited for studying current sheets flowing in a magnetized background plasma which is capable of supporting Alfvén waves. The cylindrical device is 20m long and one meter in diameter with a solenoidal magnetic field as high as 3000 Gauss. For the parameters in this experiment, the plasma column is ten shear Alfvén wavelengths along the field and 100 electron inertial lengths (δe) (or 200 ρi) in the perpendicular direction. An electron current sheet is created in the plasma by placing a thin copper plate in the plasma column at one end of the device and pulsing this plate positive with respect to the chamber wall. The current sheet extends for the length of the device and has an initial cross-field size of roughly 45 δe by 0.5δe. A parallel flow of ions is observed with similar dimensions and moves in the same direction as the electrons in the current sheet with a velocity of 0.2 times the ion sound speed. A much weaker sheared perpendicular flow is also measured. Cross-sections of the ion flow are measured at several axial locations over a distance of six meters. Second, as the ion flow increases in magnitude, a much broader (8ρi) density depletion (n=0.25nO) develops around the flow. The gradient scale length of the depletion shortens until the spontaneous growth of drift waves occurs. This disrupts the electron current and ion flow, and leads to cross-field transport of

  14. Evidence for Two Separate Heliospheric Current Sheets of Cylindrical Shape During Mid-2012

    NASA Technical Reports Server (NTRS)

    Wang, Y.-M.; Young, P. R.; Muglach, K.

    2013-01-01

    During the reversal of the Sun's polar fields at sunspot maximum, outward extrapolations of magnetograph measurements often predict the presence of two or more current sheets extending into the interplanetary medium, instead of the single heliospheric current sheet (HCS) that forms the basis of the standard 'ballerina skirt' picture. By comparing potential-field source-surface models of the coronal streamer belt with white-light coronagraph observations, we deduce that the HCS was split into two distinct structures with circular cross sections during mid-2012. These cylindrical current sheets were centered near the heliographic equator and separated in longitude by roughly 180 deg; a corresponding four-sector polarity pattern was observed at Earth. Each cylinder enclosed a negative-polarity coronal hole that was identifiable in extreme ultraviolet images and gave rise to a high-speed stream. The two current sheet systems are shown to be a result of the dominance of the Sun's nonaxisymmetric quadrupole component, as the axial dipole field was undergoing its reversal during solar cycle 24.

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

    NASA Astrophysics Data System (ADS)

    Schaffner, D. A.

    2015-12-01

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

  16. Evidence for two separate heliospheric current sheets of cylindrical shape during MID-2012

    SciTech Connect

    Wang, Y.-M.; Young, P. R.; Muglach, K. E-mail: pyoung@ssd5.nrl.navy.mil

    2014-01-01

    During the reversal of the Sun's polar fields at sunspot maximum, outward extrapolations of magnetograph measurements often predict the presence of two or more current sheets extending into the interplanetary medium, instead of the single heliospheric current sheet (HCS) that forms the basis of the standard 'ballerina skirt' picture. By comparing potential-field source-surface models of the coronal streamer belt with white-light coronagraph observations, we deduce that the HCS was split into two distinct structures with circular cross sections during mid-2012. These cylindrical current sheets were centered near the heliographic equator and separated in longitude by roughly 180°; a corresponding four-sector polarity pattern was observed at Earth. Each cylinder enclosed a negative-polarity coronal hole that was identifiable in extreme ultraviolet images and gave rise to a high-speed stream. The two current sheet systems are shown to be a result of the dominance of the Sun's nonaxisymmetric quadrupole component, as the axial dipole field was undergoing its reversal during solar cycle 24.

  17. MAGNETAR GIANT FLARES AND THEIR PRECURSORS-FLUX ROPE ERUPTIONS WITH CURRENT SHEETS

    SciTech Connect

    Yu Cong

    2013-07-10

    We propose a catastrophic magnetospheric model for magnetar precursors and their successive giant flares. Axisymmetric models of the magnetosphere, which contain both a helically twisted flux rope and a current sheet, are established based on force-free field configurations. In this model, the helically twisted flux rope would lose its equilibrium and erupt abruptly in response to the slow and quasi-static variations at the ultra-strongly magnetized neutron star's surface. In a previous model without current sheets, only one critical point exists in the flux rope equilibrium curve. New features show up in the equilibrium curves for the flux rope when current sheets appear in the magnetosphere. The causal connection between the precursor and the giant flare, as well as the temporary re-entry of the quiescent state between the precursor and the giant flare, can be naturally explained. Magnetic energy would be released during the catastrophic state transitions. The detailed energetics of the model are also discussed. The current sheet created by the catastrophic loss of equilibrium of the flux rope provides an ideal place for magnetic reconnection. We point out the importance of magnetic reconnection for further enhancement of the energy release during eruptions.

  18. Numerical study of the current sheet and PSBL in a magnetotail model

    NASA Technical Reports Server (NTRS)

    Doxas, I.; Horton, W.; Sandusky, K.; Tajima, T.; Steinolfson, R.

    1989-01-01

    The current sheet and plasma sheet boundary layer (PSBL) in a magnetotail model are discussed. A test particle code is used to study the response of ensembles of particles to a two-dimensional, time-dependent model of the geomagnetic tail, and test the proposition (Coroniti, 1985a, b; Buchner and Zelenyi, 1986; Chen and Palmadesso, 1986; Martin, 1986) that the stochasticity of the particle orbits in these fields is an important part of the physical mechanism for magnetospheric substorms. The realistic results obtained for the fluid moments of the particle distribution with this simple model, and their insensitivity to initial conditions, is consistent with this hypothesis.

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Zharkova, V.; Khabarova, O.

    2015-04-01

    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 suprathermal

  1. A test of source-surface model predictions of heliospheric current sheet inclination

    NASA Technical Reports Server (NTRS)

    Burton, M. E.; Crooker, N. U.; Siscoe, G. L.; Smith, E. J.

    1994-01-01

    The orientation of the heliospheric current sheet predicted from a source surface model is compared with the orientation determined from minimum-variance analysis of International Sun-Earth Explorer (ISEE) 3 magnetic field data at 1 AU near solar maximum. Of the 37 cases analyzed, 28 have minimum variance normals that lie orthogonal to the predicted Parker spiral direction. For these cases, the correlation coefficient between the predicted and measured inclinations is 0.6. However, for the subset of 14 cases for which transient signatures (either interplanetary shocks or bidirectional electrons) are absent, the agreement in inclinations improves dramatically, with a correlation coefficient of 0.96. These results validate not only the use of the source surface model as a predictor but also the previously questioned usefulness of minimum variance analysis across complex sector boundaries. In addition, the results imply that interplanetary dynamics have little effect on current sheet inclination at 1 AU. The dependence of the correlation on transient occurrence suggests that the leading edge of a coronal mass ejection (CME), where transient signatures are detected, disrupts the heliospheric current sheet but that the sheet re-forms between the trailing legs of the CME. In this way the global structure of the heliosphere, reflected both in the source surface maps and in the interplanetary sector structure, can be maintained even when the CME occurrence rate is high.

  2. A current disruption mechanism in the neutral sheet - A possible trigger for substorm expansions

    NASA Technical Reports Server (NTRS)

    Lui, A. T. Y.; Mankofsky, A.; Chang, C.-L.; Papadopoulos, K.; Wu, C. S.

    1990-01-01

    A linear analysis is performed to investigate the kinetic cross-field streaming instability in the earth's magnetotail neutral sheet region. Numerical solution of the dispersion equation shows that the instability can occur under conditions expected for the neutral sheet just prior to the onset of substorm expansion. The excited waves are obliquely propagating whistlers with a mixed polarization in the lower hybrid frequency range. The ensuing turbulence of this instability can lead to a local reduction of the cross-tail current causing it to continue through the ionosphere to form a substorm current wedge. A substorm expansion onset scenario is proposed based on this instability in which the relative drift between ions and electrons is primarily due to unmagnetized ions undergoing current sheet acceleration in the presence of a cross-tail electric field. The required electric field strength is within the range of electric field values detected in the neutral sheet region during substorm intervals. The skew in local time of substorm onset location and the three conditions under which substorm onset is observed can be understood on the basis of the proposed scenario.

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

    SciTech Connect

    Wyper, P. F.; Jain, Rekha

    2013-05-15

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

  4. Current sheet in plasma as a system with a controlling parameter

    SciTech Connect

    Fridman, Yu. A. Chukbar, K. V.

    2015-08-15

    A simple kinetic model describing stationary solutions with bifurcated and single-peaked current density profiles of a plane electron beam or current sheet in plasma is presented. A connection is established between the two-dimensional constructions arising in terms of the model and the one-dimensional considerations by Bernstein−Greene−Kruskal facilitating the reconstruction of the distribution function of trapped particles when both the profile of the electric potential and the free particles distribution function are known.

  5. A new research of the current sheet and Field aligned current system: IMF, Solar Wind influence? MLT dependence?

    NASA Astrophysics Data System (ADS)

    Yang, J.

    2015-12-01

    Field-aligned current systems (FACs) are the dominant process by which energy and momentum are transported between the magnetosphere and the ionosphere-thermosphere system. Both large- and small-scale FACs have been observed in the auroral zone and the current sheets have complicated spatial and temporal variations. However, It is argued that while the intensity of currents varies from event to event, the basic pattern will be maintained or not. We present a statistical study of the temporal and spatial characteristics of FACs using Swarm satellite, and show the IMF, Solar Wind influence and the MLT dependence of the FACs.

  6. Effect of Time Dependent Bending of Current Sheets in Response to Generation of Plasma Jets and Reverse Currents

    NASA Astrophysics Data System (ADS)

    Frank, Anna

    Magnetic reconnection is a basis for many impulsive phenomena in space and laboratory plasmas accompanied by effective transformation of magnetic energy. Reconnection processes usually occur in relatively thin current sheets (CSs), which separate magnetic fields of different or opposite directions. We report on recent observations of time dependent bending of CSs, which results from plasma dynamics inside the sheet. The experiments are carried out with the CS-3D laboratory device (Institute of General Physics RAS, Moscow) [1]. The CS magnetic structure with an X line provides excitation of the Hall currents and plasma acceleration from the X line to both side edges [2]. In the presence of the guide field By the Hall currents give rise to bending of the sheet: the peripheral regions located away from the X line are deflected from CS middle plane (z=0) in the opposite directions ±z [3]. We have revealed generation of reverse currents jy near the CS edges, i.e. the currents flowing in the opposite direction to the main current in the sheet [4]. There are strong grounds to believe that reverse currents are generated by the outflow plasma jets [5], accelerated inside the sheet and penetrated into the regions with strong normal magnetic field component Bz [4]. An impressive effect of sudden change in the sign of the CS bend has been disclosed recently, when analyzing distributions of plasma density [6] and current away from the X line, in the presence of the guide field By. The CS configuration suddenly becomes opposite from that observed at the initial stage, and this effect correlates well with generation of reverse currents. Consequently this effect can be related to excitation of the reverse Hall currents owing to generation of reverse currents jy in the CS. Hence it may be concluded that CSs may exhibit time dependent vertical z-displacements, and the sheet geometry depends on excitation of the Hall currents, acceleration of plasma jets and generation of reverse

  7. Magnetic Reconnection: Recursive Current Sheet Collapse Triggered by “Ideal” Tearing

    NASA Astrophysics Data System (ADS)

    Tenerani, Anna; Velli, Marco; Rappazzo, Antonio Franco; Pucci, Fulvia

    2015-11-01

    We study, by means of MHD simulations, the onset and evolution of fast reconnection via the “ideal” tearing mode within a collapsing current sheet at high Lundquist numbers (S\\gg {10}4). We first confirm that as the collapse proceeds, fast reconnection is triggered well before a Sweet–Parker-type configuration can form: during the linear stage, plasmoids rapidly grow in a few Alfvén times when the predicted “ideal” tearing threshold S‑1/3 is approached from above; after the linear phase of the initial instability, X-points collapse and reform nonlinearly. We show that these give rise to a hierarchy of tearing events repeating faster and faster on current sheets at ever smaller scales, corresponding to the triggering of “ideal” tearing at the renormalized Lundquist number. In resistive MHD, this process should end with the formation of sub-critical (S ≤ 104) Sweet–Parker sheets at microscopic scales. We present a simple model describing the nonlinear recursive evolution that explains the timescale of the disruption of the initial sheet.

  8. PIC simulations of the tearing stability of the magnetotail current sheet

    NASA Astrophysics Data System (ADS)

    Bessho, N.; Bhattacharjee, A.

    2011-12-01

    Recently, Sitnov and Schindler (2010) [1] have revisited the problem of the ion tearing instability of a current sheet with a normal magnetic field, and speculated on its possible connection with dipolarization fronts in the magnetotail current sheet. We have performed 2-dimensional particle-in-cell simulations to revisit the stability of a current sheet which has a width of the order of the ion skin depth, including a spatially varying normal magnetic field Bz. Using a particle-in-cell simulation code with open boundary conditions, we have conducted simulations where the magnetic field and the density have profiles of Bx=-[B0/g(x)]tanh[z/w/g(x)] and n=[n0/g(x)2]sech2[z/w/g(x)]+nb, respectively, where w is a width of the current sheet, and a function g(x) determines the profile of Bz along the z=0 as Bz=wB0g'(x)/g(x). We have performed two types of simulations: the first one uses g(x)=exp(ɛ1x/w), in which Bz in the z=0 plane becomes uniform in the x direction. The second type of configuration uses g(x)=exp(ɛ1h(x/w)) and h(x/w)=x/w+(α/ɛ2){1+tanh[ɛ2(x-x0)/w]}, in which Bz in the z=0 plane has a hump at x=x0. The second type of magnetic field has been studied by Sitnov and Schindler (2010). We have performed several runs by changing the mass ratio and the magnitude of the normal magnetic field Bz. In both cases, we have observed that the current sheet is unstable only when Bz is very small and the condition kρe>1 is satisfied, where ρe is the gyro radius of electron with respect to Bz. When Bz becomes large and kρe<1 is satisfied, the current sheet becomes stable. The claim that the instability, when it is excited, is some form of ion tearing is critically reviewed. [1] M. I. Sitnov and K. Schindler, GRL, 37, L08102 (2010)

  9. Dynamical and Physical Properties of a Post-Coronal Mass Ejection Current Sheet

    NASA Technical Reports Server (NTRS)

    Ko, Yuan-Kuen; Raymond, John C.; Lin, Jun; Lawrence, Gareth; Li, Jing; Fludra, Andrzej

    2003-01-01

    In the eruptive process of the Kopp-Pneuman type, the closed magnetic field is stretched by the eruption so much that it is usually believed to be " open " to infinity. Formation of the current sheet in such a configuration makes it possible for the energy in the coronal magnetic field to quickly convert into thermal and kinetic energies and cause significant observational consequences, such as growing postflare/CME loop system in the corona, separating bright flare ribbons in the chromosphere, and fast ejections of the plasma and the magnetic flux. An eruption on 2002 January 8 provides us a good opportunity to look into these observational signatures of and place constraints on the theories of eruptions. The event started with the expansion of a magnetic arcade over an active region, developed into a coronal mass ejection (CME), and left some thin streamer-like structures with successively growing loop systems beneath them. The plasma outflow and the highly ionized states of the plasma inside these streamer-like structures, as well as the growing loops beneath them, lead us to conclude that these structures are associated with a magnetic reconnection site, namely, the current sheet, of this eruptive process. We combine the data from the Ultraviolet Coronagraph Spectrometer, Large Angle and Spectrometric Coronagraph Experiment, EUV Imaging Telescope, and Coronal Diagnostic Spectrometer on board the Solar and Heliospheric Observatory, as well is from the Mauna Loa Solar Observatory Mark IV K-coronameter, to investigate the morphological and dynamical properties of this event, as well as the physical properties of the current sheet. The velocity and acceleration of the CME reached up to 1800 km/s and 1 km/sq s, respectively. The acceleration is found to occur mainly at the lower corona (<2.76 Solar Radius). The post-CME loop systems showed behaviors of both postflare loops (upward motion with decreasing speed) and soft X-ray giant arches (upward motion with constant

  10. Asymmetric evolution of magnetic reconnection in collisionless accretion disk

    SciTech Connect

    Shirakawa, Keisuke Hoshino, Masahiro

    2014-05-15

    An evolution of a magnetic reconnection in a collisionless accretion disk is investigated using a 2.5 dimensional hybrid code simulation. In astrophysical disks, magnetorotational instability (MRI) is considered to play an important role by generating turbulence in the disk and contributes to an effective angular momentum transport through a turbulent viscosity. Magnetic reconnection, on the other hand, also plays an important role on the evolution of the disk through a dissipation of a magnetic field enhanced by a dynamo effect of MRI. In this study, we developed a hybrid code to calculate an evolution of a differentially rotating system. With this code, we first confirmed a linear growth of MRI. We also investigated a behavior of a particular structure of a current sheet, which would exist in the turbulence in the disk. From the calculation of the magnetic reconnection, we found an asymmetric structure in the out-of-plane magnetic field during the evolution of reconnection, which can be understood by a coupling of the Hall effect and the differential rotation. We also found a migration of X-point whose direction is determined only by an initial sign of J{sub 0}×Ω{sub 0}, where J{sub 0} is the initial current density in the neutral sheet and Ω{sub 0} is the rotational vector of the background Keplerian rotation. Associated with the migration of X-point, we also found a significant enhancement of the perpendicular magnetic field compared to an ordinary MRI. MRI-Magnetic reconnection coupling and the resulting magnetic field enhancement can be an effective process to sustain a strong turbulence in the accretion disk and to a transport of angular momentum.

  11. Effect of Inductive Coil Geometry and Current Sheet Trajectory of a Conical Theta Pinch Pulsed Inductive Plasma Accelerator

    NASA Technical Reports Server (NTRS)

    Hallock, Ashley K.; Polzin, Kurt A.; Bonds, Kevin W.; Emsellem, Gregory D.

    2011-01-01

    Results are presented demonstrating the e ect of inductive coil geometry and current sheet trajectory on the exhaust velocity of propellant in conical theta pinch pulsed induc- tive plasma accelerators. The electromagnetic coupling between the inductive coil of the accelerator and a plasma current sheet is simulated, substituting a conical copper frustum for the plasma. The variation of system inductance as a function of plasma position is obtained by displacing the simulated current sheet from the coil while measuring the total inductance of the coil. Four coils of differing geometries were employed, and the total inductance of each coil was measured as a function of the axial displacement of two sep- arate copper frusta both having the same cone angle and length as the coil but with one compressed to a smaller size relative to the coil. The measured relationship between total coil inductance and current sheet position closes a dynamical circuit model that is used to calculate the resulting current sheet velocity for various coil and current sheet con gura- tions. The results of this model, which neglects the pinching contribution to thrust, radial propellant con nement, and plume divergence, indicate that in a conical theta pinch ge- ometry current sheet pinching is detrimental to thruster performance, reducing the kinetic energy of the exhausting propellant by up to 50% (at the upper bound for the parameter range of the study). The decrease in exhaust velocity was larger for coils and simulated current sheets of smaller half cone angles. An upper bound for the pinching contribution to thrust is estimated for typical operating parameters. Measurements of coil inductance for three di erent current sheet pinching conditions are used to estimate the magnetic pressure as a function of current sheet radial compression. The gas-dynamic contribution to axial acceleration is also estimated and shown to not compensate for the decrease in axial electromagnetic acceleration

  12. Temporal evolution of a Current Sheet with Initial Finite Perturbations by Three-dimensional MHD Simulations

    NASA Astrophysics Data System (ADS)

    Yokoyama, Takaaki

    Temporal evolution of a current sheet with initial perturbations is studied by using the threedimensional resistive magnetohydrodynamic (MHD) simulations. The magnetic reconnection is considered to be the main engine of the energy rele ase in solar flares. The structure of the diffusion region is, however, not stil l understood under the circumstances with enormously large magnetic Reynolds num ber as the solar corona. In particular, the relationship between the flare's macroscopic physics and the microscopic ones are unclear. It is generally believed that the MHD turbulence s hould play a role in the intermediate scale. The initial current sheet is in an approximately hydromagnetic equilibrium with anti-parallel magnetic field in the y-direction. We imposed a finite-amplitude perturbations (=50ee what happens. Special attention is paid upon the evolution of a three-dimens ional structure in the direction along the initial electric current (z-direction ). Our preliminary results are as follows: (1) In the early phase of the evolut ion, high wavenumber modes in the z-direction are excited and grow. (2) Many "X "-type neutral points (lines) are generated along the magnetic neutral line (pla ne) in the current sheet. When they evolve into the non-linear phase, three-dime nsional structures in the z-direction also evolve. The spatial scale in the z-di rection seems to be almost comparable with that in the xy-plane. (3) The energy release rate is reduced in case of 3D simulations compared with 2D ones probably because of the reduction of the inflow cross sections by the formation of pattc hy structures in the current sheet.

  13. Quasi-adiabatic dynamics of ions in a bifurcated current sheet

    SciTech Connect

    Kartsev, Yu. I.; Artemyev, A. V.; Malova, H. V. Zelenyi, L. M.

    2013-04-15

    The study is devoted to ion dynamics in bifurcated current sheets with a two-peak current-density distribution observed in the Earth's magnetotail and solar wind. The ion motion is described by a Hamiltonian system with two degrees of freedom. The presence of a small parameter {kappa} characterizing the ratio between the amplitudes of the normal and tangential magnetic field components allows one to separate variables into fast and slow ones and introduce the quasi-adiabatic invariant of motion I{sub z}. Conservation of this invariant makes it possible to analytically describe the dynamics of charged particles. Deviations of the particle dynamics from the quasi-adiabatic one, which are caused by the nonconservation of the quasi-adiabatic invariant, are investigated. The jump of the invariant {Delta}I{sub z} is shown to depend on the small parameter according to the power-law {Delta}I{sub z} {approx} {kappa}{sup h}, where the exponent h varies between unity and 3/4, depending on the level of current sheet bifurcation. The obtained dependence of {Delta}I{sub z} on {kappa} coincides with analytic expressions in the limiting cases of nonbifurcated and completely bifurcated current sheets.

  14. Magnetoacoustic waves propagating along a dense slab and Harris current sheet and their wavelet spectra

    SciTech Connect

    Mészárosová, Hana; Karlický, Marian; Jelínek, Petr; Rybák, Ján

    2014-06-10

    Currently, there is a common endeavor to detect magnetoacoustic waves in solar flares. This paper contributes to this topic using an approach of numerical simulations. We studied a spatial and temporal evolution of impulsively generated fast and slow magnetoacoustic waves propagating along the dense slab and Harris current sheet using two-dimensional magnetohydrodynamic numerical models. Wave signals computed in numerical models were used for computations of the temporal and spatial wavelet spectra for their possible comparison with those obtained from observations. It is shown that these wavelet spectra allow us to estimate basic parameters of waveguides and perturbations. It was found that the wavelet spectra of waves in the dense slab and current sheet differ in additional wavelet components that appear in association with the main tadpole structure. These additional components are new details in the wavelet spectrum of the signal. While in the dense slab this additional component is always delayed after the tadpole head, in the current sheet this component always precedes the tadpole head. It could help distinguish a type of the waveguide in observed data. We present a technique based on wavelets that separates wave structures according to their spatial scales. This technique shows not only how to separate the magnetoacoustic waves and waveguide structure in observed data, where the waveguide structure is not known, but also how propagating magnetoacoustic waves would appear in observations with limited spatial resolutions. The possibilities detecting these waves in observed data are mentioned.

  15. Nonlinear analysis of explosive growth of collisionless magnetic reconnection in the presence of the effect of finite electron temperature

    NASA Astrophysics Data System (ADS)

    Hirota, Makoto; Hattori, Yuji

    2014-10-01

    Explosive behavior of collisionless magnetic reconnection is investigated by analyzing a two-fluid model that includes the effects of the electron inertia and the electron temperature (or compressibility). By micrifying both the electron skin depth de and the ion-sound gyroradius ρs such that ρs =de < 0 . 01 L (where L is the system size), a direct numerical simulation is performed to enlarge strongly nonlinear regime of a collisionless tearing instability. The nonlinear evolution is shown to be explosive when the inverse of the tearing index 1 /Δ' is smaller than ρs =de , whereas the maximum reconnection speed at the fully reconnected state does not significantly depend on the size of ρs =de . The singular current-vortex sheets are generated in the form of the X shape. In the explosive phase, the expansion of this X shape as well as the magnetic island occurs locally near the reconnection point. By taking an approach similar to the asymptotic matching, the dynamics of the current-vortex sheets is analyzed and the explosive reconnection speed is estimated theoretically. This work is supported by JSPS Grant-in-Aid for Young Scientists(B) (No. 25800308).

  16. Linear theory for fast collisionless magnetic reconnection in the lower-hybrid frequency range

    NASA Astrophysics Data System (ADS)

    Jovanović, D.; Shukla, P. K.

    2005-05-01

    A linear theory is presented for the interplay between the fast collisionless magnetic reconnection and the lower-hybrid waves that has been observed in recent computer simulations [J. F. Drake, M. Swisdak, C. Cattell et al., Science 299, 873 (2003)]. In plasma configurations with a strong guide field and anisotropic electron temperature, the electron dynamics is described within the framework of standard electron magnetohydrodynamic equations, accounting also for the effects of the electron polarization and ion motions in the presence of perpendicular electric fields. In the linear phase, we find two types of instabilities of a thin current sheet with steep edges, corresponding to its filamentation (or tearing) and bending. Using a surface-wave formalism for the perturbations whose wavelength is larger than the thickness of the current sheet, the corresponding growth rates are calculated as the contributions of singularities in the plasma dispersion function. These are governed by the electron inertia and the linear coupling of the reconnecting magnetic field with local plasma modes propagating in the perpendicular direction that are subject to the Buneman instability. The linear surface wave instability may be particularly important as a secondary instability, dissipating the thin current sheets that develop in the course of the fast reconnection in the shear-Alfvén and kinetic-Alfvén regimes, and providing the anomalous resistivity for the growth of magnetic islands beyond the shear-Alfvén and kinetic-Alfvén scales.

  17. 3D MHD SIMULATION OF FLARE SUPRA-ARCADE DOWNFLOWS IN A TURBULENT CURRENT SHEET MEDIUM

    SciTech Connect

    Cécere, M.; Zurbriggen, E.; Costa, A.; Schneiter, M.

    2015-07-01

    Supra-arcade downflows (SADs) are sunward, generally dark, plasma density depletions originated above posteruption flare arcades. In this paper, using 3D MHD simulations we investigate whether the SAD cavities can be produced by a direct combination of the tearing mode and Kelvin–Helmholtz instabilities leading to a turbulent current sheet (CS) medium or if the current sheet is merely the background where SADs are produced, triggered by an impulsive deposition of energy. We find that to give an account of the observational dark lane structures an addition of local energy, provided by a reconnection event, is required. We suggest that there may be a closed relation between characteristic SAD sizes and CS widths that must be satisfied to obtain an observable SAD.

  18. The heliospheric current sheet and cosmic-ray transport in the heliosheath

    SciTech Connect

    Florinski, V.

    2012-05-21

    I propose a new mechanism of energetic particle transport in a heliosheath plasma that involves a tightly folded heliospheric current sheet. The distance between magnetic sectors of opposite polarity decreases with increasing heliocentric distance from the termination shock toward the heliopause, due to a slowdown of the flow of heliosheath plasma. If the sector width is comparable or smaller than the cyclotron radius of a galactic cosmic ray ion, the latter can efficiently traverse a stack of sectors via a drift-like or a diffusive mechanism. This mechanism could be responsible for record high intensities of galactic cosmic rays measured by Voyager 1 during 2010-2011. I also discuss the effects of the solar-cycle variations of the current sheet tilt for magnetic field topology in the vicinity of the heliopause and its implications for particle transport in that region.

  19. Observations of steady anomalous magnetic heating in thin current sheets. [of solar corona

    NASA Technical Reports Server (NTRS)

    Martens, P. C. H.; Van Den Oord, G. H. J.; Hoyng, P.

    1985-01-01

    The Hard X-ray Imaging Spectrometer of the Solar Maximum Mission has yielded observations of a faint, steadily emitting loop-like structure, which have allowed the thermal evolution of this loop over a period of about 15 hr to be followed. Only 0.1 percent of the volume of the loop appears to be steadily heated, at the large rate of 0.6 erg/cu cm sec; this suggests that the heating represents the dissipation of magnetic fields in thin current sheets. Ion-kinetic tearing, as proposed by Galeev et al. (1981), is noted to be especially consonant with these observations. The source of the present X-ray emission is identified with the H-alpha filament in the same region. The present findings are held to constitute the first direct evidence for the steady dissipation of coronal magnetic fields via enhanced thin current sheet resistivity.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  1. Instability of the current sheet in the Earth's magnetotail with normal magnetic field

    SciTech Connect

    Bessho, N.; Bhattacharjee, A.

    2014-10-15

    Instability of a current sheet in the Earth's magnetotail has been investigated by two-dimensional fully kinetic simulations. Two types of magnetic configuration have been studied; those with uniform normal magnetic field along the current sheet and those in which the normal magnetic field has a spatial hump. The latter configuration has been proposed by Sitnov and Schindler [Geophys. Res. Lett. 37, L08102 (2010)] as one in which ion tearing modes might grow. The first type of configuration exhibits electron tearing modes when the normal magnetic field is small. The second type of configuration exhibits an instability which does not tear or change the topology of magnetic field lines. The hump in the initial configuration can propagate Earthward in the nonlinear regime, leading to the formation of a dipolarization front. Secondary magnetic islands can form in regions where the normal magnetic field is very weak. Under no conditions do we find the ion tearing instability.

  2. Particle Dynamics Discrimination Between Current Sheet Magnetic Field Reversal and Magnetic Neutral Line Fields

    NASA Astrophysics Data System (ADS)

    Martin, R. F., Jr.; Holland, D. L.; Svetich, J.

    2014-12-01

    We consider dynamical signatures of ion motion that discriminate between a current sheet magnetic field reversal and a magnetic neutral line field. These two related dynamical systems have been studied previously as chaotic scattering systems with application to the Earth's magnetotail. Both systems exhibit chaotic scattering over a wide range of parameter values. The structure and properties of their respective phase spaces have been used to elucidate potential dynamical signatures that affect spacecraft measured ion distributions. In this work we consider the problem of discrimination between these two magnetic structures using charged particle dynamics. For example we show that signatures based on the well known energy resonance in the current sheet field provide good discrimination since the resonance is not present in the neutral line case. While both fields can lead to fractal exit region structuring, their characteristics are different and also may provide some field discrimination. Application to magnetotail field and particle parameters will be presented

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    Wang, G. Q.; Volwerk, M.; Nakamura, R.; Boakes, P.; Zhang, T. L.; Yoshikawa, A.; Baishev, D. G.

    2014-12-01

    A wavy current sheet event observed on 15 October 2004 between 1235 and 1300 UT has been studied by using Cluster and ground-based magnetometer data. Waves propagating from the tail center 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. Three Pi2 pulsations, with onset at ~1236, ~1251, and ~1255 UT, respectively, are observed at the Tixie 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 72 s 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.

  5. A collisionless shock wave experiment

    SciTech Connect

    Winske, D.; Jones, M.E.; Sgro, A.G.; Thomas, V.A.

    1995-04-01

    Collisionless shock waves are a very important heating mechanism for plasmas and are commonly found in space and astrophysical environments. Collisionless shocks were studied in the laboratory more than 20 years ago, and more recently in space via in situ satellite measurements. The authors propose a new laboratory shock wave experiment to address unresolved issues related to the differences in the partition of plasma heating between electrons and ions in space and laboratory plasmas, which can have important implications for a number of physical systems.

  6. Kinetic Simulations of the Electrically Charged Current Sheet of a Pulsar

    NASA Astrophysics Data System (ADS)

    Black, Carrie; DeVore, C. Richard; Antiochos, Spiro K.; Harding, Alice Kust; Kazanas, Demosthenes; Kalapotharakos, Constantinos; Timokhin, Andrey

    2014-06-01

    The pulsar magnetosphere is believed to comprise a volume of low-lying, closed field about the magnetic equator, bounded by polar open-field regions in which the pulsar wind flows into space. In the standard global-scale models, a magnetic discontinuity (electric current sheet) of nonneutral plasma separates these opposite-polarity open fields. We use the particle-in-cell Plasma Simulation Code, PSC, to examine the dynamics of a self-consistent model for the internal structure of this sheet, in which the charge-neutral Vlasov/Maxwell equilibria of Harris (1962) and Hoh (1966) are generalized to allow a net electric charge. PSC accommodates both Maxwell (nonrelativistic) and Jüttner/Synge (relativistic) distribution functions for the electrons and positrons. Numerical equilibrium solutions to the 1D Maxwell equations are initialized on the 2D PSC grid, supplemented by periodic boundary conditions in the direction parallel to the sheet and insulating-wall boundary conditions remote from the sheet in the perpendicular direction. As is typical in kinetic studies of pair plasmas, the particle thermal energy and the relative drift velocity driving the current are assumed to be of order the rest energy and the speed of light, respectively. In this limit, the Debye length, skin depth, and Harris/Hoh current-sheet width are all comparable to each other, rather than widely separated and arranged in order of increasing size as generally occurs in nonrelativistic plasmas. The qualitatively new feature of our pulsar simulations is the equilibrium electric field, whose strength can be comparable to that of the magnetic field in the relativistic limit. We expect its presence to have profound consequences for the linear stability and nonlinear evolution of charged pulsar current sheets, substantially modifying the tearing and reconnection of the magnetic field. Exploratory PSC simulations of magnetic reconnection in representative electrified Harris/Hoh equilibria will be

  7. Small-scale magnetic islands near the heliospheric current sheet and their role in particle acceleration

    NASA Astrophysics Data System (ADS)

    Khabarova, Olga; Zank, Gary; Li, Gang; le Roux, Jakobus A.; Webb, Gary M.; Dosch, Alexander; Malandraki, Olga E.; Zharkova, Valentina V.

    2015-04-01

    Increases of ion fluxes in the keV-MeV range are sometimes observed near the heliospheric current sheet (HCS) during periods when other sources are absent. These resemble solar energetic particle (SEP) events, but the events are weaker and apparently local. Conventional explanations based on either shock acceleration of charged particles or particle acceleration due to magnetic reconnection at interplanetary current sheets are not persuasive. We suggest instead that recurrent magnetic reconnection occurs at the HCS and smaller current sheets in the solar wind (Zharkova & Khabarova, ApJ, 2012), of which a consequence is particle energization by the dynamically evolving secondary current sheets and magnetic islands (Zank et al., ApJ, 2014; Drake et al., JRL, 2006). The effectiveness of the trapping and acceleration process associated with magnetic islands depends in part on the topology of the HCS. We show that the HCS possesses ripples superimposed on the large-scale flat or wavy structure. We conjecture that the ripples can efficiently confine plasma and provide tokamak-like conditions that are favorable for the appearance of small-scale magnetic islands that merge and/or contract. Particles trapped in the vicinity of merging islands and experiencing multiple small-scale reconnection events are accelerated by the induced electric field, and experience first-order Fermi acceleration in contracting magnetic islands (Zank et al., ApJ, 2014). We present multi-spacecraft observations of magnetic island merging and particle energization in the absence of other sources, providing support for theory and simulations that show particle energization by reconnection related processes of magnetic island merging and contraction.

  8. Current sheet Formation in a Conical Theta Pinch Faraday Accelerator with Radio-Frequency Assisted Discharge

    NASA Technical Reports Server (NTRS)

    Hallock, Ashley K.; Choueiri, Edgar Y.; Polzin, Kurt A.

    2007-01-01

    The inductive formation of current sheets in a conical theta pinch FARAD (Faraday Accelerator with Radio-frequency Assisted Discharge) thruster is investigated experimentally with time-integrated photography. The goal is to help in understanding the mechanisms and conditions controlling the strength and extent of the current sheet, which are two indices important for FARAD as a propulsion concept. The profiles of these two indices along the inside walls of the conical acceleration coil are assumed to be related to the profiles of the strength and extent of the luminosity pattern derived from photographs of the discharge. The variations of these profiles as a function of uniform back-fill neutral pressure (with no background magnetic field and all parameters held constant) provided the first clues on the nature and qualitative dependencies of current sheet formation. It was found that there is an optimal pressure for which both indices reach a maximum and that the rate of change in these indices with pressure differs on either side of this optimal pressure. This allowed the inference that current sheet formation follows a Townsend-like breakdown mechanism modified by the existence of a finite pressure-dependent radio-frequency-generated electron density background. The observation that the effective location of the luminosity pattern favors the exit-half of the conical coil is explained as the result of the tendency of the inductive discharge circuit to operate near its minimal self-inductance. Movement of the peak in the luminosity pattern towards the upstream side of the cone with increasing pressure is believed to result from the need of the circuit to compensate for the increase in background plasma resistivity due to increasing pressure.

  9. Ion velocity distributions in the vicinity of the current sheet in Earth's distant magnetotail

    NASA Technical Reports Server (NTRS)

    Frank, L. A.; Paterson, W. R.; Ackerson, K. L.; Kokubun, S.; Kivelson, M. G.; Yamamoto, T.; Fairfield, D. H.

    1994-01-01

    Observations of the three-dimensional velocity distributions of positive ions and electrons have been recently gained for the first time in Earth's distant magnetotail with the Galileo and Geotail spacecraft. For this brief discussion of these exciting results the focus is on the overall character of the ion velocity distributions during substorm activity. The ion velocity distributions within and near the magnetotail current sheet are not accurately described as convecting, isotropic Maxwellians. The observed velocity distributions are characterized by at least two robust types. The first type is similar to the 'lima bean'-shaped velocity distributions that are expected from the nonadiabatic acceleration of ions which execute Speiser-type trajectories in the current sheet. The second distribution is associated with the presence of cold ion beams that presumably also arise from the acceleration of plasma mantle ions in the electric and weak magnetic fields in the current sheet. The ion velocity distributions in a magnetic field structure that is similar to that for plasmoids are also examined. Again the velocity distributions are not Maxwellian but are indicative of nonadiabatic acceleration. An example of the pressure tensor within the plasmoid-like event is also presented because it is anticipated that the off-diagonal elements are important in a description of magnetotail dynamics. Thus our concept of magnetotail dynamics must advance from the present assumption of co-moving electron and ion Maxwellian distributions into reformulations in terms of global kinematical models and nonadiabatic particle motion.

  10. Kinetic model of force-free current sheets with non-uniform temperature

    SciTech Connect

    Kolotkov, D. Y.; Nakariakov, V. M.; Vasko, I. Y.

    2015-11-15

    The kinetic model of a one-dimensional force-free current sheet (CS) developed recently by Harrison and Neukirch [Phys. Rev. Lett. 102(13), 135003 (2009)] predicts uniform distributions of the plasma temperature and density across the CS. However, in realistic physical systems, inhomogeneities of these plasma parameters may arise quite naturally due to the boundary conditions or local plasma heating. Moreover, as the CS spatial scale becomes larger than the characteristic kinetic scales (the regime often referred to as the MHD limit), it should be possible to set arbitrary density and temperature profiles. Thus, an advanced model has to allow for inhomogeneities of the macroscopic plasma parameters across the CS, to be consistent with the MHD limit. In this paper, we generalise the kinetic model of a force-free current sheet, taking into account the inhomogeneity of the density and temperature across the CS. In the developed model, the density may either be enhanced or depleted in the CS central region. The temperature profile is prescribed by the density profile, keeping the plasma pressure uniform across the CS. All macroscopic parameters, as well as the distribution functions for the protons and electrons, are determined analytically. Applications of the developed model to current sheets observed in space plasmas are discussed.

  11. The Role of Current Sheets in Solar Eruptive Events: An ISSI International Team Project

    NASA Technical Reports Server (NTRS)

    Suess, Steven T.; Poletto, Giannina

    2006-01-01

    Current sheets (CSs) are a prerequisite for magnetic reconnection. An International Space Science Institute (ISSI, of Bern, Switzerland) research team will work to empirically define current sheet properties in the solar atmosphere and their signatures in the interplanetary medium, and to understand their role in the development of solar eruptive events. The project was inspired by recently acquired ground and space based observations that reveal CS signatures at the time of flares and Coronal Mass Ejections (CMEs), in the chromosphere, in the corona and in the interplanetary medium. At the same time, theoretical studies predict the formation of CSs in different models and configurations, but theories and observational results have not yet developed an interaction efficient enough to allow us to construct a unified scenario. The team will generate synergy between observers, data analysts, and theoreticians, so as to enable a significant advance in understanding of current sheet behavior and properties. A further motivation for studying CSs is related to the expected electric fields in CSs that may be the source of solar energetic particles (SEPs). The team has 14 members from Europe and the US. The first meeting is in October 2006 and the second is late in 2007.

  12. Current Sheet Statistics in Three-Dimensional Simulations of Coronal Heating

    NASA Astrophysics Data System (ADS)

    Lin, L.; Ng, C. S.; Bhattacharjee, A.

    2013-04-01

    In a recent numerical study [Ng et al., Astrophys. J. 747, 109, 2012], with a three-dimensional model of coronal heating using reduced magnetohydrodynamics (RMHD), we have obtained scaling results of heating rate versus Lundquist number based on a series of runs in which random photospheric motions are imposed for hundreds to thousands of Alfvén time in order to obtain converged statistical values. The heating rate found in these simulations saturate to a level that is independent of the Lundquist number. This scaling result was also supported by an analysis with the assumption of the Sweet-Parker scaling of the current sheets, as well as how the width, length and number of current sheets scale with Lundquist number. In order to test these assumptions, we have implemented an automated routine to analyze thousands of current sheets in these simulations and return statistical scalings for these quantities. It is found that the Sweet-Parker scaling is justified. However, some discrepancies are also found and require further study.

  13. Particle Acceleration and Magnetic Dissipation in Relativistic Current Sheet of Pair Plasmas

    NASA Astrophysics Data System (ADS)

    Zenitani, S.; Hoshino, M.

    2007-11-01

    We study linear and nonlinear development of relativistic and ultrarelativistic current sheets of pair (e+/-) plasmas with antiparallel magnetic fields. Two types of two-dimensional problems are investigated by particle-in-cell simulations. First, we present the development of relativistic magnetic reconnection, whose outflow speed is on the order of the light speed c. It is demonstrated that particles are strongly accelerated in and around the reconnection region and that most of the magnetic energy is converted into a ``nonthermal'' part of plasma kinetic energy. Second, we present another two-dimensional problem of a current sheet in a cross field plane. In this case, the relativistic drift kink instability (RDKI) occurs. Particle acceleration also takes place, but the RDKI quickly dissipates the magnetic energy into plasma heat. We discuss the mechanism of particle acceleration and the theory of the RDKI in detail. It is important that properties of these two processes are similar in the relativistic regime of T>~mc2, as long as we consider the kinetics. Comparison of the two processes indicates that magnetic dissipation by the RDKI is a more favorable process in the relativistic current sheet. Therefore, the striped pulsar wind scenario should be reconsidered by the RDKI.

  14. Multiple Current Sheet Systems in the Outer Heliosphere: Energy Release and Turbulence

    NASA Astrophysics Data System (ADS)

    Burgess, D.; Gingell, P. W.; Matteini, L.

    2016-05-01

    In the outer heliosphere, beyond the solar wind termination shock, it is expected that the warped heliospheric current sheet forms a region of closely packed, multiple, thin current sheets. Such a system may be subject to the ion-kinetic tearing instability, and hence may generate magnetic islands and hot populations of ions associated with magnetic reconnection. Reconnection processes in this environment have important implications for local particle transport, and for particle acceleration at reconnection sites and in turbulence. We study this complex environment by means of three-dimensional hybrid simulations over long timescales, in order to capture the evolution from linear growth of the tearing instability to a fully developed turbulent state at late times. The final state develops from the highly ordered initial state via both forward and inverse cascades. Component and spectral anisotropy in the magnetic fluctuations is present when a guide field is included. The inclusion of a population of newborn interstellar pickup protons does not strongly affect these results. Finally, we conclude that reconnection between multiple current sheets can act as an important source of turbulence in the outer heliosphere, with implications for energetic particle acceleration and propagation.

  15. Kinetic model of force-free current sheets with non-uniform temperature

    NASA Astrophysics Data System (ADS)

    Kolotkov, D. Y.; Vasko, I. Y.; Nakariakov, V. M.

    2015-11-01

    The kinetic model of a one-dimensional force-free current sheet (CS) developed recently by Harrison and Neukirch [Phys. Rev. Lett. 102(13), 135003 (2009)] predicts uniform distributions of the plasma temperature and density across the CS. However, in realistic physical systems, inhomogeneities of these plasma parameters may arise quite naturally due to the boundary conditions or local plasma heating. Moreover, as the CS spatial scale becomes larger than the characteristic kinetic scales (the regime often referred to as the MHD limit), it should be possible to set arbitrary density and temperature profiles. Thus, an advanced model has to allow for inhomogeneities of the macroscopic plasma parameters across the CS, to be consistent with the MHD limit. In this paper, we generalise the kinetic model of a force-free current sheet, taking into account the inhomogeneity of the density and temperature across the CS. In the developed model, the density may either be enhanced or depleted in the CS central region. The temperature profile is prescribed by the density profile, keeping the plasma pressure uniform across the CS. All macroscopic parameters, as well as the distribution functions for the protons and electrons, are determined analytically. Applications of the developed model to current sheets observed in space plasmas are discussed.

  16. Field Emission Properties of Carbon Nanotube Fibers and Sheets for a High Current Electron Source

    NASA Astrophysics Data System (ADS)

    Christy, Larry

    Field emission (FE) properties of carbon nanotube (CNT) fibers from Rice University and the University of Cambridge have been studied for use within a high current electron source for a directed energy weapon. Upon reviewing the performance of these two prevalent CNT fibers, cathodes were designed with CNT fibers from the University of Cincinnati Nanoworld Laboratory. Cathodes composed of a single CNT fiber, an array of three CNT fibers, and a nonwoven CNT sheet were investigated for FE properties; the goal was to design a cathode with emission current in excess of 10 mA. Once the design phase was complete, the cathode samples were fabricated, characterized, and then analyzed to determine FE properties. Electrical conductivity of the CNT fibers was characterized with a 4-probe technique. FE characteristics were measured in an ultra-high vacuum chamber at Wright-Patterson Air Force Base. The arrayed CNT fiber and the enhanced nonwoven CNT sheet emitter design demonstrated the most promising FE properties. Future work will include further analysis and cathode design using this nonwoven CNT sheet material to increase peak current performance during electron emission.

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

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  18. The link between shocks, turbulence, and magnetic reconnection in collisionless plasmas

    SciTech Connect

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

    2014-06-15

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

  19. A current disruption mechanism in the neutral sheet for triggering substorm expansions

    NASA Technical Reports Server (NTRS)

    Lui, A. T. Y.; Mankofsky, A.; Chang, C.-L.; Papadopoulos, K.; Wu, C. S.

    1989-01-01

    Two main areas were addressed in support of an effort to understand mechanism responsible for the broadband electrostatic noise (BEN) observed in the magnetotail. The first area concerns the generation of BEN in the boundary layer region of the magnetotail whereas the second area concerns the occassional presence of BEN in the neutral sheet region. For the generation of BEN in the boundary layer region, a hybrid simulation code was developed to perform reliable longtime, quiet, highly resolved simulations of field aligned electron and ion beam flow. The result of the simulation shows that broadband emissions cannot be generated by beam-plasma instability if realistic values of the ion beam parameters are used. The waves generated from beam-plasma instability are highly discrete and are of high frequencies. For the plasma sheet boundary layer condition, the wave frequencies are in the kHz range, which is incompatible with the observation that the peak power in BEN occur in the 10's of Hz range. It was found that the BEN characteristics are more consistent with lower hybrid drift instability. For the occasional presence of BEN in the neutral sheet region, a linear analysis of the kinetic cross-field streaming instability appropriate to the neutral sheet condition just prior to onset of substorm expansion was performed. By solving numerically the dispersion relation, it was found that the instability has a growth time comparable to the onset time scale of substorm onset. The excited waves have a mixed polarization in the lower hybrid frequency range. The imposed drift driving the instability corresponds to unmagnetized ions undergoing current sheet acceleration in the presence of a cross-tail electric field. The required electric field strength is in the 10 mV/m range which is well within the observed electric field values detected in the neutral sheet during substorms. This finding can potentially account for the disruption of cross-tail current and its diversion to

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

    NASA Astrophysics Data System (ADS)

    Malova, H. V.; Popov, V. Yu.; Grigorenko, E. E.; Dunko, A. V.; Petrukovich, A. A.

    2016-08-01

    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.

  1. Role of Plasma Sheet Source Population in Ring Current Dynamics (Invited)

    NASA Astrophysics Data System (ADS)

    Jordanova, V.; Yu, Y.; Reeves, G. D.; Kletzing, C.; Spence, H.; Sazykin, S. Y.

    2013-12-01

    Understanding the dynamics of ring current particles during disturbed conditions remains a long-standing challenge, moreover these particles represent a seed population for the hazardous radiation belts. The formation of the storm-time ring current depends on two main factors: 1) the plasma sheet as a reservoir supplying particles that are transported earthward, and 2) the electric field as a mechanism that energizes them. To investigate ring current development on a global scale, we use our four-dimensional (4-D) ring current-atmosphere interactions model (RAM-SCB) [Jordanova et al., 2010; Zaharia et al., 2010] which solves the kinetic equation for H+, O+, and He+ ions and electrons using a self-consistently calculated magnetic field in force balance with the anisotropic ring current plasma pressure. The model boundary was recently expanded from geosynchronous orbit to 9 RE, where the plasma boundary conditions are specified from the empirical plasma sheet model TM03 [Tsyganenko and Mukai, 2003] based on Geotail data. We simulate the transport, acceleration, and loss of energetic particles from the magnetotail to the inner magnetosphere during several geomagnetic storms that occurred since the launch of the Van Allen Probes in August 2012. We compare our results with simultaneous plasma and field observations from the Energetic particle, Composition, and Thermal plasma (ECT) [Spence et al., 2013] and the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) [Kletzing et al., 2013] investigations on the Van Allen Probes. We investigate the role of the plasma sheet source population in global ring current simulations considering various boundary conditions and electric field formulations. An improved understanding of the highly coupled inner magnetosphere system is provided.

  2. Formation of sheet plumes, current coils, and helical magnetic fields in a spherical magnetohydrodynamic dynamo

    NASA Astrophysics Data System (ADS)

    Miyagoshi, Takehiro; Kageyama, Akira; Sato, Tetsuya

    2011-07-01

    Aiming at understanding of magnetic field generation process in rapidly rotating stars and planets represented by the Earth, computer simulations of magnetohydrodynamic (MHD) dynamo were performed in a rotating spherical shell geometry. Thermal convection and dynamo process with Ekman number of the order of 10-7 were studied. New structures of convection motion, dynamo-generated electrical current, and magnetic field are found. The flow is organized as a set of thin, sheet-like plumes. The current is made of small-scale coil structure with magnetic flux tubes within each of the coil. These flux tubes are connected each other to form a large scale helical magnetic field structure.

  3. The equatorial current sheet and other interesting features of the pulsar magnetosphere

    NASA Astrophysics Data System (ADS)

    Contopoulos, Ioannis

    2016-06-01

    > We want to understand what drives magnetospheric dissipation in the equatorial current sheet. Numerical simulations have limitations and, unless we have a clear a priori understanding of the physical processes involved, their results can be misleading. We argue that the canonical pulsar magnetosphere is strongly dissipative and that a large fraction (up to 30-40 % in an aligned rotator) of the spindown luminosity is redirected towards the equator where it is dissipated into particle acceleration and emission of radiation. We show that this is due to the failure of the equatorial electric current to cross the Y-point at the tip of the corotating zone.

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

  5. Formation of discontinuities and expansion waves in the outflow region of magnetic reconnection in an asymmetric current sheet

    NASA Astrophysics Data System (ADS)

    Lee, L. C.; Hsupeng, B. Y.; Lee, K. H.; Chao, J. K.

    2015-12-01

    The current sheets observed in the solar wind, magnetopause, and nightside plasma sheet can be asymmetric, in which the plasma densities and/or magnetic field magnitudes on the two sides of the current sheet are not equal. A hybrid code is used to simulate the 1-D Riemann problem for the generation and evolution of MHD discontinuities and expansion waves in the outflow region of magnetic reconnection in an asymmetric current sheet. In a symmetric current sheet, four types of compound structures are found: (a) RD-SS compound structure: show shock (SS) is attached to the downstream of rotational discontinuity (RD), (b) SS-RD: SS is followed by an adjacent RD, (c) SS-RD-SS: RD is trapped inside SS, and (d) switch-off slow shock (SSS). In the asymmetric current sheet, the rotational angle of magnetic field across an RD on the side with a higher plasma density is usually larger than that with a lower plasma density. In the asymmetric cases, a pure RD, a single SS, or a pure slow expansion wave (SE) may appear. When the asymmetry is further increased, RD may become absent in the low density side. For a highly asymmetric current sheet, a slow expansion wave (SE) is formed behind the SS-RD compound structure on the side with a very high plasma density.

  6. Cluster observations near reconnection X lines in Earth's magnetotail current sheet

    NASA Astrophysics Data System (ADS)

    Hwang, K.-J.; Goldstein, M. L.; Wendel, D. E.; Fazakerley, A. N.; Gurgiolo, C.

    2013-07-01

    Magnetic reconnection is an efficient way to convert magnetic energy into particle energy. In this paper, we use Cluster thermal electron and ion measurements in the vicinity of a reconnection X line to delineate the structure of the reconnection current sheet. Multispacecraft observations made by Cluster on 18 August 2002 indicate that an X line drifted close to the spacecraft, about 3.4 RE earthward of the position where another X line had been observed earlier. Comparison of the Hall magnetic and electric field geometry and the observed properties of energetic electron beams streaming along the separatrix between the Cluster spacecraft indicates that the second X line formed within 20 s of the observation of the first X line. Repeated flow reversals and Hall field geometry together with the presence of a magnetic island embedded in the outflow region downstream of the first X line suggest that the initial current sheet was unstable, perhaps to the tearing mode. We identify a region with a thickness of 0.72 ion inertial lengths (29 electron inertial lengths, de) of super-Alfvénic electron outflow (greater than the ion in-flow Alfvén speed) during the period when the spacecraft was in the vicinity of the neutral sheet. Slightly below the neutral sheet, Cluster observed asymmetric counter-streaming electrons with a loss of axisymmetry in the electron (V⟂1,V⟂2) distribution functions over a thin boundary with a thickness of several de. This electron-scale transition layer was embedded in a much wider region where both the ion and electron Walén tests failed, and the electron super-Alfvénic bulk outflow jets with high-energy electron beams were detected. Those phenomena provide details of the substructure of the reconnection current sheet and suggest that the spacecraft traversed or skimmed the tailward edge of an elongated electron current layer. We also note that this event differs from a previously reported reconnection event in that strong electron

  7. On the contribution of plasma sheet bubbles to the storm time ring current

    NASA Astrophysics Data System (ADS)

    Yang, Jian; Toffoletto, Frank R.; Wolf, Richard A.; Sazykin, Stanislav

    2015-09-01

    Particle injections occur frequently inside 10 Re during geomagnetic storms. They are commonly associated with bursty bulk flows or plasma sheet bubbles transported from the tail to the inner magnetosphere. Although observations and theoretical arguments have suggested that they may have an important role in storm time dynamics, this assertion has not been addressed quantitatively. In this paper, we investigate which process is dominant for the storm time ring current buildup: large-scale enhanced convection or localized bubble injections. We use the Rice Convection Model-Equilibrium (RCM-E) to model a series of idealized storm main phases. The boundary conditions at 14-15 Re on the nightside are adjusted to randomly inject bubbles to a degree roughly consistent with observed statistical properties. A test particle tracing technique is then used to identify the source of the ring current plasma. We find that the contribution of plasma sheet bubbles to the ring current energy increases from ~20% for weak storms to ~50% for moderate storms and levels off at ~61% for intense storms, while the contribution of trapped particles decreases from ~60% for weak storms to ~30% for moderate and ~21% for intense storms. The contribution of nonbubble plasma sheet flux tubes remains ~20% on average regardless of the storm intensity. Consistent with previous RCM and RCM-E simulations, our results show that the mechanisms for plasma sheet bubbles enhancing the ring current energy are (1) the deep penetration of bubbles and (2) the bulk plasma pushed ahead of bubbles. Both the bubbles and the plasma pushed ahead typically contain larger distribution functions than those in the inner magnetosphere at quiet times. An integrated effect of those individual bubble injections is the gradual enhancement of the storm time ring current. We also make two predictions testable against observations. First, fluctuations over a time scale of 5-20 min in the plasma distributions and electric field

  8. Thin current sheets in the magnetotail during substorms: CDAW 6 revisited

    NASA Technical Reports Server (NTRS)

    Pulkkinen, T. I.; Baker, D. N.; Mitchell, D. G.; Mcpherron, R. L.; Huang, C. Y.; Frank, L. A.

    1994-01-01

    The global magnetic field configuration during the growth phase of the Coordinated Data Analysis Workshop (CDAW) 6 substorm (March 22, 1979, 1054 UT) is modeled using data from two suitably located spacecraft and temporally evolving variations of the Tsyganenko magnetic field model. These results are compared with a local calculation of the current sheet location and thickness carried out by McPherron et al. (1987) and Sanny et al. (this issue). Both models suggest that during the growth phase the current sheet rotated away from its nominal location, and simultaneously thinned strongly. The locations and thickness obtained from the two models are in good agreement. The global model suggests that the peak current density is approximately 120 nA/sq m and that the cross-tail current almost doubled its intensity during this very strong growth phase. The global model predicts a field configuration that is sufficiently stretched to scatter thermal electrons, which may be conducive to the onset of ion tearing in the tail. The electron plasma data further support this scenario, as the anisotropy present in the low-energy electrons disappears close to the substorm onset. The electron contribution to the intensifying current in this case is of the order of 10% before the isotropization of the distribution.

  9. Kelvin-Helmholtz instability in a current-vortex sheet at a 3D magnetic null

    SciTech Connect

    Wyper, P. F.; Pontin, D. I.

    2013-03-15

    We report here, for the first time, an observed instability of a Kelvin-Helmholtz nature occurring in a fully three-dimensional (3D) current-vortex sheet at the fan plane of a 3D magnetic null point. The current-vortex layer forms self-consistently in response to foot point driving around the spine lines of the null. The layer first becomes unstable at an intermediate distance from the null point, with the instability being characterized by a rippling of the fan surface and a filamentation of the current density and vorticity in the shear layer. Owing to the 3D geometry of the shear layer, a branching of the current filaments and vortices is observed. The instability results in a mixing of plasma between the two topologically distinct regions of magnetic flux on either side of the fan separatrix surface, as flux is reconnected across this surface. We make a preliminary investigation of the scaling of the system with the dissipation parameters. Our results indicate that the fan plane separatrix surface is an ideal candidate for the formation of current-vortex sheets in complex magnetic fields and, therefore, the enhanced heating and connectivity change associated with the instabilities of such layers.

  10. Destabilization of 2D magnetic current sheets by resonance with bouncing electron - a new theory

    NASA Astrophysics Data System (ADS)

    Fruit, Gabriel; Louarn, Philippe; Tur, Anatoly

    2016-07-01

    In the general context of understanding the possible destabilization of the magnetotail before a substorm, we propose a kinetic model for electromagnetic instabilities in resonant interaction with trapped bouncing electrons. The geometry is clearly 2D and uses Harris sheet profile. Fruit et al. 2013 already used this model to investigate the possibilities of electrostatic instabilities. Tur et al. 2014 generalizes the model for full electromagnetic perturbations. Starting with a modified Harris sheet as equilibrium state, the linearized gyrokinetic Vlasov equation is solved for electromagnetic fluctuations with period of the order of the electron bounce period (a few seconds). The particle motion is restricted to its first Fourier component along the magnetic field and this allows the complete time integration of the non local perturbed distribution functions. The dispersion relation for electromagnetic modes is finally obtained through the quasi neutrality condition and the Ampere's law for the current density. The present talk will focus on the main results of this theory. The electrostatic version of the model may be applied to the near-Earth environment (8-12 R_{E}) where beta is rather low. It is showed that inclusion of bouncing electron motion may enhance strongly the growth rate of the classical drift wave instability. This model could thus explain the generation of strong parallel electric fields in the ionosphere and the formation of aurora beads with wavelength of a few hundreds of km. In the electromagnetic version, it is found that for mildly stretched current sheet (B_{z} > 0.1 B _{lobes}) undamped modes oscillate at typical electron bounce frequency with wavelength of the order of the plasma sheet thickness. As the stretching of the plasma sheet becomes more intense, the frequency of these normal modes decreases and beyond a certain threshold in B_{z}/B _{lobes}, the mode becomes explosive (pure imaginary frequency) with typical growing rate of a few

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

    NASA Astrophysics Data System (ADS)

    Daldorff, Lars K. S.; Klimchuk, James A.

    2016-05-01

    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.

  12. Conical Current Sheets in a Source-Surface Model of the Heliosphere

    NASA Astrophysics Data System (ADS)

    Schulz, M.

    2007-12-01

    Different methods of modeling the coronal and heliospheric magnetic field are conveniently visualized and intercompared by applying them to ideally axisymmetric field models. Thus, for example, a dipolar B field with its moment parallel to the Sun's rotation axis leads to a flat heliospheric current sheet. More general solar B fields (still axisymmetric about the solar rotation axis for simplicity) typically lead to cone-shaped current sheets beyond the source surface (and presumably also in MHD models). As in the dipolar case [Schulz et al., Solar Phys., 60, 83-104, 1978], such conical current sheets can be made realistically thin by taking the source surface to be non-spherical in a way that reflects the underlying structure of the Sun's main B field. A source surface that seems to work well in this respect [Schulz, Ann. Geophysicae, 15, 1379-1387, 1997] is a surface of constant F = (1/r)kB, where B is the scalar strength of the Sun's main magnetic field and k (~ 1.4) is a shape parameter. This construction tends to flatten the source surface in regions where B is relatively weak. Thus, for example, the source surface for a dipolar B field is shaped somewhat like a Rugby football, whereas the source surface for an axisymmetric quadrupolar B field is similarly elongated but somewhat flattened (as if stuffed into a cone) at mid-latitudes. A linear combination of co-axial dipolar and quadrupolar B fields generates a somewhat pear-shaped (but still convex) source surface. If the region surrounded by the source surface is regarded as current-free, then the source surface itself should be (as nearly as possible) an equipotential surface for the corresponding magnetic scalar potential (expanded, for example, in spherical harmonics). The solar wind should then flow not quite radially, but rather in a straight line along the outward normal to the source surface, and the heliospheric B field should follow a corresponding generalization of Parker's spiral [Levine et al

  13. Differential measurement and model calculations of cosmic ray latitudinal gradient with respect to the heliospheric current sheet

    NASA Technical Reports Server (NTRS)

    Christon, S. P.; Cummings, A. C.; Stone, E. C.; Behannon, K. W.; Burlaga, L. F.

    1986-01-01

    Simultaneous magnetic field and charged particle measurements from the Voyager spacecraft with heliographic latitude separations of more than 10 deg are used to investigate the distribution of about 1-GeV galactic cosmic ray protons with respect to the heliospheric current sheet in the outer solar system. By comparing the ratio of cosmic ray flux at Voyager 1 to that at Voyager 2 during periods of relatively quiet interplanetary conditions when the spacecraft are either both north or both south of the heliospheric current sheet, an average latitude component of the gradient of the cosmic ray flux on opposite sides of the current sheet is derived under restricted interplanetary conditions of -0.22 + or - 0.03 pct/deg, equivalent to a decrease of about 1 percent/AU away from the current sheet at about 12 AU. The results for these limited periods are in qualitative agreement with propagation models incorporating particle drifts.

  14. Magnetic Reconnection during Collisionless, Stressed, X-point Collapse using Particle-in-cell Simulation

    NASA Astrophysics Data System (ADS)

    Tsiklauri, D.; Haruki, T.

    2008-09-01

    Dungey's (1953) work on X-point collapse is the earliest analysis done on magnetic reconnection and predates the tearing mode, Sweet-Parker and Petcheck reconnection models. X-point collapse soon fell out of favour because in the collisional (MHD) regime, for the plausible space plasma parameters, it was found to be inefficient. We however show [Tsiklauri D. and T. Haruki, Phys. of Plasmas, 14, 112905, (2007)] that in the collisionless regime, which is indeed more applicable to space plasmas, the reconnection is efficient. We study magnetic reconnection during collisionless, stressed, X-point collapse using kinetic, 2.5D, fully electromagnetic, relativistic Particle-in-Cell numerical code. Two cases of weakly and strongly stressed X-point collapse were considered. Here descriptors weakly and strongly refer to 20% and 124% unidirectional spatial compression of the X-point, respectively. We found that within about one Alfven time, 2% and 20% of the initial magnetic energy is converted into heat and accelerated particle energy in the case of weak and strong stress, respectively. In the both cases, during the peak of the reconnection, the quadruple out-of-plane magnetic field is generated. These results strongly suggest the importance of the collisionless, stressed X-point collapse as an efficient mechanism of converting magnetic energy into heat and super-thermal particle energy. In the weakly stressed case, the reconnection rate, defined as the out-of-plane electric field in the X-point normalized by the product of external magnetic field and Alfven speeds, peaks at 0.11, with its average over 1.25 Alfven times being 0.04. Electron energy distribution in the current sheet, at the high-energy end of the spectrum, shows a power-law distribution with the index varying in time, attaining a maximal value of -4.1 at the final simulation time step (1.25 Alfven times). In the strongly stressed case, magnetic reconnection peak occurs 3.4 times faster and is more efficient

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

    NASA Technical Reports Server (NTRS)

    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.

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

    SciTech Connect

    Loizu, J.; Hudson, S. R.; Bhattacharjee, A.; Lazerson, S.; Helander, P.

    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.

  17. Chaotic jumps in the generalized first adiabatic invariant in current sheets

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    The present study examines how the changes in the generalized first adiabatic invariant J derived from the separatrix crossing theory can be incorporated into the drift variable approach to generating distribution functions. A method is proposed for determining distribution functions for an ensemble of particles following interaction with the tail current sheet by treating the interaction as a scattering problem characterized by changes in the invariant. Generalized drift velocities are obtained for a 1D tail configuration by using the generalized first invariant. The invariant remained constant except for the discrete changes caused by chaotic scattering as the particles cross the separatrix.

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

    SciTech Connect

    Brannon, S. R.; Longcope, D. W.; Qiu, J.

    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.

  19. Particle scattering and current sheet stability in the geomagnetic tail during the substorm growth phase

    SciTech Connect

    Pulkkinen, T.I.; Pellinen, R.J.; Koskinen, H.E.J. ); Baker, D.N. ); Buechner, J. ); Lopez, R.E. ); Dyson, R.L.; Frank, L.A. )

    1992-12-01

    The degree of pitch angle scattering and chaotization of various particle populations in the geomagnetic tail during the substorm growth phase is studied by utilizing the Tsyganenko 1989 magnetic field model. A temporally evolving magnetic field model for the growth phase is constructed by enhancing the near-Earth currents and thinning the current sheet from the values given by the static Tsyganenko model. Changing the field geometry toward an increasingly taillike configuration leads to pitch angle scattering of particles whose Larmor radii become comparable to the field line radius of curvature. Several different cases representing substorms with varying levels of magnetic disturbance have been studied. In each case, the field development during the growth phase leads to considerable scattering of the thermal electrons relatively close to the Earth. The current sheet regions where the electron motion is chaotic are magnetically mapped to the ionosphere and compared with low-altitude measurements of electron precipitation. The chaotization of the thermal electron population occurs within a few minutes of the substorm onset, and the ionospheric mappings of the chaotic regions in the equatorial plane compare well with the region of brightening auroras. Even though the temporal evolution of the complex plasma system cannot be self-consistently described by the temporal evolution of the empirical field model, these models can provide the most accurate estimates of the field parameters for tail stability calculations.

  20. Space Technology 5 measurements of auroral field-aligned current sheet motion

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Le, G.; Slavin, J. A.; Boardsen, S. A.; Strangeway, R. J.

    2009-01-01

    During the 90-day Space Technology 5 (ST-5) mission, a total of 2535 auroral field-aligned current (FAC) signatures were identified. Of these 1030 were suitable to be modeled as semi-infinite current sheets aligned with L-shells and moving with constant speed in the north or south directions (hereafter called FAC speed). FAC speeds were found to range from -1 to 1 km/s with larger mean magnitude during intervals of higher geomagnetic activity. At ST-5 altitudes, ~300 to 4500 km, the median relative errors in FAC thickness and current density, when stationary FAC is assumed, are 4%. When the ST-5 FAC speed determinations are extrapolated along the IGRF-10 magnetic field lines, these errors increase to 23% and 24% at 4 RE, and 65% and 124% at 8 RE, respectively.

  1. Weighted current sheets supported in normal and inverse configurations - A model for prominence observations

    NASA Technical Reports Server (NTRS)

    Demoulin, P.; Forbes, T. G.

    1992-01-01

    A technique which incorporates both photospheric and prominence magnetic field observations is used to analyze the magnetic support of solar prominences in two dimensions. The prominence is modeled by a mass-loaded current sheet which is supported against gravity by magnetic fields from a bipolar source in the photosphere and a massless line current in the corona. It is found that prominence support can be achieved in three different kinds of configurations: an arcade topology with a normal polarity; a helical topology with a normal polarity; and a helical topology with an inverse polarity. In all cases the important parameter is the variation of the horizontal component of the prominence field with height. Adding a line current external to the prominence eliminates the nonsupport problem which plagues virtually all previous prominence models with inverse polarity.

  2. Theory and simulation of lower-hybrid drift instability for current sheet with guide field

    SciTech Connect

    Yoon, P. H.; Lin, Y.; Wang, X. Y.; Lui, A. T. Y.

    2008-11-15

    The stability of a thin current sheet with a finite guide field is investigated in the weak guide-field limit by means of linear theory and simulation. The emphasis is placed on the lower-hybrid drift instability (LHDI) propagating along the current flow direction. Linear theory is compared against the two-dimensional linear simulation based on the gyrokinetic electron/fully kinetic ion code. LHDI is a flute mode characterized by k{center_dot}B{sub total}=0; hence, it is stabilized by a finite guide field if one is confined to k vector strictly parallel to the cross-field current. Comparison of the theory and simulation shows qualitatively good agreement.

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

    NASA Technical Reports Server (NTRS)

    Singh, Nagendra; Deverapalli, Chakri; Khazanov, George

    2006-01-01

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

  4. Field-Aligned Current Sheet Motion and Its Correlation with Solar Wind Conditions and Geomagnetic Activities

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Le, G.; Boardsen, S. A.; Slavin, J. A.; Strangeway, R. J.

    2008-05-01

    Field-aligned currents (FACs) are the currents flowing into and out of the ionosphere which connect to the magnetosphere. They provide an essential linkage between the solar wind - magnetosphere system and the ionosphere, and the understanding of these currents is important for global magnetosphere dynamics and space weather prediction. The three spacecraft ST-5 constellation provides an unprecedented opportunity to study in situ FAC dynamics in time scales (10 sec to 10 min) that can not be achieved previously with single spacecraft studies or large-spaced conjugate spacecraft studies. In this study, we use the magnetic field observations during the whole ST-5 mission and their corresponding solar wind conditions to study the dependence of FAC current sheet motion and intensity on solar wind conditions. FAC peak current densities show very good correlations with some solar wind parameters, including IMF Bz, dynamic pressure, Ey, and some IMF angles, but not with other parameters. Instant FAC speeds show generally much weaker dependence on solar wind conditions comparing to FAC peak current densities. This obvious uncorrelation between FAC peak current densities and speeds implies that FAC peak current densities are more consistently controlled by solar wind conditions and geomagnetic activities, while FAC speeds are more oscillatory, sometimes with higher speeds during quieter times and lower speeds during more turbulent times.

  5. Plasmoid and Kelvin-Helmholtz instabilities in Sweet-Parker current sheets

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

    A two-dimensional (2D) linear theory of the instability of Sweet-Parker (SP) current sheets is developed in the framework of reduced magnetohydrodynamics. A local analysis is performed taking into account the dependence of a generic equilibrium profile on the outflow coordinate. The plasmoid instability [Loureiro , Phys. Plasmas 14, 100703 (2007)] is recovered, i.e., current sheets are unstable to the formation of a large-wave-number chain of plasmoids (kmaxLCS˜S3/8, where kmax is the wave number of fastest growing mode, S=LCSVA/η is the Lundquist number, LCS is the length of the sheet, VA is the Alfvén speed, and η is the plasma resistivity), which grows super Alfvénically fast (γmaxτA˜S1/4, where γmax is the maximum growth rate, and τA=LCS/VA). For typical background profiles, the growth rate and the wave number are found to increase in the outflow direction. This is due to the presence of another mode, the Kelvin-Helmholtz (KH) instability, which is triggered at the periphery of the layer, where the outflow velocity exceeds the Alfvén speed associated with the upstream magnetic field. The KH instability grows even faster than the plasmoid instability γmaxτA˜kmaxLCS˜S1/2. The effect of viscosity (ν) on the plasmoid instability is also addressed. In the limit of large magnetic Prandtl numbers Pm=ν/η, it is found that γmax˜S1/4Pm-5/8 and kmaxLCS˜S3/8Pm-3/16, leading to the prediction that the critical Lundquist number for plasmoid instability in the Pm≫1 regime is Scrit˜104Pm1/2. These results are verified via direct numerical simulation of the linearized equations, using an analytical 2D SP equilibrium solution.

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

    NASA Astrophysics Data System (ADS)

    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.

  7. Kinetic theory of electrostatic 'bounce' modes in two-dimensional current sheets

    SciTech Connect

    Tur, A.; Louarn, P.

    2010-10-15

    The role of trapped particles in the destabilization of two-dimensional (2D) current sheets is investigated for applications to theories of magnetospheric substorms. Considering a 2D 'Lembege and Pellat' equilibrium, the linearized gyrokinetic Vlasov-Maxwell equations are solved for electrostatic perturbations with periods close to the typical electron bounce period ({tau}{sub be}). The particle bounce motion is approximated to its first Fourier component ({omega}{sub b}=2{pi}/{tau}{sub b}) which allows the explicit time integration of Vlasov equation and the calculation of the nonlocal particle response. The dispersion equation of the electrostatic bounce modes is derived from the quasineutrality condition. It is shown that the bounce modes exist in a narrow domain of electron-to-ion temperature ratio (T{sub e}/T{sub i} varying from 0.2 to 1.4), with large growth rates ({delta}{approx}0.2{omega}), leading to current sheet destabilization over time scales of 1-2 min.

  8. A MODEL FOR THE ELECTRICALLY CHARGED CURRENT SHEET OF A PULSAR

    SciTech Connect

    DeVore, C. R.; Antiochos, S. K.; Black, C. E.; Harding, A. K.; Kalapotharakos, C.; Kazanas, D.; Timokhin, A. N.

    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.

  9. Magnetic relaxation, current sheets, and structure formation in an extremely Tenuous fluid medium

    SciTech Connect

    Bajer, K.; Moffatt, H. K.

    2013-12-20

    The process of relaxation of a unidirectional magnetic field in a highly conducting tenuous fluid medium is considered. Null points of the field play a critical role in this process. During an initial stage of relaxation, variations in magnetic pressure are eliminated, and current sheets build up in the immediate neighborhood of null points. This initial phase is followed by a long diffusive phase of slow algebraic decay of the field, during which fluid is continuously sucked into the current sheets, leading to exponential growth of fluid density and concentration of mass around the null points, which show a tendency to cluster. Ultimately, this second phase of algebraic decay gives way to a final period of exponential decay of the field. The peaks of density at the null points survive as a fossil relic of the decay process. Numerical solution of the governing equations provides convincing confirmation of this three-stage scenario. Generalizations to two- and three-dimensional fields are briefly considered.

  10. Chaotic scattering of pitch angles in the current sheet of the magnetotail

    NASA Technical Reports Server (NTRS)

    Burkhart, G. R.; Chen, J.

    1992-01-01

    The modified Harris field model is used to investigate the process of pitch angle scattering by a current sheet. The relationship between the incoming asymptotic pitch angle alpha(in) and the outgoing asymptotic pitch angle alpha(out) is studied from first principles by numerically integrating the equation of motion. Evidence that charged particles undergo chaotic scattering by the current sheet is found. For fixed alpha(in), it is shown that alpha(out) exhibits sensitive dependence on the energy parameter in certain energy ranges. For a fixed energy parameter value in the same energy ranges, alpha(out) sensitively depends on alpha(in). For other energy values, alpha(out) does not show sensitive dependence on alpha(in) for most phase angles. A distribution of alpha(in) is mapped from the asymptotic region to the midplane, and it is found that the resulting particle distribution should have beam structures with well-collimated pitch angles near each resonance energy value. Implications for the particle distribution functions in the earth's magnetotail are discussed.

  11. Lower-hybrid drift and Buneman instabilities in current sheets with guide field

    SciTech Connect

    Yoon, P. H.; Lui, A. T. Y.

    2008-11-15

    Lower-hybrid drift and Buneman instabilities operate in current sheets with or without the guide field. The lower-hybrid drift instability is a universal instability in that it operates for all parameters. In contrast, the excitation of Buneman instability requires sufficiently thin current sheet. That is, the relative electron-ion drift speed must exceed the threshold in order for Buneman instability to operate. Traditionally, the two instabilities were treated separately with different mathematical formalisms. In a recent paper, an improved electrostatic dispersion relation was derived that is valid for both unstable modes [P. H. Yoon and A. T. Y. Lui, Phys. Plasmas 15, 072101 (2008)]. However, the actual numerical analysis was restricted to a one-dimensional situation. The present paper generalizes the previous analysis and investigates the two-dimensional nature of both instabilities. It is found that the lower-hybrid drift instability is a flute mode satisfying k{center_dot}B=0 and k{center_dot}{nabla}n=0, where k represents the wave number for the most unstable mode, B stands for the total local magnetic field, and {nabla}n is the density gradient. This finding is not totally unexpected. However, a somewhat surprising finding is that the Buneman instability is a field-aligned mode characterized by kxB=0 and k{center_dot}{nabla}n=0, rather than being a beam-aligned instability.

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

    SciTech Connect

    Scott, Roger B.; Longcope, Dana W.; McKenzie, David E.

    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.

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

    NASA Technical Reports Server (NTRS)

    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.

  14. Electron acceleration in the turbulent reconnecting current sheets in solar flares

    NASA Astrophysics Data System (ADS)

    Wu, G. P.; Huang, G. L.

    2009-07-01

    Context: We investigate the nonlinear evolution of the electron distribution in the presence of the strong inductive electric field in the reconnecting current sheets (RCS) of solar flares. Aims: We aim to study the characteristics of nonthermal electron-beam plasma instability and its influence on electron acceleration in RCS. Methods: Including the external inductive field, the one-dimensional Vlasov simulation is performed with a realistic mass ratio for the first time. Results: Our principal findings are as follows: 1) the Buneman instability can be quickly excited on the timescale of 10-7 s for the typical parameters of solar flares. After saturation, the beam-plasma instabilities are excited due to the non-Maxwellian electron distribution; 2) the final velocity of the electrons trapped by these waves is of the same order as the phase speed of the waves, while the untrapped electrons continue to be accelerated; 3) the inferred anomalous resistance of the current sheet and the energy conversion rate are basically of the same order as those previously estimated, e.g., “the analysis of Martens”. Conclusions: The Buneman instability is excited on the timescale of 10-7 s and the wave-particle resonant interaction limits the low-energy electrons to be further accelerated in RCS.

  15. Electron Acceleration in a Dynamically Evolved Current Sheet Under Solar Coronal Conditions

    NASA Astrophysics Data System (ADS)

    Zhang, Shaohua; Du, A. M.; Feng, Xueshang; Cao, Xin; Lu, Quanming; Yang, Liping; Chen, Gengxiong; Zhang, Ying

    2014-05-01

    Electron acceleration in a drastically evolved current sheet under solar coronal conditions is investigated via the combined 2.5-dimensional (2.5D) resistive magnetohydrodynamics (MHD) and test-particle approaches. Having a high magnetic Reynolds number (105), the long, thin current sheet is torn into a chain of magnetic islands, which grow in size and coalesce with each other. The acceleration of electrons is explored in three typical evolution phases: when several large magnetic islands are formed (phase 1), two of these islands are approaching each other (phase 2), and almost merging into a "monster" magnetic island (phase 3). The results show that for all three phases electrons with an initial Maxwell distribution evolve into a heavy-tailed distribution and more than 20 % of the electrons can be accelerated higher than 200 keV within 0.1 second and some of them can even be energized up to MeV ranges. The lower-energy electrons are located away from the magnetic separatrices and the higher-energy electrons are inside the magnetic islands. The most energetic electrons have a tendency to be around the outer regions of the magnetic islands or to appear in the small secondary magnetic islands. It is the trapping effect of the magnetic islands and the distributions of E p that determine the acceleration and spatial distributions of the energetic electrons.

  16. The Effect of Electric Current and Strain Rate on Serrated Flow of Sheet Aluminum Alloy 5754

    NASA Astrophysics Data System (ADS)

    Zhao, Kunmin; Fan, Rong; Wang, Limin

    2016-03-01

    Electrically assisted tensile tests are carried out on sheet aluminum alloy AA5754 at electric current densities ranging from 0 to 30.4 A/mm2 and strain rates ranging from 10-3 to 10-1 s-1. The strain rate sensitivity and the serrated flow behavior are investigated in accordance with dynamic strain aging mechanism. The strain rate sensitivity changes from negative to positive and keeps increasing with current density. The tendency toward serrated flow is characterized by the onset of Portevin-Le Chatelier (PLC) instabilities, which are influenced by strain rate, temperature, and electric current. The evolutions of three types of serrated flow are observed and analyzed with respect to strain rate and current density. The magnitude of serration varies with strain rate and current density. The serrated flow can be suppressed by a high strain rate, a high temperature, or a strong electric current. The threshold values of these parameters are determined and discussed. Conventional oven-heated tensile tests are conducted to distinguish the electroplasticity. The flow stress reduces more in electrically assisted tension compared to oven-heated tension at the same temperature level. The electric current helps suppress the serrated flow at the similar temperature level of oven-heating.

  17. A Mechanical Model for Magnetic Bubble Domain Current-Sheet Devices

    NASA Astrophysics Data System (ADS)

    Hayashi, Nobuo

    1982-05-01

    A simple mechanical device has been constructed for the rapid simulation of magnetic bubble domain current-sheet devices. The device consists of a small ferrite magnet with a magnetic moment of 4.8 G\\cdotcm3, and layers of perforated aluminum films whose sizes match the diameter of the magnet. The magnet was placed in a light plastic boat, which was floated on the surface of a viscous fluid. A sequenced electric current of 0.1 A/cm was able to move the magnet at a speed of ˜ 0.1 cm/s. The outline of the device and experimental results showing the validity of the device are given.

  18. The resolved layer of a collisionless, high beta, supercritical, quasi-perpendicular shock wave. I - Rankine-Hugoniot geometry, currents, and stationarity

    NASA Technical Reports Server (NTRS)

    Scudder, J. D.; Aggson, T. L.; Mangeney, A.; Lacombe, C.; Harvey, C. C.

    1986-01-01

    Data collected by the ISEE dual-spacecraft mission (on November 7, 1977) on a slowly moving, supercritical, high-beta, quasi-perpendicular bow shock are presented, and the local geometry, spatial scales, and stationarity of this shock wave are assessed in a self-consistent Rankine-Hugoniot-constrained frame of reference. Included are spatial profiles of the ac and dc magnetic and electric fields, electron and proton fluid velocities, current densities, electron and proton number densities, temperatures, pressures, and partial densities of the reflected protons. The observed layer profile is shown to be nearly phase standing and one-dimensional in a Rankine-Hugoniot frame, empirically determined by the magnetofluid parameters outside the layer proper.

  19. Gravitational Instability in Collisionless Cosmological Pancakes

    NASA Astrophysics Data System (ADS)

    Valinia, Azita; Shapiro, Paul R.; Martel, Hugo; Vishniac, Ethan T.

    1997-04-01

    The gravitational instability of cosmological pancakes composed of collisionless dark matter in an Einstein-de Sitter universe is investigated numerically to demonstrate that pancakes are unstable with respect to fragmentation and the formation of filaments. A ``pancake'' is defined here as the nonlinear outcome of the growth of a one-dimensional, sinusoidal, plane-wave, adiabatic density perturbation. We have used high-resolution, two-dimensional, N-body simulations by the particle mesh (PM) method to study the response of pancakes to perturbation by either symmetric (density) or antisymmetric (bending or rippling) modes, with corresponding wavevectors ks and ka transverse to the wavevector kp of the unperturbed pancake plane wave. We consider dark matter that is initially ``cold'' (i.e., with no random thermal velocity in the initial conditions). We also investigate the effect of a finite, random, isotropic, initial velocity dispersion (i.e., initial thermal velocity) on the fate of pancake collapse and instability. Our results include the following: (1) For ``cold'' initial conditions, pancakes are gravitationally unstable with respect to all perturbations of wavenumber k >~ 1 (where k = λp/λ, and λp and λ are the wavelengths of the unperturbed pancake and of the perturbation, respectively). This is contrary to the expectations of an approximate, thin-sheet energy argument applied to the results of one-dimensional pancake simulations. The latter predicts that unstable wavenumbers are restricted to the range kmin < k < kmax, where perturbations with k < kmin ~ 1 are stabilized by Hubble expansion, while those with k > kmax > 1 are stabilized by the one-dimensional velocity dispersion of the collisionless particles along the direction of pancake collapse, within the region of shell crossing. (2) Shortly after the pancake first reaches a nonlinear state of collapse, the dimensionless growth rate of the perturbation of pancake surface density by unstable

  20. Is collisionless heating in capacitively coupled plasmas really collisionless?

    NASA Astrophysics Data System (ADS)

    Lafleur, T.; Chabert, P.

    2015-08-01

    By performing a combination of test-particle and particle-in-cell simulations, we investigate electron heating in single frequency capacitively coupled plasmas (CCPs). In agreement with previous theoretical considerations highlighted in Kaganovich et al (1996 Appl. Phys. Lett. 69 3818), we show that the level of true collisionless/stochastic heating in typical CCPs is significantly smaller than that due to collisional interactions; even at very low pressures and wide gap lengths. Fundamentally electron heating is a collisional phenomenon whereby particle collisions provide the vital phase randomization and stochastization mechanism needed to generate both a local (or ohmic) heating component, and a non-local (or hybrid) heating component.

  1. HYBRID AND HALL-MHD SIMULATIONS OF COLLISIONLESS RECONNECTION: EFFECTS OF PLASMA PRESSURE TENSOR

    SciTech Connect

    L. YIN; D. WINSKE; ET AL

    2001-05-01

    In this study we performed two-dimensional hybrid (particle ions, massless fluid electrons) and Hall-MHD simulations of collisionless reconnection in a thin current sheet. Both calculations include the full electron pressure tensor (instead of a localized resistivity) in the generalized Ohm's law to initiate reconnection, and in both an initial perturbation to the Harris equilibrium is applied. First, electron dynamics from the two calculations are compared, and we find overall agreement between the two calculations in both the reconnection rate and the global configuration. To address the issue of how kinetic treatment for the ions affects the reconnection dynamics, we compared the fluid-ion dynamics from the Hall-MHD calculation to the particle-ion dynamics obtained from the hybrid simulation. The comparison demonstrates that off-diagonal elements of the ion pressure tensor are important in correctly modeling the ion out-of-plane momentum transport from the X point. It is that these effects can be modeled efficiently using a particle Hall-MHD simulation method in which particle ions used in a predictor/corrector to implement the ion gyro-radius corrections. We also investigate the micro- macro-scale coupling in the magnetotail dynamics by using a new integrated approach in which particle Hall-MHD calculations are embedded inside a MHD simulation. Initial results of the simulation concerning current sheet thinning and reconnection dynamics are discussed.

  2. Particle description of the electron diffusion region in collisionless magnetic reconnection

    SciTech Connect

    Fujimoto, Keizo; Sydora, Richard D.

    2009-11-15

    The present study clarifies the dissipation mechanism of collisionless magnetic reconnection in two-dimensional system based on particle dynamics. The electrons are accelerated without thermalization in the electron diffusion region, carry out the meandering oscillation, and are ejected away from the X-line. This electron behavior not only generates the electron inertia resistivity based on the particle description, but also it can be the origin of the electron viscosity resulting in the off-diagonal pressure tensor term in the generalized Ohm's law near the X-line. We derive an analytical profile for the electron pressure tensor term and confirm that the profile is consistent with the particle-in-cell simulation. The present results demonstrate that the magnetic dissipation due to the electron viscosity in the fluid picture is equivalent to that due to the inertia resistivity in the particle description. It is also suggested that the width of the electron current sheet is on the order of the electron inertia length in the case without electron scattering and thermalization, while it is expected that the width is broadened if the electron scattering occurs in the current sheet.

  3. Enhanced critical currents by silver sheeting of YBa2Cu3O7-δ thin films

    NASA Astrophysics Data System (ADS)

    Kienzle, M.; Albrecht, J.; Warthmann, R.; Kronmüller, H.; Leonhardt, S.; Jooss, Ch.

    2002-08-01

    Magneto-optical investigation of flux penetration into high-temperature superconducting thin films allows the determination of the local critical current density jc by an inversion scheme of Biot-Savart's law. This method is used to examine the influence of silver sheeting on jc in thin films of YBa2Cu3O7-δ (YBCO) quantitatively. It can be found that a feasible silver covering layer on top of a YBCO thin film can enhance the critical current density by up to 50%. Spatially resolved measurements of the magnetic-flux density distribution in partly silver covered YBCO films show the influence of the cover layer on the current pattern in the superconductor. The measured enhancement of the critical current density, that is induced by the silver layer, has its origin in a spatially varying proximity effect between superconductor and silver layer which leads to a strong variation of the flux-line energies on a small length scale. This variation is directly related to an additional pinning force density on the flux lines. A detailed model is developed that can explain the measured enhancement of the critical current density by considering this additional pinning.

  4. Experiments on the tearing of a current sheet into a bundle of interacting flux ropes

    NASA Astrophysics Data System (ADS)

    Gekelman, Walter; Dehaas, Tim; van Compernolle, Bart; Latshaw, Alex; Daughton, William

    2014-10-01

    A narrow (δ/L ~ . 05 , δ ~= 3 - 10c/ωpe , δ = 1 cm) current sheet is established in a magnetized (B0z = 200 G, He, Len = 17 m, Dia = 60 cm) plasma column. The current sheet is observed to tear into multiple magnetic islands in several Alfvén transit times. Volumetric magnetic field data is acquired at 16,500 spatial locations and 16,000 time steps (δt = .34 μs). The flux ropes appear as multiple ``O'' and ``X'' points when viewed in a plane perpendicular to the local current but, in fact are three-dimensional. The kink unstable ropes writhe, and twist about each other as the ensemble of ropes spin about the background axial magnetic field. Fast framing camera images (τexp = 1 μs , 34,000 fps) clearly show the motion but differ from shot to shot. The movies are analyzed using correlation techniques. The rope dynamics becomes chaotic therefore correlation techniques using a fixed magnetic probe as well a He II line (λ = 303 A) are used to generate 3D images of the ropes. An emissive probe is used to measure the plasma potential and the total electric field, E-> = - ∇ ϕ -∂/A-> ∂ t , and plasma resistivity are evaluated. The perpendicular electric fields are two orders of magnitude larger than the parallel ones. The entropy and complexity of the flux ropes are evaluated. Work supported by a UC-LANL Lab fund and the Basic Plasma Science Facility which is funded by DOE and NSF.

  5. Particle scattering and current sheet stability in the geomagnetic tail during the substorm growth phase

    NASA Technical Reports Server (NTRS)

    Pulkkinen, T. I.; Baker, D. N.; Pellinen, R. J.; Buechner, J.; Koskinen, H. E. J.; Lopez, R. E.; Dyson, R. L.; Frank, L. A.

    1992-01-01

    The particle scattering and current sheet stability features in the geomagnetic tail during the phase of substorm growth were investigated using Tsyganenko's (1989) magnetic field model. In a study of four substorm events which were observed both in the high-altitude nightside tail and in the auroral ionosphere, the model magnetic field was adjusted to each case so as to represent the global field development during the growth phase of the substorms. The model results suggest that the auroral brightenings are connected with processes taking place in the near-earth region inside about 15 earth radii. The results also suggest that there is a connection between the chaotization of the electrons and the auroral brightenings at substorm onset.

  6. Observation of the Evolution of a Current Sheet in a Solar Flare

    NASA Astrophysics Data System (ADS)

    Zhu, Chunming; Liu, Rui; Alexander, David; McAteer, R. T. James

    2016-04-01

    We report multi-wavelength and multi-viewpoint observations of a solar eruptive event that involves loop–loop interactions. During a C2.0 flare, motions associated with inflowing and outflowing plasma provide evidence for ongoing magnetic reconnection. The flare loop top and a rising “concave-up” feature are connected by a current-sheet-like structure (CSLS). The physical properties (thickness, length, temperature, and density) of the CSLS are evaluated. In regions adjacent to the CSLS, the EUV emission (characteristic temperature at 1.6 MK) begins to increase more than 10 minutes prior to the onset of the flare, and steeply decreases during the decay phase. The reduction of the emission resembles that expected from coronal dimming. The dynamics of this event imply a magnetic reconnection rate in the range 0.01–0.05.

  7. Observation of the Evolution of a Current Sheet in a Solar Flare

    NASA Astrophysics Data System (ADS)

    Zhu, Chunming; Liu, Rui; Alexander, David; McAteer, James

    2016-05-01

    We report multi-wavelength and multi-viewpoint observations of a solar eruptive event which involves loop-loop interactions. During a C2.0 flare, motions associated with inflowing and outflowing plasma provide evidence for ongoing magnetic reconnection. The flare loop top and a rising "concave-up" feature are connected by a current-sheet-like structure (CSLS). The physical properties (thickness, length, temperature, and density) of the CSLS are evaluated. In regions adjacent to the CSLS, the EUV emission (characteristic temperature at 1.6 MK) begins to increase more than ten minutes prior to the onset of the flare, and steeply decreases during the decay phase. The reduction of the emission resembles that expected from coronal dimming. The dynamics of this event imply a magnetic reconnection rate in the range 0.01--0.05.

  8. Electron Acceleration in a Dynamically Evolved Current Sheet of Solar Coronal Conditions

    NASA Astrophysics Data System (ADS)

    Shaohua, Z.; Du, A.; Feng, X.

    2012-12-01

    Electron acceleration in a drastically evolved current sheet of solar coronal conditions is investigated via the combined resistive Magnetohydrodynamics (MHD) and test particle approaches. With high magnetic Reynolds number, the long-thin current sheet is tearing into a chain of magnetic islands, which grow in size and coalesce together. The acceleration of electrons are explored in three typical evolvement phases: when several large magnetic islands are formed (phase1), two of them are approaching each other (phase2) and almost merging into a "monster" magnetic island (phase3). The results show that for all the three phases electrons with an initially Maxwellian distribution evolve into a heavy-tailed distribution and more than 20% of the electrons can be accelerated higher than 200 keV within 0.1 second and some of them can even be energized up to MeV ranges. Most of the energetic electrons move around the magnetic islands in clockwise direction (anti-parallel to the magnetic field lines), drifting in the -Z direction. The energetic electrons with 10 keV < Ek < 200 keV are located outside the magnetic separatrices, where parallel electric field (Ep) is small. The electrons with 200 keV < Ek < 5000 keV are distributed inside the magnetic islands where Ep is moderate large but have complex structures. The electrons with Ek > 5000 keV are located around the outer regions of the magnetic islands or at the core regions of the magnetic islands. Some of the most energetic electrons even appear in the small secondary magnetic islands that are embedded in the diusion regions in between the magnetic islands. It is the trapping eect of the magnetic islands and the distributions of Ep that determine the acceleration processes and space distribution of the energetic electrons.

  9. Generation of compound structure of shock/discontinuity in the outflow region of magnetic reconnection in an asymmetric current sheet

    NASA Astrophysics Data System (ADS)

    Hsupeng, Boryau; Lee, Lou-Chuang; Chao, Jih-Kwin

    2015-04-01

    The double discontinuities, which are composed of a rotational discontinuity layer attached to an adjacent leading slow shock layer, have been observed in both the interplanetary space and geomagnetic tail. Weng et al. [2012] simulated the generation and evolution of MHD discontinuities associated with magnetic reconnection in a symmetric current sheet. Four types of compound structures were found in their research : (a) RD-SS compound structure: SS is attached to the downstream of RD, (b) SS-RD: SS is following by an adjacent RD, (c) SS-RD-SS: RD is trapped inside SS, and (d) switch-off slow shock (SSS) with a rotational wave train. However, the current sheets observed in the solar wind, magnetopause, and nightside plasma sheet can be asymmetric, in which the plasma densities and/or magnetic field magnitudes on the two sides of the current sheet are not equal. In our research, we used a hybrid code to simulate the 1-D Riemann problem for the generation and evolution of MHD discontinuities in the outflow region of magnetic reconnection in an asymmetric current sheet.

  10. Simplex-in-cell technique for collisionless plasma simulations

    NASA Astrophysics Data System (ADS)

    Kates-Harbeck, Julian; Totorica, Samuel; Zrake, Jonathan; Abel, Tom

    2016-01-01

    We extend the simplex-in-cell (SIC) technique recently introduced in the context of collisionless dark matter fluids [1,2] to the case of collisionless plasmas. The six-dimensional phase space distribution function f (x , v) is represented by an ensemble of three-dimensional manifolds, which we refer to as sheets. The electric potential field is obtained by solving the Poisson equation on a uniform mesh, where the charge density is evaluated by a spatial projection of the phase space sheets. The SIC representation of phase space density facilitates robust, high accuracy numerical evolution of the Vlasov-Poisson system using significantly fewer tracer particles than comparable particle-in-cell (PIC) approaches by reducing the numerical shot-noise associated with the latter. We introduce the SIC formulation and describe its implementation in a new code, which we validate using standard test problems including plasma oscillations, Landau damping, and two stream instabilities in one dimension. Merits of the new scheme are shown to include higher accuracy and faster convergence rates in the number of particles. We finally motivate and outline the efficient application of SIC to higher dimensional problems.

  11. Transient, small-scale field-aligned currents in the plasma sheet boundary layer during storm time substorms

    NASA Astrophysics Data System (ADS)

    Nakamura, R.; Sergeev, V. A.; Baumjohann, W.; Plaschke, F.; Magnes, W.; Fischer, D.; Varsani, A.; Schmid, D.; Nakamura, T. K. M.; Russell, C. T.; Strangeway, R. J.; Leinweber, H. K.; Le, G.; Bromund, K. R.; Pollock, C. J.; Giles, B. L.; Dorelli, J. C.; Gershman, D. J.; Paterson, W.; Avanov, L. A.; Fuselier, S. A.; Genestreti, K.; Burch, J. L.; Torbert, R. B.; Chutter, M.; Argall, M. R.; Anderson, B. J.; Lindqvist, P.-A.; Marklund, G. T.; Khotyaintsev, Y. V.; Mauk, B. H.; Cohen, I. J.; Baker, D. N.; Jaynes, A. N.; Ergun, R. E.; Singer, H. J.; Slavin, J. A.; Kepko, E. L.; Moore, T. E.; Lavraud, B.; Coffey, V.; Saito, Y.

    2016-05-01

    We report on field-aligned current observations by the four Magnetospheric Multiscale (MMS) spacecraft near the plasma sheet boundary layer (PSBL) during two major substorms on 23 June 2015. Small-scale field-aligned currents were found embedded in fluctuating PSBL flux tubes near the separatrix region. We resolve, for the first time, short-lived earthward (downward) intense field-aligned current sheets with thicknesses of a few tens of kilometers, which are well below the ion scale, on flux tubes moving equatorward/earthward during outward plasma sheet expansion. They coincide with upward field-aligned electron beams with energies of a few hundred eV. These electrons are most likely due to acceleration associated with a reconnection jet or high-energy ion beam-produced disturbances. The observations highlight coupling of multiscale processes in PSBL as a consequence of magnetotail reconnection.

  12. Weldability of thin sheet metals during small-scale resistance spot welding using an alternating-current power supply

    NASA Astrophysics Data System (ADS)

    Zhou, Y.; Gorman, P.; Tan, W.; Ely, K. J.

    2000-09-01

    The resistance weldability of 0.2-mm-thick sheet aluminum, brass, and copper in small-scale resistance spot welding (SSRSW) was studied. The effects of electrode materials and process parameters on joint strength and nugget size were investigated. The welding current ranges for SSRSW of the sheet metals were determined based on the minimum current that produced a required nugget diameter and maximum currents that did not result in electrode-sheet sticking or weld metal expulsion. A qualitative analysis indicated that resistance weldability of the metals is not only determined by their resistivity (or thermal conductivity) but is also affected by other physical properties (such as melting point, latent heat of fusion and specific heat).

  13. Formation of a very thin current sheet in the near-earth magnetotail and the explosive growth phase of substorms

    NASA Technical Reports Server (NTRS)

    Lee, L. C.; Zhang, L.; Choe, G. S.; Cai, H. J.

    1995-01-01

    A magnetofricional method is used to construct two-dimensional MHD equilibria of the Earth's magnetosphere for a given distribution of entropy functions(S = pV(exp gamma), where p is the plasma pressure and V is the tube volume per unit magnetic flux. It is found that a very thin current sheet with B (sub zeta) is less than 0.5 nu T and thickness less than 1000 km can be formed in the near-earth magnetotail (x is approximately -8 to -20R(sub e) during the growth phase of substorm. The tail current sheets are found to become thinner as the entropy or the entropy gradient increases. It is suggested that the new entropy anti-diffusion instability associated with plasma transport across field lines leads to magnetic field dipolarization and accelerates the formation of thin current sheet, which may explain the observed explosive growth phase of substorms.

  14. Cluster electric current density measurements within a magnetic flux rope in the plasma sheet

    NASA Technical Reports Server (NTRS)

    Slavin, J. A.; Lepping, R. P.; Gjerloev, J.; Goldstein, M. L.; Fairfield, D. H.; Acuna, M. H.; Balogh, A.; Dunlop, M.; Kivelson, M. G.; Khurana, K.

    2003-01-01

    On August 22, 2001 all 4 Cluster spacecraft nearly simultaneously penetrated a magnetic flux rope in the tail. The flux rope encounter took place in the central plasma sheet, Beta(sub i) approx. 1-2, near the leading edge of a bursty bulk flow. The "time-of-flight" of the flux rope across the 4 spacecraft yielded V(sub x) approx. 700 km/s and a diameter of approx.1 R(sub e). The speed at which the flux rope moved over the spacecraft is in close agreement with the Cluster plasma measurements. The magnetic field profiles measured at each spacecraft were first modeled separately using the Lepping-Burlaga force-free flux rope model. The results indicated that the center of the flux rope passed northward (above) s/c 3, but southward (below) of s/c 1, 2 and 4. The peak electric currents along the central axis of the flux rope predicted by these single-s/c models were approx.15-19 nA/sq m. The 4-spacecraft Cluster magnetic field measurements provide a second means to determine the electric current density without any assumption regarding flux rope structure. The current profile determined using the curlometer technique was qualitatively similar to those determined by modeling the individual spacecraft magnetic field observations and yielded a peak current density of 17 nA/m2 near the central axis of the rope. However, the curlometer results also showed that the flux rope was not force-free with the component of the current density perpendicular to the magnetic field exceeding the parallel component over the forward half of the rope, perhaps due to the pressure gradients generated by the collision of the BBF with the inner magnetosphere. Hence, while the single-spacecraft models are very successful in fitting flux rope magnetic field and current variations, they do not provide a stringent test of the force-free condition.

  15. PARTICLE DYNAMICS IN THE RECONNECTING HELIOSPHERIC CURRENT SHEET: SOLAR WIND DATA VERSUS THREE-DIMENSIONAL PARTICLE-IN-CELL SIMULATIONS

    SciTech Connect

    Zharkova, Valentina V.; Khabarova, Olga V. E-mail: habarova@izmiran.ru

    2012-06-10

    In this paper, we apply an assumption of the reconnecting heliospheric current sheet (HCS) for explanation of some contradictory results in the experimental detection of the sector boundaries (SBs) from the interplanetary magnetic field and electron pitch-angle measurements. Trajectories, densities, velocity, and pitch-angle distributions of particles accelerated by a super-Dreicer electric field are investigated with 2.5D full kinetic particle-in-cell approach in the HCS assumed to undergo a slow magnetic reconnection process with magnetic field configurations deduced from the solar wind observations. This approach reveals that during motion in a current sheet both kinds of particles, electrons and protons, are to be separated, either fully or partially, with respect to its midplane that can lead to their ejection to the opposite semiplanes that was also observed during the HCS crossings. This separation is found to form Hall's currents and polarization electric field across the current sheet, which distribution over the current sheets allows us to reproduce the magnitudes and temporal profiles of proton and ion velocities measured across the SB (current sheet midplane). This separation process, in turn, divides both kinds of particles on 'transit' and 'bounced' ones depending on a side of the current sheet where they enter it and where they are supposed to be ejected. The transit and bounced protons reproduce rather closely the measured distributions of proton/ion densities about the current sheet midplane with a larger maximum occurring at the heliospheric SB to be formed by the bounced protons and the other two smaller maximums on both sides from the central one to be formed by 'transit' protons. The observed electron distributions of density and energy before and after sector boundary crossings are found to fit the simulated ones for electrons accelerated in a current sheet revealing a sharp increase of density from one side from the HCS boundary and a

  16. The scaling of collisionless magnetic reconnection in an electron-positron plasma with non-scalar pressure

    NASA Astrophysics Data System (ADS)

    Hosseinpour, M.; Mohammadi, M. A.; Biabani, S.; Biabani

    2013-10-01

    Collisionless magnetic reconnection via tearing instability in non-relativistic electron-positron (pair) plasma with an anisotropic pressure is investigated. The equilibrium magnetic field is considered to be sheared force-free, and a set of linearized collisionless Magnetohydrodynamics equations describes the evolution of reconnection dynamics. A linear analytical analysis, based on scaling, demonstrates that in such a pair plasma, breaking the frozen in flow constraint for field lines can be mainly provided by the non-gyrotropic pressure of electrons and positrons (rather than the particle bulk inertia) when the current sheet width is smaller than the particle Larmor radius (Δx < r L ). This condition is satisfied when β > d 2 (d = c/ω p is the particle skin-depth with the electron/positron frequency ω p and β = 8πP (0)/B 0 2 << 1). Meanwhile, on top of the Lorentz force and in the absence of the reconnection facilitating mechanism of the Hall effect, non-scalar pressure force can accelerate bulk plasma into the diffusion region at the scale lengths of the order of dx. Therefore, the respective regime of tearing instability proceeds much faster compared with the case of an isotropic pressure with a new dimensionless growth rate of (γτ A ) ~ d.

  17. Contrasting current and projected changes in surface mass balance components across the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Langen, Peter L.; Mottran, Ruth H.; Christensen, Jens H.; Olesen, Martin

    2016-04-01

    Comparison of the last decade's low surface mass balance (SMB) on the Greenland ice sheet to the changes that are projected for a warming future allows the current mass loss to be placed in a broader perspective. We compare changes in SMB components in HIRHAM5 regional climate model experiments forced by current ERA-Interim reanalysis data and by future projections with the EC-Earth general circulation model. The EC-Earth-forced experiments run over time slices 1991-2010, 2031-2050 and 2081-2100 for both RCP4.5 and RCP8.5. SMB decreases considerably in the in the last decades of the ERA-Interim experiment. The changes between the early and later part of this experiment are therefore compared to changes in the future scenarios relative to the baseline 1991-2010 EC-Earth-forced experiment. A major increase in melting and runoff, particularly along the western margin, is common to both the current and projected situations. Over the reanalysis period, accumulation has decreased in many places, particularly in the south. This is linked to the dominant circulation pattern in the last decade and enhances the effect of increased melt and runoff in producing the recent low SMB. In the projections, however, accumulation increases and thereby partially offsets the mass loss. This offset is so efficient that only in the warmest scenario in the latest time slice is the SMB decline significantly stronger than the current one. In the mid-term in the RCP4.5 experiment, central East Greenland sees an increase in accumulation which is not yet countered by increased melt and runoff. Consequently, this basin even has an increased SMB. The increase in accumulation (both rain and snow) is projected to lead to significant SMB increase in the interior parts of the ice sheet. Rain fractions tend to increase, as seen already in reanalysis period. As melting intensifies in the ablation zone and the percolation zone migrates upward into areas that see increased snowfall, the refreezing rate

  18. Collisionless Reconnection in an Electron-Positron Plasma

    SciTech Connect

    Bessho, N.; Bhattacharjee, A.

    2005-12-09

    Electromagnetic particle-in-cell simulations of fast collisionless reconnection in a two-dimensional electron-positron plasma (without an equilibrium guide field) are presented. A generalized Ohm's law in which the Hall current cancels out exactly is given. It is suggested that the key to fast reconnection in this plasma is the localization caused by the off-diagonal components of the pressure tensors, which produce an effect analogous to a spatially localized resistivity.

  19. Intercomponent momentum transport and electrical conductivity of collisionless plasma

    NASA Technical Reports Server (NTRS)

    Wilhelm, H. E.

    1973-01-01

    Based on the Lenard-Balescu equation, the interaction integral for the intercomponent momentum transfer in a two-component, collisionless plasma is evaluated in closed form. The distribution functions of the electrons and ions are represented in the form of nonisothermal, displaced Maxwellians corresponding to the 5-moment approximation. As an application, the transport of electrical current in an electric field is discussed for infrasonic up to sonic electron-ion drift velocities.

  20. Field-aligned current signatures in the near-tail region. I - ISEE observations in the plasma sheet boundary layer

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    Field-aligned currents in the near-tail region are examined using ISEE magnetometer data. Two substorms (the 1054 UT and the 1436 UT substorms on March 22, 1979) were examined, demonstrating the consistency of the current polarity and intensity with observations at lower altitudes, which suggests that field-aligned currents in the plasma sheet boundary layer are parts of the large-scale current system, the region-1 system. An examination of the steplike changes of the magnetic field direction, which correspond to the spacecraft crossing of a net field-aligned current, showed that the field-aligned currents in the plasma sheet boundary layer have the same polarity as the region-1 system.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    In a prior paper, we considered the linear stability of magnetized jets that carry no net electric current and do not have current sheets. In this paper, in addition to physically well-motivated magnetic field structures, we also include the effects of jet shear. The jets we study have finite thermal pressure in addition to having realistic magnetic field structures and velocity shear. We find that shear has a strongly stabilizing effect on various modes of jet instability. Increasing shear stabilizes the fundamental pinch modes at long wavelengths and short wavelengths. Increasing shear also stabilizes the first reflection pinch modes at short wavelengths. Increasing shear has only a very modest stabilizing effect on the fundamental kink modes at long wavelengths; however, increasing shear does have a strong stabilizing effect on the fundamental kink modes at short wavelengths. The first reflection kink modes are strongly stabilized by increasing shear at shorter wavelengths. Overall, we find that the combined effect of magnetic field and shear stabilizes jets more than shear alone. In addition to the results from a formal linear stability analysis, we present a novel way of visualizing and understanding jet stability. This gives us a deeper understanding of the enhanced stability of sheared, magnetized jets. We also emphasize the value of our numerical approach in understanding the linear stability of jets with realistic structure.

  2. Solar wind velocity distribution on the heliospheric current sheet during Carrington rotations 1787-1795

    NASA Astrophysics Data System (ADS)

    Bala, B.; Prabhakaran Nayar, S. R.

    1995-08-01

    The solar wind velocity distribution in the heliosphere is best represented using a v-map, where velocity contours are plotted in heliographic latitude-longitude coordinates. It has already been established that low-speed regions of the solar wind on the source surface correspond to the maximum bright regions of the K-corona and the neutral line of the coronal magnetic field. In this analysis, v-maps on the source surface for Carrington rotations (CRs) 1787-1795, during 1987, have been prepared using the interplanetary scintillation measurements at Research Institute of Atmospherics (RIA), Nagoya Univ., Japan. These v-maps were then used to study the time evolution of the low-speed (leq450 km s-1) belt of the solar wind and to deduce the distribution of solar wind velocity on the heliospheric current sheet. The low-speed belt of the solar wind on the source surface was found to change from one CR to the next, implying a time evolution. Instead of a slow and systematic evolution, the pattern of distribution of solar wind changed dramatically at one particular solar rotation (CR 1792) and the distributions for the succeeding rotations were similar to this pattern. The low-speed region, in most cases, was found to be close to the solar equator and almost parallel to it. However, during some solar rotations, they were found to be organised in certain longitudes, leaving regions with longitudinal width greater than 30° free of low-speed solar wind, i.e. these regions were occupied by solar wind with velocities greater than 450 km s-1. It is also noted from this study that the low-speed belt, in general, followed the neutral line of the coronal magnetic field, except in certain cases. The solar wind velocity on the heliospheric current sheet (HCS) varied in the range 300-585 km s-1 during the period of study, and the pattern of velocity distribution varied from rotation to rotation.

  3. The role of microturbulence on collisionless reconnection. [in magnetospheric plasmas

    NASA Technical Reports Server (NTRS)

    Papadopoulos, K.

    1980-01-01

    The linear, non-linear and anomalous transport properties associated with various microinstabilities driven by cross field currents in reconnecting geometries are reviewed. An assessment of their role in collisionless tearing based on analytic theory, computer simulations and experimental evidence, supports the dominant role of lower hybrid waves. The relevance of microturbulence on macroscopic stationary and time dependent models of merging is presented. It is concluded that a fluid-numerical simulation approach that includes (at each space and time step) the effects of anomalous transport in a self consistent manner, similar to the one used for laboratory collisionless shocks, represents the best method for studying and modeling the details of the reconnection process.

  4. Physics of collisionless phase mixing

    SciTech Connect

    Tsiklauri, D.; Haruki, T.

    2008-11-15

    Previous studies of phase mixing of ion cyclotron (IC), Alfvenic, waves in the collisionless regime have established the generation of parallel electric field and hence acceleration of electrons in the regions of transverse density inhomogeneity. However, outstanding issues were left open. Here we use the 2.5 D, relativistic, fully electromagnetic particle-in-cell code and an analytic magnetohydrodynamic (MHD) formulation, to establish the following points: (i) Using the generalized Ohm's law we find that the parallel electric field is supported mostly by the electron pressure tensor, with a smaller contribution from the electron inertia term. (ii) The generated parallel electric field and the fraction of accelerated electrons are independent of the IC wave frequency remaining at a level of six orders of magnitude larger than the Dreicer value and approximately 20%, respectively. The generated parallel electric field and the fraction of accelerated electrons increase with the increase of IC wave amplitude. The generated parallel electric field seems to be independent of plasma beta, while the fraction of accelerated electrons strongly increases with the decrease of plasma beta (for plasma beta of 0.0001 the fraction of accelerated electrons can be as large as 47%). (iii) In the collisionless regime IC wave dissipation length (that is defined as the distance over which the wave damps) variation with the driving frequency shows a deviation from the analytical MHD result, which we attribute to a possible frequency dependence of the effective resistivity. (iv) Effective anomalous resistivity, inferred from our numerical simulations, is at least four orders of magnitude larger than the classical Spitzer value.

  5. Particle simulation of collisionless reconnection using TRISTAN

    NASA Astrophysics Data System (ADS)

    Kotzé, P. B.; Nishikawa, K.-I.; Büchner, J.

    Magnetic reconnection is an important mechanism in the dynamics of the magnetosphere in facilitating the change in magnetospheric topology in response to the orientation of the interplanetary magnetic field (IMF). In the magnetosphere the classical collision rate is small, while the inertia of the electrons allows the frozen-in flux constraint to be broken. At small values of resistivity, this dissipation region then controls the rate of reconnection by forming an elongated Sweet-Parker layer, with an inflow velocity νi into the x-line that scales like: νi = δ ∆ νA νA (1) where δ and ∆ are the width (controlled by resistivity) and length (macroscopic) of the dissipation region respectively and νA is the Alfvén velocity. The scale length around the x-line where the electrons become demagnetised is of the order of the electron skin depth c/ωpe. This region is however much smaller than the ion inertial length c/ωpi, below which the Hall terms in the kinetic Ohm's law become important. Within this distance from the x-line the ions decouple from the electrons and are accelerated away at Alfv´enic velocities (Burkhart et al., 1990) The dynamics of the system at the scale length of the electron dissipation layer is therefore linked to Hall physics, making it a critical ingredient in determining collisionless reconnection rates. Particle simulation techniques have been used to investigate magnetic reconnection in 2-D for a Harris sheet equilibrium. A set of parameters are chosen as well as the dimensions of the computational domain, the boundary conditions and the initial amplitude and form of a seed magnetic island to start the reconnection process. Some preliminary results will be given in this paper.

  6. Development of a Current Sheet in the Wake of a Fast Coronal Mass Ejection

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    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 & 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.

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

    SciTech Connect

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

    2014-04-01

    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 {sub ☉} 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 {sup 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.

  8. PARTICLE ACCELERATION IN FRAGMENTING PERIODIC RECONNECTING CURRENT SHEETS IN SOLAR FLARES

    SciTech Connect

    Gordovskyy, M.; Browning, P. K.; Vekstein, G. E.

    2010-09-10

    Proton and electron acceleration in a fragmenting periodic current sheet (CS) is investigated, based on the forced magnetic reconnection scenario. The aim is to understand the role of CS fragmentation in high-energy beam generation in solar flares. We combine magnetohydrodynamics and test-particle models to consider particle trajectories consistent with a time-dependent reconnection model. It is shown that accelerated particles in such a model form two distinct populations. Protons and electrons moving in open magnetic field have energy spectra that are a combination of the initial Maxwellian distribution and a power-law high-energy (E>20 keV) part. The second population contains particles moving in a closed magnetic field around O-points. These particles move predominantly along the guiding field and their energies fall within quite a narrow range between {approx}1 MeV and {approx}10 MeV. It is also found that particles moving in an open magnetic field have a considerably wider pitch-angle distribution.

  9. Distribution of Nanoflares as Spatially Resolved Current Sheets in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Ng, C. S.; Lin, L.

    2014-05-01

    In a recent numerical study [Ng et al., Astrophys. J. 747, 109, 2012], based on a three-dimensional model of coronal heating using reduced magnetohydrodynamics, we have obtained scaling results of heating rate versus Lundquist number S based on a series of runs in which random photospheric motions are imposed for hundreds to thousands of Alfvén time in order to obtain converged statistical values. The heating rate found in these simulations saturates to a level that is independent of S in the high S limit and is consistent with the required level for coronal heating. In a previous study based on the total heating rate time series [Ng and Lin, AIP Conf. Proc. 1500, 38, 2012] in these simulations, we have also calculated heating events distributions, which are consistent with observations but do not support the nanoflares scenario [Parker, Astrophys. J. 330, 474, 1988]. This method has a limitation of not distinguishing individual heating events. We now extend this analysis to investigate the distribution of energy release events defined as spatially resolved current sheets [Lin et el., ASP Conf. Ser. 474, 159, 2013]. We report preliminary results and compare to results obtained using only time-series analysis.

  10. Current Sheets in the Corona and the Complexity of Slow Wind

    NASA Technical Reports Server (NTRS)

    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.

  11. Reconnection Properties of Large-scale Current Sheets During Coronal Mass Ejection Eruptions

    NASA Astrophysics Data System (ADS)

    Lynch, B. J.; Edmondson, J. K.; Kazachenko, M. D.; Guidoni, S. E.

    2016-07-01

    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 & 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 (˜103), 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.

  12. Non-linear tearing of 3D null point current sheets

    SciTech Connect

    Wyper, P. F. Pontin, D. I.

    2014-08-15

    The manner in which the rate of magnetic reconnection scales with the Lundquist number in realistic three-dimensional (3D) geometries is still an unsolved problem. It has been demonstrated that in 2D rapid non-linear tearing allows the reconnection rate to become almost independent of the Lundquist number (the “plasmoid instability”). Here, we present the first study of an analogous instability in a fully 3D geometry, defined by a magnetic null point. The 3D null current layer is found to be susceptible to an analogous instability but is marginally more stable than an equivalent 2D Sweet-Parker-like layer. Tearing of the sheet creates a thin boundary layer around the separatrix surface, contained within a flux envelope with a hyperbolic structure that mimics a spine-fan topology. Efficient mixing of flux between the two topological domains occurs as the flux rope structures created during the tearing process evolve within this envelope. This leads to a substantial increase in the rate of reconnection between the two domains.

  13. The neutral current sheet and its radiation pairs of side sources in coronal mass ejections

    NASA Astrophysics Data System (ADS)

    Ji, Shu-Chen

    Using the data observed with the soft X-ray telescope, hard X-ray telescope aboard on Yohkoh and the Nobeyama Radioheliograph on 1998 April 23, a comprehensive study on soft X-ray coronal mass ejection (SXRCME) and radio Type IV burst is carried out and some significant results are obtained as follows: A magnetic capacity belt (MCB) between two magnetic dipole sources (MDSs) was found and there were only a few activitation sources (ASs). During the MCB changed into a magnetic energy belt (MEB) by the ASs, activating energy and shining material both concentrated to the neutral current sheet (NCS) in the course of its formation. When two MDSs were put through by the MEB, the NCS formed and the SXRCME occurred. The matter ejected not only from the NCS, but also from the whole MEB. The expanding loop of the SXRCME had two foot points, both were just two MDSs. The head of the expanding loop always tended to the foot point of the weak source, because it was equilibrium point of magnetic pressures coming from two foot points. For this reason, its locus was neutral line. From this, the neutral line can also determine the position of NCS. Finally, the radiation pairs of side sources of NCS on the MEB are found.

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

    SciTech Connect

    Wang, Y.-M.; Robbrecht, E. E-mail: eva.robbrecht@oma.be

    2011-08-01

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

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

    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.

  17. Tether-Induced Airglow: Collisionless Effects

    NASA Technical Reports Server (NTRS)

    Mishin, E. V.; Khazanov, G. V.

    2006-01-01

    Martinez-Sanchez and Sanmartin [1997] showed that a bare conducting tether can be used as a source of an energetic electron beam. Interacting with the E region atmosphere, the beam should produce airglow thus making possible to deduce the neutral density on a continuous basis. Fujii et al. [2005] suggested that this idea be tested in a specially-designed sounding rocket experiment. We show that collisionless beam-plasma interactions (BPI) complement direct impact, leading to appreciable green-line (557.7 nm) emissions in the F region. In the E region, BPI develops near the entry in the valley, resulting in a narrow layer of strongly-elevated and airglow. Besides, neutralizing electric currents carried by ionospheric electrons in the valley can become unstable or even insufficient to compensate the beam current. Developing plasma waves inhibit neutralizing currents. In the extreme case, the beam might be locked in the valley (the 'virtual cathode'). In addition to optical observations, these effects can also be observed by radiophysical means.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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.

  20. Application of a carbon nanotube (CNT) sheet as a current collector for all-solid-state lithium batteries

    NASA Astrophysics Data System (ADS)

    Choi, Sunho; Kim, Junghoon; Eom, Minyong; Meng, Xianghe; Shin, Dongwook

    2015-12-01

    To replace conventional metal electrode, flexible carbon nanotube (CNT) sheet having excellent electrical properties is first applied as a current collector in all-solid-state lithium batteries, and its effect on the performance of all-solid-state lithium batteries are investigated. In the case of cells without the CNT sheet, gaps between the all-solid-state composite cathode and metal current collector (e.g., a conventional metal foil or coin cell) limits physical contacts which is not a trivial problem for the all-solid-state composite cathode. On the contrary, the CNT sheet makes intimate contact and provides a large interfacial contact area by filling the gaps. It is a great benefit in practical process viewpoint that this sufficient physical contact is achieved even without any polymeric binder. The greatly reduced interfacial contact resistance due to the intimate contact between the all-solid-state composite cathode and CNT sheet causes improvements in reversible capacity and high-rate discharge performance.

  1. ASYMMETRIC MAGNETIC RECONNECTION IN SOLAR FLARE AND CORONAL MASS EJECTION CURRENT SHEETS

    SciTech Connect

    Murphy, N. A.; Miralles, M. P.; Pope, C. L.; Raymond, J. C.; Winter, H. D.; Reeves, K. K.; Van Ballegooijen, A. A.; Lin, J.; Seaton, D. B.

    2012-05-20

    We present two-dimensional resistive magnetohydrodynamic simulations of line-tied asymmetric magnetic reconnection in the context of solar flare and coronal mass ejection current sheets. The reconnection process is made asymmetric along the inflow direction by allowing the initial upstream magnetic field strengths and densities to differ, and along the outflow direction by placing the initial perturbation near a conducting wall boundary that represents the photosphere. When the upstream magnetic fields are asymmetric, the post-flare loop structure is distorted into a characteristic skewed candle flame shape. The simulations can thus be used to provide constraints on the reconnection asymmetry in post-flare loops. More hard X-ray emission is expected to occur at the footpoint on the weak magnetic field side because energetic particles are more likely to escape the magnetic mirror there than at the strong magnetic field footpoint. The footpoint on the weak magnetic field side is predicted to move more quickly because of the requirement in two dimensions that equal amounts of flux must be reconnected from each upstream region. The X-line drifts away from the conducting wall in all simulations with asymmetric outflow and into the strong magnetic field region during most of the simulations with asymmetric inflow. There is net plasma flow across the X-line for both the inflow and outflow directions. The reconnection exhaust directed away from the obstructing wall is significantly faster than the exhaust directed toward it. The asymmetric inflow condition allows net vorticity in the rising outflow plasmoid which would appear as rolling motions about the flux rope axis.

  2. Nonlinear evolution of the Kelvin-Helmholtz instability in the double current sheet configuration

    NASA Astrophysics Data System (ADS)

    Mao, Aohua; Li, Jiquan; Liu, Jinyuan; Kishimoto, Yasuaki

    2016-03-01

    The nonlinear evolution of the Kelvin-Helmholtz (KH) instability driven by a radially antisymmetric shear flow in the double current sheet configuration is numerically investigated based on a reduced magnetohydrodynamic model. Simulations reveal different nonlinear fate of the KH instability depending on the amplitude of the shear flow, which restricts the strength of the KH instability. For strong shear flows far above the KH instability threshold, the linear electrostatic-type KH instability saturates and achieves a vortex flow dominated quasi-steady state of the electromagnetic (EM) KH turbulence with large-amplitude zonal flows as well as zonal fields. The magnetic surfaces are twisted significantly due to strong vortices but without the formation of magnetic islands. However, for the shear flow just over the KH instability threshold, a weak EM-type KH instability is saturated and remarkably damped by zonal flows through modifying the equilibrium shear flow. Interestingly, a secondary double tearing mode (DTM) is excited subsequently in highly damped KH turbulence, behaving as a pure DTM in a flowing plasma as described in Mao et al. [Phys. Plasmas 21, 052304 (2014)]. However, the explosive growth phenomenon is replaced by a gradually growing oscillation due to the extremely twisted islands. As a result, the release of the magnetic energy becomes slow and the global magnetic reconnection tends to be gentle. A complex nonlinear interaction between the EM KH turbulence and the DTMs occurs for the medium shear flows above the KH instability threshold, turbulent EM fluctuations experience oscillatory nonlinear growth of the DTMs, finally achieves a quasi-steady state with the interplay of the fluctuations between the DTMs and the EM KH instability.

  3. CURRENT SHEET REGULATION OF SOLAR NEAR-RELATIVISTIC ELECTRON INJECTION HISTORIES

    SciTech Connect

    Agueda, N.; Sanahuja, B.; Vainio, R.; Dalla, S.; Lario, D.

    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.

  4. Magnetar giant flares in multipolar magnetic fields. II. Flux rope eruptions with current sheets

    SciTech Connect

    Huang, Lei; Yu, Cong E-mail: cyu@ynao.ac.cn

    2014-11-20

    We propose a physical mechanism to explain giant flares and radio afterglows in terms of a magnetospheric model containing both a helically twisted flux rope and a current sheet (CS). With the appearance of a CS, we solve a mixed boundary value problem to get the magnetospheric field based on a domain decomposition method. We investigate properties of the equilibrium curve of the flux rope when the CS is present in background multipolar fields. In response to the variations at the magnetar surface, it quasi-statically evolves in stable equilibrium states. The loss of equilibrium occurs at a critical point and, beyond that point, it erupts catastrophically. New features show up when the CS is considered. In particular, we find two kinds of physical behaviors, i.e., catastrophic state transition and catastrophic escape. Magnetic energy would be released during state transitions. This released magnetic energy is sufficient to drive giant flares, and the flux rope would, therefore, go away from the magnetar quasi-statically, which is inconsistent with the radio afterglow. Fortunately, in the latter case, i.e., the catastrophic escape, the flux rope could escape the magnetar and go to infinity in a dynamical way. This is more consistent with radio afterglow observations of giant flares. We find that the minor radius of the flux rope has important implications for its eruption. Flux ropes with larger minor radii are more prone to erupt. We stress that the CS provides an ideal place for magnetic reconnection, which would further enhance the energy release during eruptions.

  5. Role of the Antarctic Circumpolar Current (ACC) on the Antarctica ice-sheet

    NASA Astrophysics Data System (ADS)

    Ladant, Jean-Baptiste; Donnadieu, Yannick; Lefebvre, Vincent; Dumas, Christophe

    2013-04-01

    Since more than a decade, most publications have put forward the primary role of atmospheric CO2 for explaining the Eocene Oligocene transition while diminishing the potential for the gateways to play a major role. Here we investigate the role of the Drake Passage opening on the Antarctica ice-sheet using a new modelling system including the Fast Ocean Atmosphere Model (FOAM), the high resolution atmospheric model LMDz and the ice-sheet model GRISLI. Using a set of boundary conditions, i.e. atmospheric CO2 level, orbital parameters and continental configuration, FOAM provides SSTs required to run LMDz, which is then used to simulate ice-sheet over Antarctica with GRISLI. As demonstrated by Lefebvre et al. (2012), the opening of southern oceanic gateways does not trigger the onset of the ACC for CO2 typical of the late Eocene (>840 ppm). A cooler background climatic state such as the one prevalent at the end of the Oligocene is required to simulate a well-developed ACC. Here, we show that the formation of the East Antarctica ice-sheet triggers the onset of the ACC in FOAM. Changes in oceanographic conditions have a significative impact on the atmospheric circulation simulated by LMDz, which in turn influence the ice-sheet geometry. In particular, we show that the ACC may have triggered the onset of West Antarctica ice-sheet through a feedback loop including multiple interactions between the atmosphere, the ocean and the Antarctica ice-sheet. The sensitivity of our results to unconstrained parameters such as those fixing the ablation / freezing below the ice-shelves but also to the topography of the Antarctica (Wilson et al., 2012) will be presented. Ref.: Deciphering the role of southern gateways and carbon dioxide on the onset of the ACC, Lefebvre V. et al., vol. 27, Paleoceanography, 2012 Antarctic topography at the Eocene - Oligocene boundary, Wilson D.S. et al., vol. 335, P-cubed, 2012.

  6. Collisionless Reconnection and Electron Demagnetization

    NASA Astrophysics Data System (ADS)

    Scudder, J. D.

    Observable, dimensionless properties of the electron diffusion region of collisionless magnetic reconnection are motivated and benchmarked in two and three dimensional Particle In Cell (PIC) simulations as appropriate for measurements with present state of the art spacecraft. The dimensionless quantities of this paper invariably trace their origin to breaking the magnetization of the thermal electrons. Several observable proxies are also motivated for the rate of frozen flux violation and a parameter \\varLambda _{\\varPhi } that when greater than unity is associated with close proximity to the analogue of the saddle point region of 2D reconnection usually called the electron diffusion region. Analogous regions to the electron diffusion region of 2D reconnection with \\varLambda _{\\varPhi } > 1 have been identified in 3D simulations. 10-20 disjoint diffusion regions are identified and the geometrical patterns of their locations illustrated. First examples of associations between local observables based on electron demagnetization and global diagnostics (like squashing) are also presented. A by product of these studies is the development of a single spacecraft determinations of gradient scales in the plasma.

  7. Collisionless Hall MHD Reconnection Dynamics: Is the Nonlinear Reconnection Rate Independent of the Mechanism that Breaks Field Lines?

    NASA Astrophysics Data System (ADS)

    Bhattacharjee, A.; Germaschewski, K.; Wang, X.; Linde, T.; Rosner, R.; Siegel, A.

    2002-12-01

    There has been considerable interest in recent years in collisionless reconnection dynamics governed by the generalized Ohm's law in which electron inertia provides the mechanism for breaking field lines. It has been suggested in several theoretical studies that the nonlinear reconnection dynamics, to leading order, is independent of the mechanism that breaks field lines (that is, electron inertia). We test this suggestion carefully using the new Magnetic Reconnection Code (MRC) developed at the Center for Magnetic Reconnection Studies. The MRC is a new massively parallel code with Adaptive Mesh Refinement (AMR) that integrates the equations of Hall MHD. The use of AMR enables unprecedented levels of resolution of the current and vorticity layers and uncovers interesting secondary dynamics not seen in previous studies. We apply the MRC to the study of two problems, one involving free reconnection caused by a spontaneous and fast collisionless instability, the other involving forced reconnection induced by boundary perturbations on a stable plasma. In the case of free reconnection, over the range of parameters covered by our simulations, it is shown that the nonlinear reconnection rate is near-explosive, and furthermore, that the nonlinear magnetic island width is an invariant function of a dimensionless variable which is the product of the linear growth rate and time. Now, since the linear growth rate is a function of the ion sound radius as well as the electron skin depth, we conclude that the nonlinear reconnection rate is not independent of electron inertia. In the case of forced reconnection, after a slow growth phase, the dynamics exhibits an impulsive growth in the amplitude of the thin current sheet, and a subsequent current disruption mediated by secondary instabilities. These results, in which electron inertia provides the mechanism for breaking field lines, are contrasted with resistive Hall MHD simulations in which resistivity provides the mechanism for

  8. Simulating the Thinning Magnetotail Current Sheet During a Substorm Growth Phase with the Rice Convection Model-Equilibrium

    NASA Astrophysics Data System (ADS)

    Lemon, C. L.; Crabtree, C. E.; Chen, M.; Guild, T. B.

    2015-12-01

    Modeling the progression of the magnetotail configuration during a substorm growth phase is challenging because the current sheet becomes very thin, and is difficult to resolve while keeping the problem computationally tractable. Magnetohydrodynamics (MHD) models have dealt with this problem in various ways, and many claim to be driven by physical rather than numerical considerations. The Rice Convection Model-Equilibrium (RCM-E) is not an MHD model, and has advantages and disadvantages compared to MHD. The notable advantages are the characterization of the full energy distribution of the plasma (including the associated gradient/curvature drift), as well as its generally more comprehensive treatment of the electrodynamics of magnetosphere-ionosphere coupling. The disadvantages include the bounce-averaging of plasma drift, which limits the domain to closed field lines, and the assumption of slow flow relative to the Alfvén speed. The RCM-E has been used in the past to model a substorm growth phase, but its assumptions do not allow it to properly treat the onset mechanism or the formation of x-lines. It can simulate the approach to onset, but is limited by its ability to resolve the thinning current sheet. In this presentation, we present advances in the technique used to calculate the self-consistent magnetic field, which allows us to resolve thinner current sheets than were previously possible. We combine this with a generalized ballooning mode analysis of specific flux tubes in order to assess the stability of the magnetotail to substorm onset.

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

    SciTech Connect

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

    2013-02-15

    Harris-type current sheets with the magnetic field model of B-vector=B{sub x}(z)x-caret+B{sub 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{r_reversible}=p{sub Parallel-To }b-caretb-caret+p{sub Up-Tack }(I{r_reversible}-b-caretb-caret). Here, p{sub Parallel-To} and p{sub Up-Tack} 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{sub Parallel-To },k{sub Up-Tack },z) coordinates. Here, k{sub Parallel-To} and k{sub Up-Tack} 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.

  10. MODELING UV AND X-RAY EMISSION IN A POST-CORONAL MASS EJECTION CURRENT SHEET

    SciTech Connect

    Ko, Yuan-Kuen; Raymond, John C.; Vrsnak, Bojan; Vujic, Eugen

    2010-10-10

    A post-coronal mass ejection (CME) current sheet (CS) is a common feature developed behind an erupting flux rope in CME models. Observationally, white light observations have recorded many occurrences of a thin ray appearing behind a CME eruption that closely resembles a post-CME CS in its spatial correspondence and morphology. UV and X-ray observations further strengthen this interpretation by the observations of high-temperature emission at locations consistent with model predictions. The next question then becomes whether the properties inside a post-CME CS predicted by a model agree with observed properties. In this work, we assume that the post-CME CS is a consequence of Petschek-like reconnection and that the observed ray-like structure is bounded by a pair of slow mode shocks developed from the reconnection site. We perform time-dependent ionization calculations and model the UV line emission. We find that such a model is consistent with SOHO/UVCS observations of the post-CME CS. The change of Fe XVIII emission in one event implies an inflow speed of {approx}10 km s{sup -1} and a corresponding reconnection rate of M{sub A} {approx} 0.01. We calculate the expected X-ray emission for comparison with X-ray observations by Hinode/XRT, as well as the ionic charge states as would be measured in situ at 1 AU. We find that the predicted count rate for Hinode/XRT agrees with what was observed in a post-CME CS on 2008 April 9, and the predicted ionic charge states are consistent with high ionization states commonly measured in the interplanetary CMEs. The model results depend strongly on the physical parameters in the ambient corona, namely the coronal magnetic field, the electron density, and temperature during the CME event. It is crucial to obtain these ambient coronal parameters and as many facets of the CS properties as possible by observational means so that the post-CME CS models can be scrutinized more effectively.

  11. The North-South Asymmetry of the Heliospheric Current Sheet: Results of an MHD Simulation

    NASA Technical Reports Server (NTRS)

    Usmanov, Arcadi V.; Goldstein, Melvyn L.

    2013-01-01

    A displacement of the heliospheric current sheet (HCS) south of the helioequator by approx.10deg was proposed by Simpson et al. (1996) as a possible explanation of the north-south asymmetry in the galactic cosmic rays observed by Ulysses during its first fast transit in 1994-1995. The idea was not supported by magnetic field measurements on Ulysses and, on this ground, was dismissed by Simpson et al. (1996). In addition, Erdos & Balogh (1998) argued that any north-south symmetry was unlikely as there should be flux balance between the magnetic sectors of opposite polarity. Nonetheless, many in the scientific community have accepted the original suggestion of Simpson et al. (1996) that a displacement of the HCS was responsible for the cosmic ray asymmetry. In this paper, using a magnetohydrodynamic model of the solar corona and solar wind that includes both dipole and quadrupole magnetic source terms, we show that a north-south asymmetry of the magnetic field on the Sun does not give rise to a displacement of the HCS. The lack of displacement of the HCS results from a latitudinal redistribution of magnetic flux near the Sun where the plasma beta much < 1. The latitudinal redistribution is a direct consequence of the magnetic field gradient between pole and equator. Near the Sun, the latitudinal gradient in magnetic field generates meridional flows directed equatorward that tend to relax the gradient in the magnetic field (to make it more latitude-independent) as heliocentric distance increases. If there is an asymmetry between north and south magnetic field strength then the meridional flows are also asymmetric (i.e., stronger in the hemisphere of stronger magnetic field). Because the magnetic fluxes (positive and negative) in the hemispheres must be equal, the redistribution shifts the HCS into balance by approx. 16 R(solar mass). At larger distances, where the magnetic field is relatively weak (beta much > 1), the HCS can be displaced if there is a difference in

  12. Modeling combined collisional/collisionless plasma interpenetration

    SciTech Connect

    Thomas, V.A.

    1997-04-01

    This paper describes one technique by which multifluid modeling capability can be achieved within the context of a Lagrangean single-fluid model. This technique is applied to the interpenetration of laser-produced, substantially collisionless plasmas. A single-fluid model by itself cannot simulate the interpenetration of a collisionless plasma correctly, but must be augmented with some other tool. One tool that can calculate collisionless plasma interpenetration correctly is ISIS, a particle code for plasma simulations which includes appropriate collision models. However, ISIS does not have the necessary physics to do the laser deposition, the atomic physics, the radiation transport, and does not possess a realistic electron temperature model. With appropriate integration of the single-fluid code and ISIS, a new capability is achieved which allows simulation of the colliding plasma problem, a problem that neither code can properly simulate individually.

  13. Antarctic polar plateau vertical electric field variations across heliocentric current sheet crossings

    NASA Astrophysics Data System (ADS)

    Burns, G. B.; Tinsley, B. A.; Klekociuk, A. R.; Troshichev, O. A.; Frank-Kamenetsky, A. V.; Duldig, M. L.; Bering, E. A.; Clem, J. M.

    2006-03-01

    A superposed epoch analysis of variations of the vertical electric field measured at Vostok (78.5°S, 107°E; magnetic latitude 83.6°S) during 1998 2002 heliocentric current sheet (HCS) crossings yields no significant variation other than an association imposed by polar-cap potential differences above the site. This result contradicts published reports of a reduction ˜15% in electric field 1 3 days after HCS crossings, an observation initially made ˜30 years ago. If such a reduction had been caused by reductions in stratospheric ionising radiation, the presence of polar stratospheric clouds (PSC) would seem necessary for the occurrence of this effect. PSCs would increase the resistance of the stratosphere thus making ionisation in that region significant in the context of the ionosphere ground current flow, in a manner analogous to the role of volcanic aerosols in the stratosphere in the explanation of the weakening of northern hemisphere winter cyclones associated with HCS crossings, the so-called ‘Wilcox effect’. However, separating the present data to correspond to the likely presence of PSC above Vostok also does not yield the reported reduction. Significant increases or decreases of the vertical electric field emerge from the observations when the HCS crossings are separated into sets depending on whether the solar wind magnetic field changes from ‘toward-to-away’ (increase of ˜11%) and ‘away-to-toward’ (decrease of ˜8%). Polar-cap potential changes above the site, inferred from solar wind parameters using the Weimer model, also show such step functions that reverse with the sign of HCS transition and are broadly consistent with the measured electric field increases or decreases. Remaining differences between the measurements and the model are consistent with a somewhat stronger solar wind speed and/or magnetic activity influence on polar-cap convection above Vostok than is predicted by the model. Variations in ground-level neutron counts, a

  14. Particle-in-Cell Simulation of Collisionless Driven Reconnection with Open Boundaries

    NASA Technical Reports Server (NTRS)

    Kimas, Alex; Hesse, Michael; Zenitani, Seiji; Kuznetsova, Maria

    2010-01-01

    First results are discussed from an ongoing study of driven collisionless reconnection using a 2 1/2-dimensional electromagnetic particle-in-cell simulation model with open inflow and outflow boundaries. An extended electron diffusion region (EEDR) is defined as that region surrounding a reconnecting neutral line in which the out-of-plane nonideal electric field is positive. It is shown that the boundaries of this region in the directions of the outflow jets are at the positions where the electrons make the transition from unfrozen meandering motion in the current sheet to outward drifting with the magnetic field in the outflow jets; a turning length scale is defined to mark these positions, The initial width of the EEDR in the inflow directions is comparable to the electron bounce width. Later. as shoulders develop to form a two-scale structure. thc EEDR width expands to the ion bounce width scale. The inner portion of the EEDR or the electron diffusion region proper remains at the electron bounce width. Two methods are introduced for predicting the reconnection electric field using the dimensions of the EEDR. These results are interpreted as further evidence that the EEDR is the region that is relevant to understanding the electron role in the neutral line vicinity.

  15. Cluster observations of solitary waves near the center of the current sheet in association with magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Hupach, A.; Cattell, C. A.; Wygant, J. R.; Schwartz, S. J.; Mouikis, C.

    2010-12-01

    Cluster observations of large amplitude solitary waves (up to ~250 mV/m), identified as electron holes, were studied for six days when the satellites repeatedly crossed the plasma sheet near a reconnection region. Examination of EFW instrument burst data, with an automated program [Dombeck et al., 2001] and visual inspection, detected solitary waves on 18 of the 24 bursts. There was one 10 second burst on each spacecraft each day with solitary waves detected in at least one burst from every day. Solitary waves were seen on all four spacecraft during three of the days. The variety of positions surveyed by Cluster due to both spacecraft separation and the differing locations with respect to the reconnection region at each of the six events enables a comparison of solitary wave duration and peak to peak electric field in many different parts of the reconnection region. The study expands work by Cattell et al. [2005] which, along with simulations by Drake et al. [2003], showed that electron holes could provide some of the particle scattering needed in the reconnection process. The August 24, 2003 burst on spacecraft 2 is unique because several solitary waves were detected less than 200 km from and some within a few km of the center of the current sheet (BXgse=0). This is in contrast to the Cattell et al. [2005] results where solitary waves were only seen on spacecraft greater than 1,500 km from the center of the current sheet. Peak to peak electric fields of a few to hundreds of mV/m and durations of tenths to tens of microseconds were consistent for solitary waves both near and far from the center of the current sheet. In agreement with previous studies and independent of position in the current sheet, all solitary waves were detected during times when PEACE measured narrow field aligned electron beams. While recent studies, such as Che et al. [2009] and Goldman et al. [2008], suggested different wave modes for the evolution of solitary waves, a determination of

  16. A mean field Ohm's law for collisionless plasmas

    SciTech Connect

    Biglari, H. ); Diamond, P.H. )

    1993-11-01

    A mean field Ohm's law valid for collisionless plasmas is derived kinetically. It is shown that contrary to conventional thinking, the resulting hyperresistivity is significantly smaller than its fluid counterpart due to the fact that the turbulent decorrelation rate is linked to the rapid electron ballistic motion rather than the slower nonlinear mixing time. Moreover, the off-diagonal contributions to the parallel electron momentum flux are shown to result in Ohm's law renormalizations that dwarf the current diffusivity and break radial parity symmetry.

  17. Magnetic reconnection in collisionless plasmas - Prescribed fields

    NASA Technical Reports Server (NTRS)

    Burkhart, G. R.; Drake, J. F.; Chen, J.

    1990-01-01

    The structure of the dissipation region during magnetic reconnection in collisionless plasma is investigated by examining a prescribed two-dimensional magnetic x line configuration with an imposed inductive electric field E(y). The calculations represent an extension of recent MHD simulations of steady state reconnection (Biskamp, 1986; Lee and Fu, 1986) to the collisionless kinetic regime. It is shown that the structure of the x line reconnection configuration depends on only two parameters: a normalized inductive field and a parameter R which represents the opening angle of the magnetic x lines.

  18. Physics of collisionless shocks: theory and simulation

    NASA Astrophysics Data System (ADS)

    Stockem Novo, A.; Bret, A.; Fonseca, R. A.; Silva, L. O.

    2016-01-01

    Collisionless shocks occur in various fields of physics. In the context of space and astrophysics they have been investigated for many decades. However, a thorough understanding of shock formation and particle acceleration is still missing. Collisionless shocks can be distinguished into electromagnetic and electrostatic shocks. Electromagnetic shocks are of importance mainly in astrophysical environments and they are mediated by the Weibel or filamentation instability. In such shocks, charged particles gain energy by diffusive shock acceleration. Electrostatic shocks are characterized by a strong electrostatic field, which leads to electron trapping. Ions are accelerated by reflection from the electrostatic potential. Shock formation and particle acceleration will be discussed in theory and simulations.

  19. Time-resolved characterization of the formation of a collisionless shock.

    PubMed

    Ahmed, H; Dieckmann, M E; Romagnani, L; Doria, D; Sarri, G; Cerchez, M; Ianni, E; Kourakis, I; Giesecke, A L; Notley, M; Prasad, R; Quinn, K; Willi, O; Borghesi, M

    2013-05-17

    We report on the temporally and spatially resolved detection of the precursory stages that lead to the formation of an unmagnetized, supercritical collisionless shock in a laser-driven laboratory experiment. The measured evolution of the electrostatic potential associated with the shock unveils the transition from a current free double layer into a symmetric shock structure, stabilized by ion reflection at the shock front. Supported by a matching particle-in-cell simulation and theoretical considerations, we suggest that this process is analogous to ion reflection at supercritical collisionless shocks in supernova remnants. PMID:25167421

  20. THE TOPOLOGICAL CHANGES OF SOLAR CORONAL MAGNETIC FIELDS. III. RECONNECTED FIELD TOPOLOGY PRODUCED BY CURRENT-SHEET DISSIPATION

    SciTech Connect

    Janse, A. M.; Low, B. C.

    2010-10-20

    In this paper, the third in a series of papers on topological changes of magnetic fields, we study how the dissipation of an initial current sheet (CS) in a closed three-dimensional (3D) field affects the field topology. The initial field is everywhere potential except at the location of the CS which is in macroscopic equilibrium under the condition of perfect conductivity. In the physical world of extremely high, but finite, conductivity, the CS dissipates and the field seeks a new equilibrium state in the form of an everywhere potential field since the initial field is everywhere untwisted. Our semi-analytical study indicates that the dissipation of the single initial CS must induce formation of additional CSs in extensive parts of the magnetic volume. The subsequent dissipation of these other sheets brings about topological changes by magnetic reconnection in order for the global field to become potential. In 2D fields, the magnetic reconnection due to the dissipation of a CS is limited to the magnetic vicinity of the dissipating sheet. Thus, the consequence of CS dissipation is physically and topologically quite different in 2D and 3D fields. A discussion of this result is given in general relation to the Parker theory of spontaneous CSs and heating in the solar corona and solar flares.

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

    PubMed

    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. PMID:21517318

  2. Effect of Current Sheets on the Solar Wind Magnetic Field Power Spectrum from the Ulysses Observation: From Kraichnan to Kolmogorov Scaling

    SciTech Connect

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

    2011-03-25

    The MHD turbulence theory developed by Iroshnikov and Kraichnan predicts a k{sup -1.5} power spectrum. Solar wind observations, however, often show a k{sup -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.

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

    PubMed

    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.

  4. Transition from Collisionless to Collisional MRI

    SciTech Connect

    Prateek Sharma; Gregory W. Hammett; Eliot Quataert

    2003-07-24

    Recent calculations by Quataert et al. (2002) found that the growth rates of the magnetorotational instability (MRI) in a collisionless plasma can differ significantly from those calculated using MHD. This can be important in hot accretion flows around compact objects. In this paper, we study the transition from the collisionless kinetic regime to the collisional MHD regime, mapping out the dependence of the MRI growth rate on collisionality. A kinetic closure scheme for a magnetized plasma is used that includes the effect of collisions via a BGK operator. The transition to MHD occurs as the mean free path becomes short compared to the parallel wavelength 2*/k(sub)||. In the weak magnetic field regime where the Alfven and MRI frequencies w are small compared to the sound wave frequency k(sub)||c(sub)0, the dynamics are still effectively collisionless even if omega << v, so long as the collision frequency v << k(sub)||c(sub)0; for an accretion flow this requires n less than or approximately equal to *(square root of b). The low collisionality regime not only modifies the MRI growth rate, but also introduces collisionless Landau or Barnes damping of long wavelength modes, which may be important for the nonlinear saturation of the MRI.

  5. 3D electrostatic gyrokinetic electron and fully kinetic ion simulation of lower-hybrid drift instability of Harris current sheet

    DOE PAGESBeta

    Wang, Zhenyu; Lin, Yu; Wang, Xueyi; Tummel, Kurt; Chen, Liu

    2016-07-07

    The eigenmode stability properties of three-dimensional lower-hybrid-drift-instabilities (LHDI) in a Harris current sheet with a small but finite guide magnetic field have been systematically studied by employing the gyrokinetic electron and fully kinetic ion (GeFi) particle-in-cell (PIC) simulation model with a realistic ion-to-electron mass ratio mi/me. In contrast to the fully kinetic PIC simulation scheme, the fast electron cyclotron motion and plasma oscillations are systematically removed in the GeFi model, and hence one can employ the realistic mi/me. The GeFi simulations are benchmarked against and show excellent agreement with both the fully kinetic PIC simulation and the analytical eigenmode theory. Our studies indicate that, for small wavenumbers, ky, along the current direction, the most unstable eigenmodes are peaked at the location wheremore » $$\\vec{k}$$• $$\\vec{B}$$ =0, consistent with previous analytical and simulation studies. Here, $$\\vec{B}$$ is the equilibrium magnetic field and $$\\vec{k}$$ is the wavevector perpendicular to the nonuniformity direction. As ky increases, however, the most unstable eigenmodes are found to be peaked at $$\\vec{k}$$ •$$\\vec{B}$$ ≠0. Additionally, the simulation results indicate that varying mi/me, the current sheet width, and the guide magnetic field can affect the stability of LHDI. Simulations with the varying mass ratio confirm the lower hybrid frequency and wave number scalings.« less

  6. 3D electrostatic gyrokinetic electron and fully kinetic ion simulation of lower-hybrid drift instability of Harris current sheet

    NASA Astrophysics Data System (ADS)

    Wang, Zhenyu; Lin, Yu; Wang, Xueyi; Tummel, Kurt; Chen, Liu

    2016-07-01

    The eigenmode stability properties of three-dimensional lower-hybrid-drift-instabilities (LHDI) in a Harris current sheet with a small but finite guide magnetic field have been systematically studied by employing the gyrokinetic electron and fully kinetic ion (GeFi) particle-in-cell (PIC) simulation model with a realistic ion-to-electron mass ratio mi/me . In contrast to the fully kinetic PIC simulation scheme, the fast electron cyclotron motion and plasma oscillations are systematically removed in the GeFi model, and hence one can employ the realistic mi/me . The GeFi simulations are benchmarked against and show excellent agreement with both the fully kinetic PIC simulation and the analytical eigenmode theory. Our studies indicate that, for small wavenumbers, ky, along the current direction, the most unstable eigenmodes are peaked at the location where k →.B → =0 , consistent with previous analytical and simulation studies. Here, B → is the equilibrium magnetic field and k → is the wavevector perpendicular to the nonuniformity direction. As ky increases, however, the most unstable eigenmodes are found to be peaked at k →.B → ≠0 . In addition, the simulation results indicate that varying mi/me , the current sheet width, and the guide magnetic field can affect the stability of LHDI. Simulations with the varying mass ratio confirm the lower hybrid frequency and wave number scalings.

  7. Collisionless Reconnection with Weak Slow Shocks Under Anisotropic MHD Approximation

    NASA Astrophysics Data System (ADS)

    Hirabayashi, K.; Hoshino, M.

    2014-12-01

    Magnetic reconnection accompanied by a pair of slow-mode shock waves, known as Petschek's theory, has been widely studied as an efficient mechanism to convert magnetically stored energy to thermal and/or kinetic energy in plasmas. Satellite observations in the Earth's magnetotail, on the other hand, report that the detection of slow shocks is rare compared with the theory. As an important step to bridge the gap between the observational fact and the Petschek-type reconnection, we performed one- and two- dimensional collisionless magnetohydrodynamic (MHD) simulations of magnetic reconnection paying special attention to the effect of temperature anisotropy. In high-beta plasmas such as a plasma sheet in the magnetotail, it is expected that even weak temperature anisotropy can greatly modify the dynamics. We demonstrate that the slow shocks do exist in the reconnection layer even under the anisotropic temperature. The resultant shocks, however, are weaker than those in isotropic MHD in terms of plasma compression. In addition, the amount of magnetic energy released across the shock is extremely small, that is, the shock is no longer switch-off type. In spite of the weakness of the shocks, the reconnection rates measured by the inflow velocities are kept at the same level as the isotropic cases. Once the slow shock forms, the downstream plasma is heated in highly anisotropic manner, and the firehose-sense anisotropy affects the wave structure in the system. In particular, it is remarkable that the sequential order of propagation of slow shocks and rotational discontinuities reverses depending upon the magnitude of a superposed guide field. Our result is consistent with the rareness of the slow shock detection in the magnetotail, and implies that shocks do not necessarily play an important role. Furthermore, a variety of wave structure of a reconnection layer shown here will help interpretation of observational data in collisionless reconnection.

  8. Relation of the current sheet flapping waves to Pi2 pulsation and aurora arcs

    NASA Astrophysics Data System (ADS)

    Du, Aimin; Zhang, Tielong

    Data from satellite THEMIS, GOES11 and ground-based magnetometers are used to investigate characteristics of field line resonance (FLR) in ionosphere and the plasma sheet. The Pi2 ULF waves observed by CARISMA array show the signatures of field line resonance. The FLR occurred narrowly in latitude band and wide in longitude. A large amplitude Pi2 was observed by the THEMIS-A (P5) and GOES11 satellites near equator in the near-Earth magnetotail on March 9, 2008. P5 was located in X~ -5 Re. Firstly P5 detected a compressional wave, then a shear Alfven wave. The Alfven wave accelerated the electron to precipitate into the footprint of P5, resulted in the discrete auroral arcs.

  9. ANALYTIC SOLUTIONS FOR CURRENT SHEET STRUCTURE DETERMINED BY SELF-CONSISTENT, ANISOTROPIC TRANSPORT PROCESSES IN A GRAVITATIONAL FIELD

    SciTech Connect

    Goodman, Michael L.

    2011-04-10

    A Harris sheet magnetic field with maximum magnitude B{sub 0} and length scale L is combined with the anisotropic electrical conductivity, viscosity, and thermoelectric tensors for an electron-proton plasma to define a magnetohydrodynamic model that determines the steady state of the plasma. The transport tensors are functions of temperature, density, and magnetic field strength, and are computed self-consistently as functions of position x normal to the current sheet. The flow velocity, magnetic field, and gravitational force lie along the z-axis. The plasma is supported against gravity by the viscous force. Analytic solutions are obtained for temperature, density, and velocity. They are valid over a broad range of temperature, density, and magnetic field strength, and so may be generally useful in astrophysical applications. Numerical examples of solutions in the parameter range of the solar atmosphere are presented. The objective is to compare Joule and viscous heating rates, determine the velocity shear that generates viscous forces that support the plasma and are self-consistent with a mean outward mass flux comparable to the solar wind mass flux, and compare the thermoelectric and conduction current contributions to the Joule heating rate. The ratio of the viscous to Joule heating rates per unit mass can exceed unity by orders of magnitude, and increases rapidly with L. The viscous heating rate can be concentrated outside the region where the current density is localized, corresponding to a resistively heated layer of plasma bounded by viscously heated plasma. The temperature gradient drives a thermoelectric current density that can have a magnitude greater than that of the electric-field-driven conduction current density, so thermoelectric effects are important in determining the Joule heating rate.

  10. Simulation of electrostatic turbulence in the plasma sheet boundary layer with electron currents and bean-shaped ion beams

    NASA Technical Reports Server (NTRS)

    Nishikawa, K.-I.; Frank, L. A.; Huang, C. Y.

    1988-01-01

    Plasma data from ISEE-1 show the presence of electron currents as well as energetic ion beams in the plasma sheet boundary layer. Broadband electrostatic noise and low-frequency electromagnetic bursts are detected in the plasma sheet boundary layer, especially in the presence of strong ion flows, currents, and steep spacial gradients in the fluxes of few-keV electrons and ions. Particle simulations have been performed to investigate electrostatic turbulence driven by a cold electron beam and/or ion beams with a bean-shaped velocity distribution. The simulation results show that the counterstreaming ion beams as well as the counterstreaming of the cold electron beam and the ion beam excite ion acoustic waves with a given Doppler-shifted real frequency. However, the effect of the bean-shaped ion velocity distributions reduces the growth rates of ion acoustic instability. The simulation results also show that the slowing down of the ion bean is larger at the larger perpendicular velocity. The wave spectra of the electric fields at some points of the simulations show turbulence generated by growing waves.

  11. Controlling Influence of Magnetic Field on Solar Wind Outflow: An Investigation using Current Sheet Source Surface Model

    NASA Astrophysics Data System (ADS)

    Poduval, B.

    2016-08-01

    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.

  12. Controlling Influence of Magnetic Field on Solar Wind Outflow: An Investigation using Current Sheet Source Surface Model

    NASA Astrophysics Data System (ADS)

    Poduval, B.

    2016-08-01

    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.

  13. Impact of Temperature-dependent Resistivity and Thermal Conduction on Plasmoid Instabilities in Current Sheets in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Ni, Lei; Roussev, Ilia I.; Lin, Jun; Ziegler, Udo

    2012-10-01

    In this paper, we investigate, by means of two-dimensional magnetohydrodynamic simulations, the impact of temperature-dependent resistivity and thermal conduction on the development of plasmoid instabilities in reconnecting current sheets in the solar corona. We find that the plasma temperature in the current-sheet region increases with time and it becomes greater than that in the inflow region. As secondary magnetic islands appear, the highest temperature is not always found at the reconnection X-points, but also inside the secondary islands. One of the effects of anisotropic thermal conduction is to decrease the temperature of the reconnecting X-points and transfer the heat into the O-points, the plasmoids, where it gets trapped. In the cases with temperature-dependent magnetic diffusivity, η ~ T -3/2, the decrease in plasma temperature at the X-points leads to (1) an increase in the magnetic diffusivity until the characteristic time for magnetic diffusion becomes comparable to that of thermal conduction, (2) an increase in the reconnection rate, and (3) more efficient conversion of magnetic energy into thermal energy and kinetic energy of bulk motions. These results provide further explanation of the rapid release of magnetic energy into heat and kinetic energy seen during flares and coronal mass ejections. In this work, we demonstrate that the consideration of anisotropic thermal conduction and Spitzer-type, temperature-dependent magnetic diffusivity, as in the real solar corona, are crucially important for explaining the occurrence of fast reconnection during solar eruptions.

  14. Thermal structure of current sheets and supra-arcade downflows in the solar corona

    SciTech Connect

    Hanneman, Will J.; Reeves, Katharine K. E-mail: kreeves@cfa.harvard.edu

    2014-05-10

    After the peak intensity of many large solar flares, magnetic and thermodynamic processes give rise to a phenomenon known as supra-arcade downflows (SADs). SADs are sunward flowing density depletions, often observed in post-flare plasma sheets. Some models have suggested that the plasma in the dark lanes is heated to temperatures of 20-80 MK, which is much hotter than temperatures of the surrounding plasma. In this work, we use data from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory and the X-Ray Telescope on the Hinode satellite to determine the thermal structure of SADs in the solar corona. We examine four flares that took place on 2011 October 22, 2012 January 14, 2012 January 16, and 2012 January 27. Differential emission measures are calculated for each flare and we compare the temperatures in the SADs to those of the surrounding plasma. We find that the SADs are hotter than the background, but cooler than the surrounding plasma in most cases, with only 1 out of the 11 SADs examined here having a slightly higher temperature than its surroundings.

  15. Lessons on collisionless reconnection from quantum fluids

    NASA Astrophysics Data System (ADS)

    Narita, Yasuhito; Baumjohann, Wolfgang

    2014-12-01

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

  16. Expansion techniques for collisionless stellar dynamical simulations

    NASA Astrophysics Data System (ADS)

    Meiron, Yohai

    2016-02-01

    We present ETICS, a collisionless N-body code based on two kinds of series expansions of the Poisson equation, implemented for graphics processing units (GPUs). The code is publicly available and can be used as a standalone program or as a library (an AMUSE plugin is included). One of the two expansion methods available is the self-consistent field (SCF) method, which is a Fourier-like expansion of the density field in some basis set; the other is the multipole expansion (MEX) method, which is a Taylor-like expansion of the Green's function. MEX, which has been advocated in the past, has not gained as much popularity as SCF. Both are particle-field methods and optimized for collisionless galactic dynamics, but while SCF is a ``pure'' expansion, MEX is an expansion in just the angular part; thus, MEX is capable of capturing radial structure easily, while SCF needs a large number of radial terms.

  17. Supermagnetosonic Jets behind a Collisionless Quasiparallel Shock

    SciTech Connect

    Hietala, H.; Vainio, R.; Laitinen, T. V.; Vaivads, A.; Andreeova, K.; Palmroth, M.; Pulkkinen, T. I.; Koskinen, H. E. J.; Lucek, E. A.; Reme, H.

    2009-12-11

    The downstream region of a collisionless quasiparallel shock is structured containing bulk flows with high kinetic energy density from a previously unidentified source. We present Cluster multispacecraft measurements of this type of supermagnetosonic jet as well as of a weak secondary shock front within the sheath, that allow us to propose the following generation mechanism for the jets: The local curvature variations inherent to quasiparallel shocks can create fast, deflected jets accompanied by density variations in the downstream region. If the speed of the jet is super(magneto)sonic in the reference frame of the obstacle, a second shock front forms in the sheath closer to the obstacle. Our results can be applied to collisionless quasiparallel shocks in many plasma environments.

  18. Dawn-dusk asymmetries in plasma sheet particle distributions and the average behaviour of magnetotail current systems

    NASA Astrophysics Data System (ADS)

    Walsh, A. P.; Forsyth, C.; Owen, C. J.; Fazakerley, A. N.; Dandouras, I. S.

    2011-12-01

    We present the results of a survey of Cluster PEACE and CIS-CODIF data taken in the 2001-2006 tail seasons, building on the work of Walsh et al. (GRL, 2011). We examine the average pitch angle distributions of protons and electrons in the magnetotail as a function of proton plasma beta, restricted to times when the magnetosphere was exposed to steady (on a 3 hour timescale) IMF conditions and focussing in particular on dawn-dusk asymmetries. We confirm that, on average, the 2 component proton plasma sheet exists duskward of the noon-midnight meridian under steady northward IMF. An associated population of cold electrons is also observed. Dawnward of the noon-midnight meridian there are no significant fluxes of the cold component of protons and much reduced fluxes of the cold electron component, implying transport across the dusk magnetopause is the dominant formation mechanism of the two component plasma sheet for both protons and electrons. Under southward IMF, dawn-dusk asymmetries in the protons are controlled by the Y component of the IMF. For the electrons higher fluxes of high energy, field-aligned, particles are observed at dusk than at dawn. This suggests a link to a duskward offset of the tail neutral line and the preferential observation of substorm-related tail signatures in the premidnight sector. We also consider the relationship between the observed particle populations and the average behaviour of the large-scale magnetotail current systems as revealed by the Curlometer.

  19. Perpendicular diffusion of energetic particles in collisionless plasmas

    SciTech Connect

    Shalchi, A.

    2015-01-15

    A fundamental problem in plasma and astrophysics is the interaction between energetic particles and magnetized plasmas. In the current paper, we focus on particle diffusion across the guide magnetic field. It is shown that the perpendicular diffusion coefficient depends only on the parallel diffusion coefficient and the Kubo number. Therefore, one can find four asymptotic limits depending on the values of these two parameters. These regimes are the quasilinear limit, the Kadomtsev and Pogutse limit, the scaling of Rechester and Rosenbluth, and the scaling found by Zybin and Istomin. In the current article, we focus on the Rechester and Rosenbluth scenario because this was not discovered before in the context of collisionless plasmas. Examples and applications are discussed as well. We show that an energy independent ratio of perpendicular and parallel diffusion coefficients can be found and that this ratio can be very small but also close to unity. This is exactly what one observes in the solar wind.

  20. Perpendicular diffusion of energetic particles in collisionless plasmas

    NASA Astrophysics Data System (ADS)

    Shalchi, A.

    2015-01-01

    A fundamental problem in plasma and astrophysics is the interaction between energetic particles and magnetized plasmas. In the current paper, we focus on particle diffusion across the guide magnetic field. It is shown that the perpendicular diffusion coefficient depends only on the parallel diffusion coefficient and the Kubo number. Therefore, one can find four asymptotic limits depending on the values of these two parameters. These regimes are the quasilinear limit, the Kadomtsev and Pogutse limit, the scaling of Rechester and Rosenbluth, and the scaling found by Zybin and Istomin. In the current article, we focus on the Rechester and Rosenbluth scenario because this was not discovered before in the context of collisionless plasmas. Examples and applications are discussed as well. We show that an energy independent ratio of perpendicular and parallel diffusion coefficients can be found and that this ratio can be very small but also close to unity. This is exactly what one observes in the solar wind.

  1. THE THREE-DIMENSIONAL EVOLUTION OF ION-SCALE CURRENT SHEETS: TEARING AND DRIFT-KINK INSTABILITIES IN THE PRESENCE OF PROTON TEMPERATURE ANISOTROPY

    SciTech Connect

    Gingell, P. W.; Burgess, D.; Matteini, L.

    2015-03-20

    We present the first three-dimensional (3D) hybrid simulations of the evolution of ion-scale current sheets, with an investigation of the role of temperature anisotropy and associated kinetic instabilities on the growth of the tearing instability and particle heating. We confirm the ability of the ion cyclotron and firehose instabilities to enhance or suppress reconnection, respectively. The simulations demonstrate the emergence of persistent 3D structures, including patchy reconnection sites and the fast growth of a narrow-band drift-kink instability, which suppresses reconnection for thin current sheets with weak guide fields. Potential observational signatures of the 3D evolution of solar wind current sheets are also discussed. We conclude that kinetic instabilities, arising from non-Maxwellian ion populations, are significant to the evolution of 3D current sheets, and two-dimensional studies of heating rates by reconnection may therefore over-estimate the ability of thin, ion-scale current sheets to heat the solar wind by reconnection.

  2. The Three-dimensional Evolution of Ion-scale Current Sheets: Tearing and Drift-kink Instabilities in the Presence of Proton Temperature Anisotropy

    NASA Astrophysics Data System (ADS)

    Gingell, P. W.; Burgess, D.; Matteini, L.

    2015-03-01

    We present the first three-dimensional (3D) hybrid simulations of the evolution of ion-scale current sheets, with an investigation of the role of temperature anisotropy and associated kinetic instabilities on the growth of the tearing instability and particle heating. We confirm the ability of the ion cyclotron and firehose instabilities to enhance or suppress reconnection, respectively. The simulations demonstrate the emergence of persistent 3D structures, including patchy reconnection sites and the fast growth of a narrow-band drift-kink instability, which suppresses reconnection for thin current sheets with weak guide fields. Potential observational signatures of the 3D evolution of solar wind current sheets are also discussed. We conclude that kinetic instabilities, arising from non-Maxwellian ion populations, are significant to the evolution of 3D current sheets, and two-dimensional studies of heating rates by reconnection may therefore over-estimate the ability of thin, ion-scale current sheets to heat the solar wind by reconnection.

  3. Dynamic topology and flux rope evolution during non-linear tearing of 3D null point current sheets

    SciTech Connect

    Wyper, P. F. Pontin, D. I.

    2014-10-15

    In this work, the dynamic magnetic field within a tearing-unstable three-dimensional current sheet about a magnetic null point is described in detail. We focus on the evolution of the magnetic null points and flux ropes that are formed during the tearing process. Generally, we find that both magnetic structures are created prolifically within the layer and are non-trivially related. We examine how nulls are created and annihilated during bifurcation processes, and describe how they evolve within the current layer. The type of null bifurcation first observed is associated with the formation of pairs of flux ropes within the current layer. We also find that new nulls form within these flux ropes, both following internal reconnection and as adjacent flux ropes interact. The flux ropes exhibit a complex evolution, driven by a combination of ideal kinking and their interaction with the outflow jets from the main layer. The finite size of the unstable layer also allows us to consider the wider effects of flux rope generation. We find that the unstable current layer acts as a source of torsional magnetohydrodynamic waves and dynamic braiding of magnetic fields. The implications of these results to several areas of heliophysics are discussed.

  4. Electric fields associated with small-scale magnetic holes in the plasma sheet: Evidence for electron currents

    NASA Astrophysics Data System (ADS)

    Goodrich, Katherine A.; Ergun, Robert E.; Stawarz, Julia E.

    2016-06-01

    We report observations of magnetic holes (MHs) in the near-Earth (8 RE to 12 RE) plasma sheet that have physical sizes perpendicular to the magnetic field (B) on the order of the ion Larmor radius (ρi) and, more importantly, have current layers less than ρi in thickness. Small-scale MHs can have >90% depletion in |B| and are commonly associated with the braking of bursty bulk flow events. The generation of MHs is often attributed to magnetohydrodynamic (MHD) instabilities, which requires a size greater than ρi; the depletion in |B| is from an ion current consistent with a pressure gradient. Electric field (E) observations indicate a negative potential inside of small-scale MHs that creates an outward E at the boundary, which drives an E × B electron current in a thin layer. These observations indicate that a Hall electron current is primarily responsible for the depletion of |B| in small-scale magnetic holes, rather than the ion pressure gradient.

  5. Dipolarization, current sheet flapping motion and periodic particle flux enhancements observed during the Galaxy 15 spacecraft anomaly

    NASA Astrophysics Data System (ADS)

    Loto'aniu, Paul; Rodriguez, Juan; Redmon, Robert

    2016-04-01

    On 5 April 2010, the Galaxy 15 spacecraft, orbiting at geosynchronous altitudes experienced an anomaly near local midnight when it stopped responding to any ground commands. Galaxy 15 spacecraft encountered severe plasma conditions while it was in eclipse and during the subsequent anomaly interval and these conditions included a massive magnetic field dipolarization that injected energetic particles from the magnetotail during a substorm. This anomaly was interesting for many reasons including that multiple spacecraft (GOES and THEMIS probes) were well located in the nightside to observe the substorm. At the time of the field line stretching and dipolarization some of the satellites observed magnetic variations together with particle flux enhancements with periodicities of a few minutes. In this study, we detail characteristics of this dipolarization, which was one of the strongest ever observed by a GOES spacecraft, as well as discuss perturbations in the magnetic field and particle fluxes that are indicative of magnetotail current sheet flapping motion.

  6. Lightning as a space-weather hazard: UK thunderstorm activity modulated by the passage of the heliospheric current sheet

    NASA Astrophysics Data System (ADS)

    Owens, M. J.; Scott, C. J.; Bennett, A. J.; Thomas, S. R.; Lockwood, M.; Harrison, R. G.; Lam, M. M.

    2015-11-01

    Lightning flash rates, RL, are modulated by corotating interaction regions (CIRs) and the polarity of the heliospheric magnetic field (HMF) in near-Earth space. As the HMF polarity reverses at the heliospheric current sheet (HCS), typically within a CIR, these phenomena are likely related. In this study, RL is found to be significantly enhanced at the HCS and at 27 days prior/after. The strength of the enhancement depends on the polarity of the HMF reversal at the HCS. Near-Earth solar and galactic energetic particle fluxes are also ordered by HMF polarity, though the variations qualitatively differ from RL, with the main increase occurring prior to the HCS crossing. Thus, the CIR effect on lightning is either the result of compression/amplification of the HMF (and its subsequent interaction with the terrestrial system) or that energetic particle preconditioning of the Earth system prior to the HMF polarity change is central to solar wind lightning coupling mechanism.

  7. DOES THE COMPRESSION OR THE EXPANSION OF A SIMPLE TOPOLOGY POTENTIAL MAGNETIC FIELD LEAD TO THE DEVELOPMENT OF CURRENT SHEETS?

    SciTech Connect

    Aly, J. J.; Amari, T.

    2010-02-01

    Janse and Low have most recently addressed the following question. Consider a cylindrical domain containing a simple topology potential magnetic field threading its lower and upper horizontal faces, and a perfectly conducting plasma. Suppose that this domain is made to slowly contract or expand in the vertical direction, so driving the field into a quasi-static evolution through a series of force-free configurations. Then are these configurations smooth, or do they contain current sheets (CSs)? We reexamine here their three-step argument leading to the conclusion that CSs form most generally. We prove analytically that the field has to evolve through 'topologically untwisted' and 'nonpotential' configurations, thus confirming the first two steps. However, we find the third step-leading to the conclusion that a smooth untwisted force-free field is necessarily potential-to be very disputable.

  8. IMPACT OF TEMPERATURE-DEPENDENT RESISTIVITY AND THERMAL CONDUCTION ON PLASMOID INSTABILITIES IN CURRENT SHEETS IN THE SOLAR CORONA

    SciTech Connect

    Ni Lei; Roussev, Ilia I.; Lin Jun; Ziegler, Udo E-mail: iroussev@ifa.hawaii.edu

    2012-10-10

    In this paper, we investigate, by means of two-dimensional magnetohydrodynamic simulations, the impact of temperature-dependent resistivity and thermal conduction on the development of plasmoid instabilities in reconnecting current sheets in the solar corona. We find that the plasma temperature in the current-sheet region increases with time and it becomes greater than that in the inflow region. As secondary magnetic islands appear, the highest temperature is not always found at the reconnection X-points, but also inside the secondary islands. One of the effects of anisotropic thermal conduction is to decrease the temperature of the reconnecting X-points and transfer the heat into the O-points, the plasmoids, where it gets trapped. In the cases with temperature-dependent magnetic diffusivity, {eta} {approx} T {sup -3/2}, the decrease in plasma temperature at the X-points leads to (1) an increase in the magnetic diffusivity until the characteristic time for magnetic diffusion becomes comparable to that of thermal conduction, (2) an increase in the reconnection rate, and (3) more efficient conversion of magnetic energy into thermal energy and kinetic energy of bulk motions. These results provide further explanation of the rapid release of magnetic energy into heat and kinetic energy seen during flares and coronal mass ejections. In this work, we demonstrate that the consideration of anisotropic thermal conduction and Spitzer-type, temperature-dependent magnetic diffusivity, as in the real solar corona, are crucially important for explaining the occurrence of fast reconnection during solar eruptions.

  9. Time-dependence in relativistic collisionless shocks: theory of the variable

    SciTech Connect

    Spitkovsky, A

    2004-02-05

    We describe results from time-dependent numerical modeling of the collisionless reverse shock terminating the pulsar wind in the Crab Nebula. We treat the upstream relativistic wind as composed of ions and electron-positron plasma embedded in a toroidal magnetic field, flowing radially outward from the pulsar in a sector around the rotational equator. The relativistic cyclotron instability of the ion gyrational orbit downstream of the leading shock in the electron-positron pairs launches outward propagating magnetosonic waves. Because of the fresh supply of ions crossing the shock, this time-dependent process achieves a limit-cycle, in which the waves are launched with periodicity on the order of the ion Larmor time. Compressions in the magnetic field and pair density associated with these waves, as well as their propagation speed, semi-quantitatively reproduce the behavior of the wisp and ring features described in recent observations obtained using the Hubble Space Telescope and the Chandra X-Ray Observatory. By selecting the parameters of the ion orbits to fit the spatial separation of the wisps, we predict the period of time variability of the wisps that is consistent with the data. When coupled with a mechanism for non-thermal acceleration of the pairs, the compressions in the magnetic field and plasma density associated with the optical wisp structure naturally account for the location of X-ray features in the Crab. We also discuss the origin of the high energy ions and their acceleration in the equatorial current sheet of the pulsar wind.

  10. Hybrid numerical model of shock waves in collisionless plasma

    NASA Astrophysics Data System (ADS)

    Vshivkova, L.; Dudnikova, G.; Vshivkov, K.

    2016-10-01

    We present a 2D hybrid numerical plasma model of generation and structure of collisionless shock waves in plasma and ion acceleration on their front considering physical processes in supernova remnant shock precursor. In modeling a shock wave is generated by sending a supersonic flow against a reflecting wall. The consequent interaction between incoming and reflected plasma flows lead to formation of waves, the structure of which depends on a flow velocity. The hybrid approach reduces the computational expenses relative to a fully kinetic one, and on the other hand, permits to model ions with a greater accuracy than the magnetohydrodynamics (MHD) allows. Also, another important advantage of the hybrid approach is the possibility to study the important instabilities on an ion time scale, neglecting the modes associated with electrons. In the current work a new computational scheme where stability condition allows carry out computations on more wide set of computational and physical parameters is presented.

  11. Effects of electron inertia in collisionless magnetic reconnection

    SciTech Connect

    Andrés, Nahuel Gómez, Daniel; Martin, Luis; Dmitruk, Pablo

    2014-07-15

    We present a study of collisionless magnetic reconnection within the framework of full two-fluid MHD for a completely ionized hydrogen plasma, retaining the effects of the Hall current, electron pressure and electron inertia. We performed 2.5D simulations using a pseudo-spectral code with no dissipative effects. We check that the ideal invariants of the problem are conserved down to round-off errors. Our numerical results confirm that the change in the topology of the magnetic field lines is exclusively due to the presence of electron inertia. The computed reconnection rates remain a fair fraction of the Alfvén velocity, which therefore qualifies as fast reconnection.

  12. Collisionless Plasma Modeling in an Arbitrary Potential Energy Distribution

    NASA Technical Reports Server (NTRS)

    Liemohn, M. W.; Khazanov, G. V.

    1997-01-01

    A new technique for calculating a collisionless plasma along a field line is presented. The primary feature of the new model is that it can handle an arbitrary (including nonmonotonic) potential energy distribution. This was one of the limiting constraints on the existing models in this class, and these constraints are generalized for an arbitrary potential energy composition. The formulation for relating current density to the field-aligned potential as well as formulas for density, temperature and energy flux calculations are presented for several distribution functions, ranging from a bi-Lorentzian with a loss cone to an isotropic Maxwellian. A comparison of these results with previous models shows that the formulation reduces.to the earlier models under similar assumptions.

  13. Formability of Al 5xxx Sheet Metals Using Pulsed Current for Various Heat Treatments

    SciTech Connect

    Salandro, Wesley A.; Jones, Joshua J.; McNeal, Timothy A.; Roth, John T.; Hong, Sung Tae; Smith, Mark T.

    2010-10-01

    Previous studies have shown that the presence of a pulsed electrical current, applied during the deformation process of an aluminum specimen, can significantly improve the formability of the aluminum without heating the metal above its maximum operating temperature range. The research herein extends these findings by examining the effect of electrical pulsing on 5052 and 5083 Aluminum Alloys. Two different parameter sets were used while pulsing three different heat treatments (As Is, 398°C, and 510°C) for each of the two aluminum alloys. For this research, the electrical pulsing is applied to the aluminum while the specimens are deformed, without halting the deformation process (a manufacturing technique known as Electrically-Assisted Manufacturing). The analysis focuses on establishing the effect the electrical pulsing has on the aluminum alloy’s various heat treatments by examining the displacement of the material throughout the testing region of dogbone-shaped specimens. The results from this research show that pulsing significantly increases the maximum achievable elongation of the aluminum (when compared to baseline tests conducted without electrical pulsing). Another beneficial effect produced by electrical pulsing is that the engineering flow stress within the material is considerably reduced. The electrical pulses also cause the aluminum to deform non-uniformly, such that the material exhibits a diffuse neck where the minimum deformation occurs near the ends of the specimen (near the clamps) and the maximum deformation occurs near the center of the specimen (where fracture ultimately occurs). This diffuse necking effect is similar to what can be experienced during superplastic deformation. However, when comparing the presence of a diffuse neck in this research, electrical pulsing does not create as significant of a diffuse neck as superplastic deformation. Electrical pulsing has the potential to be more efficient than traditional methods of incremental

  14. New Expression for Collisionless Magnetic Reconnection Rate

    NASA Technical Reports Server (NTRS)

    Klimas, Alexander J.

    2014-01-01

    For 2D, symmetric, anti-parallel, collisionless magnetic reconnection, a new expression for the reconnection rate in the electron diffusion region is introduced. It is shown that this expression can be derived in just a few simple steps from a physically intuitive starting point; the derivation is given in its entirety and the validity of each step is confirmed. The predictions of this expression are compared to the results of several long-duration, open-boundary PIC reconnection simulations to demonstrate excellent agreement.

  15. Evidence for collisionless magnetic reconnection at Mars

    NASA Astrophysics Data System (ADS)

    Eastwood, J. P.; Brain, D. A.; Halekas, J. S.; Drake, J. F.; Phan, T. D.; Øieroset, M.; Mitchell, D. L.; Lin, R. P.; Acuña, M.

    2008-01-01

    Using data from Mars Global Surveyor (MGS) in combination with Particle-In-Cell (PIC) simulations of reconnection, we present the first direct evidence of collisionless magnetic reconnection at Mars. The evidence indicates that the spacecraft passed through the diffusion region where reconnection is initiated and observed the magnetic field signatures of differential electron and ion motion - the Hall magnetic field - that uniquely indicate the reconnection process. These are the first such in-situ reconnection observations at an astronomical body other than the Earth. Reconnection may be the source of Mars' recently discovered auroral activity and the changing boundaries of the closed regions of crustal magnetic field.

  16. Thin-shell instability in collisionless plasma.

    PubMed

    Dieckmann, M E; Ahmed, H; Doria, D; Sarri, G; Walder, R; Folini, D; Bret, A; Ynnerman, A; Borghesi, M

    2015-09-01

    Thin-shell instability is one process which can generate entangled structures in astrophysical plasma on collisional (fluid) scales. It is driven by a spatially varying imbalance between the ram pressure of the inflowing upstream plasma and the downstream's thermal pressure at a nonplanar shock. Here we show by means of a particle-in-cell simulation that an analog process can destabilize a thin shell formed by two interpenetrating, unmagnetized, and collisionless plasma clouds. The amplitude of the shell's spatial modulation grows and saturates after about ten inverse proton plasma frequencies, when the shell consists of connected piecewise linear patches.

  17. Scattering of radiation in collisionless dusty plasmas

    SciTech Connect

    Tolias, P.; Ratynskaia, S.

    2013-04-15

    Scattering of electromagnetic waves in collisionless dusty plasmas is studied in the framework of a multi-component kinetic model. The investigation focuses on the spectral distribution of the scattered radiation. Pronounced dust signatures are identified in the coherent spectrum due to scattering from the shielding cloud around the dust grains, dust acoustic waves, and dust-ion acoustic waves. The magnitude and shape of the scattered signal near these spectral regions are determined with the aid of analytical expressions and its dependence on the dust parameters is investigated. The use of radiation scattering as a potential diagnostic tool for dust detection is discussed.

  18. Cascaded proton acceleration by collisionless electrostatic shock

    NASA Astrophysics Data System (ADS)

    Xu, T. J.; Shen, B. F.; Zhang, X. M.; Yi, L. Q.; Wang, W. P.; Zhang, L. G.; Xu, J. C.; Zhao, X. Y.; Shi, Y.; Liu, C.; Pei, Z. K.

    2015-07-01

    A new scheme for proton acceleration by cascaded collisionless electrostatic shock (CES) is proposed. By irradiating a foil target with a moderate high-intensity laser beam, a stable CES field can be induced, which is employed as the accelerating field for the booster stage of proton acceleration. The mechanism is studied through simulations and theoretical analysis, showing that a 55 MeV seed proton beam can be further accelerated to 265 MeV while keeping a good energy spread. This scheme offers a feasible approach to produce proton beams with energy of hundreds of MeV by existing available high-intensity laser facilities.

  19. Cascaded proton acceleration by collisionless electrostatic shock

    SciTech Connect

    Xu, T. J.; Shen, B. F. E-mail: zhxm@siom.ac.cn; Zhang, X. M. E-mail: zhxm@siom.ac.cn; Yi, L. Q.; Wang, W. P.; Zhang, L. G.; Xu, J. C.; Zhao, X. Y.; Shi, Y.; Liu, C.; Pei, Z. K.

    2015-07-15

    A new scheme for proton acceleration by cascaded collisionless electrostatic shock (CES) is proposed. By irradiating a foil target with a moderate high-intensity laser beam, a stable CES field can be induced, which is employed as the accelerating field for the booster stage of proton acceleration. The mechanism is studied through simulations and theoretical analysis, showing that a 55 MeV seed proton beam can be further accelerated to 265 MeV while keeping a good energy spread. This scheme offers a feasible approach to produce proton beams with energy of hundreds of MeV by existing available high-intensity laser facilities.

  20. Collisionless Relaxation in Non-Neutral Plasmas

    SciTech Connect

    Levin, Yan; Pakter, Renato; Teles, Tarcisio N.

    2008-02-01

    A theoretical framework is presented which allows us to quantitatively predict the final stationary state achieved by a non-neutral plasma during a process of collisionless relaxation. As a specific application, the theory is used to study relaxation of charged-particle beams. It is shown that a fully matched beam relaxes to the Lynden-Bell distribution. However, when a mismatch is present and the beam oscillates, parametric resonances lead to a core-halo phase separation. The approach developed accounts for both the density and the velocity distributions in the final stationary state.

  1. New expression for collisionless magnetic reconnection rate

    SciTech Connect

    Klimas, Alex

    2015-04-15

    For 2D, symmetric, anti-parallel, collisionless magnetic reconnection, new expressions for the reconnection rate in the electron diffusion region are introduced. It is shown that these expressions can be derived in just a few simple steps from a physically intuitive starting point; the derivations are given in their entirety, and the validity of each step is confirmed. The predictions of these expressions are compared to the results of several long-duration, open-boundary particle-in-cell reconnection simulations to demonstrate excellent agreement.

  2. Controlling Influence of Magnetic Field on Solar Wind Outflow: An Investigation using Current Sheet Source Surface Model

    NASA Astrophysics Data System (ADS)

    Poduval, Bala

    2016-05-01

    The Wang and Sheeley empirical relationship between magnetic flux tube expansion (FTE) in the inner corona and the solar wind speed (SWS) observed near the Earth's orbit forms the basis of current solar wind prediction techniques such as WSA/ENLIL. Based on this concept, the Current Sheet Source Surface (CSSS) model, built on a corona in magnetostatic equilibrium incorporating electric currents, has recently been validated for solar wind prediction. We present the initial results of an investigation of the influence of solar magnetic field in determining the solar wind outflow using the CSSS model. We found that there is significant temporal variation in the functional form of FTE--SWS relation and that the accuracy of CSSS predictions are nearly twice better than the PFSS predcitions. We attribute the greater accuracy of CSSS predictions to the model's capability to trace the solar wind sources better than the PFSS model and, perhaps, the treatment of electric currents in the inner corona in the CSSS model.Synoptic maps of coronal magnetic field, similar to the photospheric ones, are still a long way away, though techniques are under development, especially using the Coronal Multi-Channel Polarimeter data. And the near--Sun regions below 0.3 AU remain unexplored until Solar Probe Plus and Solar Orbiter are launched. A well-validated model of the corona capable of providing reliable solar wind conditions in the near-Sun region will be of great use in interpreting the data collected by these spacecraft. The magnetohydrodynamic models such as ENLIL for space weather prediction, require ambient plasma and magnetic field information at their inner boundaries, usually provided by magnetostatic models, such as PFSS, in the absence of sufficient observational data. Our present work is an attempt to provide methods to generate reliable solar wind conditions in the near-Sun region.

  3. Superposed Epoch Analysis of Ring Current Geoeffectiveness Related to Solar Wind and Plasma Sheet Drivers

    NASA Technical Reports Server (NTRS)

    Liemohm, M. W.; Kozyra, J. U.; Thomsen, M. F.; Borovsky, J. E.; Gahurthakurta, Madulika (Technical Monitor)

    2004-01-01

    The goal of that proposal was to examine the relationship between solar wind drivers and ring current dynamics through data analysis and numerical simulations. The data analysis study was a statistical examination (via superposed epoch analyses) of a solar cycle's worth of storm data. Solar wind data, geophysical indices, and geosynchronous plasma data were collected for every time period with Dst< -50 nT from 1989 through 2002, and the storm list now exceeds 400 entries. This work was first conducted by a summer undergraduate student, Mr. John Vann (University of Kansas), with funding from the NSF Research Experience for Undergraduates program. It was then continued by a University of Michigan graduate student, Mr. Jichun Zhang. Mr. Zhang is now in his fourth year at U-M and is progressing very well toward a PhD in space science. His dissertation will be based on his data analysis and modeling efforts using this geomagnetic storm database. The results of the data analysis study have been the focus of several conference presentations, and the first manuscript has just been published. Two additional papers are presently being prepared, one on average (superposed) solar wind features for various storm subsets (e.g., intense storms at solar maximum), and another on geosynchronous plasma features for these same storm subsets. The latter result was highlighted by the TR&T program director in his presentation at the COSPAR meeting this summer.

  4. Landmark Report Analyzes Current State of U.S. Offshore Wind Industry (Fact Sheet)

    SciTech Connect

    Not Available

    2011-09-01

    New report assesses offshore wind industry, offshore wind resource, technology challenges, economics, permitting procedures, and potential risks and benefits. The National Renewable Energy Laboratory (NREL) recently published a new report that analyzes the current state of the offshore wind energy industry, Large-Scale Offshore Wind Power in the United States. It provides a broad understanding of the offshore wind resource, and details the associated technology challenges, economics, permitting procedures, and potential risks and benefits of developing this clean, domestic, renewable resource. The United States possesses large and accessible offshore wind energy resources. The availability of these strong offshore winds close to major U.S. coastal cities significantly reduces power transmission issues. The report estimates that U.S. offshore winds have a gross potential generating capacity four times greater than the nation's present electric capacity. According to the report, developing the offshore wind resource along U.S. coastlines and in the Great Lakes would help the nation: (1) Achieve 20% of its electricity from wind by 2030 - Offshore wind could supply 54 gigawatts of wind capacity to the nation's electrical grid, increasing energy security, reducing air and water pollution, and stimulating the domestic economy. (2) Provide clean power to its coastal demand centers - Wind power emits no carbon dioxide (CO2) and there are plentiful winds off the coasts of 26 states. (3) Revitalize its manufacturing sector - Building 54 GW of offshore wind energy facilities would generate an estimated $200 billion in new economic activity, and create more than 43,000 permanent, well-paid technical jobs in manufacturing, construction, engineering, operations and maintenance. NREL's report concludes that the development of the nation's offshore wind resources can provide many potential benefits, and with effective research, policies, and commitment, offshore wind energy can

  5. Full particle-in-cell simulations of kinetic equilibria and the role of the initial current sheet on steady asymmetric magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Dargent, J.; Aunai, N.; Belmont, G.; Dorville, N.; Lavraud, B.; Hesse, M.

    2016-06-01

    > Tangential current sheets are ubiquitous in space plasmas and yet hard to describe with a kinetic equilibrium. In this paper, we use a semi-analytical model, the BAS model, which provides a steady ion distribution function for a tangential asymmetric current sheet and we prove that an ion kinetic equilibrium produced by this model remains steady in a fully kinetic particle-in-cell simulation even if the electron distribution function does not satisfy the time independent Vlasov equation. We then apply this equilibrium to look at the dependence of magnetic reconnection simulations on their initial conditions. We show that, as the current sheet evolves from a symmetric to an asymmetric upstream plasma, the reconnection rate is impacted and the X line and the electron flow stagnation point separate from one another and start to drift. For the simulated systems, we investigate the overall evolution of the reconnection process via the classical signatures discussed in the literature and searched in the Magnetospheric MultiScale data. We show that they seem robust and do not depend on the specific details of the internal structure of the initial current sheet.

  6. Use of a spread sheet to calculate the current-density distribution produced in human and rat models by low-frequency electric fields.

    PubMed

    Hart, F X

    1990-01-01

    The current-density distribution produced inside irregularly shaped, homogeneous human and rat models by low-frequency electric fields is obtained by a two-stage finite-difference procedure. In the first stage the model is assumed to be equipotential. Laplace's equation is solved by iteration in the external region to obtain the capacitive-current densities at the model's surface elements. These values then provide the boundary conditions for the second-stage relaxation solution, which yields the internal current-density distribution. Calculations were performed with the Excel spread-sheet program on a Macintosh-II microcomputer. A spread sheet is a two-dimensional array of cells. Each cell of the sheet can represent a square element of space. Equations relating the values of the cells can represent the relationships between the potentials in the corresponding spatial elements. Extension to three dimensions is readily made. Good agreement was obtained with current densities measured on human models with both, one, or no legs grounded and on rat models in four different grounding configurations. The results also compared well with predictions of more sophisticated numerical analyses. Spread sheets can provide an inexpensive and relatively simple means to perform good, approximate dosimetric calculations on irregularly shaped objects.

  7. The collisionless magnetoviscous-thermal instability

    SciTech Connect

    Islam, Tanim

    2014-05-20

    It is likely that nearly all central galactic massive and supermassive black holes are nonradiative: their accretion luminosities are orders of magnitude below what can be explained by efficient black hole accretion within their ambient environments. These objects, of which Sagittarius A* is the best-known example, are also dilute (mildly collisional to highly collisionless) and optically thin. In order for accretion to occur, magnetohydrodynamic (MHD) instabilities must develop that not only transport angular momentum, but also gravitational energy generated through matter infall, outward. A class of new magnetohydrodynamical fluid instabilities—the magnetoviscous-thermal instability (MVTI)—was found to transport angular momentum and energy along magnetic field lines through large (fluid) viscosities and thermal conductivities. This paper describes the analog to the MVTI, the collisionless MVTI (CMVTI), that similarly transports energy and angular momentum outward, expected to be important in describing the flow properties of hot, dilute, and radiatively inefficient accretion flows around black holes. We construct a local equilibrium for MHD stability analysis in this differentially rotating disk. We then find and characterize specific instabilities expected to be important in describing their flow properties, and show their qualitative similarities to instabilities derived using the fluid formalism. We conclude with further work needed in modeling this class of accretion flow.

  8. Nonlinear Gyroviscous Force in a Collisionless Plasma

    SciTech Connect

    Belova, E.V.

    2001-05-23

    Nonlinear gyroviscous forces in a collisionless plasma with temperature variations are calculated from the gyrofluid moments of the gyrokinetic Vlasov equation. The low-frequency gyrokinetic ordering and electrostatic perturbations are assumed, and an additional finite Larmor radius (FLR) expansion is performed. This approach leads naturally to an expression for the gyroviscous force in terms of the gyrocenter distribution function, thus including all resonant effects, and represents a systematic FLR expansion in a general form (no assumption of any closure is made). The expression for the gyroviscous force is also calculated in terms of the particle-fluid moments by making the transformation from the gyrocenter to particle coordinates. The calculated expression represents a modification of the Braginskii gyroviscosity for a collisionless plasma with nonuniform temperature. It is compared with previous calculations based on the traditional fluid approach. As a byproduct of the gyroviscosity calculations, we derive a set of nonlinear reduced gyrofluid (and a corresponding set of particle-fluid) moment equations with FLR corrections, which exhibit a generalized form of the ''gyroviscous cancellation.''

  9. Properties of a large-scale flux rope and current sheet region on the dayside of Mars: MGS MAG/ER and MEX ASPERA-3 ELS observations

    NASA Astrophysics Data System (ADS)

    Soobiah, Yasir I. J.; Wild, James A.; Beharrell, Mathew J.; Barabash, Stas; Lillis, Robert J.; Mitchell, David L.; Coates, Andrew J.; Winningham, J. David; Frahm, Rudy A.

    2014-11-01

    We present dual spacecraft observations by MGS MAG/ER and MEX ASPERA-3 ELS of a large-scale magnetic flux rope on the dayside of Mars that occurs in close proximity to the crustal magnetic fields and a dayside current sheet region. A current sheet (including the large-scale flux rope) was observed on repeated MGS orbits when the draped solar wind magnetic field present in the ionosphere had a +By component (in MSO). Minimum Variance Analysis (MVA) of the large-scale flux rope and two current sheet crossings that occur after show a common peak in magnetic field along the intermediate variance direction, indicating the normal component of a reconnecting current sheet. All repeated orbits demonstrated evidence of a plasma boundary by the decrease in electron differential flux above 100 eV when moving into regions dominated by the crustal magnetic field, and coincided with the measured magnetic field strength being double the undisturbed crustal magnetic field. We argue this forms evidence of magnetic reconnection between crustal magnetic fields and draped solar wind magnetic field (from ionosphere or magnetosheath) at a "mini-magnetopause" type boundary on the dayside of Mars. Similar electron pitch angle distributions observed during the large-scale flux rope, current sheet crossings, and regions of radial crustal magnetic field, suggest these regions share a common magnetic field topology for the trapping of magnetosheath particles on open crustal magnetic fields on the dayside of Mars. As such, indicates a trapping quadrupole magnetic field exist either at the magnetic reconnection X-line region or where open crustal magnetic fields meet oppositely directed solar wind magnetic field. At a time when the draped solar wind magnetic field present in the ionosphere was weaker in strength, the current sheet crossing was observed over an extended region of 2000 km. The extended current sheet demonstrated properties of a hot diamagnetic region and features of a mirror mode

  10. Effect of plasma-β on the onset of plasmoid instability in Sweet-Parker current sheets

    NASA Astrophysics Data System (ADS)

    Baty, H.; Baty

    2014-10-01

    A numerical study of magnetic reconnection in two-dimensional resistive magnetohydrodynamics for Sweet-Parker current sheets that are subject to plasmoid instability is carried out. The effect of the initial upstream plasma-β on the critical Lundquist number Sc for the onset of plasmoid instability is studied. Our results indicate a weak dependence, with a value of Sc ~= 1.5 × 104 in the limit of zero β, and a value of Sc ~= 1 × 104 in the opposite high β regime (β >> 1). A similar dependence was previously obtained (Ni et al. 2012 Phys. Plasm. 19, 072902), but with a somewhat much larger variation, that can be largely attributed to the different configuration setup used in their study, and also to the definition of the Lundquist number. This conclusion does not depend significantly on the equilibrium used, i.e. both initial configurations with either plasma density or temperature spatial variations lead to very similar results. Finally, we show that the inner plasmoid structure appears as an under-dense hotted magnetic island, with a local temperature increase that is noticeably strengthened for low β cases.

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

    SciTech Connect

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

    2010-10-10

    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.

  12. Tracing the dark matter sheet in phase space

    NASA Astrophysics Data System (ADS)

    Abel, Tom; Hahn, Oliver; Kaehler, Ralf

    2012-11-01

    The primordial velocity dispersion of dark matter is small compared to the velocities attained during structure formation. The initial density distribution is close to uniform, and it occupies an initial sheet in phase space that is single valued in velocity space. Because of gravitational forces, this 3D manifold evolves in phase space without ever tearing, conserving phase-space volume and preserving the connectivity of nearby points. N-body simulations already follow the motion of this sheet in phase space. This fact can be used to extract full fine-grained phase-space structure information from existing cosmological N-body simulations. Particles are considered as the vertices of an unstructured 3D mesh moving in 6D phase space. On this mesh, mass density and momentum are uniquely defined. We show how to obtain the space density of the fluid, detect caustics and count the number of streams as well as their individual contributions to any point in configuration space. We calculate the bulk velocity, local velocity dispersions and densities from the sheet - all without averaging over control volumes. This gives a wealth of new information about dark matter fluid flow which had previously been thought of as inaccessible to N-body simulations. We outline how this mapping may be used to create new accurate collisionless fluid simulation codes that may be able to overcome the sparse sampling and unphysical two-body effects that plague current N-body techniques.

  13. National Renewable Energy Laboratory (NREL) Reports Increase in Durability and Reliability for Current Generation Fuel Cell Buses (Fact Sheet)

    SciTech Connect

    Not Available

    2010-11-01

    This fact sheet describes NREL's accomplishments in evaluating the durability and reliability of fuel cell buses being demonstrated in transit service. Work was performed by the Hydrogen Technology Validation team in the Hydrogen Technologies and Systems Center.

  14. Evidence for Collisionless Magnetic Reconnection at Mars

    NASA Astrophysics Data System (ADS)

    Brain, D.; Eastwood, J.; Halekas, J.; Drake, J.; Phan, T.; Oieroset, M.; Mitchell, D.; Lin, R.; Acuna, M.

    2007-12-01

    Magnetic reconnection is a fundamental plasma process that enables the rapid conversion of magnetic to particle energy and is important in astrophysics as well as solar, space and planetary physics. Using data from the Mars Global Surveyor (MGS) spacecraft in combination with simulations of reconnection, we present the first direct evidence of collisionless magnetic reconnection at Mars. The evidence indicates that the spacecraft passed through the diffusion region where reconnection is initiated and observed the magnetic field signatures of differential electron and ion motion that uniquely indicate the reconnection process. These are the first such in- situ reconnection observations at an astronomical body other than the Earth. Reconnection may be the source of Mars" recently discovered auroral activity and the changing boundaries of the closed regions of crustal magnetic field.

  15. Collisionless Dynamics and the Cosmic Web

    NASA Astrophysics Data System (ADS)

    Hahn, Oliver

    2016-10-01

    I review the nature of three-dimensional collapse in the Zeldovich approximation, how it relates to the underlying nature of the three-dimensional Lagrangian manifold and naturally gives rise to a hierarchical structure formation scenario that progresses through collapse from voids to pancakes, filaments and then halos. I then discuss how variations of the Zeldovich approximation (based on the gravitational or the velocity potential) have been used to define classifications of the cosmic large-scale structure into dynamically distinct parts. Finally, I turn to recent efforts to devise new approaches relying on tessellations of the Lagrangian manifold to follow the fine-grained dynamics of the dark matter fluid into the highly non-linear regime and both extract the maximum amount of information from existing simulations as well as devise new simulation techniques for cold collisionless dynamics.

  16. Weak collisionless shocks in laser-plasmas

    NASA Astrophysics Data System (ADS)

    Cairns, R. A.; Bingham, R.; Trines, R. G. M.; Norreys, P.

    2015-04-01

    We obtain a theory describing laminar shock-like structures in a collisionless plasma and examine the parameter limits, in terms of the ion sound Mach number and the electron/ion temperature ratio, within which these structures exist. The essential feature is the inclusion of finite ion temperature with the result that some ions are reflected from a potential ramp. This destroys the symmetry between upstream and downstream regions that would otherwise give the well-known ion solitary wave solution. We have shown earlier (Cairns et al 2014 Phys. Plasmas 21 022112) that such structures may be relevant to problems such as the existence of strong, localized electric fields observed in laser compressed pellets and laser acceleration of ions. Here we present results on the way in which these structures may produce species separation in fusion targets and suggest that it may be possible to use shock ion acceleration for fast ignition.

  17. Kink-mode oscillations of the magnetotail current sheet driven by quasi-continuous reconnection during a steady magnetospheric convection: Geotail and THEMIS conjunction

    NASA Astrophysics Data System (ADS)

    Hasegawa, H.; Shinohara, I.; Nagai, T.; Hoshino, M.; Saito, Y.; Angelopoulos, V.; Teramoto, M.; Higashimori, K.

    2015-12-01

    We present in situ evidence for MHD-scale kink-mode waves propagating earthward in the Earth's magnetotail. The event occurred on 11 October 2014 when the Geotail spacecraft, situated at the GSM position (-26, 9, 0) Re, observed earthward reconnection jets almost continuously for a few hours under stably southward interplanetary magnetic field conditions. The reconnection jets had a speed of ~700 km/s, comparable to the lobe Alfven speed, and concurred with quasi-periodic crossings of the tail current sheet with a period of 2-3 min. Two of the THEMIS spacecraft, located in the pre-midnight sector at X ~ -10 Re, observed no significant flows, and the cross-polar cap potential estimated from SuperDARN remained more than 50 kV and roughly constant, signatures expected for a steady magnetospheric convection (SMC) interval. The Grad-Shafranov reconstruction of the oscillatory current sheet indicates that kink-mode waves propagated roughly earthward, with a wavelength of ~15 Re and amplitude of order 1 Re. The ions observed off the center of the tail current sheet consisted of field-aligned ion beams and cold lobe ions, characteristic of the plasma sheet boundary layer, which led to parallel ion temperature being higher than the perpendicular temperature. We interpret the observed kink-mode waves as being due to the streaming kink instability (SKI) excited in the reconnection jet and in the presence of temperature anisotropy. Since the SKI can generate Alfvénic waves or turbulence, the observed field fluctuations may be an energy source for auroral activities during SMC intervals. Our observations show that the tail plasma sheet can be dynamic even under a globally steady magnetospheric condition.

  18. The microphysics of collisionless shock waves

    NASA Astrophysics Data System (ADS)

    Marcowith, A.; Bret, A.; Bykov, A.; Dieckman, M. E.; O'C Drury, L.; Lembège, B.; Lemoine, M.; Morlino, G.; Murphy, G.; Pelletier, G.; Plotnikov, I.; Reville, B.; Riquelme, M.; Sironi, L.; Stockem Novo, A.

    2016-04-01

    Collisionless shocks, that is shocks mediated by electromagnetic processes, are customary in space physics and in astrophysics. They are to be found in a great variety of objects and environments: magnetospheric and heliospheric shocks, supernova remnants, pulsar winds and their nebulæ, active galactic nuclei, gamma-ray bursts and clusters of galaxies shock waves. Collisionless shock microphysics enters at different stages of shock formation, shock dynamics and particle energization and/or acceleration. It turns out that the shock phenomenon is a multi-scale non-linear problem in time and space. It is complexified by the impact due to high-energy cosmic rays in astrophysical environments. This review adresses the physics of shock formation, shock dynamics and particle acceleration based on a close examination of available multi-wavelength or in situ observations, analytical and numerical developments. A particular emphasis is made on the different instabilities triggered during the shock formation and in association with particle acceleration processes with regards to the properties of the background upstream medium. It appears that among the most important parameters the background magnetic field through the magnetization and its obliquity is the dominant one. The shock velocity that can reach relativistic speeds has also a strong impact over the development of the micro-instabilities and the fate of particle acceleration. Recent developments of laboratory shock experiments has started to bring some new insights in the physics of space plasma and astrophysical shock waves. A special section is dedicated to new laser plasma experiments probing shock physics.

  19. The microphysics of collisionless shock waves.

    PubMed

    Marcowith, A; Bret, A; Bykov, A; Dieckman, M E; Drury, L O'C; Lembège, B; Lemoine, M; Morlino, G; Murphy, G; Pelletier, G; Plotnikov, I; Reville, B; Riquelme, M; Sironi, L; Novo, A Stockem

    2016-04-01

    Collisionless shocks, that is shocks mediated by electromagnetic processes, are customary in space physics and in astrophysics. They are to be found in a great variety of objects and environments: magnetospheric and heliospheric shocks, supernova remnants, pulsar winds and their nebulæ, active galactic nuclei, gamma-ray bursts and clusters of galaxies shock waves. Collisionless shock microphysics enters at different stages of shock formation, shock dynamics and particle energization and/or acceleration. It turns out that the shock phenomenon is a multi-scale non-linear problem in time and space. It is complexified by the impact due to high-energy cosmic rays in astrophysical environments. This review adresses the physics of shock formation, shock dynamics and particle acceleration based on a close examination of available multi-wavelength or in situ observations, analytical and numerical developments. A particular emphasis is made on the different instabilities triggered during the shock formation and in association with particle acceleration processes with regards to the properties of the background upstream medium. It appears that among the most important parameters the background magnetic field through the magnetization and its obliquity is the dominant one. The shock velocity that can reach relativistic speeds has also a strong impact over the development of the micro-instabilities and the fate of particle acceleration. Recent developments of laboratory shock experiments has started to bring some new insights in the physics of space plasma and astrophysical shock waves. A special section is dedicated to new laser plasma experiments probing shock physics. PMID:27007555

  20. Oscillation of Current Sheets in the Wake of a Flux Rope Eruption Observed by the Solar Dynamics Observatory

    NASA Astrophysics Data System (ADS)

    Li, L. P.; Zhang, J.; Su, J. T.; Liu, Y.

    2016-10-01

    An erupting flux rope (FR) draws its overlying coronal loops upward, causing a coronal mass ejection. The legs of the overlying loops with opposite polarities are driven together. Current sheets (CSs) form, and magnetic reconnection, producing underneath flare arcades, occurs in the CSs. Employing Solar Dynamic Observatory/Atmospheric Imaging Assembly images, we study a FR eruption on 2015 April 23, and for the first time report the oscillation of CSs underneath the erupting FR. The FR is observed in all AIA extreme-ultraviolet passbands, indicating that it has both hot and warm components. Several bright CSs, connecting the erupting FR and the underneath flare arcades, are observed only in hotter AIA channels, e.g., 131 and 94 Å. Using the differential emission measure (EM) analysis, we find that both the temperature and the EM of CSs temporally increase rapidly, reach the peaks, and then decrease slowly. A significant delay between the increases of the temperature and the EM is detected. The temperature, EM, and density spatially decrease along the CSs with increasing heights. For a well-developed CS, the temperature (EM) decreases from 9.6 MK (8 × 1028 cm‑5) to 6.2 MK (5 × 1027 cm‑5) in 52 Mm. Along the CSs, dark supra-arcade downflows (SADs) are observed, and one of them separates a CS into two. While flowing sunward, the speeds of the SADs decrease. The CSs oscillate with a period of 11 minutes, an amplitude of 1.5 Mm, and a phase speed of 200 ± 30 km s‑1. One of the oscillations lasts for more than 2 hr. These oscillations represent fast-propagating magnetoacoustic kink waves.

  1. Cosmic Ray Intensity Variations near the Heliospheric Current Sheet during the Minimum of Solar Cycles 20 - 23

    NASA Astrophysics Data System (ADS)

    Aslam, O. P. M.; Badruddin, B.

    2016-07-01

    We study the Galactic Cosmic Ray (GCR) intensity variation, with respect to the Heliospheric Current Sheet (HCS) crossings of the Earth during four solar cycle minima including the peculiar solar cycle 23 deep minimum. As the Sun rotates, the HCS crosses the earth at least once during each solar rotation (≈ 27 days). We perform the analysis of cosmic ray-intensity data as well as solar wind plasma and field parameters data with respect to the crossings of the HCS. We consider those crossings with at least five continuous days with the same polarity (positive or negative) before and after the HCS crossings. Special attention is given during solar minimum conditions as these periods are almost free from large transient decreases and increases in cosmic ray intensity. The solar minima during the last three solar cycles 20, 21, 22 (1976 - 1977, 1986 - 1987, 1996 - 1997) and the recent unusual deep minimum between solar cycles 23 and 24 (2008 - 2009) fall during alternate solar polarity epochs (A<0 and A>0). Solar wind high speed streams (HSS) are frequent during solar minima, we perform analysis of cosmic ray as well as interplanetary plasma and field parameters during solar minimum periods with respect to the arrival time of HSS also. In this way, we study the GCR intensity modulation during different solar minima and different solar polarity epochs with reference to (i) HCS crossing dates and (ii) arrival time of HSS. These results are compared with predictions of simulation results based on modulation theories in low solar activity conditions but different polarity epochs of the heliosphere. Special emphasis is placed to discuss about the GCR modulation during the recent unusual deep minimum between solar cycle 23 and 24, in terms of convection/diffusion versus drift dominated modulation models.

  2. CMEs FROM AR 10365: MORPHOLOGY AND PHYSICAL PARAMETERS OF THE EJECTIONS AND OF THE ASSOCIATED CURRENT SHEET

    SciTech Connect

    Schettino, G.; Romoli, M.; Poletto, G.

    2010-01-10

    We study the evolution and physical parameters of three consecutive coronal mass ejections (CMEs) that occurred at the west limb of the Sun on 2003 June 2 at 00:30, 08:54, 16:08 UT, respectively. The Large Angle and Spectrometric Coronagraph Experiment (LASCO) CME catalog shows that the CMEs entered the C2 field of view with position angles within a 5 deg. interval. This suggests a common origin for the ejections, to be identified with the magnetic system associated with the active region that lies below the CMEs. The close proximity in time and source location of the events prompted us to analyze LASCO white light data and Ultraviolet Coronagraph Spectrometer (UVCS) spectra with the aim of identifying similarities and differences among the three CMEs. It turns out that two of them display the typical three-part structure, while no conclusion can be drawn about the morphology of the third ejection. The CMEs plasma is 'cool', i.e., electron temperatures in the CMEs front are of the order of 2 x 10{sup 5} K, with no significant variation between different events. However, ejection speeds vary by a factor of approx1.5 between consecutive events and electron densities (more precisely emission measures) by a factor of approx6 between the first CME and the second and third CMEs. In the aftermath of all events, we found evidence of current sheets (CSs) both in LASCO and UVCS. We give here the CS physical parameters (electron temperature, density, and kinetic temperature) and follow, in one of the events, their temporal evolution over a 6 hr time interval. A discussion of our results, in the framework of previous findings, concludes the paper.

  3. Theory of a cylindrical probe in a collisionless magnetoplasma

    NASA Technical Reports Server (NTRS)

    Laframboise, J. G.; Rubinstein, J.

    1976-01-01

    A theory is presented for a cylindrical electrostatic probe in a collisionless plasma in the case where the probe axis is inclined at an angle to a uniform magnetic field. The theory is applicable to electron collection, and under more restrictive conditions, to ion collection. For a probe at space potential, the theory is exact in the limit where probe radius is much less than Debye length. At attracting probe potentials, the theory yields an upper bound and an adiabatic limit for current collection. At repelling probe potentials, it provides a lower bound. The theory is valid if the ratios of probe radius to Debye length and probe radius to mean gyroradius are not simultaneously large enough to produce extrema in the probe sheath potential. The numerical current calculations are based on the approximation that particle orbits are helices near the probe, together with the use of kinetic theory to relate velocity distributions near the probe to those far from it. Probe characteristics are presented for inclination angles from 0 to 90 deg and for probe-radius mean-gyroradius ratios from 0.1 to infinity. For an angle of 0 deg, the end-effect current is calculated separately.

  4. Diamagnetic boundary layers - A kinetic theory. [for collisionless magnetized plasmas

    NASA Technical Reports Server (NTRS)

    Lemaire, J.; Burlaga, L. F.

    1976-01-01

    A kinetic theory is presented for boundary layers associated with MHD tangential 'discontinuities' in a collisionless magnetized plasma, such as those observed in the solar wind. The theory consists of finding self-consistent solutions of Vlasov's equation and Maxwell's equation for stationary one-dimensional boundary layers separating two Maxwellian plasma states. Layers in which the current is carried by electrons are found to have a thickness of the order of a few electron gyroradii, but the drift speed of the current-carrying electrons is found to exceed the Alfven speed, and accordingly such layers are not stable. Several types of layers in which the current is carried by protons are discussed; in particular, cases are considered in which the magnetic-field intensity, direction, or both, changed across the layer. In every case, the thickness was of the order of a few proton gyroradii, and the field changed smoothly, although the characteristics depended somewhat on the boundary conditions. The drift speed was always less than the Alfven speed, consistent with stability of such structures. These results are consistent with observations of boundary layers in the solar wind near 1 AU.

  5. Kinetic model for the collisionless sheath of a collisional plasma

    NASA Astrophysics Data System (ADS)

    Tang, Xian-Zhu; Guo, Zehua

    2016-08-01

    Collisional plasmas typically have mean-free-path still much greater than the Debye length, so the sheath is mostly collisionless. Once the plasma density, temperature, and flow are specified at the sheath entrance, the profile variation of electron and ion density, temperature, flow speed, and conductive heat fluxes inside the sheath is set by collisionless dynamics, and can be predicted by an analytical kinetic model distribution. These predictions are contrasted here with direct kinetic simulations, showing good agreement.

  6. Global Scale-Invariant Dissipation in Collisionless Plasma Turbulence

    SciTech Connect

    Kiyani, K. H.; Chapman, S. C.; Khotyaintsev, Yu. V.; Dunlop, M. W.; Sahraoui, F.

    2009-08-14

    A higher-order multiscale analysis of the dissipation range of collisionless plasma turbulence is presented using in situ high-frequency magnetic field measurements from the Cluster spacecraft in a stationary interval of fast ambient solar wind. The observations, spanning five decades in temporal scales, show a crossover from multifractal intermittent turbulence in the inertial range to non-Gaussian monoscaling in the dissipation range. This presents a strong observational constraint on theories of dissipation mechanisms in turbulent collisionless plasmas.

  7. Measuring Collisionless Damping in Heliospheric Plasmas using Field-Particle Correlations

    NASA Astrophysics Data System (ADS)

    Klein, K. G.; Howes, G. G.

    2016-08-01

    An innovative field-particle correlation technique is proposed that uses single-point measurements of the electromagnetic fields and particle velocity distribution functions to investigate the net transfer of energy from fields to particles associated with the collisionless damping of turbulent fluctuations in weakly collisional plasmas, such as the solar wind. In addition to providing a direct estimate of the local rate of energy transfer between fields and particles, it provides vital new information about the distribution of that energy transfer in velocity space. This velocity-space signature can potentially be used to identify the dominant collisionless mechanism responsible for the damping of turbulent fluctuations in the solar wind. The application of this novel field-particle correlation technique is illustrated using the simplified case of the Landau damping of Langmuir waves in an electrostatic 1D-1V Vlasov-Poisson plasma, showing that the procedure both estimates the local rate of energy transfer from the electrostatic field to the electrons and indicates the resonant nature of this interaction. Modifications of the technique to enable single-point spacecraft measurements of fields and particles to diagnose the collisionless damping of turbulent fluctuations in the solar wind are discussed, yielding a method with the potential to transform our ability to maximize the scientific return from current and upcoming spacecraft missions, such as the Magnetospheric Multiscale (MMS) and Solar Probe Plus missions.

  8. Measuring Collisionless Damping in Heliospheric Plasmas using Field–Particle Correlations

    NASA Astrophysics Data System (ADS)

    Klein, K. G.; Howes, G. G.

    2016-08-01

    An innovative field–particle correlation technique is proposed that uses single-point measurements of the electromagnetic fields and particle velocity distribution functions to investigate the net transfer of energy from fields to particles associated with the collisionless damping of turbulent fluctuations in weakly collisional plasmas, such as the solar wind. In addition to providing a direct estimate of the local rate of energy transfer between fields and particles, it provides vital new information about the distribution of that energy transfer in velocity space. This velocity-space signature can potentially be used to identify the dominant collisionless mechanism responsible for the damping of turbulent fluctuations in the solar wind. The application of this novel field–particle correlation technique is illustrated using the simplified case of the Landau damping of Langmuir waves in an electrostatic 1D-1V Vlasov–Poisson plasma, showing that the procedure both estimates the local rate of energy transfer from the electrostatic field to the electrons and indicates the resonant nature of this interaction. Modifications of the technique to enable single-point spacecraft measurements of fields and particles to diagnose the collisionless damping of turbulent fluctuations in the solar wind are discussed, yielding a method with the potential to transform our ability to maximize the scientific return from current and upcoming spacecraft missions, such as the Magnetospheric Multiscale (MMS) and Solar Probe Plus missions.

  9. Flexible heat-flow sensing sheets based on the longitudinal spin Seebeck effect using one-dimensional spin-current conducting films

    NASA Astrophysics Data System (ADS)

    Kirihara, Akihiro; Kondo, Koichi; Ishida, Masahiko; Ihara, Kazuki; Iwasaki, Yuma; Someya, Hiroko; Matsuba, Asuka; Uchida, Ken-Ichi; Saitoh, Eiji; Yamamoto, Naoharu; Kohmoto, Shigeru; Murakami, Tomoo

    2016-03-01

    Heat-flow sensing is expected to be an important technological component of smart thermal management in the future. Conventionally, the thermoelectric (TE) conversion technique, which is based on the Seebeck effect, has been used to measure a heat flow by converting the flow into electric voltage. However, for ubiquitous heat-flow visualization, thin and flexible sensors with extremely low thermal resistance are highly desired. Recently, another type of TE effect, the longitudinal spin Seebeck effect (LSSE), has aroused great interest because the LSSE potentially offers favourable features for TE applications such as simple thin-film device structures. Here we demonstrate an LSSE-based flexible TE sheet that is especially suitable for a heat-flow sensing application. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as “ferrite plating”. The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors. This newly developed thin TE sheet may be attached to differently shaped heat sources without obstructing an innate heat flux, paving the way to versatile heat-flow measurements and management.

  10. Flexible heat-flow sensing sheets based on the longitudinal spin Seebeck effect using one-dimensional spin-current conducting films.

    PubMed

    Kirihara, Akihiro; Kondo, Koichi; Ishida, Masahiko; Ihara, Kazuki; Iwasaki, Yuma; Someya, Hiroko; Matsuba, Asuka; Uchida, Ken-ichi; Saitoh, Eiji; Yamamoto, Naoharu; Kohmoto, Shigeru; Murakami, Tomoo

    2016-03-15

    Heat-flow sensing is expected to be an important technological component of smart thermal management in the future. Conventionally, the thermoelectric (TE) conversion technique, which is based on the Seebeck effect, has been used to measure a heat flow by converting the flow into electric voltage. However, for ubiquitous heat-flow visualization, thin and flexible sensors with extremely low thermal resistance are highly desired. Recently, another type of TE effect, the longitudinal spin Seebeck effect (LSSE), has aroused great interest because the LSSE potentially offers favourable features for TE applications such as simple thin-film device structures. Here we demonstrate an LSSE-based flexible TE sheet that is especially suitable for a heat-flow sensing application. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as "ferrite plating". The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors. This newly developed thin TE sheet may be attached to differently shaped heat sources without obstructing an innate heat flux, paving the way to versatile heat-flow measurements and management.

  11. Flexible heat-flow sensing sheets based on the longitudinal spin Seebeck effect using one-dimensional spin-current conducting films.

    PubMed

    Kirihara, Akihiro; Kondo, Koichi; Ishida, Masahiko; Ihara, Kazuki; Iwasaki, Yuma; Someya, Hiroko; Matsuba, Asuka; Uchida, Ken-ichi; Saitoh, Eiji; Yamamoto, Naoharu; Kohmoto, Shigeru; Murakami, Tomoo

    2016-01-01

    Heat-flow sensing is expected to be an important technological component of smart thermal management in the future. Conventionally, the thermoelectric (TE) conversion technique, which is based on the Seebeck effect, has been used to measure a heat flow by converting the flow into electric voltage. However, for ubiquitous heat-flow visualization, thin and flexible sensors with extremely low thermal resistance are highly desired. Recently, another type of TE effect, the longitudinal spin Seebeck effect (LSSE), has aroused great interest because the LSSE potentially offers favourable features for TE applications such as simple thin-film device structures. Here we demonstrate an LSSE-based flexible TE sheet that is especially suitable for a heat-flow sensing application. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as "ferrite plating". The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors. This newly developed thin TE sheet may be attached to differently shaped heat sources without obstructing an innate heat flux, paving the way to versatile heat-flow measurements and management. PMID:26975208

  12. Flexible heat-flow sensing sheets based on the longitudinal spin Seebeck effect using one-dimensional spin-current conducting films

    PubMed Central

    Kirihara, Akihiro; Kondo, Koichi; Ishida, Masahiko; Ihara, Kazuki; Iwasaki, Yuma; Someya, Hiroko; Matsuba, Asuka; Uchida, Ken-ichi; Saitoh, Eiji; Yamamoto, Naoharu; Kohmoto, Shigeru; Murakami, Tomoo

    2016-01-01

    Heat-flow sensing is expected to be an important technological component of smart thermal management in the future. Conventionally, the thermoelectric (TE) conversion technique, which is based on the Seebeck effect, has been used to measure a heat flow by converting the flow into electric voltage. However, for ubiquitous heat-flow visualization, thin and flexible sensors with extremely low thermal resistance are highly desired. Recently, another type of TE effect, the longitudinal spin Seebeck effect (LSSE), has aroused great interest because the LSSE potentially offers favourable features for TE applications such as simple thin-film device structures. Here we demonstrate an LSSE-based flexible TE sheet that is especially suitable for a heat-flow sensing application. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4 film which was formed on a flexible plastic sheet using a spray-coating method known as “ferrite plating”. The experimental results suggest that the ferrite-plated film, which has a columnar crystal structure aligned perpendicular to the film plane, functions as a unique one-dimensional spin-current conductor suitable for bendable LSSE-based sensors. This newly developed thin TE sheet may be attached to differently shaped heat sources without obstructing an innate heat flux, paving the way to versatile heat-flow measurements and management. PMID:26975208

  13. Global, quasi-steady dynamics of the distant solar wind 2: Deformation of the heliospheric current sheet

    NASA Technical Reports Server (NTRS)

    Pizzo, V. J.

    1994-01-01

    A three-dimensional (3-D) magnetohydrodynamic (MHD) numerical model is used to trace global deformations of the heliospheric current sheet (HCS) caused by large-scale dynamical interactions associated with corotating solar wind flows. Configurations incorporating the tilted-dipole geometry are investigated out past 30 AU for a variety of dipole tilt angles, alpha. Inclusion of the full, 3-D interplanetary dynamics allows north-south displacements and the east-west warping of the HCS by advective corotational effects to be accurately assessed for the first time. It is found that large-scale spatial correlations between velocity and density imposed at the coronal source (i.e., the geometric arrangement whereby regions of high-speed low-density material lying adjacent to areas of slow, dense flow interact obliquely under the influence of solar rotation) result in a distinctive pattern of deformation of the HCS. For an alpha = 30 deg tilted-dipole example, it is shown that typical zonal variations in radial velocity lead to significant folding of the HCS within about 5 AU of the Sun. By 10 AU, additional sharp bends appear near the latitudinal extremes of the HCS surface, where it is overtaken by shock fronts driven by 3-D corotating interaction regions (CIRs). Moreover, the model suggests that inside about 20 AU, major plasma structures are systematically organized, about the HCS, such that the greatest concentrations of material and magnetic field (the centroids of the 3-D CIR structures) are coincident with the folded crests of the HCS (near heliographic latitudes lambda = +/- alpha). Thus, in these circumstances many of the more interesting dynamical features inconveniently lie well away from the heliographic equator. At larger heliocentric distances, where neighboring CIRs begin to interact strongly, the warping of the HCS abates dramatically and the association between folds in the HCS and major field and density concentrations is weakened and ultimately breaks

  14. Hybrid simulations of whistler waves generation and current closure by a pulsed tether in the ionosphere

    NASA Technical Reports Server (NTRS)

    Chang, C. L.; Lipatov, A. S.; Drobot, A. T.; Papadopoulos, K.; Satya-Narayana, P.

    1994-01-01

    The dynamic response of a magnetized collisionless plasma to an externally driven, finite size, sudden switch-on current source across the magnetic field has been studied using a two dimensional hybrid code. It was found that the predominant plasma response was the excitation of whistler waves and the formation of current closure by induced currents in the plasma. The results show that the current closure path consists of: (a) two antiparallel field-aligned current channels at the end of the imposed current sheet; and (b) a cross-field current region connecting these channels. The formation of the current closure path occured in the whistler timescale much shorter than that of MHD and the closure region expanded continuously in time. The current closure process was accompanied by significant energy loss due to whistler radiation.

  15. Effects of Pulse Current on Transient Liquid Phase (TLP) Diffusion Bonding of SiCp/2024Al Composites Sheet Using Mixed Al, Cu, and Ti Powder Interlayer

    NASA Astrophysics Data System (ADS)

    Wang, Bo; Jiang, Shaosong; Zhang, Kaifeng

    2012-09-01

    The effects of pulse current on transient liquid phase (TLP) diffusion bonding of SiCp/2024Al composites sheet were investigated at 853 K (580 °C) using a mixed slurry of Al, Cu, and Ti powder interlayer. The process parameters were as follows: the pulse current density of 1.15 × 102 A/mm2, the original pressure of 0.5 MPa, the vacuum of 1.3 × 10-3 Pa, and the bonding time from 15 to 60 minutes. Moreover, the bonding mechanism in correlation with the microstructural and mechanical properties variation was analyzed.

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

    NASA Technical Reports Server (NTRS)

    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.

  17. Dispersion discontinuities of strong collisionless shocks

    NASA Technical Reports Server (NTRS)

    Coroniti, F. V.

    1970-01-01

    Linear fluid equations are used to estimate wave train properties of strong collisionless shocks. Fast shocks exhibit several dispersion changes with increasing Mach number. For perpendicular propagation into a finite-beta plasma, an ion cyclotron radius trailing wave train exists only for (M sub F)2 is smaller than 2. Oblique fast shocks have a leading ion inertia wave train if M sub A is smaller than root of M(+)/M(-) cos theta/2 and a trailing electron inertia train if M sub A is greater than root of M(+)/M(-) cos theta/2. If the downstream sound speed exceeds the flow speed, linear wave theory predicts a trailing ion acoustic structure which probably resides within the magnetic shock. For a turbulent shock model in which an effective electron-ion collision frequency exceeds the lower hybrid frequency, ions decouple from the magnetic field; the shock wave train now trails with electron inertia and electron gyroradius lengths. Comparisons of this turbulent model and observations on the earth's bow shock are made.

  18. Turbulent dynamo in a collisionless plasma.

    PubMed

    Rincon, François; Califano, Francesco; Schekochihin, Alexander A; Valentini, Francesco

    2016-04-12

    Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas. PMID:27035981

  19. Turbulent dynamo in a collisionless plasma

    PubMed Central

    Rincon, François; Califano, Francesco; Schekochihin, Alexander A.; Valentini, Francesco

    2016-01-01

    Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas. PMID:27035981

  20. Expansion techniques for collisionless stellar dynamical simulations

    SciTech Connect

    Meiron, Yohai; Li, Baile; Holley-Bockelmann, Kelly; Spurzem, Rainer

    2014-09-10

    We present graphics processing unit (GPU) implementations of two fast force calculation methods based on series expansions of the Poisson equation. One method is the self-consistent field (SCF) method, which is a Fourier-like expansion of the density field in some basis set; the other method is the multipole expansion (MEX) method, which is a Taylor-like expansion of the Green's function. MEX, which has been advocated in the past, has not gained as much popularity as SCF. Both are particle-field methods and optimized for collisionless galactic dynamics, but while SCF is a 'pure' expansion, MEX is an expansion in just the angular part; thus, MEX is capable of capturing radial structure easily, while SCF needs a large number of radial terms. We show that despite the expansion bias, these methods are more accurate than direct techniques for the same number of particles. The performance of our GPU code, which we call ETICS, is profiled and compared to a CPU implementation. On the tested GPU hardware, a full force calculation for one million particles took ∼0.1 s (depending on expansion cutoff), making simulations with as many as 10{sup 8} particles fast for a comparatively small number of nodes.

  1. Turbulent dynamo in a collisionless plasma

    NASA Astrophysics Data System (ADS)

    Rincon, François; Califano, Francesco; Schekochihin, Alexander A.; Valentini, Francesco

    2016-04-01

    Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas.

  2. Turbulent dynamo in a collisionless plasma.

    PubMed

    Rincon, François; Califano, Francesco; Schekochihin, Alexander A; Valentini, Francesco

    2016-04-12

    Magnetic fields pervade the entire universe and affect the formation and evolution of astrophysical systems from cosmological to planetary scales. The generation and dynamical amplification of extragalactic magnetic fields through cosmic times (up to microgauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions, and on scales of at least tens of kiloparsecs) are major puzzles largely unconstrained by observations. A dynamo effect converting kinetic flow energy into magnetic energy is often invoked in that context; however, extragalactic plasmas are weakly collisional (as opposed to magnetohydrodynamic fluids), and whether magnetic field growth and sustainment through an efficient turbulent dynamo instability are possible in such plasmas is not established. Fully kinetic numerical simulations of the Vlasov equation in a 6D-phase space necessary to answer this question have, until recently, remained beyond computational capabilities. Here, we show by means of such simulations that magnetic field amplification by dynamo instability does occur in a stochastically driven, nonrelativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that the dynamo self-accelerates and becomes entangled with kinetic instabilities as magnetization increases. The results suggest that such a plasma dynamo may be realizable in laboratory experiments, support the idea that intracluster medium turbulence may have significantly contributed to the amplification of cluster magnetic fields up to near-equipartition levels on a timescale shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas.

  3. Landau Damping and Anomalous Skin Effect in Low-pressure Gas Discharges: Self-consistent Treatment of Collisionless Heating

    SciTech Connect

    Igor D. Kaganovich; Oleg V. Polomarov; Constantine E. Theodosiou

    2004-01-30

    In low-pressure discharges, where the electron mean free path is larger or comparable with the discharge length, the electron dynamics is essentially nonlocal. Moreover, the electron energy distribution function (EEDF) deviates considerably from a Maxwellian. Therefore, an accurate kinetic description of the low-pressure discharges requires knowledge of the nonlocal conductivity operator and calculation of the non-Maxwellian EEDF. The previous treatments made use of simplifying assumptions: a uniform density profile and a Maxwellian EEDF. In the present study a self-consistent system of equations for the kinetic description of nonlocal, nonuniform, nearly collisionless plasmas of low-pressure discharges is reported. It consists of the nonlocal conductivity operator and the averaged kinetic equation for calculation of the non-Maxwellian EEDF. This system was applied to the calculation of collisionless heating in capacitively and inductively coupled plasmas. In particular, the importance of accounting for the nonuniform plasma density profile for computing the current density profile and the EEDF is demonstrated. The enhancement of collisionless heating due to the bounce resonance between the electron motion in the potential well and the external radio-frequency electric field is investigated. It is shown that a nonlinear and self-consistent treatment is necessary for the correct description of collisionless heating.

  4. COSMIC-RAY-INDUCED FILAMENTATION INSTABILITY IN COLLISIONLESS SHOCKS

    SciTech Connect

    Caprioli, D.; Spitkovsky, A.

    2013-03-01

    We used unprecedentedly large two-dimensional and three-dimensional hybrid (kinetic ions-fluid electrons) simulations of non-relativistic collisionless strong shocks in order to investigate the effects of self-consistently accelerated ions on the overall shock dynamics. The current driven by suprathermal particles streaming ahead of the shock excites modes transverse to the background magnetic field. The Lorentz force induced by these self-amplified fields tends to excavate tubular, underdense, magnetic-field-depleted cavities that are advected with the fluid and perturb the shock surface, triggering downstream turbulent motions. These motions further amplify the magnetic field, up to factors of 50-100 in knot-like structures. Once downstream, the cavities tend to be filled by hot plasma plumes that compress and stretch the magnetic fields in elongated filaments; this effect is particularly evident if the shock propagates parallel to the background field. Highly magnetized knots and filaments may provide explanations for the rapid X-ray variability observed in RX J1713.7-3946 and for the regular pattern of X-ray bright stripes detected in Tycho's supernova remnant.

  5. Physics of collisionless reconnection in a stressed X-point collapse

    SciTech Connect

    Tsiklauri, D.; Haruki, T.

    2008-10-15

    Recently, magnetic reconnection during collisionless, stressed, X-point collapse was studied using kinetic, 2.5-dimensional, fully electromagnetic, relativistic particle-in-cell numerical code [D. Tsiklauri and T. Haruki, Phys. Plasmas 14, 112905 (2007)]. Here we finalize the investigation of this topic by addressing key outstanding physical questions: (i) Which term in the generalized Ohm's law is responsible for the generation of the reconnection electric field? (ii) How does the time evolution of the reconnected flux vary with the ion-electron mass ratio? (iii) What is the exact energy budget of the reconnection process; i.e., in which proportion initial (mostly magnetic) energy is converted into other forms of energy? (iv) Are there any anisotropies in the velocity distribution of the accelerated particles? The following points have been established. (i) A reconnection electric field is generated by the electron pressure tensor off-diagonal terms, resembling to the case of tearing unstable Harris current sheet studied by the GEM reconnection challenge. (ii) For m{sub i}/m{sub e}>>1, the time evolution of the reconnected flux is independent of ion-electron mass ratio. In addition, in the case of m{sub i}/m{sub e}=1, we show that reconnection proceeds slowly as the Hall term is zero; when m{sub i}/m{sub e}>>1 (i.e., the Hall term is nonzero) reconnection is fast and we conjecture that this is due to magnetic field being frozen into electron fluid, which moves significantly faster than ion fluid. (iii) Within one Alfven time, somewhat less than half ({approx}40%) of the initial total (roughly magnetic) energy is converted into the kinetic energy of electrons, and somewhat more than half ({approx}60%) into kinetic energy of ions (similar to solar flare observations). (iv) In the strongly stressed X-point case, in about one Alfven time, a full isotropy in all three spatial directions of the velocity distribution is seen for superthermal electrons (also commensurate

  6. Two Case Studies of Stochastic Transport: Anomalous Transport in Two Drift Waves, and Collisionless Reconnection.

    NASA Astrophysics Data System (ADS)

    Doxas, Isidoros

    1988-12-01

    One-wave vec E times vec B motion in a slab geometry is described by a hamiltonian with a phase space composed of an infinite square lattice of counterrotating rolls. When a small amount of a second wave is added, the hamiltonian becomes time dependent, the energy of a single particle is no longer conserved, and all energy values are accessible to the particle. Most of the contribution to the change in the energy of a particle that moves close to the separatrix from the vicinity of one X-point to the next, is shown to be imparted to the particle during a short interaction time around the midpoint of the particle's trajectory. The magnitude of the change in energy is calculated, and particle motion near the separatrix is reduced to the standard map. Collisionless magnetic reconnection is studied in the context of a reversed field with a small normal component b, modelling the geomagnetic tail. The magnetic moment is adiabatically conserved far from the reversal layer, but it changes in small increments Deltamu as the particle crosses the layer. The magnitude of Deltamu is calculated and the analytic expression is found to agree well with numerical calculations for epsilon < 1, where epsilon is the small parameter in the adiabatic expansion. A test particle code is used to study the time evolution of ensembles of particles placed in the model magnetic field. The code gives ion temperatures of a few keV and earthward drift velocities of 400 -900 km/s in the Plasma Sheet Boundary Layer, in good quantitative agreement with observed values. The numerical value of the height-integrated in-phase current < jcdot E> seems to be in qualitative agreement with theoretical values based on a decorrelation time equal to half a gyroperiod around the normal field, while a decorrelation time equal to 1/kv, where k is the wavenumber of the tearing mode, seems to give the wrong scaling. Finally the system seems to always tend to the same (qualitatively) state around the time the

  7. Collisionless inter-species energy transfer and turbulent heating in drift wave turbulence

    SciTech Connect

    Zhao, L.; Diamond, P. H.

    2012-08-15

    We reconsider the classic problems of calculating 'turbulent heating' and collisionless inter-species transfer of energy in drift wave turbulence. These issues are of interest for low collisionality, electron heated plasmas, such as ITER, where collisionless energy transfer from electrons to ions is likely to be significant. From the wave Poynting theorem at steady state, a volume integral over an annulus r{sub 1}=-S{sub r}|{sub r{sub 1}{sup r{sub 2}}}{ne}0. Here S{sub r} is the wave energy density flux in the radial direction. Thus, a wave energy flux differential across an annular region indeed gives rise to a net heating, in contrast to previous predictions. This heating is related to the Reynolds work by the zonal flow, since S{sub r} is directly linked to the zonal flow drive. In addition to net heating, there is inter-species heat transfer. For collisionless electron drift waves, the total turbulent energy source for collisionless heat transfer is due to quasilinear electron cooling. Subsequent quasilinear ion heating occurs through linear ion Landau damping. In addition, perpendicular heating via ion polarization currents contributes to ion heating. Since at steady state, Reynolds work of the turbulence on the zonal flow must balance zonal flow frictional damping ({approx}{nu}{sub ii}{sup 2}{approx}|(e{phi}(tilde sign)/T)|{sup 4}), it is no surprise that zonal flow friction appears as an important channel for ion heating. This process of energy transfer via zonal flow has not previously been accounted for in analyses of energy transfer. As an application, we compare the rate of turbulent energy transfer in a low collisionality plasma with the rate of the energy transfer by collisions. The result shows that the collisionless turbulent energy transfer is a significant energy coupling process for ITER plasma.

  8. Driving Weibel-mediated collisionless shocks with NIF

    NASA Astrophysics Data System (ADS)

    Fiuza, Frederico; Spitkovsky, Anatoly; Ryutov, Dmitri; Ross, Steven; Huntington, Channing; Mori, Warren; Silva, Luis; Park, Hye-Sook; Remington, Bruce

    2013-10-01

    Collisionless shocks are ubiquitous in astrophysical plasmas and are known to be responsible for particle acceleration; however, the microphysics underlying shock formation and particle acceleration is not yet fully understood. High-power lasers are bringing the study of collisionless shocks into the realm of laboratory experiments. In particular, the National Ignition Facility allows for the generation of collisionless plasma flows that are hundreds of ion skin-depths long and provides ideal conditions for the study of Weibel-mediated shocks. We have performed detailed 2D and 3D particle-in-cell simulations with OSIRIS to explore the laboratory conditions associated with counter-streaming high-velocity plasma flows for realistic profiles. We have modeled the proton radiography of the interaction for self-consistent fields and determined the experimental signatures of the generation of Weibel B-fields and collisionless shocks. We will discuss the importance of modeling realistic ion to electron mass ratios and of taking into account Biermann battery B-fields. Our work identifies the conditions for the formation of collisionless shocks in laboratory, both in unmagnetized and magnetized scenarios, showing the possibility of observing for the first time Weibel-mediated shocks in near future experiments.

  9. Shearing Box Simulations of the MRI in a Collisionless Plasma

    SciTech Connect

    Sharma, Prateek; Hammett, Gregory, W.; Quataert, Eliot; Stone, James, M.

    2005-08-31

    We describe local shearing box simulations of turbulence driven by the magnetorotational instability (MRI) in a collisionless plasma. Collisionless effects may be important in radiatively inefficient accretion flows, such as near the black hole in the Galactic Center. The MHD version of ZEUS is modified to evolve an anisotropic pressure tensor. A fluid closure approximation is used to calculate heat conduction along magnetic field lines. The anisotropic pressure tensor provides a qualitatively new mechanism for transporting angular momentum in accretion flows (in addition to the Maxwell and Reynolds stresses). We estimate limits on the pressure anisotropy due to pitch angle scattering by kinetic instabilities. Such instabilities provide an effective ''collision'' rate in a collisionless plasma and lead to more MHD-like dynamics. We find that the MRI leads to efficient growth of the magnetic field in a collisionless plasma, with saturation amplitudes comparable to those in MHD. In the saturated state, the anisotropic stress is comparable to the Maxwell stress, implying that the rate of angular momentum transport may be moderately enhanced in a collisionless plasma.

  10. Collisionless Plasma Turbulence: Insights from Magnetohydrodynamic and Hall Magnetohydrodynamic Simulations and Observations of the Earth's Magnetosphere

    NASA Astrophysics Data System (ADS)

    Stawarz, Julia E.

    Turbulence is a ubiquitous phenomenon that occurs throughout the universe, in both neutral fluids and plasmas. For collisionless plasmas, kinetic effects, which alter the nonlinear dynamics and result in small-scale dissipation, are still not well understood in the context of turbulence. This work uses direct numerical simulations (DNS) and observations of Earth's magnetosphere to study plasma turbulence. Long-time relaxation in magnetohydrodynamic (MHD) turbulence is examined using DNS with particular focus on the role of magnetic and cross helicity and symmetries of the initial configurations. When strong symmetries are absent or broken through perturbations, flows evolve towards states predicted by statistical mechanics with an energy minimization principle, which features two main regimes; one magnetic helicity dominated and one with quasi-equipartition of kinetic and magnetic energy. The role of the Hall effect, which contributes to the dynamics of collisionless plasmas, is also explored numerically. At scales below the ion inertial length, a transition to a magnetically dominated state, associated with advection becoming subdominant to dissipation, occurs. Real-space current, vorticity, and electric fields are examined. Strong current structures are associated with alignment between the current and magnetic field, which may be important in collisionless plasmas where field-aligned currents can be unstable. Turbulence within bursty bulk flow braking events, thought to be associated with near-Earth magnetotail reconnection, are then studied using the THEMIS spacecraft. It is proposed that strong field-aligned currents associated with turbulent intermittency destabilize into double layers, providing a collisionless dissipation mechanism for the turbulence. Plasma waves may also radiate from the region, removing energy from the turbulence and potentially depositing it in the aurora. Finally, evidence for turbulence in the Kelvin-Helmholtz instability (KHI) on the

  11. Rubella - Fact Sheet for Parents

    MedlinePlus

    ... this page: About CDC.gov . Redirect for the Rubella fact sheet page. The current fact sheet can ... http://www.cdc.gov/vaccines/parents/diseases/child/rubella.html Print page Share Compartir File Formats Help: ...

  12. A new approach to the linear theory of single-species tearing in two-dimensional quasi-neutral sheets

    NASA Technical Reports Server (NTRS)

    Brittnacher, M.; Quest, K. B.; Karimabadi, H.

    1995-01-01

    We have developed the linear theory of collisionless ion tearing in a two-dimensional magnetotail equilibrium for a single resonant species. We have solved the normal mode problem for tearing instability by an algorithm that employs particle-in-cell simulation to calculate the orbit integrals in the Maxwell-Vlasov eigenmode equation. The results of our single-species tearing analysis can be applied to ion tearing where electron effects are not included. We have calculated the tearing growth rate as a function of the magnetic field component B(sub n) normal to the current sheet for thick and thin current sheets, and we show that marginal stability occurs when the normal gyrofrequency Omega(sub n) is comparable to the Harris neutral sheet growth rate. A cross-tail B(sub y) component has little effect on the growth rate for B(sub y) approximately = B(sub n). Even in the limit B(sub y) much greater than B(sub n), the mode is strongly stabilized by B(sub n). We report than random pitch angle scattering can overcome the stabilizing effect of B(sub n) and drive the growth rate up toward the Harris neutral sheet (B(sub n) = 0) value when the pitch angle diffusion rate is comparable to Omega(sub n).

  13. ICPP: Collisionless shock and supernova remnant simulation experiments on VULCAN.

    NASA Astrophysics Data System (ADS)

    Woolsey, Nigel C.

    2000-10-01

    The VULCAN laser at the Central Laser Facility is used for laboratory-based simulations of collisionless shocks. One of the most difficult aspects of collisionless shock behaviour, the role of the magnetic field, is to be tested directly against experiment. Preliminary experiments to generate strong magnetic fields using a laser-driven mm-scale Helmholtz coil, and the formation of collisionless colliding plasmas using two counter-streaming exploding foil plasmas will be discussed. We consider the scaling of the hydrodynamics and magnetic field of the these experiments to those in supernova remnants (SNR) impacting the interstellar medium (ISM). This is achieved by ensuring the experiment and the SNR-ISM exhibit similar values of key dimensionless parameters. Work supported in part by EPSRC, CLF Direct Access, CEC-ERB FMR XCT 980168, Euratom and the UK DTI.

  14. Low Frequency Waves at and Upstream of Collisionless Shocks

    NASA Astrophysics Data System (ADS)

    Wilson, L. B.

    2016-02-01

    This chapter focuses on the range of low frequency electromagnetic modes observed at and upstream of collisionless shocks in the heliosphere. It discusses a specific class of whistler mode wave observed immediately upstream of collisionless shock ramps, called a whistler precursor. Though these modes have been (and are often) observed upstream of quasi-parallel shocks, the authors limit their discussion to those observed upstream of quasi-perpendicular shocks. The chapter discusses the various ion velocity distributions observed at and upstream of collisionless shocks. It also introduces some terminology and relevant instabilities for ion foreshock waves. The chapter discusses the most common ultra-low frequency (ULF) wave types, their properties, and their free energy sources. It discusses modes that are mostly Alfvénic (i.e., mostly transverse but can be compressive) in nature.

  15. In situ detection of collisionless reconnection in the Earth's magnetotail.

    PubMed

    Oieroset, M; Phan, T D; Fujimoto, M; Lin, R P; Lepping, R P

    2001-07-26

    Magnetic reconnection is the process by which magnetic field lines of opposite polarity reconfigure to a lower-energy state, with the release of magnetic energy to the surroundings. Reconnection at the Earth's dayside magnetopause and in the magnetotail allows the solar wind into the magnetosphere. It begins in a small 'diffusion region', where a kink in the newly reconnected lines produces jets of plasma away from the region. Although plasma jets from reconnection have previously been reported, the physical processes that underlie jet formation have remained poorly understood because of the scarcity of in situ observations of the minuscule diffusion region. Theoretically, both resistive and collisionless processes can initiate reconnection, but which process dominates in the magnetosphere is still debated. Here we report the serendipitous encounter of the Wind spacecraft with an active reconnection diffusion region, in which are detected key processes predicted by models of collisionless reconnection. The data therefore demonstrate that collisionless reconnection occurs in the magnetotail.

  16. Multiscale dynamics based on kinetic simulation of collisionless magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Fujimoto, Keizo; Takamoto, Makoto

    2016-07-01

    Magnetic reconnection is a natural energy converter which allows explosive energy release of the magnetic field energy into plasma kinetic energy. The reconnection processes inherently involve multi-scale process. The breaking of the field lines takes place predominantly in a small region called the diffusion region formed near the x-line, while the fast plasma jets resulting from reconnection extend to a distance far beyond the ion kinetic scales from the x-line. There has been a significant gap in understanding of macro-scale and micro-scale processes. The macro-scale model of reconnection has been developed using the magnetohydrodynamics (MHD) equations, while the micro-scale processes around the x-line have been based on kinetic equations including the ion and electron inertia. The problem is that these two kinds of model have significant discrepancies. It has been believed without any guarantee that the microscopic model near the x-line would connect to the macroscopic model far downstream of the x-line. In order to bridge the gap between the macro and micro-scale processes, we have performed large-scale particle-in-cell simulations with the adaptive mesh refinement. The simulation results suggest that the microscopic processes around the x-line do not connect to the previous MHD model even in the region far downstream of the x-line. The slow mode shocks and the associated plasma acceleration do not appear at the exhaust boundary of kinetic reconnection. Instead, the ions are accelerated due to the Speiser motion in the current layer extending to a distance beyond the kinetic scales. The different acceleration mechanisms between the ions and electrons lead to the Hall current system in broad area of the exhaust. Therefore, the previous MHD model could be inappropriate for collisionless magnetic reconnection. Ref. K. Fujimoto & M. Takamoto, Phys. Plasmas, 23, 012903 (2016).

  17. PARTICLE ACCELERATION DURING MAGNETOROTATIONAL INSTABILITY IN A COLLISIONLESS ACCRETION DISK

    SciTech Connect

    Hoshino, Masahiro

    2013-08-20

    Particle acceleration during the magnetorotational instability (MRI) in a collisionless accretion disk was investigated by using a particle-in-cell simulation. We discuss the important role that magnetic reconnection plays not only on the saturation of MRI but also on the relativistic particle generation. The plasma pressure anisotropy of p > p{sub ||} induced by the action of MRI dynamo leads to rapid growth in magnetic reconnection, resulting in the fast generation of nonthermal particles with a hard power-law spectrum. This efficient particle acceleration mechanism involved in a collisionless accretion disk may be a possible model to explain the origin of high-energy particles observed around massive black holes.

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

    SciTech Connect

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

    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.

  19. Resistive Magnetohydrodynamic Simulations of Fast Reconnection in Thin Current Sheets: Analysis of the Linear and Nonlinear Stages of the "Ideal" Tearing Mode

    NASA Astrophysics Data System (ADS)

    Landi, S.; Del Zanna, L.; Papini, E.; Pucci, F.; Velli, M.

    2015-12-01

    Thin current sheets are known to be unstable to tearing and even super-tearing modes, leading to explosive reconnection events as required to explain the rapid release of magnetic energy in astrophysical plasmas (solar flares, magnetar bursts, dissipation in pulsar winds). Here we study by means of resistive, compressible MHD simulations the behavior of current sheets whose inverse aspect ratio scales with the Lundquist number S as S-1/3, known to give rise to fast, ideal reconnection, with an evolution and growth that are independent of S. In the linear phase we retrieve the expected eigenmodes and the growth rate, which can be as high as γ ≈ 0.6 τA-1, where τA is the ideal Alfvénic time set by the macroscopic scales. The nonlinear stages are characterized by the coalescence of magnetic islands and by secondary reconnection events, obeying the same critical scaling with the local S, leading to the production and ejection of plasmoids on increasingly shorter timescales. Preliminary simulations of the ideal tearing mode are presented also for magnetically dominated plasmas, in the relativistic MHD regime.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

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

    SciTech Connect

    Khabarova, O.; Zank, G. P.; Li, G.; Roux, J. A. le; Webb, G. M.; Dosch, A.; Malandraki, O. E.

    2015-08-01

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

  2. Small-scale Magnetic Islands in the Solar Wind and Their Role in Particle Acceleration. I. Dynamics of Magnetic Islands Near the Heliospheric Current Sheet

    NASA Astrophysics Data System (ADS)

    Khabarova, O.; Zank, G. P.; Li, G.; le Roux, J. A.; Webb, G. M.; Dosch, A.; Malandraki, O. E.

    2015-08-01

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

  3. Collisionless encounters and the origin of the lunar inclination.

    PubMed

    Pahlevan, Kaveh; Morbidelli, Alessandro

    2015-11-26

    The Moon is generally thought to have formed from the debris ejected by the impact of a planet-sized object with the proto-Earth towards the end of planetary accretion. Models of the impact process predict that the lunar material was disaggregated into a circumplanetary disk and that lunar accretion subsequently placed the Moon in a near-equatorial orbit. Forward integration of the lunar orbit from this initial state predicts a modern inclination at least an order of magnitude smaller than the lunar value--a long-standing discrepancy known as the lunar inclination problem. Here we show that the modern lunar orbit provides a sensitive record of gravitational interactions with Earth-crossing planetesimals that were not yet accreted at the time of the Moon-forming event. The currently observed lunar orbit can naturally be reproduced via interaction with a small quantity of mass (corresponding to 0.0075-0.015 Earth masses eventually accreted to the Earth) carried by a few bodies, consistent with the constraints and models of late accretion. Although the encounter process has a stochastic element, the observed value of the lunar inclination is among the most likely outcomes for a wide range of parameters. The excitation of the lunar orbit is most readily reproduced via collisionless encounters of planetesimals with the Earth-Moon system with strong dissipation of tidal energy on the early Earth. This mechanism obviates the need for previously proposed (but idealized) excitation mechanisms, places the Moon-forming event in the context of the formation of Earth, and constrains the pristineness of the dynamical state of the Earth-Moon system. PMID:26607544

  4. Collisionless encounters and the origin of the lunar inclination.

    PubMed

    Pahlevan, Kaveh; Morbidelli, Alessandro

    2015-11-26

    The Moon is generally thought to have formed from the debris ejected by the impact of a planet-sized object with the proto-Earth towards the end of planetary accretion. Models of the impact process predict that the lunar material was disaggregated into a circumplanetary disk and that lunar accretion subsequently placed the Moon in a near-equatorial orbit. Forward integration of the lunar orbit from this initial state predicts a modern inclination at least an order of magnitude smaller than the lunar value--a long-standing discrepancy known as the lunar inclination problem. Here we show that the modern lunar orbit provides a sensitive record of gravitational interactions with Earth-crossing planetesimals that were not yet accreted at the time of the Moon-forming event. The currently observed lunar orbit can naturally be reproduced via interaction with a small quantity of mass (corresponding to 0.0075-0.015 Earth masses eventually accreted to the Earth) carried by a few bodies, consistent with the constraints and models of late accretion. Although the encounter process has a stochastic element, the observed value of the lunar inclination is among the most likely outcomes for a wide range of parameters. The excitation of the lunar orbit is most readily reproduced via collisionless encounters of planetesimals with the Earth-Moon system with strong dissipation of tidal energy on the early Earth. This mechanism obviates the need for previously proposed (but idealized) excitation mechanisms, places the Moon-forming event in the context of the formation of Earth, and constrains the pristineness of the dynamical state of the Earth-Moon system.

  5. Coupled electron and ion nonlinear oscillations in a collisionless plasma

    SciTech Connect

    Karimov, A. R.

    2013-05-15

    Dynamics of coupled electrostatic electron and ion nonlinear oscillations in a collisionless plasma is studied with reference to a kinetic description. Proceeding from the exact solution of Vlasov-Maxwell equations written as a function of linear functions in the electron and ion velocities, we arrive at the two coupled nonlinear equations which describe the evolution of the system.

  6. Hydrodynamics of Collisionless Boltzmann Equation for a Highly Flattened Galaxy

    NASA Astrophysics Data System (ADS)

    Aoki, S.

    The collisionless Boltzmann equation is studied in order to be connected with hydrodynamic equations. Each of the later equations can be obtained by taking a moment of the former equation. The difficulty against the system of moment equations, called closure problem, can be overtaken by a trick of neglecting the terms of higher order moments under small-pressure assumption.

  7. Temporal variations in a four-sheet field-aligned current system and associated aurorae as observed during a Polar-ground magnetic conjunction in the midmorning sector

    NASA Astrophysics Data System (ADS)

    Farrugia, C. J.; Sandholt, P. E.; Maynard, N. C.; Torbert, R. B.; Ober, D. M.

    2003-06-01

    We relate measurements of temporarily varying field-aligned current systems (FACs) and their associated plasmas made by the Polar spacecraft at midmorning local times and likewise temporarily varying aurorae observed from Svalbard, Norway, when the magnetic footprint of the spacecraft passed across the field-of-view of the ground instruments on 3 December 1997. We combine the in situ observations of plasma and magnetic and electric fields with meridian scanning photometry and all-sky imagery from the ground site. The interplanetary magnetic field (IMF) pointed strongly east (By ≫ 0) and generally south. Descending from ˜7.5 to ˜5.5 RE and heading south, Polar traversed a four-sheet current system: a twin-sheet cusp current system C1-C2, spanning 80.6°-77.7° invariant latitudes (ILT), and then the traditional regions 1 (R1) and 2 (R2) currents, extending from 77.7° to 73.3° ILT. A convection reversal separated the C1-C2 from the R1-R2 FACs. Currents C1 and R2 flow out of the ionosphere, while C2 and R1 flow into the ionosphere. Within C1, Polar observed six bursts of ions of typically magnetosheath energies (≤2 keV) repeating every ˜5 min, accompanied by intensified field-aligned electron beams and magnetic field depressions. Auroral data, acquired later but under very similar IMF conditions and at the same latitudes as when Polar was within C1, suggest auroral forms which are pulsed in both red and green lines with a similar period to the plasma bursts observed earlier at Polar. Within C2, at Polar, the pulsing ceased, but magnetosheath plasma was still present, albeit at diminished intensity. This was in part also a temporal change as the IMF clock angle decreased to ˜60°. Equatorward of the cusp aurora we find a mixing region of magnetosheath and magnetospheric plasmas with spectral characteristics of the boundary plasma sheet (BPS) forming the source of the R1 current. Plasma inhomogeneities and bipolar current elements embedded therein were related

  8. Mode-conversion induced tearing effects in a plasma neutral sheet

    SciTech Connect

    Kaw, P.K.; Sudan, R.N.

    1981-01-01

    A new collisionless dissipation mechanism which can drive tearing modes in a plasma neutral sheet is described. The new mechanism relies on the presence of a background cold plasma which leads to mode conversion into a continuous spectrum of cold plasma waves.

  9. Final Report for DOE Grant DE-FG02-03ER54712, Experimental Studies of Collisionless Reconnection Processes in Plasmas

    SciTech Connect

    Porkolab, Miklos; Egedal, Jan

    2007-11-30

    The Grant DE-FG-02-00ER54712, ?Experimental Studies of Collisionless Reconnection Processes in Plasmas?, financed within the DoE/NSF, spanned a period from September , 2003 to August, 2007. It partly supported an MIT Research scientist, two graduate students and material expenses. The grant enabled the operation of a basic plasma physics experiment (on magnetic reconnection) at the MIT Plasma Science and Fusion Center and the MIT Physics Department. A strong educational component characterized this work throughout, with the participation of a large number of graduate and undergraduate students and interns to the experimental activities. The study of the collisionless magnetic reconnection constituted the primary work carried out under this grant. The investigations utilized two magnetic configurations with distinct boundary conditions. Both configurations were based upon the Versatile Toroidal Facility (VTF). The first configuration is characterized by open boundary conditions where the magnetic field lines interface directly with the vacuum vessel walls. The reconnection dynamics for this configuration has been methodically characterized and it has been shown that kinetic effects related to trapped electron trajectories are responsible for the high rates of reconnection observed [7]. This type of reconnection has not been investigated before. Nevertheless, the results are directly relevant to observations by the Wind spacecraft of fast reconnection deep in the Earth magnetotail [9]. The second configuration was developed to be specifically relevant to numerical simulations of magnetic reconnection, allowing the magnetic field-lines to be contained inside the device. The configuration is compatible with the presence of large current sheets in the reconnection region and reconnection is observed in fast powerful bursts. These reconnection events facilitate the first experimental investigations of the physics governing the spontaneous onset of fast reconnection [12

  10. Modeling of the Convection and Interaction of Ring Current, Plasmaspheric and Plasma Sheet Plasmas in the Inner Magnetosphere

    NASA Technical Reports Server (NTRS)

    Fok, Mei-Ching; Chen, Sheng-Hsien; Buzulukova, Natalia; Glocer, Alex

    2010-01-01

    Distinctive sources of ions reside in the plasmasphere, plasmasheet, and ring current regions at discrete energies constitute the major plasma populations in the inner/middle magnetosphere. They contribute to the electrodynamics of the ionosphere-magnetosphere system as important carriers of the global current system, in triggering; geomagnetic storm and substorms, as well as critical components of plasma instabilities such as reconnection and Kelvin-Helmholtz instability at the magnetospheric boundaries. Our preliminary analysis of in-situ measurements shoves the complexity of the plasmas pitch angle distributions at particularly the cold and warm plasmas, vary dramatically at different local times and radial distances from the Earth in response to changes in solar wind condition and Dst index. Using an MHD-ring current coupled code, we model the convection and interaction of cold, warm and energetic ions of plasmaspheric, plasmasheet, and ring current origins in the inner magnetosphere. We compare our simulation results with in-situ and remotely sensed measurements from recent instrumentation on Geotail, Cluster, THEMIS, and TWINS spacecraft.

  11. Collisionless shock experiments with lasers and observation of Weibel instabilitiesa)

    NASA Astrophysics Data System (ADS)

    Park, H.-S.; Huntington, C. M.; Fiuza, F.; Drake, R. P.; Froula, D. H.; Gregori, G.; Koenig, M.; Kugland, N. L.; Kuranz, C. C.; Lamb, D. Q.; Levy, M. C.; Li, C. K.; Meinecke, J.; Morita, T.; Petrasso, R. D.; Pollock, B. B.; Remington, B. A.; Rinderknecht, H. G.; Rosenberg, M.; Ross, J. S.; Ryutov, D. D.; Sakawa, Y.; Spitkovsky, A.; Takabe, H.; Turnbull, D. P.; Tzeferacos, P.; Weber, S. V.; Zylstra, A. B.

    2015-05-01

    Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without pre-existing magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagnetic in nature with an inferred magnetization level as high as ˜1% [C. M. Huntington et al., "Observation of magnetic field generation via the weibel instability in interpenetrating plasma flows," Nat. Phys. 11, 173-176 (2015)]. These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.

  12. Collisionless shock experiments with lasers and observation of Weibel instabilities

    SciTech Connect

    Park, H. -S.; Huntington, C. M.; Fiuza, F.; Drake, R. P.; Froula, D. H.; Gregori, G.; Koenig, M.; Kugland, N. L.; Kuranz, C. C.; Lamb, D. Q.; Levy, M. C.; Li, C. K.; Meinecke, J.; Morita, T.; Petrasso, R. D.; Pollock, B. B.; Remington, B. A.; Rinderknecht, H. G.; Rosenberg, M.; Ross, J. S.; Ryutov, D. D.; Sakawa, Y.; Spitkovsky, A.; Takabe, H.; Turnbull, D. P.; Tzeferacos, P.; Weber, S. V.; Zylstra, A. B.

    2015-05-13

    Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without preexisting magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagnetic in nature with an inferred magnetization level as high as ~1% These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.

  13. Exploring the nature of collisionless shocks under laboratory conditions

    PubMed Central

    Stockem, A.; Fiuza, F.; Bret, A.; Fonseca, R. A.; Silva, L. O.

    2014-01-01

    Collisionless shocks are pervasive in astrophysics and they are critical to understand cosmic ray acceleration. Laboratory experiments with intense lasers are now opening the way to explore and characterise the underlying microphysics, which determine the acceleration process of collisionless shocks. We determine the shock character – electrostatic or electromagnetic – based on the stability of electrostatic shocks to transverse electromagnetic fluctuations as a function of the electron temperature and flow velocity of the plasma components, and we compare the analytical model with particle-in-cell simulations. By making the connection with the laser parameters driving the plasma flows, we demonstrate that shocks with different and distinct underlying microphysics can be explored in the laboratory with state-of-the-art laser systems. PMID:24488212

  14. Evolution of velocity dispersion along cold collisionless flows

    NASA Astrophysics Data System (ADS)

    Banik, Nilanjan; Sikivie, Pierre

    2016-05-01

    The infall of cold dark matter onto a galaxy produces cold collisionless flows and caustics in its halo. If a signal is found in the cavity detector of dark matter axions, the flows will be readily apparent as peaks in the energy spectrum of photons from axion conversion, allowing the densities, velocity vectors and velocity dispersions of the flows to be determined. We discuss the evolution of velocity dispersion along cold collisionless flows in one and two dimensions. A technique is presented for obtaining the leading behavior of the velocity dispersion near caustics. The results are used to derive an upper limit on the energy dispersion of the big flow from the sharpness of its nearby caustic and a prediction for the dispersions in its velocity components.

  15. Collisionless shock formation, spontaneous electromagnetic fluctuations, and streaming instabilities

    SciTech Connect

    Bret, A.; Stockem, A.; Fiuza, F.; Silva, L. O.; Narayan, R.

    2013-04-15

    Collisionless shocks are ubiquitous in astrophysics and in the lab. Recent numerical simulations and experiments have shown how they can arise from the encounter of two collisionless plasma shells. When the shells interpenetrate, the overlapping region turns unstable, triggering the shock formation. As a first step towards a microscopic understanding of the process, we analyze here in detail the initial instability phase. On the one hand, 2D relativistic Particle-In-Cell simulations are performed where two symmetric initially cold pair plasmas collide. On the other hand, the instabilities at work are analyzed, as well as the field at saturation and the seed field which gets amplified. For mildly relativistic motions and onward, Weibel modes govern the linear phase. We derive an expression for the duration of the linear phase in good agreement with the simulations. This saturation time constitutes indeed a lower-bound for the shock formation time.

  16. Collisionless shock experiments with lasers and observation of Weibel instabilities

    DOE PAGESBeta

    Park, H. -S.; Huntington, C. M.; Fiuza, F.; Drake, R. P.; Froula, D. H.; Gregori, G.; Koenig, M.; Kugland, N. L.; Kuranz, C. C.; Lamb, D. Q.; et al

    2015-05-13

    Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without preexisting magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagneticmore » in nature with an inferred magnetization level as high as ~1% These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.« less

  17. Evolution of velocity dispersion along cold collisionless flows

    DOE PAGESBeta

    Banik, Nilanjan; Sikivie, Pierre

    2016-05-01

    We found that the infall of cold dark matter onto a galaxy produces cold collisionless flows and caustics in its halo. If a signal is found in the cavity detector of dark matter axions, the flows will be readily apparent as peaks in the energy spectrum of photons from axion conversion, allowing the densities, velocity vectors and velocity dispersions of the flows to be determined. We also discuss the evolution of velocity dispersion along cold collisionless flows in one and two dimensions. A technique is presented for obtaining the leading behaviour of the velocity dispersion near caustics. The results aremore » used to derive an upper limit on the energy dispersion of the Big Flow from the sharpness of its nearby caustic, and a prediction for the dispersions in its velocity components.« less

  18. Multiple eigenmodes of geodesic acoustic mode in collisionless plasmas

    SciTech Connect

    Gao Zhe; Itoh, K.; Sanuki, H.; Dong, J. Q.

    2006-10-15

    We report a series of eigenmodes of the geodesic acoustic mode (GAM), which includes the standard GAM, a branch of low-frequency mode, and a series of ion sound wave-like modes. The case of T{sub i}>>T{sub e} is investigated, and eigenfrequencies of these modes are obtained analytically from a linear gyrokinetic model in collisionless plasmas with a rigid constant electrostatic potential around a magnetic surface.

  19. How to Patch Active Plasma and Collisionless Sheath: Practical Guide

    SciTech Connect

    Kaganovich, Igor D.

    2002-08-22

    Most plasmas have a very thin sheath compared with the plasma dimension. This necessitates separate calculations of the plasma and sheath. The Bohm criterion provides the boundary condition for calculation of plasma profiles. To calculate sheath properties, a value of electric field at the plasma-sheath interface has to be specified in addition to the Bohm criterion. The value of the boundary electric field and robust procedure to approximately patch plasma and collisionless sheath with a very good accuracy are reported.

  20. MHD instabilities of collisionless space plasma with heat fluxes

    NASA Astrophysics Data System (ADS)

    Kuznetsov, V. D.; Dzhalilov, N. S.

    2014-12-01

    Properties of instabilities in a collisionless plasma are considered based on 16-moment MHD equations with allowance for differences between the heat fluxes along the magnetic field due to longitudinal and transverse thermal ion motions. It is shown that the increments and thresholds appreciably depend on these two heat fluxes for all compressible instabilities arising in the MHD approach (second compressible fire-hose, mirror, and thermal instabilities).

  1. Comparison of multi-fluid moment models with particle-in-cell simulations of collisionless magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Wang, Liang; Hakim, Ammar H.; Bhattacharjee, A.; Germaschewski, K.

    2015-01-01

    We introduce an extensible multi-fluid moment model in the context of collisionless magnetic reconnection. This model evolves full Maxwell equations and simultaneously moments of the Vlasov-Maxwell equation for each species in the plasma. Effects like electron inertia and pressure gradient are self-consistently embedded in the resulting multi-fluid moment equations, without the need to explicitly solving a generalized Ohm's law. Two limits of the multi-fluid moment model are discussed, namely, the five-moment limit that evolves a scalar pressures for each species and the ten-moment limit that evolves the full anisotropic, non-gyrotropic pressure tensor for each species. We first demonstrate analytically and numerically that the five-moment model reduces to the widely used Hall magnetohydrodynamics (Hall MHD) model under the assumptions of vanishing electron inertia, infinite speed of light, and quasi-neutrality. Then, we compare ten-moment and fully kinetic particle-in-cell (PIC) simulations of a large scale Harris sheet reconnection problem, where the ten-moment equations are closed with a local linear collisionless approximation for the heat flux. The ten-moment simulation gives reasonable agreement with the PIC results regarding the structures and magnitudes of the electron flows, the polarities and magnitudes of elements of the electron pressure tensor, and the decomposition of the generalized Ohm's law. Possible ways to improve the simple local closure towards a nonlocal fully three-dimensional closure are also discussed.

  2. Comparison of multi-fluid moment models with particle-in-cell simulations of collisionless magnetic reconnection

    SciTech Connect

    Wang, Liang Germaschewski, K.; Hakim, Ammar H.; Bhattacharjee, A.

    2015-01-15

    We introduce an extensible multi-fluid moment model in the context of collisionless magnetic reconnection. This model evolves full Maxwell equations and simultaneously moments of the Vlasov-Maxwell equation for each species in the plasma. Effects like electron inertia and pressure gradient are self-consistently embedded in the resulting multi-fluid moment equations, without the need to explicitly solving a generalized Ohm's law. Two limits of the multi-fluid moment model are discussed, namely, the five-moment limit that evolves a scalar pressures for each species and the ten-moment limit that evolves the full anisotropic, non-gyrotropic pressure tensor for each species. We first demonstrate analytically and numerically that the five-moment model reduces to the widely used Hall magnetohydrodynamics (Hall MHD) model under the assumptions of vanishing electron inertia, infinite speed of light, and quasi-neutrality. Then, we compare ten-moment and fully kinetic particle-in-cell (PIC) simulations of a large scale Harris sheet reconnection problem, where the ten-moment equations are closed with a local linear collisionless approximation for the heat flux. The ten-moment simulation gives reasonable agreement with the PIC results regarding the structures and magnitudes of the electron flows, the polarities and magnitudes of elements of the electron pressure tensor, and the decomposition of the generalized Ohm's law. Possible ways to improve the simple local closure towards a nonlocal fully three-dimensional closure are also discussed.

  3. PARTICLE ACCELERATION IN RELATIVISTIC MAGNETIZED COLLISIONLESS ELECTRON-ION SHOCKS

    SciTech Connect

    Sironi, Lorenzo; Spitkovsky, Anatoly E-mail: anatoly@astro.princeton.edu

    2011-01-10

    We investigate shock structure and particle acceleration in relativistic magnetized collisionless electron-ion shocks by means of 2.5-dimensional particle-in-cell simulations with ion-to-electron mass ratios (m{sub i} /m{sub e} ) ranging from 16 to 1000. We explore a range of inclination angles between the pre-shock magnetic field and the shock normal. In 'subluminal' shocks, where relativistic particles can escape ahead of the shock along the magnetic field lines, ions are efficiently accelerated via the first-order Fermi process. The downstream ion spectrum consists of a relativistic Maxwellian and a high-energy power-law tail, which contains {approx}5% of ions and {approx}30% of ion energy. Its slope is -2.1 {+-} 0.1. The scattering is provided by short-wavelength non-resonant modes produced by Bell's instability, whose growth is seeded by the current of shock-accelerated ions that propagate ahead of the shock. Upstream electrons enter the shock with lower energy than ions (albeit by only a factor of {approx}5 << m{sub i} /m{sub e} ), so they are more strongly tied to the field. As a result, only {approx}1% of the incoming electrons are accelerated at the shock before being advected downstream, where they populate a steep power-law tail (with slope -3.5 {+-} 0.1). For 'superluminal' shocks, where relativistic particles cannot outrun the shock along the field, the self-generated turbulence is not strong enough to permit efficient Fermi acceleration, and the ion and electron downstream spectra are consistent with thermal distributions. The incoming electrons are heated up to equipartition with ions, due to strong electromagnetic waves emitted by the shock into the upstream. Thus, efficient electron heating ({approx}>15% of the upstream ion energy) is the universal property of relativistic electron-ion shocks, but significant nonthermal acceleration of electrons ({approx}>2% by number, {approx}>10% by energy, with slope flatter than -2.5) is hard to achieve in

  4. Evidence for the Late Cenozoic Antarctic Ice Sheet evolution and bottom current dynamics in the central-western Ross Sea outer margin, Antarctica

    NASA Astrophysics Data System (ADS)

    Kim, Sookwan; De Santis, Laura; Kuk Hong, Jong; Cottlerle, Diego; Petronio, Lorenzo; Colizza, Ester; Bergamasco, Andrea; Kim, Young-Gyun; Kang, Seung-Goo; Kim, Hyoungjun; Kim, Suhwan; Wardell, Nigel; Geletti, Riccardo; McKay, Robert; Jin, Young Keun; Kang, Sung-Ho

    2016-04-01

    Sedimentary records in polar continental margins provide clues for understanding paleo-depositional environments, related to ice sheet evolution and bottom-water current dynamics, during times of past climate and global sea level changes. Previous seismostratigraphic studies of the Ross Sea embayment, Antarctica, illustrated its general stratigraphic framework and the distribution of glacial sedimentary features over the continental shelf, since the onset of Antarctic ice-sheets at the Eocene-Oligocene boundary (~34.0 Ma). In contrast, there are a fewer studies for the outer continental margin, where continuous sedimentary deposits generally preserve the record of past climate cycles with minimum hiatus, comparing to the inner- and mid-continental shelf, where grounding ice streams eroded most of the sediments. Here we present a seismostratigraphic analysis of 2-D multichannel seismic reflection profiles, from the Central Basin located in the central-western Ross Sea outer margin. A glacial prograding wedge developed at the mouth of the Joides Basin since early-middle Miocene times (RSU4: ~14.0 Ma). And the Central Basin was filled with stacked debris-flow deposits and turbidites. The sediment depocenter shifted from the Central Basin toward the slope in the Pliocene (after RSU2: ~3.3 Ma). Pliocene foreset beds are steep and pinch out at the base of the continental slope. Bottom current controlled sediment drifts well developed since the middle Miocene, along the western slope of the central Basin and on the basement highs These areas are far from the mouth of the Joides trough, where most of the glacial sediment is deposited, and they are also more elevated than the basinal areas, where gravity flow maximum thickness accumulated. Along the western slope of the central Basin and over the basement highs, the signature in the sediments of the action of bottom current reworking and shaping the sea floor can be then clearly recognized. We present the sediment drifts

  5. Steady-State Electrostatic Layers From Weibel Instability in Relativistic Collisionless Shocks

    SciTech Connect

    Milosavljevic, Milos; Nakar, Ehud; Spitkovsky, Anatoly; /KIPAC, Menlo Park

    2005-08-04

    It is generally accepted that magnetic fields generated in the nonlinear development of the transverse Weibel instability provide effective collisionality in unmagnetized collisionless shocks. Recently, extensive two and three dimensional simulations improved our understanding of the growth and saturation of the instability in colliding plasma shells. However, the steady-state structure of the shock wave transition layers remains poorly understood. We use basic physical considerations and order-of-magnitude arguments to study the steady state structure in relativistic unmagnetized collisionless shocks in pair plasmas. The shock contains an electrostatic layer resulting from the formation of stationary, magnetically-focused current filaments. The filaments form where the cold upstream plasma and the counterstreaming thermal plasma interpenetrate. The filaments are not entirely neutral and strong electrostatic fields are present. Most of the downstream particles cannot cross this layer into the upstream because they are trapped by the electrostatic field. We identify the critical location in the shock transition layer where the electromagnetic field ceases to be static. At this location, the degree of charge separation in the filaments reaches a maximum value, the current inside the filaments comes close to the Alfven limit, and the phase space distribution function starts to isotropize. We argue that the radius of the current filaments upstream of the critical location is about twice the upstream plasma skin depth. Finally, we show that some downstream particles cross the electrostatic layer and run ahead of the shock into the preshock medium without causing instability. These particles may play an important role in particle acceleration.

  6. THREE-DIMENSIONAL MODELING OF RELATIVISTIC COLLISIONLESS ION-ELECTRON SHOCKS

    SciTech Connect

    Haugboelle, Troels

    2011-10-01

    Two-dimensional (2D) modeling of collisionless shocks has been of tremendous importance in understanding the physics of nonlinear evolution, momentum transfer, and particle acceleration, but current computer capacities have now reached a point where three-dimensional (3D) modeling is becoming feasible. We present the first 3D model of a fully developed and relaxed relativistic ion-electron shock, and analyze and compare it to similar 2D models. Quantitative and qualitative differences are found with respect to the 2D models. The shock jump conditions are naturally different, because of the extra degree of freedom, but in addition it is found that strong parallel electric fields develop at the shock interface, the level of magnetic field energy is lower, and the non-thermal particle distribution is shallower with a power-law index of {approx}2.2.

  7. PLASMA HEATING IN A POST ERUPTION CURRENT SHEET: A CASE STUDY BASED ON ULTRAVIOLET, SOFT, AND HARD X-RAY DATA

    SciTech Connect

    Susino, R.; Bemporad, A.; Krucker, Säm E-mail: krucker@ssl.berkeley.edu

    2013-11-10

    Off-limb observations of the solar corona after coronal mass ejections (CMEs) often show strong, compact, and persistent UV sources behind the eruption. They are primarily observed by the SOHO/UVCS instrument in the 'hot' [Fe XVIII] λ974 line and are usually interpreted as a signature of plasma heating due to magnetic reconnection in the post-CME current sheet (CS). Nevertheless, the physical process itself and the altitude of the main energy release are currently not fully understood. In this work, we study the evolution of plasma heating after the CME of 2004 July 28 by comparing UV spectra acquired by UVCS with soft and hard X-ray (SXR, HXR) images of the post-flare loops taken by GOES/SXI and RHESSI. The X-ray data show a long-lasting extended source that is rising upward, toward the high-temperature source detected by UVCS. UVCS data show the presence of significant non-thermal broadening in the CS (a signature of turbulent motions) and a strong density gradient across the CS region. The thermal energy released in the HXR source is on the order of ∼10{sup 32} erg, a factor ∼2-5 larger than the energy required to explain the high-temperature plasma sampled by UVCS. Nevertheless, the very different time evolutions of SXR and HXR sources compared with the UV emission suggest that reconnection occurring above the post-eruption arcades is not directly responsible for the high-temperature plasma sampled higher up by UVCS. We conclude that an additional plasma heating mechanism (such as turbulent reconnection) in the CS is likely required.

  8. Time-dependent closure relations for relativistic collisionless fluid equations

    SciTech Connect

    Bendib-Kalache, K.; Bendib, A.; El Hadj, K. Mohammed

    2010-11-15

    Linear fluid equations for relativistic and collisionless plasmas are derived. Closure relations for the fluid equations are analytically computed from the relativistic Vlasov equation in the Fourier space ({omega},k), where {omega} and k are the conjugate variables of time t and space x variables, respectively. The mathematical method used is based on the projection operator techniques and the continued fraction mathematical tools. The generalized heat flux and stress tensor are calculated for arbitrary parameter {omega}/kc where c is the speed of light, and for arbitrary relativistic parameter z=mc{sup 2}/T, where m is the particle rest mass and T, the plasma temperature in energy units.

  9. Neoclassical Transport Caused by Collisionless Scattering across an Asymmetric Separatrix

    SciTech Connect

    Dubin, Daniel H. E.; Driscoll, C. F.; Tsidulko, Yu. A.

    2010-10-29

    Plasma loss due to apparatus asymmetries is a ubiquitous phenomenon in magnetic plasma confinement. When the plasma equilibrium has locally trapped particle populations partitioned by a separatrix from one another and from passing particles, the asymmetry transport is enhanced. The trapped and passing particle populations react differently to the asymmetries, leading to the standard 1/{nu} and {radical}({nu}) transport regimes of superbanana orbit theory as particles collisionally scatter from one orbit type to another. However, when the separatrix is itself asymmetric, particles can collisionlessly transit from trapped to passing and back, leading to enhanced transport.

  10. Generation of collisionless shock in laser-produced plasmas

    NASA Astrophysics Data System (ADS)

    Fiuza, Frederico

    2015-08-01

    Collisionless shocks are ubiquitous in astrophysical environments and are tightly connected with magnetic-field amplification and particle acceleration. The fast progress in high-power laser technology is bringing the study of high Mach number shocks into the realm of laboratory plasmas, where in situ measurements can be made helping us understand the fundamental kinetic processes behind shocks. I will discuss the recent progress in laser-driven shock experiments at state-of-the-art facilities like NIF and Omega and how these results, together with ab initio massively parallel simulations, can impact our understanding of magnetic field amplification and particle acceleration in astrophysical plasmas.

  11. Entropy production rate as a constraint for collisionless fluid closures

    SciTech Connect

    Fleurence, E.; Sarazin, Y.; Garbet, X.; Dif-Pradalier, G.; Ghendrih, Ph.; Grandgirard, V.; Ottaviani, M.

    2006-11-30

    A novel method is proposed to construct collisionless fluid closures accounting for some kinetic properties. The first dropped fluid moment is assumed to be a linear function of the lower order ones. Optimizing the agreement between the fluid and kinetic entropy production rates is used to constrain the coefficients of the linear development. This procedure is applied to a reduced version of the interchange instability. The closure, involving the absolute value of the wave vector, is non-local in real space. In this case, the linear instability thresholds are the same, and the linear growth rates exhibit similar characteristics. Such a method is applicable to other models and classes of instabilities.

  12. Vlasov equation and collisionless hydrodynamics adapted to curved spacetime

    SciTech Connect

    Dodin, I. Y.; Fisch, N. J.

    2010-11-15

    The modification of the Vlasov equation, in its standard form describing a charged particle distribution in the six-dimensional phase space, is derived explicitly within a formal Hamiltonian approach for arbitrarily curved spacetime. The equation accounts simultaneously for the Lorentz force and the effects of general relativity, with the latter appearing as the gravity force and an additional force due to the extrinsic curvature of spatial hypersurfaces. For an arbitrary spatial metric, the equations of collisionless hydrodynamics are also obtained in the usual three-vector form.

  13. Analytical collisionless damping rate of geodesic acoustic mode

    NASA Astrophysics Data System (ADS)

    Ren, H.; Xu, X. Q.

    2016-10-01

    Collisionless damping of geodesic acoustic mode (GAM) is analytically investigated by considering the finite-orbit-width (FOW) resonance effect to the 3rd order in the gyro-kinetic equations. A concise and transparent expression for the damping rate is presented for the first time. Good agreement is found between the analytical damping rate and the previous TEMPEST simulation result (Xu 2008 et al Phys. Rev. Lett. 100 215001) for systematic q scans. Our result also shows that it is of sufficient accuracy and has to take into account the FOW effect to the 3rd order.

  14. Collisionless drift-tearing modes in the magnetopause

    NASA Technical Reports Server (NTRS)

    Gladd, N. T.

    1990-01-01

    The linear stability properties of collisionless drift-tearing modes are analyzed in a modified Harris equilibrium model of the magnetopause. Particular attention is paid to the relevance of the parametric behavior of growth rates to the 'magnetic percolation' theory of flux transfer event formation (Galeev et al., 1986). Numerical methods are used to solve the drift-tearing eigenmode equations and the results are compared with those previously obtained by analytical methods. The analytical results are found to correctly model important parametric dependencies but to typically overestimate the rate of growth. The eigenmode equations are numerically difficult, and an integration scheme utilizing Ricatti transforms is developed to affect their solution.

  15. Time-dependent closure relations for relativistic collisionless fluid equations.

    PubMed

    Bendib-Kalache, K; Bendib, A; El Hadj, K Mohammed

    2010-11-01

    Linear fluid equations for relativistic and collisionless plasmas are derived. Closure relations for the fluid equations are analytically computed from the relativistic Vlasov equation in the Fourier space (ω,k), where ω and k are the conjugate variables of time t and space x variables, respectively. The mathematical method used is based on the projection operator techniques and the continued fraction mathematical tools. The generalized heat flux and stress tensor are calculated for arbitrary parameter ω/kc where c is the speed of light, and for arbitrary relativistic parameter z=mc²/T , where m is the particle rest mass and T, the plasma temperature in energy units.

  16. Collisionless shock experiments with lasers and observation of Weibel instabilities

    SciTech Connect

    Park, H.-S. Huntington, C. M.; Fiuza, F.; Levy, M. C.; Pollock, B. B.; Remington, B. A.; Ross, J. S.; Ryutov, D. D.; Turnbull, D. P.; Weber, S. V.; Drake, R. P.; Kuranz, C. C.; Froula, D. H.; Rosenberg, M.; Gregori, G.; Meinecke, J.; Koenig, M.; Kugland, N. L.; Lamb, D. Q.; Tzeferacos, P.; and others

    2015-05-15

    Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without pre-existing magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagnetic in nature with an inferred magnetization level as high as ∼1% [C. M. Huntington et al., “Observation of magnetic field generation via the weibel instability in interpenetrating plasma flows,” Nat. Phys. 11, 173–176 (2015)]. These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.

  17. Magneto-Hydro-Dynamic Waves In The Collisionless Space Plasma

    NASA Astrophysics Data System (ADS)

    Dzhalilov, N. S.; Kuznetsov, V. D.; Staude, J.

    2007-12-01

    The instability of magneto-hydro-dynamic (MHD) waves in an anisotropic, collisionless, rarefied hot plasma is studied. Anisotropy properties of such a plasma are caused by a strong magnetic field, when the thermal gas pressures across and along the field become unequal. Moreover, there appears an anisotropy of the thermal fluxes. The study of the anisotropy features of the plasma are motivated by observed solar coronal data. The 16 moments equations derived from the Boltzmann-Vlasov kinetic equation are used. These equations strongly differ from the usual isotropic MHD case. For linear disturbances the wave equations in homogenous anisotropic plasma are deduced. The general dispersion relation for the incompressible wave modes is derived, solved and analyzed. It is shown that a wide wave spectrum with stable and unstable behavior is possible, in contrast to the usual isotropic MHD case. The dependence of the instability on magnetic field, pressure anisotropy, and heat fluxes is investigated. The general instability condition is obtained. The results can be applied to the theory of solar and stellar coronal heating, to wind models and in other modeling, where the collisionless approximation is valid.

  18. Laboratory astrophysical collisionless shock experiments on Omega and NIF

    NASA Astrophysics Data System (ADS)

    Park, Hye-Sook; Ross, J. S.; Huntington, C. M.; Fiuza, F.; Ryutov, D.; Casey, D.; Drake, R. P.; Fiksel, G.; Froula, D.; Gregori, G.; Kugland, N. L.; Kuranz, C.; Levy, M. C.; Li, C. K.; Meinecke, J.; Morita, T.; Petrasso, R.; Plechaty, C.; Remington, B.; Sakawa, Y.; Spitkovsky, A.; Takabe, H.; Zylstra, A. B.

    2016-03-01

    We are performing scaled astrophysics experiments on Omega and on NIF. Laser driven counter-streaming interpenetrating supersonic plasma flows can be studied to understand astrophysical electromagnetic plasma phenomena in a controlled laboratory setting. In our Omega experiments, the counter-streaming flow plasma state is measured using Thomson scattering diagnostics, demonstrating the plasma flows are indeed super-sonic and in the collisionless regime. We observe a surprising additional electron and ion heating from ion drag force in the double flow experiments that are attributed to the ion drag force and electrostatic instabilities. [1] A proton probe is used to image the electric and magnetic fields. We observe unexpected large, stable and reproducible electromagnetic field structures that arise in the counter-streaming flows [2]. The Biermann battery magnetic field generated near the target plane, advected along the flows, and recompressed near the midplane explains the cause of such self-organizing field structures [3]. A D3He implosion proton probe image showed very clear filamentary structures; three-dimensional Particle-In-Cell simulations and simulated proton radiography images indicate that these filamentary structures are generated by Weibel instabilities and that the magnetization level (ratio of magnetic energy over kinetic energy in the system) is ∼0.01 [4]. These findings have very high astrophysical relevance and significant implications. We expect to observe true collisionless shock formation when we use >100 kJ laser energy on NIF.

  19. Horizontal electromagnetic casting of thin metal sheets

    DOEpatents

    Hull, John R.; Lari, Robert J.; Praeg, Walter F.; Turner, Larry R.

    1987-01-01

    Thin metal sheets are cast by magnetically suspending molten metal deposited within a ferromagnetic yoke and between AC conducting coils and linearly displacing the magnetically levitated liquid metal while it is being cooled to form a solid metal sheet. Magnetic flux increases as the molten metal sheet moves downward and decreases as the molten metal sheet moves upward to stabilize the sheet and maintain it in equilibrium as it is linearly displaced and solidified by cooling gases. A conducting shield is electrically coupled to the molten metal sheet by means of either metal sheet engaging rollers or brushes on the solidified metal, and by means of an electrode in the vessel containing the molten metal thereby providing a return path for the eddy currents induced in the metal sheet by the AC coil generated magnetic flux. Variation in the geometry of the conducting shield allows the magnetic flux between the metal sheet and the conducting shield to be varied and the thickness in surface quality of the metal sheet to be controlled. Side guards provide lateral containment for the molten metal sheet and stabilize and shape the magnetic field while a leader sheet having electromagnetic characteristics similar to those of the metal sheet is used to start the casting process and precedes the molten metal sheet through the magnet and forms a continuous sheet therewith. The magnet may be either U-shaped with a single racetrack coil or may be rectangular with a pair of facing bedstead coils.

  20. Horizontal electromagnetic casting of thin metal sheets

    DOEpatents

    Hull, John R.; Lari, Robert J.; Praeg, Walter F.; Turner, Larry R.

    1988-01-01

    Thin metal sheets are cast by magnetically suspending molten metal deposited within a ferromagnetic yoke and between AC conducting coils and linearly displacing the magnetically levitated liquid metal while it is being cooled to form a solid metal sheet. Magnetic flux increases as the molten metal sheet moves downward and decreases as the molten metal sheet moves upward to stabilize the sheet and maintain it in equilibrium as it is linearly displaced and solidified by cooling gases. A conducting shield is electrically coupled to the molten metal sheet by means of either metal sheet engaging rollers or brushes on the solidified metal, and by means of an electrode in the vessel containing the molten metal thereby providing a return path for the eddy currents induced in the metal sheet by the AC coil generated magnetic flux. Variation in the geometry of the conducting shield allows the magnetic flux between the metal sheet and the conducting shield to be varied and the thickness in surface quality of the metal sheet to be controlled. Side guards provide lateral containment for the molten metal sheet and stabilize and shape the magnetic field while a leader sheet having electromagnetic characteristics similar to those of the metal sheet is used to start the casting process and precedes the molten metal sheet through the magnet and forms a continuous sheet therewith. The magnet may be either U-shaped with a single racetrack coil or may be rectangular with a pair of facing bedstead coils.

  1. Responsive systems for cell sheet detachment

    PubMed Central

    Patel, Nikul G.; Zhang, Ge

    2013-01-01

    Cell sheet engineering has been progressing rapidly during the past few years and has emerged as a novel approach for cell based therapy. Cell sheet harvest technology enables fabrication of viable, transplantable cell sheets for various tissue engineering applications. Currently, the majority of cell sheet studies use thermo-responsive systems for cell sheet detachment. However, other responsive systems began showing their potentials for cell sheet harvest. This review provides an overview of current techniques in creating cell sheets using different types of responsive systems including thermo-responsive, electro-responsive, photo-responsive, pH-responsive and magnetic systems. Their mechanism, approach, as well as applications for cell detachment have been introduced. Further development of these responsive systems will allow efficient cell sheet harvesting and patterning of cells to reconstruct complex tissue for broad clinical applications. PMID:23820033

  2. Dependence of Langmuir probe data on distance from the axis of a collisionless plasma

    SciTech Connect

    Knappmiller, Scott; Robertson, Scott

    2007-03-15

    A cylindrical Langmuir probe in a low-density, collisionless plasma (density {approx}10{sup 8} cm{sup -3}, electron temperature 0.2 eV) has been scanned radially through the presheath region to determine the effect of distance from the axis on the current-voltage characteristic. In the ion part of the probe characteristic, the collected ion current decreases with distance from the axis as a consequence of ion acceleration by the presheath. The part of the ion current from charge-exchange collisions remains relatively constant. In the electron part of the probe characteristic, the collected current decreases with distance from the axis, consistent with the existence of a small potential barrier from the presheath between the axis and the probe. The electron temperature from the slope of the probe characteristic is nearly constant across the presheath region. The plasma potential from the Langmuir probe characteristic is also nearly constant, indicating that the probe analysis finds the plasma potential on the axis, even when the probe is not on the axis. The plasma potential from an emissive probe shows an approximately parabolic profile. The plasma potential from the emissive probe and the Boltzmann relation give nearly the same density profile in the presheath that is obtained from the Langmuir probe data.

  3. Collisionless microtearing modes in hot tokamaks: Effect of trapped electrons

    SciTech Connect

    Swamy, Aditya K.; Ganesh, R.; Brunner, S.; Vaclavik, J.; Villard, L.

    2015-07-15

    Collisionless microtearing modes have recently been found linearly unstable in sharp temperature gradient regions of large aspect ratio tokamaks. The magnetic drift resonance of passing electrons has been found to be sufficient to destabilise these modes above a threshold plasma β. A global gyrokinetic study, including both passing electrons as well as trapped electrons, shows that the non-adiabatic contribution of the trapped electrons provides a resonant destabilization, especially at large toroidal mode numbers, for a given aspect ratio. The global 2D mode structures show important changes to the destabilising electrostatic potential. The β threshold for the onset of the instability is found to be generally downshifted by the inclusion of trapped electrons. A scan in the aspect ratio of the tokamak configuration, from medium to large but finite values, clearly indicates a significant destabilizing contribution from trapped electrons at small aspect ratio, with a diminishing role at larger aspect ratios.

  4. Kinetic dissipation and anisotropic heating in a turbulent collisionless plasma

    SciTech Connect

    Parashar, T. N.; Shay, M. A.; Cassak, P. A.; Matthaeus, W. H.

    2009-03-15

    The kinetic evolution of the Orszag-Tang vortex is studied using collisionless hybrid simulations. In magnetohydrodynamics (MHD) this configuration leads rapidly to broadband turbulence. At large length scales, the evolution of the hybrid simulations is very similar to MHD, with magnetic power spectra displaying scaling similar to a Kolmogorov scaling of -5/3. At small scales, differences from MHD arise, as energy dissipates into heat almost exclusively through the magnetic field. The magnetic energy spectrum of the hybrid simulation shows a break where linear theory predicts that the Hall term in Ohm's law becomes significant, leading to dispersive kinetic Alfven waves. A key result is that protons are heated preferentially in the plane perpendicular to the mean magnetic field, creating a proton temperature anisotropy of the type observed in the corona and solar wind.

  5. Nonlinear Weibel Instability and Turbulence in Strong Collisionless Shocks

    SciTech Connect

    Medvedev, Mikhail M.

    2008-08-31

    This research project was devoted to studies of collisionless shocks, their properties, microphysics and plasma physics of underlying phenomena, such as Weibel instability and generation of small-scale fields at shocks, particle acceleration and transport in the generated random fields, radiation mechanisms from these fields in application to astrophysical phenomena and laboratory experiments (e.g., laser-plasma and beam-plasma interactions, the fast ignition and inertial confinement, etc.). Thus, this study is highly relevant to astrophysical sciences, the inertial confinement program and, in particular, the Fast Ignition concept, etc. It makes valuable contributions to the shock physics, nonlinear plasma theory, as well as to the basic plasma science, in general.

  6. Scaling of Magnetic Reconnection in Relativistic Collisionless Pair Plasmas

    NASA Technical Reports Server (NTRS)

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

    2015-01-01

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

  7. ENTROPY PRODUCTION IN COLLISIONLESS SYSTEMS. III. RESULTS FROM SIMULATIONS

    SciTech Connect

    Barnes, Eric I.; Egerer, Colin P. E-mail: egerer.coli@uwlax.edu

    2015-05-20

    The equilibria formed by the self-gravitating, collisionless collapse of simple initial conditions have been investigated for decades. We present the results of our attempts to describe the equilibria formed in N-body simulations using thermodynamically motivated models. Previous work has suggested that it is possible to define distribution functions for such systems that describe maximum entropy states. These distribution functions are used to create radial density and velocity distributions for comparison to those from simulations. A wide variety of N-body code conditions are used to reduce the chance that results are biased by numerical issues. We find that a subset of initial conditions studied lead to equilibria that can be accurately described by these models, and that direct calculation of the entropy shows maximum values being achieved.

  8. Nonlinear Particle Pinch in Collisionless Trapped Electron Mode Turbulence

    NASA Astrophysics Data System (ADS)

    Terry, P. W.; Gatto, R.

    2005-10-01

    Collisionless trapped electron mode turbulence is shown to have an anomalous particle pinch fundamentally unlike pinches identified previously. It arises from a nonlinear fluctuation eigenmode, placing it outside the purview of quasilinear theory. The nonlinear eigenmode develops because the nonlinearity excites a damped linear eigenmode, changing the density- potential correlation. The flux is solved from spectrum balance equations in a complete basis spanning the fluctuation space under a joint expansion in collision frequency and instability threshold parameter. The solution accounts for saturation by anisotropic energy transfer to zonal wavenumbers of the damped eigenmode. To lowest order the pinch is a convective-like flux driven by temperature gradient. It arises from the damped eigenmode energy and the real part of the correlation between damped and growing eigenmodes. The pinch is slightly smaller than the outwardly directed flux associated with the growing eigenmode, making the flux a small fraction of the quasilinear value. Work supported by US DOE.

  9. The evolution of 1 AU equatorial solar wind and its association with the morphology of the heliospheric current sheet from solar cycles 23 to 24

    SciTech Connect

    Zhao, L.; Landi, E.; Zurbuchen, T. H.; Fisk, L. A.; Lepri, S. T.

    2014-09-20

    The solar wind can be categorized into three types based on its 'freeze-in' temperature (T {sub freeze-in}) in the coronal source: low T {sub freeze-in} wind mostly from coronal holes, high T {sub freeze-in} wind mostly from regions outside of coronal holes, including streamers (helmet streamer and pseudostreamer), active regions, etc., and transient interplanetary coronal mass ejections (ICMEs) usually possessing the hottest T {sub freeze-in}. The global distribution of these three types of wind has been investigated by examining the most effective T {sub freeze-in} indicator, the O{sup 7+}/O{sup 6+} ratio, as measured by the Solar Wind Ion Composition Spectrometer on board the Advanced Composition Explorer (ACE) during 1998-2008 by Zhao et al. In this study, we extend the previous investigation to 2011 June, covering the unusual solar minimum between solar cycles 23 and 24 (2007-2010) and the beginning of solar cycle 24. We find that during the entire solar cycle, from the ascending phase of cycle 23 in 1998 to the ascending phase of cycle 24 in 2011, the average fractions of the low O{sup 7+}/O{sup 6+} ratio (LOR) wind, the high O{sup 7+}/O{sup 6+} ratio (HOR) wind, and ICMEs at 1 AU are 50.3%, 39.4%, and 10.3%, respectively; the contributions of the three types of wind evolve with time in very different ways. In addition, we compare the evolution of the HOR wind with two heliospheric current sheet (HCS) parameters, which indicate the latitudinal standard deviation (SD) and the slope (SL) of the HCS on the synoptic Carrington maps at 2.5 solar radii surface. We find that the fraction of HOR wind correlates with SD and SL very well (slightly better with SL than with SD), especially after 2005. This result verifies the link between the production of HOR wind and the morphology of the HCS, implying that at least one of the major sources of the HOR wind must be associated with the HCS.

  10. Hamiltonian derivation of a gyrofluid model for collisionless magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Tassi, E.

    2014-11-01

    We consider a simple electromagnetic gyrokinetic model for collisionless plasmas and show that it possesses a Hamiltonian structure. Subsequently, from this model we derive a two-moment gyrofluid model by means of a procedure which guarantees that the resulting gyrofluid model is also Hamiltonian. The first step in the derivation consists of imposing a generic fluid closure in the Poisson bracket of the gyrokinetic model, after expressing such bracket in terms of the gyrofluid moments. The constraint of the Jacobi identity, which every Poisson bracket has to satisfy, selects then what closures can lead to a Hamiltonian gyrofluid system. For the case at hand, it turns out that the only closures (not involving integro/differential operators or an explicit dependence on the spatial coordinates) that lead to a valid Poisson bracket are those for which the second order parallel moment, independently for each species, is proportional to the zero order moment. In particular, if one chooses an isothermal closure based on the equilibrium temperatures and derives accordingly the Hamiltonian of the system from the Hamiltonian of the parent gyrokinetic model, one recovers a known Hamiltonian gyrofluid model for collisionless reconnection. The proposed procedure, in addition to yield a gyrofluid model which automatically conserves the total energy, provides also, through the resulting Poisson bracket, a way to derive further conservation laws of the gyrofluid model, associated with the so called Casimir invariants. We show that a relation exists between Casimir invariants of the gyrofluid model and those of the gyrokinetic parent model. The application of such Hamiltonian derivation procedure to this two-moment gyrofluid model is a first step toward its application to more realistic, higher-order fluid or gyrofluid models for tokamaks. It also extends to the electromagnetic gyrokinetic case, recent applications of the same procedure to Vlasov and drift- kinetic systems.

  11. Origins of effective resistivity in collisionless magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Singh, Nagendra

    2014-07-01

    The mechanisms that provide effective resistivity for supporting collisonless magnetic reconnection have remained unsettled despite numerous studies. Some of these studies demonstrated that the electron pressure nongyrotropy generates the resistivity (ηnpg) in the electron diffusion region (EDR). We derive an analytical relation for the effective resistivity (ηkin) by momentum balance in a control volume in the EDR. Both ηnpg and ηkin mutually compare well and they also compare well with the resistivity required to support reconnection electric field Erec in multi-dimensional particle-in-cell simulations as well as in satellite observations when reconnection occurs in an EDR. But they are about an order of magnitude or so smaller than that required when the reconnection occurred in a much wider reconnecting current sheet (RCS) of half width (w) of the order of the ion skin depth (di), observed in the Earth magnetosphere. The chaos-induced resistivity reported in the literature is found to be even more deficient. We find that for reconnection in RCS with w ˜ di, anomalous diffusion, such as the universal Bhom diffusion and/or that arising from kinetic Alfven waves, could fairly well account for the required resistivity.

  12. Origins of effective resistivity in collisionless magnetic reconnection

    SciTech Connect

    Singh, Nagendra

    2014-07-15

    The mechanisms that provide effective resistivity for supporting collisonless magnetic reconnection have remained unsettled despite numerous studies. Some of these studies demonstrated that the electron pressure nongyrotropy generates the resistivity (η{sub npg}) in the electron diffusion region (EDR). We derive an analytical relation for the effective resistivity (η{sub kin}) by momentum balance in a control volume in the EDR. Both η{sub npg} and η{sub kin} mutually compare well and they also compare well with the resistivity required to support reconnection electric field E{sub rec} in multi-dimensional particle-in-cell simulations as well as in satellite observations when reconnection occurs in an EDR. But they are about an order of magnitude or so smaller than that required when the reconnection occurred in a much wider reconnecting current sheet (RCS) of half width (w) of the order of the ion skin depth (d{sub i}), observed in the Earth magnetosphere. The chaos-induced resistivity reported in the literature is found to be even more deficient. We find that for reconnection in RCS with w ∼ d{sub i}, anomalous diffusion, such as the universal Bhom diffusion and/or that arising from kinetic Alfven waves, could fairly well account for the required resistivity.

  13. Collisionless Magnetic Reconnection and Dynamo Processes in a Spatially Rotating Magnetic Field

    NASA Astrophysics Data System (ADS)

    Choe, Gwangson; Lee, Junggi

    2016-04-01

    Spatially rotating magnetic fields have been observed in the solar wind and in the Earth's magnetopause as well as in reversed field pinch (RFP) devices. Such field configurations have a similarity with extended current layers having a spatially varying plasma pressure instead of the spatially varying guide field. It is thus expected that magnetic reconnection may take place in a rotating magnetic field no less than in an extended current layer. We have investigated the spontaneous evolution of a collisionless plasma system embedding a rotating magnetic field with a two-and-a-half-dimensional electromagnetic particle-in-cell (PIC) simulation. It is found that a magnetic-flux-reducing diffusion phase and a magnetic-flux-increasing dynamo phase are alternating with a certain period. The temperature of the system also varies with the same period, showing a similarity to sawtooth oscillations in tokamaks. We have shown that a modified theory of sawtooth oscillations can explain the periodic behavior observed in the simulation. A strong guide field distorts the current layer as was observed in laboratory experiments. This distortion is smoothed out as magnetic islands fade away by the O-line diffusion, but is soon strengthened by the growth of magnetic islands. These processes are all repeating with a fixed period. Our results suggest that a rotating magnetic field configuration continuously undergoes deformation and relaxation in a short time-scale although it might look rather steady in a long-term view.

  14. On the quasi-linear diffusion in collisionless plasmas (to say nothing about Landau damping)

    SciTech Connect

    Hellinger, Petr; Travnicek, Pavel M.

    2012-06-15

    General quasi-linear diffusion coefficients for nonrelativistic collisionless plasmas are derived for unstable modes and analytically continued to damped modes. Properties of the resulting diffusion are investigated and discussed.

  15. Vertically scanned laser sheet microscopy.

    PubMed

    Dong, Di; Arranz, Alicia; Zhu, Shouping; Yang, Yujie; Shi, Liangliang; Wang, Jun; Shen, Chen; Tian, Jie; Ripoll, Jorge

    2014-01-01

    Laser sheet microscopy is a widely used imaging technique for imaging the three-dimensional distribution of a fluorescence signal in fixed tissue or small organisms. In laser sheet microscopy, the stripe artifacts caused by high absorption or high scattering structures are very common, greatly affecting image quality. To solve this problem, we report here a two-step procedure which consists of continuously acquiring laser sheet images while vertically displacing the sample, and then using the variational stationary noise remover (VSNR) method to further reduce the remaining stripes. Images from a cleared murine colon acquired with a vertical scan are compared with common stitching procedures demonstrating that vertically scanned light sheet microscopy greatly improves the performance of current light sheet microscopy approaches without the need for complex changes to the imaging setup and allows imaging of elongated samples, extending the field of view in the vertical direction.

  16. Collisionless absorption, hot electron generation, and energy scaling in intense laser-target interaction

    SciTech Connect

    Liseykina, T.; Mulser, P.; Murakami, M.

    2015-03-15

    Among the various attempts to understand collisionless absorption of intense and superintense ultrashort laser pulses, a whole variety of models and hypotheses has been invented to describe the laser beam target interaction. In terms of basic physics, collisionless absorption is understood now as the interplay of the oscillating laser field with the space charge field produced by it in the plasma. A first approach to this idea is realized in Brunel's model the essence of which consists in the formation of an oscillating charge cloud in the vacuum in front of the target, therefore frequently addressed by the vague term “vacuum heating.” The investigation of statistical ensembles of orbits shows that the absorption process is localized at the ion-vacuum interface and in the skin layer: Single electrons enter into resonance with the laser field thereby undergoing a phase shift which causes orbit crossing and braking of Brunel's laminar flow. This anharmonic resonance acts like an attractor for the electrons and leads to the formation of a Maxwellian tail in the electron energy spectrum. Most remarkable results of our investigations are the Brunel like spectral hot electron distribution at the relativistic threshold, the minimum of absorption at Iλ{sup 2}≅(0.3−1.2)×10{sup 21} Wcm{sup −2}μm{sup 2} in the plasma target with the electron density of n{sub e}λ{sup 2}∼10{sup 23}cm{sup −3}μm{sup 2}, the drastic reduction of the number of hot electrons in this domain and their reappearance in the highly relativistic domain, and strong coupling, beyond expectation, of the fast electron jets with the return current through Cherenkov emission of plasmons. The hot electron energy scaling shows a strong dependence on intensity in the moderately relativistic domain Iλ{sup 2}≅(10{sup 18}−10{sup 20}) Wcm{sup −2}μm{sup 2}, a scaling in vague accordance with current published estimates in the range Iλ{sup 2}≅(0.14−3.5)×10{sup 21} Wcm{sup −2}

  17. Micro-instabilities and anomalous transport effects in collisionless guide field reconnection

    NASA Astrophysics Data System (ADS)

    Munoz Sepulveda, Patricio Alejandro; Büchner, Jörg; Kilian, Patrick

    2016-07-01

    It is often the case that magnetic reconnection takes place in collisionless plasmas with a current aligned guide magnetic field, such as in the Solar corona. The general characteristics of this process have been exhaustively analyzed with theory and numerical simulations, under different approximations, since some time ago. However, some consequences and properties of the secondary instabilities arising spontaneously -other than tearing instability-, and their dependence on the guide field strength, have not been completely understood yet. For this sake, we use the results of fully kinetic 2D PIC numerical simulations of guide field reconnection. By using a mean field approach for the Generalized Ohm's law that explains the balance of the reconnected electric field, we find that some of the cross-streaming and gradient driven instabilities -in the guide field case- produce an additional anomalous transport term. The latter can be interpreted as a result of the enhanced correlated electromagnetic fluctuations, leading to a slow down of the current carriers and kinetic scale turbulence. We characterize these processes on dependence on the guide field strength, and explore the causal relation with the source of free energy driving the mentioned instabilities. Finally, we show the main consequences that a fully 3D approach have on all those phenomena in contrast to the reduced 2D description.

  18. Modeling the Lyα Forest in Collisionless Simulations

    NASA Astrophysics Data System (ADS)

    Sorini, Daniele; Oñorbe, José; Lukić, Zarija; Hennawi, Joseph F.

    2016-08-01

    Cosmological hydrodynamic simulations can accurately predict the properties of the intergalactic medium (IGM), but only under the condition of retaining the high spatial resolution necessary to resolve density fluctuations in the IGM. This resolution constraint prohibits simulating large volumes, such as those probed by BOSS and future surveys, like DESI and 4MOST. To overcome this limitation, we present “Iteratively Matched Statistics” (IMS), a novel method to accurately model the Lyα forest with collisionless N-body simulations, where the relevant density fluctuations are unresolved. We use a small-box, high-resolution hydrodynamic simulation to obtain the probability distribution function (PDF) and the power spectrum of the real-space Lyα forest flux. These two statistics are iteratively mapped onto a pseudo-flux field of an N-body simulation, which we construct from the matter density. We demonstrate that our method can reproduce the PDF, line of sight and 3D power spectra of the Lyα forest with good accuracy (7%, 4%, and 7% respectively). We quantify the performance of the commonly used Gaussian smoothing technique and show that it has significantly lower accuracy (20%–80%), especially for N-body simulations with achievable mean inter-particle separations in large-volume simulations. In addition, we show that IMS produces reasonable and smooth spectra, making it a powerful tool for modeling the IGM in large cosmological volumes and for producing realistic “mock” skies for Lyα forest surveys.

  19. Collisionless electron heating in periodic arrays of inductively coupled plasmas

    SciTech Connect

    Czarnetzki, U.; Tarnev, Kh.

    2014-12-15

    A novel mechanism of collisionless heating in large planar arrays of small inductive coils operated at radio frequencies is presented. In contrast to the well-known case of non-local heating related to the transversal conductivity, when the electrons move perpendicular to the planar coil, we investigate the problem of electrons moving in a plane parallel to the coils. Two types of periodic structures are studied. Resonance velocities where heating is efficient are calculated analytically by solving the Vlasov equation. Certain scaling parameters are identified. The concept is further investigated by a single particle simulation based on the ergodic principle and combined with a Monte Carlo code allowing for collisions with Argon atoms. Resonances, energy exchange, and distribution functions are obtained. The analytical results are confirmed by the numerical simulation. Pressure and electric field dependences are studied. Stochastic heating is found to be most efficient when the electron mean free path exceeds the size of a single coil cell. Then the mean energy increases approximately exponentially with the electric field amplitude.

  20. THE FINAL-PARSEC PROBLEM IN THE COLLISIONLESS LIMIT

    SciTech Connect

    Vasiliev, Eugene; Antonini, Fabio; Merritt, David E-mail: fabio.antonini@northwestern.edu

    2015-09-01

    A binary supermassive black hole loses energy via ejection of stars in a galactic nucleus, until emission of gravitational waves becomes strong enough to induce rapid coalescence. Evolution via the gravitational slingshot requires that stars be continuously supplied to the binary, and it is known that in spherical galaxies the reservoir of such stars is quickly depleted, leading to stalling of the binary at parsec-scale separations. Recent N-body simulations of galaxy mergers and isolated nonspherical galaxies suggest that this stalling may not occur in less idealized systems. However, it remains unclear to what degree these conclusions are affected by collisional relaxation, which is much stronger in the numerical simulations than in real galaxies. In this study, we present a novel Monte Carlo method that can efficiently deal with both collisional and collisionless dynamics, and with galaxy models having arbitrary shapes. We show that without relaxation, the final-parsec problem may be overcome only in triaxial galaxies. Axisymmetry is not enough, but even a moderate departure from axisymmetry is sufficient to keep the binary shrinking. We find that the binary hardening rate is always substantially lower than the maximum possible, “full-loss-cone” rate, and that it decreases with time, but that stellar-dynamical interactions are nevertheless able to drive the binary to coalescence on a timescale ≲1 Gyr in any triaxial galaxy.

  1. Modeling the Lyα Forest in Collisionless Simulations

    NASA Astrophysics Data System (ADS)

    Sorini, Daniele; Oñorbe, José; Lukić, Zarija; Hennawi, Joseph F.

    2016-08-01

    Cosmological hydrodynamic simulations can accurately predict the properties of the intergalactic medium (IGM), but only under the condition of retaining the high spatial resolution necessary to resolve density fluctuations in the IGM. This resolution constraint prohibits simulating large volumes, such as those probed by BOSS and future surveys, like DESI and 4MOST. To overcome this limitation, we present “Iteratively Matched Statistics” (IMS), a novel method to accurately model the Lyα forest with collisionless N-body simulations, where the relevant density fluctuations are unresolved. We use a small-box, high-resolution hydrodynamic simulation to obtain the probability distribution function (PDF) and the power spectrum of the real-space Lyα forest flux. These two statistics are iteratively mapped onto a pseudo-flux field of an N-body simulation, which we construct from the matter density. We demonstrate that our method can reproduce the PDF, line of sight and 3D power spectra of the Lyα forest with good accuracy (7%, 4%, and 7% respectively). We quantify the performance of the commonly used Gaussian smoothing technique and show that it has significantly lower accuracy (20%-80%), especially for N-body simulations with achievable mean inter-particle separations in large-volume simulations. In addition, we show that IMS produces reasonable and smooth spectra, making it a powerful tool for modeling the IGM in large cosmological volumes and for producing realistic “mock” skies for Lyα forest surveys.

  2. STATISTICAL MECHANICS OF COLLISIONLESS ORBITS. II. STRUCTURE OF HALOS

    SciTech Connect

    Williams, Liliya L. R.; Hjorth, Jens E-mail: jens@dark-cosmology.d

    2010-10-10

    In this paper, we present the density, {rho}, velocity dispersion, {sigma}, and {rho}/{sigma}{sup 3} profiles of isotropic systems which have the energy distribution, N({epsilon}) {proportional_to} [exp({phi}{sub 0} - {epsilon}) - 1], derived in Paper I. This distribution, dubbed {sup D}ARKexp{sup ,} is the most probable final state of a collisionless self-gravitating system, which is relaxed in terms of particle energies, but not necessarily in terms of angular momentum. We compare the DARKexp predictions with the results obtained using the extended secondary infall model (ESIM). The ESIM numerical scheme is optimally suited for this purpose because (1) it relaxes only through energy redistribution, leaving shell/particle angular momenta unaltered and (2) being a shell code with radially increasing shell thickness, it has very good mass resolution in the inner halo, where the various theoretical treatments give different predictions. The ESIM halo properties, and especially their energy distributions, are very well fit by DARKexp, implying that the techniques of statistical mechanics can be used to explain the structure of relaxed self-gravitating systems.

  3. Collisionless spectral-kinetic Simulation of the Multipole Resonance Probe

    NASA Astrophysics Data System (ADS)

    Dobrygin, Wladislaw; Szeremley, Daniel; Schilling, Christian; Oberrath, Jens; Eremin, Denis; Mussenbrock, Thomas; Brinkmann, Ralf Peter

    2012-10-01

    Plasma resonance spectroscopy is a well established plasma diagnostic method realized in several designs. One of these designs is the multipole resonance probe (MRP). In its idealized - geometrically simplified - version it consists of two dielectrically shielded, hemispherical electrodes to which an RF signal is applied. A numerical tool is under development, which is capable of simulating the dynamics of the plasma surrounding the MRP in electrostatic approximation. In the simulation the potential is separeted in an inner and a vacuum potential. The inner potential is influenced by the charged partilces and is calculated by a specialized Poisson solver. The vacuum potential fulfills Laplace's equetion and consists of the applied voltage of the probe as boundary condition. Both potentials are expanded in spherical harmonics. For a practical particle pusher implementation, the expansion must be appropriately truncated. Compared to a PIC simulation a grid is unnecessary to calculate the force on the particles. This work purpose is a collisionless kinetic simulation, which can be used to investigate kinetic effects on the resonance behavior of the MRP.[4pt] [1] M. Lapke et al., Appl. Phys. Lett. 93, 2008, 051502.

  4. Electron nongyrotropy in the context of collisionless magnetic reconnection

    SciTech Connect

    Aunai, Nicolas; Hesse, Michael; Kuznetsova, Maria

    2013-09-15

    Collisionless magnetized plasmas have the tendency to isotropize their velocity distribution function around the local magnetic field direction, i.e., to be gyrotropic, unless some spatial and/or temporal fluctuations develop at the particle gyroscales. Electron gyroscale inhomogeneities are well known to develop during the magnetic reconnection process. Nongyrotropic electron velocity distribution functions have been observed to play a key role in the dissipative process breaking the field line connectivity. In this paper, we present a new method to quantify the deviation of a particle population from gyrotropy. The method accounts for the full 3D shape of the distribution and its analytical formulation allows fast numerical computation. Regions associated with a significant degree of nongyrotropy are shown, as well as the kinetic origin of the nongyrotropy and the fluid signature it is associated with. Using the result of 2.5D Particle-In-Cell simulations of magnetic reconnection in symmetric and asymmetric configurations, it is found that neither the reconnection site nor the topological boundaries are generally associated with a maximized degree of nongyrotropy. Nongyrotropic regions do not correspond to a specific fluid behavior as equivalent nongyrotropy is found to extend over the electron dissipation region as well as in non-dissipative diamagnetic drift layers. The localization of highly nongyrotropic regions in numerical models and their correlation with other observable quantities can, however, improve the characterization of spatial structures explored by spacecraft missions.

  5. Improved Boundary Model for Particle Simulation of Collisionless Driven Reconnection

    NASA Astrophysics Data System (ADS)

    Ohtani, H.; Horiuchi, R.

    2006-10-01

    To clarify the relationship between particle kinetic effects and anomalous resistivity due to plasma instabilities in collisionless driven reconnection, we develop a three-dimensional Particle Simulation code for Magnetic reconnection in an Open system (PASMO). Recently, we have improved a model of upstream boundary to satisfy sufficiently the frozen-in condition both for ions and electrons. From the condition, plasma inflow is driven by ExB drift due to a driving electric field. In the previous model, particles are supplied into the system each time step, based on the particle flux through upstream boundary. The number density changes in proportion to magnetic field. In the improved model, particles in a cell near upstream boundary are newly loaded so as to satisfy shifted Maxwellian rigorously every time step. Using this model, the frozen-in condition is satisfied near the boundary both for electrons and ions. We will discuss the relationship between excitation of instability and mechanism of magnetic reconnection in the meeting.

  6. Collisionless shock structures of Earth and other planets

    NASA Technical Reports Server (NTRS)

    Greenstadt, Eugene W.; Moses, Stewart L.

    1993-01-01

    This report summarizes the closing segment of our multi-spacecraft, multi-instrument study of collisionless shock structure. In this last year of our study, we have necessarily concentrated on subjects that limited time and remaining resources could be expected to bring to reasonable stopping points, if not full conclusions. Our attention has been focused therefore on matters that were either well underway when the year began or that could be expected to yield rapidly completed reports publishable quickly in abbreviated versions. Contemporary publication delays prevent any new initiatives from reaching the literature within the year in the best of circumstances. The topics that fell into these categories were detailed plasma wave (pw) phenomenology in slow shocks in the Earth's distant geomagnetic tail, instantaneous orientations of theta(sub Bn) in quasiparallel (Q(sub parallel)) shock structure, and a comprehensive overview of the relationship between structural ULF waves in the Qll shock environment and waves in the magnetosphere, i.e. geomagnetic ULF pulsations. The remainder of this report describes our freshly completed results, discusses two related investigations of pw waves in the foreshock and magnetosheath, and appends the abstracts of published papers and the texts of papers in press.

  7. Kinetic Study of the Collisionless Expansion of Spherical Nanoplasmas

    NASA Astrophysics Data System (ADS)

    Peano, Fabio; Peinetti, Federico; Coppa, Gianni; Silva, Luis

    2006-10-01

    The collisionless expansion of spherical plasmas composed of cold ions and hot electrons is analyzed using a novel Lagrangian model [1], which allows a highly accurate, kinetic description of the radial motion of the ions and of the three-dimensional motion of nonrelativistic electrons (the validity of the model is checked both with 3D particle-in-cell simulations, performed with the OSIRIS framework [2], and using a new, ad-hoc developed particle method). The paradigmatic case of initially-Maxwellian electrons is investigated in detail for a wide range of initial conditions: simple relationships are deduced for the key expansion features [1], and a threshold in the electron energy is identified, beyond which the energy spectrum becomes monotonic and the Coulomb explosion regime is approached. Non-Maxwellian initial distributions of the electrons are also considered. [1] F. Peano et al., Phys. Rev. Lett. 96, 175002 (2006). [2] R.A. Fonseca et al., Lect. Notes Comp. Sci. 2331, 342 (Springer-Verlag, Heidelberg, 2002).

  8. Constraints on fluid modeling of magnetized collisionless plasmas

    NASA Astrophysics Data System (ADS)

    Sulem, Pierre-Louis; Passot, Thierry; Laveder, Dimitri; Hunana, Peter; Henri, Pierre

    2013-04-01

    It is well known that a complete description of the solar wind requires a kinetic description and that, particularly at sub-proton scales, kinetic effects cannot be ignored. It is nevertheless usually assumed that, at scales significantly larger than the proton gyroscale, MHD or bifluid models with isotropic pressures provide a satisfactory description. We demonstrate that in order to accurately capture, even at large scales, the low-frequency dynamics of a collisionless plasma, a fluid model should actually include kinetic effects such as Landau damping and finite Larmor radius corrections. Indeed, the usual polytropic bi-fluid models strongly overestimate the magnetic compressibility of oblique Alfvén waves. Retaining pressure anisotropy and Landau damping partially corrects this deficiency, but an accurate description of the Alfvén wave polarization and of the mirror instability growth rate actually requires to take into account the finite-Larmor corrections to all the retained moments. These remarks lead us to use the so-called FLR Landau fluid model (Phys. Plasmas, 19, 082113, 2012), for which a three-dimensional parallel code has been developed. Preliminary simulations in the turbulent regime will be presented, showing the reduction of the fluid compressibility and the inhibition of the parallel energy transfer. We will also report on the development of temperature anisotropy, associated with non-resonant perpendicular ion heating and constrained by the onset of the mirror instability.

  9. Firehose, Mirror, and Magnetorotational Instabilities in a Collisionless Shearing Plasma

    NASA Astrophysics Data System (ADS)

    Kunz, Matthew; Schekochihin, Alexander; Stone, James; Melville, Scott; Quataert, Eliot

    2015-11-01

    Describing the large-scale behavior of weakly collisional magnetized plasmas, such as the solar wind, black-hole accretion flows, or the intracluster medium of galaxy clusters, necessitates a detailed understanding of the kinetic-scale physics governing the dynamics of magnetic fields and the transport of momentum and heat. This physics is complicated by the fact that such plasmas are expected to exhibit particle distribution functions with unequal thermal pressures in the directions parallel and perpendicular to the local magnetic field. This pressure anisotropy can trigger fast Larmor-scale instabilities - namely, firehose and mirror - which solar-wind observations suggest to be effective at regulating the pressure anisotropy to marginally stable levels. Results from weakly nonlinear theory and hybrid-kinetic particle-in-cell simulations that address how marginal stability is achieved and maintained in a plasma whose pressure anisotropy is driven by a shearing magnetic field are presented. Fluctuation spectra and effective collisionality are highlighted. These results are placed in the context of our ongoing studies of magnetorotational turbulence in collisionless astrophysical accretion disks, in which microscale plasma instabilities regulate angular-momentum transport.

  10. The Final-parsec Problem in the Collisionless Limit

    NASA Astrophysics Data System (ADS)

    Vasiliev, Eugene; Antonini, Fabio; Merritt, David

    2015-09-01

    A binary supermassive black hole loses energy via ejection of stars in a galactic nucleus, until emission of gravitational waves becomes strong enough to induce rapid coalescence. Evolution via the gravitational slingshot requires that stars be continuously supplied to the binary, and it is known that in spherical galaxies the reservoir of such stars is quickly depleted, leading to stalling of the binary at parsec-scale separations. Recent N-body simulations of galaxy mergers and isolated nonspherical galaxies suggest that this stalling may not occur in less idealized systems. However, it remains unclear to what degree these conclusions are affected by collisional relaxation, which is much stronger in the numerical simulations than in real galaxies. In this study, we present a novel Monte Carlo method that can efficiently deal with both collisional and collisionless dynamics, and with galaxy models having arbitrary shapes. We show that without relaxation, the final-parsec problem may be overcome only in triaxial galaxies. Axisymmetry is not enough, but even a moderate departure from axisymmetry is sufficient to keep the binary shrinking. We find that the binary hardening rate is always substantially lower than the maximum possible, “full-loss-cone” rate, and that it decreases with time, but that stellar-dynamical interactions are nevertheless able to drive the binary to coalescence on a timescale ≲1 Gyr in any triaxial galaxy.

  11. Landau, Case, van Kampen and Collisionless Fluid Closures

    NASA Astrophysics Data System (ADS)

    Joseph, Ilon

    2015-11-01

    Landau damping represents a fundamental paradox within plasma physics. The equations of motion of classical particles and fields are symmetric under time-reversal; yet, the open system formed by integration over velocity space is not invariant and damping results from phase-mixing. Here, it is shown that the Case-van Kampen theorem can be extended to magnetized plasmas: the linear eigenfunctions provide a complete representation of the particle distribution function and exponentially damped and growing eigenmodes must appear in pairs. The numerical Case-van Kampen transformation can performed efficiently in Fourier velocity space and allows fast timescales in the evolution of the system to be treated using exponential integration. On the other hand, fluid moments require integration over velocity space, and, thus, representation of Landau damping requires explicit introduction of the arrow of time through a collisionless damping operator. This operator captures linear phenomena at the cost of damping nonlinear phenomena such as the plasma echo. Numerical comparisons of these two rather different representations will be presented. LLNL-ABS-674917 prepared by LLNL under Contract DE-AC52-07NA27344.

  12. Secondary island formation in collisional and collisionless kinetic simulations of magnetic reconnection

    SciTech Connect

    Dayton, William S; Roytershteyn, Vadim; Gary, Peter; Yin, L; Albright, B J; Bowers, K J; Karimabadi, H

    2009-01-01

    The evolution of magnetic reconnection in large-scale systems often gives rise to extended current layers that are unstable to the formation of secondary magnetic islands. The role of these islands in the reconnection process and the conditions under which they form remains a subject of debate. In this work, we benchmark two different kinetic particle-in-cell codes to address the formation of secondary islands for several types of global boundary conditions. The influence on reconnection is examined for a range of conditions and collisionality limits. Although secondary islands are observed in all cases, their influence on reconnection may be different depending on the regime. In the collisional limit, the secondary islands playa key role in breaking away from the Sweet-Parker scaling and enabling faster reconnection. In the collisionless limit, their formation is one mechanism for controlling the length of the diffusion region. In both limits, the onset of secondary islands leads to a time dependent behavior in the reconnection rate. In all cases considered, the number of secondary islands increases for larger systems.

  13. Theory of spatially non-symmetric kinetic equilibria for collisionless plasmas

    SciTech Connect

    Cremaschini, Claudio; Tessarotto, Massimo

    2013-01-15

    The problem posed by the possible existence/non-existence of spatially non-symmetric kinetic equilibria has remained unsolved in plasma theory. For collisionless magnetized plasmas, this involves the construction of stationary solutions of the Vlasov-Maxwell equations. In this paper, the issue is addressed for non-relativistic plasmas both i