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Sample records for forced magnetic reconnection

  1. Forced magnetic reconnection

    SciTech Connect

    Hahm, T.S.; Kulsrud, R.M.

    1984-11-01

    By studying a simple model problem, we examine the time evolution of magnetic field islands which are induced by perturbing the boundary surrounding an incompressible plasma with a resonant surface inside. We find that for sufficiently small boundary perturbations, the reconnection and island formation process occurs on the tearing mode time scale defined by Furth, Killeen, and Rosenbluth. For larger perturbations the time scale is that defined by Rutherford. The resulting asymptotic equilibrium is such that surface currents in the resonant region vanish. A detailed analytical picture of this reconnection process is presented.

  2. Nonlinear regimes of forced magnetic reconnection

    SciTech Connect

    Vekstein, G.; Kusano, K.

    2015-09-15

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

  3. Forced Magnetic Reconnection In A Tokamak Plasma

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    The theory of forced magnetic field reconnection induced by an externally imposed resonant magnetic perturbation usually uses a sheared slab or cylindrical magnetic field model and often focuses on the potential time-asymptotic induced magnetic island state. However, tokamak plasmas have significant magnetic geometry and dynamical plasma toroidal rotation screening effects. Also, finite ion Larmor radius (FLR) and banana width (FBW) effects can damp and thus limit the width of a nascent magnetic island. A theory that is more applicable for tokamak plasmas is being developed. This new model of the dynamics of forced magnetic reconnection considers a single helicity magnetic perturbation in the tokamak magnetic field geometry, uses a kinetically-derived collisional parallel electron flow response, and employs a comprehensive dynamical equation for the plasma toroidal rotation frequency. It is being used to explore the dynamics of bifurcation into a magnetically reconnected state in the thin singular layer around the rational surface, evolution into a generalized Rutherford regime where the island width exceeds the singular layer width, and assess the island width limiting effects of FLR and FBW polarization currents. Support by DoE grants DE-FG02-86ER53218, DE-FG02-92ER54139.

  4. Forced magnetic reconnection in Tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Cole, Andrew Joseph

    This dissertation addresses two related problems in the study of forced magnetic reconnection in Tokamak plasmas. First, a recent controversy concerning a model forced magnetic reconnection problem, the Taylor problem, has been resolved. The criticisms of Ishizawa and Tokuda [21] concerning the original analysis of Hahm and Kulsrud [17] are shown to be unwarranted, both analytically and numerically. Second, one possible reason for the discrepancy between recent experimental [29] and previous theoretical [13] scaling of the critical error-field penetration threshold with device parameters is addressed. The theory in question is entirely based on a single-fluid MHD (magnetohydrodynamical) treatment of the plasma. As is well-known, high temperature plasmas are far better modeled using the drift-MHD ordering.[18] Hence we develop a drift-MHD theory of error-field penetration. Although two new drift-MHD plasma response regimes are identified, the overall threshold scaling with device parameters is not altogether different from that predicted by single-fluid MHD.

  5. Magnetic Reconnection

    NASA Video Gallery

    This science visualization shows a magnetospheric substorm, during which, magnetic reconnection causes energy to be rapidly released along the field lines in the magnetotail, that part of the magne...

  6. Visco-Resistive MHD Modeling Benchmark of Forced Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Beidler, M. T.; Hegna, C. C.; Sovinec, C. R.; Callen, J. D.; Ferraro, N. M.

    2016-10-01

    The presence of externally-applied 3D magnetic fields can affect important phenomena in tokamaks, including mode locking, disruptions, and edge localized modes. External fields penetrate into the plasma and can lead to forced magnetic reconnection (FMR), and hence magnetic islands, on resonant surfaces if the local plasma rotation relative to the external field is slow. Preliminary visco-resistive MHD simulations of FMR in a slab geometry are consistent with theory. Specifically, linear simulations exhibit proper scaling of the penetrated field with resistivity, viscosity, and flow, and nonlinear simulations exhibit a bifurcation from a flow-screened to a field-penetrated, magnetic island state as the external field is increased, due to the 3D electromagnetic force. These results will be compared to simulations of FMR in a circular cross-section, cylindrical geometry by way of a benchmark between the NIMROD and M3D-C1 extended-MHD codes. Because neither this geometry nor the MHD model has the physics of poloidal flow damping, the theory of will be expanded to include poloidal flow effects. The resulting theory will be tested with linear and nonlinear simulations that vary the resistivity, viscosity, flow, and external field. Supported by OFES DoE Grants DE-FG02-92ER54139, DE-FG02-86ER53218, DE-AC02-09CH11466, and the SciDAC Center for Extended MHD Modeling.

  7. Magnetic Reconnection

    SciTech Connect

    Masaaki Yamada, Russell Kulsrud and Hantao Ji

    2009-09-17

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

  8. Reconnection rates in driven magnetic reconnection

    SciTech Connect

    Birn, J.; Hesse, M.

    2007-08-15

    Using resistive magnetohydrodynamic simulations, we investigate the influence of various parameters on the reconnection rate in two scenarios of magnetic reconnection. The first scenario consists of the ''Newton Challenge'' problem [Birn et al., Geophys. Res. Lett. 32, L06105 (2005)]. In this scenario, reconnection is initiated in a plane Harris-type current sheet by temporally limited, spatially varying, inflow of magnetic flux. The second scenario consists of the well-studied island coalescence problem. This scenario starts from an equilibrium containing periodic magnetic islands with parallel current filaments. Due to the attraction between parallel currents, pairs of islands may move toward each other, forming a current sheet in between. This leads to reconnection and ultimately the merging of islands. In either scenario, magnetic reconnection may be considered as being driven by external or internal forcing. Consistent with that interpretation we find that in either case the maximum reconnection rate (electric field) depends approximately linearly on the maximum driving electric field, when other parameters remain unchanged. However, this can be understood mostly from the change of characteristic background parameters; particularly, the increase of the magnetic field strength in the inflow region due to the added magnetic flux. This interpretation is consistent with the result that the maximum of the reconnection electric field is assumed significantly later (tens of Alfven times) than the maximum driving and typically does not match the instantaneous driving electric field. Furthermore, the reconnection rate also depends on the resistivity and the time scale of the driving.

  9. On transition from Alfvén resonance to forced magnetic reconnection

    SciTech Connect

    Luan, Q.; Wang, X.

    2014-07-15

    We revisit the transition from Alfvén resonance to forced magnetic reconnection with a focus on the property of their singularities. As the driven frequency tends to zero, the logarithmic singularity of Alfvén resonance shifts to the power-law singularity of forced reconnection, due to merging of the two resonance layers. The transition criterion depends on either kinetic effects or dissipations that resolve the singularity. As an example, a small but finite resistivity η is introduced to investigate the transition process. The transition threshold is then obtained as the driven frequency reaches a level of ∼O((η/k){sup 1/3})

  10. Physics of forced magnetic reconnection in coaxial helicity injection experiments in National Spherical Torus Experiment

    SciTech Connect

    Ebrahimi, F.; Bhattacharjee, A.; Raman, R.; Hooper, E. B.; Sovinec, C. R.

    2014-05-15

    We numerically examine the physics of fast flux closure in transient coaxial helicity injection (CHI) experiments in National Spherical Torus Experiment (NSTX). By performing resistive Magnetohydrodynamics (MHD) simulations with poloidal injector coil currents held constant in time, we find that closed flux surfaces are formed through forced magnetic reconnection. Through a local Sweet-Parker type reconnection with an elongated current sheet in the injector region, closed flux surfaces expand in the NSTX global domain. Simulations demonstrate outflows approaching poloidally Alfvénic flows and reconnection times consistent with the Sweet-Parker model. Critical requirements for magnetic reconnection and flux closure are studied in detail. These primary effects, which are magnetic diffusivity, injector flux, injector flux footprint width, and rate of injector voltage reduction, are simulated for transient CHI experiments. The relevant time scales for effective reconnection are τ{sub V}<τ{sub rec}≈τ{sub A}√(S)(1+Pm){sup 1/4}<τ{sub R}, where τ{sub V} is the time for the injector voltage reduction, τ{sub A} is the poloidal Alfvén transit time, τ{sub R} is the global resistive diffusion time, and Pm and S are Prandtl and Lundquist numbers.

  11. Reconnection of Magnetic Fields

    NASA Technical Reports Server (NTRS)

    1984-01-01

    Spacecraft observations of steady and nonsteady reconnection at the magnetopause are reviewed. Computer simulations of three-dimensional reconnection in the geomagnetic tail are discussed. Theoretical aspects of the energization of particles in current sheets and of the microprocesses in the diffusion region are presented. Terrella experiments in which magnetospheric reconnection is simulated at both the magnetopause and in the tail are described. The possible role of reconnection in the evolution of solar magnetic fields and solar flares is discussed. A two-dimensional magnetohydrodynamic computer simulation of turbulent reconnection is examined. Results concerning reconnection in Tokamak devices are also presented.

  12. Magnetic field reconnection

    NASA Astrophysics Data System (ADS)

    Axford, W. I.

    The fundamental principles of particle acceleration by magnetic reconnection in cosmic plasmas are reviewed. The history of reconnection models is traced, and consideration is given to the Kelvin-Helmholtz theorem, the frozen-field theorem, the application of the Kelvin-Helmholtz theorem to a collisionless plasma, solutions to specific reconnection problems, and configurational instability. Diagrams and graphs are provided, and the objections raised by critics of the reconnection theory and/or its astrophysical applications are discussed.

  13. Magnetic reconnection launcher

    SciTech Connect

    Cowan, M.

    1989-04-04

    An electromagnetic launcher is described, which includes a plurality of electrical stages which are energized sequentially in synchrony with the passage of a projectile. Each stage of the launcher includes two or more coils which are arranged coaxially on either closed-loop or straight lines to form gaps between their ends. The projectile has an electrically conductive gap-portion that passes through all the gaps of all the stages in a direction transverse to the axes of the coils. The coils receive an electric current, store magnetic energy, and convert a significant portion of the stored magnetic energy into kinetic energy of the projectile by magnetic reconnection as the gap portion of the projectile moves through the gap. The magnetic polarity of the opposing coils is in the same direction, e.g. N-S-N-S. A gap portion of the projectile may be made from aluminum and is propelled by the reconnection of magnetic flux stored in the coils which causes accelerating forces to act upon the projectile at both the rear vertical surface of the projectile and at the horizontal surfaces of the projectile near its rear. The gap portion of the projectile may be flat, rectangular and longer than the length of the opposing coils and fit loosely within the gap between the opposing coils.

  14. Magnetic reconnection launcher

    DOEpatents

    Cowan, Maynard

    1989-01-01

    An electromagnetic launcher includes a plurality of electrical stages which are energized sequentially in synchrony with the passage of a projectile. Each stage of the launcher includes two or more coils which are arranged coaxially on either closed-loop or straight lines to form gaps between their ends. The projectile has an electrically conductive gap-portion that passes through all the gaps of all the stages in a direction transverse to the axes of the coils. The coils receive an electric current, store magnetic energy, and convert a significant portion of the stored magnetic energy into kinetic energy of the projectile by magnetic reconnection as the gap portion of the projectile moves through the gap. The magnetic polarity of the opposing coils is in the same direction, e.g. N-S-N-S. A gap portion of the projectile may be made from aluminum and is propelled by the reconnection of magnetic flux stored in the coils which causes accelerating forces to act upon the projectile at both the rear vertical surface of the projectile and at the horizontal surfaces of the projectile near its rear. The gap portion of the projectile may be flat, rectangular and longer than the length of the opposing coils and fit loosely within the gap between the opposing coils.

  15. Perspectives on magnetic reconnection

    PubMed Central

    Yamada, Masaaki

    2016-01-01

    Magnetic reconnection is a topological rearrangement of magnetic field that occurs on time scales much faster than the global magnetic diffusion time. Since the field lines break on microscopic scales but energy is stored and the field is driven on macroscopic scales, reconnection is an inherently multi-scale process that often involves both magnetohydrodynamic (MHD) and kinetic phenomena. In this article, we begin with the MHD point of view and then describe the dynamics and energetics of reconnection using a two-fluid formulation. We also focus on the respective roles of global and local processes and how they are coupled. We conclude that the triggers for reconnection are mostly global, that the key energy conversion and dissipation processes are either local or global, and that the presence of a continuum of scales coupled from microscopic to macroscopic may be the most likely path to fast reconnection. PMID:28119547

  16. Perspectives on magnetic reconnection

    SciTech Connect

    Zweibel, Ellen G.; Yamada, Masaaki

    2016-12-07

    Magnetic reconnection is a topological rearrangement of magnetic field that occurs on time scales much faster than the global magnetic diffusion time. Since the field lines break on microscopic scales but energy is stored and the field is driven on macroscopic scales, reconnection is an inherently multi-scale process that often involves both magnetohydrodynamic (MHD) and kinetic phenomena. In this article, we begin with the MHD point of view and then describe the dynamics and energetics of reconnection using a two-fluid formulation. We also focus on the respective roles of global and local processes and how they are coupled. Here, we conclude that the triggers for reconnection are mostly global, that the key energy conversion and dissipation processes are either local or global, and that the presence of a continuum of scales coupled from microscopic to macroscopic may be the most likely path to fast reconnection.

  17. Perspectives on magnetic reconnection

    DOE PAGES

    Zweibel, Ellen G.; Yamada, Masaaki

    2016-12-07

    Magnetic reconnection is a topological rearrangement of magnetic field that occurs on time scales much faster than the global magnetic diffusion time. Since the field lines break on microscopic scales but energy is stored and the field is driven on macroscopic scales, reconnection is an inherently multi-scale process that often involves both magnetohydrodynamic (MHD) and kinetic phenomena. In this article, we begin with the MHD point of view and then describe the dynamics and energetics of reconnection using a two-fluid formulation. We also focus on the respective roles of global and local processes and how they are coupled. Here, wemore » conclude that the triggers for reconnection are mostly global, that the key energy conversion and dissipation processes are either local or global, and that the presence of a continuum of scales coupled from microscopic to macroscopic may be the most likely path to fast reconnection.« less

  18. THEMIS Sees Magnetic Reconnection

    NASA Video Gallery

    THEMIS observations confirm for the first time that magnetic reconnection in the magnetotail triggers the onset of substorms. Substorms are the sudden violent eruptions of space weather that releas...

  19. 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.

  20. Forced Magnetic Reconnection and Field Penetration of an Externally Applied Rotating Helical Magnetic Field in the TEXTOR Tokamak

    SciTech Connect

    Kikuchi, Y.; Finken, K. H.; Jakubowski, M.; Koslowski, H. R.; Kraemer-Flecken, A.; Lehnen, M.; Liang, Y.; Reiser, D.; Wolf, R. C.; Zimmermann, O.; Bock, M. F. M. de; Jaspers, R.; Matsunaga, G.

    2006-08-25

    The magnetic field penetration process into a magnetized plasma is of basic interest both for plasma physics and astrophysics. In this context special measurements on the field penetration and field amplification are performed by a Hall probe on the dynamic ergodic divertor (DED) on the TEXTOR tokamak and the data are interpreted by a two-fluid plasma model. It is observed that the growth of the forced magnetic reconnection by the rotating DED field is accompanied by a change of the plasma fluid rotation. The differential rotation frequency between the DED field and the plasma plays an important role in the process of the excitation of tearing modes. The momentum input from the rotating DED field to the plasma is interpreted by both a ponderomotive force at the rational surface and a radial electric field modified by an edge ergodization.

  1. Gyrotropy During Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Swisdak, M.

    2015-12-01

    Gyrotropic particle distributions -- those that can be characterized completely by temperatures meausred parallel and perpendicular to the local magnetic field -- are the norm in many plasmas. However, near locations where magnetic topology suddenly changes, e.g., where magnetic reconnection occurs, gyrotropy can be expected to be violated. If these departures from gyrotropy are quantifiable they are useful as probes since magnetic topological changes are, in some sense, non-local while gyrotropy can be measured locally. I will discuss previously proposed measures of gyrotropy, give examples of cases where they give unphysical results, and propose a new measure. By applying this measure to particle-in-cell simulations of reconnection I will show that it does an excellent job of localizing reconnection sites. I will also show how gyrotropy can be quickly calculated in any case where the full pressure tensor is available. This has obvious applications to the interpretation of MMS data.

  2. Forced magnetic reconnection in a plasma sheet with localized resistivity profile excited by lower hybrid drift type instability

    NASA Technical Reports Server (NTRS)

    Hoshino, M.

    1991-01-01

    A forced magnetic reconnection process with a temporal evolution of resistivity is studied for a plasma sheet with a nonuniform resistivity profile based on the nonlocal mode structure of the lower hybrid drift type instability. The growth rate of the mode found is almost independent of the resistivity at the neutral sheet, but depends on the resistivity of the region of maximum density gradient away from the neutral sheet. This is studied by using both a nonlinear numerical MHD simulation and a linear theory. The mode may be relevant to the prevalent theoretical concept of MHD reconnection and the localized anomalous resistivity profile based on the lower hybrid drift instability.

  3. Magnetic reconnection launcher

    DOEpatents

    Cowan, M.

    1987-04-06

    An electromagnetic launcher includes a plurality of electrical stages which are energized sequentially in the launcher with the passage of a projectiles. Each stage of the launcher includes two or more coils which are arranged coaxially on either closed-loop or straight lines to form gaps between their ends. The projectile has an electrically conductive gap-portion that passes through all the gaps of all the stages in a direction transverse to the axes of the coils. The coils receive an electric current, store magnetic energy, and convert a significant portion of the stored magnetic energy into kinetic energy of the projectile moves through the gap. The magnetic polarity of the opposing coils is in the same direction, e.g. N-S-N-S. A gap portion of the projectile may be made from aluminum and is propelled by the reconnection of magnetic flux stored in the coils which causes accelerating forces to act upon the projectile and at the horizontal surfaces of the projectile near its rear. The gap portion of the projectile may be flat, rectangular and longer than the length of the opposing coils. The gap portion of the projectile permits substantially unrestricted distribution of the induced currents so that current densities are only high where the useful magnetic force is high. This allows designs which permit ohmic oblation from the rear surfaces of the gap portion of the projectile allowing much high velocities to be achieved. An electric power apparatus controls the electric power supplied to the opposing coils until the gap portion of the projectile substantially occupies the gap between the coils, at which time the coils are supplied with peak current quickly. 8 figs.

  4. Forced reconnection in the Hall limit

    NASA Astrophysics Data System (ADS)

    Huba, J. D.

    2006-12-01

    We present new numerical results of the dynamics of forced magnetic reconnection in the Hall limit using the NRL Hall MHD code VooDoo. The system is forced by imposing inflow boundary conditions on the plasma density and velocity, and the magnetic field. A magnetic field of opposite polarity is injected from opposite boundaries. The inflow velocity is spatially uniform but the density profile is spatially nonuniform which allows an X-line to develop and magnetic reconnection to proceed. We present simulation results for various inflow conditions in both 2D and 3D geometries. We apply our results to laboratory and space plasma processes. Research supported by ONR and NASA.

  5. Forced Reconnection in the Hall Limit

    NASA Astrophysics Data System (ADS)

    Huba, J.

    2006-10-01

    We present new numerical results of the dynamics of forced magnetic reconnection in the Hall limit using the NRL Hall MHD code VooDoo. The system is forced by imposing inflow boundary conditions on the plasma density and velocity, and the magnetic field. A magnetic field of opposite polarity is injected from opposite boundaries. The inflow velocity is spatially uniform but the density profile is spatially nonuniform which allows an X-line to develop and magnetic reconnection to proceed. We present simulation results for various inflow conditions in both 2D and 3D geometries. We apply our results to laboratory and space plasma processes.

  6. TURBULENT GENERAL MAGNETIC RECONNECTION

    SciTech Connect

    Eyink, G. L.

    2015-07-10

    Plasma flows with a magnetohydrodynamic (MHD)-like turbulent inertial range, such as the solar wind, require a generalization of general magnetic reconnection (GMR) theory. We introduce the slip velocity source vector per unit arclength of field line, the ratio of the curl of the non-ideal electric field in the generalized Ohm’s Law and magnetic field strength. It diverges at magnetic nulls, unifying GMR with null-point reconnection. Only under restrictive assumptions is the slip velocity related to the gradient of quasi-potential (which is the integral of parallel electric field along magnetic field lines). In a turbulent inertial range, the non-ideal field becomes tiny while its curl is large, so that line slippage occurs even while ideal MHD becomes accurate. The resolution is that ideal MHD is valid for a turbulent inertial range only in a weak sense that does not imply magnetic line freezing. The notion of weak solution is explained in terms of renormalization group (RG) type theory. The weak validity of the ideal Ohm’s law in the inertial range is shown via rigorous estimates of the terms in the generalized Ohm’s Law. All non-ideal terms are irrelevant in the RG sense and large-scale reconnection is thus governed solely by ideal dynamics. We discuss the implications for heliospheric reconnection, in particular for deviations from the Parker spiral model. Solar wind observations show that reconnection in a turbulence-broadened heliospheric current sheet, which is consistent with Lazarian–Vishniac theory, leads to slip velocities that cause field lines to lag relative to the spiral model.

  7. Forcing continuous reconnection in hybrid simulations

    SciTech Connect

    Laitinen, T. V. Janhunen, P.; Jarvinen, R.; Kallio, E.

    2014-07-15

    We have performed hybrid simulations of driven continuous reconnection with open boundary conditions. Reconnection is started by a collision of two subsonic plasma fronts with opposite magnetic fields, without any specified magnetic field configuration as initial condition. Due to continued forced plasma inflow, a current sheet co-located with a dense and hot plasma sheet develops. The translational symmetry of the current sheet is broken by applying a spatial gradient in the inflow speed. We compare runs with and without localized resistivity: reconnection is initiated in both cases, but localized resistivity stabilizes it and enhances its efficiency. The outflow speed reaches about half of Alfvén speed. We quantify the conversion of magnetic energy to kinetic energy of protons and to Joule heating and show that with localized resistivity, kinetic energy of protons is increased on average five-fold in the reconnection in our simulation case.

  8. Relativistic Magnetic Reconnection in Kerr Spacetime.

    PubMed

    Asenjo, Felipe A; Comisso, Luca

    2017-02-03

    The magnetic reconnection process is analyzed for relativistic magnetohydrodynamical plasmas around rotating black holes. A simple generalization of the Sweet-Parker model is used as a first approximation to the problem. The reconnection rate, as well as other important properties of the reconnection layer, has been calculated taking into account the effect of spacetime curvature. Azimuthal and radial current sheet configurations in the equatorial plane of the black hole have been studied, and the case of small black hole rotation rate has been analyzed. For the azimuthal configuration, it is found that the black hole rotation decreases the reconnection rate. On the other hand, in the radial configuration, it is the gravitational force created by the black hole mass that decreases the reconnection rate. These results establish a fundamental interaction between gravity and magnetic reconnection in astrophysical contexts.

  9. Relativistic Magnetic Reconnection in Kerr Spacetime

    NASA Astrophysics Data System (ADS)

    Asenjo, Felipe A.; Comisso, Luca

    2017-02-01

    The magnetic reconnection process is analyzed for relativistic magnetohydrodynamical plasmas around rotating black holes. A simple generalization of the Sweet-Parker model is used as a first approximation to the problem. The reconnection rate, as well as other important properties of the reconnection layer, has been calculated taking into account the effect of spacetime curvature. Azimuthal and radial current sheet configurations in the equatorial plane of the black hole have been studied, and the case of small black hole rotation rate has been analyzed. For the azimuthal configuration, it is found that the black hole rotation decreases the reconnection rate. On the other hand, in the radial configuration, it is the gravitational force created by the black hole mass that decreases the reconnection rate. These results establish a fundamental interaction between gravity and magnetic reconnection in astrophysical contexts.

  10. Synchrotron Cooling in Relativistic Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Fish, Jake; Werner, Gregory; Uzdensky, Dmitri

    2016-10-01

    Radiative processes are typically unimportant to the dynamics of plasmas investigated by most magnetic reconnection studies. However, some astrophysical phenomena exhibit conditions in which radiative cooling is significant over dynamic timescales. For example, strong synchrotron cooling controls the energetics of reconnection in magnetospheres of pulsars with strong magnetic fields, including the Crab pulsar. We performed a series of simulations of reconnection in the presence of radiative cooling using the particle-in-cell code Zeltron which self-consistently includes the synchrotron radiation reaction force. We examine the resulting global particle energy distribution, which is strongly cooled by radiation over time at high energies. Basic plasma parameters, such as the average particle energy and density in the reconnection layer and at magnetic O-points, are also measured as functions of radiative cooling's importance. Our results show strong plasma cooling and compression in plasmoids due to radiation well before the reconnecting layer is significantly affected. This work is supported by DOE and NASA.

  11. Acceleration during magnetic reconnection

    SciTech Connect

    Beresnyak, Andrey; Li, Hui

    2015-07-16

    The presentation begins with colorful depictions of solar x-ray flares and references to pulsar phenomena. Plasma reconnection is complex, could be x-point dominated or turbulent, field lines could break due to either resistivity or non-ideal effects, such as electron pressure anisotropy. Electron acceleration is sometimes observed, and sometimes not. One way to study this complex problem is to have many examples of the process (reconnection) and compare them; the other way is to simplify and come to something robust. Ideal MHD (E=0) turbulence driven by magnetic energy is assumed, and the first-order acceleration is sought. It is found that dissipation in big (length >100 ion skin depths) current sheets is universal and independent on microscopic resistivity and the mean imposed field; particles are regularly accelerated while experiencing curvature drift in flows driven by magnetic tension. One example of such flow is spontaneous reconnection. This explains hot electrons with a power-law tail in solar flares, as well as ultrashort time variability in some astrophysical sources.

  12. Collisionless Magnetic Reconnection in Space Plasmas

    NASA Astrophysics Data System (ADS)

    Treumann, Rudolf A.; Baumjohann, Wolfgang

    2013-12-01

    Magnetic reconnection, the merging of oppositely directed magnetic fields that leads to field reconfiguration, plasma heating, jetting and acceleration, is one of the most celebrated processes in collisionless plasmas. It requires the violation of the frozen-in condition which ties gyrating charged particles to the magnetic field inhibiting diffusion. Ongoing reconnection has been identified in near-Earth space as being responsible for the excitation of substorms, magnetic storms, generation of field aligned currents and their consequences, the wealth of auroral phenomena. Its theoretical understanding is now on the verge of being completed. Reconnection takes place in thin current sheets. Analytical concepts proceeded gradually down to the microscopic scale, the scale of the electron skin depth or inertial length, recognizing that current layers that thin do preferentially undergo spontaneous reconnection. Thick current layers start reconnecting when being forced by plasma inflow to thin. For almost half a century the physical mechanism of reconnection has remained a mystery. Spacecraft in situ observations in combination with sophisticated numerical simulations in two and three dimensions recently clarified the mist, finding that reconnection produces a specific structure of the current layer inside the electron inertial (also called electron diffusion) region around the reconnection site, the X line. Onset of reconnection is attributed to pseudo-viscous contributions of the electron pressure tensor aided by electron inertia and drag, creating a complicated structured electron current sheet, electric fields, and an electron exhaust extended along the current layer. We review the general background theory and recent developments in numerical simulation on collisionless reconnection. It is impossible to cover the entire field of reconnection in a short space-limited review. The presentation necessarily remains cursory, determined by our taste, preferences, and kn

  13. Observational Signatures of Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina

    2014-01-01

    Magnetic reconnection is often referred to as the primary source of energy release during solar flares. Directly observing reconnection occurring in the solar atmosphere, however, is not trivial considering that the scale size of the diffusion region is magnitudes smaller than the observational capabilities of current instrumentation, and coronal magnetic field measurements are not currently sufficient to capture the process. Therefore, predicting and studying observationally feasible signatures of the precursors and consequences of reconnection is necessary for guiding and verifying the simulations that dominate our understanding. I will present a set of such observations, particularly in connection with long-duration solar events, and compare them with recent simulations and theoretical predictions.

  14. Properties of asymmetric magnetic reconnection

    SciTech Connect

    Birn, J.; Borovsky, J. E.; Hesse, M.

    2008-03-15

    Properties of magnetic reconnection are investigated in two-dimensional, resistive magnetohydrodynamic (MHD) simulations of current sheets separating plasmas with different magnetic field strengths and densities. Specific emphasis is on the influence of the external parameters on the reconnection rate. The effect of the dissipation in the resistive MHD model is separated from this influence by evaluating resistivity dependence together with the dependence on the background parameters. Two scenarios are considered, which may be distinguished as driven and nondriven reconnection. In either scenario, the maximum reconnection rate (electric field) is found to depend on appropriate hybrid expressions based on a magnetic field strength and an Alfven speed derived from the characteristic values in the two inflow regions. The scaling compares favorably with an analytic formula derived recently by Cassak and Shay [Phys. Plasmas 14, 102114 (2007)] applied to the regime of fast reconnection. An investigation of the energy flow and conversion in the vicinity of the reconnection site revealed a significant role of enthalpy flux generation, in addition to the expected conversion of Poynting flux to kinetic energy flux. This enthalpy flux generation results from Ohmic heating as well as adiabatic, that is, compressional heating. The latter is found more important when the magnetic field strengths in the two inflow regions are comparable in magnitude.

  15. Magnetic Reconnection in Solar Flares

    NASA Astrophysics Data System (ADS)

    Forbes, Terry G.

    2016-05-01

    Reconnection has at least three possible roles in solar flares: First, it may contribute to the build-up of magnetic energy in the solar corona prior to flare onset; second, it may directly trigger the onset of the flare; and third, it may allow the release of magnetic energy by relaxing the magnetic field configuration to a lower energy state. Although observational support for the first two roles is somewhat limited, there is now ample support for the third. Within the last few years EUV and X-ray instruments have directly observed the kind of plasma flows and heating indicative of reconnection. Continued improvements in instrumentation will greatly help to determine the detailed physics of the reconnection process in the solar atmosphere. Careful measurement of the reconnection outflows will be especially helpful in this regard. Current observations suggest that in some flares the jet outflows are accelerated within a short diffusion region that is more characteristic of Petschek-type reconnection than Sweet-Parker reconnection. Recent resistive MHD theoretical and numerical analyses predict that the length of the diffusion region should be just within the resolution range of current X-ray and EUV telescopes if the resistivity is uniform. On the other hand, if the resistivity is not uniform, the length of the diffusion region could be too short for the outflow acceleration region to be observable.

  16. Improved Magnetic Reconnection Experiment at FRC Device

    NASA Astrophysics Data System (ADS)

    Xu, Ming; Zhou, Ruijie; Vasquez, Daniel; Huang, Tian-Sen; Prairie View Solar Observatory Team

    2014-10-01

    With experimental facility's improvement, magnetic reconnection has been further studied at Prairie View rotamak device. By adding one toroidal current in the central part of the rotamak device, the cutting of one magnetic field reverse configuration (FRC) as two FRCs in the experiment process becomes more obvious. Differing from the magnetic reconnection experiments conducted at other labs, where magnetic reconnection is formed with two ware-coiled currents buried in a chamber with large scale magnetic field, in our magnetic reconnection experiment the main source of the magnetic field is plasma current. Thus, the magnetic reconnection experiments conducted at rotamak device are closer to the one occurring in the space and on the sun. At the present stage, our experiments focus on the study of the change in electron temperature during the magnetic reconnection process. Furthermore, the ion temperature and plasma flow can be easily achieved from fast ion Doppler spectroscopy (IDS) diagnostic system, which makes the magnetic reconnection process more clearly.

  17. Turbulent Reconnection in the Magnetic Reconnection Experiment (MRX)

    NASA Astrophysics Data System (ADS)

    Dorfman, S.; Ji, H.; Yamada, M.; Oz, E.; Yoo, J.; Daughton, W.; Roytershteyn, V.

    2009-11-01

    One of the key open questions in Magnetic Reconnection is the nature of the mechanism that governs the reconnection rate in real astrophysical and laboratory systems. For collisonless plasmas, the Hall effect removes an important bottleneck to fast reconnection as the heavier ions exit the reconnection layer over a broader region [1]. However, the Hall term cannot balance the reconnection electric field at the layer center, and the 2-D, collisionless expression for the electric field due to particle dynamics [2] has been shown to be insufficient in the Magnetic Reconnection Experiment (MRX) [1,3]. Turbulent 3-D effects such as lower hybrid frequency range fluctuations [4] may play an important role in fast reconnection in MRX. These electromagnetic fluctuations tend to be associated with high local currents and a rapid local reconnection rate. The precise relation of these fluctuations and associated 3-D asymmetries to fast reconnection is a topic of active investigations; the most up to date results will be discussed. This work was supported by NDSEG, DOE, NASA, and NSF.[4pt] [1] Y. Ren, et al., Phys. Plasmas 15, 082113 (2008). [2] M. Hesse, et al., Phys. Plasmas, 6:1781 (1999). [3] S. Dorfman, et al., Phys. Plasmas 15, 102107 (2008). [4] H. Ji, et al., Phys.Rev.Lett. 92 (2004) 115001.

  18. Fundamental Concepts Associated with Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Gonzalez, W. D.; Parker, E. N.; Mozer, F. S.; Vasyliūnas, V. M.; Pritchett, P. L.; Karimabadi, H.; Cassak, P. A.; Scudder, J. D.; Yamada, M.; Kulsrud, R. M.; Koga, D.

    The chapter starts with a discussion about the importance of the concept of magnetic field lines in space plasmas and magnetic reconnection, followed by presentations on: (a) the meaning and validity of empirical constructs related with magnetic reconnection research, such as: "moving" magnetic field lines, "frozen-in" condition and "diffusion region" of reconnection; and (b) experimental evidence of the diffusion region and related energetics. Next, aims to link external (MHD) with internal (non-MHD) regions of reconnection are discussed in association with the so-called "Axford conjecture", followed by short presentations on: (a) global equilibria in reconnection; and (b) the role of the separatrices in global aspects of reconnection. In the last section, we present additional discussion about the concept of "diffusion region" and about the two fundamental questions associated with magnetic reconnection reviewed in this chapter.

  19. 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

  20. Plasma Compression in Magnetic Reconnection Regions in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Provornikova, E.; Laming, J. M.; Lukin, V. S.

    2016-07-01

    It has been proposed that particles bouncing between magnetized flows converging in a reconnection region can be accelerated by the first-order Fermi mechanism. Analytical considerations of this mechanism have shown that the spectral index of accelerated particles is related to the total plasma compression within the reconnection region, similarly to the case of the diffusive shock acceleration mechanism. As a first step to investigate the efficiency of Fermi acceleration in reconnection regions in producing hard energy spectra of particles in the solar corona, we explore the degree of plasma compression that can be achieved at reconnection sites. In particular, we aim to determine the conditions for the strong compressions to form. Using a two-dimensional resistive MHD numerical model, we consider a set of magnetic field configurations where magnetic reconnection can occur, including a Harris current sheet, a force-free current sheet, and two merging flux ropes. Plasma parameters are taken to be characteristic of the solar corona. Numerical simulations show that strong plasma compressions (≥4) in the reconnection regions can form when the plasma heating due to reconnection is efficiently removed by fast thermal conduction or the radiative cooling process. The radiative cooling process that is negligible in the typical 1 MK corona can play an important role in the low corona/transition region. It is found that plasma compression is expected to be strongest in low-beta plasma β ˜ 0.01-0.07 at reconnection magnetic nulls.

  1. Slip Running Reconnection in Magnetic Flux Ropes

    NASA Astrophysics Data System (ADS)

    Gekelman, W. N.; Van Compernolle, B.; Vincena, S. T.; De Hass, T.

    2012-12-01

    Magnetic flux ropes are due to helical currents and form a dense carpet of arches on the surface of the sun. Occasionally one tears loose as a coronal mass ejection and its rope structure can be detected by satellites close to the earth. Current sheets can tear into filaments and these are nothing other than flux ropes. Ropes are not static, they exert mutual ěc{J}×ěc{B} forces causing them to twist about each other and eventually merge. Kink instabilities cause them to violently smash into each other and reconnect at the point of contact. We report on experiments on two adjacent ropes done in the large plasma device (LAPD) at UCLA ( ne ˜ 1012, Te ˜ 6 eV, B0z=330G, Brope}\\cong{10G,trep=1 Hz). The currents and magnetic fields form exotic shapes with no ignorable direction and no magnetic nulls. Volumetric space-time data (70,600 spatial locations) show multiple reconnection sites with time-dependent locations. The concept of a quasi-separatrix layer (QSL), a tool to understand and visualize 3D magnetic field lines reconnection without null points is introduced. Three-dimensional measurements of the QSL derived from magnetic field data are presented. Within the QSL field lines that start close to one another rapidly diverge as they pass through one or more reconnection regions. The motion of magnetic field lines are traced as reconnection proceeds and they are observed to slip through the regions of space where the QSL is largest. As the interaction proceeds we double the current in the ropes. This accompanied by intense heating as observed in uv light and plasma flows measured by Mach probes. The interaction of the ropes is clearly seen by vislaulizng magnetic field data , as well as in images from a fast framing camera. Work supported by the Dept. of Energy and The National Science Foundation, done at the Basic Plasma Science Facility at UCLA.Magnetic Field lines (measured) of three flux ropes and the plasma currents associated with them

  2. 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.

  3. Magnetic reconnection in a compressible MHD plasma

    SciTech Connect

    Hesse, Michael; Zenitani, Seiji; Birn, Joachim

    2011-04-15

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

  4. Magnetic Reconnection in a Compressible MHD Plasma

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Birn, Joachim; Zenitani, Seiji

    2011-01-01

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

  5. The Onset of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Daldorff, Lars K. S.; Klimchuk, James A.; van der Holst, Bart

    2015-04-01

    A fundamental question concerning magnetic energy release on the Sun is why the release occurs only after substantial stresses have been built up in the field. If reconnection were to occur readily, the released energy would be insufficient to explain coronal heating, CMEs, flares, jets, spicules, etc. How can we explain this switch-on property? What is the physical nature of the onset conditions? One idea involves the "secondary instability" of current sheets, which switches on when the rotation of the magnetic field across a current sheet reaches a critical angle. Such conditions would occur at the boundaries of flux tubes that become tangled and twisted by turbulent photospheric convection, for example. Other ideas involve a critical thickness for the current sheet. We report here on the preliminary results of our investigation of reconnect onset. Unlike our earlier work on the secondary instability (Dahlburg, Klimchuk, and Antiochos 2005), we treat the coupled chromosphere-corona system. Using the BATS-R-US MHD code, we simulate a single current sheet in a sheared magnetic field that extends from the chromosphere into the corona. Driver motions are applied at the base of the model. The configuration and chromosphere are both idealized, but capture the essential physics of the problem. The advantage of this unique approach is that it resolves the current sheet to the greatest extent possible while maintaining a realistic solar atmosphere. It thus bridges the gap between "reconnection in a box" studies and studies of large-scale systems such as active regions. One question we will address is whether onset conditions are met first in the chromosphere or corona. We will report on the work done on the project.

  6. The Onset of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    A fundamental question concerning magnetic energy release on the Sun is why the release occurs only after substantial stresses have been built up in the field. If reconnection were to occur readily, the released energy would be insufficient to explain coronal heating, CMEs, flares, jets, spicules, etc. How can we explain this switch-on property? What is the physical nature of the onset conditions? One idea involves the "secondary instability" of current sheets, which switches on when the rotation of the magnetic field across a current sheet reaches a critical angle. Such conditions would occur at the boundaries of flux tubes that become tangled and twisted by turbulent photospheric convection, for example. Other ideas involve a critical thickness for the current sheet. We report here on the preliminary results of our investigation of reconnect onset. Unlike our earlier work on the secondary instability (Dahlburg, Klimchuk, and Antiochos 2005), we treat the coupled chromosphere-corona system. Using the BATS-R-US MHD code, we simulate a single current sheet in a sheared magnetic field that extends from the chromosphere into the corona. Driver motions are applied at the base of the model. The configuration and chromosphere are both idealized, but capture the essential physics of the problem. The advantage of this unique approach is that it resolves the current sheet to the greatest extent possible while maintaining a realistic solar atmosphere. It thus bridges the gap between"reconnection in a box" studies and studies of large-scale systems such as active regions. One question we will address is whether onset conditions are met first in the chromosphere or corona. We will report on the work done on the project.

  7. Magnetic reconnection from a multiscale instability cascade

    NASA Astrophysics Data System (ADS)

    Moser, Auna L.; Bellan, Paul M.

    2012-02-01

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

  8. Frontiers for Laboratory Research of Magnetic Reconnection

    SciTech Connect

    Ji, Hantao; Guo, Fan

    2015-07-16

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

  9. Gyrokinetic Studies of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Pueschel, Moritz J.; Jenko, Frank; Told, Daniel; Buechner, Joerg

    2011-10-01

    Collisionless magnetic reconnection constitutes an effective mechanism for particle acceleration in astrophysical plasmas, in particular the solar corona. In addition, it is also of relevance to fusion experiments. Gyrokinetic simulations with the GENE code are performed to explore the temporal evolution of current sheets in two-dimensional slab geometry with a strong guide field. After successful code-code benchmarking, Extensive parameter studies are performed, covering a wide range of physical scenarios. In particular, differing findings regarding the influence of the ion temperature are explained. In its nonlinear phase, the characteristics of the reconnection process depend on whether the system is driven or decaying. Decaying turbulence sees an inverse cascade, and all energy is ultimately transferred to the largest radial scale. If driven by a Krook-type term, the system develops into a turbulent, quasi-stationary state. An important quantity to investigate in nonlinear simulations is the parallel electric field which is able to accelerate particles along the background magnetic field. The spatial structure of this field is studied for the different nonlinear cases, and its amplitude reported as a function of the drive frequency.

  10. Understanding Magnetic Reconnection: The Physical Mechanism Driving Space Weather

    NASA Astrophysics Data System (ADS)

    Black, Carrie; Antiochos, Spiro K.; Karpen, Judith T.; Germaschewski, Kai; Bessho, Naoki

    2015-04-01

    The explosive energy release in solar eruptive events is believed to be due to magnetic reconnection. In the standard model for coronal mass ejections (CME) and/or solar flares, the free energy for the event resides in the strongly sheared magnetic field of a filament channel. The pre-eruption force balance consists of an upward force due to the magnetic pressure of the sheared field countered by the downward tension of the overlying unsheared field. Magnetic reconnection disrupts this force balance. Therefore, to understand CME/flare initiation, it is critical to model the onset of reconnection driven by the build-up of magnetic shear. In MHD simulations, the application of a magnetic-field shear is trivial. However, kinetic effects are important in the diffusion region and thus, it is important to examine this process with PIC simulations as well. The implementation of such a driver in PIC methods is nontrivial, however, and indicates the necessity of a true multiscale model for such processes in the solar environment. The field must be sheared self-consistently and indirectly to prevent the generation of waves that destroy the desired system. In the work presented here, we show reconnection in an X-Point geometry due to a velocity shear driver perpendicular to the plane of reconnection.This material is based upon work supported by the National Science Foundation under Award No. AGS-1331356 and NASA's Living With a Star Targeted Research and Technology program.

  11. High-Frequency Fluctuations During Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Jara-Almonte, J.; Ji, H.; Daughton, W. S.; Roytershteyn, V.; Yamada, M.; Yoo, J.; Fox, W. R., II

    2014-12-01

    During collisionless reconnection, the decoupling of the field from the plasma is known to occur only within the localized ion and electron diffusion regions, however predictions from fully kinetic simulations do not agree with experimental observations on the size of the electron diffusion region, implying differing reconnection mechanisms. Previous experiments, along with 2D and 3D simulations, have conclusively shown that this discrepancy cannot be explained by either classical collisions or Lower-Hybrid Drift Instability (Roytershtyn 2010, 2013). Due to computational limitations, however, previous simulations were constrained to have minimal scale separation between the electron skin depth and the Debye length (de/λD ~ 10), much smaller than in experiments (de/λD ~ 300). This lack of scale-separation can drastically modify the electrostatic microphysics within the diffusion layer. Using 3D, fully explicit kinetic simulations with a realistic and unprecedentedly large separation between the Debye length and the electron skin depth, de/λD = 64, we show that high frequency electrostatic waves (ω >> ωLH) can exist within the electron diffusion region. These waves generate small-scale turbulence within the electron diffusion region which acts to broaden the layer. Anomalous resistivity is also generated by the turbulence and significantly modifies the force balance. In addition to simulation results, initial experimental measurements of high frequency fluctuations (electrostatic and electromagnetic, f ≤ 1 GHz) in the Magnetic Reconnection Experiment (MRX) will be presented.

  12. Definitions of Reconnection Revisited: Distinction Between Magnetic Reconnection and Plasma Reconnection

    NASA Astrophysics Data System (ADS)

    Vasyliunas, V. M.

    2015-12-01

    The term "magnetic reconnection" has been used with several different meanings, and sometimes (particularly in discussions of observations) it is not clear which one of them (if any) is meant. Most common is a more or less literal definition of "cutting" and "reconnecting" two magnetic field lines (often illustrated by a sketch of field lines in two dimensions, or a perspective drawing of isolated spaghetti-like flux tubes); this concept can be formulated more precisely in terms of plasma flow across (or, equivalently, electric field in) a bounding surface (separatrix) between topologically distinct magnetic fields. The so-called "generalized reconnection" invokes only deviations from ideal MHD in a localized region; a more precise formulation is by integrals of the electric field along magnetic field lines. These two definitions can be related to two different physical processes, which I call magnetic reconnection and plasma reconnection, respectively. Magnetic reconnection involves field lines that change from one topological class to another (e.g., between open and closed). Its occurrence, requiring the presence of singular magnetic null points, can be identified (at least in principle, conceptually) from the magnetic field alone. When representing magnetic reconnection graphically, it is important to show all the singular points explicitly and to keep in mind that field lines are a continuum: between any two field lines, there is always another field line (even arbitrarily close to the singular points). Plasma reconnection involves plasma flow in which plasma elements initially located on a single field line do not remain on a field line, and this may occur without any changes in the topology or other properties of the magnetic field. To understand either one, the process must be visualized always in three dimensions and without special symmetries. Prototype of magnetic reconnection is the well-known open-magnetosphere model of Dungey (1961). Prototype of

  13. On phase diagrams of magnetic reconnection

    SciTech Connect

    Cassak, P. A.; Drake, J. F.

    2013-06-15

    Recently, “phase diagrams” of magnetic reconnection were developed to graphically organize the present knowledge of what type, or phase, of reconnection is dominant in systems with given characteristic plasma parameters. Here, a number of considerations that require caution in using the diagrams are pointed out. First, two known properties of reconnection are omitted from the diagrams: the history dependence of reconnection and the absence of reconnection for small Lundquist number. Second, the phase diagrams mask a number of features. For one, the predicted transition to Hall reconnection should be thought of as an upper bound on the Lundquist number, and it may happen for considerably smaller values. Second, reconnection is never “slow,” it is always “fast” in the sense that the normalized reconnection rate is always at least 0.01. This has important implications for reconnection onset models. Finally, the definition of the relevant Lundquist number is nuanced and may differ greatly from the value based on characteristic scales. These considerations are important for applications of the phase diagrams. This is demonstrated by example for solar flares, where it is argued that it is unlikely that collisional reconnection can occur in the corona.

  14. Relativistic Magnetic Reconnection in the Laboratory

    NASA Astrophysics Data System (ADS)

    Krushelnick, Karl; Raymond, Anthony; Dong, Cf; McKelvey, A.; Zulick, C.; Alexander, N.; Bhattacharjee, A.; Campbell, Pt; Chen, H.; Chvykov, V.; Del Rio, E.; Fitzsimmons, P.; Fox, W.; Hou, Bx; Maksimchuk, A.; Mileham, C.; Nees, J.; Nilson, Pm; Stoekl, C.; Thomas, Agr; Wei, Ms; Yanovsky, V.; Willingale, L.

    2016-10-01

    Magnetic reconnection is a fundamental plasma process involving an exchange of magnetic energy to plasma kinetic energy through changes in the magnetic field topology. Here we present experimental measurements using the OMEGA EP laser at LLE and the HERCULES laser at the University of Michigan as well as numerical modeling which indicate that relativistic magnetic reconnection can be driven by short-pulse, high-intensity lasers that produce a relativistic plasma along with very strong magnetic fields. Evidence of magnetic reconnection was identified by the plasma's X-ray emission patterns, changes to the electron energy spectrum, and by measuring the time over which reconnection occurs. Funded by DOE Award No. DE-NA0002727.

  15. TWO-FLUID MAGNETOHYDRODYNAMIC SIMULATIONS OF RELATIVISTIC MAGNETIC RECONNECTION

    SciTech Connect

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex

    2009-05-10

    We investigate the large-scale evolution of a relativistic magnetic reconnection in an electron-positron pair plasma by a relativistic two-fluid magnetohydrodynamic (MHD) code. We introduce an interspecies friction force as an effective resistivity to dissipate magnetic fields. We demonstrate that magnetic reconnection successfully occurs in our two-fluid system, and that it involves Petschek-type bifurcated current layers in a later stage. We further observe a quasi-steady evolution thanks to an open boundary condition, and find that the Petschek-type structure is stable over the long time period. Simulation results and theoretical analyses exhibit that the Petschek outflow channel becomes narrower when the reconnection inflow contains more magnetic energy, as previously claimed. Meanwhile, we find that the reconnection rate goes up to {approx}1 in extreme cases, which is faster than previously thought. The role of the resistivity, implications for reconnection models in the magnetically dominated limit, and relevance to kinetic reconnection works are discussed.

  16. Dissipation in magnetic reconnection with a guide magnetic field

    SciTech Connect

    Hesse, Michael

    2006-12-15

    A combination of numerical simulation results and analytical theory is applied to the problem of magnetic reconnection in a guide magnetic field. An investigation of electron distribution functions within the electron diffusion region leads to a picture of mixing of particles with different acceleration histories on electron Larmor scales. Based on an apparent average loss of accelerated particles by field-aligned and ExB transport, it is proposed that the role of the reconnection electric field is to replenish this loss by acceleration of particles that enter the electron diffusion region. Analytic theory is employed to verify this model, and an equation is derived, which balances the average electric field force density by a diffusion term applied to the electron momentum density. The diffusion coefficient contains explicitly the electron Larmor spatial scale and a poloidal transport time scale.

  17. The Role of Geometry in Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Aunai, Nicholas; Birn, Joachim; Zenitani, Seiji

    2012-01-01

    Magnetic reconnection is arguably the most effective energy conversion and transport process in plasmas. Reconnection is subject to topological considerations in two ways. First, the process itself involves a change in topology of the combined plasma-magnetic field system. This change in topology transcends that of the magnetic field alone and accounts for flux transport relative to the motion of the plasma in the system under investigation. The second way topology is important to magnetic reconnection is through modifications of the diffUSion/dissipation physics brought about by the structure of the reconnecting system. This presentation will present an overview and summary of both past and recent results pertaining to both aspects.

  18. Magnetohydrodynamic Numerical Simulations of Magnetic Reconnection in Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Tanuma, Syuniti

    2000-03-01

    -ray gas in Galaxy. Part IV We examine the magnetic reconnection triggered by Parker instability and the resulting magnetic structure in Galaxy, by performing 2D MHD numerical simulations with simple assumptions. We assume, as the initial condition, that there exists horizontal magnetic flux sheet unstable to Parker instability in the disk, and anti-parallel field in the halo, because there is another magnetic field (which is not parallel) generated by Colioris force or shear motion. The magnetic field in the disk inflates toward Galactic halo, collide with magnetic field in the halo, and trigger the magnetic reconnection. The magnetic reconnection accelerates the interstellar gas, and releases the magnetic energy to heat the gas in Galactic halo. The released magnetic energy is determined by the interstellar magnetic field strength. We suggest that the magnetic reconnection is a possible mechanism to generate X-ray plasma in Galactic halo. Part V We examine the magnetic reconnection triggered by a supernova shock (or a pont explosion) in interstellar medium, by performing 3D MHD numerical simulations. We extend the 2D numerical simulations, performed in part III, to 3D. All assumption is same with those in 2D model except for the grid size and simulation region size. The magnetic reconnection occurs in the current sheet, which is similar to 2D model with the large glid size. We study the 3D effects on the magnetic reconnection. Part VI We discuss how can we apply the results to magnetic reconnections in the actual interstellar medium. We estimate the actual time scale and length scale of the magnetic reconnection and tearing instability. Magnetic reconnection will occur by the current-sheet thinning by the secondary tearing instability in nonlinear phase. Otherwise, the magnetic reconnection will occur through third, forth, and fifth tearing instability. We discuss the implications for the observations and possibility of oblique shock in reconnection jets and particle

  19. Momentum transport near a magnetic X line in collisionless reconnection

    NASA Technical Reports Server (NTRS)

    Cai, H. J.; Ding, D. Q.; Lee, L. C.

    1994-01-01

    Plasma dynamics and momentum transport near an X line during time-dependent magnetic reconnection in a collisionless plasma are investigated based on two-dimensional particle simulations. We find that a weakly skewed velocity distribution is formed near the magnetic X line, leading to the presence of off-diagonal elements of the plasma pressure tensor. Let the reconnection electric field be in the y direction. The gradients of the off-diagonal elements of the pressure tensor can provide a transport of the y momentum. During the normal magnetic reconnection, the momentum transport associated with the off-diagonal terms of the pressure tensor mediates a transfer of the y momentum from the region near the X line to regions outside the X line. A period of 'reverse magnetic reconnection,' during which the plasma kinetic energy is converted into magnetic energy, is also observed in the simulation. When reverse reconnection occurs, the gradients of the off-diagonal pressure tensor elements can mediate a transfer of y momentum into the X line. It is found that the inertial term also plays a significant role in the force balance near the magnetic X line. An explanation for the origin of the off-diagonal pressure terms is also given in this paper.

  20. Electron acceleration during guide field magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Wan, Weigang; Lapenta, Giovanni; Delzanno, Gian Luca; Egedal, Jan

    2008-03-01

    Particle-in-cell simulations of the guide field intermittent magnetic reconnection are performed to study electron acceleration and pitch angle distributions. During the growing stage of reconnection, the power-law distribution function for the high-energy electrons and the pitch angle distributions of the low-energy electrons are obtained and compare favorably with observations by the Wind spacecraft. Direct evidence is found for the secondary acceleration during the later reconnection stage. A correlation between the generation of energetic electrons and the induced reconnection electric field is found. Energetic electrons are accelerated first around the X line, and then in the region outside the diffusion region, when the reconnection electric field has a bipolar structure. The physical mechanisms of these accelerations are discussed. The in-plane electrostatic field that traps the low-energy electrons and causes the anisotropic pitch angle distributions has been observed.

  1. Relating magnetic reconnection to coronal heating.

    PubMed

    Longcope, D W; Tarr, L A

    2015-05-28

    It is clear that the solar corona is being heated and that coronal magnetic fields undergo reconnection all the time. Here we attempt to show that these two facts are related--i.e. coronal reconnection generates heat. This attempt must address the fact that topological change of field lines does not automatically generate heat. We present one case of flux emergence where we have measured the rate of coronal magnetic reconnection and the rate of energy dissipation in the corona. The ratio of these two, [Formula: see text], is a current comparable to the amount of current expected to flow along the boundary separating the emerged flux from the pre-existing flux overlying it. We can generalize this relation to the overall corona in quiet Sun or in active regions. Doing so yields estimates for the contribution to coronal heating from magnetic reconnection. These estimated rates are comparable to the amount required to maintain the corona at its observed temperature.

  2. Relating magnetic reconnection to coronal heating

    PubMed Central

    Longcope, D. W.; Tarr, L. A.

    2015-01-01

    It is clear that the solar corona is being heated and that coronal magnetic fields undergo reconnection all the time. Here we attempt to show that these two facts are related—i.e. coronal reconnection generates heat. This attempt must address the fact that topological change of field lines does not automatically generate heat. We present one case of flux emergence where we have measured the rate of coronal magnetic reconnection and the rate of energy dissipation in the corona. The ratio of these two, , is a current comparable to the amount of current expected to flow along the boundary separating the emerged flux from the pre-existing flux overlying it. We can generalize this relation to the overall corona in quiet Sun or in active regions. Doing so yields estimates for the contribution to coronal heating from magnetic reconnection. These estimated rates are comparable to the amount required to maintain the corona at its observed temperature. PMID:25897089

  3. Magnetic reconnection in a weakly ionized plasma

    SciTech Connect

    Leake, James E.; Lukin, Vyacheslav S.; Linton, Mark G.

    2013-06-15

    Magnetic reconnection in partially ionized plasmas is a ubiquitous phenomenon spanning the range from laboratory to intergalactic scales, yet it remains poorly understood and relatively little studied. Here, we present results from a self-consistent multi-fluid simulation of magnetic reconnection in a weakly ionized reacting plasma with a particular focus on the parameter regime of the solar chromosphere. The numerical model includes collisional transport, interaction and reactions between the species, and optically thin radiative losses. This model improves upon our previous work in Leake et al.[“Multi-fluid simulations of chromospheric magnetic reconnection in a weakly ionized reacting plasma,” Astrophys. J. 760, 109 (2012)] by considering realistic chromospheric transport coefficients, and by solving a generalized Ohm's law that accounts for finite ion-inertia and electron-neutral drag. We find that during the two dimensional reconnection of a Harris current sheet with an initial width larger than the neutral-ion collisional coupling scale, the current sheet thins until its width becomes less than this coupling scale, and the neutral and ion fluids decouple upstream from the reconnection site. During this process of decoupling, we observe reconnection faster than the single-fluid Sweet-Parker prediction, with recombination and plasma outflow both playing a role in determining the reconnection rate. As the current sheet thins further and elongates, it becomes unstable to the secondary tearing instability, and plasmoids are seen. The reconnection rate, outflows, and plasmoids observed in this simulation provide evidence that magnetic reconnection in the chromosphere could be responsible for jet-like transient phenomena such as spicules and chromospheric jets.

  4. Magnetic reconnection, merging, and viscous interaction in the magnetosphere

    NASA Technical Reports Server (NTRS)

    Heikkila, W. J.

    1990-01-01

    This paper discusses the historical development of the reconnection theory, with consideration given to the effects of a magnetic field within the plasma and the mechanisms of magnetic reconnection, merging, and viscouslike interaction. Particular attention is given to Dungey's (1958, 1961) steady-state reconnection model of the magnetosphere and to its criticism. Observational evidence supporting the reconnection model is presented.

  5. Three-dimensional Spontaneous Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Beresnyak, Andrey

    2017-01-01

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

  6. Intuitive approach to magnetic reconnection

    SciTech Connect

    Kulsrud, Russell M.

    2011-11-15

    Two reconnection problems are considered. The first problem concerns global physics. The plasma in the global reconnection region is in magnetostatic equilibrium. It is shown that this equilibrium can be uniquely characterized by a set of constraints. During reconnection and independently of the local reconnection physics, these constraints can be uniquely evolved from any initial state. The second problem concerns Petschek reconnection. Petschek's model for fast reconnection, which is governed by resistive MHD equations with constant resistivity is not validated by numerical simulations. Malyshkin et al.[Phys. Plasmas 12, 102920 (2005)], showed that the reason for the discrepancy is that Petschek did not employ Ohm's law throughout the local diffusion region, but only at the X-point. A derivation of Petschek reconnection, including Ohm's law throughout the entire diffusion region, removes the discrepancy. This derivation is based largely on Petschek's original 1964 calculation [in AAS-NASA Symposium on Solar Flares (National Aeronautics and Space Administration, Washington, D.C., 1964), NASA SP50, p. 425]. A useful physical interpretation of the role which Ohm's law plays in the diffusion region is presented.

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

    NASA Astrophysics Data System (ADS)

    DiBraccio, Gina A.

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

  8. 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.

  9. 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.

  10. Fast Reconnection of Weak Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Zweibel, Ellen G.

    1998-01-01

    Fast magnetic reconnection refers to annihilation or topological rearrangement of magnetic fields on a timescale that is independent (or nearly independent) of the plasma resistivity. The resistivity of astrophysical plasmas is so low that reconnection is of little practical interest unless it is fast. Yet, the theory of fast magnetic reconnection is on uncertain ground, as models must avoid the tendency of magnetic fields to pile up at the reconnection layer, slowing down the flow. In this paper it is shown that these problems can be avoided to some extent if the flow is three dimensional. On the other hand, it is shown that in the limited but important case of incompressible stagnation point flows, every flow will amplify most magnetic fields. Although examples of fast magnetic reconnection abound, a weak, disordered magnetic field embedded in stagnation point flow will in general be amplified, and should eventually modify the flow. These results support recent arguments against the operation of turbulent resistivity in highly conducting fluids.

  11. RESISTIVE MAGNETOHYDRODYNAMIC SIMULATIONS OF RELATIVISTIC MAGNETIC RECONNECTION

    SciTech Connect

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex

    2010-06-20

    Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten-Lan-van Leer method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfvenic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the 'diamond-chain' structure due to multiple shock reflections. Under a uniform resistivity, Sweet-Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.

  12. Resistive Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex

    2010-01-01

    Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten-Lan-van Leer method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfv enic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the "diamond-chain" structure due to multiple shock reflections. Under a uniform resistivity, Sweet-Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.

  13. Magnetic Reconnection Models of Prominence Formation

    NASA Astrophysics Data System (ADS)

    Welsch, B. T.; DeVore, C. R.; Antiochos, S. K.

    2005-12-01

    To investigate the hypothesis that prominences form by magnetic reconnection between initially distinct flux systems in the solar corona, we simulate coronal magnetic field evolution when two flux systems are driven together by boundary motions. In particular, we focus on configurations similar to those in the quiescent prominence formation model of Martens & Zwaan. We find that reconnection proceeds very weakly, if at all, in configurations driven with global shear flows (i.e., differential rotation); reconnection proceeds much more efficiently in similar configurations that are driven to collide directly, with converging motions along the neutral line that lead to flux cancellation; reconnected fields from this process can exhibit sheared, dipped field lines along the neutral line, consistent with prominence observations. Our field configurations do not possess the ``breakout'' topology, and eruptions are not observed, even though a substantial amount of flux is canceled in some runs.

  14. Resistive Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex

    2010-06-01

    Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten-Lan-van Leer method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfvénic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the "diamond-chain" structure due to multiple shock reflections. Under a uniform resistivity, Sweet-Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.

  15. Explosive Turbulent Magnetic Reconnection: A New Approach of MHD-Turbulent Simulation

    NASA Astrophysics Data System (ADS)

    Hoshino, Masahiro; Yokoi, Nobumitsu; Higashimori, Katsuaki

    2013-04-01

    Turbulent flows are often observed in association with magnetic reconnection in space and astrophysical plasmas, and it is often hypothesized that the turbulence can contribute to the fast magnetic reconnection through the enhancement of magnetic dissipation. In this presentation, we demonstrate that an explosive turbulent reconnection can happen by using a new turbulent MHD simulation, in which the evolution of the turbulent transport coefficients are self-consistently solved together with the standard MHD equations. In our model, the turbulent electromotive force defined by the correlation of turbulent fluctuations between v and B is added to the Ohm's law. We discuss that the level of turbulent can control the topology of reconnection, namely the transition from the Sweet-Parker reconnection to the Petscheck reconnection occurs when the level of fluctuations becomes of order of the ambient physical quantities, and show that the growth of the turbulent Petscheck reconnection becomes much faster than the conventional one.

  16. The Diffusion Region in Collisionless Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Neukirch, Thomas; Schindler, Karl; Kuznetsova, Masha; Zenitani, Seiji

    2011-01-01

    A review of present understanding of the dissipation region in magnetic reconnection is presented. The review focuses on results of the thermal inertia-based dissipation mechanism but alternative mechanisms are mentioned as well. For the former process, a combination of analytical theory and numerical modeling is presented. Furthermore, a new relation between the electric field expressions for anti-parallel and guide field reconnection is developed.

  17. Turbulent magnetic fluctuations in laboratory reconnection

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  18. Observations and models of magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Barta, Miroslav

    2015-08-01

    Magnetic reconnection is now almost unanimously considered to be a key plasma process for energy release in solar and stellar flares. Recent decade have seen rapid development in the theory, simulations and searching for observational evidences of magnetic reconnection being in action in the core of flares. Modern modeling approach involves many realistic aspects of magnetic reconnection such as intrinsically 3D nature of the process and, namely, its highly dynamic character connected with violent formation of plasmoids at many scales. The cascade of plasmoid formation represents natural process of fast, turbulent energy transfer to the kinetic dissipation scale. This concept, revealed by numerical simulations, has found its ground in the theory of (ideal) plasmoid instability in current layers with high aspect ratio. The plasmoid dominated reconnection regime is capable to account for many puzzling dilemmas in the flare physics ranging from the observation-demanded energy release rate vs. standard reconnection-regime timescales, observed organized large-scale structures vs. signatures of fragmented energy release etc. The talk aims at reviewing recent theoretical and simulation development in this direction and observational support for the concept of plasmoid-driven reconnection cascade namely in solar flares.

  19. Entropy conservation in simulations of magnetic reconnection

    SciTech Connect

    Birn, J.; Hesse, M.; Schindler, K.

    2006-09-15

    Entropy and mass conservation are investigated for the dynamic field evolution associated with fast magnetic reconnection, based on the 'Newton Challenge' problem [Birn et al., Geophys. Res. Lett. 32, L06105 (2005)]. In this problem, the formation of a thin current sheet and magnetic reconnection are initiated in a plane Harris-type current sheet by temporally limited, spatially varying, inflow of magnetic flux. Using resistive magnetohydrodynamic (MHD) and particle-in-cell (PIC) simulations, specifically the entropy and mass integrated along the magnetic flux tubes are compared between the simulations. In the MHD simulation these should be exactly conserved quantities, when slippage and Ohmic dissipation are negligible. It is shown that there is very good agreement between the conservation of these quantities in the two simulation approaches, despite the effects of dissipation, provided that the resistivity in the MHD simulation is strongly localized. This demonstrates that dissipation is highly localized in the PIC simulation also, and that heat flux across magnetic flux tubes has negligible effect as well, so that the entropy increase on a full flux tube remains small even during reconnection. The mass conservation also implies that the frozen-in flux condition of ideal MHD is a good integral approximation outside the reconnection site. This result lends support for using the entropy-conserving MHD approach not only before and after reconnection but even as a constraint connecting the two phases.

  20. Asymmetric Magnetic Reconnection in the Solar Atmosphere

    NASA Astrophysics Data System (ADS)

    Murphy, N. A.; Miralles, M. P.; Ranquist, D. A.; Pope, C. L.; Raymond, J. C.; Lukin, V. S.; McKillop, S.; Shen, C.; Winter, H. D.; Reeves, K. K.; Lin, J.

    2013-12-01

    Models of solar flares and coronal mass ejections typically predict the development of an elongated current sheet in the wake behind the rising flux rope. In reality, reconnection in these current sheets will be asymmetric along the inflow, outflow, and out-of-plane directions. We perform resistive MHD simulations to investigate the consequences of asymmetry during solar reconnection. We predict several observational signatures of asymmetric reconnection, including flare loops with a skewed candle flame shape, slow drifting of the current sheet into the strong field upstream region, asymmetric footpoint speeds and hard X-ray emission, and rolling motions within the erupting flux rope. There is net plasma flow across the magnetic field null along both the inflow and outflow directions. We compare simulations to SDO/AIA, Hinode/XRT, and STEREO observations of flare loop shapes, current sheet drifting, and rolling motions during prominence eruptions. Simulations of the plasmoid instability with different upstream magnetic fields show that the reconnection rate remains enhanced even during the asymmetric case. The islands preferentially grow into the weak field upstream region. The islands develop net vorticity because the outflow jets impact them obliquely rather than directly. Asymmetric reconnection in the chromosphere occurs when emerging flux interacts with pre-existing overlying flux. We present initial results on asymmetric reconnection in partially ionized chromospheric plasmas. Finally, we discuss how comparisons to observations are necessary to understand the role of three-dimensional effects.

  1. Asymmetric Magnetic Reconnection in the Solar Atmosphere

    NASA Astrophysics Data System (ADS)

    Murphy, N. A.; Miralles, M. P.; Ranquist, D. A.; Pope, C. L.; Raymond, J. C.; Lukin, V. S.; McKillop, S. C.; Shen, C.; Winter, H. D.; Reeves, K. K.; Lin, J.

    2013-12-01

    Models of solar flares and coronal mass ejections typically predict the development of an elongated current sheet in the wake behind the rising flux rope. In reality, reconnection in these current sheets will be asymmetric along the inflow, outflow, and out-of-plane directions. We perform resistive MHD simulations to investigate the consequences of asymmetry during solar reconnection. We predict several observational signatures of asymmetric reconnection, including flare loops with a skewed candle flame shape, slow drifting of the current sheet into the strong field upstream region, asymmetric footpoint speeds and hard X-ray emission, and rolling motions within the erupting flux rope. There is net plasma flow across the magnetic field null along both the inflow and outflow directions. We compare simulations to SDO/AIA, Hinode/XRT, and STEREO observations of flare loop shapes, current sheet drifting, and rolling motions during prominence eruptions. Simulations of the plasm! oid instability with different upstream magnetic fields show that the reconnection rate remains enhanced even during the asymmetric case. The islands preferentially grow into the weak field upstream region. The islands develop net vorticity because the outflow jets impact them obliquely rather than directly. Asymmetric reconnection in the chromosphere occurs when emerging flux interacts with pre-existing overlying flux. We present initial results on asymmetric reconnection in partially ionized chromospheric plasmas. Finally, we discuss how comparisons to observations are necessary to understand the role of three-dimensional effects.

  2. Recurrent Magnetic Reconnection in Protostellar Magnetospheres

    NASA Astrophysics Data System (ADS)

    Hayashi, Mitsuru; Shibata, K.; Matsumoto, R.

    The solar X-ray satellite Yohkoh, has found extensive evidence for magnetic reconnection in the solar corona. Here we extend the magnetic reconnection model of solar flares to hard X-ray flares observed in star forming regions. A new ingredient is a protostellar disk which can inject helicity into the magnetosphere if the disk is threaded by the dipole magnetic field of the protostar. We carried out 2.5-dimensional magnetohydrodynamical (MHD) simulations of the disk-star interaction. The closed magnetic loops connecting the central star and the disk are twisted by the rotation of the disk. In the presence of resistivity, magnetic reconnection takes place in the current sheet formed inside the expanding loops. A hot, outgoing plasmoid and hot post flare loops are formed as a result of the reconnection. Numerical results are consistent with the observed plasma temperature (107 - 108K), the length of the flaring loop (1011 - 1012cm), and the velocity of optical jets (200 - 400km/s). We use high-resolution numerical simulations to show that multiple magnetic islands are created in the current sheet due to the growth of the tearing mode instability. The magnetic islands are ejected quasi-periodically. Intermittent flaring activity continues as long as the disk matter twists the dipole magnetic field

  3. Prospects for Fermi Particle Acceleration at Coronal Magnetic Reconnection Sites

    NASA Astrophysics Data System (ADS)

    Provornikova, E.; Laming, J. M.; Lukin, V.

    2015-12-01

    The mechanism of first order Fermi acceleration of particles interacting with the converging magnetized flows at a reconnection site was introduced recently in an attempt to predict the energy distribution of particles resulting from violent reconnection in galactic microquasars. More careful consideration of this mechanism showed that the spectral index of accelerated particles is related to the total plasma compression within a reconnection region, similar to that in the formulation for diffusive shock acceleration. In the solar context, reconnection regions producing strong compression could be the source of suprathermal "seed particles". A hard spectrum of such suprathermal particles is believed to be necessary to initiate the particle acceleration process at low Mach number coronal mass ejection shocks close to the Sun where the gradual solar energetic particle events originate. As a first step to investigate the efficiency of Fermi acceleration, we explore the degree of plasma compression that can be achieved at reconnection sites in the solar corona. This work presents a set of 2D two-temperature resistive MHD simulations of the dynamics of several magnetic configurations within a range of lower corona plasma parameters. Energy transport processes in the MHD model include anisotropic thermal conduction for electrons and ions and radiative cooling. Magnetic configurations considered are a Harris current sheet, a force-free current sheet, a flux rope sitting above an arcade of magnetic loops, and two merging flux ropes. We demonstrate that only for some magnetic topologies, corresponding in particular to 3D magnetic nulls, the compression ratio, sufficient for first order Fermi acceleration in the reconnection region, can be achieved. These represent the potential sites in the solar corona where a hard seed particle energetic spectrum could be produced.

  4. Magnetic reconnection in the near Venusian magnetotail.

    PubMed

    Zhang, T L; Lu, Q M; Baumjohann, W; Russell, C T; Fedorov, A; Barabash, S; Coates, A J; Du, A M; Cao, J B; Nakamura, R; Teh, W L; Wang, R S; Dou, X K; Wang, S; Glassmeier, K H; Auster, H U; Balikhin, M

    2012-05-04

    Observations with the Venus Express magnetometer and low-energy particle detector revealed magnetic field and plasma behavior in the near-Venus wake that is symptomatic of magnetic reconnection, a process that occurs in Earth's magnetotail but is not expected in the magnetotail of a nonmagnetized planet such as Venus. On 15 May 2006, the plasma flow in this region was toward the planet, and the magnetic field component transverse to the flow was reversed. Magnetic reconnection is a plasma process that changes the topology of the magnetic field and results in energy exchange between the magnetic field and the plasma. Thus, the energetics of the Venus magnetotail resembles that of the terrestrial tail, where energy is stored and later released from the magnetic field to the plasma.

  5. Magnetic reconnection in a magnetohydrodynamic plasma

    SciTech Connect

    Kulsrud, R.M.

    1998-05-01

    Magnetic reconnection is important because of its connection with the topology of field lines. In general, a change in topology means a change of equilibrium, and a release of energy, such as occurs in solar flares. In the context of the solar flare two models for magnetic reconnection, the Sweet{endash}Parker and the Petschek mechanism are presented. The pros and cons of these two models are presented. The role of anomalous resistivity in the Sweet{endash}Parker model is discussed. The bearing of a laboratory experiment and a boundary layer analysis of the problem are described. {copyright} {ital 1998 American Institute of Physics.}

  6. OBSERVATIONS OF A SMALL INTERPLANETARY MAGNETIC FLUX ROPE ASSOCIATED WITH A MAGNETIC RECONNECTION EXHAUST

    SciTech Connect

    Feng, H. Q.; Wu, D. J.

    2009-11-10

    A small interplanetary magnetic flux rope prior to an X-line magnetic reconnection exhaust was observed on 1998 March 25 at 1 AU. The X-line magnetic reconnection exhaust has been identified and reported by Gosling et al. The duration of this small magnetic flux rope is about 2 hr. We fitted the constant alpha force-free model to the observed magnetic fields. The model fitting results show that the spacecraft crosses the magnetic flux rope well away from the axis, with d {sub 0}/R {sub 0} being 0.76. The fitting results also show that its magnetic configuration is a right-handed helical flux rope, that the estimated field intensity at the axis is 16.3 nT, and that its diameter is 0.0190 AU. In addition, the axial direction of this rope is (theta = 6 deg., phi = 214 deg.), namely, this magnetic flux rope is lying nearly in the ecliptic plane. According to the geometric relation of the small flux rope and the reconnection exhaust, it is very possible that the small magnetic flux rope has a larger scale initially and comes from the corona; its magnetic fields are peeled off when moving from the Sun to the Earth and at last it reaches a small scale. Though magnetic reconnection can produce a flux-rope topology, in this case the X-line magnetic reconnection is destroying rather than generating the small magnetic flux rope.

  7. Self-generated Turbulence in Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Oishi, Jeffrey S.; Mac Low, Mordecai-Mark; Collins, David C.; Tamura, Moeko

    2015-06-01

    Classical Sweet-Parker models of reconnection predict that reconnection rates depend inversely on the resistivity, usually parameterized using the dimensionless Lundquist number (S). We describe magnetohydrodynamic (MHD) simulations using a static, nested grid that show the development of a three-dimensional (3D) instability in the plane of a current sheet between reversing field lines without a guide field. The instability leads to rapid reconnection of magnetic field lines at a rate independent of S over at least the range 3.2× {{10}3}≲ S≲ 3.2× {{10}5} resolved by the simulations. We find that this instability occurs even for cases with S≲ {{10}4} that in our models appear stable to the recently described, two-dimensional, plasmoid instability. Our results suggest that 3D, MHD processes alone produce fast (resistivity independent) reconnection without recourse to kinetic effects or external turbulence. The unstable reconnection layers provide a self-consistent environment in which the extensively studied turbulent reconnection process can occur.

  8. Magnetic Reconnection Onset and Energy Release at Current Sheets

    NASA Astrophysics Data System (ADS)

    DeVore, C. R.; Antiochos, Spiro K.

    2015-04-01

    Reconnection and energy release at current sheets are important at the Sun (coronal heating, coronal mass ejections, flares, and jets) and at the Earth (magnetopause flux transfer events and magnetotail substorms) and other magnetized planets, and occur also at the interface between the Heliosphere and the interstellar medium, the heliopause. The consequences range from relatively quiescent heating of the ambient plasma to highly explosive releases of energy and accelerated particles. We use the Adaptively Refined Magnetohydrodynamics Solver (ARMS) model to investigate the self-consistent formation and reconnection of current sheets in an initially potential 2D magnetic field containing a magnetic null point. Unequal stresses applied to the four quadrants bounded by the X-line separatrix distort the potential null into a double-Y-type current sheet. We find that this distortion eventually leads to onset of fast magnetic reconnection across the sheet, with copious production, merging, and ejection of magnetic islands due to plasmoid instability. In the absence of a mechanism for ideal instability or loss of equilibrium of the global structure, however, this reconnection leads to minimal energy release. Essentially, the current sheet oscillates about its force-free equilibrium configuration. When the structure is susceptible to a large-scale rearrangement of the magnetic field, on the other hand, the energy release becomes explosive. We identify the conditions required for reconnection to transform rapidly a large fraction of the magnetic free energy into kinetic and other forms of plasma energy, and to restructure the current sheet and its surrounding magnetic field dramatically. We discuss the implications of our results for understanding heliophysical activity, particularly eruptions, flares, and jets in the corona.Our research was supported by NASA’s Heliophysics Supporting Research and Living With a Star Targeted Research and Technology programs.

  9. Formation of Plasmoid Chains in Magnetic Reconnection

    SciTech Connect

    Samtaney, R.; Loureiro, N. F.; Uzdensky, D. A.; Schekochihin, A. A.; Cowley, S. C.

    2009-09-09

    A detailed numerical study of magnetic reconnection in resistive MHD for very large, previously inaccessible, Lundquist numbers (104 ≤ S ≤ 108) is reported. Large-aspect-ratio Sweet-Parker current sheets are shown to be unstable to super-Alfvenically fast formation of plasmoid (magnetic-island) chains. The plasmoid number scales as S3/8 and the instability growth rate in the linear stage as S1/4, in agreement with the theory by Loureiro et al. [Phys. Plasmas 14, 100703 (2007)]. In the nonlinear regime, plasmoids continue to grow faster than they are ejected and completely disrupt the reconnection layer. These results suggest that high-Lundquist-number reconnection is inherently time-dependent and hence call for a substantial revision of the standard Sweet-Parker quasistationary picture for S>104.

  10. Magnetic Reconnection: Theoretical and Observational Perspectives: Preface

    NASA Technical Reports Server (NTRS)

    Lewis, W. S.; Antiochos, S. K,; Drake, J. F.

    2011-01-01

    Magnetic reconnection is a fundamental plasma-physical process by which energy stored in a magnetic field is converted, often explosively, into heat and the kinetic energy of the charged particles that constitute the plasma. It occurs in a variety of astrophysical settings, ranging from the solar corona to pulsar magnetospheres and winds, as well as in laboratory fusion experiments, where it is responsible for sawtooth crashes. First proposed by R.G. Giovanelli in the late I 940s as the mechanism responsible for solar flares, magnetic reconnection was invoked at the beginning of the space age to explain not just solar flares but also the transfer of energy, mass, and momentum from the solar wind to Earth's magnetosphere and the subsequent storage and release of the transferred energy in the magnetotai\\. During the half century or so that has followed the seminal theoretical works by J.W. Dungey, P.A. Sweet, E.N. Parker, and H.E. Petschek, in-situ measurements by Earth-orbiting satellites and remote-sensing observations of the solar corona have provided a growing body of evidence for the occurrence of reconnection at the Sun, in the solar wind, and in the near-Earth space environment. The last thirty years have also seen the development of laboratory reconnection experiments at a number of institutions. In parallel with the efforts of experimentalists in both space and laboratory plasma physics, theorists have investigated, analytically and with the help of increasingly powerful MHD, hybrid, and kinetic numerical simulations, the structure of the diffusion region, the factors controlling the rate, onset, and cessation of reconnection, and the detailed physics that enables the demagnetization of the ions and electrons and the topological reconfiguration of the magnetic field. Moreover, the scope of theoretical reconnection studies has been extended well beyond solar system and laboratory plasmas to include more exotic astrophysical plasma systems whose strong (10

  11. Magnetic reconnection under anisotropic magnetohydrodynamic approximation

    SciTech Connect

    Hirabayashi, K.; Hoshino, M.

    2013-11-15

    We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless MHD codes based on the double adiabatic approximation and the Landau closure model. We 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 observations. Our results showed that once magnetic reconnection takes place, a firehose-sense (p{sub ∥}>p{sub ⊥}) pressure anisotropy arises in the downstream region, and the generated slow shocks are quite weak comparing with those in an isotropic MHD. In spite of the weakness of the shocks, however, the resultant reconnection rate is 10%–30% higher than that in an isotropic case. This 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.

  12. Quantitative, comprehensive, analytical model for magnetic reconnection in Hall magnetohydrodynamics.

    PubMed

    Simakov, Andrei N; Chacón, L

    2008-09-05

    Dissipation-independent, or "fast", magnetic reconnection has been observed computationally in Hall magnetohydrodynamics (MHD) and predicted analytically in electron MHD. However, a quantitative analytical theory of reconnection valid for arbitrary ion inertial lengths, d{i}, has been lacking and is proposed here for the first time. The theory describes a two-dimensional reconnection diffusion region, provides expressions for reconnection rates, and derives a formal criterion for fast reconnection in terms of dissipation parameters and d{i}. It also confirms the electron MHD prediction that both open and elongated diffusion regions allow fast reconnection, and reveals strong dependence of the reconnection rates on d{i}.

  13. Magnetic reconnection: from MHD to QED

    NASA Astrophysics Data System (ADS)

    Bulanov, S. V.

    2017-01-01

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

  14. Quantized Chiral Magnetic Current from Reconnections of Magnetic Flux

    DOE PAGES

    Hirono, Yuji; Kharzeev, Dmitri E.; Yin, Yi

    2016-10-20

    We introduce a new mechanism for the chiral magnetic e ect that does not require an initial chirality imbalance. The chiral magnetic current is generated by reconnections of magnetic ux that change the magnetic helicity of the system. The resulting current is entirely determined by the change of magnetic helicity, and it is quantized.

  15. VINETA II: A linear magnetic reconnection experiment

    SciTech Connect

    Bohlin, H. Von Stechow, A.; Rahbarnia, K.; Grulke, O.; Klinger, T.

    2014-02-15

    A linear experiment dedicated to the study of driven magnetic reconnection is presented. The new device (VINETA II) is suitable for investigating both collisional and near collisionless reconnection. Reconnection is achieved by externally driving magnetic field lines towards an X-point, inducing a current in the background plasma which consequently modifies the magnetic field topology. Owing to the open field line configuration of the experiment, the current is limited by the axial sheath boundary conditions. A plasma gun is used as an additional electron source in order to counterbalance the charge separation effects and supply the required current. Two drive methods are used in the device. First, an oscillating current through two parallel conductors drive the reconnection. Second, a stationary X-point topology is formed by the parallel conductors, and the drive is achieved by an oscillating current through a third conductor. In the first setup, the magnetic field of the axial plasma current dominates the field topology near the X-point throughout most of the drive. The second setup allows for the amplitude of the plasma current as well as the motion of the flux to be set independently of the X-point topology of the parallel conductors.

  16. Kinetic simulations of collisionless magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Aunai, N.; Dargent, J.; Lavraud, B.; Ciardi, A.; Drouin, M.; Smets, R.

    2016-12-01

    This paper focuses on magnetic reconnection and its role in magnetospheric physics, where collisions are inexistant. In this context, the presence of a very cold ion population of ionospheric origin is known to have an important contribution to the particle density at the magnetopause. However, besides this mass loading effect, consequences of their extremely low temperature, and therefore of their must smaller gyroscale, have not yet been addressed from a modeling viewpoint. This study presents two fully kinetic simulations with and without cold ions in the magnetosphere and highlights how their small Larmor radius can change signatures expected to be proxy of the X line in spacecraft measurements. In a second part, this paper addresses shortly the problem of the X line orientation in an asymmetric system. Using this time hybrid kinetic simulations, we show the X line aligned with the bisector of upstream magnetic field vectors results in faster reconnection rate. This have consequences regarding where reconnection at the magnetopause, although models here do not include large scale dynamics. We conclude with perspectives regarding future developments to address multi-scale magnetic reconnection dynamics at the magnetopause.

  17. Magnetic Reconnection in Extreme Astrophysical Environments

    NASA Astrophysics Data System (ADS)

    Uzdensky, Dmitri A.

    2011-10-01

    Magnetic reconnection is a fundamental plasma physics process in which ideal-MHD's frozen-in constraints are broken and the magnetic field topology is dramatically re-arranged, which often leads to a violent release of the free magnetic energy. Most of the magnetic reconnection research done to date has been motivated by the applications to systems such as the solar corona, Earth's magnetosphere, and magnetic confinement devices for thermonuclear fusion. These environments have relatively low energy densities and the plasma is adequately described as a mixture of equal numbers of electrons and ions and where the dissipated magnetic energy always stays with the plasma. In contrast, in this paper I would like to introduce a different, new direction of research—reconnection in high energy density radiative plasmas, in which photons play as important a role as electrons and ions; in particular, in which radiation pressure and radiative cooling become dominant factors in the pressure and energy balance. This research is motivated in part by rapid theoretical and experimental advances in High Energy Density Physics, and in part by several important problems in modern high-energy astrophysics. I first discuss some astrophysical examples of high-energy-density reconnection and then identify the key physical processes that distinguish them from traditional reconnection. Among the most important of these processes are: special-relativistic effects; radiative effects (radiative cooling, radiation pressure, and radiative resistivity); and, at the most extreme end—QED effects, including pair creation. The most notable among the astrophysical applications are situations involving magnetar-strength fields (1014-1015 G, exceeding the quantum critical field B ∗≃4×1013 G). The most important examples are giant flares in soft gamma repeaters (SGRs) and magnetic models of the central engines and relativistic jets of Gamma Ray Bursts (GRBs). The magnetic energy density in

  18. Magnetic reconnection process in transient coaxial helicity injection

    SciTech Connect

    Ebrahimi, F.; Hooper, E. B.; Sovinec, C. R.; Raman, R.

    2013-09-15

    The physics of magnetic reconnection and fast flux closure in transient coaxial helicity injection experiments in NSTX is examined using resistive MHD simulations. These simulations have been performed using the NIMROD code with fixed boundary flux (including NSTX poloidal coil currents) in the NSTX experimental geometry. Simulations show that an X point is formed in the injector region, followed by formation of closed flux surfaces within 0.5 ms after the driven injector voltage and injector current begin to rapidly decrease. As the injector voltage is turned off, the field lines tend to untwist in the toroidal direction and magnetic field compression exerts a radial J × B force and generates a bi-directional radial E{sub toroidal}×B{sub poloidal} pinch flow to bring oppositely directed field lines closer together to reconnect. At sufficiently low magnetic diffusivity (high Lundquist number), and with a sufficiently narrow injector flux footprint width, the oppositely directed field lines have sufficient time to reconnect (before dissipating), leading to the formation of closed flux surfaces. The reconnection process is shown to have transient Sweet-Parker characteristics.

  19. Turbulent reconnection of magnetic bipoles in stratified turbulence

    NASA Astrophysics Data System (ADS)

    Jabbari, S.; Brandenburg, A.; Mitra, Dhrubaditya; Kleeorin, N.; Rogachevskii, I.

    2016-07-01

    We consider strongly stratified forced turbulence in a plane-parallel layer with helicity and corresponding large-scale dynamo action in the lower part and non-helical turbulence in the upper. The magnetic field is found to develop strongly concentrated bipolar structures near the surface. They form elongated bands with a sharp interface between opposite polarities. Unlike earlier experiments with imposed magnetic field, the inclusion of rotation does not strongly suppress the formation of these structures. We perform a systematic numerical study of this phenomenon by varying magnetic Reynolds number, scale-separation ratio, and Coriolis number. We focus on the formation of a current sheet between bipolar regions where reconnection of oppositely oriented field lines occurs. We determine the reconnection rate by measuring either the inflow velocity in the vicinity of the current sheet or by measuring the electric field in the reconnection region. We demonstrate that for large Lundquist numbers, S > 103, the reconnection rate is nearly independent of S in agreement with results of recent numerical simulations performed by other groups in simpler settings.

  20. Magnetic reconnection process in accretion disk systems

    NASA Astrophysics Data System (ADS)

    Piovezan, P.; de Gouveia Dal Pino, E. M.

    2009-08-01

    At the present study, we investigate the role of magnetic reconnection in three different astrophysical systems, namely young stellar objects (YSO's), microquasars, and active galactic nuclei (AGN's). In the case of microquasars and AGN's, violent reconnection episodes between the magnetic field lines of the inner disk region (which are established by a turbulent dynamo) and those anchored into the black hole are able to heat the coronal/disk gas and accelerate particles to relativistic velocities through a diffusive first-order Fermi-like process within the reconnection site that will produce relativistic blobs. The heating of the coronal/disk gas is able to produce a steep X-ray spectrum with a luminosity that is consistent with the observations and we argue that it is being produced mainly at the foot of the reconnection zone, while the Fermi-like acceleration process within the reconnection site results a power-law electron distribution with N(E) ∝ E-α, with α=5/2, and a corresponding synchrotron radio power-law spectrum with a spectral index that is compatible with that observed during the radio flares in microquasars (Sν ∝ ν-0.75). The scaling laws that we derive for AGN's indicate that the same mechanism may be occurring there. Finally, in the case of the YSO's, a similar magnetic configuration can be reached. The amount of magnetic energy that can be extracted from the inner disk region can heat the coronal gas to temperatures of the order of 10^8 K and could explain the observed X-ray flaring emission.

  1. Magnetic reconnection in Saturn's magnetotail: A comprehensive magnetic field survey.

    NASA Astrophysics Data System (ADS)

    Smith, A. W.; Jackman, C. M.; Thomsen, M. F.; Dougherty, M. K.

    2015-10-01

    Magnetic reconnection is a fundamental process throughout the solar system, significantly shaping and modulating the magnetospheres of the magnetized planets. Within planetary magnetotails reconnection can be responsible for energizing particles and potentially changing the total flux and mass contained within the magnetosphere. The Kronian magnetosphere is thought to be a middle ground between the rotationally dominated Jovian magnetosphere and the solar wind driven terrestrial magnetosphere. However, previous studies have not been able to find a statistical reconnection x-line, as has been possible at both Jupiter and Earth. Additionally the standard picture of magnetotail reconnection at Saturn, developed by Cowley et al. [2004], suggests a potential asymmetry between the dawn and dusk flanks, caused by different reconnection processes dominating. This work centers on the development of an algorithm designed to find reconnection related events in spacecraft magnetometer data, aiming to reduce the bias that manual searches could inherently introduce, thereby ensuring the validity of any statistical analysis. The algorithm primarily identifies the reconnection related events from deflections in the north-south component of the magnetic field, allowing an almost uninterrupted in-situ search (when the spacecraft is situated within the magnetotail). The new catalogue of candidate reconnection events, produced by the algorithm, enables a more complete statistical view of reconnection in the Kronian magnetotail. Well-studied data encompassing the deep magnetotail and dawn flank (particularly from orbits in 2006) were used to train the algorithm and develop reasonable criteria. The algorithm was then applied to data encompassing the dusk flank (including orbits from 2009, for which plasma data have been examined by Thomsen et al. [2014]). This combination enables a robust, and global, comparison of reconnection rates, signatures and properties in the Kronian magnetotail.

  2. Magnetic Reconnection in Different Environments: Similarities and Differences

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  3. Fast magnetic reconnection with large guide fields

    DOE PAGES

    Stanier, A.; Simakov, Andrei N.; Chacón, L.; ...

    2015-01-09

    We domonstrate, using two-fluid simulations, that low-βmagnetic reconnection remains fast, regardless of the presence of fast dispersive waves, which have been previously suggested to play a critical role. In order to understand these results, a discrete model is constructed that offers scaling relationships for the reconnection rate and dissipation region (DR) thickness in terms of the upstream magnetic field and DR length. Moreover, we verify these scalings numerically and show how the DR self-adjusts to process magnetic flux at the same rate that it is supplied to a larger region where two-fluid effects become important. The rate is therefore independentmore » of the DR physics and is in good agreement with kinetic results.« less

  4. Model of magnetic reconnection in space and astrophysical plasmas

    SciTech Connect

    Boozer, Allen H.

    2013-03-15

    Maxwell's equations imply that exponentially smaller non-ideal effects than commonly assumed can give rapid magnetic reconnection in space and astrophysical plasmas. In an ideal evolution, magnetic field lines act as stretchable strings, which can become ever more entangled but cannot be cut. High entanglement makes the lines exponentially sensitive to small non-ideal changes in the magnetic field. The cause is well known in popular culture as the butterfly effect and in the theory of deterministic dynamical systems as a sensitive dependence on initial conditions, but the importance to magnetic reconnection is not generally recognized. Two-coordinate models are too constrained geometrically for the required entanglement, but otherwise the effect is general and can be studied in simple models. A simple model is introduced, which is periodic in the x and y Cartesian coordinates and bounded by perfectly conducting planes in z. Starting from a constant magnetic field in the z direction, reconnection is driven by a spatially smooth, bounded force. The model is complete and could be used to study the impulsive transfer of energy between the magnetic field and the ions and electrons using a kinetic plasma model.

  5. Gyro-induced acceleration of magnetic reconnection

    SciTech Connect

    Comisso, L.; Grasso, D.; Waelbroeck, F. L.; Borgogno, D.

    2013-09-15

    The linear and nonlinear evolution of magnetic reconnection in collisionless high-temperature plasmas with a strong guide field is analyzed on the basis of a two-dimensional gyrofluid model. The linear growth rate of the reconnecting instability is compared to analytical calculations over the whole spectrum of linearly unstable wave numbers. In the strongly unstable regime (large Δ′), the nonlinear evolution of the reconnecting instability is found to undergo two distinctive acceleration phases separated by a stall phase in which the instantaneous growth rate decreases. The first acceleration phase is caused by the formation of strong electric fields close to the X-point due to ion gyration, while the second acceleration phase is driven by the development of an open Petschek-like configuration due to both ion and electron temperature effects. Furthermore, the maximum instantaneous growth rate is found to increase dramatically over its linear value for decreasing diffusion layers. This is a consequence of the fact that the peak instantaneous growth rate becomes weakly dependent on the microscopic plasma parameters if the diffusion region thickness is sufficiently smaller than the equilibrium magnetic field scale length. When this condition is satisfied, the peak reconnection rate asymptotes to a constant value.

  6. Magnetic diffusion and ion nonlinear dynamics in magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Zenitani, S.; Shinohara, I.; Nagai, T.; Wada, T.

    2013-12-01

    Magnetic reconnection is a fundamental process in many plasma systems, ranging from laboratory and solar-terrestrial environments to extreme astrophysical settings. The reconnection process is controlled by magnetic dissipation physics in a small-scale region near the reconnection point (X-line), and therefore the structure of the reconnection site is of strong interest. According to the standard picture of collisionless reconnection, the X-line is surrounded by a compact electron diffusion region and by an outer ion diffusion region. While the electron region has been extensively studied, much less is known about the ion region. In this work, we examine key aspects of the ion region in magnetic reconnection. First, we evaluate the ''diffusion'' of magnetic field lines, going back to the topology theorems. Unlike in the MHD, the idealness, the frozen-in, magnetic diffusion, and the energy dissiation can be all different in a kinetic plasma. We will apply these concepts to the reconnection site in two-dimensional particle-in-cell (PIC) simulations. Importantly, in the outer part of the ion region, even though the ion ideal condition is violated, the magnetic fields are frozen to plasma fluids. This raises a serious question to the widespread definition of the ion diffusion region, based on the ion nonidealness. We further examine the ion velocity distribution function in the same region. The distribution function contains multiple populations such as global Speiser ions, local Speiser ions, and trapped ions. The particle motion of the local Speiser ions in an appropriately rotated frame explains the plasma nonidealness. The trapped ions are the first demonstration of the regular orbits in Chen & Palmadesso (1986), in self-consistent PIC simulations. They would be observational signatures in the ion current layer near reconnection sites.

  7. Electron Layer Dissipation Mechanisms in Driven Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Dorfman, S.; Ji, H.; Yamada, M.; McGeehan, B.; Oz, E.; Schroeder, J.; Daughton, W.; Roytershteyn, V.; Ren, Y.

    2008-11-01

    An open question in magnetic reconnection is the nature of the dissipation mechanism(s) responsible for fast reconnection rates in laboratory and astrophysical plasmas. In 2-D collisionless particle in cell simulations, the off-diagonal terms in the electron pressure tensor provide the necessary force balance at the electron diffusion layer center [1]. Recent comparisons between the Magnetic Reconnection Experiment (MRX) and a well-matched PIC code have shown that this mechanism is insufficient to balance the reconnecting electric field in MRX [2,3]. Candidate mechanisms not present in the simulation are under investigation, including electromagnetic fluctuations and other 3-D effects such as layer distortions. The relationship between fluctuations and equilibrium parameters such as the outflow current and layer width is examined, and first investigations into the 3-D symmetry of the layer are presented. On the simulation side, analysis is underway to gain further insight into the nature of the off-diagonal pressure tensor terms, especially effects due to the driven nature of the simulation. [1] M. Hesse, et al., Phys. Plasmas, 6:1781 (1999). [2] S. Dorfman, et al., submitted to Phys. Plasmas (2008). [3] H. Ji, et al., Geophys. Res. Lett., 35, L13106 (2008). This work was supported by NDSEG, DOE, NASA, and NSF.

  8. Laboratory experiments on magnetic reconnection and current systems

    NASA Astrophysics Data System (ADS)

    Stenzel, R. L.; Urrutia, J. M.; Gekelman, W.; Pfister, H.

    After a brief review of laboratory experiments involving magnetic reconnection a series of basic physics experiments on reconnection phenomena is described. These include magnetic annihilation, transport of magnetic energy by waves, stable and unstable current sheets, energy conversion mechanisms, and the role of global current systems vs. local reconnection processes. Current systems driven by electric fields resulting in particle flows are examined. Also, the role of a magnetic field component B(y) along the separator has been investigated.

  9. Quantitative analytical model for magnetic reconnection in hall magnetohydrodynamics

    SciTech Connect

    Simakov, Andrei N

    2008-01-01

    Magnetic reconnection is of fundamental importance for laboratory and naturally occurring plasmas. Reconnection usually develops on time scales which are much shorter than those associated with classical collisional dissipation processes, and which are not fully understood. While such dissipation-independent (or 'fast') reconnection rates have been observed in particle and Hall magnetohydrodynamics (MHD) simulations and predicted analytically in electron MHD, a quantitative analytical theory of fast reconnection valid for arbitrary ion inertial lengths d{sub i} has been lacking. Here we propose such a theory without a guide field. The theory describes two-dimensional magnetic field diffusion regions, provides expressions for the reconnection rates, and derives a formal criterion for fast reconnection in terms of dissipation parameters and di. It also demonstrates that both open X-point and elongated diffusion regions allow dissipation-independent reconnection and reveals a possibility of strong dependence of the reconnection rates on d{sub i}.

  10. Magnetic Reconnection During Major Magnetospheric Storms

    NASA Astrophysics Data System (ADS)

    Hubert, B. A.; Milan, S. E.; Cowley, S. W. H.

    2014-12-01

    We combine imaging of the proton aurora from the SI12-IMAGE instrument with ionospheric convection measurement from the SuperDARN radar network to analyze the cycle of magnetic flux opening and closure of the Earth magnetosphere. Interaction between the solar wind and the Earth geomagnetic environment causes a reconfiguration of the magnetic field that connects the interplanetary magnetic field (IMF) to the geomagnetic field. This reconnection process produces open magnetic field lines (i.e. field lines of the magnetosphere that close through the interplanetary medium) that are dragged to the magnetotail by the solar wind flow, where they eventually reconnect again, back to a closed topology. The SI12 imaging of the Doppler-shifted Lyman-α emission of the proton aurora is used to estimate the location of the boundary separating open and closed field lines at ionospheric altitude. We then estimate the open magnetic flux of the Earth magnetosphere, encircled by this boundary. The rate of reconnection causing a variation of the open magnetic flux can be expressed as a voltage in application of Faraday's law. This voltage is measured along the open/closed field line boundary determined from the imaging data. The electric field associated with the voltage has two origins: motion of the boundary and the ionospheric field. We use the ionospheric electric field deduced from ionospheric convection measurement from the SuperDARN to estimate the reconnection voltage at the magnetopause (flux opening) and in the magnetotail (flux closure) accounting for the motion of the open/closed field line boundary determined from the SI12 images. The method is applied during several (strong) geomagnetic storms. These intervals are characterized by large values of open flux and reconnection rates, as a result of coupling between the solar wind and the geomagnetic environment. We present these results in terms of a magnetospheric mode that develops under strong coupling with the solar wind

  11. Particle acceleration and plasma dynamics during magnetic reconnection in the magnetically dominated regime

    DOE PAGES

    Guo, Fan; Liu, Yi -Hsin; Daughton, William; ...

    2015-06-17

    Magnetic reconnection is thought to be the driver for many explosive phenomena in the universe. The energy release and particle acceleration during reconnection have been proposed as a mechanism for producing high-energy emissions and cosmic rays. We carry out two- and three-dimensional (3D) kinetic simulations to investigate relativistic magnetic reconnection and the associated particle acceleration. The simulations focus on electron–positron plasmas starting with a magnetically dominated, force-free current sheet (σ ≡ B2 / (4πnemec2) >> 1). For this limit, we demonstrate that relativistic reconnection is highly efficient at accelerating particles through a first-order Fermi process accomplished by the curvature driftmore » of particles along the electric field induced by the relativistic flows. This mechanism gives rise to the formation of hard power-law spectra f α (γ - 1)-p and approaches p = 1 for sufficiently large σ and system size. Eventually most of the available magnetic free energy is converted into nonthermal particle kinetic energy. An analytic model is presented to explain the key results and predict a general condition for the formation of power-law distributions. The development of reconnection in these regimes leads to relativistic inflow and outflow speeds and enhanced reconnection rates relative to nonrelativistic regimes. In the 3D simulation, the interplay between secondary kink and tearing instabilities leads to strong magnetic turbulence, but does not significantly change the energy conversion, reconnection rate, or particle acceleration. This paper suggests that relativistic reconnection sites are strong sources of nonthermal particles, which may have important implications for a variety of high-energy astrophysical problems.« less

  12. Particle acceleration and plasma dynamics during magnetic reconnection in the magnetically dominated regime

    SciTech Connect

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

    2015-06-17

    Magnetic reconnection is thought to be the driver for many explosive phenomena in the universe. The energy release and particle acceleration during reconnection have been proposed as a mechanism for producing high-energy emissions and cosmic rays. We carry out two- and three-dimensional (3D) kinetic simulations to investigate relativistic magnetic reconnection and the associated particle acceleration. The simulations focus on electron–positron plasmas starting with a magnetically dominated, force-free current sheet (σ ≡ B2 / (4πnemec2) >> 1). For this limit, we demonstrate that relativistic reconnection is highly efficient at accelerating particles through a first-order Fermi process accomplished by the curvature drift of particles along the electric field induced by the relativistic flows. This mechanism gives rise to the formation of hard power-law spectra f α (γ - 1)-p and approaches p = 1 for sufficiently large σ and system size. Eventually most of the available magnetic free energy is converted into nonthermal particle kinetic energy. An analytic model is presented to explain the key results and predict a general condition for the formation of power-law distributions. The development of reconnection in these regimes leads to relativistic inflow and outflow speeds and enhanced reconnection rates relative to nonrelativistic regimes. In the 3D simulation, the interplay between secondary kink and tearing instabilities leads to strong magnetic turbulence, but does not significantly change the energy conversion, reconnection rate, or particle acceleration. This paper suggests that relativistic reconnection sites are strong sources of nonthermal particles, which may have important implications for a variety of high-energy astrophysical problems.

  13. FAST MAGNETIC RECONNECTION AND SPONTANEOUS STOCHASTICITY

    SciTech Connect

    Eyink, Gregory L.; Lazarian, A.; Vishniac, E. T.

    2011-12-10

    Magnetic field lines in astrophysical plasmas are expected to be frozen-in at scales larger than the ion gyroradius. The rapid reconnection of magnetic-flux structures with dimensions vastly larger than the gyroradius requires a breakdown in the standard Alfven flux-freezing law. We attribute this breakdown to ubiquitous MHD plasma turbulence with power-law scaling ranges of velocity and magnetic energy spectra. Lagrangian particle trajectories in such environments become 'spontaneously stochastic', so that infinitely many magnetic field lines are advected to each point and must be averaged to obtain the resultant magnetic field. The relative distance between initial magnetic field lines which arrive at the same final point depends upon the properties of two-particle turbulent dispersion. We develop predictions based on the phenomenological Goldreich and Sridhar theory of strong MHD turbulence and on weak MHD turbulence theory. We recover the predictions of the Lazarian and Vishniac theory for the reconnection rate of large-scale magnetic structures. Lazarian and Vishniac also invoked 'spontaneous stochasticity', but of the field lines rather than of the Lagrangian trajectories. More recent theories of fast magnetic reconnection appeal to microscopic plasma processes that lead to additional terms in the generalized Ohm's law, such as the collisionless Hall term. We estimate quantitatively the effect of such processes on the inertial-range turbulence dynamics and find them to be negligible in most astrophysical environments. For example, the predictions of the Lazarian and Vishniac theory are unchanged in Hall MHD turbulence with an extended inertial range, whenever the ion skin depth {delta}{sub i} is much smaller than the turbulent integral length or injection-scale L{sub i} .

  14. 3-D, Impulsive Magnetic Reconnection in a Laboratory Plasma (Invited)

    NASA Astrophysics Data System (ADS)

    Dorfman, S. E.; Ji, H.; Yamada, M.; Yoo, J.; Myers, C. E.; Roytershteyn, V.; Daughton, W. S.; Jara-Almonte, J.

    2013-12-01

    Magnetic reconnection is a fundamental plasma process involving the efficient conversion of magnetic field energy to plasma kinetic energy through changing field line topology. In many space and astrophysical systems, including the solar surface and the Earth's magnetotail, reconnection is not only fast, but also impulsive; in other words, a slow buildup phase is followed by a comparatively quick release of magnetic energy. An important question in the literature is if these examples of impulsive reconnection can be described by a two-dimensional model with no variation in the out-of-plane direction or if impulsive reconnection is fundamentally three-dimensional. Events observed on the Magnetic Reconnection Experiment (MRX) are characterized by large local gradients in the third direction and cannot be explained by 2-D models [1]. Detailed measurements show that the ejection of flux rope structures from the current sheet plays a key role in these events. By contrast, even though electromagnetic fluctuations in the lower hybrid frequency range are also observed concurrently with the impulsive behavior, they are not the key physics responsible. Furthermore, an important discrepancy in the layer width and force balance between the collisionless regime of MRX and kinetic simulations [2-4] persists when the fluctuations are small or absent, implying that they are not the cause of the wider electron layers observed in the experiment [5]. These wider layers may instead be due to the formation of flux ropes with a wide range of sizes; consistent with this hypothesis, flux rope signatures are observed down to the smallest scales resolved by the diagnostics. Finally, a qualitative, 3-D, two-fluid model is proposed to explain the observed disruptions. Many of the features observed in MRX including current disruptions [6], flux ropes [7], and electromagnetic fluctuations [8] have analogues in space observations. Thus, further detailed comparisons may enhance our understanding

  15. Properties of Magnetic Reconnection as a function of magnetic shear

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Daughton, W. S.; Karimabadi, H.; Li, H.; Gary, S. P.; Guo, F.

    2013-12-01

    Observations of reconnection events at the Earth's magnetopause and in the solar wind show that reconnection occurs for a large range in magnetic shear angles extending to the very low shear limit 1. Here we report a fully kinetic study of the influence of the magnetic shear on details of reconnection such as its structure and rate. In previous work, we found that the electron diffusion region bifurcates into two or more distinct layers in regimes with weak magnetic shear2, a new feature that may be observable by NASA's up-coming Magnetospheric Multiscale mission. In this work, we have systematically extended the study to lower shear cases and found a new regime, where the reconnection electric field becomes much smaller and the properties of the reconnection changes significantly. We will discuss the role of various physics mechanisms in determining the observed scaling of the reconnection rate, including the dispersive properties of the waves in the system, the dissipation mechanisms and the tearing instability. 1 J. T. Goslings and T. D. Phan. APJL 763, L39, 2013 2 Yi-Hsin Liu et al. Phys. Rev. Lett. 110 , 265004, 2013

  16. Fluctuation dynamo based on magnetic reconnections

    NASA Astrophysics Data System (ADS)

    Baggaley, A. W.; Shukurov, A.; Barenghi, C. F.; Subramanian, K.

    2010-01-01

    We develop a new model of the fluctuation dynamo in which the magnetic field is confined to thin flux ropes advected by a multi-scale flow which models turbulence. Magnetic dissipation occurs only via reconnections of flux ropes. The model is particularly suitable for rarefied plasma, such as the solar corona or galactic halos. We investigate the kinetic energy release into heat, mediated by dynamo action, both in our model and by solving the induction equation with the same flow. We find that the flux rope dynamo is more than an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy released during reconnections has a power-law form with the slope -3, consistent with the solar corona heating by nanoflares. We also present a nonlinear extension of the model. This shows that a plausible saturation mechanism of the fluctuation dynamo is the suppression of turbulent magnetic diffusivity, due to suppression of random stretching at the location of the flux ropes. We confirm that the probability distribution function of the magnetic line curvature has a power-law form suggested by \\citet{Sheck:2002b}. We argue, however, using our results that this does not imply a persistent folded structure of magnetic field, at least in the nonlinear stage.

  17. Aspects of collisionless magnetic reconnection in asymmetric systems

    SciTech Connect

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

    2013-06-15

    Asymmetric reconnection is being investigated by means of particle-in-cell simulations. The research has two foci: the direction of the reconnection line in configurations with nonvanishing magnetic fields; and the question why reconnection can be faster if a guide field is added to an otherwise unchanged asymmetric configuration. We find that reconnection prefers a direction, which maximizes the available magnetic energy, and show that this direction coincides with the bisection of the angle between the asymptotic magnetic fields. Regarding the difference in reconnection rates between planar and guide field models, we demonstrate that a guide field can provide essential confinement for particles in the reconnection region, which the weaker magnetic field in one of the inflow directions cannot necessarily provide.

  18. Aspects of Collisionless Magnetic Reconnection in Asymmetric Systems

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

    Asymmetric reconnection is being investigated by means of particle-in-cell simulations. The research has two foci: the direction of the reconnection line in configurations with non-vanishing magnetic fields; and the question why reconnection can be faster if a guide field is added to an otherwise unchanged asymmetric configuration. We find that reconnection prefers a direction, which maximizes the available magnetic energy, and show that this direction coincides with the bisection of the angle between the asymptotic magnetic fields. Regarding the difference in reconnection rates between planar and guide field models, we demonstrate that a guide field can provide essential confinement for particles in the reconnection region, which the weaker magnetic field in one of the inflow directions cannot necessarily provide.

  19. Aspects of Collisionless Magnetic Reconnection in Asymmetric Systems

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

    Asymmetric reconnection is being investigated by means of particle-in-cell simulations. The research has two foci: The direction of the reconnection line in configurations with nonvanishing magnetic fields; and the question why reconnection can be faster if a guide field is added to an otherwise unchanged asymmetric configuration. We find that reconnection prefers a direction, which maximizes the available magnetic energy, and show that this direction coincides with the bisection of the angle between the asymptotic magnetic fields. Regarding the difference in reconnection rates between planar and guide field models, we demonstrate that a guide field can provide essential confinement for particles in the reconnection region, which the weaker magnetic field in one of the inflow directions cannot necessarily provide.

  20. On the Location of Magnetic Reconnection at the Dayside Magnetopause

    NASA Astrophysics Data System (ADS)

    Komar, C. M.; Cassak, P.; Fermo, R. L.

    2013-12-01

    Predicting where magnetic reconnection occurs at Earth's dayside magnetopause has been the subject of studies for nearly 50 years and remains an unsolved problem. The location of dayside magnetic reconnection was originally discussed in terms of anti-parallel vs. component (guide field) reconnection, but it is now known that these descriptions are too basic to fully describe the observations. Recent models suggest that reconnection orients itself such that the local properties maximize some measure of asymmetric reconnection efficiency [Swisdak and Drake, 2007; Borovsky, 2013; Hesse, et al., 2013]. Alternatively, Trattner, et al., [2007] proposed the Maximum Magnetic Shear model, in which reconnection occurs along the curve where the shear angle between the magnetospheric and magnetosheath magnetic fields is a maximum. Each of these models is independent of the reconnection dissipation mechanism, so they should hold for any self-consistent magnetospheric model. We use global magnetospheric resistive magnetohydrodynamic simulations to identify the locus of possible magnetic reconnection sites by finding the magnetic separator where different magnetic topologies meet at the dayside magnetopause. Employing image processing techniques, we compare the separator locations with the predictions of these models to determine which, if any, accurately predict the location of reconnection.

  1. Three-dimensional modeling of electron quasiviscous dissipation in guide-field magnetic reconnection

    SciTech Connect

    Hesse, Michael; Kuznetsova, Masha; Schindler, Karl; Birn, Joachim

    2005-10-01

    A numerical study of guide-field magnetic reconnection in a three-dimensional model is presented. Starting from an initial, perturbed, force-free current sheet, it is shown that reconnection develops to an almost translationally invariant state, where magnetic perturbations are aligned primarily along the main current flow direction. An analysis of guide-field and electron flow signatures indicates behavior that is very similar to earlier, albeit not three-dimensional, simulations. Furthermore, a detailed investigation of electron pressure nongyrotropies in the central diffusion region confirms the major role the associated dissipation process plays in establishing the reconnection electric field.

  2. RELATIVISTIC TWO-FLUID SIMULATIONS OF GUIDE FIELD MAGNETIC RECONNECTION

    SciTech Connect

    Zenitani, Seiji; Hesse, Michael; Klimas, Alex

    2009-11-01

    The nonlinear evolution of relativistic magnetic reconnection in sheared magnetic configuration (with a guide field) is investigated by using two-dimensional relativistic two-fluid simulations. Relativistic guide field reconnection features the charge separation and the guide field compression in and around the outflow channel. As the guide field increases, the composition of the outgoing energy changes from enthalpy-dominated to Poynting-dominated. The inertial effects of the two-fluid model play an important role to sustain magnetic reconnection. Implications for the single-fluid magnetohydrodynamic approach and the physics models of relativistic reconnection are briefly addressed.

  3. Experimental study of ion heating and acceleration during magnetic reconnection

    SciTech Connect

    Hsu, S.C.

    2000-01-28

    This dissertation reports an experimental study of ion heating and acceleration during magnetic reconnection, which is the annihilation and topological rearrangement of magnetic flux in a conductive plasma. Reconnection is invoked often to explain particle heating and acceleration in both laboratory and naturally occurring plasmas. However, a simultaneous account of reconnection and its associated energy conversion has been elusive due to the extreme inaccessibility of reconnection events, e.g. in the solar corona, the Earth's magnetosphere, or in fusion research plasmas. Experiments for this work were conducted on MRX (Magnetic Reconnection Experiment), which creates a plasma environment allowing the reconnection process to be isolated, reproduced, and diagnosed in detail. Key findings of this work are the identification of local ion heating during magnetic reconnection and the determination that non-classical effects must provide the heating mechanism. Measured ion flows are sub-Alfvenic and can provide only slight viscous heating, and classical ion-electron interactions can be neglected due to the very long energy equipartition time. The plasma resistivity in the reconnection layer is seen to be enhanced over the classical value, and the ion heating is observed to scale with the enhancement factor, suggesting a relationship between the magnetic energy dissipation mechanism and the ion heating mechanism. The observation of non-classical ion heating during reconnection has significant implications for understanding the role played by non-classical dissipation mechanisms in generating fast reconnection. The findings are relevant for many areas of space and laboratory plasma research, a prime example being the currently unsolved problem of solar coronal heating. In the process of performing this work, local measurements of ion temperature and flows in a well-characterized reconnection layer were obtained for the first time in either laboratory or observational

  4. Three-dimensional lattice Boltzmann model for magnetic reconnection

    SciTech Connect

    Mendoza, M.; Munoz, J. D.

    2008-02-15

    We develop a three-dimensional (3D) lattice Boltzmann model that recovers in the continuous limit the two-fluids theory for plasmas, and consequently includes the generalized Ohm's law. The model reproduces the magnetic reconnection process just by giving the right initial equilibrium conditions in the magnetotail, without any assumption on the resistivity in the diffusive region. In this model, the plasma is handled similar to two fluids with an interaction term, each one with distribution functions associated to a cubic lattice with 19 velocities (D3Q19). The electromagnetic fields are considered as a third fluid with an external force on a cubic lattice with 13 velocities (D3Q13). The model can simulate either viscous fluids in the incompressible limit or nonviscous compressible fluids, and successfully reproduces both the Hartmann flow and the magnetic reconnection in the magnetotail. The reconnection rate in the magnetotail obtained with this model lies between R=0.062 and R=0.073, in good agreement with the observations.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  6. Magnetic reconnection in Saturn's magnetotail: A comprehensive magnetic field survey

    NASA Astrophysics Data System (ADS)

    Smith, A. W.; Jackman, C. M.; Thomsen, M. F.

    2016-04-01

    Reconnection within planetary magnetotails is responsible for locally energizing particles and changing the magnetic topology. Its role in terms of global magnetospheric dynamics can involve changing the mass and flux content of the magnetosphere. We have identified reconnection related events in spacecraft magnetometer data recorded during Cassini's exploration of Saturn's magnetotail. The events are identified from deflections in the north-south component of the magnetic field, significant above a background level. Data were selected to provide full tail coverage, encompassing the dawn and dusk flanks as well as the deepest midnight orbits. Overall 2094 reconnection related events were identified, with an average rate of 5.0 events per day. The majority of events occur in clusters (within 3 h of other events). We examine changes in this rate in terms of local time and latitude coverage, taking seasonal effects into account. The observed reconnection rate peaks postmidnight with more infrequent but steady loss seen on the dusk flank. We estimate the mass loss from the event catalog and find it to be insufficient to balance the input from the moon Enceladus. Several reasons for this discrepancy are discussed. The reconnection X line location appears to be highly variable, though a statistical separation between events tailward and planetward of the X line is observed at a radial distance of between 20 and 30RS downtail. The small sample size at dawn prevents comprehensive statistical comparison with the dusk flank observations in terms of flux closure.

  7. Test particle acceleration in turbulent reconnecting magnetic fields

    NASA Technical Reports Server (NTRS)

    Ambrosiano, John; Matthaeus, William H.; Goldstein, Melvyn L.; Plante, Daniel

    1988-01-01

    The effect of turbulence on particle acceleration in a MHD field was investigated by computing test particle trajectories in turbulent MHD reconnecting fields, including reconnection simulations at different magnetic Reynolds numbers. The dynamics of individual particles were investigated making it possible to examine the acceleration mechanism in great detail. It was found that turbulence influences the acceleration in two ways. It enhances the reconnection electric field while producing a stochastic electric field that gives rise to momentum diffusion; and it produces magnetic 'bubbles' and other irregularities that can temporarily trap test particles in the strong reconnection electric field for times comparable to the magnetofluid characteristic time.

  8. On the relationship between quadrupolar magnetic field and collisionless reconnection

    SciTech Connect

    Smets, R. Belmont, G.; Aunai, N.; Boniface, C.

    2014-06-15

    Using hybrid simulations, we investigate the onset of fast reconnection between two cylindrical magnetic shells initially close to each other. This initial state mimics the plasma structure in High Energy Density Plasmas induced by a laser-target interaction and the associated self-generated magnetic field. We clearly observe that the classical quadrupolar structure of the out-of-plane magnetic field appears prior to the reconnection onset. Furthermore, a parametric study reveals that, with a non-coplanar initial magnetic topology, the reconnection onset is delayed and possibly suppressed. The relation between the out-of-plane magnetic field and the out-of-plane electric field is discussed.

  9. Reconnection of vorticity lines and magnetic lines

    NASA Technical Reports Server (NTRS)

    Greene, John M.

    1993-01-01

    Magnetic field and fluid vorticity share many features. First, as divergence-free vector fields they are conveniently visualized in terms of their field lines, curves that are everywhere tangent to the field. The lines indicate direction and their density indicates field strength. The question arises of the extent to which the evolution of the fields can be treated in terms of the evolution of their field lines. Newcomb (1958) derived the general conditions on the evolution of vector fields that permit the identification of field lines from one instant to the next. The equations of evolution of the vorticity field and the magnetic field fall within Newcomb's analysis. The dynamics of the flows differ between these two systems, so that geometrically similar phenomena happen in different ways in the two systems. In this paper the geometrical similarities are emphasized. Reconnection will be defined here as evolution in which it is not possible to preserve the global identification of some field lines. There is a close relation between reconnection and the topology of the vector field lines. Nontrivial topology occurs where the field has null points or there are field lines that are closed loops.

  10. Statistical Properties of Magnetic Reconnection in MHD turbulence

    NASA Astrophysics Data System (ADS)

    Servidio, Sergio; Matthaeus, William; Cassak, Paul; Shay, Michael; Dmitruk, Pablo

    2009-11-01

    Magnetic reconnection is an integral part of MHD turbulence[1] in that the fragmentation of magnetic eddies into smaller structures necessarily involves change of magnetic topology. To better understand this relationship, recently the properties of thousands of magnetic reconnection events in moderate Reynolds number MHD turbulence have been studied [1] using 2D spectral method simulations of compressible and incompressible MHD. Reconnection between magnetic islands, different in size and energy, occurs locally and sporadically in time. The associated reconnection rates are distributed over a wide range of values and scale with the geometry of the diffusion region. Matching classical turbulence analysis with the Sweet-Parker theory, the main statistical features of these multi-scale reconnection events are identified. Magnetic reconnection in turbulence can be described through an asymmetric Sweet-Parker model, in which the parameters that control the reconnection rates are determined by turbulence itself. This new and general perspective on reconnection is relevant in space and astrophysical systems, where plasma is generally in a fully nonlinear regime. [1] W. Matthaeus and S. Lamkin, Phys. Fluids, 29, 2513 (1986). [2] S. Servidio et al, PRL, 102, 115003 (2009).

  11. MAVEN Observations of Magnetic Reconnection on the Dayside Martian Magnetosphere

    NASA Astrophysics Data System (ADS)

    DiBraccio, Gina A.; Espley, Jared R.; Connerney, John E. P.; Brain, David A.; Halekas, Jasper S.; Mitchell, David L.; Harada, Yuki; Hara, Takuya

    2015-04-01

    The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission offers a unique opportunity to investigate the complex solar wind-planetary interaction at Mars. The Martian magnetosphere is formed as the interplanetary magnetic field (IMF) drapes around the planet's ionosphere and localized crustal magnetic fields. As the solar wind interacts with this induced magnetosphere, magnetic reconnection can occur at any location where a magnetic shear is present. Reconnection between the IMF and the induced and crustal fields facilitates a direct plasma exchange between the solar wind and the Martian ionosphere. Here we address the occurrence of magnetic reconnection on the dayside magnetosphere of Mars using MAVEN magnetic field and plasma data. When reconnection occurs on the dayside, a non-zero magnetic field component normal to the obstacle, B_N, will result. Using minimum variance analysis, we measure BN by transforming Magnetometer data into boundary-normal coordinates. Selected events are then further examined to identify plasma heating and energization, in the form of Alfvénic outflow jets, using Solar Wind Ion Analyzer measurements. Additionally, the topology of the crustal fields is validated from electron pitch angle distributions provided by the Solar Wind Electron Analyzer. To understand which parameters are responsible for the onset of reconnection, we test the dependency of the dimensionless reconnection rate, calculated from BN measurements, on magnetic field shear angle and plasma beta (the ratio of plasma pressure to magnetic pressure). We assess the global impact of reconnection on Mars' induced magnetosphere by combining analytical models with MAVEN observations to predict the regions where reconnection may occur. Using this approach we examine how IMF orientation and magnetosheath parameters affect reconnection on a global scale. With the aid of analytical models we are able to assess the role of reconnection on a global scale to better understand which

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

    PubMed

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

    2017-03-24

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

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

    NASA Astrophysics Data System (ADS)

    Wilson, Fiona; Neukirch, Thomas; Hesse, Michael

    2016-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

  16. Observing the release of twist by magnetic reconnection in a solar filament eruption

    PubMed Central

    Xue, Zhike; Yan, Xiaoli; Cheng, Xin; Yang, Liheng; Su, Yingna; Kliem, Bernhard; Zhang, Jun; Liu, Zhong; Bi, Yi; Xiang, Yongyuan; Yang, Kai; Zhao, Li

    2016-01-01

    Magnetic reconnection is a fundamental process of topology change and energy release, taking place in plasmas on the Sun, in space, in astrophysical objects and in the laboratory. However, observational evidence has been relatively rare and typically only partial. Here we present evidence of fast reconnection in a solar filament eruption using high-resolution H-alpha images from the New Vacuum Solar Telescope, supplemented by extreme ultraviolet observations. The reconnection is seen to occur between a set of ambient chromospheric fibrils and the filament itself. This allows for the relaxation of magnetic tension in the filament by an untwisting motion, demonstrating a flux rope structure. The topology change and untwisting are also found through nonlinear force-free field modelling of the active region in combination with magnetohydrodynamic simulation. These results demonstrate a new role for reconnection in solar eruptions: the release of magnetic twist. PMID:27306479

  17. 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.

  18. BIDIRECTIONAL OUTFLOWS AS EVIDENCE OF MAGNETIC RECONNECTION LEADING TO A SOLAR MICROFLARE

    SciTech Connect

    Hong, Jie; Ding, M. D.; Li, Ying; Yang, Kai; Cheng, Xin; Fang, Cheng; Chen, Feng; Cao, Wenda

    2016-03-20

    Magnetic reconnection is a rapid energy release process that is believed to be responsible for flares on the Sun and stars. Nevertheless, such flare-related reconnection is mostly detected to occur in the corona, while there have been few studies concerning the reconnection in the chromosphere or photosphere. Here, we present both spectroscopic and imaging observations of magnetic reconnection in the chromosphere leading to a microflare. During the flare peak time, chromospheric line profiles show significant blueshifted/redshifted components on the two sides of the flaring site, corresponding to upflows and downflows with velocities of ±(70–80) km s{sup −1}, comparable with the local Alfvén speed as expected by the reconnection in the chromosphere. The three-dimensional nonlinear force-free field configuration further discloses twisted field lines (a flux rope) at a low altitude, cospatial with the dark threads in He i 10830 Å images. The instability of the flux rope may initiate the flare-related reconnection. These observations provide clear evidence of magnetic reconnection in the chromosphere and show the similar mechanisms of a microflare to those of major flares.

  19. Identifying magnetic reconnection events using the FOTE method

    NASA Astrophysics Data System (ADS)

    Fu, H. S.; Cao, J. B.; Vaivads, A.; Khotyaintsev, Y. V.; Andre, M.; Dunlop, M.; Liu, W. L.; Lu, H. Y.; Huang, S. Y.; Ma, Y. D.; Eriksson, E.

    2016-02-01

    A magnetic reconnection event detected by Cluster is analyzed using three methods: Single-spacecraft Inference based on Flow-reversal Sequence (SIFS), Multispacecraft Inference based on Timing a Structure (MITS), and the First-Order Taylor Expansion (FOTE). Using the SIFS method, we find that the reconnection structure is an X line; while using the MITS and FOTE methods, we find it is a magnetic island (O line). We compare the efficiency and accuracy of these three methods and find that the most efficient and accurate approach to identify a reconnection event is FOTE. In both the guide and nonguide field reconnection regimes, the FOTE method is equally applicable. This study for the first time demonstrates the capability of FOTE in identifying magnetic reconnection events; it would be useful to the forthcoming Magnetospheric Multiscale (MMS) mission.

  20. Enhanced magnetic reconnection in the presence of pressure gradients

    SciTech Connect

    Pueschel, M. J.; Terry, P. W.; Told, D.; Jenko, F.

    2015-06-15

    Magnetic reconnection in the presence of background pressure gradients is studied, with special attention to parallel (compressional) magnetic fluctuations. A process is reported that reconnects fields through coupling of drift-wave-type instabilities with current sheets. Its time scale is set not by the reconnecting field but by inhomogeneities of the background density or temperature. The observed features can be attributed to a pressure-gradient-driven linear instability which interacts with the reconnecting system but is fundamentally different from microtearing. In particular, this mode relies on parallel magnetic fluctuations and the associated drift. For turbulent reconnection, similar or even stronger enhancements are reported. In the solar corona, this yields a critical pressure gradient scale length of about 200 km below which this new process becomes dominant over the tearing instability.

  1. Experimental onset threshold and magnetic pressure pileup for 3D Sweet-Parker reconnection

    SciTech Connect

    Intrator, Thomas P; Sun, Xuan; Lapenta, Giovanni; Furno, Ivo

    2008-01-01

    In space, astrophysical and laboratory plasmas, magnetic reconnect ion converts magnetic into particle energy during unsteady, explosive events. The abrupt onset and cessation has been a long standing puzzle. We show the first three-dimensional (3D) laboratory example of onset and stagnation of Sweet-Parker type magnetic reconnection between magnetized and parallel current (flux) ropes driven by magnetohydrodynamic (MHD) attraction and 3D instability. Mutually attracting flux ropes advect and merge oppositely directed magnetic fields. Magnetic flux is annihilated, but reaches soon a threshold where magnetic flux and pressure pile up, and reconnection magnetic topology appears. This occurs when inflow speeds exceed the SweetParker speed v{sub SP} = v{sub A} / S{sup 1/2}, where v{sub A} is the Alfven speed and S is the Lundquist number for the reconnection layer, as magnetic flux arrives faster than flux annihilation can process it. Finally piled up fields generate MHD reaction forces that stall the inflow and the reconnection process.

  2. Electron-scale measurements of magnetic reconnection in space

    NASA Astrophysics Data System (ADS)

    Burch, J. L.; Torbert, R. B.; Phan, T. D.; Chen, L.-J.; Moore, T. E.; Ergun, R. E.; Eastwood, J. P.; Gershman, D. J.; Cassak, P. A.; Argall, M. R.; Wang, S.; Hesse, M.; Pollock, C. J.; Giles, B. L.; Nakamura, R.; Mauk, B. H.; Fuselier, S. A.; Russell, C. T.; Strangeway, R. J.; Drake, J. F.; Shay, M. A.; Khotyaintsev, Yu. V.; Lindqvist, P.-A.; Marklund, G.; Wilder, F. D.; Young, D. T.; Torkar, K.; Goldstein, J.; Dorelli, J. C.; Avanov, L. A.; Oka, M.; Baker, D. N.; Jaynes, A. N.; Goodrich, K. A.; Cohen, I. J.; Turner, D. L.; Fennell, J. F.; Blake, J. B.; Clemmons, J.; Goldman, M.; Newman, D.; Petrinec, S. M.; Trattner, K. J.; Lavraud, B.; Reiff, P. H.; Baumjohann, W.; Magnes, W.; Steller, M.; Lewis, W.; Saito, Y.; Coffey, V.; Chandler, M.

    2016-06-01

    Magnetic reconnection is a fundamental physical process in plasmas whereby stored magnetic energy is converted into heat and kinetic energy of charged particles. Reconnection occurs in many astrophysical plasma environments and in laboratory plasmas. Using measurements with very high time resolution, NASA's Magnetospheric Multiscale (MMS) mission has found direct evidence for electron demagnetization and acceleration at sites along the sunward boundary of Earth's magnetosphere where the interplanetary magnetic field reconnects with the terrestrial magnetic field. We have (i) observed the conversion of magnetic energy to particle energy; (ii) measured the electric field and current, which together cause the dissipation of magnetic energy; and (iii) identified the electron population that carries the current as a result of demagnetization and acceleration within the reconnection diffusion/dissipation region.

  3. Electron-Scale Measurements of Magnetic Reconnection in Space

    NASA Technical Reports Server (NTRS)

    Burch, J. L.; Torbert, R. B.; Phan, T. D.; Chen, L.-J.; Moore, T. E.; Ergun, R. E.; Eastwood, J. P.; Gershman, D. J.; Cassak, P. A.; Argall, M. R.; Wang, S.; Hesse, M.; Pollock, C. J.; Jiles, B. L.; Nakamura, R.; Mauk, B. H.; Fuselier, S. A.; Russell, C. T.; Strangeway, R. J.; Drake, J. F.; Shay, M. A.; Khotyaintsev, Yu. V.; Lindqvist, P.-A.; Marklund, G.; Wilder, F. D.

    2016-01-01

    Magnetic reconnection is a fundamental physical process in plasmas whereby stored magnetic energy is converted into heat and kinetic energy of charged particles. Reconnection occurs in many astrophysical plasma environments and in laboratory plasmas. Using measurements with very high time resolution, NASA's Magnetospheric Multiscale (MMS) mission has found direct evidence for electron demagnetization and acceleration at sites along the sunward boundary of Earth's magnetosphere where the interplanetary magnetic field reconnects with the terrestrial magnetic field. We have (i) observed the conversion of magnetic energy to particle energy; (ii) measured the electric field and current, which together cause the dissipation of magnetic energy; and (iii) identified the electron population that carries the current as a result of demagnetization and acceleration within the reconnection diffusion/dissipation region.

  4. Anisotropic Electron Tail Generation during Tearing Mode Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    DuBois, Ami M.; Almagri, Abdulgader F.; Anderson, Jay K.; Den Hartog, Daniel J.; Lee, John David; Sarff, John S.

    2017-02-01

    The first experimental evidence of anisotropic electron energization during magnetic reconnection that favors a direction perpendicular to the guide magnetic field in a toroidal, magnetically confined plasma is reported in this Letter. Magnetic reconnection plays an important role in particle heating, energization, and transport in space and laboratory plasmas. In toroidal devices like the Madison Symmetric Torus, discrete magnetic reconnection events release large amounts of energy from the equilibrium magnetic field. Fast x-ray measurements imply a non-Maxwellian, anisotropic energetic electron tail is formed at the time of reconnection. The tail is well described by a power-law energy dependence. The expected bremsstrahlung from an electron distribution with an anisotropic energetic tail (v⊥>v∥ ) spatially localized in the core region is consistent with x-ray emission measurements. A turbulent process related to tearing fluctuations is the most likely cause for the energetic electron tail formation.

  5. Measurements of Fast Magnetic Reconnection Driven by Relativistic Electrons

    NASA Astrophysics Data System (ADS)

    Raymond, Anthony; McKelvey, Andrew; Zulick, Calvin; Chuanfei, Dong; Maksimchuk, Anatoly; Thomas, Alexander; Yanovsky, Victor; Krushelnick, Karl; Willingale, Louise; Chykov, Vladimir; Nilson, Phil; Chen, Hui; Williams, Gerald; Bhattacharjee, Amitava; Fox, Will

    2015-11-01

    Magnetic reconnection is a process whereby opposing magnetic field lines are forced together and topologically rearrange, resulting in lower magnetic potential energy and in corresponding plasma heating. Such occurrences are ubiquitous in astrophysics as well as appearing in laboratory plasmas such as in ICF in the form of instabilities. We report measurements in the domain of ultra-fast, ultra-intense lasers, in which the mechanism responsible follows from radially expanding surface electrons with v ~ c . Results are compared from two laser facilities (HERCULES and Omega EP), both of which produced two relativistic intensity pulses focused within close proximity onto copper foils. A spherical X-ray crystal was used to image the Kα radiation induced by electron currents, revealing the midplane diffusion region wherein electrons are accelerated into the target by the electric field generated during reconnection. The characteristics of this signal are studied as a function of the focal spot separation, laser energy, and pulse duration. The results are then compared to 3D PIC simulations.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  7. Ion Bernstein waves in a magnetic reconnection region

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Four-dimensional energy spectra and a diagram for dispersion relations are determined for the first time in a magnetic reconnection region in the magnetotail using the four-point magnetometer data from the Cluster mission on a spatial scale of 200 km, about 0.1 ion inertial lengths. The energy spectra are anisotropic with an extension in the perpendicular direction and axially asymmetric with respect to the mean magnetic field. The dispersion diagram for the waves in the quasi-perpendicular directions in the plasma rest frame is in reasonably good agreement with the ion Bernstein waves particularly at the second harmonic of the proton gyro-frequency. Perpendicular-propagating ion Bernstein waves likely exist in an outflow region of magnetic reconnection. We discuss the causality of the Bernstein waves with magnetic reconnection with an estimate of the anomalous resistivity, and propose an observationally-driven model of turbulent magnetic reconnection.

  8. MESSENGER observations of magnetic reconnection in Mercury's magnetosphere.

    PubMed

    Slavin, James A; Acuña, Mario H; Anderson, Brian J; Baker, Daniel N; Benna, Mehdi; Boardsen, Scott A; Gloeckler, George; Gold, Robert E; Ho, George C; Korth, Haje; Krimigis, Stamatios M; McNutt, Ralph L; Raines, Jim M; Sarantos, Menelaos; Schriver, David; Solomon, Sean C; Trávnícek, Pavel; Zurbuchen, Thomas H

    2009-05-01

    Solar wind energy transfer to planetary magnetospheres and ionospheres is controlled by magnetic reconnection, a process that determines the degree of connectivity between the interplanetary magnetic field (IMF) and a planet's magnetic field. During MESSENGER's second flyby of Mercury, a steady southward IMF was observed and the magnetopause was threaded by a strong magnetic field, indicating a reconnection rate ~10 times that typical at Earth. Moreover, a large flux transfer event was observed in the magnetosheath, and a plasmoid and multiple traveling compression regions were observed in Mercury's magnetotail, all products of reconnection. These observations indicate that Mercury's magnetosphere is much more responsive to IMF direction and dominated by the effects of reconnection than that of Earth or the other magnetized planets.

  9. Implications of RHESSI Flare Observations for Magnetic Reconnection Models

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.; Sui, Linhui; Dennis, Brian R.

    2004-01-01

    The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations of the 2002 April 15 solar flare and related flares provide compelling evidence for the formation of a large-scale, reconnecting current sheet in at least some flares. We describe the observed evolution of the April 15 flare in terms of magnetic reconnection models. We argue that the flare most likely evolved through magnetic geometries associated with super-slow reconnection (early rise phase), fast reconnection (impulsive phase), and slow reconnection (gradual phase). We also provide evidence for X-ray brightenings within the evolving current sheet, possibly induced by the tearing mode instability. This work was supported in part by the RHESSI Program and NASA's Sun-Earth Connection Program. This work would not have been possible without the dedicated efforts of the entire RHESSI team.

  10. Efficiency of the FOTE method in identifying magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Fu, Huishan; Cao, Jinbin; Vaivads, Andris; Khotyaintsev, Yuri; Andre, Mats; Dunlop, Malcolm; Liu, Wenlong; Lu, Haoyu; Huang, Shiyong; Ma, Yuduan; Eriksson, Elin

    2016-04-01

    A magnetic reconnection event detected by Cluster is analyzed using three methods: Single-spacecraft Inference based on Flow-reversal Sequence (SIFS), Multi-spacecraft Inference based on Timing a Structure (MITS), and the First-Order Taylor Expansion (FOTE). Using the SIFS method, we find that the reconnection structure is an X-line; while using the MITS and FOTE methods, we find it is a magnetic island (O-line). We compare the efficiency and accuracy of these three methods, and find that the most efficient and accurate approach to identify a reconnection event is FOTE. Even in the guide-field reconnection, the FOTE method still works. This study for the first time demonstrates the capability of FOTE in identifying guide- and non-guide-field reconnection. It would be useful to the NASA MMS mission.

  11. Small-Scale Magnetic Reconnection at Equatorial Coronal Hole Boundaries

    NASA Astrophysics Data System (ADS)

    Lamb, Derek; DeForest, C. E.

    2011-05-01

    Coronal holes have long been known to be the source of the fast solar wind at both high and low latitudes. The equatorial extensions of polar coronal holes have long been assumed to have substantial magnetic reconnection at their boundaries, because they rotate more rigidly than the underlying photosphere. However, evidence for this reconnection has been sparse until very recently. We present some evidence that reconnection due to the evolution of small-scale magnetic fields may be sufficient to drive coronal hole boundary evolution. We hypothesize that a bias in the direction of that reconnection is sufficient to give equatorial coronal holes their rigid rotation. We discuss the prospects for investigating this using FLUX, a reconnection-controlled coronal MHD simulation framework. This work was funded by the NASA SHP-GI program.

  12. Cross-Scale Observational Signatures of Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina; Malaspina, David

    2014-01-01

    Magnetic reconnection is a significant mechanism for energy release across many astrophysical applications. In the solar atmosphere, reconnection is considered a primary contributor of flare evolution and coronal heating. Directly observing reconnection occurring in the solar atmosphere, however, is not trivial considering that the scale size of the diffusion region is magnitudes smaller than the observational capabilities of current instrumentation, and coronal magnetic field measurements are not currently sufficient to capture the process. Meanwhile, reconnection occurring in the Earth's magnetosphere transfers energy from the solar wind through a comparable process, although on vastly different scales. Magnetospheric measurements are made in situ rather than remotely; ergo, comparison of observations between the two regimes allows for potentially significant insight into reconnection as a stochastic and possibly turbulent process. We will present a set of observations from long-duration solar events and compare them to in situ measurements from the magnetosphere.

  13. Scaling of asymmetric magnetic reconnection: General theory and collisional simulations

    SciTech Connect

    Cassak, P. A.; Shay, M. A.

    2007-10-15

    A Sweet-Parker-type scaling analysis for asymmetric antiparallel reconnection (in which the reconnecting magnetic field strengths and plasma densities are different on opposite sides of the dissipation region) is performed. Scaling laws for the reconnection rate, outflow speed, the density of the outflow, and the structure of the dissipation region are derived from first principles. These results are independent of the dissipation mechanism. It is shown that a generic feature of asymmetric reconnection is that the X-line and stagnation point are not colocated, leading to a bulk flow of plasma across the X-line. The scaling laws are verified using two-dimensional resistive magnetohydrodynamics numerical simulations for the special case of asymmetric magnetic fields with symmetric density. Observational signatures and applications to reconnection in the magnetosphere are discussed.

  14. Cross-scale Observational Signatures of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Savage, S. L.; Malaspina, D.

    2014-12-01

    Magnetic reconnection is a significant mechanism for energy release across many astrophysical applications. In the solar atmosphere, reconnection is considered a primary contributor of flare evolution and coronal heating. Directly observing reconnection occurring in the solar atmosphere, however, is not trivial considering that the scale size of the diffusion region is magnitudes smaller than the observational capabilities of current instrumentation, and coronal magnetic field measurements are not currently sufficient to capture the process. Meanwhile, reconnection occurring in the Earth's magnetosphere transfers energy from the solar wind through a comparable process, although on vastly different scales. Magnetospheric measurements are made in situ rather than remotely; ergo, comparison of observations between the two regimes allows for potentially significant insight into reconnection as a stochastic and possibly turbulent process. We will present a set of observations from long-duration solar events and compare them to in situ measurements from the magnetosphere.

  15. Simulation and Analysis of Magnetic Reconnection in an Experimental Geometry

    NASA Astrophysics Data System (ADS)

    Murphy, Nicholas Arnold; Sovinec, C. R.; Cassak, P. A.

    2009-01-01

    The process of magnetic reconnection is important in space, laboratory, and astrophysical plasmas. The Magnetic Reconnection Experiment (MRX) is designed to study controlled reconnection in collisional and marginally collisionless plasmas (Yamada et al. 1997). We present single and two-fluid simulations of MRX using the NIMROD extended MHD code (Sovinec et al. 2004). These simulations highlight the interrelationship between the small-scale physics of the reconnection layer and the global magnetic field geometry. The communication between small and large scales is dominated by pressure gradients that result from a pileup of reconnection outflow. Toroidicity leads to asymmetry in either the inflow direction or the outflow direction, depending on the experimental mode of operation. To explain effects observed during reconnection with asymmetry in the outflow direction, we present an extension of the Sweet-Parker model that takes into account asymmetric downstream pressure. This model is applicable to reconnection in coronal mass ejections, the Earth's magnetotail, and in circumstellar disks present in hot star winds. This research is supported by the NSF Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas.

  16. Sub-grid-scale description of turbulent magnetic reconnection in magnetohydrodynamics

    NASA Astrophysics Data System (ADS)

    Widmer, F.; Büchner, J.; Yokoi, N.

    2016-04-01

    Magnetic reconnection requires, at least locally, a non-ideal plasma response. In collisionless space and astrophysical plasmas, turbulence could transport energy from large to small scales where binary particle collisions are rare. We have investigated the influence of small scale magnetohydrodynamics (MHD) turbulence on the reconnection rate in the framework of a compressible MHD approach including sub-grid-scale (SGS) turbulence. For this sake, we considered Harris-type and force-free current sheets with finite guide magnetic fields directed out of the reconnection plane. The goal is to find out whether unresolved by conventional simulations MHD turbulence can enhance the reconnection process in high-Reynolds-number astrophysical plasmas. Together with the MHD equations, we solve evolution equations for the SGS energy and cross-helicity due to turbulence according to a Reynolds-averaged turbulence model. The SGS turbulence is self-generated and -sustained through the inhomogeneities of the mean fields. By this way, the feedback of the unresolved turbulence into the MHD reconnection process is taken into account. It is shown that the turbulence controls the regimes of reconnection by its characteristic timescale τt. The dependence on resistivity was investigated for large-Reynolds-number plasmas for Harris-type as well as force-free current sheets with guide field. We found that magnetic reconnection depends on the relation between the molecular and apparent effective turbulent resistivity. We found that the turbulence timescale τt decides whether fast reconnection takes place or whether the stored energy is just diffused away to small scale turbulence. If the amount of energy transferred from large to small scales is enhanced, fast reconnection can take place. Energy spectra allowed us to characterize the different regimes of reconnection. It was found that reconnection is even faster for larger Reynolds numbers controlled by the molecular resistivity η, as

  17. Particle Acceleration Due to Coronal Non-null Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Threlfall, James; Neukirch, Thomas; Parnell, Clare Elizabeth

    2017-03-01

    Various topological features, for example magnetic null points and separators, have been inferred as likely sites of magnetic reconnection and particle acceleration in the solar atmosphere. In fact, magnetic reconnection is not constrained to solely take place at or near such topological features and may also take place in the absence of such features. Studies of particle acceleration using non-topological reconnection experiments embedded in the solar atmosphere are uncommon. We aim to investigate and characterise particle behaviour in a model of magnetic reconnection which causes an arcade of solar coronal magnetic field to twist and form an erupting flux rope, crucially in the absence of any common topological features where reconnection is often thought to occur. We use a numerical scheme that evolves the gyro-averaged orbit equations of single electrons and protons in time and space, and simulate the gyromotion of particles in a fully analytical global field model. We observe and discuss how the magnetic and electric fields of the model and the initial conditions of each orbit may lead to acceleration of protons and electrons up to 2 MeV in energy (depending on model parameters). We describe the morphology of time-dependent acceleration and impact sites for each particle species and compare our findings to those recovered by topologically based studies of three-dimensional (3D) reconnection and particle acceleration. We also broadly compare aspects of our findings to general observational features typically seen during two-ribbon flare events.

  18. A Rosetta Stone for in situ Observations of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Scudder, J. D.; Daughton, W. S.; Karimabadi, H.; Roytershteyn, V.

    2015-12-01

    Local conditions that constrain the physics of magnetic reconnection in space in 3D will be discussed, including those observable conditions presently used and new ones that enhance experimental closure. Three classes of tests will be discussed: i) proxies for unmeasurable theoretical properties II) observable properties satisfied by all layers that pass mass flux, including those of the reconnection layer, and (iii) observable kinetic tests that are increasingly peculiar to collisionless magnetic reconnection. A Rosetta Stone of state of the art observables will be proposed, including proxies for unmeasurable theoretical local rate of frozen flux violation and measures of the significance of frozen flux encountered. A suite of kinetic observables involving properties peculiar to electrons will also be demonstrated as promising litmus tests for certifying sites of collisionless magnetic reconnection.

  19. General Method for Describing Three-Dimensional Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Titov, Viacheslav; Forbes, Terry; Priest, Eric; Mikic, Zoran; Linker, Jon

    2009-11-01

    A general method for describing magnetic reconnection in arbitrary three-dimensional magnetic configurations is proposed. The method is based on the field-line mapping technique previously used only for the analysis of magnetic structure at a given time. This technique is extended here so as to analyze the evolution of magnetic structure. Such a generalization is made with the help of new dimensionless quantities called ``slip-squashing factors''. Their large values define the surfaces that border the reconnected or to-be-reconnected magnetic flux tubes for a given period of time during the magnetic evolution. The proposed method is universal, since it assumes only that the time sequence of evolving magnetic field and the tangential boundary flows are known. We illustrate our method for several examples and compare it with the general magnetic reconnection theory, proposed previously by Hesse and coworkers. The new method admits a straightforward numerical implementation and provides a powerful tool for the diagnostics of numerical data obtained in theoretical or experimental studies of magnetic reconnection in space and laboratory plasmas.

  20. ASYMMETRIC MAGNETIC RECONNECTION IN WEAKLY IONIZED CHROMOSPHERIC PLASMAS

    SciTech Connect

    Murphy, Nicholas A.; Lukin, Vyacheslav S.

    2015-06-01

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

  1. The Role of Magnetic Reconnection in Solar Activity

    NASA Technical Reports Server (NTRS)

    Antiochos, Spiro; DeVore, C. R.

    2008-01-01

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

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

    PubMed

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

    2014-09-10

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

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

    SciTech Connect

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

    2014-09-10

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

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

    DOE PAGES

    Yamada, Masaaki; Yoo, Jongsoo; Jara-Almonte, Jonathan; ...

    2014-09-10

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

  5. Magnetic Field Shear in Kinetic Models Steps Toward Understanding Magnetic Reconnection Drivers

    NASA Astrophysics Data System (ADS)

    Black, Carrie; Antiochos, Spiro; DeVore, Rick; Karpen, Judith

    2015-11-01

    In the standard model for coronal mass ejections (CME) and/or solar flares, the free energy for the eruptive event resides in a strongly sheared magnetic. A pre-eruption force balance consists of an upward force due to the magnetic pressure of the sheared field and a downward tension due to overlying unsheared field. Magnetic reconnection disrupts this force balance; therefore, it is critical for understanding CME/flare initiation, to model the onset of reconnection driven by the build-up of magnetic shear. In MHD simulations, the application of a magnetic-field shear is a trivial matter. However, kinetic effects are dominant in the diffusion region and thus, it is important to examine this process with PIC simulations as well. The implementation of such a driver in PIC methods is challenging, however, and indicates the necessity of a true multiscale model for such processes in the solar environment. The field must be sheared self-consistently and indirectly to prevent the generation of waves that destroy the desired system. Plasma instabilities can arise nonetheless. Here, we show that we can control this instability and generate a predicted out-of-plane magnetic flux. This material is based upon work supported by the National Science Foundation under Award No. AGS-1331356.

  6. A new magnetic reconnection paradigm: Stochastic plasmoid chains

    NASA Astrophysics Data System (ADS)

    Loureiro, Nuno

    2015-11-01

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

  7. Magnetic reconnection in turbulence: from Cluster to MMS and beyond

    NASA Astrophysics Data System (ADS)

    Retino, Alessandro; Sundkvist, David; Matthaeus, William; Vaivads, Andris; Califano, Francesco; Khotyaintsev, Yuri; LeContel, Olivier; Sorriso-valvo, Luca; Chasapis, Alexandros; Lavraud, Benoit; Valentini, Francesco; Servidio, Sergio; Rossi, Claudia; Camporeale, Enrico

    2016-07-01

    Magnetic reconnection is a universal energy dissipation mechanism occurring in space and astrophysical magnetized plasmas. Such plasmas are frequently in a turbulent state, raising the fundamental question of the role reconnection for energy dissipation in turbulence. Understanding reconnection in turbulence is of pivotal importance to explain phenomena such as particle acceleration in stellar atmospheres, the heating of interplanetary and interstellar media as well as particle energization in accretion disks and cosmic rays acceleration. Many numerical simulations support the role of reconnection for efficiently dissipate turbulent energy and heat and accelerated particles. Such simulations indicate that reconnection occurs in small-scale current sheets spontaneously forming within the turbulence. Yet experimental evidence of reconnection in turbulence has been provided only recently thanks to high resolution in situ measurements by modern spacecraft. Here we present ESA/Cluster and more recent NASA/MMS observations in near-Earth space showing evidence of reconnection in turbulence and its importance for energy dissipation and particle energization. We also discuss implications for upcoming spacecraft missions such as Solar Orbiter and Solar Probe Plus, as well as for missions currently under study pahse such as ESA/THOR.

  8. Plasma dynamics and heating/acceleration during driven magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Cheng, C. Z.; Inoue, Shizuo; Ono, Yasushi; Horiuchi, Ritoku

    2015-11-01

    Highlights of the plasma dynamics and energization during driven anti-parallel magnetic reconnection are presented. The MHD condition breaks down in the entire reconnection layer (the reconnection current layer, the separatrix region and the whole downstream), and the plasma dynamics is significantly different from the results of the Hall-MHD model. In particular, we explain (1) how electron and ion dynamics decouple and how the charge separation and electrostatic electric field are produced in the magnetic field reversal region (reconnection current layer and outflow exhaust) and around the separatrix regions, (2) how electrons and ions gain energy in the reconnection current layer, (3) why the electron outflow velocity in the reconnection exhaust reaches super-Alfvenic speed and the ion outflow velocity reaches Alfvenic speed and how the parallel electric field is produced, (4) how electrons are accelerated by the parallel electric field around the separatrix region, and (5) how ions gain energy when they move across the separatrix region into the downstream. Finally we show that electrons and ions gain energy mainly from the inductive reconnection driven electric field and less from the electrostatic electric field.

  9. Kinetic Vlasov simulations of collisionless magnetic reconnection

    SciTech Connect

    Schmitz, H.; Grauer, R.

    2006-09-15

    A fully kinetic Vlasov simulation of the Geospace Environment Modeling Magnetic Reconnection Challenge is presented. Good agreement is found with previous kinetic simulations using particle in cell (PIC) codes, confirming both the PIC and the Vlasov code. In the latter the complete distribution functions f{sub k} (k=i,e) are discretized on a numerical grid in phase space. In contrast to PIC simulations, the Vlasov code does not suffer from numerical noise and allows a more detailed investigation of the distribution functions. The role of the different contributions of Ohm's law are compared by calculating each of the terms from the moments of the f{sub k}. The important role of the off-diagonal elements of the electron pressure tensor could be confirmed. The inductive electric field at the X line is found to be dominated by the nongyrotropic electron pressure, while the bulk electron inertia is of minor importance. Detailed analysis of the electron distribution function within the diffusion region reveals the kinetic origin of the nongyrotropic terms.

  10. Comments on Magnetic Reconnection Models of Canceling Magnetic Features on the Sun

    NASA Astrophysics Data System (ADS)

    Litvinenko, Yuri E.

    2015-06-01

    Data analysis and theoretical arguments support magnetic reconnection in a chromospheric current sheet as the mechanism of the observed photospheric magnetic flux cancellation on the Sun. Flux pile-up reconnection in a Sweet-Parker current sheet can explain the observed properties of canceling mag-netic features, including the speeds of canceling magnetic fragments, the magnetic uxes in the fragments, and the flux cancellation rates, inferred from the data. It is discussed how more realistic chromospheric reconnection models can be developed by relaxing the assumptions of a negligible current sheet curvature and a constant height of the reconnection site above the photosphere.

  11. Imaging Observations of Magnetic Reconnection in a Solar Eruptive Flare

    NASA Astrophysics Data System (ADS)

    Li, Y.; Sun, X.; Ding, M. D.; Qiu, J.; Priest, E. R.

    2017-02-01

    Solar flares are among the most energetic events in the solar atmosphere. It is widely accepted that flares are powered by magnetic reconnection in the corona. An eruptive flare is usually accompanied by a coronal mass ejection, both of which are probably driven by the eruption of a magnetic flux rope (MFR). Here we report an eruptive flare on 2016 March 23 observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The extreme-ultraviolet imaging observations exhibit the clear rise and eruption of an MFR. In particular, the observations reveal solid evidence of magnetic reconnection from both the corona and chromosphere during the flare. Moreover, weak reconnection is observed before the start of the flare. We find that the preflare weak reconnection is of tether-cutting type and helps the MFR to rise slowly. Induced by a further rise of the MFR, strong reconnection occurs in the rise phases of the flare, which is temporally related to the MFR eruption. We also find that the magnetic reconnection is more of 3D-type in the early phase, as manifested in a strong-to-weak shear transition in flare loops, and becomes more 2D-like in the later phase, as shown by the apparent rising motion of an arcade of flare loops.

  12. The role of compressibility in energy release by magnetic reconnection

    SciTech Connect

    Birn, J.; Borovsky, J. E.; Hesse, M.

    2012-08-15

    Using resistive compressible magnetohydrodynamics, we investigate the energy release and transfer by magnetic reconnection in finite (closed or periodic) systems. The emphasis is on the magnitude of energy released and transferred to plasma heating in configurations that range from highly compressible to incompressible, based on the magnitude of the background {beta} (ratio of plasma pressure over magnetic pressure) and of a guide field in two-dimensional reconnection. As expected, the system becomes more incompressible, and the role of compressional heating diminishes, with increasing {beta} or increasing guide field. Nevertheless, compressional heating may dominate over Joule heating for values of the guide field of 2 or 3 (in relation to the reconnecting magnetic field component) and {beta} of 5-10. This result stems from the strong localization of the dissipation near the reconnection site, which is modeled based on particle simulation results. Imposing uniform resistivity, corresponding to a Lundquist number of 10{sup 3} to 10{sup 4}, leads to significantly larger Ohmic heating. Increasing incompressibility greatly reduces the magnetic flux transfer and the amount of energy released, from {approx}10% of the energy associated with the reconnecting field component, for zero guide field and low {beta}, to {approx}0.2%-0.4% for large values of the guide field B{sub y0}>5 or large {beta}. The results demonstrate the importance of taking into account plasma compressibility and localization of dissipation in investigations of heating by turbulent reconnection, possibly relevant for solar wind or coronal heating.

  13. The Role of Compressibility in Energy Release by Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Birn, J.; Borovosky, J. E.; Hesse, M.

    2012-01-01

    Using resistive compressible magnetohydrodynamics, we investigate the energy release and transfer by magnetic reconnection in finite (closed or periodic) systems. The emphasis is on the magnitude of energy released and transferred to plasma heating in configurations that range from highly compressible to incompressible, based on the magnitude of the background beta (ratio of plasma pressure over magnetic pressure) and of a guide field in two-dimensional reconnection. As expected, the system becomes more incompressible, and the role of compressional heating diminishes, with increasing beta or increasing guide field. Nevertheless, compressional heating may dominate over Joule heating for values of the guide field of 2 or 3 (in relation to the reconnecting magnetic field component) and beta of 5-10. This result stems from the strong localization of the dissipation near the reconnection site, which is modeled based on particle simulation results. Imposing uniform resistivity, corresponding to a Lundquist number of 10(exp 3) to 10(exp 4), leads to significantly larger Ohmic heating. Increasing incompressibility greatly reduces the magnetic flux transfer and the amount of energy released, from approx. 10% of the energy associated with the reconnecting field component, for zero guide field and low beta, to approx. 0.2%-0.4% for large values of the guide field B(sub y0) > 5 or large beta. The results demonstrate the importance of taking into account plasma compressibility and localization of dissipation in investigations of heating by turbulent reconnection, possibly relevant for solar wind or coronal heating.

  14. New Measure of the Dissipation Region in Collisionless Magnetic Reconnection

    SciTech Connect

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

    2011-05-13

    A new measure to identify a small-scale dissipation region in collisionless magnetic reconnection is proposed. The energy transfer from the electromagnetic field to plasmas in the electron's rest frame is formulated as a Lorentz-invariant scalar quantity. The measure is tested by two-dimensional particle-in-cell simulations in typical configurations: symmetric and asymmetric reconnection, with and without the guide field. The innermost region surrounding the reconnection site is accurately located in all cases. We further discuss implications for nonideal MHD dissipation.

  15. The Development of Drift Wave Turbulence in Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    McMurtrie, L.; Drake, J. F.; Swisdak, M. M.

    2013-12-01

    An important feature in collisionless magnetic reconnection is the development of sharp discontinuities along the separatrices bounding the Alfvenic outflow. The typical scale length of these features is ρs (the Larmor radius based on the sound speed) for guide field reconnection. Temperature gradients in the inflowing plasma (as might be found in the magnetopause) can lead to instabilities at these separatrices, specifically drift wave turbulence. We present standalone 2D and 3D PIC simulations of drift wave turbulence to investigate scaling properties and growth rates. Further investigations of the relative importance of drift wave turbulence in the development of reconnection will also be considered.

  16. ONSET OF FAST MAGNETIC RECONNECTION IN PARTIALLY IONIZED GASES

    SciTech Connect

    Malyshkin, Leonid M.; Zweibel, Ellen G. E-mail: zweibel@astro.wisc.edu

    2011-10-01

    We consider quasi-stationary two-dimensional magnetic reconnection in a partially ionized incompressible plasma. We find that when the plasma is weakly ionized and the collisions between the ions and the neutral particles are significant, the transition to fast collisionless reconnection due to the Hall effect in the generalized Ohm's law is expected to occur at much lower values of the Lundquist number, as compared to a fully ionized plasma case. We estimate that these conditions for fast reconnection are satisfied in molecular clouds and in protostellar disks.

  17. Magnetic Reconnection by a Self-Retreating X Line

    SciTech Connect

    Oka, M.; Nishikawa, K.-I.; Fujimoto, M.; Nakamura, T. K. M.; Shinohara, I.

    2008-11-14

    Particle-in-cell simulations of collisionless magnetic reconnection are performed to study asymmetric reconnection in which an outflow is blocked by a hard wall while leaving sufficiently large room for the outflow of the opposite direction. This condition leads to a slow, roughly constant motion of the diffusion region away from the wall, the so-called 'X-line retreat'. The typical retreat speed is {approx}0.1 times the Alfven speed. At the diffusion region, ion flow pattern shows strong asymmetry and the ion stagnation point and the X line are not collocated. A surprise, however, is that the reconnection rate remains the same unaffected by the retreat motion.

  18. New Measure of the Dissipation Region in Collisionless Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    A new measure to identify a small-scale dissipation region in collisionless magnetic reconnection is proposed. The energy transfer from the electromagnetic field to plasmas in the electron s rest frame is formulated as a Lorentz-invariant scalar quantity. The measure is tested by two-dimensional particle-in-cell simulations in typical configurations: symmetric and asymmetric reconnection, with and without the guide field. The innermost region surrounding the reconnection site is accurately located in all cases. We further discuss implications for nonideal MHD dissipation.

  19. Does the Rate of Collisionless Magnetic Reconnection Depend on the Dissipation Mechanism?

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    The importance of the electron dissipation effect on the reconnection rate is investigated in the general case of asymmetric collisionless magnetic reconnection. Contrary to the standard collisionless reconnection model, it is found that the reconnection rate, and the macroscopic evolution of the reconnecting system, crucially depend on the nature of the dissipation mechanism and that the Hall effect alone is not able to sustain fast reconnection.

  20. High power heating of magnetic reconnection in merging tokamak experiments

    SciTech Connect

    Ono, Y.; Tanabe, H.; Gi, K.; Watanabe, T.; Ii, T.; Yamada, T.; Gryaznevich, M.; Scannell, R.; Conway, N.; Crowley, B.; Michael, C.

    2015-05-15

    Significant ion/electron heating of magnetic reconnection up to 1.2 keV was documented in two spherical tokamak plasma merging experiment on MAST with the significantly large Reynolds number R∼10{sup 5}. Measured 1D/2D contours of ion and electron temperatures reveal clearly energy-conversion mechanisms of magnetic reconnection: huge outflow heating of ions in the downstream and localized heating of electrons at the X-point. Ions are accelerated up to the order of poloidal Alfven speed in the reconnection outflow region and are thermalized by fast shock-like density pileups formed in the downstreams, in agreement with recent solar satellite observations and PIC simulation results. The magnetic reconnection efficiently converts the reconnecting (poloidal) magnetic energy mostly into ion thermal energy through the outflow, causing the reconnection heating energy proportional to square of the reconnecting (poloidal) magnetic field B{sub rec}{sup 2}  ∼  B{sub p}{sup 2}. The guide toroidal field B{sub t} does not affect the bulk heating of ions and electrons, probably because the reconnection/outflow speeds are determined mostly by the external driven inflow by the help of another fast reconnection mechanism: intermittent sheet ejection. The localized electron heating at the X-point increases sharply with the guide toroidal field B{sub t}, probably because the toroidal field increases electron confinement and acceleration length along the X-line. 2D measurements of magnetic field and temperatures in the TS-3 tokamak merging experiment also reveal the detailed reconnection heating mechanisms mentioned above. The high-power heating of tokamak merging is useful not only for laboratory study of reconnection but also for economical startup and heating of tokamak plasmas. The MAST/TS-3 tokamak merging with B{sub p} > 0.4 T will enables us to heat the plasma to the alpha heating regime: T{sub i} > 5 keV without using any additional heating facility.

  1. Observations of Slow Electron Holes at a Magnetic Reconnection Site

    SciTech Connect

    Khotyaintsev, Yu. V.; Vaivads, A.; Andre, M.; Fujimoto, M.; Retino, A.; Owen, C. J.

    2010-10-15

    We report in situ observations of high-frequency electrostatic waves in the vicinity of a reconnection site in the Earth's magnetotail. Two different types of waves are observed inside an ion-scale magnetic flux rope embedded in a reconnecting current sheet. Electron holes (weak double layers) produced by the Buneman instability are observed in the density minimum in the center of the flux rope. Higher frequency broadband electrostatic waves with frequencies extending up to f{sub pe} are driven by the electron beam and are observed in the denser part of the rope. Our observations demonstrate multiscale coupling during the reconnection: Electron-scale physics is induced by the dynamics of an ion-scale flux rope embedded in a yet larger-scale magnetic reconnection process.

  2. Time Scales for Energy Release in Hall Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Huba, J. D.; Rudakov, L. I.

    2004-05-01

    We present a study of the time scales for energy release in 2D Hall magnetic reconnection. We use the NRL Hall MHD code VooDoo for this study. We consider a 2D reversed field current layer with a magnetic perturbation that initiates the reconnection process. We use boundary conditions that allow inflow and outflow (i.e., not periodic) and let the system reach a steady state. We find that the system goes through three stages: a relatively long current layer thinning process, a fast reconnection phase, and a final steady state phase. We define the time scale for energy release as the fast reconnection period: from onset to steady state. Preliminary results indicate that the time for energy release scales as the initial thickness of the current layer. We apply these results to the magnetotail and magnetopause. Research supported by NASA and ONR.

  3. Relativistic magnetic reconnection driven by intense lasers in preformed plasma

    NASA Astrophysics Data System (ADS)

    Campbell, Paul; Raymond, A.; McKelvey, A.; Maksimchuk, A.; Nees, J.; Yanovsky, V.; Krushelnick, K.; Dong, C. F.; Fox, W.; Zulick, C.; Wei, M. S.; Chen, H.; Chvykov, V.; Mileham, C.; Nilson, P. M.; Stoeckl, C.; Thomas, A. G. R.; Willingale, L.

    2016-10-01

    Experiments were performed with the OMEGA EP laser system focusing the two short pulse beams to high intensities on foil targets. Relativistic electrons drive fast reconnection self-generated magnetic fields. To investigate the effects of a preformed plasma on this relativistic magnetic reconnection, a long pulse UV beam was used to ablate the front surface of layered targets. The density and reconnection dynamics in the preformed copper or CH plasma were diagnosed with a 4 ω optical probe. A spherically bent crystal imaged characteristic copper Kα emission induced by fast electrons accelerated into the target in the reconnection diffusion region. This work was supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0002727.

  4. THE ACCELERATION OF IONS IN SOLAR FLARES DURING MAGNETIC RECONNECTION

    SciTech Connect

    Knizhnik, K.; Swisdak, M.; Drake, J. F. E-mail: swisdak@umd.edu

    2011-12-20

    The acceleration of solar flare ions during magnetic reconnection is explored via particle-in-cell simulations that self-consistently and simultaneously follow the motions of both protons and {alpha} particles. We show that the dominant heating of thermal ions during guide field reconnection, the usual type in the solar corona, results from pickup behavior during the entry into reconnection exhausts. In contrast to anti-parallel reconnection, the temperature increment is dominantly transverse, rather than parallel, to the local magnetic field. A comparison of protons and {alpha} reveals a mass-to-charge (M/Q) threshold in pickup behavior that favors the heating of high-M/Q ions, which is consistent with impulsive flare observations.

  5. Experimental study of energy conversion in the magnetic reconnection layer

    NASA Astrophysics Data System (ADS)

    Yamada, Masaaki

    2014-10-01

    Magnetic reconnection, in which magnetic field lines break and reconnect to change their topology, occurs throughout the universe: in solar flares, the earth's magnetosphere, star forming galaxies, and laboratory fusion plasmas. The essential feature of reconnection is that it energizes plasma particles by converting magnetic energy to particle energy; this process both accelerates and heats the plasma particles. Despite the recent advances of reconnection research, the exact mechanisms for bulk plasma heating, particle acceleration, and energy flow channels remain unresolved. In this work, the mechanisms responsible for the energization of plasma particles in the magnetic reconnection layer are investigated in the MRX device together with a quantitative evaluation of the conversion of magnetic energy to ions and electrons. A comprehensive analysis of the reconnection layer is made in terms of two-fluid physics based on the measurements of two-dimensional profiles of 1) electric potential, 2) flow vectors of electrons and ions, and 3) the electron temperature, Te and the ion temperature, Ti in the layer. It is experimentally verified that a saddle shaped electrostatic electric potential profile is formed in the reconnection plane. Ions are accelerated across the separatrices by the strong electrostatic field and enter the exhaust region where they become thermalized. Electron heating is observed to extend beyond the electron diffusion region, and non-classical heating mechanisms associated with high frequency fluctuations is found to play a role. Our quantitative analysis of the energy transport processes and energy inventory concludes that more than 50% of magnetic energy is converted to plasma particles, of which 2/3 transferred to ions and 1/3 to electrons. The results which demonstrate that conversion of magnetic energy occurs in a significantly larger region than theoretically considered before, are compared with the two-fluid simulations and the recent space

  6. The local dayside reconnection rate for oblique interplanetary magnetic fields

    NASA Astrophysics Data System (ADS)

    Komar, C. M.; Cassak, P. A.

    2016-06-01

    We present an analysis of local properties of magnetic reconnection at the dayside magnetopause for various interplanetary magnetic field (IMF) orientations in global magnetospheric simulations. This has heretofore not been practical because it is difficult to locate where reconnection occurs for oblique IMF, but new techniques make this possible. The approach is to identify magnetic separators, the curves separating four regions of differing magnetic topology, which map the reconnection X line. The electric field parallel to the X line is the local reconnection rate. We compare results to a simple model of local two-dimensional asymmetric reconnection. To do so, we find the plasma parameters that locally drive reconnection in the magnetosheath and magnetosphere in planes perpendicular to the X line at a large number of points along the X line. The global magnetohydrodynamic simulations are from the three-dimensional Block-Adaptive, Tree Solarwind Roe-type Upwind Scheme (BATS-R-US) code with a uniform resistivity, although the techniques described here are extensible to any global magnetospheric simulation model. We find that the predicted local reconnection rates scale well with the measured values for all simulations, being nearly exact for due southward IMF. However, the absolute predictions differ by an undetermined constant of proportionality, whose magnitude increases as the IMF clock angle changes from southward to northward. We also show similar scaling agreement in a simulation with oblique southward IMF and a dipole tilt. The present results will be an important component of a full understanding of the local and global properties of dayside reconnection.

  7. Effects of guide field in driven magnetic reconnection

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    Decoupling of electron and ion dynamics is the key physical process in the magnetic reconnection layer. It leads to the generation of parallel E-field and in-plane electrostatic E-field, and determines how particles gain energy. For antiparallel magnetic reconnection (zero guide field case), the electron and ion dynamics decoupling is due to meandering particle (unmagnetized) orbits in the field reversal region and particle acceleration by parallel electric field in the separatrix region. The parallel E-field is produced mainly from the driven inductive E-field due to the quadrupole out-of-plane magnetic field generation. The decoupling of electron and ion dynamics causes charge separation which produces the in-plane electrostatic E-field. If the guide field is stronger than the reconnecting magnetic field, both electrons and ions are magnetized in the entire magnetic reconnection domain, and the electron-ion dynamics decoupling process changes from the zero guide field case. Then, the structure of parallel and electrostatic E-fields, and thus how electrons/ions gain energy also changes. We will explain the physical mechanisms of electron-ion dynamics decoupling on the E-field generation, and how electron and ion are heated/accelerated based on the driven reconnection simulation results.

  8. Plasmoid instability in high-Lundquist-number magnetic reconnection

    SciTech Connect

    Huang, Yi-Min; Bhattacharjee, A.

    2013-05-15

    Our understanding of magnetic reconnection in resistive magnetohydrodynamics has gone through a fundamental change in recent years. The conventional wisdom is that magnetic reconnection mediated by resistivity is slow in laminar high Lundquist (S) plasmas, constrained by the scaling of the reconnection rate predicted by Sweet-Parker theory. However, recent studies have shown that when S exceeds a critical value ∼10{sup 4}, the Sweet-Parker current sheet is unstable to a super-Alfvénic plasmoid instability, with a linear growth rate that scales as S{sup 1/4}. In the fully developed statistical steady state of two-dimensional resistive magnetohydrodynamic simulations, the normalized average reconnection rate is approximately 0.01, nearly independent of S, and the distribution function f(ψ) of plasmoid magnetic flux ψ follows a power law f(ψ)∼ψ{sup −1}. When Hall effects are included, the plasmoid instability may trigger onset of Hall reconnection even when the conventional criterion for onset is not satisfied. The rich variety of possible reconnection dynamics is organized in the framework of a phase diagram.

  9. 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.

  10. Global impact of collisionless magnetic reconnection on the structure of planetary magnetospheres

    NASA Astrophysics Data System (ADS)

    Dorelli, J.; Glocer, A.; Collinson, G.; Toth, G.

    2014-12-01

    While the local physics of collisionless magnetic reconnection has been well studied, the consequences for global magnetospheric structure remain largely unexplored. It is well known, for example, that Hall electric fields generate a new system of field-aligned currents propagating from the reconnection site along the magnetic separatrices; but it is not known how these currents contribute to the global region 1 and region 2 current systems or to auroral substorm features. In this presentation, we show that collisionless reconnection has a significant impact on the large scale structure of planetary magnetospheres. Using global Hall MHD simulations, we demonstrate that field-aligned currents generated at the reconnection sites (and carried by whistler or kinetic Alfven waves) extend all the way down to the surface of the magnetized body and must therefore be included in the magnetosphere-ionosphere coupling physics (e.g., Harang-like discontinuities in the ionospheric convection pattern -- absent in MHD -- are introduced, and the current densities are large enough to produce auroral emission). More surprisingly, ions and electrons pick up magnetic drifts (due to JxB forces in the ion diffusion regions) that significantly alter the global magnetospheric convection pattern. Ions in the plasma sheet drift duskward while electrons drift dawnward, producing large asymmetries in the plasma sheet structure even in the absense of solar wind asymmetry, asymmetric ionospheric conductance or co-rotation. We discuss the implications of these effects for the reconnection-driven magnetospheres of Ganymede, Mercury and Earth.

  11. Experimental Study of Current-Driven Turbulence During Magnetic Reconnection

    SciTech Connect

    Porkolab, Miklos; Egedal-Pedersen, Jan; Fox, William

    2010-08-31

    CMPD Final Report Experimental Study of Current-Driven Turbulence During Magnetic Reconnection Miklos Porkolab, PI, Jan Egedal, co-PI, William Fox, graduate student. This is the final report for Grant DE-FC02-04ER54786, MIT Participation in the Center for Multiscale Plasma Dynamics, which was active from 8/1/2004 to 7/31/2010. This Grant supported the thesis work of one MIT graduate student, William Fox, The thesis research consisted of an experimental study of the fluctuations arising during magnetic reconnection in plasmas on the Versatile Toroidal Facility (VTF) at MIT Plasma Science and Fusion Center (PSFC). The thesis was submitted and accepted by the MIT physics Department,. Fox, Experimental Study of Current-Driven Turbulence During Magnetic Reconnection, Ph.D. Thesis, MIT (2009). In the VTF experiment reconnection and current-sheet formation is driven by quickly changing currents in a specially arranged set of internal conductors. Previous work on this device [Egedal, et al, PRL 98, 015003, (2007)] identified a spontaneous reconnection regime. In this work fluctuations were studied using impedance-matched, high-bandwidth Langmuir probes. Strong, broadband fluctuations, with frequencies extending from near the lower-hybrid frequency [fLH = (fcefci)1/2] to the electron cyclotron frequency fce were found to arise during the reconnection events. Based on frequency and wavelength measurements, lower-hybrid waves and Trivelpiece-Gould waves were identified. The lower-hybrid waves are easiest to drive with strong perpendicular drifts or gradients which arise due to the reconnection events; an appealing possibility is strong temperature gradients. The Trivelpiece-Gould modes can result from kinetic, bump-on-tail instability of a runaway electron population energized by the reconnection events. We also observed that the turbulence is often spiky, consisting of discrete positive-potential spikes, which were identified as electron phase-space holes, a class of

  12. Magnetic reconnection in incompressible fluids. [of solar atmosphere and interior

    NASA Technical Reports Server (NTRS)

    Deluca, Edward E.; Craig, Ian J.

    1992-01-01

    The paper investigates the dynamical relaxation of a disturbed X-type magnetic neutral point in a periodic geometry, with an ignorable coordinate, for an incompressible fluid. It is found that the properties of the current sheet cannot be understood in terms of steady state reconnection theory or more recent linear dynamical solutions. Accordingly, a new scaling law for magnetic reconnection is presented, consistent with fast energy dissipation (i.e., the dissipation rate at current maximum is approximately independent of magnetic diffusivity (eta)). The flux annihilation rate, however, scales at eta exp 1/4, faster than the Sweet-Parker rate of sq rt eta but asymptotically much slower than the dissipation rate. These results suggest a flux pile-up regime in which the bulk of the free magnetic energy is released as heat rather than as kinetic energy of mass motion. The implications of our results for reconnection in the solar atmosphere and interior are discussed.

  13. The relation between reconnected flux, the parallel electric field, and the reconnection rate in a three-dimensional kinetic simulation of magnetic reconnection

    SciTech Connect

    Wendel, D. E.; Olson, D. K.; Hesse, M.; Kuznetsova, M.; Adrian, M. L.; Aunai, N.; Karimabadi, H.; Daughton, W.

    2013-12-15

    We investigate the distribution of parallel electric fields and their relationship to the location and rate of magnetic reconnection in a large particle-in-cell simulation of 3D turbulent magnetic reconnection with open boundary conditions. The simulation's guide field geometry inhibits the formation of simple topological features such as null points. Therefore, we derive the location of potential changes in magnetic connectivity by finding the field lines that experience a large relative change between their endpoints, i.e., the quasi-separatrix layer. We find a good correspondence between the locus of changes in magnetic connectivity or the quasi-separatrix layer and the map of large gradients in the integrated parallel electric field (or quasi-potential). Furthermore, we investigate the distribution of the parallel electric field along the reconnecting field lines. We find the reconnection rate is controlled by only the low-amplitude, zeroth and first–order trends in the parallel electric field while the contribution from fluctuations of the parallel electric field, such as electron holes, is negligible. The results impact the determination of reconnection sites and reconnection rates in models and in situ spacecraft observations of 3D turbulent reconnection. It is difficult through direct observation to isolate the loci of the reconnection parallel electric field amidst the large amplitude fluctuations. However, we demonstrate that a positive slope of the running sum of the parallel electric field along the field line as a function of field line length indicates where reconnection is occurring along the field line.

  14. Full Two-Fluid Collisionless Magnetic Reconnection Simulations

    NASA Astrophysics Data System (ADS)

    Gomez, D. O.; Andres, N.; Dmitruk, P.

    2015-12-01

    Magnetic reconnection is an important energy conversion process in space environments such as the solar corona or planetary magnetospheres. At the theoretical level of resistive one-fluid MHD, the Sweet-Parker model leads to extremely low reconnection rates for virtually all space physics applications. Kinetic plasma effects introduce new spatial and temporal scales into the theoretical description, which are expected to increase the reconnection rates. Within the theoretical framework of two-fluid MHD, we retain the effects of the Hall current and electron inertia and neglect dissipative effects such as viscosity and electric resistivity. This level of description brings two new spatial scales into play, namely, the ion and electron inertial scales. In absence of resistive dissipation, reconnection can only be attained by the action of electron inertia. We performed 2.5D two-fluid simulations using a pseudo-spectral code which yields exact conservation (to round-off errors) of the ideal invariants. Our simulations show that when the effects of electron inertia are retained, magnetic reconnection takes place. In a stationary regime, the reconnection rate is simply proportional to the ion inertial length, as also emerges from a scaling law derived from dimensional arguments.

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

    SciTech Connect

    Bhattacharjee, Amitava

    2012-02-16

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

  16. Magnetic reconnection in Hall-MHD including electron inertia

    NASA Astrophysics Data System (ADS)

    Gomez, D. O.; Andres, N.; Martin, L. N.; Dmitruk, P.

    2013-12-01

    Magnetic reconnection is an important energy conversion process in highly conducting plasmas, such as those present in the solar corona or in planetary magnetospheres. Within the framework of resistive one-fluid MHD, the Sweet-Parker model leads to extremely low reconnection rates for virtually all space physics applications. Kinetic plasma effects introduce new spatial and temporal scales into the theoretical description, which might significantly increase the reconnection rates. Within the more general framework of two-fluid MHD for a fully ionized hydrogen plasma, we retain the effects of the Hall current and electron inertia. We performed 2.5D Hall MHD simulations including electron inertia using a pseudo-spectral code which yields exact conservation (to round-off errors) of all the ideal invariants. We obtain finite reconnection rates even in the case of zero resistivity, thus showing the important influence of the electron inertia.

  17. Evidence for magnetic field reconnection at the Earth's magnetopause

    NASA Technical Reports Server (NTRS)

    Sonnerup, B. U. O.; Paschmann, G.; Papamastorakis, I.; Sckopke, N.; Haerendel, G.; Bame, S. J.; Asbridge, J. R.; Gosling, J. T.; Russell, C. T.

    1981-01-01

    Eleven passes of the ISEE satellites through the frontside terrestrial magnetopause were identified, where the plasma velocity in the magnetopause and boundary layer was substantially larger than in the magnetosheath. The nature of the plasma flow, magnetic field, and energetic particle fluxes in these regions were examined, with a view to determining whether the velocity enhancements can be explained by magnetic field reconnection.

  18. The Impact of Geometrical Constraints on Collisionless Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

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

  19. Scaling Laws for Magnetic Reconnection when Electron Pressure Anisotropy is near the Firehose Threshold

    NASA Astrophysics Data System (ADS)

    Ohia, Obioma; Egedal, Jan; Lukin, Vyacheslav S.; Daughton, William; Le, Ari

    2015-11-01

    Magnetic reconnection in weakly-collisional, a process linked to solar flares, coronal mass ejections, and magnetic substorms, has been widely studied through fluid and kinetic simulations. While two-fluid models often reproduce the fast reconnection rate of kinetic simulations, significant differences are observed in the structure of the reconnection regions. Recently, new equations of state that accurately account for the development of anisotropic electron pressure due to the electric and magnetic trapping of electrons have been developed. Guide-field, fluid simulations using these equations of state have been shown to reproduce the detailed reconnection region observed in kinetic simulations. Implementing this two-fluid simulation using the HiFi framework, we describe a mechanism for regulation of electron pressure anisotropy as well as study force balance of the electron layers in guide-field reconnection. Scaling laws for the heating observed in these layers based on upstream conditions are derived. Formerly of U.S. Naval Research Laboratory. Any opinions, findings, conclusions and/or recommendations are those of author and do not necessarily reflect the views of the National Science Foundation.

  20. Understanding the dynamics and energetics of magnetic reconnection in a laboratory plasma: Review of recent progress on selected fronts

    DOE PAGES

    Yamada, Masaaki; Yoo, Jongsoo; Myers, Clayton E.

    2016-05-11

    solar flare eruptions, including “storage and release” mechanisms of magnetic energy. We show that toroidalmagnetic flux generated by magnetic relaxation (reconnection) processes generates a new stabilizing force which prevents plasma eruption. This result has led us to discover a new stabilizing force for solar flares [Myers et al., Nature 528, 526 (2015)].« less

  1. Understanding the dynamics and energetics of magnetic reconnection in a laboratory plasma: Review of recent progress on selected fronts

    SciTech Connect

    Yamada, Masaaki; Yoo, Jongsoo; Myers, Clayton E.

    2016-05-11

    flare eruptions, including “storage and release” mechanisms of magnetic energy. We show that toroidalmagnetic flux generated by magnetic relaxation (reconnection) processes generates a new stabilizing force which prevents plasma eruption. This result has led us to discover a new stabilizing force for solar flares [Myers et al., Nature 528, 526 (2015)].

  2. Slowing of magnetic reconnection concurrent with weakening plasma inflows and increasing collisionality in strongly-driven laser-plasma experiments

    SciTech Connect

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

    2015-05-20

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

  3. Slowing of magnetic reconnection concurrent with weakening plasma inflows and increasing collisionality in strongly-driven laser-plasma experiments

    DOE PAGES

    Rosenberg, M.  J.; Li, C.  K.; Fox, W.; ...

    2015-05-20

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

  4. Evolution of field line helicity during magnetic reconnection

    SciTech Connect

    Russell, A. J. B. Hornig, G.; Wilmot-Smith, A. L.; Yeates, A. R.

    2015-03-15

    We investigate the evolution of field line helicity for magnetic fields that connect two boundaries without null points, with emphasis on localized finite-B magnetic reconnection. Total (relative) magnetic helicity is already recognized as an important topological constraint on magnetohydrodynamic processes. Field line helicity offers further advantages because it preserves all topological information and can distinguish between different magnetic fields with the same total helicity. Magnetic reconnection changes field connectivity and field line helicity reflects these changes; the goal of this paper is to characterize that evolution. We start by deriving the evolution equation for field line helicity and examining its terms, also obtaining a simplified form for cases where dynamics are localized within the domain. The main result, which we support using kinematic examples, is that during localized reconnection in a complex magnetic field, the evolution of field line helicity is dominated by a work-like term that is evaluated at the field line endpoints, namely, the scalar product of the generalized field line velocity and the vector potential. Furthermore, the flux integral of this term over certain areas is very small compared to the integral of the unsigned quantity, which indicates that changes of field line helicity happen in a well-organized pairwise manner. It follows that reconnection is very efficient at redistributing helicity in complex magnetic fields despite having little effect on the total helicity.

  5. Evolution of field line helicity during magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Russell, A. J. B.; Yeates, A. R.; Hornig, G.; Wilmot-Smith, A. L.

    2015-03-01

    We investigate the evolution of field line helicity for magnetic fields that connect two boundaries without null points, with emphasis on localized finite-B magnetic reconnection. Total (relative) magnetic helicity is already recognized as an important topological constraint on magnetohydrodynamic processes. Field line helicity offers further advantages because it preserves all topological information and can distinguish between different magnetic fields with the same total helicity. Magnetic reconnection changes field connectivity and field line helicity reflects these changes; the goal of this paper is to characterize that evolution. We start by deriving the evolution equation for field line helicity and examining its terms, also obtaining a simplified form for cases where dynamics are localized within the domain. The main result, which we support using kinematic examples, is that during localized reconnection in a complex magnetic field, the evolution of field line helicity is dominated by a work-like term that is evaluated at the field line endpoints, namely, the scalar product of the generalized field line velocity and the vector potential. Furthermore, the flux integral of this term over certain areas is very small compared to the integral of the unsigned quantity, which indicates that changes of field line helicity happen in a well-organized pairwise manner. It follows that reconnection is very efficient at redistributing helicity in complex magnetic fields despite having little effect on the total helicity.

  6. The plasmoid instability during asymmetric inflow magnetic reconnection

    SciTech Connect

    Murphy, Nicholas A.; Young, Aleida K.; Shen, Chengcai; Lin, Jun; Ni, Lei

    2013-06-15

    Theoretical studies of the plasmoid instability generally assume that the reconnecting magnetic fields are symmetric. We relax this assumption by performing two-dimensional resistive magnetohydrodynamic simulations of the plasmoid instability during asymmetric inflow magnetic reconnection. Magnetic asymmetry modifies the onset, scaling, and dynamics of this instability. Magnetic islands develop preferentially into the weak magnetic field upstream region. Outflow jets from individual X-points impact plasmoids obliquely rather than directly as in the symmetric case. Consequently, deposition of momentum by the outflow jets into the plasmoids is less efficient, the plasmoids develop net vorticity, and shear flow slows down secondary merging between islands. Secondary merging events have asymmetry along both the inflow and outflow directions. Downstream plasma is more turbulent in cases with magnetic asymmetry because islands are able to roll around each other after exiting the current sheet. As in the symmetric case, plasmoid formation facilitates faster reconnection for at least small and moderate magnetic asymmetries. However, when the upstream magnetic field strengths differ by a factor of 4, the reconnection rate plateaus at a lower value than expected from scaling the symmetric results. We perform a parameter study to investigate the onset of the plasmoid instability as a function of magnetic asymmetry and domain size. There exist domain sizes for which symmetric simulations are stable but asymmetric simulations are unstable, suggesting that moderate magnetic asymmetry is somewhat destabilizing. We discuss the implications for plasmoid and flux rope formation in solar eruptions, laboratory reconnection experiments, and space plasmas. The differences between symmetric and asymmetric simulations provide some hints regarding the nature of the three-dimensional plasmoid instability.

  7. Magnetic Reconnection: A Fundamental Process in Space Plasmas

    NASA Technical Reports Server (NTRS)

    Hesse, Michael

    2010-01-01

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

  8. Flux Rope Acceleration and Enhanced Magnetic Reconnection Rate

    SciTech Connect

    C.Z. Cheng; Y. Ren; G.S. Choe; Y.-J. Moon

    2003-03-25

    A physical mechanism of flares, in particular for the flare rise phase, has emerged from our 2-1/2-dimensional resistive MHD simulations. The dynamical evolution of current-sheet formation and magnetic reconnection and flux-rope acceleration subject to continuous, slow increase of magnetic shear in the arcade are studied by employing a non-uniform anomalous resistivity in the reconnecting current sheet under gravity. The simulation results directly relate the flux rope's accelerated rising motion with an enhanced magnetic reconnection rate and thus an enhanced reconnection electric field in the current sheet during the flare rise phase. The simulation results provide good quantitative agreements with observations of the acceleration of flux rope, which manifests in the form of SXR ejecta or erupting filament or CMEs, in the low corona. Moreover, for the X-class flare events studied in this paper the peak reconnection electric field is about O(10{sup 2} V/m) or larger, enough to accelerate p articles to over 100 keV in a field-aligned distance of 10 km. Nonthermal electrons thus generated can produce hard X-rays, consistent with impulsive HXR emission observed during the flare rise phase.

  9. 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.

  10. 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.

  11. Magnetic Reconnection in the Interior of Interplanetary Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Fermo, R. L.; Opher, M.; Drake, J. F.

    2014-07-01

    Recent in situ observations of interplanetary coronal mass ejections (ICMEs) found signatures of reconnection exhausts in their interior or trailing edge. Whereas reconnection on the leading edge of an ICME would indicate an interaction with the coronal or interplanetary environment, this result suggests that the internal magnetic field reconnects with itself. In light of this data, we consider the stability properties of flux ropes first developed in the context of astrophysics, then further elaborated upon in the context of reversed field pinches (RFPs). It was shown that the lowest energy state of a flux rope corresponds to ∇×B=λB with λ a constant, the so-called Taylor state. Variations from this state will result in the magnetic field trying to reorient itself into the Taylor state solution, subject to the constraints that the toroidal flux and magnetic helicity are invariant. In reversed field pinches, this relaxation is mediated by the reconnection of the magnetic field, resulting in a sawtooth crash. If we likewise treat the ICME as a flux rope, any deviation from the Taylor state will result in reconnection within the interior of the flux tube, in agreement with the observations by Gosling et al. Such a departure from the Taylor state takes place as the flux tube cross section expands in the latitudinal direction, as seen in magnetohydrodynamic (MHD) simulations of flux tubes propagating through the interplanetary medium. We show analytically that this elongation results in a state which is no longer in the minimum energy Taylor state. We then present magnetohydrodynamic simulations of an elongated flux tube which has evolved away from the Taylor state and show that reconnection at many surfaces produces a complex stochastic magnetic field as the system evolves back to a minimum energy state configuration.

  12. The Driving Magnetic Field and Reconnection in CME/Flare Eruptions and Coronal Jets

    NASA Technical Reports Server (NTRS)

    Moore, Ronald L.

    2010-01-01

    Signatures of reconnection in major CME (coronal mass ejection)/flare eruptions and in coronal X-ray jets are illustrated and interpreted. The signatures are magnetic field lines and their feet that brighten in flare emission. CME/flare eruptions are magnetic explosions in which: 1. The field that erupts is initially a closed arcade. 2. At eruption onset, most of the free magnetic energy to be released is not stored in field bracketing a current sheet, but in sheared field in the core of the arcade. 3. The sheared core field erupts by a process that from its start or soon after involves fast "tether-cutting" reconnection at an initially small current sheet low in the sheared core field. If the arcade has oppositely-directed field over it, the eruption process from its start or soon after also involves fast "breakout" reconnection at an initially small current sheet between the arcade and the overarching field. These aspects are shown by the small area of the bright field lines and foot-point flare ribbons in the onset of the eruption. 4. At either small current sheet, the fast reconnection progressively unleashes the erupting core field to erupt with progressively greater force. In turn, the erupting core field drives the current sheet to become progressively larger and to undergo progressively greater fast reconnection in the explosive phase of the eruption, and the flare arcade and ribbons grow to become comparable to the pre-eruption arcade in lateral extent. In coronal X-ray jets: 1. The magnetic energy released in the jet is built up by the emergence of a magnetic arcade into surrounding unipolar "open" field. 2. A simple jet is produced when a burst of reconnection occurs at the current sheet between the arcade and the open field. This produces a bright reconnection jet and a bright reconnection arcade that are both much smaller in diameter that the driving arcade. 3. A more complex jet is produced when the arcade has a sheared core field and undergoes an

  13. 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.

  14. Asymmetric evolution of magnetic reconnection in collisionless accretion disk

    NASA Astrophysics Data System (ADS)

    Shirakawa, Keisuke; Hoshino, Masahiro

    2014-05-01

    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 J0×Ω0, where J0 is the initial current density in the neutral sheet and Ω0 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.

  15. Observational Evidence of Magnetic Reconnection for Brightenings and Transition Region Arcades in IRIS Observations

    NASA Astrophysics Data System (ADS)

    Zhao, Jie; Schmieder, Brigitte; Li, Hui; Pariat, Etienne; Zhu, Xiaoshuai; Feng, Li; Grubecka, Michalina

    2017-02-01

    By using a new method of forced-field extrapolation, we study the emerging flux region AR11850 observed by the Interface Region Imaging Spectrograph and Solar Dynamical Observatory. Our results suggest that the bright points (BPs) in this emerging region exhibit responses in lines formed from the upper photosphere to the transition region, which have relatively similar morphologies. They have an oscillation of several minutes according to the Atmospheric Imaging Assembly data at 1600 and 1700 Å. The ratio between the BP intensities measured in 1600 and 1700 Å filtergrams reveals that these BPs are heated differently. Our analysis of the Helioseismic and Magnetic Imager vector magnetic field and the corresponding topology in AR11850 indicates that the BPs are located at the polarity inversion line and most of them are related to magnetic reconnection or cancelation. The heating of the BPs might be different due to different magnetic topology. We find that the heating due to the magnetic cancelation would be stronger than the case of bald patch reconnection. The plasma density rather than the magnetic field strength could play a dominant role in this process. Based on physical conditions in the lower atmosphere, our forced-field extrapolation shows consistent results between the bright arcades visible in slit-jaw image 1400 Å and the extrapolated field lines that pass through the bald patches. It provides reliable observational evidence for testing the mechanism of magnetic reconnection for the BPs and arcades in the emerging flux region, as proposed in simulation studies.

  16. Relaxation of flux ropes and magnetic reconnection in the Reconnection Scaling Experiment at LANL

    NASA Astrophysics Data System (ADS)

    Furno, Ivo

    2004-11-01

    Magnetic reconnection and plasma relaxation are studied in the Reconnection Scaling Experiment (RSX) with current carrying plasma columns (magnetic flux ropes). Using plasma guns, multiple flux ropes (B_pol < 100 Gauss, L=90 cm, r < 3 cm) are generated in a three-dimensional (3D) cylindrical geometry and are observed to evolve dynamically during the injection of magnetic helicity. Detailed evolution of electron density, temperature, plasma potential and magnetic field structures is reconstructed experimentally and visible light emission is captured with a fast-gated, intensified CCD camera to provide insight into the global flux rope dynamics. Experiments with two flux ropes in collisional plasmas and in a strong axial guide field (Bz / B_pol > 10) suggest that magnetic reconnection plays an important role in the initial stages of flux rope evolution. During the early stages of the applied current drive (t < 20τ_Alfven), the flux ropes are observed to twist, partially coalesce and form a thin current sheet with a scale size comparable to that of the ion sound gyro-radius. Here, non-ideal terms in a generalized Ohm's Law appear to play a significant role in the 3D reconnection process as shown by the presence of a strong axial pressure gradient in the current sheet. In addition, a density perturbation with a structure characteristic of a kinetic Alfvén wave is observed to propagate axially in the current layer, anti-parallel to the induced sheet current. Later in the evolution, when a sufficient amount of helicity is injected into the system, a critical threshold for the kink instability is exceeded and the helical twisting of each individual flux rope can dominate the dynamics of the system. This may prevent the complete coalescence of the flux ropes.

  17. Relaxation of flux ropes and magnetic reconnection in the Reconnection Scaling Experiment at LANL

    NASA Astrophysics Data System (ADS)

    Furno, I.; Intrator, T.; Hemsing, E.; Hsu, S.; Lapenta, G.; Abbate, S.

    2004-12-01

    Magnetic reconnection and plasma relaxation are studied in the Reconnection Scaling Experiment (RSX) with current carrying plasma columns (magnetic flux ropes). Using plasma guns, multiple flux ropes (Bθ ≤ 100 Gauss, L=90 cm, r≤3 cm) are generated in a three-dimensional (3D) cylindrical geometry and are observed to evolve dynamically during the injection of magnetic helicity. Detailed evolution of electron density, temperature, plasma potential and magnetic field structures is reconstructed experimentally and visible light emission is captured with a fast-gated, intensified CCD camera to provide insight into the global flux rope dynamics. Experiments with two flux ropes in collisional plasmas and in a strong axial guide field (Bz / Bθ > 10) suggest that magnetic reconnection plays an important role in the initial stages of flux rope evolution. During the early stages of the applied current drive (t≤ 20 τ Alfv´ {e}n), the flux ropes are observed to twist, partially coalesce and form a thin current sheet with a scale size comparable to that of the ion sound gyro-radius. Here, non-ideal terms in a generalized Ohm's Law appear to play a significant role in the 3D reconnection process as shown by the presence of a strong axial pressure gradient in the current sheet. In addition, a density perturbation with a structure characteristic of a kinetic Alfvén wave is observed to propagate axially in the current layer, anti-parallel to the induced sheet current. Later in the evolution, when a sufficient amount of helicity is injected into the system, a critical threshold for the kink instability is exceeded and the helical twisting of each individual flux rope can dominate the dynamics of the system. This may prevent the complete coalescence of the flux ropes.

  18. 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.

  19. Three-dimensional outflow jets generated in collisionless magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Fujimoto, Keizo

    2016-10-01

    The present study proposes a new theoretical model generating three-dimensional (3-D) outflow jets in collisionless magnetic reconnection by means of a large-scale particle-in-cell simulation. The key mechanism is the formation of 3-D flux ropes arising in the turbulent electron current layer formed around the magnetic x line. The scale of the flux ropes along the current density is determined by the wavelength of an electron flow shear mode which is a macroscopic scale larger than the typical kinetic scales. The 3-D flux ropes are intermittently ejected from the current layer and regulates the outflow jets into three dimensions. The gross reconnection rate is sufficiently large, since reconnection takes place almost uniformly along the x line.

  20. Three-Dimensional Modeling of Guide-Field Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Hesse, Michael

    2005-01-01

    The dissipation mechanism of guide field magnetic reconnection remains a subject of intense scientific interest. On one hand, one set of recent studies have shown that particle inertia-based processes, which include thermal and bulk inertial effects, provide the reconnection electric field in the diffusion region. On the other hand, a second set of studies emphasizes the role of wave-particle interactions in providing anomalous resistivity in the diffusion region. In this presentation, we analyze three-dimensional PIC simulations of guide-field magnetic reconnection. Specific emphasis will be on the question whether thermal-inertia processes, mediated by the electron pressure tensor, remain a viable dissipation mechanism in fully three-dimensional systems.

  1. Effects of electron inertia in collisionless magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Andrés, Nahuel; Martin, Luis; Dmitruk, Pablo; Gómez, Daniel

    2014-07-01

    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.

  2. Local and Global 3-D Effects in the Magnetic Reconnection Experiment (MRX)

    NASA Astrophysics Data System (ADS)

    Dorfman, S.; Ji, H.; Yamada, M.; Oz, E.; Yoo, J.; Daughton, W.; Roytershteyn, V.

    2009-11-01

    One of the key open questions in Magnetic Reconnection is the nature of the mechanism that governs the reconnection rate in real astrophysical and laboratory systems. Comparisons between fully kinetic 2-D simulations of the Magnetic Reconnection Experiment (MRX) and experimental data show that the 2-D, collisionless expression for the electric field due to particle dynamics [1] does not match MRX data; related to this is a factor of 3-5 discrepancy in the layer width [2,3]. Adding collisions to the simulation leads to a broadening of the layer, but the level of collisionality present in MRX may not be high enough to resolve the discrepancy. Ongoing research on MRX explores the role of fluctuations and 3-D effects in the force balance. Significant toroidal asymmetries have been found, manifested by regions of high inductive electric field moving in the electron flow direction within the layer. Electromagnetic fluctuations in the lower hybrid frequency range [4] tend to occur in discharges with high local currents and a rapid local reconnection rate. The precise relation of these phenomena to fast reconnection is actively being investigated. [1] M. Hesse, et al., Phys. Plasmas, 6:1781 (1999). [2] Y. Ren, et al., Phys. Plasmas 15, 082113 (2008). [3] S. Dorfman, et al., Phys. Plasmas 15, 102107 (2008). [4] H. Ji, et al., Phys.Rev.Lett. 92 (2004) 115001. Supported by NDSEG, DOE, NASA, and NSF.

  3. Plasma Heating During Magnetic Reconnection: Implications for Turbulent Dissipation

    NASA Astrophysics Data System (ADS)

    Shay, M. A.; Parashar, T.; Matthaeus, W. H.; Haggerty, C. C.

    2015-12-01

    Current sheets and associated intermittency are known to be prevalent in many turbulent plasmas and have been shown to be correlated with heating in observations of solar wind turbulence [1] and dissipation in kinetic particle-in-cell simulations [5]. Most intriguing, recent PIC simulations have found that the relative ion to electron heating ratio is strongly dependent on the turbulence amplitude [3]. An important question is whether magnetic reconnection is an important mechanism responsible for this heating. Studies focused on laminar reconnection have made significant progress recently on the magnitude and physics responsible for heating during magnetic reconnection [2,4]. The ambient Alfven speed of plasma flowing into the reconnection region plays a critical role, with heating initially taking the form of counterstreaming beams generated by non-local acceleration mechanism. However, there are significant uncertainties with how to link this basic reconnection heating with generic heating in a turbulent plasma. In this presentation, our current understanding of heating due to reconnection will be reviewed, and the factors determining the applicability of this heating to turbulent dissipation and heating will be discussed. These ideas will be explored through the comparison of kinetic PIC simulations of turbulence with reconnection heating models. Key aspects that will be examined are the effect of differing turbulent conditions on the magnitude and anisotropy of the heating, as well as the ion to electron heating ratio. [1] Osman et al., ApJ Letters, 727, L11, 2011. [2] Phan, et al., GRL, 40, 50917, 2013. [3] Wu et al., ApJ Letters, 763, L30, 2013. [4] Shay et al., Phys. Plasmas, 21, 122902, 2014. [5] Wan et al., PRL, 114, 175002, 2015.

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

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Birn, Joachim; Kuznetsova, Masha

    1999-01-01

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

  5. Effect of electron inertia in two-fluid magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Gomez, Daniel; Dmitruk, Pablo; Andrés, Nahuel

    2016-07-01

    In space plasmas, magnetic reconnection is an important energy conversion process. Within the traditional one-fluid resistive MHD description, the Sweet-Parker model leads to extremely low reconnection rates for virtually all space physics applications. Within the theoretical framework of two-fluid MHD, we retain the effects of the Hall current and electron inertia and neglect dissipative effects such as viscosity and electric resistivity. This description brings two new spatial scales into play, such as the ion and electron inertial lengths. In absence of resistive dissipation, reconnection can only be attained by the action of electron inertia. We performed two-fluid simulations using a pseudo-spectral code which yields exact conservation (to round-off errors) of the ideal invariants. Our simulations show that when the effects of electron inertia are retained, magnetic reconnection takes place. Moreover, in a stationary regime the reconnection rate is simply proportional to the ion inertial length, as also emerges from a scaling law derived from dimensional arguments.

  6. The plasmoid instability and Hall effect during chromospheric magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Murphy, Nicholas Arnold; Lukin, Vyacheslav

    2016-01-01

    Magnetic reconnection is a ubiquitous process in the partially ionized solar chromosphere. Recent two-dimensional simulations have shown that the plasmoid instability onsets during partially ionized reconnection [1-4]. We use the plasma-neutral module of the HiFi framework to simulate the nonlinear evolution of the plasmoid instability during symmetric and asymmetric reconnection. These simulations model the plasma and neutrals as separate fluids and include ionization, recombination, charge exchange, thermal conduction, and the Hall effect. The Hall effect leads to the development of significant out-of-plane magnetic fields in the current sheet region in the laminar phase, but we do not observe shortening of the current sheet or significant acceleration of the reconnection rate as a result. After the onset of the plasmoid instability, structure develops on scales comparable to the ion inertial length. We compare simulations of the plasmoid instability with and without the Hall effect to determine its impact on the reconnection process. Finally, we discuss ongoing efforts to connect these simulations with solar observations and laboratory experiments.[1] Leake et al. 2012, ApJ, 760, 109 [2] Leake et al. 2013, PhPl, 20, 062102 [3] Ni et al. 2015, ApJ, 799, 79 [4] Murphy & Lukin 2015, ApJ, 805, 134

  7. Kinetic simulation of magnetic reconnection in the presence of shear

    SciTech Connect

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

    1988-09-05

    The basic physical processes associated with collisionless magnetic reconnection are investigated using the implicit PIC code AVANTI. The code is based on a 2.5-D fully electromagnetic direct implicit algorithm which has proven stable for arbitrary time step. This stability makes it possible to separate out the respective roles of the highly magnetized electrons and the un-magnetized ions for large ion-electron mass ratios. It is found that the inclusion of a guide magnetic field (magnetic shear) severely slows the initial stages of reconnection and damps out the electrostatic ringing if local values of the guide field are above a threshold determined by questions of electron mobility. 9 refs., 6 figs.

  8. Energy conversion during magnetic reconnection for magnetotail-like equilibria

    SciTech Connect

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

    2006-10-15

    The principle of magnetic field-to-particle energy conversion for magnetic reconnection, originally developed by the authors for Harris-Fadeev equilibria, is extended to include a finite north-south (normal) component of the magnetic field, which is typical of the Earth's magnetotail environment. On the basis of the exact conservation laws derived from the nonlinear Vlasov equation, it is demonstrated that a small portion of the energy stored in the magnetic field is released and converted to particle thermal energy as a result of the magnetic field topological transformation, i.e., reconnection. It is also found that the normal field component has a minimal impact on the efficacy of the energy exchange.

  9. Magnetic reconnection in the solar atmosphere: from proposal to paradigm

    NASA Astrophysics Data System (ADS)

    Cargill, Peter; Parnell, Clare; Browning, Philippa; de Moortel, Ineke; Hood, Alan

    2010-06-01

    MEETING REPORT On 13 November 2009, the RAS hosted a discussion meeting to commemorate the formal retirement of Prof. Eric Priest. Here Peter Cargill, Clare Parnell, Philippa Browning, Ineke de Moortel and Alan Hood examine how magnetic reconnection has evolved over the past 50 years from an important but controversial proposal, to a general paradigm.

  10. Effects of Magnetic Reconnection Processes in the Near Magnetosphere

    NASA Astrophysics Data System (ADS)

    Coppi, B.; Fletcher, A.

    2016-10-01

    Magnetic reconnection processes in collisionless plasmas on the Earth's dayside and nightside are shown to be capable of producing high energy populations of both ions and electrons. These particles can interact with the Radiation Belts and reach the regions close to the Earth where auroral substorms can be produced. The main theoretical issues faced in identifying plasma modes with realistic characteristics, given the scale distances and time scales, that can be responsible for the needed reconnection processes are pointed out. Solution of relevant equations obtained by a combined analytical and numerical approach. Sponsored in part by the U.S. D.O.E. and the N.S.F.

  11. Solar flares as cascades of reconnecting magnetic loops.

    PubMed

    Hughes, D; Paczuski, M; Dendy, R O; Helander, P; McClements, K G

    2003-04-04

    A model for the solar coronal magnetic field is proposed where multiple directed loops evolve in space and time. Loops injected at small scales are anchored by footpoints of opposite polarity moving randomly on a surface. Nearby footpoints of the same polarity aggregate, and loops can reconnect when they collide. This may trigger a cascade of further reconnection, representing a solar flare. Numerical simulations show that a power law distribution of flare energies emerges, associated with a scale-free network of loops, indicating self-organized criticality.

  12. Fast Magnetic Reconnection in the Plasmoid-Dominated Regime

    SciTech Connect

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

    2010-12-03

    A conceptual model of resistive magnetic reconnection via a stochastic plasmoid chain is proposed. The global reconnection rate is shown to be independent of the Lundquist number. The distribution of fluxes in the plasmoids is shown to be an inverse-square law. It is argued that there is a finite probability of emergence of abnormally large plasmoids, which can disrupt the chain (and may be responsible for observable large abrupt events in solar flares and sawtooth crashes). A criterion for the transition from the resistive magnetohydrodynamic to the collisionless regime is provided.

  13. A New Electric Field in Asymmetric Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Malakit, K.; Shay, M. A.; Cassak, P.; Ruffolo, D. J.

    2013-12-01

    Magnetic reconnection is an important plasma process that drives the dynamics of the plasma in the magnetosphere and plays a crucial role in the interaction between magnetospheric and magnetosheath plasma. It has been shown that when a reconnection occurs in a collisionless plasma, it exhibits the Hall electric field, an in-plane electric field structure pointing toward the X-line. In this work, we show that when the reconnection has asymmetric inflow conditions such as the reconnection at the day-side magnetopause, a new in-plane electric field structure can exist. This electric field points away from the X-line and is distinct from the known Hall electric field. We argue that the origin of the electric field is associated with the physics of finite Larmor radius. A theory and predictions of the electric field properties are presented and backed up by results from fully kinetic particle-in-cell simulations of asymmetric reconnection with various inflow conditions. Under normal day-side reconnection inflow conditions, the electric field is expected to occur on the magnetospheric side of the X-line pointing Earthward. Hence, it has a potential to be used as a signature for satellites, such as the upcoming Magnetospheric Multi-Scale (MMS) mission, to locate the reconnection sites at the day-side magnetopause. This research was supported by the postdoctoral research sponsorship of Mahidol University (KM), NSF grants ATM-0645271 - Career Award (MAS) and AGS-0953463 (PAC), NASA grants NNX08A083G - MMS IDS, NNX11AD69G, and NNX13AD72G (MAS) and NNX10AN08A (PAC), and the Thailand Research Fund (DR).

  14. Three-dimensional, Impulsive Magnetic Reconnection in a Laboratory Plasma

    SciTech Connect

    S Dorfman, et al

    2013-05-03

    Impulsive, local, 3-D reconnection is identified for the first time in a laboratory current sheet. The events observed in the Magnetic Reconnection Experiment (MRX) are characterized by large local gradients in the third direction and cannot be explained by 2-D models. Detailed measurements show that the ejection of flux rope structures from the current sheet plays a key role in these events. By contrast, even though electromagnetic fluctuations in the lower hybrid frequency range are also observed concurrently with the impulsive behavior, they are not the key physics responsible. A qualitative, 3-D, two-fluid model is proposed to explain the observations. The experimental results may be particularly applicable to space and astrophysical plasmas where impulsive reconnection occurs.

  15. Localized electron heating during magnetic reconnection in MAST

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  16. Fast magnetic reconnection due to anisotropic electron pressure

    SciTech Connect

    Cassak, P. A.; Baylor, R. N.; Fermo, R. L.; Beidler, M. T.; Shay, M. A.; Swisdak, M.; Drake, J. F.; Karimabadi, H.

    2015-02-15

    A new regime of fast magnetic reconnection with an out-of-plane (guide) magnetic field is reported in which the key role is played by an electron pressure anisotropy described by the Chew-Goldberger-Low gyrotropic equations of state in the generalized Ohm's law, which even dominates the Hall term. A description of the physical cause of this behavior is provided and two-dimensional fluid simulations are used to confirm the results. The electron pressure anisotropy causes the out-of-plane magnetic field to develop a quadrupole structure of opposite polarity to the Hall magnetic field and gives rise to dispersive waves. In addition to being important for understanding what causes reconnection to be fast, this mechanism should dominate in plasmas with low plasma beta and a high in-plane plasma beta with electron temperature comparable to or larger than ion temperature, so it could be relevant in the solar wind and some tokamaks.

  17. Observational Signatures of Magnetic Reconnection in the Extended Corona

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina; West, Matthew J.; Seaton, Daniel B.; Kobelski, Adam

    2016-01-01

    Observational signatures of reconnection have been studied extensively in the lower corona for decades, successfully providing insight into energy release mechanisms in the region above post-flare arcade loops and below 1.5 solar radii. During large eruptive events, however, energy release continues to occur well beyond the presence of reconnection signatures at these low heights. Supra-Arcade Downflows (SADs) and Supra-Arcade Downflowing Loops (SADLs) are particularly useful measures of continual reconnection in the corona as they may indicate the presence and path of retracting post-reconnection loops. SADs and SADLs have been faintly observed up to 18 hours beyond the passage of coronas mass ejections through the SOHO/LASCO field of view, but a recent event from 2014 October 14 associated with giant arches provides very clear observations of these downflows for days after the initial eruption. We report on this unique event and compare these findings with observational signatures of magnetic reconnection in the extended corona for more typical eruptions.

  18. Observational Signatures of Magnetic Reconnection in the Extended Corona

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina; West, Matthew J.; Seaton, Danial B.; Kobelski, Adam

    2016-01-01

    Observational signatures of reconnection have been studied extensively in the lower corona for decades, successfully providing insight into energy release mechanisms in the region above post-flare arcade loops and below 1.5 solar radii. During large eruptive events, however, energy release continues to occur well beyond the presence of reconnection signatures at these low heights. Supra-Arcade Downflows (SADs) and Supra-Arcade Downflowing Loops (SADLs) are particularly useful measures of continual reconnection in the corona as they may indicate the presence and path of retracting post-reconnection loops. SADs and SADLs have been faintly observed up to 18 hours beyond the passage of corona mass ejections through the SOHO/LASCO field of view, but a recent event from 2014 October 14 associated with giant arches provides very clear observations of these downflows for days after the initial eruption. We report on this unique event and compare these findings with observational signatures of magnetic reconnection in the extended corona for more typical eruptions.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  20. Experimental Evidence for Cerenkov Emission of Whistler Waves by Electron Holes Associated with Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Eastwood, J. P.; Goldman, M. V.; Zhang, X.; Hietala, H.; Krupar, V.; Newman, D. L.; Angelopoulos, V.; Lapenta, G.

    2015-12-01

    Whistler waves are a ubiquitous plasma phenomenon, observed in a variety of space and laboratory plasma environments. They play a key role in many important and diverse processes, such as particle acceleration in the radiation belts and auroral acceleration region, the dissipation of plasma turbulence at small scales below the inertial range, collisionless shock physics, and magnetic reconnection. In reconnection they may modify the reconnection rate and also whistler physics is crucial to enabling fast reconnection in the Hall reconnection model. Consequently, understanding how whistler waves are generated and how they subsequently interact with the plasma is a problem of wide importance and application. It is well known that whistlers can arise as a result of kinetic instabilities, which grow exponentially from noise as a consequence of unstable electron distributions, for example temperature anisotropy. This is used ubiquitously to predict where and when whistler waves are likely to exist and therefore be of importance in many plasma phenomena. Recently it has been demonstrated theoretically and via computer simulations that whistler waves may also arise via Cerenkov emission from electron hole quasi-particles [Goldman et al., PRL, 2014]. Such wave emission can arise even when the temperature anisotropy leads to damping; in this case the system is analogous to a damped forced oscillator. Here we present novel experimental analysis from THEMIS showing for the first time evidence consistent with the generation of whistlers via Cerenkov emission during magnetotail reconnection. By considering the electromagnetic properties of the electron holes, the amplitude, phase speed and frequency of the associated whistlers, and also the available sub-spin observations of the electron distribution function, we find that the data are best explained by the Cerenkov emission theory rather than by kinetic instabilities due to the electron temperature anisotropy. Whilst the

  1. Unsteady magnetic reconnection in laboratory experiments with current sheets

    NASA Astrophysics Data System (ADS)

    Frank, Anna

    2009-11-01

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

  2. MESSENGER Observations of Magnetic Reconnection in Mercury's Magnetosphere

    NASA Technical Reports Server (NTRS)

    Slavin. James A.

    2009-01-01

    During MESSENGER'S second flyby of Mercury on October 6,2008, very intense reconnection was observed between the planet's magnetic field and a steady southward interplanetary magnetic field (IMF). The dawn magnetopause was threaded by a strong magnetic field normal to its surface, approx.14 nT, that implies a rate of reconnection approx.10 times the typical rate at Earth and a cross-magnetospheric electric potential drop of approx.30 kV. The highest magnetic field observed during this second flyby, approx.160 nT, was found at the core of a large dayside flux transfer event (FTE). This FTE is estimated to contain magnetic flux equal to approx.5% that of Mercury's magnetic tail or approximately one order of magnitude higher fraction of the tail flux than is typically found for FTEs at Earth. Plasmoid and traveling compression region (TCR) signatures were observed throughout MESSENGER'S traversal of Mercury's magnetotail with a repetition rate comparable to the Dungey cycle time of approx.2 min. The TCR signatures changed from south-north, indicating tailward motion, to north-south, indicating sunward motion, at a distance approx.2.6 RM (where RM is Mercury's radius) behind the terminator indicating that the near-Mercury magnetotail neutral line was crossed at that point. Overall, these new MESSENGER observations suggest that magnetic reconnection at the dayside magnetopause is very intense relative to what is found at Earth and other planets, while reconnection in Mercury's tail is similar to that in other planetary magnetospheres, but with a very short Dungey cycle time.

  3. The Relation between Reconnected Flux, the Parallel Electric Field, and the Reconnection Rate in a Three-Dimensional Kinetic Simulation of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Wendel, D. E.; Olson, D. K.; Hesse, M.; Karimabadi, H.; Daughton, W. S.

    2013-12-01

    We investigate the distribution of parallel electric fields and their relationship to the location and rate of magnetic reconnection of a large particle-in-cell simulation of 3D turbulent magnetic reconnection with open boundary conditions. The simulation's guide field geometry inhibits the formation of topological features such as separators and null points. Therefore, we derive the location of potential changes in magnetic connectivity by finding the field lines that experience a large relative change between their endpoints, i.e., the quasi-separatrix layer. We find a correspondence between the locus of changes in magnetic connectivity, or the quasi-separatrix layer, and the map of large gradients in the integrated parallel electric field (or quasi-potential). Furthermore, we compare the distribution of parallel electric fields along field lines with the reconnection rate. We find the reconnection rate is controlled by only the low-amplitude, zeroth and first-order trends in the parallel electric field, while the contribution from high amplitude parallel fluctuations, such as electron holes, is negligible. The results impact the determination of reconnection sites within models of 3D turbulent reconnection as well as the inference of reconnection rates from in situ spacecraft measurements. It is difficult through direct observation to isolate the locus of the reconnection parallel electric field amidst the large amplitude fluctuations. However, we demonstrate that a positive slope of the partial sum of the parallel electric field along the field line as a function of field line length indicates where reconnection is occurring along the field line.

  4. SIGNATURES OF MAGNETIC RECONNECTION AT BOUNDARIES OF INTERPLANETARY SMALL-SCALE MAGNETIC FLUX ROPES

    SciTech Connect

    Tian Hui; Yao Shuo; Zong Qiugang; Qi Yu; He Jiansen

    2010-09-01

    The interaction between interplanetary small-scale magnetic flux ropes and the magnetic field in the ambient solar wind is an important topic in the understanding of the evolution of magnetic structures in the heliosphere. Through a survey of 125 previously reported small flux ropes from 1995 to 2005, we find that 44 of them reveal clear signatures of Alfvenic fluctuations and thus classify them as Alfven wave trains rather than flux ropes. Signatures of magnetic reconnection, generally including a plasma jet of {approx}30 km s{sup -1} within a magnetic field rotational region, are clearly present at boundaries of about 42% of the flux ropes and 14% of the wave trains. The reconnection exhausts are often observed to show a local increase in the proton temperature, density, and plasma beta. About 66% of the reconnection events at flux rope boundaries are associated with a magnetic field shear angle larger than 90{sup 0} and 73% of them reveal a decrease of 20% or more in the magnetic field magnitude, suggesting a dominance of anti-parallel reconnection at flux rope boundaries. The occurrence rate of magnetic reconnection at flux rope boundaries through the years 1995-2005 is also investigated and we find that it is relatively low around the solar maximum and much higher when approaching solar minima. The average magnetic field depression and shear angle for reconnection events at flux rope boundaries also reveal a similar trend from 1995 to 2005. Our results demonstrate for the first time that boundaries of a substantial fraction of small-scale flux ropes have properties similar to those of magnetic clouds, in the sense that both of them exhibit signatures of magnetic reconnection. The observed reconnection signatures could be related either to the formation of small flux ropes or to the interaction between flux ropes and the interplanetary magnetic fields.

  5. The Pressure Limitations on Flux Pile-Up Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Litvinenko, Y. E.

    1999-05-01

    Flux pile-up magnetic reconnection was thought to be able to provide fast energy dissipation a strongly magnetized plasma, for example, in solar flares. We examine the problem of the plasma pressure limitations on the rapidity of flux pile-up reconnection. It is shown that for a two-dimensional stagnation point flow with nonzero vorticity the magnetic merging rate cannot exceed the Sweet-Parker scaling in a low-beta plasma, which is too slow to explain flares. Moreover, the solution has some undesireable properties such as a diffusion layer at the external boundary and the massively increasing inflow speed. The pressure limitation appears to be somewhat less restrictive for three-dimensional flux pile-up. This work was supported by NSF grant ATM-9813933.

  6. Ion Bernstein waves in the magnetic reconnection region

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  7. Design of a Magnetic Reconnection Experiment in the Collisionless Regime

    NASA Astrophysics Data System (ADS)

    Egedal, J.; Le, A.; Daughton, W. S.

    2012-12-01

    A new model for effective heating of electrons during reconnection is now gaining support from spacecraft observations, theoretical considerations and kinetic simulations [1]. The key ingredient in the model is the physics of trapped electrons whose dynamics causes the electron pressure tensor to be strongly anisotropic [2]. The heating mechanism becomes highly efficient for geometries with low upstream electron pressure, conditions relevant to the magnetotail. We propose a new experiment that will be optimized for the study of kinetic reconnection including the dynamics of trapped electrons and associated pressure anisotropy. This requires an experiment that accesses plasmas with much lower collisionality and lower plasma beta than are available in present reconnection experiments. The new experiment will be designed such that a large variety of magnetic configurations can be established and tailored for continuation of our ongoing study of spontaneous 3D reconnection [3]. The flexible design will also allow for configurations suitable for the study of merging magnetic islands, which may be a source of super thermal electrons in naturally occurring plasmas. [1] Egedal J et al., Nature Physics, 8, 321 (2012). [2] Le A et al., Phys. Rev. Lett. 102, 085001 (2009). [3] Katz N et al., Phys. Rev. Lett. 104, 255004 (2010).;

  8. Do dispersive waves play a role in collisionless magnetic reconnection?

    SciTech Connect

    Liu, Yi-Hsin; Daughton, W.; Li, H.; Karimabadi, H.; Peter Gary, S.

    2014-02-15

    Using fully kinetic simulations, we demonstrate that the properly normalized reconnection rate is fast ∼0.1 for guide fields up to 80× larger than the reconnecting field and is insensitive to both the system size and the ion to electron mass ratio. These results challenge conventional explanations of reconnection based on fast dispersive waves, which are completely absent for sufficiently strong guide fields. In this regime, the thickness of the diffusion layer is set predominantly by the electron inertial length with an inner sublayer that is controlled by finite gyro-radius effects. As the Alfvén velocity becomes relativistic for very strong guide fields, the displacement current becomes important and strong deviations from charge neutrality occur, resulting in the build-up of intense electric fields which absorb a portion of the magnetic energy release. Over longer time scales, secondary magnetic islands are generated near the active x-line while an electron inertial scale Kelvin-Helmholtz instability is driven within the outflow. These secondary instabilities give rise to time variations in the reconnection rate but do not alter the average value.

  9. Magnetic Reconnection with Strong Synchrotron Cooling in Pulsar Magnetospheres

    NASA Astrophysics Data System (ADS)

    Uzdensky, Dmitri; Spitkovsky, Anatoly

    2012-10-01

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

  10. The transfer between electron bulk kinetic energy and thermal energy in collisionless magnetic reconnection

    SciTech Connect

    Lu, San; Lu, Quanming; Huang, Can; Wang, Shui

    2013-06-15

    By performing two-dimensional particle-in-cell simulations, we investigate the transfer between electron bulk kinetic and electron thermal energy in collisionless magnetic reconnection. In the vicinity of the X line, the electron bulk kinetic energy density is much larger than the electron thermal energy density. The evolution of the electron bulk kinetic energy is mainly determined by the work done by the electric field force and electron pressure gradient force. The work done by the electron gradient pressure force in the vicinity of the X line is changed to the electron enthalpy flux. In the magnetic island, the electron enthalpy flux is transferred to the electron thermal energy due to the compressibility of the plasma in the magnetic island. The compression of the plasma in the magnetic island is the consequence of the electromagnetic force acting on the plasma as the magnetic field lines release their tension after being reconnected. Therefore, we can observe that in the magnetic island the electron thermal energy density is much larger than the electron bulk kinetic energy density.

  11. The mechanisms of electron heating and acceleration during magnetic reconnection

    SciTech Connect

    Dahlin, J. T. Swisdak, M.; Drake, J. F.

    2014-09-15

    The heating of electrons in collisionless magnetic reconnection is explored in particle-in-cell simulations with non-zero guide fields so that electrons remain magnetized. In this regime, electric fields parallel to B accelerate particles directly, while those perpendicular to B do so through gradient-B and curvature drifts. The curvature drift drives parallel heating through Fermi reflection, while the gradient B drift changes the perpendicular energy through betatron acceleration. We present simulations in which we evaluate each of these mechanisms in space and time in order to quantify their role in electron heating. For a case with a small guide field (20% of the magnitude of the reconnecting component), the curvature drift is the dominant source of electron heating. However, for a larger guide field (equal to the magnitude of the reconnecting component) electron acceleration by the curvature drift is comparable to that of the parallel electric field. In both cases, the heating by the gradient B drift is negligible in magnitude. It produces net cooling because the conservation of the magnetic moment and the drop of B during reconnection produce a decrease in the perpendicular electron energy. Heating by the curvature drift dominates in the outflow exhausts where bent field lines expand to relax their tension and is therefore distributed over a large area. In contrast, the parallel electric field is localized near X-lines. This suggests that acceleration by parallel electric fields may play a smaller role in large systems where the X-line occupies a vanishing fraction of the system. The curvature drift and the parallel electric field dominate the dynamics and drive parallel heating. A consequence is that the electron energy spectrum becomes extremely anisotropic at late time, which has important implications for quantifying the limits of electron acceleration due to synchrotron emission. An upper limit on electron energy gain that is substantially higher than

  12. Reciprocatory magnetic reconnection in a coronal bright point

    NASA Astrophysics Data System (ADS)

    Zhang, Q. M.; Chen, P. F.; Ding, M. D.; Ji, H. S.

    2014-08-01

    Context. Coronal bright points (CBPs) are small-scale and long-duration brightenings in the lower solar corona. They are often explained in terms of magnetic reconnection. Aims: We aim to study the substructures of a CBP and clarify the relationship among the brightenings of different patches inside the CBP. Methods: The event was observed by the X-ray Telescope (XRT) aboard the Hinode spacecraft on 2009 August 22-23. Results: The CBP showed repeated brightenings (or CBP flashes). During each of the two successive CBP flashes, that is, weak and strong flashes that were separated by ~2 hr, the XRT images revealed that the CBP was composed of two chambers, patches A and B. During the weak flash, patch A brightened first, and patch B brightened ~2 min later. During the transition, the right leg of a large-scale coronal loop drifted from the right side of the CBP to the left side. During the strong flash, patch B brightened first, and patch A brightened ~2 min later. During the transition, the right leg of the large-scale coronal loop drifted from the left side of the CBP to the right side. In each flash, the rapid change of the connectivity of the large-scale coronal loop is strongly suggestive of the interchange reconnection. Conclusions: For the first time we found reciprocatory reconnection in the CBP, which means that reconnected loops in the outflow region of the first reconnection process serve as the inflow of the second reconnection process. Movies associated with Figs. 2 and 5 are available in electronic form at http://www.aanda.org

  13. Multi-scale structures of turbulent magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Nakamura, T. K. M.; Nakamura, R.; Narita, Y.; Baumjohann, W.; Daughton, W.

    2016-05-01

    We have analyzed data from a series of 3D fully kinetic simulations of turbulent magnetic reconnection with a guide field. A new concept of the guide filed reconnection process has recently been proposed, in which the secondary tearing instability and the resulting formation of oblique, small scale flux ropes largely disturb the structure of the primary reconnection layer and lead to 3D turbulent features [W. Daughton et al., Nat. Phys. 7, 539 (2011)]. In this paper, we further investigate the multi-scale physics in this turbulent, guide field reconnection process by introducing a wave number band-pass filter (k-BPF) technique in which modes for the small scale (less than ion scale) fluctuations and the background large scale (more than ion scale) variations are separately reconstructed from the wave number domain to the spatial domain in the inverse Fourier transform process. Combining with the Fourier based analyses in the wave number domain, we successfully identify spatial and temporal development of the multi-scale structures in the turbulent reconnection process. When considering a strong guide field, the small scale tearing mode and the resulting flux ropes develop over a specific range of oblique angles mainly along the edge of the primary ion scale flux ropes and reconnection separatrix. The rapid merging of these small scale modes leads to a smooth energy spectrum connecting ion and electron scales. When the guide field is sufficiently weak, the background current sheet is strongly kinked and oblique angles for the small scale modes are widely scattered at the kinked regions. Similar approaches handling both the wave number and spatial domains will be applicable to the data from multipoint, high-resolution spacecraft observations such as the NASA magnetospheric multiscale (MMS) mission.

  14. Three-dimensional fast magnetic reconnection driven by relativistic ultraintense femtosecond lasers.

    PubMed

    Ping, Y L; Zhong, J Y; Sheng, Z M; Wang, X G; Liu, B; Li, Y T; Yan, X Q; He, X T; Zhang, J; Zhao, G

    2014-03-01

    Three-dimensional fast magnetic reconnection driven by two ultraintense femtosecond laser pulses is investigated by relativistic particle-in-cell simulation, where the two paralleled incident laser beams are shot into a near-critical plasma layer to form a magnetic reconnection configuration in self-generated magnetic fields. A reconnection X point and out-of-plane quadrupole field structures associated with magnetic reconnection are formed. The reconnection rate is found to be faster than that found in previous two-dimensional Hall magnetohydrodynamic simulations and electrostatic turbulence contribution to the reconnection electric field plays an essential role. Both in-plane and out-of-plane electron and ion accelerations up to a few MeV due to the magnetic reconnection process are also obtained.

  15. A mechanism to produce a dawn-dusk component of plasma flow during magnetic reconnection in the magnetotail

    NASA Technical Reports Server (NTRS)

    Hawkins, J. G.; Lee, L. C.; Yan, M.; Lin, Y.; Perkins, F. W.; Yamada, M.

    1994-01-01

    Magnetic reconnection between antiparallel field lines in the magnetotail is generally thought to produce plasma acceleration in the earthward-tailward direction. However, measurements of the plasma velocity in the magnetotail during substorm activity sometimes reveal a dawn-dusk component of plasma flow. In this paper, we show that a dawn-dusk component of plasma acceleration may be produced during reconnection if the neutral line is not perpendicular to the magnetic field. In this case, Magnetohydrodynamic (MHD) simulations show that reconnection between antiparallel field lines will initially produce plasma acceleration that is nearly parallel to the neutral line because the magnetic tension force is not opposed by a pressure gradient force in this direction. As the magnetic field topology evolves to a steady state, the plasma flow direction rotates until it is nearly parallel to the plane that initially contained the antiparallel magnetic field lines before reconnection (hereafter referred to as the initial field plane). However, the time required to reach a steady state (typically several hundred seconds in the magnetotail region) may be greater than the time during which the reconnection process is active. Consequently, bursts of plasma flow with a dawn-dusk component may occur in the magnetotail. The initial acceleration along the neutral line depends on the angle theta (sub B) between the neutral line and the initial field plane, with the largest burst of plasma flow along the neutral line occuring when theta (s ub B) = 45 degs.

  16. Undriven magnetic reconnection in magnetohydrodynamics and Hall magnetohydrodynamics

    NASA Astrophysics Data System (ADS)

    Lottermoser, R.-F.; Scholer, M.

    1997-03-01

    Undriven magnetic reconnection in a one-dimensional current sheet is investigated by means of a two-dimensional compressible and resistive Hall MHD (HMHD) code. Reconnection is set up by applying a spatially limited resistivity in the center of an isothermal Harris sheet. Although the magnetic fields on the two sides of the initial current sheet are equal and exactly antiparallel, both magnetic field and flow velocity components out of the simulation plane are self-consistently generated in the course of the reconnection process. The quasi steady state exhibits all features of Petschek-like reconnection, such as two pairs of shock waves attached to the diffusion region, a strongly converging flow toward the field line reversal region, and a weak fast mode expansion of the inflowing plasma. The reconnection rate measured in terms of the Alfvén Mach number well upstream of the diffusion region is within the analytic limits for compressible Petschek reconnection and slightly higher than in the corresponding MHD case. In contrast to MHD, the shock in HMHD is a subfast, strong (2->4), intermediate shock; the thickness is ~=10ion inertial lengths, and the shocks exhibit an internal structure. The trailing left-handed slow mode wave train predicted from the integration of the stationary one-dimensional Hall MHD equations is not found. This is probably due to the fact that waves downstream of the shock are smeared out along the shock layer by the fast outflow jet. The shock waves generated during the decay of a current sheet are studied by a one-dimensional (1-D) Hall MHD simulation. In the 1-D case, the shocks are of slow mode type, and thus a left-handed intermediate mode wave train can form upstream of the shocks. The shock thickness is estimated to be at least a factor of 3 thicker than in 2-D HMHD fast reconnection. The intermediate shock in the 2-D HMHD simulation as well as the slow shock in the 1-D HMHD simulation exhibit an S-shaped hodogram. When starting the

  17. 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.

  18. Relativistic jets shine through shocks or magnetic reconnection?

    NASA Astrophysics Data System (ADS)

    Sironi, Lorenzo; Petropoulou, Maria; Giannios, Dimitrios

    2015-06-01

    Observations of gamma-ray-bursts and jets from active galactic nuclei reveal that the jet flow is characterized by a high radiative efficiency and that the dissipative mechanism must be a powerful accelerator of non-thermal particles. Shocks and magnetic reconnection have long been considered as possible candidates for powering the jet emission. Recent progress via fully-kinetic particle-in-cell simulations allows us to revisit this issue on firm physical grounds. We show that shock models are unlikely to account for the jet emission. In fact, when shocks are efficient at dissipating energy, they typically do not accelerate particles far beyond the thermal energy, and vice versa. In contrast, we show that magnetic reconnection can deposit more than 50 per cent of the dissipated energy into non-thermal leptons as long as the energy density of the magnetic field in the bulk flow is larger than the rest-mass energy density. The emitting region, i.e. the reconnection downstream, is characterized by a rough energy equipartition between magnetic fields and radiating particles, which naturally accounts for a commonly observed property of blazar jets.

  19. Magnetic flipping - Reconnection in three dimensions without null points

    NASA Technical Reports Server (NTRS)

    Priest, E. R.; Forbes, T. G.

    1992-01-01

    In three dimensions, magnetic reconnection may take place in a sheared magnetic field at any singular field line, where the nearby field has X-type topology in planes perpendicular to the field line and where an electric field is present parallel to the field line. In the ideal region around the singular line there will, in general, be singularities in the plasma flow and electric field, both at the singular line and at 'magnetic flipping layers', which are remnants of local magnetic separatrices. In the absence of a three-dimensional magnetic neutral point or null point, reconnection of field lines can still occur by a process of magnetic flipping, in which the plasma crosses the flipping layers but the field lines rapidly flip along them by magnetic diffusion. Depending on the boundary conditions, there may be two or four flipping layers which converge on the singular line. A boundary layer analysis of a flipping layer is given, in which the magnetic field parallel to the layer decreases as one crosses it while the plasma pressure (or magnetic pressure associated with the field along the singular line) increases. The width of the flipping layer decreases with distance from the singular line.

  20. Simulation study of magnetic reconnection in high magnetic Reynolds number plasmas

    NASA Astrophysics Data System (ADS)

    Nakabo, T.; Kusano, K.; Miyoshi, T.; Vekstein, G.

    2013-12-01

    Magnetic reconnection is an important process for dynamics in space and laboratory plasmas. Magnetic reconnection is basically dominated by magnetic diffusion at thin current sheet as proposed by Sweet (1958) and Parker (1963). According to their theory, the reconnection rate must be inversely proportional to the square root of the magnetic Reynolds number (S). In magnetosphere and the solar corona, however, in spite of high magnetic Reynolds number (>10^12), reconnection rate is measured to be about 10^-2 that is much higher than the Sweet and Parker's prediction. Although Petschek proposed that the slow mode shock may accelerate reconnection, numerical simulations suggested that the Petschek's type reconnection cannot be sustained with uniform resistivity. On the other hand, it is pointed out that in high magnetic Reynolds number, the thin current sheet becomes unstable to the so-called secondary tearing instability, which generates many plasmoids and drives a sort of fast reconnection. Although Baty (2012) recently investigated the possibility of Petschek-like structure in relatively high-S (~10^4) regime, it is still unclear whether and how the magnetic reconnection is able to be accelerated in higher-S regime (S>10^5). In this paper, we developed the high-resolution magnetohydrodynamics (MHD) simulation of magnetic reconnection for very high-S (S~10^4-10^6) aiming at revealing the acceleration mechanism of magnetic reconnection. We applied the HLLD Riemann solver, which was developed by Miyoshi and Kusano (2005), to the high resolution two-dimensional MHD simulation of current sheet dynamics. In our model, the initial state is given by the Harris sheet equilibrium plus perturbation. As a result, in the case for S=10^5, multiple X-line reconnection appears as a result of the secondary tearing instability and magnetic reconnection is accelerated through the formation of multiple magnetic islands as pointed out by the previous studies. Furthermore, we found that

  1. 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.

  2. Particle acceleration at 3D reconnecting magnetic separators

    NASA Astrophysics Data System (ADS)

    Threlfall, James; Neukirch, Thomas; Parnell, Clare; Stevenson, Julie

    2015-04-01

    We present results of test particle orbit calculations in three different environments which model separator reconnection in three dimensions. The test particle (electron and proton) orbits are calculated using the relativistic guiding centre approximation. We investigate test particle orbits in a time-dependent (analytical) electro-magnetic field configuration [detailed in Threlfall et al. (A&A, in press); arXiv:1410.6465]. These results are also compared with orbits based upon large-scale 3D MHD simulations of both a single reconnecting magnetic separator and an observationally driven 3D model of a solar active region which contains several topological features of interest, including separators. We discuss how the test-particle orbits and the energy gain depend on the initial conditions, and how observations (for example, of solar flares) may be used to constrain model parameters.

  3. New Kind of Magnetic Reconnection in Neutral Sheet Configurations

    NASA Astrophysics Data System (ADS)

    Fletcher, Alex; Coppi, Bruno

    2016-10-01

    Neutral Sheet configurations are relatively simple models of the plasma and field configuration found in space physics that lend themselves to investigate the onset of relevant reconnection processes. In weakly collisional regimes these are shown to be intrinsically different from those occurring in plasma current sheets where the magnetic field is sheared but does not vanish. Considering an inhomogenous electron temperature profile with finite curvature at the center of the sheet, and anisotropic thermal conductivities one of the two kinds of mode that can produce magnetic reconnection is localized over a layer that remains significant when the macroscopic scale distances involved are very large as is the case in space and astrophysics. This mode lends itself to produce high-energy particle populations through a realistic combination of mode-particle resonances. Sponsored in part by the U.S. D.O.E. and the N.S.F.

  4. 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.

  5. Localized electron heating by strong guide-field magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Guo, Xuehan; Inomoto, Michiaki; Sugawara, Takumichi; Yamasaki, Kotaro; Ushiki, Tomohiko; Ono, Yasushi

    2015-10-01

    Localized electron heating of magnetic reconnection was studied under strong guide-field using two merging spherical tokamak plasmas in the University of Tokyo Spherical Tokamak experiment. Our new slide-type two-dimensional Thomson scattering system is documented for the first time the electron heating localized around the X-point. Shape of the high electron temperature area does not agree with that of energy dissipation term Et.jt . If we include a guide-field effect term Bt/(Bp+αBt) for Et.jt , the energy dissipation area becomes localized around the X-point, suggesting that the electrons are accelerated by the reconnection electric field parallel to the magnetic field and thermalized around the X-point.

  6. New models for fast steady state magnetic reconnection

    NASA Technical Reports Server (NTRS)

    Priest, E. R.; Forbes, T. G.

    1986-01-01

    A new unified family of models for incompressible, steady-state magnetic reconnection in a finite region is presented. The models are obtained by expanding in powers of the Alfven Mach number and may be used to elucidate some of the puzzling properties of numerical experiments on reconnection which are not present in the classical models. The conditions imposed on the inflow boundary of the finite region determine which member of the family occurs. Petscheklien and Sonnerup like solutions are particular members. The Sonneruplike regime is a special case of a weak slow mode expansion in the inflow region, and it separates two classes of members with reversed currents. The Petscheklike regime is a singular case of a weak fast mode expansion, and it separates the hybrid regime from a regime of slow mode compressions. Care should be taken in deciding which type of reconnection is operating in a numerical experiment. Indeed, no experiment to date has used boundary conditions appropriate for demonstrating steady state Petschek reconnection.

  7. Particle acceleration in laser-driven magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Totorica, Samuel; Abel, Tom; Fiuza, Frederico

    2016-10-01

    Particle acceleration induced by magnetic reconnection is a promising candidate for producing the nonthermal emissions associated with explosive astrophysical phenomena. We have used two- and three-dimensional particle-in-cell simulations to explore the possibility of studying particle acceleration from reconnection in laser-driven plasma experiments. For current experimental conditions, we show that nonthermal electrons can be accelerated to energies up to two orders of magnitude larger than the initial thermal energy. The nonthermal electrons gain energy primarily by the reconnection electric field near the X-points, and particle injection into the reconnection layer and escape from the finite system establishes a distribution of energies resembling a power-law spectrum. Energetic electrons can also become trapped inside the plasmoids that form in the current layer and gain additional energy from the electric field arising from the motion of the plasmoid. Based on our findings, we provide an analytical estimate of the maximum electron energy and threshold condition for suprathermal electron acceleration in terms of experimentally tunable parameters. Finally, we investigate future experiments with a more energetic laser drive and larger system size. We discuss the influence of plasmoids on the particle acceleration, and the use of proton radiography to probe plasmoids. This work was supported by the DOE Office of Science, Fusion Energy Science (FWP 100182).

  8. Magnetic reconnection driven by Gekko XII lasers with a Helmholtz capacitor-coil target

    NASA Astrophysics Data System (ADS)

    Pei, X. X.; Zhong, J. Y.; Sakawa, Y.; Zhang, Z.; Zhang, K.; Wei, H. G.; Li, Y. T.; Li, Y. F.; Zhu, B. J.; Sano, T.; Hara, Y.; Kondo, S.; Fujioka, S.; Liang, G. Y.; Wang, F. L.; Zhao, G.

    2016-03-01

    We demonstrate a novel plasma device for magnetic reconnection, driven by Gekko XII lasers irradiating a double-turn Helmholtz capacitor-coil target. Optical probing revealed an accumulated plasma plume near the magnetic reconnection outflow. The background electron density and magnetic field were measured to be approximately 1018 cm-3 and 60 T by using Nomarski interferometry and the Faraday effect, respectively. In contrast with experiments on magnetic reconnection constructed by the Biermann battery effect, which produced high beta values, our beta value was much lower than one, which greatly extends the parameter regime of laser-driven magnetic reconnection and reveals its potential in astrophysical plasma applications.

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

    NASA Astrophysics Data System (ADS)

    Hoshino, M.

    2014-12-01

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

  10. Extreme ultraviolet imaging of three-dimensional magnetic reconnection in a solar eruption.

    PubMed

    Sun, J Q; Cheng, X; Ding, M D; Guo, Y; Priest, E R; Parnell, C E; Edwards, S J; Zhang, J; Chen, P F; Fang, C

    2015-06-26

    Magnetic reconnection, a change of magnetic field connectivity, is a fundamental physical process in which magnetic energy is released explosively, and it is responsible for various eruptive phenomena in the universe. However, this process is difficult to observe directly. Here, the magnetic topology associated with a solar reconnection event is studied in three dimensions using the combined perspectives of two spacecraft. The sequence of extreme ultraviolet images clearly shows that two groups of oppositely directed and non-coplanar magnetic loops gradually approach each other, forming a separator or quasi-separator and then reconnecting. The plasma near the reconnection site is subsequently heated from ∼1 to ≥5 MK. Shortly afterwards, warm flare loops (∼3 MK) appear underneath the hot plasma. Other observational signatures of reconnection, including plasma inflows and downflows, are unambiguously revealed and quantitatively measured. These observations provide direct evidence of magnetic reconnection in a three-dimensional configuration and reveal its origin.

  11. OSCILLATION OF NEWLY FORMED LOOPS AFTER MAGNETIC RECONNECTION IN THE SOLAR CHROMOSPHERE

    SciTech Connect

    Yang, Shuhong; Xiang, Yongyuan

    2016-03-10

    With the high spatial and temporal resolution Hα images from the New Vacuum Solar Telescope, we focus on two groups of loops with an X-shaped configuration in the dynamic chromosphere. We find that the anti-directed loops approach each other and reconnect continually. The connectivity of the loops is changed and new loops are formed and stack together. The stacked loops are sharply bent, implying that they are greatly impacted by the magnetic tension force. When another reconnection process takes place, one new loop is formed and stacks with the previously formed ones. Meanwhile, the stacked loops retract suddenly and move toward the balance position, performing an overshoot movement, which led to an oscillation with an average period of about 45 s. The oscillation of newly formed loops after magnetic reconnection in the chromosphere is observed for the first time. We suggest that the stability of the stacked loops is destroyed due to the attachment of the last new loop and then suddenly retract under the effect of magnetic tension. Because of the retraction, another lower loop is pushed outward and performs an oscillation with a period of about 25 s. The different oscillation periods may be due to their difference in three parameters, i.e., loop length, plasma density, and magnetic field strength.

  12. Observation of Two Slow Shocks Associated with Magnetic Reconnection Exhausts in the Interplanetary Space

    NASA Astrophysics Data System (ADS)

    Feng, HengQiang; Li, QiuHuan; Wang, JieMin; Zhao, GuoQing

    2017-04-01

    In the Petschek magnetic reconnection model, two groups of slow shocks play an important role in the energy release. In the past half century, a large number of slow shocks were observed in the geomagnetic tail, and many slow shocks were associated with magnetic reconnection events in the geomagnetic tail. Slow shocks in the interplanetary space are rarer than in the geomagnetic tail. We investigated whether slow shocks associated with interplanetary reconnection exhausts are rare. We examined the boundaries of 50 reconnection exhausts reported by Phan, Gosling, and Davis (Geophys. Res. Lett. 36:L09108, 2009) in interplanetary space to identify slow shocks by fitting the Rankine-Hugoniot relations. Two slow shocks associated with magnetic reconnection exhausts were found and evaluated using observations from Wind and the Advanced Composition Explorer. The observed slow shocks associated with interplanetary reconnection exhausts are rarer than the observed slow shocks associated with geomagnetic tail reconnection exhausts.

  13. Distinct characteristics of asymmetric magnetic reconnections: Observational results from the exhaust region at the dayside magnetopause

    NASA Astrophysics Data System (ADS)

    Zhang, Y. C.

    2016-06-01

    Magnetic reconnection plays a key role in the conversion of magnetic energy into the thermal and kinetic energy of plasma. On either side of the diffusion region in space plasma, the conditions for the occurrence of reconnections are usually not symmetric. Previous theoretical studies have predicted that reconnections under asymmetric conditions will bear different features compared with those of symmetric reconnections, and numerical simulations have verified these distinct features. However, to date, the features of asymmetric reconnections have not been thoroughly investigated using in situ observations; thus, some results from theoretical studies and simulations have not been tested with observations sufficiently well. Here, spacecraft observations are used in a statistical investigation of asymmetric magnetic reconnection exhaust at the dayside magnetopause. The resulting observational features are consistent with the theoretical predictions. The results presented here advance our understanding of the development of reconnections under asymmetric conditions.

  14. Distinct characteristics of asymmetric magnetic reconnections: Observational results from the exhaust region at the dayside magnetopause

    PubMed Central

    Zhang, Y. C.

    2016-01-01

    Magnetic reconnection plays a key role in the conversion of magnetic energy into the thermal and kinetic energy of plasma. On either side of the diffusion region in space plasma, the conditions for the occurrence of reconnections are usually not symmetric. Previous theoretical studies have predicted that reconnections under asymmetric conditions will bear different features compared with those of symmetric reconnections, and numerical simulations have verified these distinct features. However, to date, the features of asymmetric reconnections have not been thoroughly investigated using in situ observations; thus, some results from theoretical studies and simulations have not been tested with observations sufficiently well. Here, spacecraft observations are used in a statistical investigation of asymmetric magnetic reconnection exhaust at the dayside magnetopause. The resulting observational features are consistent with the theoretical predictions. The results presented here advance our understanding of the development of reconnections under asymmetric conditions. PMID:27270685

  15. Observation of Magnetic Reconnection Driven by Granular Scale Advection

    NASA Astrophysics Data System (ADS)

    Zeng, Zhichen; Cao, W.; Ji, H.

    2013-07-01

    We report the first evidence of magnetic reconnection driven by advection in a rapidly developing large granule, using high spatial resolution observations of a small surge event (base size 4‧‧ by 4‧‧) with the 1.6 meter aperture New Solar Telescope (NST) at Big Bear Solar Observatory. The observations were carried out in narrow-band (0.5 Å) Helium I 10830 Å and broad-band (10 Å) TiO 7057 Å. Since He I 10830 Å triplet has very high excitation level and is optically thin, its filtergrams enable us to investigate the surge from the photosphere through the chromosphere into the lower corona. Simultaneous space data from Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) were used in the analysis. It is shown that the surge is spatio-temporally associated with magnetic flux emergence in the rapidly developing large granule. During the development of the granule, its advecting flow ( 2 km/ s) squeezed the magnetic flux into an intergranular lane area, where a magnetic flux concentration was formed and the neighboring flux with opposite magnetic polarity was cancelled. During the cancellation, the surge was produced as absorption in He I 10830 Å filtergrams while simultaneous EUV brightening occurred at its base. The observations clearly indicate evidence of finest-scale reconnection process driven by the granule’s motion.

  16. Observation of Magnetic Reconnection Driven by Granular Scale Advection

    NASA Astrophysics Data System (ADS)

    Zeng, Zhicheng; Cao, Wenda; Ji, Haisheng

    2013-06-01

    We report the first evidence of magnetic reconnection driven by advection in a rapidly developing large granule using high spatial resolution observations of a small surge event (base size ~ 4'' × 4'') with the 1.6 m aperture New Solar Telescope at the Big Bear Solar Observatory. The observations were carried out in narrowband (0.5 Å) He I 10830 Å and broadband (10 Å) TiO 7057 Å. Since He I 10830 Å triplet has a very high excitation level and is optically thin, its filtergrams enable us to investigate the surge from the photosphere through the chromosphere into the lower corona. Simultaneous space data from the Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory were used in the analysis. It is shown that the surge is spatio-temporally associated with magnetic flux emergence in the rapidly developing large granule. During the development of the granule, its advecting flow (~2 km s-1) squeezed the magnetic flux into an intergranular lane area, where a magnetic flux concentration was formed and the neighboring flux with opposite magnetic polarity was canceled. During the cancellation, the surge was produced as absorption in He I 10830 Å filtergrams while simultaneous EUV brightening occurred at its base. The observations clearly indicate evidence of a finest-scale reconnection process driven by the granule's motion.

  17. The Structure of the Separatix in Collisionless Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Daughton, W.; Scudder, J.; Karimabadi, H.

    2005-12-01

    Recent kinetic simulations of magnetic reconnection indicate the formation of intense electrostatic fields that start at the x-point and form sheet-like structures that extend outward for large distances along the separatrices. In the presence of a significant guide field, the characteristic thickness of these layers is on the order of the local electron gyroradius and there are significant deviations from charge neutrality within the layer. The resulting electrostatic fields are primarily perpendicular and may exceed the reconnection electric field by a factor of 20. A serious impediment to understanding the possible role of these structures is the use of periodic boundary conditions typically employed in kinetic simulations. In particular, the strong outward electron flow generated along one leg of a separatrix is allowed to circulate back through the system along the opposite side. This recirculation may artificially enhance beam driven instabilities and/or strongly modify the structure of the separatrix. In this work, we describe initial efforts to employ open boundary conditions in 2D fully kinetic PIC simulations, with the goal of better understanding the structure and role of the separatrix in collisionless magnetic reconnection.

  18. Spontaneous three-dimensional magnetic reconnection in merging toroidal plasma experiment

    SciTech Connect

    Ii, Toru; Ono, Yasushi

    2013-01-15

    We investigated a new phenomenon of three-dimensional (3D) magnetic reconnection in TS-4 torus plasma merging experiments by directly measuring the 3D structures of the current sheet. Removal of all toroidal asymmetry of the device reveals that a strong external drive of reconnection inflow increases the toroidal asymmetry of the current sheet only during the reconnection. This spontaneous 3D deformation of the current sheet increases the reconnection outflow as well as the reconnection electric field, probably because local compression of the current sheet to a thickness less than the ion gyroradius triggers its strong dissipation of the current sheet, responsible for the onset of 3D reconnection. These mechanisms indicate that the 3D reconnection is a newly observed spontaneous process of fast reconnection.

  19. Structures of diffusion regions in collisionless magnetic reconnection

    SciTech Connect

    Umeda, Takayuki; Togano, Kentaro; Ogino, Tatsuki

    2010-05-15

    Detailed structures of diffusion regions in two-dimensional collisionless magnetic reconnection are studied by using an electromagnetic Vlasov simulation. It has been well known that plasma number density decreases near the X-point of the reconnection. However, numerical thermal fluctuations exist in particle-in-cell simulations, and there is a possibility that detailed structures near the X-point diffuse numerically when the number of particles per cell is not enough. In the present study, a high-resolution two-dimensional Vlasov simulation is performed. It is found that electron number density in the electron diffusion region decreases to a hundredth of the initial value. Structures of electron diffusion region are determined by the local electron inertial length.

  20. MAGNETIC RECONNECTION BETWEEN SMALL-SCALE LOOPS OBSERVED WITH THE NEW VACUUM SOLAR TELESCOPE

    SciTech Connect

    Yang, Shuhong; Zhang, Jun; Xiang, Yongyuan

    2015-01-01

    Using the high tempo-spatial resolution Hα images observed with the New Vacuum Solar Telescope, we report solid observational evidence of magnetic reconnection between two sets of small-scale, anti-parallel loops with an X-shaped topology. The reconnection process contains two steps: a slow step with a duration of more than several tens of minutes, and a rapid step lasting for only about three minutes. During the slow reconnection, two sets of anti-parallel loops gradually reconnect, and new loops are formed and stacked together. During the rapid reconnection, the anti-parallel loops approach each other quickly, and then rapid reconnection takes place, resulting in the disappearance of the former loops. In the meantime, new loops are formed and separate. The region between the approaching loops is brightened, and the thickness and length of this region are determined to be about 420 km and 1.4 Mm, respectively. During the rapid reconnection process, obvious brightenings at the reconnection site and apparent material ejections outward along reconnected loops are observed. These observed signatures are consistent with predictions by reconnection models. We suggest that the successive slow reconnection changes the conditions around the reconnection site and triggers instabilities, thus leading to the rapid approach of the anti-parallel loops and resulting in the rapid reconnection.

  1. Magnetic Reconnection in a Solar Eruption -Formation of the Flux Tube and its Eruption-

    NASA Astrophysics Data System (ADS)

    Inoue, Satoshi; Büchner, Jörg

    2016-07-01

    A solar eruption is one of a dramatic phenomenon observed in the solar corona. The flux tube, which is a bundle of highly twisted lines, is widely believed as a driver source of the eruption. Although the magnetic reconnection is a key process of the formation of the flux tube as well as the eruptive process, these dynamics are still open to be solved. In order to clarify these dynamics, we first perform a magnetohydrodynamic (MHD) simulation using a force-free field extrapolated from the photospheric magnetic field. Our simulation successfully produced the typical eruptive processes in which the twisted flux tube slowly ascends in the beginning of the eruption; afterwards, it shows the fast ascending. We found that the reconnection is a key process to break the force-free field initially constructed, and highly twisted flux tube formation during the slow rising phase and even after the fast eruption. Next we compare with Büchner + Skala simulations and compressively discuss the play of the reconnection in the solar eruption.

  2. Beaming of Particles and Synchrotron Radiation in Relativistic Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Kagan, Daniel; Nakar, Ehud; Piran, Tsvi

    2016-08-01

    Relativistic reconnection has been invoked as a mechanism for particle acceleration in numerous astrophysical systems. According to idealized analytical models, reconnection produces a bulk relativistic outflow emerging from the reconnection sites (X-points). The resulting radiation is therefore highly beamed. Using two-dimensional particle-in-cell simulations, we investigate particle and radiation beaming, finding a very different picture. Instead of having a relativistic average bulk motion with an isotropic electron velocity distribution in its rest frame, we find that the bulk motion of the particles in X-points is similar to their Lorentz factor γ, and the particles are beamed within ˜ 5/γ . On the way from the X-point to the magnetic islands, particles turn in the magnetic field, forming a fan confined to the current sheet. Once they reach the islands they isotropize after completing a full Larmor gyration and their radiation is no longer strongly beamed. The radiation pattern at a given frequency depends on where the corresponding emitting electrons radiate their energy. Lower-energy particles that cool slowly spend most of their time in the islands and their radiation is not highly beamed. Only particles that quickly cool at the edge of the X-points generate a highly beamed fan-like radiation pattern. The radiation emerging from these fast cooling particles is above the burn-off limit (˜100 MeV in the overall rest frame of the reconnecting plasma). This has significant implications for models of gamma-ray bursts and active galactic nuclei that invoke beaming in that frame at much lower energies.

  3. Possible Properties of Kinetic Flux Ropes Generated by Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Ng, C. S.

    2015-12-01

    We present latest results of numerical studies of a recently obtained analytic solution that can describe small-scale kinetic flux ropes. Such exact nonlinear solution of the Vlasov-Poisson-Ampere system of equations can be regarded as two-dimensional Bernstein-Greene-Kruskal (BGK) mode, generalizing from a solution in a magnetized plasma with finite magnetic field strength [Ng, Bhattacharjee, and Skiff, Phys. Plasmas 13, 055903 (2006)], with the additional effect of field-aligned current. Such solution might explain magnetic flux ropes observed to form within the diffusion region in 3D kinetic simulations of magnetic reconnection, and the 2D version of them (plasmoids, secondary islands). We will present properties of solutions based on a range of typical plasma parameters within regions of the magnetosphere where magnetic reconnection could happen. These solutions could potentially be used to compare with future Magnetospheric Multiscale Mission (MMS) observation. This work is supported by a National Science Foundation grant PHY-1004357 and the Alaska NASA EPSCoR Program (NNX13AB28A).

  4. Defining and identifying three-dimensional magnetic reconnection in resistive magnetohydrodynamic simulations of Earth's magnetosphere

    SciTech Connect

    Dorelli, John C.; Bhattacharjee, A.

    2008-05-15

    Magnetic reconnection is thought to be the primary mode by which the solar wind couples to the terrestrial magnetosphere, driving phenomena such as magnetic storms and aurorae. While the theory of two-dimensional reconnection is well developed and has been applied with great success to axisymmetric and toroidal systems such as laboratory plasma experiments and fusion devices, it is difficult to justify the application of two-dimensional theory to nontoroidal plasma systems such as Earth's magnetosphere. Unfortunately, the theory of three-dimensional magnetic reconnection is much less well developed, and even defining magnetic reconnection has turned out to be controversial. In this paper, recent progress in the use of magnetohydrodynamics (MHD) to address the physics of three-dimensional reconnection in Earth's magnetosphere is reviewed. The paper consists of two parts. In the first part, various definitions of three-dimensional reconnection are reviewed, with the goal of mapping these definitions to sets of physical phenomena that have been identified as 'reconnection' in various contexts. In the second part of the paper, MHD simulation results for the magnetosphere are presented, and two qualitatively distinct types of reconnection phenomena are identified: (1) Steady separator reconnection under generic northward interplanetary magnetic field (IMF) conditions, involving plasma flow across magnetic separatrices, and (2) time-dependent reconnection under generic southward IMF conditions, involving a locally detectable change in the magnetic field topology. It is concluded that magnetic reconnection phenomena at Earth's dayside magnetopause are adequately captured by two distinct definitions: The Vasyliunas definition [V. M. Vasyliunas, Rev. Geophys 13, 303 (1975)], which identifies magnetic reconnection with plasma flow across magnetic separatrices, and the Greene definition [J. Greene, Phys. Fluids B 5, 2355 (1993)], which identifies magnetic reconnection with a

  5. EVIDENCE FOR SOLAR TETHER-CUTTING MAGNETIC RECONNECTION FROM CORONAL FIELD EXTRAPOLATIONS

    SciTech Connect

    Liu, Chang; Deng, Na; Lee, Jeongwoo; Wang, Haimin; Wiegelmann, Thomas; Moore, Ronald L.

    2013-12-01

    Magnetic reconnection is one of the primary mechanisms for triggering solar eruptive events, but direct observation of this rapid process has been a challenge. In this Letter, using a nonlinear force-free field (NLFFF) extrapolation technique, we present a visualization of field line connectivity changes resulting from tether-cutting reconnection over about 30 minutes during the 2011 February 13 M6.6 flare in NOAA AR 11158. Evidence for the tether-cutting reconnection was first collected through multiwavelength observations and then by analysis of the field lines traced from positions of four conspicuous flare 1700 Å footpoints observed at the event onset. Right before the flare, the four footpoints are located very close to the regions of local maxima of the magnetic twist index. In particular, the field lines from the inner two footpoints form two strongly twisted flux bundles (up to ∼1.2 turns), which shear past each other and reach out close to the outer two footpoints, respectively. Immediately after the flare, the twist index of regions around the footpoints diminishes greatly and the above field lines become low-lying and less twisted (≲0.6 turns), overarched by loops linking the two flare ribbons formed later. About 10% of the flux (∼3 × 10{sup 19} Mx) from the inner footpoints undergoes a footpoint exchange. This portion of flux originates from the edge regions of the inner footpoints that are brightened first. These rapid changes of magnetic field connectivity inferred from the NLFFF extrapolation are consistent with the tether-cutting magnetic reconnection model.

  6. Electron heating during magnetic reconnection: A simulation scaling study

    SciTech Connect

    Shay, M. A. Haggerty, C. C.; Phan, T. D.; Oieroset, M.; Drake, J. F.; Swisdak, M.; Cassak, P. A.; Wu, P.; Malakit, K.

    2014-12-15

    Electron bulk heating during magnetic reconnection with symmetric inflow conditions is examined using kinetic particle-in-cell simulations. Inflowing plasma parameters are varied over a wide range of conditions, and the increase in electron temperature is measured in the exhaust well downstream of the x-line. The degree of electron heating is well correlated with the inflowing Alfvén speed c{sub Ar} based on the reconnecting magnetic field through the relation ΔT{sub e}=0.033 m{sub i} c{sub Ar}{sup 2}, where ΔT{sub e} is the increase in electron temperature. For the range of simulations performed, the heating shows almost no correlation with inflow total temperature T{sub tot}=T{sub i}+T{sub e} or plasma β. An out-of-plane (guide) magnetic field of similar magnitude to the reconnecting field does not affect the total heating, but it does quench perpendicular heating, with almost all heating being in the parallel direction. These results are qualitatively consistent with a recent statistical survey of electron heating in the dayside magnetopause (Phan et al., Geophys. Res. Lett. 40, 4475, 2013), which also found that ΔT{sub e} was proportional to the inflowing Alfvén speed. The net electron heating varies very little with distance downstream of the x-line. The simulations show at most a very weak dependence of electron heating on the ion to electron mass ratio. In the antiparallel reconnection case, the largely parallel heating is eventually isotropized downstream due a scattering mechanism, such as stochastic particle motion or instabilities. The simulation size is large enough to be directly relevant to reconnection in the Earth's magnetosphere, and the present findings may prove to be universal in nature with applications to the solar wind, the solar corona, and other astrophysical plasmas. The study highlights key properties that must be satisfied by an electron heating mechanism: (1) preferential heating in the parallel direction; (2) heating

  7. Spreading of Magnetic Reconnection X-lines in Three Dimensions

    NASA Astrophysics Data System (ADS)

    Cassak, Paul; Shepherd, Lucas

    2012-03-01

    Naturally occurring magnetic reconnection often begins in a spatially localized region and spreads in the out-of-plane direction in time. A number of authors have studied this problem for magnetotail applications such as substorms and bursty bulk flows, for which the out-of-plane (guide) field is typically small. However, spreading also occurs in laboratory experiments and two-ribbon solar flares (such as the Bastille Day flare), and is inferred to occur at the dayside magnetopause. The reconnection site in each of these settings is known or thought to have a significant guide field. With no guide field, it was shown that the reconnection spreading is controlled by the species that carries the current. However, laboratory experiments with a large guide field (Katz et al., Phys. Rev. Lett., 104, 255004, 2010) revealed that spreading takes place in both directions at the Alfven speed based on the guide field. This implies a qualitative change of behavior as the guide field varies. We present a scaling argument for the condition on the guide field at which the nature of the spreading switches from being caused by current carriers to Alfven waves. Further, we show results of three-dimensional two-fluid simulations that agree with the theory. We discuss applications to observations.

  8. Transient Magnetic Reconnection and Dipolarization Fronts in the Terrestrial Magnetotail

    NASA Astrophysics Data System (ADS)

    Zhou, Meng; Deng, Xiaohua; Pang, Ye; Xu, Xiaojun; Huang, Shiyong; Tang, Rongxin; Yuan, Zhigang

    2015-04-01

    We report a Cluster observation of transient magnetic reconnection in the Earth's magnetotail at the location of [Xgsm~ -17.2 RE, Ygsm~ -4.5 RE and Zgsm~ 0]. The reconnection X-line retreated tailward with a speed of 34 km/s based on multi-spacecraft analysis. An ion diffusion region with a weak guide field (~10% of lobe field) was encountered during the flow reversal. A flux rope was embedded in the tailward flow. Transient suprathermal electron beams, which directed away from the X-line, were detected repeatedly around the separatrix region with periods of about 60s during the tailward flow bursts. On the earthward side of X-line, multiple earthward-propagating dipolarization fronts were observed quasi-periodically at the edge of the ion diffusion region with time period of 60s-90s. Particle and wave characteristics also show distinct signatures at different stages of the transient reconnection. The implications of this observation will be discussed.

  9. Genesis of Interplanetary Intermittent Turbulence: A Case Study of Rope&enrope Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Chian, Abraham C.-L.; Feng, Heng Q.; Hu, Qiang; Loew, Murray H.; Miranda, Rodrigo A.; Muñoz, Pablo R.; Sibeck, David G.; Wu, De J.

    2016-12-01

    In a recent paper, the relation between current sheet, magnetic reconnection, and turbulence at the leading edge of an interplanetary coronal mass ejection was studied. We report here the observation of magnetic reconnection at the interface region of two interplanetary magnetic flux ropes. The front and rear boundary layers of three interplanetary magnetic flux ropes are identified, and the structures of magnetic flux ropes are reconstructed by the Grad-Shafranov method. A quantitative analysis of the reconnection condition and the degree of intermittency reveals that rope-rope magnetic reconnection is the most likely site for genesis of interplanetary intermittency turbulence in this event. The dynamic pressure pulse resulting from this reconnection triggers the onset of a geomagnetic storm.

  10. Windsock memory COnditioned RAM (CO-RAM) pressure effect: Forced reconnection in the Earth's magnetotail

    NASA Astrophysics Data System (ADS)

    Vörös, Z.; Facskó, G.; Khodachenko, M.; Honkonen, I.; Janhunen, P.; Palmroth, M.

    2014-08-01

    Magnetic reconnection (MR) is a key physical concept explaining the addition of magnetic flux to the magnetotail and closed flux lines back-motion to the dayside magnetosphere. This scenario elaborated by Dungey (1963) can explain many aspects of solar wind-magnetosphere interaction processes, including substorms. However, neither the Dungey model nor its numerous modifications were able to explain fully the onset conditions for MR in the tail. In this paper, we introduce new onset conditions for forced MR in the tail. We call our scenario the "windsock memory conditioned ram pressure effect." Our nonflux transfer-associated forcing is introduced by a combination of the large-scale windsock motions exhibiting memory effects and solar wind dynamic pressure actions on the nightside magnetopause during northward oriented interplanetary magnetic field (IMF). Using global MHD Grand Unified Magnetosphere Ionosphere Coupling Simulation version 4 simulation results, upstream data from Wind, magnetosheath data from Cluster 1 and distant tail data from the two-probe Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun mission, we show that the simultaneous occurrence of vertical windsock motions of the magnetotail and enhanced solar wind dynamic pressure introduces strong nightside disturbances, including enhanced electric fields and persistent vertical cross-tail shear flows. These perturbations, associated with a stream interaction region in the solar wind, drive MR in the tail during episodes of northward oriented interplanetary magnetic field (IMF). We detect MR indirectly, observing plasmoids in the tail and ground-based signatures of earthward moving fast flows. We also consider the application to solar system planets and close-in exoplanets, where the proposed scenario can elucidate some new aspects of solar/stellar wind-magnetosphere interactions.

  11. Rapid change of field line connectivity and reconnection in stochastic magnetic fields

    SciTech Connect

    Huang, Yi-Min; Bhattacharjee, A.; Boozer, Allen H.

    2014-10-01

    Magnetic fields without a direction of continuous symmetry have the generic feature that neighboring field lines exponentiate away from each other and become stochastic, and hence the ideal constraint of preserving magnetic field line connectivity becomes exponentially sensitive to small deviations from ideal Ohm's law. The idea of breaking field line connectivity by stochasticity as a mechanism for fast reconnection is tested with numerical simulations based on reduced magnetohydrodynamics equations with a strong guide field line-tied to two perfectly conducting end plates. Starting from an ideally stable force-free equilibrium, the system is allowed to undergo resistive relaxation. Two distinct phases are found in the process of resistive relaxation. During the quasi-static phase, rapid change of field line connectivity and strong induced flow are found in regions of high field line exponentiation. However, although the field line connectivity of individual field lines can change rapidly, the overall pattern of field line mapping appears to deform gradually. From this perspective, field line exponentiation appears to cause enhanced diffusion rather than reconnection. In some cases, resistive quasi-static evolution can cause the ideally stable initial equilibrium to cross a stability threshold, leading to formation of intense current filaments and rapid change of field line mapping into a qualitatively different pattern. It is in this onset phase that the change of field line connectivity is more appropriately designated as magnetic reconnection. Our results show that rapid change of field line connectivity appears to be a necessary, but not a sufficient condition for fast reconnection.

  12. Global Extended MHD Studies of Fast Magnetic Reconnection

    SciTech Connect

    Breslau J.A.; Jardin, S.C.

    2002-09-18

    Recent experimental and theoretical results have led to two lines of thought regarding the physical processes underlying fast magnetic reconnection. One is based on the traditional Sweet-Parker model but replaces the Spitzer resistivity with an enhanced resistivity caused by electron scattering by ion acoustic turbulence. The other includes the finite gyroradius effects that enter Ohm's law through the Hall and electron pressure gradient terms. A 2-D numerical study, conducted with a new implicit parallel two-fluid code, has helped to clarify the similarities and differences in predictions between these two models and provides some insight into their respective ranges of validity.

  13. Energetic electrons associated with magnetic reconnection in the magnetic cloud boundary layer.

    PubMed

    Wang, Y; Wei, F S; Feng, X S; Zhang, S H; Zuo, P B; Sun, T R

    2010-11-05

    Here is reported in situ observation of energetic electrons (∼100-500 keV) associated with magnetic reconnection in the solar wind by the ACE and Wind spacecraft. The properties of this magnetic cloud driving reconnection and the associated energetic electron acceleration problem are discussed. Further analyses indicate that the electric field acceleration and Fermi-type mechanism are two fundamental elements in the electron acceleration processes and the trapping effect of the specific magnetic field configuration maintains the acceleration status that increases the totally gained energy.

  14. Hybrid simulations of magnetic reconnection with kinetic ions and fluid electron pressure anisotropy

    DOE PAGES

    Le, A.; Daughton, W.; Karimabadi, H.; ...

    2016-03-16

    We present the first hybrid simulations with kinetic ions and recently developed equations of state for the electron fluid appropriate for reconnection with a guide field. The equations of state account for the main anisotropy of the electron pressure tensor.Magnetic reconnection is studied in two systems, an initially force-free current sheet and a Harris sheet. The hybrid model with the equations of state is compared to two other models, hybrid simulations with isothermal electrons and fully kinetic simulations. Including the anisotropicequations of state in the hybrid model provides a better match to the fully kinetic model. In agreement with fullymore » kinetic results, the main feature captured is the formation of an electron current sheet that extends several ion inertial lengths. This electron current sheet modifies the Hall magnetic field structure near the X-line, and it is not observed in the standard hybrid model with isotropic electrons. The saturated reconnection rate in this regime nevertheless remains similar in all three models. Here, implications for global modeling are discussed.« less

  15. Hybrid simulations of magnetic reconnection with kinetic ions and fluid electron pressure anisotropy

    SciTech Connect

    Le, A.; Daughton, W.; Karimabadi, H.; Egedal, J.

    2016-03-16

    We present the first hybrid simulations with kinetic ions and recently developed equations of state for the electron fluid appropriate for reconnection with a guide field. The equations of state account for the main anisotropy of the electron pressure tensor.Magnetic reconnection is studied in two systems, an initially force-free current sheet and a Harris sheet. The hybrid model with the equations of state is compared to two other models, hybrid simulations with isothermal electrons and fully kinetic simulations. Including the anisotropicequations of state in the hybrid model provides a better match to the fully kinetic model. In agreement with fully kinetic results, the main feature captured is the formation of an electron current sheet that extends several ion inertial lengths. This electron current sheet modifies the Hall magnetic field structure near the X-line, and it is not observed in the standard hybrid model with isotropic electrons. The saturated reconnection rate in this regime nevertheless remains similar in all three models. Here, implications for global modeling are discussed.

  16. Hybrid simulations of magnetic reconnection with kinetic ions and fluid electron pressure anisotropy

    NASA Astrophysics Data System (ADS)

    Le, A.; Daughton, W.; Karimabadi, H.; Egedal, J.

    2016-03-01

    We present the first hybrid simulations with kinetic ions and recently developed equations of state for the electron fluid appropriate for reconnection with a guide field. The equations of state account for the main anisotropy of the electron pressure tensor. Magnetic reconnection is studied in two systems, an initially force-free current sheet and a Harris sheet. The hybrid model with the equations of state is compared to two other models, hybrid simulations with isothermal electrons and fully kinetic simulations. Including the anisotropic equations of state in the hybrid model provides a better match to the fully kinetic model. In agreement with fully kinetic results, the main feature captured is the formation of an electron current sheet that extends several ion inertial lengths. This electron current sheet modifies the Hall magnetic field structure near the X-line, and it is not observed in the standard hybrid model with isotropic electrons. The saturated reconnection rate in this regime nevertheless remains similar in all three models. Implications for global modeling are discussed.

  17. Localized Electron Heating by Strong Guide-Field Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Guo, Xuehan; Sugawara, Takumichi; Inomoto, Michiaki; Yamasaki, Kotaro; Ono, Yasushi; UTST Team

    2015-11-01

    Localized electron heating of magnetic reconnection was studied under strong guide-field (typically Bt 15Bp) using two merging spherical tokamak plasmas in Univ. Tokyo Spherical Tokamak (UTST) experiment. Our new slide-type two-dimensional Thomson scattering system documented for the first time the electron heating localized around the X-point. The region of high electron temperature, which is perpendicular to the magnetic field, was found to have a round shape with radius of 2 [cm]. Also, it was localized around the X-point and does not agree with that of energy dissipation term Et .jt . When we include a guide-field effect term Bt / (Bp + αBt) for Et .jt where α =√{ (vin2 +vout2) /v∥2 } , the energy dissipation area becomes localized around the X-point, suggesting that the electrons are accelerated by the reconnection electric field parallel to the magnetic field and thermalized around the X-point. This work was supported by JSPS A3 Foresight Program ``Innovative Tokamak Plasma Startup and Current Drive in Spherical Torus,'' a Grant-in-Aid from the Japan Society for the Promotion of Science (JSPS) Fellows 15J03758.

  18. Double layer electric fields aiding the production of superthermal electrons within magnetic reconnection exhausts

    NASA Astrophysics Data System (ADS)

    Egedal, Jan; Daughton, William; Le, Ari

    2015-11-01

    Using a kinetic simulation of magnetic reconnection it was recently shown that parallel electric fields (E∥) can be present over large spatial scales in reconnection exhausts. The largest values of E∥ are observed within double layers, which form through large parallel streaming of electrons into the reconnection region. The electron confinement, provided in part by the structure in E∥, allows sustained energization by perpendicular electric fields (E⊥). The energization is a consequence of the confined electrons' chaotic orbital motion that includes drifts aligned with the reconnection electric field. The mechanism is effective in an extended region of the reconnection exhaust allowing for the generation of superthermal electrons in reconnection scenarios, including those with only a single x-line. The numerical and analytical results agree with detailed spacecraft observations recorded during reconnection events in the Earth's magnetotail. Supported by NSF GEM award 1405166 and NASA grant NNX14AC68G.

  19. Three-dimensional magnetic reconnection and its application to solar flares

    NASA Astrophysics Data System (ADS)

    Janvier, Miho

    2017-02-01

    Solar flares are powerful radiations occurring in the Sun's atmosphere. They are powered by magnetic reconnection, a phenomenon that can convert magnetic energy into other forms of energy such as heat and kinetic energy, and which is believed to be ubiquitous in the universe. With the ever increasing spatial and temporal resolutions of solar observations, as well as numerical simulations benefiting from increasing computer power, we can now probe into the nature and the characteristics of magnetic reconnection in three dimensions to better understand the phenomenon's consequences during eruptive flares in our star's atmosphere. We review in the following the efforts made on different fronts to approach the problem of magnetic reconnection. In particular, we will see how understanding the magnetic topology in three dimensions helps in locating the most probable regions for reconnection to occur, how the current layer evolves in three dimensions and how reconnection leads to the formation of flux ropes, plasmoids and flaring loops.

  20. Study of Magnetic Reconnection in Plasma: how it works and energizes plasma particles

    NASA Astrophysics Data System (ADS)

    Yamada, Masaaki

    2015-11-01

    Magnetic reconnection is a phenomenon of nature in which magnetic field lines change their topology in plasma and convert magnetic energy to plasma particles by acceleration and heating. It is a fundamental process at work in laboratory, space and astrophysical plasmas. Magnetic reconnection occurs throughout the Universe: in star forming galaxies; around supernovae; in solar flares; in the earth's magnetosphere; and in fusion plasmas. One of the great challenges in reconnection research has been to understand why reconnection occurs so much faster than predicted by MHD theory. This talk begins with a review of recent discoveries and findings in the research of fast magnetic reconnection in laboratory plasmas and space astrophysical plasmas. I compare the experimental results and space observations with theory and numerical simulations. The collaboration between space and laboratory scientists in reconnection research has reached a point where we can directly compare measurements of the reconnection layer using recently-advanced numerical simulations. In spite of the huge difference in physical scales, we find remarkable commonality between the characteristics of the magnetic reconnection in laboratory and space-astrophysical plasmas. In this talk, I will focus especially on the energy flow, a key feature of reconnection process. We have recently reported our results on the energy conversion and partitioning in a laboratory reconnection layer. In Magnetic Reconnection Experiment (MRX) the mechanisms of ion acceleration and heating are identified and a systematic study of the quantitative inventory of converted energy within a reconnection layer has been made with a well-defined but variable boundary. The measured energy partition in a reconnection region of similar effective size (L ~ 3 ion skin depth) of the Earth's magneto-tail is remarkably consistent with the laboratory results. A more comprehensive study is proposed using MMS satellites very recently put into

  1. Laboratory Experiment of Magnetic Reconnection between Merging Flux Tubes with Strong Guide FIeld

    NASA Astrophysics Data System (ADS)

    Inomoto, M.; Kamio, S.; Kuwahata, A.; Ono, Y.

    2013-12-01

    Magnetic reconnection governs variety of energy release events in the universe, such as solar flares, geomagnetic substorms, and sawtooth crash in laboratory nuclear fusion experiments. Differently from the classical steady reconnection models, non-steady behavior of magnetic reconnection is often observed. In solar flares, intermittent enhancement of HXR emission is observed synchronously with multiple ejection of plammoids [1]. In laboratory reconnection experiments, the existence of the guide field, that is perpendicular to the reconnection field, makes significant changes on reconnection process. Generally the guide field will slow down the reconnection rate due to the increased magnetic pressure inside the current sheet. It also brings about asymmetric structure of the separatrices or effective particle acceleration in collisionless conditions. We have conducted laboratory experiments to study the behavior of the guide-field magnetic reconnection using plasma merging technique (push reconnection). Under substantial guide field even larger than the reconnection field, the reconnection generally exhibits non-steady feature which involves intermittent detachment of X-point and reconnection current center[2]. Transient enhancement of reconnection rate is observed simultaneously with the X-point motion[3]. We found two distinct phenomena associated with the guide-field non-steady reconnection. The one is the temporal and localized He II emission from X-point region, suggesting the production of energetic electrons which could excite the He ions in the vicinity of the X-point. The other is the excitation of large-amplitude electromagnetic waves which have similar properties with kinetic Alfven waves, whose amplitude show positive correlation with the enhancement of the reconnection electric field[4]. Electron beam instability caused by the energetic electrons accelerated to more than twice of the electron thermal velocity could be a potential driver of the

  2. Development of Turbulent Magnetic Reconnection in a Magnetic Island

    NASA Astrophysics Data System (ADS)

    Huang, Can; Lu, Quanming; Wang, Rongsheng; Guo, Fan; Wu, Mingyu; Lu, San; Wang, Shui

    2017-02-01

    In this paper, with two-dimensional particle-in-cell simulations, we report that the electron Kelvin–Helmholtz instability is unstable in the current layer associated with a large-scale magnetic island, which is formed in multiple X-line guide field reconnections. The current sheet is fragmented into many small current sheets with widths down to the order of the electron inertial length. Secondary magnetic reconnection then occurs in these fragmented current sheets, which leads to a turbulent state. The electrons are highly energized in such a process.

  3. Magnetic reconnection in multispecies plasmas investigated by a kinetic fluid code

    NASA Astrophysics Data System (ADS)

    Dong, Chuanfei; Wang, Liang; Bhattacharjee, Amitava; Hakim, Ammar; Huang, Yi-Min; Germaschewski, Kai

    2016-10-01

    We first study the reconnection process in multispecies plasmas by using Gkeyll, which is a kinetic fluid code solving the continuity, momentum and energy equations of each species, and the full Maxwell equations. Thus, there is no assumption by solving the generalized ohm's law in Gkeyll. We studied the reconnection processes in the plasma consisting of electrons, protons and oxygen ions. If time allows, we also plan to show some preliminary results of magnetic reconnection in dusty plasmas with negatively charged dust.

  4. Simulating Magnetic Reconnection Experiment (MRX) with a Guide Field using Fluid Code, HiFi

    NASA Astrophysics Data System (ADS)

    Budner, Tamas; Chen, Yangao; Meier, Eric; Ji, Hantao; MRX Team

    2015-11-01

    Magnetic reconnection is a phenomenon that occurs in plasmas when magnetic field lines effectively ``break'' and reconnect resulting in a different topological configuration. In this process, energy that was once stored in the magnetic field is transfered into the thermal velocity of the particles, effectively heating the plasma. MRX at the Princeton Plasma Physics Laboratory creates the conditions under which reconnection can occur by initially ramping the current in two adjacent coils and then rapidly decreasing with and without a guide magnetic field along the reconnecting current. We simulate this experiment using a fluid code called HiFi, an implicit and adaptive high order spectral element modeling framework, and compare our results to experimental data from MRX. The purpose is to identify physics behind the observed reconnection process for the field line break and the resultant plasma heating.

  5. Two Types of Magnetic Reconnection in Coronal Bright Points and the Corresponding Magnetic Configuration

    NASA Astrophysics Data System (ADS)

    Zhang, Q. M.; Chen, P. F.; Guo, Y.; Fang, C.; Ding, M. D.

    2012-02-01

    Coronal bright points (CBPs) are long-lived small-scale brightenings in the solar corona. They are generally explained by magnetic reconnection. However, the corresponding magnetic configurations are not well understood. We carry out a detailed multi-wavelength analysis of two neighboring CBPs on 2007 March 16, observed in soft X-ray (SXR) and EUV channels. It is seen that the SXR light curves present quasi-periodic flashes with an interval of ~1 hr superposed over the long-lived mild brightenings, suggesting that the SXR brightenings of this type of CBPs might consist of two components: one is the gentle brightenings and the other is the CBP flashes. It is found that the strong flashes of the bigger CBP are always accompanied by SXR jets. The potential field extrapolation indicates that both CBPs are covered by a dome-like separatrix surface, with a magnetic null point above. We propose that the repetitive CBP flashes, as well as the recurrent SXR jets, result from the impulsive null-point reconnection, while the long-lived brightenings are due to the interchange reconnection along the separatrix surface. Although the EUV images at high-temperature lines resemble the SXR appearance, the 171 Å and 195 Å channels reveal that the blurry CBP in SXR consists of a cusp-shaped loop and several separate bright patches, which are explained to be due to the null-point reconnection and the separatrix reconnection, respectively.

  6. TWO TYPES OF MAGNETIC RECONNECTION IN CORONAL BRIGHT POINTS AND THE CORRESPONDING MAGNETIC CONFIGURATION

    SciTech Connect

    Zhang, Q. M.; Chen, P. F.; Guo, Y.; Fang, C.; Ding, M. D.

    2012-02-10

    Coronal bright points (CBPs) are long-lived small-scale brightenings in the solar corona. They are generally explained by magnetic reconnection. However, the corresponding magnetic configurations are not well understood. We carry out a detailed multi-wavelength analysis of two neighboring CBPs on 2007 March 16, observed in soft X-ray (SXR) and EUV channels. It is seen that the SXR light curves present quasi-periodic flashes with an interval of {approx}1 hr superposed over the long-lived mild brightenings, suggesting that the SXR brightenings of this type of CBPs might consist of two components: one is the gentle brightenings and the other is the CBP flashes. It is found that the strong flashes of the bigger CBP are always accompanied by SXR jets. The potential field extrapolation indicates that both CBPs are covered by a dome-like separatrix surface, with a magnetic null point above. We propose that the repetitive CBP flashes, as well as the recurrent SXR jets, result from the impulsive null-point reconnection, while the long-lived brightenings are due to the interchange reconnection along the separatrix surface. Although the EUV images at high-temperature lines resemble the SXR appearance, the 171 Angstrom-Sign and 195 Angstrom-Sign channels reveal that the blurry CBP in SXR consists of a cusp-shaped loop and several separate bright patches, which are explained to be due to the null-point reconnection and the separatrix reconnection, respectively.

  7. Measurement of the current sheet during magnetic reconnection in a toroidal plasma.

    PubMed

    Crocker, N A; Fiksel, G; Prager, S C; Sarff, J S

    2003-01-24

    The current and magnetic-field fluctuations associated with magnetic-field-line reconnection have been measured in the reversed field pinch plasma configuration. The current sheet resulting from this reconnection has been measured. The current layer is radially broad, comparable to a magnetic-island width, as may be expected from current transport along magnetic-field lines. It is much larger than that predicted by resistive MHD for linear tearing modes and larger than prediction from two-fluid linear theory.

  8. Particle-in-cell simulations of electron energization in laser-driven magnetic reconnection

    DOE PAGES

    Lu, San; Lu, Quanming; Guo, Fan; ...

    2016-01-25

    Electrons can be energized during laser-driven magnetic reconnection, and the energized electrons form three super-Alfvénic electron jets in the outflow region (Lu et al 2014 New J. Phys. 16 083021). In this paper, by performing two-dimensional particle-in-cell simulations, we find that the electrons can also be significantly energized before magnetic reconnection occurs. When two plasma bubbles with toroidal magnetic fields expand and squeeze each other, the electrons in the magnetic ribbons are energized through betatron acceleration due to the enhancement of the magnetic field, and an electron temperature anisotropymore » $${T}_{{\\rm{e}}\\perp }\\gt {T}_{{\\rm{e}}| | }$$ develops. Meanwhile, some electrons are trapped and bounced repeatedly between the two expanding/approaching bubbles and get energized through a Fermi-like process. Furthermore, the energization before magnetic reconnection is more significant (or important) than that during magnetic reconnection.« less

  9. Particle-in-cell simulations of electron energization in laser-driven magnetic reconnection

    SciTech Connect

    Lu, San; Lu, Quanming; Guo, Fan; Sheng, Zhengming; Wang, Huanyu; Wang, Shui

    2016-01-25

    Electrons can be energized during laser-driven magnetic reconnection, and the energized electrons form three super-Alfvénic electron jets in the outflow region (Lu et al 2014 New J. Phys. 16 083021). In this paper, by performing two-dimensional particle-in-cell simulations, we find that the electrons can also be significantly energized before magnetic reconnection occurs. When two plasma bubbles with toroidal magnetic fields expand and squeeze each other, the electrons in the magnetic ribbons are energized through betatron acceleration due to the enhancement of the magnetic field, and an electron temperature anisotropy ${T}_{{\\rm{e}}\\perp }\\gt {T}_{{\\rm{e}}| | }$ develops. Meanwhile, some electrons are trapped and bounced repeatedly between the two expanding/approaching bubbles and get energized through a Fermi-like process. Furthermore, the energization before magnetic reconnection is more significant (or important) than that during magnetic reconnection.

  10. Slip-Squashing Factors as a Measure of Three-Dimensional Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Titov, V. S.; Forbes, T. G.; Priest, E. R.; Mikić, Z.; Linker, J. A.

    2009-03-01

    A general method for describing magnetic reconnection in arbitrary three-dimensional magnetic configurations is proposed. The method is based on the field-line mapping technique previously used only for the analysis of a magnetic structure at a given time. This technique is extended here so as to analyze the evolution of a magnetic structure. Such a generalization is made with the help of new dimensionless quantities called "slip-squashing factors." Their large values define the surfaces that border the reconnected or to-be-reconnected magnetic flux tubes for a given period of time during the magnetic evolution. The proposed method is universal, since it assumes only that the time sequence of evolving magnetic field and the tangential boundary flows are known. The application of the method is illustrated for simple examples, one of which was considered previously by Hesse and coworkers in the framework of the general magnetic reconnection theory. The examples help us to compare these two approaches; it reveals also that, just as for magnetic null points, hyperbolic and cusp minimum points of a magnetic field serve as favorable sites for magnetic reconnection. The new method admits a straightforward numerical implementation and provides a powerful tool for the diagnostics of magnetic reconnection in numerical models of solar-flare-like phenomena in space and laboratory plasmas.

  11. Slip-Squashing Factors as a Measure of Three-Dimensional Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Titov, V. S.; Forbes, T. G.; Priest, E. R.; Mikic, Z.; Linker, J. A.

    2008-12-01

    A general method for describing magnetic reconnection in arbitrary three-dimensional magnetic configurations is proposed. The method is based on the field-line mapping technique previously used only for the analysis of magnetic structure at a given time. This technique is extended here so as to analyze the evolution of magnetic structure. Such a generalization is made with the help of new dimensionless quantities called "slip-squashing factors". Their large values define the surfaces that border the reconnected or to-be-reconnected magnetic flux tubes for a given period of time during the magnetic evolution. The proposed method is universal, since it assumes only that the time sequence of the evolving magnetic field and the tangential boundary flows are known. The application of the method is illustrated for simple examples, one of which was considered previously by Hesse and coworkers in the framework of the general magnetic reconnection theory. The examples help to compare these two approaches; they reveal also that, just as for magnetic null points, hyperbolic and cusp minimum points of a magnetic field may serve as favorable sites for magnetic reconnection. The new method admits a straightforward numerical implementation and provides a powerful tool for the diagnostics of magnetic reconnection in numerical models of solar-flare-like phenomena in space and laboratory plasmas. Research partially supported by NASA and NSF.

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

    PubMed

    Zenitani, S; Hoshino, M

    2005-08-26

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

  13. Magnetic reconnection in 3D magnetosphere models: magnetic separators and open flux production

    NASA Astrophysics Data System (ADS)

    Glocer, A.; Dorelli, J.; Toth, G.; Komar, C. M.; Cassak, P.

    2014-12-01

    There are multiple competing definitions of magnetic reconnection in 3D (e.g., Hesse and Schindler [1988], Lau and Finn [1990], and Boozer [2002]). In this work we focus on separator reconnection. A magnetic separator can be understood as the 3D analogue of a 2D x line with a guide field, and is defined by the line corresponding to the intersection of the separatrix surfaces associated with the magnetic nulls. A separator in the magnetosphere represents the intersection of four distinct magnetic topologies: solar wind, closed, open connected to the northern hemisphere, and open connected to the southern hemisphere. The integral of the parallel electric field along the separator defines the rate of open flux production, and is one measure of the reconnection rate. We present three methods for locating magnetic separators and apply them to 3D resistive MHD simulations of the Earth's magnetosphere using the BATS-R-US code. The techniques for finding separators and determining the reconnection rate are insensitive to IMF clock angle and can in principle be applied to any magnetospheric model. The present work examines cases of high and low resistivity, for two clock angles. We also examine the separator during Flux Transfer Events (FTEs) and Kelvin-Helmholtz instability.

  14. Influence of Spontaneously Generated Turbulence on Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Daughton, William; Roytershteyn, Vadim; Karimabadi, Homa

    2012-10-01

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

  15. Magnetic reconnection mediated by hyper-resistive plasmoid instability

    SciTech Connect

    Huang, Yi-Min; Bhattacharjee, A.; Forbes, Terry G.

    2013-08-15

    Magnetic reconnection mediated by the hyper-resistive plasmoid instability is studied with both linear analysis and nonlinear simulations. The linear growth rate is found to scale as S{sub H}{sup 1/6} with respect to the hyper-resistive Lundquist number S{sub H}≡L{sup 3}V{sub A}/η{sub H}, where L is the system size, V{sub A} is the Alfvén velocity, and η{sub H} is the hyper-resistivity. In the nonlinear regime, reconnection rate becomes nearly independent of S{sub H}, the number of plasmoids scales as S{sub H}{sup 1/2}, and the secondary current sheet length and width both scale as S{sub H}{sup −1/2}. These scalings are consistent with a heuristic argument assuming secondary current sheets are close to marginal stability. The distribution of plasmoids as a function of the enclosed flux ψ is found to obey a ψ{sup −1} power law over an extended range, followed by a rapid fall off for large plasmoids. These results are compared with those from resistive magnetohydrodynamic studies.

  16. Double-reconnected magnetic structures driven by Kelvin-Helmholtz vortices at the Earth's magnetosphere

    SciTech Connect

    Borgogno, D.; Califano, F.; Pegoraro, F.; Faganello, M.

    2015-03-15

    In an almost collisionless magnetohydrodynamic plasma in a relatively strong magnetic field, stresses can be conveyed far from the region where they are exerted, e.g., through the propagation of Alfvèn waves. The forced dynamics of line-tied magnetic structures in solar and stellar coronae (see, e.g., A. F. Rappazzo and E. N. Parker, Astrophys. J. 773, L2 (2013) and references therein) is a paradigmatic case. Here, we investigate how this action at a distance develops from the equatorial region of the Kelvin-Helmholtz unstable flanks of the Earth's magnetosphere leading to the onset, at mid latitude in both hemispheres, of correlated double magnetic field line reconnection events that can allow the solar wind plasma to enter the Earth's magnetosphere.

  17. A comparison of analytical and numerical models for steadily driven magnetic reconnection

    NASA Technical Reports Server (NTRS)

    Forbes, T. G.; Priest, E. R.

    1987-01-01

    The effect of boundary conditions in both analytical and numerical solutions of steadily driven reconnection on the reconnection of antiparallel magnetic fields is considered, with special attention given to the mathematical problem of properly specifying boundary conditions for the MHD equation. A unified formulation developed by Priest and Forbes (1986) for steady state reconnection, which includes the Petschek solution and the Sonnerup (1970) solution as special cases, is used to reinterpret the previous numerical experiments of steadily driven reconnection. It is shown that many contradictory features of these experiments were caused by the use of boundary conditions which are different from those required by Petschek's (1964) theory.

  18. Jet Formation in Solar Atmosphere due to Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    González-Avilés, J. J.; Guzmán, F. S.; Fedun, V.

    2017-02-01

    Using numerical simulations, we show that jets with features of type II spicules and cool coronal jets corresponding to temperatures of 104 K can be formed as a result of magnetic reconnection in a scenario with magnetic resistivity. For this, we model the low chromosphere–corona region using the C7 equilibrium solar atmosphere model, assuming that resistive MHD rules the dynamics of the plasma. The magnetic field configurations we analyze correspond to two neighboring loops with opposite polarity. The formation of a high-speed and sharp structure depends on the separation of the loops’ feet. We analyze the cases where the magnetic field strength of the two loops is equal and different. In the first case, with a symmetric configuration the jets rise vertically, whereas in an asymmetric configuration the structure shows an inclination. With a number of simulations carried out under a 2.5D approach, we explore various properties of the excited jets, namely, inclination, lifetime, and velocity. The parameter space involves a magnetic field strength between 20 and 40 G, and the resistivity is assumed to be uniform with a constant value of the order {10}-2{{Ω }}\\cdot m.

  19. Fundamental limitation of a two-dimensional description of magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Firpo, Marie-Christine

    2014-10-01

    For magnetic reconnection to be possible, the electrons have at some point to ``get free from magnetic slavery,'' according to von Steiger's formulation. Stochasticity may be considered as one possible ingredient through which this may be realized in the magnetic reconnection process. It will be argued that non-ideal effects may be considered as a ``hidden'' way to introduce stochasticity. Then it will be shown that there exists a generic intrinsic stochasticity of magnetic field lines that does not require the invocation of non-ideal effects but cannot show up in effective two-dimensional models of magnetic reconnection. Possible implications will be discussed in the frame of tokamak sawteeth that form a laboratory prototype of magnetic reconnection.

  20. Multifractal dissipation of intermittent turbulence generated by the magnetic reconnection in the solar wind

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Wei, F.; Feng, X.

    2013-12-01

    Recent observations revealed a scale-invariant dissipation process in the fast ambient solar wind, while numerical simulations indicated that the dissipation process in collisionless reconnection was multifractal. Here, we investigate the properties of turbulent fluctuations in the magnetic reconnection prevailed region. It is found that there are large magnetic field shear angle and obvious intermittent structures in these regions. The deduced scaling exponents in the dissipation subrange show a multifractal scaling. In comparison, in the nearby region where magnetic reconnection is less prevailed, we find smaller magnetic field shear angle, less intermittent structures, and most importantly, a monofractal dissipation process. These results provide additionally observational evidence for previous observation and simulation work, and they also imply that magnetic dissipation in the solar wind magnetic reconnection might be caused by the intermittent cascade as multifractal processes.

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

    SciTech Connect

    Shibayama, Takuya Nakabou, Takashi; Kusano, Kanya; Miyoshi, Takahiro; Vekstein, Grigory

    2015-10-15

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

  2. The onset of ion heating during magnetic reconnection with a strong guide field

    SciTech Connect

    Drake, J. F.; Swisdak, M.

    2014-07-15

    The onset of the acceleration of ions during magnetic reconnection is explored via particle-in-cell simulations in the limit of a strong ambient guide field that self-consistently and simultaneously follow the motions of protons and α particles. Heating parallel to the local magnetic field during reconnection with a guide field is strongly reduced compared with the reconnection of anti-parallel magnetic fields. The dominant heating of thermal ions during guide field reconnection results from pickup behavior of ions during their entry into reconnection exhausts and dominantly produces heating perpendicular rather than parallel to the local magnetic field. Pickup behavior requires that the ion transit time across the exhaust boundary (with a transverse scale of the order of the ion sound Larmor radius) be short compared with the ion cyclotron period. This translates into a threshold in the strength of reconnecting magnetic field that favors the heating of ions with high mass-to-charge. A simulation with a broad initial current layer produces a reconnecting system in which the amplitude of the reconnecting magnetic field just upstream of the dissipation region increases with time as reconnection proceeds. The sharp onset of perpendicular heating when the pickup threshold is crossed is documented. A comparison of the time variation of the parallel and perpendicular ion heating with that predicted based on the strength of the reconnecting field establishes the scaling of ion heating with ambient parameters both below and above the pickup threshold. The relevance to observations of ion heating in the solar corona is discussed.

  3. Formation of sub-ion scale filamentary force-free structures in the vicinity of reconnection region

    NASA Astrophysics Data System (ADS)

    Zelenyi, L. M.; Frank, A. G.; Artemyev, A. V.; Petrukovich, A. A.; Nakamura, R.

    2016-05-01

    In this paper we review the results of spacecraft observations of current sheets (CSs) of sub-ion spatial scales in the Earth’s magnetotail as well as experiments with these structures in laboratory devices. We demonstrate that such sub-ion CSs having a thickness less than the ion gyroradius are usually formed in the vicinity of the magnetic reconnection region and are supported by strong electron currents flowing along magnetic field lines. The magnetic field configuration of sub-ion CSs is close to the force-free configuration, with a strong shear magnetic field component in the CS central region. Spacecraft observations suggest that parallel electron currents are generated by electron beams (pronounced enhancement of the phase space density for electrons with small pitch angles and energies  ˜1-3 keV). We discuss several models describing such force-free sub-ion CSs.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  5. Asymmetric magnetic reconnection with out-of-plane shear flows in a two dimensional hybrid model

    SciTech Connect

    Wang, Lin; Wang, Xiao-Gang; Wang, Xian-Qu; Liu, Yue

    2015-05-15

    Effects of out-of-plane shear flows on asymmetric magnetic reconnect are investigated in a two-dimensional (2D) hybrid model with an initial Harris sheet equilibrium. It is found that the out-of-plane flow with an in-plane shear can significantly change the asymmetric reconnection process as well as the related geometry. The magnetic flux, out-of-plane magnetic field, in-plane flow vorticity, plasma density, and the reconnection rate are discussed in detail. The results are in comparison with the cases without the shear flows to further understand the effect.

  6. Onset and Evolution of Magnetic Reconnection in Line-Tied Systems

    NASA Astrophysics Data System (ADS)

    Daughton, W. S.; Akcay, C.; Billey, Z.; Finn, J.; Zweibel, E.; Gekelman, W. N.

    2014-12-01

    In space and astrophysical plasmas, current sheets arise spontaneously from the interaction of large-scale flows or magnetic structures. As these current layers approach kinetic scales, they may become unstable to the collisionless tearing instability, resulting in the formation and interaction of magnetic flux ropes. While theoretical treatments of the tearing instability have largely focused on 1D equilibria with periodic boundary conditions, current sheets in nature have a finite spatial extent and are embedded within larger open systems. In many applications, the field boundary conditions are line-tied as in the case of flux ropes on the dayside magnetopause where the ionosphere acts as a conducting surface. To assess the applicability of existing tearing theory to these more realistic configurations, we consider a series of 3D kinetic simulations of initially force-free current layers with line-tied boundary conditions for the fields, and open boundaries for the particles. The geometry and plasma parameters are motivated by a new laboratory experiment on the Large Plasma Device at UCLA. For sufficiently long systems, we demonstrate that key aspects of the theory remain valid, and a threshold condition is derived for the onset of reconnection in line-tied systems. To gain additional insight into the nonlinear evolution, field-line mapping diagnostics are employed to characterize the 3D structure of the magnetic field, the nonlinear reconnection rate and the dominant non-ideal terms in the generalized Ohm's law.

  7. Magnetic reconnection in three-dimensional magnetohydrodynamic Taylor-Green flows

    NASA Astrophysics Data System (ADS)

    Hao, Jinhua; Yang, Yue

    2016-10-01

    We develop the magnetic-surface field (MSF), a Lagrangian-based structure identification method, to study the evolution of magnetic surfaces in magnetohydrodynamics (MHD). Every isosurface of the MSF defines a magnetic surface consisting of magnetic lines. This method is rooted in the Alfven theorem, which is the analogue of the Helmholtz vorticity theorem to illustrate the ``frozen-in'' nature of magnetic fields. A two-time approach and a numerical dissipative regularization are introduced for evolving MSF in the conducting fluids with a finite conductivity. From the construction and evolution of MSFs in three-dimensional MHD Taylor-Green (TG-MHD) flows, the topological changes of magnetic surfaces and the reconnection of magnetic lines are characterized. By comparing the structural evolutions in a TG-MHD flow and in a Taylor-Green hydrodynamic (TG-HD) flow, we elucidate the effects of the Lorenz force on the evolution of magnetic surfaces and vortex surfaces. Moreover, we find that the significant changes in energy spectra and dissipation rates in the transition are related to the appearance of some characteristic magnetic and vortex surfaces. This work is supported by the NSFC (No. 11522215) and the Thousand Young Talent Program of China.

  8. On the magnetic reconnection of resistive tearing mode with the dynamic flow effects

    SciTech Connect

    Ali, A.; Li, Jiquan Kishimoto, Y.

    2015-04-15

    Magnetic reconnection usually occurs in turbulent environments, which may not only provide anomalous resistivity to enhance reconnection rates but also significantly modify the reconnection process through direct nonlinear interaction with magnetic islands. This study presents numerical simulations investigating the effects of an imposed dynamic flow on magnetic reconnection, based on a two-dimensional reduced resistive MHD model. Results show that while the linear stability properties of the resistive tearing mode are moderately affected by the dynamic flow, nonlinear evolution is significantly modified by radial parity, amplitude, and frequency of the dynamic flow. After the slowly evolving nonlinear Rutherford stage, the reconnection process is found to progress in two phases by including the dynamic flow. A Sweet-Parker like current sheet is formed in the first phase. Afterwards, plasmoid instability is triggered in the second phase, where multiple plasmoids are continuously generated and ejected along the current sheet, leading to an impulsive bursty reconnection. The reconnection rate is considerably enhanced in the range of low resistivity as compared to without flow. We found that plasmoid instability onset and evolution are strongly influenced by the frequency and radial parity of the dynamic flows. The scaling of effective reconnection rates with the flow is found to be independent of resistivity.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  10. High-frequency Plasma Waves Associated with Magnetic Reconnection in the Solar Wind

    NASA Astrophysics Data System (ADS)

    Wang, Y.

    2015-12-01

    Activities of high-frequency plasma waves associated with magnetic reconnection in the solar wind observed by Time Domain Sampler (TDS) experiments on STEREO/WAVES are preliminarily analyzed. The TDS instrument can provide burst mode electric fields data with as long as 16384 sample points at 250 kHz sampling rate. In all 1120 suspected reconnection events, it is found that the most commonly occurred waves are neither ion acoustic waves, electrostatic solitary waves, nor Langmuir/upper hybrid waves, but Bernstein-like waves with harmonics of the electron cyclotron frequency. In addition, to each type of waves, Langmuir/upper hybrid waves reveal the largest occurrence rate in the reconnection region than in the ambient solar wind. These results indicate that Bernstein-like waves and Langmuir/upper hybrid waves might play important roles in the reconnection associated particle heating processes and they might also influence the dissipation of magnetic reconnection.

  11. 3D magnetic field configuration of small-scale reconnection events in the solar plasma atmosphere

    NASA Astrophysics Data System (ADS)

    Shimizu, T.

    2015-10-01

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

  12. 3D magnetic field configuration of small-scale reconnection events in the solar plasma atmosphere

    SciTech Connect

    Shimizu, T.

    2015-10-15

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

  13. Observations of Ion Signatures of Magnetic Reconnection for Northward IMF

    NASA Technical Reports Server (NTRS)

    Chandler, Michael O.; Moore, Thomas E.; Fuselier, S.; Lockwood, Michael

    1998-01-01

    Magnetic merging at Earth's magnetopause produces distinct mixtures of ions and electrons as well as signatures in their distribution functions. High resolution measurements allow for the separation of the different distributions and quantification of their characteristics. This provides details on the temporal and spatial nature of the merging site and the resulting history of the merged fields. The event of May 29, 1996 resulted in remote observations of the effects of reconnection on both magnetosheath and magnetosphere populations for a period of approximately three hours. Three-dimensional ion distributions obtained by the Thermal Ion Dynamics Experiment on the Polar spacecraft show that field lines threading the spacecraft's location in the northern cusp region contained a mix of D-shaped ions from the magnetosheath and accelerated magnetospheric ions both moving parallel to the local magnetic field. This mix of ions resulted from transmission of magnetosheath ions across the magnetopause at speeds greater than the de-Hoffman-Teller speed and the reflection of cold, slow-moving plasmasphere-like ions at the magnetopause. These observations are used to conclude that these field lines were connected to the ionosphere in the northern hemisphere and, southward of the spacecraft, the interplanetary magnetic field and crossed the magnetopause in the equatorial region southward of the spacecraft.

  14. Magnetic reconnection in numerical simulations of the Bastille day flare

    NASA Astrophysics Data System (ADS)

    Vincent, A. P.; Charbonneau, P.

    2011-12-01

    If neither waves nor adiabatic heating due to compression are taken into account, coronal heating may be obtained in numerical simulations from current dissipation inside solar flares. To increase Joule heating locally we used a model for hyper resistivity (Klimas et al., 2004: Journal of Geophysical Research, 109, 2218-2231). Here the change in resistivity is due to small scale (less than 1Mm in our simulations) current density fluctuations. Whenever the current exceeds a cut-off value, magnetic resistivity jumps sharply to reach a maximum locally thus increasing magnetic gradients at the border of the flare. In this way, not only the current increases but also the maximum is slowly displaced and simulations of the full set of 3-D MHD equations show a progression westward as can be seen in SOHO-EIT images of the ''slinky''. In our simulations of the Bastille day flare, most of the reconnection events take place just above the transition and mostly follow the neutral line but it is Spitzer thermal diffusivity together with radiative cooling that illuminates magnetic arcades in a way similar to what can be seen in extreme ultra-violet animations of the slinky.

  15. Experimental Studies on the 3D Macro- and Microphysics of Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Jara-Almonte, J.; Ji, H.; Yamada, M.; Yoo, J.; Fox, W. R., II

    2015-12-01

    Magnetic reconnection has been extensively studied in 2D geometries for many decades and considerable progress has been made in understating 2D reconnection physics, yet in real plasmas reconnection is fundamentally 3D in nature. Only recently has it become possible to study 3D reconnection using simulations, however some initial results have suggested that the inclusion of 3D effects does not strongly affect the basic properties of reconnection (e.g. reconnection rate or particle acceleration). Yet on the other hand, previous experiments, without direct 3D measurements, have implied that 3D effects could be important even in a quasi-2D system. Here we experimentally study both the (1) macro- and (2) microphysics of 3D reconnection in order to directly test the importance of 3D effects in a quasi-2D experiment. Using fully simultaneous 3D measurements, it is shown that during highly driven reconnection the macroscopic structure of the current sheet can become strongly 3D despite an essentially 2D upstream region. The correlation length along the current sheet is measured to be far shorter than suggested by kinetic simulations. Results from new experiments with stronger reconnection drive and diagnostics designed to estimate the 3D reconnection rate will be discussed. With regards to (2), the 3D microphysics, new diagnostics capable of measuring fluctuations at frequencies up to the electron cyclotron frequency (~ 300 MHz) have been developed and have identified the presence of very high frequency waves (~ 100 MHz) during asymmetric reconnection, localized to the low-density side. The detailed properties of these waves, including the measured power spectra and dispersion relation, will be discussed and compared with both previous satellite observations of high-frequency waves as well as with theoretical predictions on the generation of whistler waves during reconnection.

  16. Integrating kinetic effects in fluid models for magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Wang, Liang

    The integration of kinetic effects in global fluid models is a grand challenge in space plasma physics, and has implication for our ability to model space weather in collisionless plasma environments such as the Earth's magnetosphere. We propose an extensible multi-fluid moment model, with focus on the physics of magnetic reconnection. This model evolves the full Maxwell equations, and simultaneously moments of the Vlasov-Maxwell equation for each species in the plasma. Effects like the Hall effect, the electron inertia, and the 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. Particularly, 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. In this thesis, we first numerically confirm the reduction of five-moment to Hall MHD under the limit of vanishing electron inertia. 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 closure towards a non-local, fully three-dimensional description are also discussed.

  17. Integrating kinetic effects in fluid models for magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Wang, L.; Hakim, A.; Bhattacharjee, A.; Germaschewski, K.

    2014-12-01

    The integration of kinetic effects in global fluid models is a grand challenge in space plasma physics, and has implication for our ability to model space weather in collisionless plasma environments such as the Earth's magnetosphere. We propose an extensible multi-fluid moment model, with focus on the physics of magnetic reconnection. This model evolves the full Maxwell equations, and simultaneously moments of the Vlasov-Maxwell equation for each species in the plasma. Effects like the Hall effect, the electron inertia, and the 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 pressure for each species, and the ten-moment limit that evolves the full anisotropic, non-gyrotropic pressure tensor. Particularly, 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. In this presentation, we first 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. Preliminary results of application of the multi-fluid moment model to Ganymede are also discussed.

  18. "Smoking-Gun" Observables of Magnetic Reconnection: Spatiotemporal Evolution of Electron Characteristics Throughout the Diffusion Region

    NASA Astrophysics Data System (ADS)

    Shuster, Jason R.

    How does magnetic reconnection happen in a collisionless plasma? Knowledge of electron-scale dynamics is necessary to answer this outstanding question of plasma physics. Based on fully kinetic particle-in-cell (PIC) simulations of symmetric reconnection, the spatiotemporal evolution of velocity distribution functions in and around the electron diffusion region (EDR) elucidates how electrons are accelerated and heated by the cooperating reconnection electric and normal magnetic fields. The discrete, triangular structures characteristic of EDR distributions rotate and gyrotropize in velocity space as electrons remagnetize, forming multicomponent arc and ring structures. Further downstream, exhaust electrons are found to exhibit highly structured, time-dependent anisotropies that can be used to infer the temporal stage of reconnection. Cluster spacecraft measurements from a magnetotail reconnection exhaust region agree with these simulation predictions. In PIC simulations of asymmetric reconnection, EDR distributions acquire crescent-shaped populations, indicative of accelerated magnetosheath electrons mixing with electrons of magnetospheric origin. NASA's successfully launched Magnetospheric Multiscale (MMS) mission caught an EDR at the magnetopause and confirmed the signature crescent electron populations. A virtual spacecraft trajectory through the PIC domain is determined quantitatively by inputting MMS magnetic field measurements into an algorithm that outputs a trajectory along which the input measurements are matched. The crescent structures observed by MMS in the EDR are consistent with the simulation distributions at the corresponding time along the computed trajectory. This work demonstrates that electron characteristics can serve as "smoking-gun" observables of the EDR at the heart of the magnetic reconnection mystery.

  19. The role of guide field in magnetic reconnection driven by island coalescence

    NASA Astrophysics Data System (ADS)

    Stanier, A.; Daughton, W.; Simakov, Andrei N.; Chacón, L.; Le, A.; Karimabadi, H.; Ng, Jonathan; Bhattacharjee, A.

    2017-02-01

    A number of studies have considered how the rate of magnetic reconnection scales in large and weakly collisional systems by the modelling of long reconnecting current sheets. However, this set-up neglects both the formation of the current sheet and the coupling between the diffusion region and a larger system that supplies the magnetic flux. Recent studies of magnetic island merging, which naturally include these features, have found that ion kinetic physics is crucial to describe the reconnection rate and global evolution of such systems. In this paper, the effect of a guide field on reconnection during island merging is considered. In contrast to the earlier current sheet studies, we identify a limited range of guide fields for which the reconnection rate, outflow velocity, and pile-up magnetic field increase in magnitude as the guide field increases. The Hall-MHD fluid model is found to reproduce kinetic reconnection rates only for a sufficiently strong guide field, for which ion inertia breaks the frozen-in condition and the outflow becomes Alfvénic in the kinetic system. The merging of large islands occurs on a longer timescale in the zero guide field limit, which may in part be due to a mirror-like instability that occurs upstream of the reconnection region.

  20. The role of magnetic reconnection on astrophysical jets launching and particle acceleration

    NASA Astrophysics Data System (ADS)

    De Gouveia Dal Pino, Elisabete

    2012-07-01

    Magnetic reconnection events like those associated to solar flares can be also a very powerful mechanism operating on accretion disk/jet systems. We have recently found that the magnetic power released in fast reconnection flares is more than sufficient to accelerate relativistic plasmons and produce the observed radio luminosity of the nuclear jets associated both to galactic stellar mass black holes and low luminous active galactic nuclei (AGNs). The famous observed correlation between the radio luminosity and the black hole mass of these sources, spanning ^10^9 orders of magnitude in mass, can be naturally explained in this model as simply due to the magnetic reconnection activity at the jet launching region of the accretion disk coronae of these sources. A similar process may explain the observed x-ray flares in young stars (YSOs) as well. In this talk, we review this mechanism and show results of numerical MHD tests of its validity. Also, particle acceleration in the magnetic reconnection sites of these sources can be rather efficient . In this talk, we will also discuss this acceleration process showing the energy distribution evolution of several thousands of test particles injected in a three-dimensional MHD domain of magnetic reconnection with embedded turbulence. The particle acceleration rate, which depends on the reconnection rate, is highly enhanced in this case. This is because reconnection becomes fast and independent of magnetic resistivity in the presence of turbulence and allows the formation of a thick volume in the current sheet filled with multiple, simultaneously reconnecting magnetic fluxes. The particles trapped within this volume then suffer several head-on scatterings with the contracting magnetic fluctuations in a first-order Fermi process. Particles are thus exponentially accelerated to energies which are several orders of magnitude larger than their injected energy.

  1. Extreme ultraviolet imaging of three-dimensional magnetic reconnection in a solar eruption

    PubMed Central

    Sun, J. Q.; Cheng, X.; Ding, M. D.; Guo, Y.; Priest, E. R.; Parnell, C. E.; Edwards, S. J.; Zhang, J.; Chen, P. F.; Fang, C.

    2015-01-01

    Magnetic reconnection, a change of magnetic field connectivity, is a fundamental physical process in which magnetic energy is released explosively, and it is responsible for various eruptive phenomena in the universe. However, this process is difficult to observe directly. Here, the magnetic topology associated with a solar reconnection event is studied in three dimensions using the combined perspectives of two spacecraft. The sequence of extreme ultraviolet images clearly shows that two groups of oppositely directed and non-coplanar magnetic loops gradually approach each other, forming a separator or quasi-separator and then reconnecting. The plasma near the reconnection site is subsequently heated from ∼1 to ≥5 MK. Shortly afterwards, warm flare loops (∼3 MK) appear underneath the hot plasma. Other observational signatures of reconnection, including plasma inflows and downflows, are unambiguously revealed and quantitatively measured. These observations provide direct evidence of magnetic reconnection in a three-dimensional configuration and reveal its origin. PMID:26113464

  2. Current disruption and its spreading in collision-less magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Jain, Neeraj; Buechner, Joerg; Dorfman, Seth; Ji, Hantao; Sharma, A. Surjalal; Max-Planck/Princeton CenterPlasma Physics Collaboration

    2013-10-01

    Recent magnetic reconnection experiments (MRX) [Dorfman et al., Geophys. Res. Lett. 40, 233 (2012)] have disclosed current disruption in the absence of guide field. During current disruption in MRX, current density and total out-of-reconnection-plane current drop simultaneous with a rise in out-of-reconnection-plane electric field. Here we show that current disruption is an intrinsic property of dynamic formation of X-point configuration of magnetic field in magnetic reconnection, independent of the model used for plasma description and of dimensionality (2-D or 3-D) of reconnection. An analytic expression for the current drop is derived from Ampere's equation and its predictions are verified by 2-D and 3-D electron-magnetohydrodynamic (EMHD) simulations. Three dimensional EMHD simulations show that the current disruption due to localized reconnection spreads along the direction of electron flow with a speed which depends on the wave number of the perturbation. The implications of these results for MRX and other reconnection experiments will be presented. This work was partially funded by the Max-Planck/Princeton Center for Plasma Physics.

  3. Three Dimensional Dynamics of Magnetic Reconnection in Large-Scale Pair Plasmas

    NASA Astrophysics Data System (ADS)

    Yin, L.; Daughton, W.; Albright, B. J.; Bowers, K. J.; Karimabad, H.; Roytershteyn, V.

    2009-05-01

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

  4. 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

  5. INTERCHANGE RECONNECTION FORCED BY THE FILAMENT ERUPTION INSIDE A PSEUDO-STREAMER

    SciTech Connect

    Yang, Jiayan; Jiang, Yunchun; Xu, Zhe; Bi, Yi; Hong, Junchao

    2015-04-20

    We present rare observational signatures of interchange reconnection (IR) forced by the filament eruption inside a pseudo-streamer (PS). The PS was centered above a positive-polarity region bounded by two negative-polarity coronal holes (CHs), and thus its base contained two polarity inversion lines and a pair of loop arcades where two filaments were harbored. In white-light coronagraph data from two different views, it showed up as a fan-shaped structure consisting of fine rays and a coronal streamer. Followed by a two-ribbon flare and a coronal mass ejection, one of the filaments and its overlying arcade erupted away from the nearby CH and flew over the other arcade to interact with the PS's remote CH. As a result, distinct ribbon-like remote brightenings formed along the remote CH boundary and were connected to the positive-polarity flare ribbon by a loop system, but the nearby open-field region largely remained unchanged except that compact brightenings and a following small coronal dimming appeared close to one end of the erupted filament. In combination with the coronal magnetic configuration that derived from the potential-field source-surface model, these observations can be interpreted as follows: the erupting field was first deflected and guided by the nearby CH's open field and then reconnected with the oppositely oriented open field of the remote CH, during which both the closed field bridging the erupted filament and the remoter CH's open field were transported in the opposite direction. The observations thus supported the idea that PSs provide favorable environments for IR to take place and remote brightenings along their CH boundaries represent a credible IR signature on the solar surface.

  6. What is the role of dayside magnetic reconnection in solar wind-magnetosphere coupling?

    NASA Astrophysics Data System (ADS)

    Dorelli, J. C.

    2008-05-01

    Our current understanding of magnetic storm triggering invokes magnetic reconnection as the basic solar wind- magnetosphere coupling mechanism. It is clear that the storm time ring current enhancement cannot be understood as a simple superposition of substorm injections (e.g., McPherron [AGU monograph 98, 131, 1998]). Instead, the storm time ring current is now thought to be produced by the global convection electric field which results from a prolonged southward IMF and the associated enhanced dayside reconnection rate. Gonzalez [Planet. Space. Sci., 38, 627, 1990]) has reviewed various solar wind magnetosphere coupling functions which have appeared in the literature, arguing that they are all special cases of a general expression (e.g., Sonnerup [J. Geophys. Res., 79, 1546, 1974]) for the rate of component reconnection at the dayside magnetopause. Sonnerup [1974] assumed that the dayside reconnection X line is parallel to the local current density, so that there is a critical IMF clock angle below which reconnection is geometrically impossible. Further, in the special case for which the magnitudes of the IMF and magnetospheric magnetic fields are equal, the reconnection electric field is proportional to sin2(θc/2), where θc is the IMF clock angle. Thus, the Sonnerup [1974] formula seems to explain the rapid decrease in solar wind magnetosphere coupling efficiency with decreasing IMF clock angle. In this talk, we revisit the role of dayside magnetic reconnection in the triggering of magnetic storms, taking into account the global, three-dimensional nature of the magnetopause magnetic field topology. We find that in contrast to the Sonnerup [1974] model -- in which two-dimensional reconnection theory is applied to a local patch of the magnetopause -- the three-dimensional X line is not parallel to the local current density. Further, we argue that the magnetopause has a null-null separator topology for all northward IMF clock angles (save due north, when the

  7. Locating magnetic reconnection x-lines in 3D PIC simulations

    NASA Astrophysics Data System (ADS)

    Olson, D. K.; Dorelli, J.; Daughton, W. S.; Karimabadi, H.

    2013-12-01

    In a three-dimensional PIC simulation of turbulent magnetic reconnection, a reconnection 'X-line' can be identified as a separator in the magnetic topology. From this x-line, it is possible to compute the reconnection rate by evaluating the line integral of the electric field along the separator. This technique is used in a reconnection simulation of a symmetric Harris sheet driven by inflow at the upstream boundaries with a strong guide field (such that the magnetic field is non-vanishing everywhere and there are no magnetic nulls). The results of this analysis are compared to the General Magnetic Reconnection theory (GMR) [Hesse and Schindler, 1998], showing that in this symmetric case GMR agrees with our topological approach to finding the location of the x-line. The parallel electric field is non-trivial along the entire length of the x-line, however, suggesting that the reconnection diffusion region cannot be identified by local measures of the breakdown of ideal MHD alone. We discuss the implications of these results for NASA's upcoming Magnetospheric Multiscale mission.

  8. Simulations of Magnetic Reconnection - Kinetic Mechanisms Underlying the Fluid Description of Ions

    NASA Technical Reports Server (NTRS)

    Aunai, icolas; Belmont, Gerard; Smets, Roch

    2012-01-01

    Because of its ability to transfer the energy stored in magnetic field together with the breaking of the flux freezing constraint, magnetic reconnection is considered as one of the most important phenomena in plasma physics. When it happens in a collision less environment such as the terrestrial magnetosphere, it should a priori be modelled with in the framework of kinetic physics. The evidence of kinetic features has incidentally for a long time, been shown by researchers with the help of both numerical simulations and satellite observations. However, most of our understanding of the process comes from the more intuitive fluid interpretation with simple closure hypothesis which do not include kinetic effects. To what extent are these two separate descriptions of the same phenomenon related? What is the role of kinetic effects in the averaged/fluid dynamics of reconnection? This thesis addresses these questions for the proton population in the particular case of anti parallel merging with the help of 2D Hybrid simulations. We show that one can not assume, as is usually done, that the acceleration of the proton flow is only due to the Laplace force. Our results show, for symmetric and asymmetric connection, the importance of the pressure force, opposed to the electric one on the separatrices, in the decoupling region. In the symmetric case, we emphasize the kinetic origin of this force by analyzing the proton distribution functions and explain their structure by studying the underlying particle dynamics. Protons, as individual particles, are shown to bounce in the electric potential well created by the Hall effect. The spatial divergence of this well results in a mixing in phase space responsible for the observed structure of the pressure tensor. A detailed energy budget analysis confirms the role of the pressure force for the acceleration; but, contrary to what is sometimes assumed, it also reveals that the major part of the incoming Poynting flux is transferred to

  9. Coronal magnetic reconnection driven by CME expansion—the 2011 June 7 event

    SciTech Connect

    Van Driel-Gesztelyi, L.; Baker, D.; Green, L. M.; Williams, D. R.; Carlyle, J.; Kliem, B.; Long, D. M.; Matthews, S. A.; Török, T.; Pariat, E.; Valori, G.; Démoulin, P.; Malherbe, J.-M.

    2014-06-10

    Coronal mass ejections (CMEs) erupt and expand in a magnetically structured solar corona. Various indirect observational pieces of evidence have shown that the magnetic field of CMEs reconnects with surrounding magnetic fields, forming, e.g., dimming regions distant from the CME source regions. Analyzing Solar Dynamics Observatory (SDO) observations of the eruption from AR 11226 on 2011 June 7, we present the first direct evidence of coronal magnetic reconnection between the fields of two adjacent active regions during a CME. The observations are presented jointly with a data-constrained numerical simulation, demonstrating the formation/intensification of current sheets along a hyperbolic flux tube at the interface between the CME and the neighboring AR 11227. Reconnection resulted in the formation of new magnetic connections between the erupting magnetic structure from AR 11226 and the neighboring active region AR 11227 about 200 Mm from the eruption site. The onset of reconnection first becomes apparent in the SDO/AIA images when filament plasma, originally contained within the erupting flux rope, is redirected toward remote areas in AR 11227, tracing the change of large-scale magnetic connectivity. The location of the coronal reconnection region becomes bright and directly observable at SDO/AIA wavelengths, owing to the presence of down-flowing cool, dense (10{sup 10} cm{sup –3}) filament plasma in its vicinity. The high-density plasma around the reconnection region is heated to coronal temperatures, presumably by slow-mode shocks and Coulomb collisions. These results provide the first direct observational evidence that CMEs reconnect with surrounding magnetic structures, leading to a large-scale reconfiguration of the coronal magnetic field.

  10. Magnetic reconnection in the presence of externally driven and self-generated turbulence

    SciTech Connect

    Karimabadi, H.; Lazarian, A.

    2013-11-15

    Magnetic reconnection is an important process that violates flux freezing and induces change of magnetic field topology in conducting fluids and, as a consequence, converts magnetic field energy into particle energy. It is thought to be operative in laboratory, heliophysical, and astrophysical plasmas. These environments exhibit wide variations in collisionality, ranging from collisionless in the Earth's magnetosphere to highly collisional in molecular clouds. A common feature among these plasmas is, however, the presence of turbulence. We review the present understanding of the effects of turbulence on the reconnection rate, discussing both how strong pre-existing turbulence modifies Sweet-Parker reconnection and how turbulence may develop as a result of reconnection itself. In steady state, reconnection rate is proportional to the aspect ratio of the diffusion region. Thus, two general MHD classes of models for fast reconnection have been proposed, differing on whether they keep the aspect ratio finite by increasing the width due to turbulent broadening or shortening the length of the diffusion layer due to plasmoid instability. One of the consequences of the plasmoid instability model is the possibility that the current sheet thins down to collisionless scales where kinetic effects become dominant. As a result, kinetic effects may be of importance for many astrophysical applications which were considered to be in the realm of MHD. Whether pre-existing turbulence can significantly modify the transition to the kinetic regime is not currently known. Although most studies of turbulent reconnection have been based on MHD, recent advances in kinetic simulations are enabling 3D studies of turbulence and reconnection in the collisionless regime. A summary of these recent works, highlighting similarities and differences with the MHD models of turbulent reconnection, as well as comparison with in situ observations in the magnetosphere and in the solar wind, are presented

  11. Nonlinear instability and intermittent nature of magnetic reconnection in solar chromosphere

    NASA Astrophysics Data System (ADS)

    Singh, K. A. P.; Hillier, Andrew; Isobe, Hiroaki; Shibata, Kazunari

    2015-10-01

    The recent observations of Singh et al. (2012, ApJ, 759, 33) have shown multiple plasma ejections and the intermittent nature of magnetic reconnection in the solar chromosphere, highlighting the need for fast reconnection to occur in highly collisional plasma. However, the physical process through which fast magnetic reconnection occurs in partially ionized plasma, like the solar chromosphere, is still poorly understood. It has been shown that for sufficiently high magnetic Reynolds numbers, Sweet-Parker current sheets can become unstable leading to tearing mode instability and plasmoid formation, but when dealing with a partially ionized plasma the strength of coupling between the ions and neutrals plays a fundamental role in determining the dynamics of the system. We propose that as the reconnecting current sheet thins and the tearing instability develops, plasmoid formation passes through strongly, intermediately, and weakly coupled (or decoupled) regimes, with the time scale for the tearing mode instability depending on the frictional coupling between ions and neutrals. We present calculations for the relevant time scales for fractal tearing in all three regimes. We show that as a result of the tearing mode instability and the subsequent non-linear instability due to the plasmoid-dominated reconnection, the Sweet-Parker current sheet tends to have a fractal-like structure, and when the chromospheric magnetic field is sufficiently strong the tearing instability can reach down to kinetic scales, which are hypothesized to be necessary for fast reconnection.

  12. Magnetospheric Multiscale Satellites Observations of Parallel Electric Fields Associated with Magnetic Reconnection.

    PubMed

    Ergun, R E; Goodrich, K A; Wilder, F D; Holmes, J C; Stawarz, J E; Eriksson, S; Sturner, A P; Malaspina, D M; Usanova, M E; Torbert, R B; Lindqvist, P-A; Khotyaintsev, Y; Burch, J L; Strangeway, R J; Russell, C T; Pollock, C J; Giles, B L; Hesse, M; Chen, L J; Lapenta, G; Goldman, M V; Newman, D L; Schwartz, S J; Eastwood, J P; Phan, T D; Mozer, F S; Drake, J; Shay, M A; Cassak, P A; Nakamura, R; Marklund, G

    2016-06-10

    We report observations from the Magnetospheric Multiscale satellites of parallel electric fields (E_{∥}) associated with magnetic reconnection in the subsolar region of the Earth's magnetopause. E_{∥} events near the electron diffusion region have amplitudes on the order of 100  mV/m, which are significantly larger than those predicted for an antiparallel reconnection electric field. This Letter addresses specific types of E_{∥} events, which appear as large-amplitude, near unipolar spikes that are associated with tangled, reconnected magnetic fields. These E_{∥} events are primarily in or near a current layer near the separatrix and are interpreted to be double layers that may be responsible for secondary reconnection in tangled magnetic fields or flux ropes. These results are telling of the three-dimensional nature of magnetopause reconnection and indicate that magnetopause reconnection may be often patchy and/or drive turbulence along the separatrix that results in flux ropes and/or tangled magnetic fields.

  13. A Parallel Two-fluid Code for Global Magnetic Reconnection Studies

    SciTech Connect

    J.A. Breslau; S.C. Jardin

    2001-08-09

    This paper describes a new algorithm for the computation of two-dimensional resistive magnetohydrodynamic (MHD) and two-fluid studies of magnetic reconnection in plasmas. It has been implemented on several parallel platforms and shows good scalability up to 32 CPUs for reasonable problem sizes. A fixed, nonuniform rectangular mesh is used to resolve the different spatial scales in the reconnection problem. The resistive MHD version of the code uses an implicit/explicit hybrid method, while the two-fluid version uses an alternating-direction implicit (ADI) method. The technique has proven useful for comparing several different theories of collisional and collisionless reconnection.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  15. Transition in Electron Physics of Magnetic Reconnection in Weakly Collisional Plasma

    NASA Astrophysics Data System (ADS)

    Le, A.; Roytershteyn, V.; Karimabadi, H.; Daughton, W. S.; Egedal, J.; Forest, C.

    2013-12-01

    Using self-consistent fully kinetic simulations with a Monte-Carlo treatment of the Coulomb collision operator, we explore the transition between collisional and kinetic regimes of magnetic reconnection in high-Lundquist-number current sheets. Recent research in collisionless reconnection has shown that electron kinetic physics plays a key role in the evolution. Large-scale electron current sheets may form, leading to secondary island formation and turbulent flux rope interactions in 3D. The new collisional simulations demonstrate how increasing collisionality modifies or eliminates these electron structures in the kinetic regimes. Additional basic questions that are addressed include how the reconnection rate and the release of magnetic energy into electrons and ions vary with collisionality. The numerical study provides insight into reconnection in dense regions of the solar corona, the solar wind, and upcoming laboratory experiments at MRX (Princeton) and MPDX (UW-Madison). The implications of these results for studies of turbulence dissipation in weakly collisional plasmas are discussed.

  16. Scaling the energy conversion rate from magnetic field reconnection to different bodies

    SciTech Connect

    Mozer, F. S.; Hull, A.

    2010-10-15

    Magnetic field reconnection is often invoked to explain electromagnetic energy conversion in planetary magnetospheres, stellar coronae, and other astrophysical objects. Because of the huge dynamic range of magnetic fields in these bodies, it is important to understand energy conversion as a function of magnetic field strength and related parameters. It is conjectured theoretically and shown experimentally that the energy conversion rate per unit area in reconnection scales as the cube of an appropriately weighted magnetic field strength divided by the square root of an appropriately weighted density. With this functional dependence, the energy release in flares on the Sun, the large and rapid variation of the magnetic flux in the tail of Mercury, and the apparent absence of reconnection on Jupiter and Saturn, may be understood. Electric fields at the perihelion of the Solar Probe Plus mission may be tens of V/m.

  17. Magnetic force microscopy

    PubMed Central

    Passeri, Daniele; Dong, Chunhua; Reggente, Melania; Angeloni, Livia; Barteri, Mario; Scaramuzzo, Francesca A; De Angelis, Francesca; Marinelli, Fiorenzo; Antonelli, Flavia; Rinaldi, Federica; Marianecci, Carlotta; Carafa, Maria; Sorbo, Angela; Sordi, Daniela; Arends, Isabel WCE; Rossi, Marco

    2014-01-01

    Magnetic force microscopy (MFM) is an atomic force microscopy (AFM) based technique in which an AFM tip with a magnetic coating is used to probe local magnetic fields with the typical AFM spatial resolution, thus allowing one to acquire images reflecting the local magnetic properties of the samples at the nanoscale. Being a well established tool for the characterization of magnetic recording media, superconductors and magnetic nanomaterials, MFM is finding constantly increasing application in the study of magnetic properties of materials and systems of biological and biomedical interest. After reviewing these latter applications, three case studies are presented in which MFM is used to characterize: (i) magnetoferritin synthesized using apoferritin as molecular reactor; (ii) magnetic nanoparticles loaded niosomes to be used as nanocarriers for drug delivery; (iii) leukemic cells labeled using folic acid-coated core-shell superparamagnetic nanoparticles in order to exploit the presence of folate receptors on the cell membrane surface. In these examples, MFM data are quantitatively analyzed evidencing the limits of the simple analytical models currently used. Provided that suitable models are used to simulate the MFM response, MFM can be used to evaluate the magnetic momentum of the core of magnetoferritin, the iron entrapment efficiency in single vesicles, or the uptake of magnetic nanoparticles into cells. PMID:25050758

  18. Geo-effectiveness and radial dependence of magnetic cloud erosion by magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Lavraud, Benoit; Ruffenach, Alexis; Rouillard, Alexis P.; Kajdic, Primoz; Manchester, Ward B.; Lugaz, Noé

    2014-01-01

    flux erosion by magnetic reconnection occurs at the front of at least some magnetic clouds (MCs). We first investigate how erosion influences the geo-effectiveness of MCs in a general sense and using a south-north magnetic polarity MC observed on 18-20 October 1995. Although the magnetic shear at its front may not be known during propagation, measurements at 1 AU show signatures of local reconnection. Using a standard MC model, an empirical model of the geomagnetic response (Dst), and an observational estimate of the magnetic flux erosion, we find that the strength of the observed ensuing storm was ~30% lower than if no erosion had occurred. We then discuss the interplay between adiabatic compression and magnetic erosion at the front of MCs. We conclude that the most geo-effective configuration for a south-north polarity MC is to be preceded by a solar wind with southward IMF. This stems not only from the formation of a geo-effective sheath ahead of it but also from the adiabatic compression and reduced (or lack thereof) magnetic erosion which constructively conspire for the structure to be more geo-effective. Finally, assuming simple semiempirical and theoretical Alfvén speed profiles expected from expansion to 1 AU, we provide first-order estimates of the erosion process radial evolution. We find that the expected reconnection rates during propagation allow for significant erosion, on the order of those reported. Calculations also suggest that most of the erosion should occur in the inner heliosphere, and up to ~50% may yet occur beyond Mercury's orbit.

  19. Magnetic Dissipation in Asymmetric Strong Guide 3D Simulations: Examples of Magnetic Diffusion and Reconnection

    NASA Astrophysics Data System (ADS)

    Scudder, J. D.; Karimabadi, H.; Daughton, W. S.

    2013-12-01

    Interpretations of 2D simulations of magnetic reconnection are greatly simplified by using the flux function, usually the out of plane component of the vector potential. This theoretical device is no longer available when simulations are analyzed in 3-D. We illustrate the results of determining the locale rates of flux slippage in simulations by a technique based on Maxwell's equations. The technique recovers the usual results obtained for the flux function in 2D simulations, but remains viable in 3D simulations where there is no flux function. The method has also been successfully tested for full PIC simulations where reconnection is geometrically forbiddden. While such layers possess measurable flux slippages (diffusion) their level is not as strong as recorded in known 2D PIC reconnection sites using the same methodology. This approach will be used to explore the spatial incidence and strength of flux slippages across a 3D, asymmetric, strong guide field run discussed previously in the literature. Regions of diffusive behavior are illustrated where LHDI has been previously identified out on the separatrices, while much stronger flux slippages, typical of the X-regions of 2D simulations, are shown to occur elsewhere throughout the simulation. These results suggest that reconnection requires sufficiently vigorous flux slippage to be self sustaining, while non-zero flux slippage can and does occur without being at the reconnection site. A cross check of this approach is provided by the mixing ratio of tagged simulation particles of known spatial origin discussed by Daughton et al., 2013 (this meeting); they provide an integral measure of flux slippage up to the present point in the simulation. We will discuss the correlations between our Maxwell based flux slippage rates and the inferred rates of change of this mixing ratio (as recorded in the local fluid frame).

  20. SIMULATIONS OF PARTICLE ACCELERATION BEYOND THE CLASSICAL SYNCHROTRON BURNOFF LIMIT IN MAGNETIC RECONNECTION: AN EXPLANATION OF THE CRAB FLARES

    SciTech Connect

    Cerutti, B.; Werner, G. R.; Uzdensky, D. A.; Begelman, M. C. E-mail: greg.werner@colorado.edu E-mail: mitch@jila.colorado.edu

    2013-06-20

    It is generally accepted that astrophysical sources cannot emit synchrotron radiation above 160 MeV in their rest frame. This limit is given by the balance between the accelerating electric force and the radiation reaction force acting on the electrons. The discovery of synchrotron gamma-ray flares in the Crab Nebula, well above this limit, challenges this classical picture of particle acceleration. To overcome this limit, particles must accelerate in a region of high electric field and low magnetic field. This is possible only with a non-ideal magnetohydrodynamic process, like magnetic reconnection. We present the first numerical evidence of particle acceleration beyond the synchrotron burnoff limit, using a set of two-dimensional particle-in-cell simulations of ultra-relativistic pair plasma reconnection. We use a new code, Zeltron, that includes self-consistently the radiation reaction force in the equation of motion of the particles. We demonstrate that the most energetic particles move back and forth across the reconnection layer, following relativistic Speiser orbits. These particles then radiate >160 MeV synchrotron radiation rapidly, within a fraction of a full gyration, after they exit the layer. Our analysis shows that the high-energy synchrotron flux is highly variable in time because of the strong anisotropy and inhomogeneity of the energetic particles. We discover a robust positive correlation between the flux and the cut-off energy of the emitted radiation, mimicking the effect of relativistic Doppler amplification. A strong guide field quenches the emission of >160 MeV synchrotron radiation. Our results are consistent with the observed properties of the Crab flares, supporting the reconnection scenario.

  1. MMS observations of large guide field symmetric reconnection between colliding reconnection jets at the center of a magnetic flux rope at the magnetopause

    NASA Astrophysics Data System (ADS)

    Øieroset, M.; Phan, T. D.; Haggerty, C.; Shay, M. A.; Eastwood, J. P.; Gershman, D. J.; Drake, J. F.; Fujimoto, M.; Ergun, R. E.; Mozer, F. S.; Oka, M.; Torbert, R. B.; Burch, J. L.; Wang, S.; Chen, L. J.; Swisdak, M.; Pollock, C.; Dorelli, J. C.; Fuselier, S. A.; Lavraud, B.; Giles, B. L.; Moore, T. E.; Saito, Y.; Avanov, L. A.; Paterson, W.; Strangeway, R. J.; Russell, C. T.; Khotyaintsev, Y.; Lindqvist, P. A.; Malakit, K.

    2016-06-01

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

  2. Pulsating Magnetic Reconnection Driven by Three-Dimensional Flux-Rope Interactions

    NASA Astrophysics Data System (ADS)

    Gekelman, W.; De Haas, T.; Daughton, W.; Van Compernolle, B.; Intrator, T.; Vincena, S.

    2016-06-01

    The dynamics of magnetic reconnection is investigated in a laboratory experiment consisting of two magnetic flux ropes, with currents slightly above the threshold for the kink instability. The evolution features periodic bursts of magnetic reconnection. To diagnose this complex evolution, volumetric three-dimensional data were acquired for both the magnetic and electric fields, allowing key field-line mapping quantities to be directly evaluated for the first time with experimental data. The ropes interact by rotating about each other and periodically bouncing at the kink frequency. During each reconnection event, the formation of a quasiseparatrix layer (QSL) is observed in the magnetic field between the flux ropes. Furthermore, a clear correlation is demonstrated between the quasiseparatrix layer and enhanced values of the quasipotential computed by integrating the parallel electric field along magnetic field lines. These results provide clear evidence that field lines passing through the quasiseparatrix layer are undergoing reconnection and give a direct measure of the nonlinear reconnection rate. The measurements suggest that the parallel electric field within the QSL is supported predominantly by electron pressure; however, resistivity may play a role.

  3. Pulsating Magnetic Reconnection Driven by Three-Dimensional Flux-Rope Interactions.

    PubMed

    Gekelman, W; De Haas, T; Daughton, W; Van Compernolle, B; Intrator, T; Vincena, S

    2016-06-10

    The dynamics of magnetic reconnection is investigated in a laboratory experiment consisting of two magnetic flux ropes, with currents slightly above the threshold for the kink instability. The evolution features periodic bursts of magnetic reconnection. To diagnose this complex evolution, volumetric three-dimensional data were acquired for both the magnetic and electric fields, allowing key field-line mapping quantities to be directly evaluated for the first time with experimental data. The ropes interact by rotating about each other and periodically bouncing at the kink frequency. During each reconnection event, the formation of a quasiseparatrix layer (QSL) is observed in the magnetic field between the flux ropes. Furthermore, a clear correlation is demonstrated between the quasiseparatrix layer and enhanced values of the quasipotential computed by integrating the parallel electric field along magnetic field lines. These results provide clear evidence that field lines passing through the quasiseparatrix layer are undergoing reconnection and give a direct measure of the nonlinear reconnection rate. The measurements suggest that the parallel electric field within the QSL is supported predominantly by electron pressure; however, resistivity may play a role.

  4. A LABORATORY EXPERIMENT OF MAGNETIC RECONNECTION: OUTFLOWS, HEATING, AND WAVES IN CHROMOSPHERIC JETS

    SciTech Connect

    Nishizuka, N.; Shimizu, T.; Hayashi, Y.; Tanabe, H.; Kuwahata, A.; Kaminou, Y.; Ono, Y.; Inomoto, M.

    2012-09-10

    Hinode observations have revealed intermittent recurrent plasma ejections/jets in the chromosphere. These are interpreted as a result of non-perfectly anti-parallel magnetic reconnection, i.e., component reconnection, between a twisted magnetic flux tube and the pre-existing coronal/chromospheric magnetic field, though the fundamental physics of component reconnection is not revealed. In this paper, we experimentally reproduced the magnetic configuration and investigated the dynamics of plasma ejections, heating, and wave generation triggered by component reconnection in the chromosphere. We set plasma parameters as in the chromosphere (density 10{sup 14} cm{sup -3}, temperature 5-10 eV, i.e., (5-10) Multiplication-Sign 10{sup 4} K, and reconnection magnetic field 200 G) using argon plasma. Our experiment shows bi-directional outflows with the speed of 5 km s{sup -1} at maximum, ion heating in the downstream area over 30 eV, and magnetic fluctuations mainly at 5-10 {mu}s period. We succeeded in qualitatively reproducing chromospheric jets, but quantitatively, we still have some differences between observations and experiments such as in jet velocity, total energy, and wave frequency. Some of them can be explained by the scale gap between solar and laboratory plasma, while the others are probably due to the difference in microscopy and macroscopy, collisionality, and the degree of ionization, which have not been achieved in our experiment.

  5. Impact of Magnetic Draping, Convection, and Field Line Tying on Magnetopause Reconnection Under Northward IMF

    NASA Technical Reports Server (NTRS)

    Wendel, Deirdre E.; Reiff, Patricia H.; Goldstein, Melvyn L.

    2010-01-01

    We simulate a northward IMF cusp reconnection event at the magnetopause using the OpenGGCM resistive MHD code. The ACE input data, solar wind parameters, and dipole tilt belong to a 2002 reconnection event observed by IMAGE and Cluster. Based on a fully three-dimensional skeleton separators, nulls, and parallel electric fields, we show magnetic draping, convection, ionospheric field line tying play a role in producing a series of locally reconnecting nulls with flux ropes. The flux ropes in the cusp along the global separator line of symmetry. In 2D projection, the flux ropes the appearance of a tearing mode with a series of 'x's' and 'o's' but bearing a kind of 'guide field' that exists only within the magnetopause. The reconnecting field lines in the string of ropes involve IMF and both open and closed Earth magnetic field lines. The observed magnetic geometry reproduces the findings of a superposed epoch impact parameter study derived from the Cluster magnetometer data for the same event. The observed geometry has repercussions for spacecraft observations of cusp reconnection and for the imposed boundary conditions reconnection simulations.

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

    NASA Astrophysics Data System (ADS)

    Uzdensky, Dmitri; Werner, Gregory; Zhdankin, Vladimir

    2016-10-01

    Magnetic reconnection is a fundamental plasma process that converts magnetic energy into particle kinetic energy. ``Relativistic'' reconnection is of interest in astrophysical contexts because it can accelerate particles to relativistic energies high enough for synchrotron (or inverse Compton) emission to explain observed high-energy radiation. After several 2D particle-in-cell (PIC) simulations of reconnection in pair plasmas demonstrated power-law electron-energy spectra extending to high energies, a few 3D simulations surprisingly confirmed the robustness of nonthermal particle acceleration, despite fundamental differences, such as the development of the relativistic drift-kink instability (RDKI) in 3D. We present a comprehensive PIC study of 3D relativistic pair-plasma reconnection characterizing the effect of the third dimension. We investigate how reconnection dynamics and particle acceleration depend on guide magnetic field Bz and on the simulation box length Lz in the third dimension. We find that, while the RDKI does indeed grow in 3D reconnection, it does not inhibit particle acceleration, even in the absence of guide field. This work was funded by NSF, DOE, and NASA.

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

    SciTech Connect

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

    2015-05-15

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

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

    DOE PAGES

    Yamada, Masaaki; Yoo, Jongsoo; Jara-Almonte, Jonathan; ...

    2015-05-15

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

  9. Why does Steady-State Magnetic Reconnection have a Maximum Local Rate of Order 0.1?

    NASA Astrophysics Data System (ADS)

    Liu, Yi-Hsin; Hesse, M.; Guo, F.; Daughton, W.; Li, H.; Cassak, P. A.; Shay, M. A.

    2017-02-01

    Simulations suggest collisionless steady-state magnetic reconnection of Harris-type current sheets proceeds with a rate of order 0.1, independent of dissipation mechanism. We argue this long-standing puzzle is a result of constraints at the magnetohydrodynamic (MHD) scale. We predict the reconnection rate as a function of the opening angle made by the upstream magnetic fields, finding a maximum reconnection rate close to 0.2. The predictions compare favorably to particle-in-cell simulations of relativistic electron-positron and nonrelativistic electron-proton reconnection. The fact that simulated reconnection rates are close to the predicted maximum suggests reconnection proceeds near the most efficient state allowed at the MHD scale. The rate near the maximum is relatively insensitive to the opening angle, potentially explaining why reconnection has a similar fast rate in differing models.

  10. How Does Collisionless Magnetic Reconnection Work in the Presence of a Guide Magnetic Field?

    NASA Technical Reports Server (NTRS)

    Hesse, Michael

    2006-01-01

    The dissipation mechanism of guide field magnetic reconnection remains a subject of intense scientific interest. On one hand, one set of recent studies have shown that particle inertia-based processes, which include thermal and bulk inertial effects, provide the reconnection electric field in the diffusion region. On the other hand, a second set of studies emphasizes the role of wave-particle interactions in providing anomalous resistivity in the diffusion region. In this presentation, we present analytical theory results, as well as 2.5 and three-dimensional PIC simulations of guide-field magnetic reconnection. We will show that diffusion region scale sizes in moderate and large guide field cases are determined by electron Larmor radii, and that analytical estimates of diffusion region dimensions need to include description of the heat flux tensor. The dominant electron dissipation process appears to be based on thermal electron inertia, expressed through nongyrotropic electron pressure tensors. We will argue that this process remains viable in three dimensions by means of a detailed comparison of high resolution particle-in-cell simulations.

  11. Tunneling magnetic force microscopy

    NASA Technical Reports Server (NTRS)

    Burke, Edward R.; Gomez, Romel D.; Adly, Amr A.; Mayergoyz, Isaak D.

    1993-01-01

    We have developed a powerful new tool for studying the magnetic patterns on magnetic recording media. This was accomplished by modifying a conventional scanning tunneling microscope. The fine-wire probe that is used to image surface topography was replaced with a flexible magnetic probe. Images obtained with these probes reveal both the surface topography and the magnetic structure. We have made a thorough theoretical analysis of the interaction between the probe and the magnetic fields emanating from a typical recorded surface. Quantitative data about the constituent magnetic fields can then be obtained. We have employed these techniques in studies of two of the most important issues of magnetic record: data overwrite and maximizing data-density. These studies have shown: (1) overwritten data can be retrieved under certain conditions; and (2) improvements in data-density will require new magnetic materials. In the course of these studies we have developed new techniques to analyze magnetic fields of recorded media. These studies are both theoretical and experimental and combined with the use of our magnetic force scanning tunneling microscope should lead to further breakthroughs in the field of magnetic recording.

  12. The role of magnetic reconnection on jet/accretion disk systems

    NASA Astrophysics Data System (ADS)

    de Gouveia Dal Pino, E. M.; Piovezan, P. P.; Kadowaki, L. H. S.

    2010-07-01

    Context. It was proposed earlier that the relativistic ejections observed in microquasars could be produced by violent magnetic reconnection episodes at the inner disk coronal region (de Gouveia Dal Pino & Lazarian 2005). Aims: Here we revisit this model, which employs a standard accretion disk description and fast magnetic reconnection theory, and discuss the role of magnetic reconnection and associated heating and particle acceleration in different jet/disk accretion systems, namely young stellar objects (YSOs), microquasars, and active galactic nuclei (AGNs). Methods: In microquasars and AGNs, violent reconnection episodes between the magnetic field lines of the inner disk region and those that are anchored in the black hole are able to heat the coronal/disk gas and accelerate the plasma to relativistic velocities through a diffusive first-order Fermi-like process within the reconnection site that will produce intermittent relativistic ejections or plasmons. Results: The resulting power-law electron distribution is compatible with the synchrotron radio spectrum observed during the outbursts of these sources. A diagram of the magnetic energy rate released by violent reconnection as a function of the black hole (BH) mass spanning 109 orders of magnitude shows that the magnetic reconnection power is more than sufficient to explain the observed radio luminosities of the outbursts from microquasars to low luminous AGNs. In addition, the magnetic reconnection events cause the heating of the coronal gas, which can be conducted back to the disk to enhance its thermal soft X-ray emission as observed during outbursts in microquasars. The decay of the hard X-ray emission right after a radio flare could also be explained in this model due to the escape of relativistic electrons with the evolving jet outburst. In the case of YSOs a similar magnetic configuration can be reached that could possibly produce observed X-ray flares in some sources and provide the heating at the

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  14. The Effect of Cooling on Particle Trajectories and Acceleration in Relativistic Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Kagan, Daniel; Nakar, Ehud; Piran, Tsvi

    2016-12-01

    The maximum synchrotron burnoff limit of 160 MeV represents a fundamental limit to radiation resulting from electromagnetic particle acceleration in one-zone ideal plasmas. In magnetic reconnection, however, particle acceleration and radiation are decoupled because the electric field is larger than the magnetic field in the diffusion region. We carry out two-dimensional particle-in-cell simulations to determine the extent to which magnetic reconnection can produce synchrotron radiation above the burnoff limit. We use the test particle comparison (TPC) method to isolate the effects of cooling by comparing the trajectories and acceleration efficiencies of test particles incident on such a reconnection region with and without cooling them. We find that the cooled and uncooled particle trajectories are typically similar during acceleration in the reconnection region, and derive an effective limit on particle acceleration that is inversely proportional to the average magnetic field experienced by the particle during acceleration. Using the calculated distribution of this average magnetic field as a function of uncooled final particle energy, we find analytically that cooling does not affect power-law particle energy spectra except at energies far above the synchrotron burnoff limit. Finally, we compare fully cooled and uncooled simulations of reconnection, confirming that the synchrotron burnoff limit does not produce a cutoff in the particle energy spectrum. Our results indicate that the TPC method accurately predicts the effects of cooling on particle acceleration in relativistic reconnection, and that, even far above the burnoff limit, the synchrotron energy of radiation produced in reconnection is not limited by cooling.

  15. Chaos-induced resistivity of collisionless magnetic reconnection in the presence of a guide field

    NASA Astrophysics Data System (ADS)

    Shang, Meng; Wu, De-Jin; Chen, Ling; Chen, Peng-Fei

    2017-01-01

    One of the most puzzling problems in astrophysics is to understand the anomalous resistivity in collisionless magnetic reconnection that is believed extensively to be responsible for the energy release in various eruptive phenomena. The magnetic null point in the reconnecting current sheet, acting as a scattering center, can lead to chaotic motions of particles in the current sheet, which is one of the possible mechanisms for anomalous resistivity and is called chaos-induced resistivity. In many interesting cases, however, instead of the magnetic null point, there is a nonzero magnetic field perpendicular to the merging field lines, usually called the guide field, whose effect on chaos-induced resistivity has been an open problem. By use of the test particle simulation method and statistical analysis, we investigate chaos-induced resistivity in the presence of a constant guide field. The characteristics of particle motion in the reconnecting region, in particular, the chaotic behavior of particle orbits and evolving statistical features, are analyzed. The results show that as the guide field increases, the radius of the chaos region increases and the Lyapunov index decreases. However, the effective collision frequency, and hence the chaos-induced resistivity, reach their peak values when the guide field approaches half of the characteristic strength of the reconnection magnetic field. The presence of a guide field can significantly influence the chaos of the particle orbits and hence the chaos-induced resistivity in the reconnection sheet, which decides the collisionless reconnection rate. The present result is helpful for us to understand the microphysics of anomalous resistivity in collisionless reconnection with a guide field.

  16. Frozen flux violation, electron demagnetization and magnetic reconnection

    SciTech Connect

    Scudder, J. D.; Karimabadi, H.; Roytershteyn, V.; Daughton, W.

    2015-10-15

    We argue that the analogue in collisionless plasma of the collisional diffusion region of magnetic reconnection is properly defined in terms of the demagnetization of the plasma electrons that enable “frozen flux” slippage to occur. This condition differs from the violation of the “frozen-in” condition, which only implies that two fluid effects are involved, rather than the necessary slippage of magnetic flux as viewed in the electron frame. Using 2D Particle In Cell (PIC) simulations, this approach properly finds the saddle point region of the flux function. Our demagnetization conditions are the dimensionless guiding center approximation expansion parameters for electrons which we show are observable and determined locally by the ratio of non-ideal electric to magnetic field strengths. Proxies for frozen flux slippage are developed that (a) are measurable on a single spacecraft, (b) are dimensionless with theoretically justified threshold values of significance, and (c) are shown in 2D simulations to recover distinctions theoretically possible with the (unmeasurable) flux function. A new potentially observable dimensionless frozen flux rate, Λ{sub Φ}, differentiates significant from anecdotal frozen flux slippage. A single spacecraft observable, ϒ, is shown with PIC simulations to be essentially proportional to the unobservable local Maxwell frozen flux rate. This relationship theoretically establishes electron demagnetization in 3D as the general cause of frozen flux slippage. In simple 2D cases with an isolated central diffusion region surrounded by separatrices, these diagnostics uniquely identify the traditional diffusion region (without confusing it with the two fluid “ion-diffusion” region) and clarify the role of the separatrices where frozen flux violations do occur but are not substantial. In the more complicated guide and asymmetric 2D cases, substantial flux slippage regions extend out along, but inside of, the preferred separatrices

  17. MAGNETIZATION OF CLOUD CORES AND ENVELOPES AND OTHER OBSERVATIONAL CONSEQUENCES OF RECONNECTION DIFFUSION

    SciTech Connect

    Lazarian, A.; Esquivel, A.; Crutcher, R.

    2012-10-01

    Recent observational results for magnetic fields in molecular clouds reviewed by Crutcher seem to be inconsistent with the predictions of the ambipolar diffusion theory of star formation. These include the measured decrease in mass to flux ratio between envelopes and cores, the failure to detect any self-gravitating magnetically subcritical clouds, the determination of the flat probability distribution function (PDF) of the total magnetic field strengths implying that there are many clouds with very weak magnetic fields, and the observed scaling B{proportional_to}{rho}{sup 2/3} that implies gravitational contraction with weak magnetic fields. We consider the problem of magnetic field evolution in turbulent molecular clouds and discuss the process of magnetic field diffusion mediated by magnetic reconnection. For this process that we termed 'reconnection diffusion', we provide a simple physical model and explain that this process is inevitable in view of the present-day understanding of MHD turbulence. We address the issue of the expected magnetization of cores and envelopes in the process of star formation and show that reconnection diffusion provides an efficient removal of magnetic flux that depends only on the properties of MHD turbulence in the core and the envelope. We show that as the amplitude of turbulence as well as the scale of turbulent motions decrease from the envelope to the core of the cloud, the diffusion of the magnetic field is faster in the envelope. As a result, the magnetic flux trapped during the collapse in the envelope is being released faster than the flux trapped in the core, resulting in much weaker fields in envelopes than in cores, as observed. We provide simple semi-analytical model calculations which support this conclusion and qualitatively agree with the observational results. Magnetic reconnection is also consistent with the lack of subcritical self-gravitating clouds, with the observed flat PDF of field strengths, and with the

  18. Signatures of complex magnetic topologies from multiple reconnection sites induced by Kelvin-Helmholtz instability

    NASA Astrophysics Data System (ADS)

    Vernisse, Y.; Lavraud, B.; Eriksson, S.; Gershman, D. J.; Dorelli, J.; Pollock, C.; Giles, B.; Aunai, N.; Avanov, L.; Burch, J.; Chandler, M.; Coffey, V.; Dargent, J.; Ergun, R. E.; Farrugia, C. J.; Génot, V.; Graham, D. B.; Hasegawa, H.; Jacquey, C.; Kacem, I.; Khotyaintsev, Y.; Li, W.; Magnes, W.; Marchaudon, A.; Moore, T.; Paterson, W.; Penou, E.; Phan, T. D.; Retino, A.; Russell, C. T.; Saito, Y.; Sauvaud, J.-A.; Torbert, R.; Wilder, F. D.; Yokota, S.

    2016-10-01

    The Magnetospheric Multiscale mission has demonstrated the frequent presence of reconnection exhausts at thin current sheets within Kelvin-Helmholtz (KH) waves at the flank magnetopause. Motivated by these recent observations, we performed a statistical analysis of the boundary layers on the magnetosheath side of all KH current sheets on 8 September 2015. We show 86% consistency between the exhaust flows and particle leakage in the magnetosheath boundary layers but further highlight the very frequent presence of additional boundary layer signatures that do not come from the locally observed reconnection exhausts. These additional electron and ion boundary layers, of various durations and at various positions with respect to the leading and trailing boundaries of the KH waves, signal connections to reconnection sites at other locations. Based on the directionality and extent of these layers, we provide an interpretation whereby complex magnetic topologies can arise within KH waves from the combination of reconnection in the equatorial plane and at midlatitudes in the Southern and Northern Hemispheres, where additional reconnection sites are expected to be triggered by the three-dimensional field lines interweaving induced by the KH waves at the flanks (owing to differential flow and magnetic field shear with latitude). The present event demonstrates that the three-dimensional development of KH waves can induce plasma entry (through reconnection at both midlatitude and equatorial regions) already sunward of the terminator where the instability remains in its linear stage.

  19. Measuring Properties of Magnetic Reconnection in Nonlinear Resistive and Two-Fluid Toroidal Simulations of Sawteeth

    NASA Astrophysics Data System (ADS)

    Beidler, Matthew; Cassak, Paul; Jardin, Stephen; Ferraro, Nathaniel

    2015-11-01

    The sawtooth crash in tokamaks limits the core temperature, harms confinement, and seeds disruptions. A predictive capability of its ramifications has been elusive. Extended-MHD physics is needed to properly analyze the magnetic reconnection that occurs during the crash phase, but it has only recently been integrated into codes using a toroidal geometry. In this study, we employ the three-dimensional toroidal, extended-MHD code M3D-C1 to study reconnection during the sawtooth crash. We study the nonlinear evolution of a test equilibrium in a non-reduced field representation for resistive-MHD and the two-fluid model. We find that the toroidal mode growth rates for the two-fluid reconnection process exhibit a nonlinear acceleration and greatly exceed that of a similar resistive MHD model, more closely in line with experimental results. Furthermore, by sampling the two-fluid simulation data in the plane perpendicular to the helical (m,n) =(1,1) mode, we present the first observation of the quadrupole out-of-plane magnetic field appearing during sawtooth reconnection with the Hall term. We also explore how reconnection as viewed in the helically perpendicular plane varies toroidally, which affects the symmetry of the reconnection geometry and the local diamagnetic effects.

  20. Localization and propagation of the energy release during 3D kinetic magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Lapenta, Giovanni; Markidis, Stefano; Goldman, Marty; Newman, David

    2013-04-01

    Reconnection is a key processes where energy is released: magnetic field lines break, merge in a new configuration. In the process some of the energy is released. Recent work by Shay and collaborators has pointed out that energy is released far and moving fast away from the reconnection site, at a speed exceeding several times the Alfven speed. We revisit this point, considering the release of energy from reconnection and considering both laminar processes and turbulent reconnection. We analyse the energy budget and the processes of energy transfer via Poynting flux and particle flows. The results are compared with the recent findings by Shay. The effect of the guide field can be very significant at even relatively weak strength, as our recent analysis shows. The effect on the life cycle of energy is considered. The research leading to these results has received funding from the European Commission's Seventh Framework Programme (FP7/2007-2013) under the grant agreement SWIFF (project n° 263340, www.swiff.eu). [1] M. A. Shay, J. F. Drake, J. P. Eastwood, and T. D. Phan, Super-Alfvénic Propagation of Substorm Reconnection Signatures and Poynting Flux, Phys. Rev. Lett. 107, 089901, 2011. [2] M.V. Goldman, G. Lapenta, D. L. Newman, S. Markidis, H. Che, Jet Deflection by Very Weak Guide Fields during Magnetic Reconnection, Physical Review Letters, 107, 135001, 2011.

  1. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  3. Fast magnetic reconnection in low-density electron-positron plasmas

    SciTech Connect

    Bessho, Naoki; Bhattacharjee, A.

    2010-10-15

    Two-dimensional particle-in-cell simulations have been performed to study magnetic reconnection in low-density electron-positron plasmas without a guide magnetic field. Impulsive reconnection rates become of the order of unity when the background density is much smaller than 10% of the density in the initial current layer. It is demonstrated that the outflow speed is less than the upstream Alfven speed, and that the time derivative of the density must be taken into account in the definition of the reconnection rate. The reconnection electric fields in the low-density regime become much larger than the ones in the high-density regime, and it is possible to accelerate the particles to high energies more efficiently. The inertial term in the generalized Ohm's law is the most dominant term that supports a large reconnection electric field. An effective collisionless resistivity is produced and tracks the extension of the diffusion region in the late stage of the reconnection dynamics, and significant broadening of the diffusion region is observed. Because of the broadening of the diffusion region, no secondary islands, which have been considered to play a role to limit the diffusion region, are generated during the extension of the diffusion region in the outflow direction.

  4. Evidence of "Tether-Cutting" Reconnection in the Onset of a Quadrupolar Solar Magnetic Eruption

    NASA Technical Reports Server (NTRS)

    Choudhary, Debi Prasad; Sterling, Alphonse C.; Moore, Ronald L.; Yurchyshyn, Vasyl

    2004-01-01

    Extensive study of the near-limb solar filament eruption event on 2000 February 26, involving coronal images from YOHKOH, SOHO EIT and photospheric magnetogram from MID have shown that that both "runaway-tether-cutting-type reconnection" and "fast breakout-type reconnection" may have occurred early in the fast phase of the eruption and may have played an important role in unleashing the explosion (Sterling & Moore 2004). That study did not identify which or if either of these types of reconnection actually triggered the fast phase. Here, together with a magnetogram and He1 10830 A filtergram from NSO/KP, we present Halpha filtergrams from Big Bear Solar Observatory, that show evidence of "tether-cutting-type reconnection" before and during the eruption of the southern filament, situated at one of the neutral lines of the quadrupole magnetic structure.

  5. Three Dimensional Dynamics of Collisionless Magnetic Reconnection in Large-Scale Pair Plasmas

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    A numerical study of magnetic reconnection in the large-Lundquist-number (S), plasmoid-dominated regime is carried out for S up to 107. The theoretical model of Uzdensky et al. [Phys. Rev. Lett. 105, 235002 (2010)] is confirmed and partially amended. The normalized reconnection rate is E~eff~0.02 independently of S for S>>104. The plasmoid flux (Ψ) and half-width (wx) distribution functions scale as f(Ψ)~Ψ-2 and f(wx)~wx-2. The joint distribution of Ψ and wx shows that plasmoids populate a triangular region wx>~Ψ/B0, where B0 is the reconnecting field. It is argued that this feature is due to plasmoid coalescence. Macroscopic ``monster'' plasmoids with wx~10% of the system size are shown to emerge in just a few Alfvén times, independently of S, suggesting that large disruptive events are an inevitable feature of large-S reconnection.

  7. Nonthermally dominated electron acceleration during magnetic reconnection in a low-β plasma

    DOE PAGES

    Li, Xiaocan; Guo, Fan; Li, Hui; ...

    2015-09-24

    By means of fully kinetic simulations, we investigate electron acceleration during magnetic reconnection in a nonrelativistic proton–electron plasma with conditions similar to solar corona and flares. We demonstrate that reconnection leads to a nonthermally dominated electron acceleration with a power-law energy distribution in the nonrelativistic low-β regime but not in the high-β regime, where β is the ratio of the plasma thermal pressure and the magnetic pressure. The accelerated electrons contain most of the dissipated magnetic energy in the low-β regime. A guiding-center current description is used to reveal the role of electron drift motions during the bulk nonthermal energization.more » We find that the main acceleration mechanism is a Fermi-type acceleration accomplished by the particle curvature drift motion along the electric field induced by the reconnection outflows. Although the acceleration mechanism is similar for different plasma β, low-β reconnection drives fast acceleration on Alfvénic timescales and develops power laws out of thermal distribution. Thus, the nonthermally dominated acceleration resulting from magnetic reconnection in low-β plasma may have strong implications for the highly efficient electron acceleration in solar flares and other astrophysical systems.« less

  8. Nonthermally dominated electron acceleration during magnetic reconnection in a low-β plasma

    SciTech Connect

    Li, Xiaocan; Guo, Fan; Li, Hui; Li, Gang

    2015-09-24

    By means of fully kinetic simulations, we investigate electron acceleration during magnetic reconnection in a nonrelativistic proton–electron plasma with conditions similar to solar corona and flares. We demonstrate that reconnection leads to a nonthermally dominated electron acceleration with a power-law energy distribution in the nonrelativistic low-β regime but not in the high-β regime, where β is the ratio of the plasma thermal pressure and the magnetic pressure. The accelerated electrons contain most of the dissipated magnetic energy in the low-β regime. A guiding-center current description is used to reveal the role of electron drift motions during the bulk nonthermal energization. We find that the main acceleration mechanism is a Fermi-type acceleration accomplished by the particle curvature drift motion along the electric field induced by the reconnection outflows. Although the acceleration mechanism is similar for different plasma β, low-β reconnection drives fast acceleration on Alfvénic timescales and develops power laws out of thermal distribution. Thus, the nonthermally dominated acceleration resulting from magnetic reconnection in low-β plasma may have strong implications for the highly efficient electron acceleration in solar flares and other astrophysical systems.

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  10. NONTHERMALLY DOMINATED ELECTRON ACCELERATION DURING MAGNETIC RECONNECTION IN A LOW-β PLASMA

    SciTech Connect

    Li, Xiaocan; Li, Gang; Guo, Fan; Li, Hui

    2015-10-01

    By means of fully kinetic simulations, we investigate electron acceleration during magnetic reconnection in a nonrelativistic proton–electron plasma with conditions similar to solar corona and flares. We demonstrate that reconnection leads to a nonthermally dominated electron acceleration with a power-law energy distribution in the nonrelativistic low-β regime but not in the high-β regime, where β is the ratio of the plasma thermal pressure and the magnetic pressure. The accelerated electrons contain most of the dissipated magnetic energy in the low-β regime. A guiding-center current description is used to reveal the role of electron drift motions during the bulk nonthermal energization. We find that the main acceleration mechanism is a Fermi-type acceleration accomplished by the particle curvature drift motion along the electric field induced by the reconnection outflows. Although the acceleration mechanism is similar for different plasma β, low-β reconnection drives fast acceleration on Alfvénic timescales and develops power laws out of thermal distribution. The nonthermally dominated acceleration resulting from magnetic reconnection in low-β plasma may have strong implications for the  highly efficient electron acceleration in solar flares and other astrophysical systems.

  11. Acceleration of charged particles in magnetic reconnection Solar flares, the magnetosphere, and solar wind

    NASA Technical Reports Server (NTRS)

    Goldstein, M. L.; Matthaeus, W. H.; Ambrosiano, J. J.

    1986-01-01

    A possible source of free energy available for accelerating charged particles is conversion of magnetic energy to particle energy in reconnecting magnetic fields. Recent simulations using test particles suggests that reconnection may efficiently accelerate particles to the maximum energies that are observed in several astrophysical contexts. A simple analytic formula is used in conjunction with the simulation results to predict the maximum energy achievable in a particular plasma environment with the result that in solar flares reconnection is capable of accelerating particles to several GeV. In magnetospheric substorms the predicted maximum can reach several hundred keV, and near magnetic sector crossings in the solar wind the maximum energy can approach 100 keV.

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

    SciTech Connect

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

    2014-04-18

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

  13. Inside the Black Box: Magnetic Reconnection and the Magnetospheric Multiscale Mission

    NASA Astrophysics Data System (ADS)

    Cassak, P. A.

    2016-03-01

    The motivation for the recently launched Magnetospheric Multiscale mission is learning about the process of magnetic reconnection, especially the physics of what is called the diffusion region. The diffusion region is often treated as a black box but is the home of very important physics, which is of great significance to understanding space weather. This article is a brief review of what is known—and not known—about the diffusion region in magnetic reconnection, written for the broad space weather community and its stakeholders (with an appendix for readers interested in more technical matters). The focus is on the physics of magnetic reconnection and the diffusion region, why it has been challenging to study, how MMS will contribute, and how the community will benefit from its measurements.

  14. `Effective' collisions in weakly magnetized collisionless plasma: importance of Pitaevski's effect for magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Zelenyi, Lev M.; Artemyev, Anton V.

    2016-02-01

    In this paper we revisit the paradigm of space science turbulent dissipation traditionally considered as myth (Coroniti, Space Sci. Rev., vol. 42, 1985, pp. 399-410). We demonstrate that due to approach introduced by Pitaevskii (Sov. J. Expl Theor. Phys., vol. 44, 1963, pp. 969-979 (in Russian)) (the effect of a finite Larmor radius on a classical collision integral) dissipation induced by effective interaction with microturbulence produces a significant effect on plasma dynamics, especially in the vicinity of the reconnection region. We estimate the multiplication factor of collision frequency in the collision integral for short wavelength perturbations. For waves propagating transverse to the background magnetic field, this factor is approximately ρekx)2 an electron gyroradius and where kx a transverse wavenumber. We consider recent spacecraft observations in the Earth's magnetotail reconnection region to the estimate possible impact of this multiplication factor. For small-scale reconnection regions this factor can significantly increase the effective collision frequency produced both by lower-hybrid drift turbulence and by kinetic Alfvén waves. We discuss the possibility that the Pitaevskii's effect may be responsible for the excitation of a resistive electron tearing mode in thin current sheets formed in the outflow region of the primary X-line.

  15. Forced Reconnection in the Near Magnetotail: Onset and Energy Conversion in PIC and MHD Simulations

    NASA Technical Reports Server (NTRS)

    Birn, J.; Hesse, Michael

    2014-01-01

    Using two-dimensional particle-in-cell (PIC) together with magnetohydrodynamic (MHD) Q1 simulations of magnetotail dynamics, we investigate the evolution toward onset of reconnection and the subsequent energy transfer and conversion. In either case, reconnection onset is preceded by a driven phase, during which magnetic flux is added to the tail at the high-latitude boundaries, followed by a relaxation phase, during which the configuration continues to respond to the driving. The boundary deformation leads to the formation of thin embedded current sheets, which are bifurcated in the near tail, converging to a single sheet farther out in the MHD simulations. The thin current sheets in the PIC simulation are carried by electrons and are associated with a strong perpendicular electrostatic field, which may provide a connection to parallel potentials and auroral arcs and an ionospheric signal even prior to the onset of reconnection. The PIC simulation very well satisfies integral entropy conservation (intrinsic to ideal MHD) during this phase, supporting ideal ballooning stability. Eventually, the current intensification leads to the onset of reconnection, the formation and ejection of a plasmoid, and a collapse of the inner tail. The earthward flow shows the characteristics of a dipolarization front: enhancement of Bz, associated with a thin vertical electron current sheet in the PIC simulation. Both MHD and PIC simulations show a dominance of energy conversion from incoming Poynting flux to outgoing enthalpy flux, resulting in heating of the inner tail. Localized Joule dissipation plays only a minor role.

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

    NASA Astrophysics Data System (ADS)

    Fox, William

    2015-08-01

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

  17. On the electron dynamics during island coalescence in asymmetric magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Cazzola, E.; Innocenti, M. E.; Markidis, S.; Goldman, M. V.; Newman, D. L.; Lapenta, G.

    2015-09-01

    We present an analysis of the electron dynamics during rapid island merging in asymmetric magnetic reconnection. We consider a doubly periodic system with two asymmetric transitions. The upper layer is an asymmetric Harris sheet of finite width perturbed initially to promote a single reconnection site. The lower layer is a tangential discontinuity that promotes the formation of many X-points, separated by rapidly merging islands. Across both layers, the magnetic field and the density have a strong jump, but the pressure is held constant. Our analysis focuses on the consequences of electron energization during island coalescence. We focus first on the parallel and perpendicular components of the electron temperature to establish the presence of possible anisotropies and non-gyrotropies. Thanks to the direct comparison between the two different layers simulated, we can distinguish three main types of behavior characteristic of three different regions of interest. The first type represents the regions where traditional asymmetric reconnections take place without involving island merging. The second type of regions instead shows reconnection events between two merging islands. Finally, the third regions identify the regions between two diverging island and where typical signature of reconnection is not observed. Electrons in these latter regions additionally show a flat-top distribution resulting from the saturation of a two-stream instability generated by the two interacting electron beams from the two nearest reconnection points. Finally, the analysis of agyrotropy shows the presence of a distinct double structure laying all over the lower side facing the higher magnetic field region. This structure becomes quadrupolar in the proximity of the regions of the third type. The distinguishing features found for the three types of regions investigated provide clear indicators to the recently launched Magnetospheric Multiscale NASA mission for investigating magnetopause

  18. On the electron dynamics during island coalescence in asymmetric magnetic reconnection

    SciTech Connect

    Cazzola, E. Innocenti, M. E. Lapenta, G.; Markidis, S.; Goldman, M. V. Newman, D. L.

    2015-09-15

    We present an analysis of the electron dynamics during rapid island merging in asymmetric magnetic reconnection. We consider a doubly periodic system with two asymmetric transitions. The upper layer is an asymmetric Harris sheet of finite width perturbed initially to promote a single reconnection site. The lower layer is a tangential discontinuity that promotes the formation of many X-points, separated by rapidly merging islands. Across both layers, the magnetic field and the density have a strong jump, but the pressure is held constant. Our analysis focuses on the consequences of electron energization during island coalescence. We focus first on the parallel and perpendicular components of the electron temperature to establish the presence of possible anisotropies and non-gyrotropies. Thanks to the direct comparison between the two different layers simulated, we can distinguish three main types of behavior characteristic of three different regions of interest. The first type represents the regions where traditional asymmetric reconnections take place without involving island merging. The second type of regions instead shows reconnection events between two merging islands. Finally, the third regions identify the regions between two diverging island and where typical signature of reconnection is not observed. Electrons in these latter regions additionally show a flat-top distribution resulting from the saturation of a two-stream instability generated by the two interacting electron beams from the two nearest reconnection points. Finally, the analysis of agyrotropy shows the presence of a distinct double structure laying all over the lower side facing the higher magnetic field region. This structure becomes quadrupolar in the proximity of the regions of the third type. The distinguishing features found for the three types of regions investigated provide clear indicators to the recently launched Magnetospheric Multiscale NASA mission for investigating magnetopause

  19. Partially Ionized Plasma Three-Fluid Modeling of Magnetic Reconnection in the Sun Chromosphere

    NASA Astrophysics Data System (ADS)

    Alvarez Laguna, A.; Lani, A.; Mansour, N. N.; Kosovichev, A. G.; Poedts, D. S.

    2015-12-01

    Magnetic reconnection is present in most of the unsteady and eruptive phenomena in the Sun atmosphere, including Coronal Mass Ejections (CMEs) and solar flares. Also, it occurs in the chromosphere, bringing about chromospheric jets and spicules and being considered a likely mechanism to play an important role in heating up the corona. In this work, we present a computational model that simulates magnetic reconnection in the Sun chromosphere using a three-fluid model (electrons + ions + neutrals). The model treats separately ions, electrons and neutrals, considering mass, momentum and energy conservation for each fluid. The fluids interact among each other by means of collisions and chemical reactions. The charged particles heat fluxes are anisotropic with the magnetic field, following Braginskii's description. This model also considers non-equilibrium partial ionization effects including electron impact ionization, radiative recombination reactions and charge exchange. The electromagnetic field evolution is represented by the full Maxwell's equations, allowing for high frequency waves disregarded by the MHD approximation. Previous two-fluid simulations showed that the dynamics of ions and neutrals are decoupled during the reconnection process when the width of the current sheet becomes comparable to the ion scales. Also, the effect of the chemical non-equilibrium in the reconnection region plays a crucial role, yielding faster reconnection rates. We extended these simulations with a three-fluid model that considers separately the dynamics of electrons. This new model provides a better description of the complex dynamics taking place during the reconnection, both in Sweet-Parker reconnections and during the tearing instability. The results are compared with the two-fluid simulations.

  20. Plasma behavior during energetic electron streaming events further evidence for substorm-associated magnetic reconnection

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

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

  1. Exact energy principle in magnetic reconnection for current-sheet models.

    PubMed

    Yoon, Peter H; Lui, Anthony T Y

    2005-05-06

    On the basis of an exact nonlinear energy principle, it is shown that the change in magnetic topology (i.e., reconnection) in a finite-domain system leads to the conversion of magnetic field energy to particle energy. However, it is also shown that the conversion efficiency gradually disappears as the system size increases. This principle is demonstrated with model current-sheet equilibria including Harris and Fadeev solutions, as well as a current-sheet equilibrium which contains a singular current layer. The finding that energy conversion in reconnection is highly dependent on the system size may have an important implication for numerical simulations performed under finite geometry.

  2. Exact Energy Principle in Magnetic Reconnection for Current-Sheet Models

    SciTech Connect

    Yoon, Peter H.; Lui, Anthony T.Y.

    2005-05-06

    On the basis of an exact nonlinear energy principle, it is shown that the change in magnetic topology (i.e., reconnection) in a finite-domain system leads to the conversion of magnetic field energy to particle energy. However, it is also shown that the conversion efficiency gradually disappears as the system size increases. This principle is demonstrated with model current-sheet equilibria including Harris and Fadeev solutions, as well as a current-sheet equilibrium which contains a singular current layer. The finding that energy conversion in reconnection is highly dependent on the system size may have an important implication for numerical simulations performed under finite geometry.

  3. Comparison between hybrid and fully kinetic models of asymmetric magnetic reconnection: Coplanar and guide field configurations

    SciTech Connect

    Aunai, Nicolas; Hesse, Michael; Kuznetsova, Maria; Black, Carrie; Evans, Rebekah; Zenitani, Seiji; Smets, Roch

    2013-02-15

    Magnetic reconnection occurring in collisionless environments is a multi-scale process involving both ion and electron kinetic processes. Because of their small mass, the electron scales are difficult to resolve in numerical and satellite data, it is therefore critical to know whether the overall evolution of the reconnection process is influenced by the kinetic nature of the electrons, or is unchanged when assuming a simpler, fluid, electron model. This paper investigates this issue in the general context of an asymmetric current sheet, where both the magnetic field amplitude and the density vary through the discontinuity. A comparison is made between fully kinetic and hybrid kinetic simulations of magnetic reconnection in coplanar and guide field systems. The models share the initial condition but differ in their electron modeling. It is found that the overall evolution of the system, including the reconnection rate, is very similar between both models. The best agreement is found in the guide field system, which confines particle better than the coplanar one, where the locality of the moments is violated by the electron bounce motion. It is also shown that, contrary to the common understanding, reconnection is much faster in the guide field system than in the coplanar one. Both models show this tendency, indicating that the phenomenon is driven by ion kinetic effects and not electron ones.

  4. Investigation of magnetic reconnection during a sawtooth crash in a high temperature tokamak

    SciTech Connect

    Yamada, M.; Pomphrey, N.; Budney, R.; Macickam, J.; Levinton, F.; Nagayama, Y.

    1994-09-01

    This paper reports on a recent laboratory investigation on magnetic reconnection in high temperature tokamak plasmas. The motional stark effect(MSE) diagnostic is employed to measure the pitch angle of magnetic field lines, and hence the q profile. An analytical expression that relates pitch angle to q profile has been developed for a toroidal plasma with circular cross section. During the crash phase of sawtooth oscillations in the plasma discharges, the ECE (electron cyclotron emission) diagnostic measures a fast flattening of the 2-D electron temperature profile in a poloidal plane, an observation consistent with the Kadomtsev reconnection theory. On the other hand motional the MSE measurements indicate that central q values do not relax to unity after the crash, but increase only by 5-10%, typically from 0.7 to 0.75. The latter result is in contradiction with the models of Kadomtsev and/or Wesson. The present study addresses this puzzle by a simultaneous analysis of electron temperature and q profile evolutions. Based on a heuristic model for the magnetic reconnection during the sawtooth crash, the small change of q, i.e. partial reconnection, is attributed to the precipitous drop of pressure gradients which drive the instability and the reconnection process as well as flux conserving plasma dynamics.

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

    NASA Astrophysics Data System (ADS)

    Liu, Chang; Fox, Will; Bhattacharjee, Amitava

    2016-10-01

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

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

    SciTech Connect

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

    2015-02-04

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

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

    DOE PAGES

    Rosenberg, M. J.; Li, C. K.; Fox, W.; ...

    2015-02-04

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

  8. 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

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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

  10. Observed Aspects of Reconnection in Solar Eruptions

    NASA Astrophysics Data System (ADS)

    Moore, Ronald L.; Sterling, Alphonse C.; Gary, G. Allen; Cirtain, Jonathan W.; Falconer, David A.

    2011-10-01

    The observed magnetic field configuration and signatures of reconnection in the large solar magnetic eruptions that make major flares and coronal mass ejections and in the much smaller magnetic eruptions that make X-ray jets are illustrated with cartoons and representative observed eruptions. The main reconnection signatures considered are the imaged bright emission from the heated plasma on reconnected field lines. In any of these eruptions, large or small, the magnetic field that drives the eruption and/or that drives the buildup to the eruption is initially a closed bipolar arcade. From the form and configuration of the magnetic field in and around the driving arcade and from the development of the reconnection signatures in coordination with the eruption, we infer that (1) at the onset of reconnection the reconnection current sheet is small compared to the driving arcade, and (2) the current sheet can grow to the size of the driving arcade only after reconnection starts and the unleashed erupting field dynamically forces the current sheet to grow much larger, building it up faster than the reconnection can tear it down. We conjecture that the fundamental reason the quasi-static pre-eruption field is prohibited from having a large current sheet is that the magnetic pressure is much greater than the plasma pressure in the chromosphere and low corona in eruptive solar magnetic fields.

  11. 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.

  12. 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.

  13. Formation of hard power laws in the energetic particle spectra resulting from relativistic magnetic reconnection.

    PubMed

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

    2014-10-10

    Using fully kinetic simulations, we demonstrate that magnetic reconnection in relativistic plasmas is highly efficient at accelerating particles through a first-order Fermi process resulting from the curvature drift of particles in the direction of the electric field induced by the relativistic flows. This mechanism gives rise to the formation of hard power-law spectra in parameter regimes where the energy density in the reconnecting field exceeds the rest mass energy density σ ≡ B(2)/(4πnm(e)c(2))>1 and when the system size is sufficiently large. In the limit σ ≫ 1, the spectral index approaches p = 1 and most of the available energy is converted into nonthermal particles. A simple analytic model is proposed which explains these key features and predicts a general condition under which hard power-law spectra will be generated from magnetic reconnection.

  14. Debye scale turbulence within the electron diffusion layer during magnetic reconnection

    SciTech Connect

    Jara-Almonte, J.; Ji, H.

    2014-03-15

    During collisionless, anti-parallel magnetic reconnection, the electron diffusion layer is the region of both fieldline breaking and plasma mixing. Due to the in-plane electrostatic fields associated with collisionless reconnection, the inflowing plasmas are accelerated towards the X-line and form counter-streaming beams within the unmagnetized diffusion layer. This configuration is inherently unstable to in-plane electrostatic streaming instabilities provided that there is sufficient scale separation between the Debye length λ{sub D} and the electron skin depth c/ω{sub pe}. This scale separation has hitherto not been well resolved in kinetic simulations. Using both 2D fully kinetic simulations and a simple linear model, we demonstrate that these in-plane streaming instabilities generate Debye scale turbulence within the electron diffusion layer at electron temperatures relevant to magnetic reconnection both in the magnetosphere and in laboratory experiments.

  15. Orientation of X Lines in Asymmetric Magnetic Reconnection-Mass Ratio Dependency

    NASA Technical Reports Server (NTRS)

    Liu, Yi-Hsin; Hesse, M.; Kuznetsova, M.

    2015-01-01

    Using fully kinetic simulations, we study the X line orientation of magnetic reconnection in an asymmetric configuration. A spatially localized perturbation is employed to induce a single X line, which has sufficient freedom to choose its orientation in three-dimensional systems. The effect of ion to electron mass ratio is investigated, and the X line appears to bisect the magnetic shear angle across the current sheet in the large mass ratio limit. The orientation can generally be deduced by scanning through the corresponding 2-D simulations to find the reconnection plane that maximizes the peak reconnection electric field. The deviation from the bisection angle in the lower mass ratio limit is consistent with the orientation shift of the most unstable linear tearing mode in an electron-scale current sheet.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  17. EVIDENCE OF MAGNETIC FIELD SWITCH-OFF IN COLLISIONLESS MAGNETIC RECONNECTION

    SciTech Connect

    Innocenti, M. E.; Lapenta, G.; Goldman, M.; Newman, D.; Markidis, S. E-mail: giovanni.lapenta@wis.kuleuven.be E-mail: david.newman@colorado.edu

    2015-09-10

    The long-term evolution of large domain particle-in-cell simulations of collisionless magnetic reconnection is investigated following observations that show two possible outcomes for collisionless reconnection: toward a Petschek-like configuration or toward multiple X points. In the present simulation, a mixed scenario develops. At earlier time, plasmoids are emitted, disrupting the formation of Petschek-like structures. Later, an almost stationary monster plasmoid forms, preventing the emission of other plasmoids. A situation reminiscent of Petschek’s switch-off then ensues. Switch-off is obtained through a slow shock/rotational discontinuity compound structure. Two external slow shocks (SS) located at the separatrices reduce the in-plane tangential component of the magnetic field, but not to zero. Two transitions reminiscent of rotational discontinuities (RD) in the internal part of the exhaust then perform the final switch-off. Both the SS and the RD are characterized through analysis of their Rankine–Hugoniot jump conditions. A moderate guide field is used to suppress the development of the firehose instability in the exhaust.

  18. Evidence of Magnetic Field Switch-off in Collisionless Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Innocenti, M. E.; Goldman, M.; Newman, D.; Markidis, S.; Lapenta, G.

    2015-09-01

    The long-term evolution of large domain particle-in-cell simulations of collisionless magnetic reconnection is investigated following observations that show two possible outcomes for collisionless reconnection: toward a Petschek-like configuration or toward multiple X points. In the present simulation, a mixed scenario develops. At earlier time, plasmoids are emitted, disrupting the formation of Petschek-like structures. Later, an almost stationary monster plasmoid forms, preventing the emission of other plasmoids. A situation reminiscent of Petschek’s switch-off then ensues. Switch-off is obtained through a slow shock/rotational discontinuity compound structure. Two external slow shocks (SS) located at the separatrices reduce the in-plane tangential component of the magnetic field, but not to zero. Two transitions reminiscent of rotational discontinuities (RD) in the internal part of the exhaust then perform the final switch-off. Both the SS and the RD are characterized through analysis of their Rankine-Hugoniot jump conditions. A moderate guide field is used to suppress the development of the firehose instability in the exhaust.

  19. Magnetic Reconnection Instabilities in Soft-Gamma Repeaters

    NASA Astrophysics Data System (ADS)

    Heyl, Jeremy S.; Gill, Ramandeep

    2015-01-01

    We examine an external trigger mechanism that gives rise to the intense soft gamma-ray repeater (SGR) giant flares. Out of the three giant flares, two showcased the existence of a precursor, which we show to have had initiated the main flare. We develop a reconnection model based on the hypothesis that shearing motion of the footpoints causes the materialization of a Sweet-Parker current layer in the magnetosphere. The thinning of this oscopic layer due to the development of an embedded super-hot turbulent current layer switches on the impulsive Hall reconnection, which powers the giant flare. We show that the thinning time is on the order of the pre-flare quiescent time.

  20. The Formation of Magnetic Depletions and Flux Annihilation Due to Reconnection in the Heliosheath

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

    The misalignment of the solar rotation axis and the magnetic axis of the Sun produces a periodic reversal of the Parker spiral magnetic field and the sectored solar wind. The compression of the sectors is expected to lead to reconnection in the heliosheath (HS). We present particle-in-cell simulations of the sectored HS that reflect the plasma environment along the Voyager 1 and 2 trajectories, specifically including unequal positive and negative azimuthal magnetic flux as seen in the Voyager data. Reconnection proceeds on individual current sheets until islands on adjacent current layers merge. At late time, bands of the dominant flux survive, separated by bands of deep magnetic field depletion. The ambient plasma pressure supports the strong magnetic pressure variation so that pressure is anticorrelated with magnetic field strength. There is little variation in the magnetic field direction across the boundaries of the magnetic depressions. At irregular intervals within the magnetic depressions are long-lived pairs of magnetic islands where the magnetic field direction reverses so that spacecraft data would reveal sharp magnetic field depressions with only occasional crossings with jumps in magnetic field direction. This is typical of the magnetic field data from the Voyager spacecraft. Voyager 2 data reveal that fluctuations in the density and magnetic field strength are anticorrelated in the sector zone, as expected from reconnection, but not in unipolar regions. The consequence of the annihilation of subdominant flux is a sharp reduction in the number of sectors and a loss in magnetic flux, as documented from the Voyager 1 magnetic field and flow data.

  1. ON THE ROLE OF FAST MAGNETIC RECONNECTION IN ACCRETING BLACK HOLE SOURCES

    SciTech Connect

    Singh, C. B.; De Gouveia Dal Pino, E. M.; Kadowaki, L. H. S. E-mail: dalpino@iag.usp.br

    2015-01-30

    We attempt to explain the observed radio and gamma-ray emission produced in the surroundings of black holes by employing a magnetically dominated accretion flow model and fast magnetic reconnection triggered by turbulence. In earlier work, a standard disk model was used and we refine the model by focusing on the sub-Eddington regime to address the fundamental plane of black hole activity. The results do not change substantially with regard to previous work, ensuring that the details of accretion physics are not relevant in the magnetic reconnection process occurring in the corona. Rather, our work puts fast magnetic reconnection events as a powerful mechanism operating in the core region near the jet base of black hole sources on more solid ground. For microquasars and low-luminosity active galactic nuclei, the observed correlation between radio emission and the mass of the sources can be explained by this process. The corresponding gamma-ray emission also seems to be produced in the same core region. On the other hand, emission from blazars and gamma-ray bursts cannot be correlated to core emission based on fast reconnection.

  2. Rapid magnetic reconnection in the Earth's magnetosphere mediated by whistler waves.

    PubMed

    Deng, X H; Matsumoto, H

    2001-03-29

    Magnetic reconnection has a crucial role in a variety of plasma environments in providing a mechanism for the fast release of stored magnetic energy. During reconnection the plasma forms a 'magnetic nozzle', like the nozzle of a hose, and the rate is controlled by how fast plasma can flow out of the nozzle. But the traditional picture of reconnection has been unable to explain satisfactorily the short timescales associated with the energy release, because the flow is mediated by heavy ions with a slow resultant velocity. Recent theoretical work has suggested that the energy release is instead mediated by electrons in waves called 'whistlers', which move much faster for a given perturbation of the magnetic field because of their smaller mass. Moreover, the whistler velocity and associated plasma velocity both increase as the 'nozzle' becomes narrower. A narrower nozzle therefore no longer reduces the total plasma flow-the outflow is independent of the size of the nozzle. Here we report observations demonstrating that reconnection in the magnetosphere is driven by whistlers, in good agreement with the theoretical predictions.

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  5. Study of Electron-scale Dissipation near the X-line During Magnetic Reconnection in a Laboratory Plasma

    NASA Astrophysics Data System (ADS)

    Ji, H.; Yoo, J.; Dorfman, S. E.; Jara-Almonte, J.; Yamada, M.; Swanson, C.; Daughton, W. S.; Roytershteyn, V.; Kuwahata, A.; Ii, T.; Inomoto, M.; Ono, Y.; von Stechow, A.; Grulke, O.; Phan, T.; Mozer, F.; Bale, S. D.

    2013-12-01

    Despite its disruptive influences on the large-scale structures of space and solar plasmas, the crucial topological changes and associated dissipation during magnetic reconnection take place only near an X-line within thin singular layers. In the modern collisionless models where electrons and ions are allowed to move separately, it has been predicted that ions exhaust efficiently through a thicker, ion-scale dissipative layer while mobile electrons can evacuate through a thinner, electron-scale dissipation layer, allowing for efficient release of magnetic energy. While ion dissipation layers have been frequently detected, the existence of election layers near the X-line and the associated dissipation structures and mechanisms are still an open question, and will be a main subject of the coming MMS mission. In this presentation, we will summarize our efforts in the past a few years to study electron-scale dissipation in a well-controlled and well-diagnosed reconnecting current sheet in a laboratory plasma, with close comparisons with the state-of-the-art, 2D and 3D fully kinetic simulations. Key results include: (1) positive identification of electromagnetic waves detected at the current sheet center as long wave-length, lower-hybrid drift instabilities (EM-LHDI), (2) however, there is strong evidence that this EM-LHDI cannot provide the required force to support the reconnection electric field, (3) detection of 3D flux-rope-like magnetic structures during impulsive reconnection events, and (4) electrons are heated through non-classical mechanisms near the X-line with a small but clear temperature anisotropy. These results, unfortunately, do not resolve the outstanding discrepancies on electron layer thickness between best available experiments and fully kinetic simulations. To make further progress, we are continuously pushing in the both experimental and numerical frontiers. Experimentally, we started investigations on EM-LHDI and electron heating as a function

  6. A FLUX ROPE NETWORK AND PARTICLE ACCELERATION IN THREE-DIMENSIONAL RELATIVISTIC MAGNETIC RECONNECTION

    SciTech Connect

    Kagan, Daniel; Milosavljevic, Milos; Spitkovsky, Anatoly

    2013-09-01

    We investigate magnetic reconnection and particle acceleration in relativistic pair plasmas with three-dimensional particle-in-cell simulations of a kinetic-scale current sheet in a periodic geometry. We include a guide field that introduces an inclination between the reconnecting field lines and explore outside-of-the-current sheet magnetizations that are significantly below those considered by other authors carrying out similar calculations. Thus, our simulations probe the transitional regime in which the magnetic and plasma pressures are of the same order of magnitude. The tearing instability is the dominant mode in the current sheet for all guide field strengths, while the linear kink mode is less important even without the guide field, except in the lower magnetization case. Oblique modes seem to be suppressed entirely. In its nonlinear evolution, the reconnection layer develops a network of interconnected and interacting magnetic flux ropes. As smaller flux ropes merge into larger ones, the reconnection layer evolves toward a three-dimensional, disordered state in which the resulting flux rope segments contain magnetic substructure on plasma skin depth scales. Embedded in the flux ropes, we detect spatially and temporally intermittent sites of dissipation reflected in peaks in the parallel electric field. Magnetic dissipation and particle acceleration persist until the end of the simulations, with simulations with higher magnetization and lower guide field strength exhibiting greater and faster energy conversion and particle energization. At the end of our largest simulation, the particle energy spectrum attains a tail extending to high Lorentz factors that is best modeled with a combination of two additional thermal components. We confirm that the primary energization mechanism is acceleration by the electric field in the X-line region. The highest-energy positrons (electrons) are moderately beamed with median angles {approx}30 Degree-Sign -40 Degree

  7. Using radiative energy losses to constrain the magnetization and magnetic reconnection rate at the base of black hole jets

    NASA Astrophysics Data System (ADS)

    Potter, William J.

    2017-02-01

    We calculate the severe radiative energy losses which occur at the base of black hole jets using a relativistic fluid jet model, including in situ acceleration of non-thermal leptons by magnetic reconnection. Our results demonstrate that including a self-consistent treatment of radiative energy losses is necessary to perform accurate magnetohydrodynamic simulations of powerful jets and that jet spectra calculated via post-processing are liable to vastly overestimate the amount of non-thermal emission. If no more than 95 per cent of the initial total jet power is radiated away by the plasma travels as it travels along the length of the jet, we can place a lower bound on the magnetization of the jet plasma at the base of the jet. For typical powerful jets, we find that the plasma at the jet base is required to be highly magnetized, with at least 10 000 times more energy contained in magnetic fields than in non-thermal leptons. Using a simple power-law model of magnetic reconnection, motivated by simulations of collisionless reconnection, we determine the allowed range of the large-scale average reconnection rate along the jet, by restricting the total radiative energy losses incurred and the distance at which the jet first comes into equipartition. We calculate analytic expressions for the cumulative radiative energy losses due to synchrotron and inverse-Compton emission along jets, and derive analytic formulae for the constraint on the initial magnetization.

  8. Photoinduced magnetic force between nanostructures

    NASA Astrophysics Data System (ADS)

    Guclu, Caner; Tamma, Venkata Ananth; Wickramasinghe, Hemantha Kumar; Capolino, Filippo

    2015-12-01

    Photoinduced magnetic force between nanostructures, at optical frequencies, is investigated theoretically. Till now optical magnetic effects were not used in scanning probe microscopy because of the vanishing natural magnetism with increasing frequency. On the other hand, artificial magnetism in engineered nanostructures led to the development of measurable optical magnetism. Here two examples of nanoprobes that are able to generate strong magnetic dipolar fields at optical frequency are investigated: first, an ideal magnetically polarizable nanosphere and then a circular cluster of silver nanospheres that has a looplike collective plasmonic resonance equivalent to a magnetic dipole. Magnetic forces are evaluated based on nanostructure polarizabilities, i.e., induced magnetic dipoles, and magnetic-near field evaluations. As an initial assessment on the possibility of a magnetic nanoprobe to detect magnetic forces, we consider two identical magnetically polarizable nanoprobes and observe magnetic forces on the order of piconewtons, thereby bringing it within detection limits of conventional atomic force microscopes at ambient pressure and temperature. The detection of magnetic force is a promising method in studying optical magnetic transitions that can be the basis of innovative spectroscopy applications.

  9. THE MECHANISMS OF ELECTRON ACCELERATION DURING MULTIPLE X LINE MAGNETIC RECONNECTION WITH A GUIDE FIELD

    SciTech Connect

    Wang, Huanyu; Lu, Quanming; Huang, Can; Wang, Shui

    2016-04-20

    The interactions between magnetic islands are considered to play an important role in electron acceleration during magnetic reconnection. In this paper, two-dimensional particle-in-cell simulations are performed to study electron acceleration during multiple X line reconnection with a guide field. Because the electrons remain almost magnetized, we can analyze the contributions of the parallel electric field, Fermi, and betatron mechanisms to electron acceleration during the evolution of magnetic reconnection through comparison with a guide-center theory. The results show that with the magnetic reconnection proceeding, two magnetic islands are formed in the simulation domain. Next, the electrons are accelerated by both the parallel electric field in the vicinity of the X lines and the Fermi mechanism due to the contraction of the two magnetic islands. Then, the two magnetic islands begin to merge into one, and, in such a process, the electrons can be accelerated by both the parallel electric field and betatron mechanisms. During the betatron acceleration, the electrons are locally accelerated in the regions where the magnetic field is piled up by the high-speed flow from the X line. At last, when the coalescence of the two islands into one big island finishes, the electrons can be further accelerated by the Fermi mechanism because of the contraction of the big island. With the increase of the guide field, the contributions of the Fermi and betatron mechanisms to electron acceleration become less and less important. When the guide field is sufficiently large, the contributions of the Fermi and betatron mechanisms are almost negligible.

  10. Perpendicular Localization of Electron Holes by Spatially Inhomogeneous Flows During Magnetic Reconnection*

    NASA Astrophysics Data System (ADS)

    Newman, D. L.; Goldman, M. V.

    2008-12-01

    Bipolar fields signaling the presence of electron phase space holes have been observed in situ by satellites near regions of magnetic reconnection in Earth's magnetopause and magnetotail. In order to identify possible origins for such holes, a recent numerical study [1] employed 1D and 2D electrostatic Vlasov simulations initialized with electron and ion distributions taken from 2D electromagnetic Particle in Cell (PIC) simulations of magnetic reconnection. Both electron-electron instabilities along the X-line and electron-ion (i.e., Buneman) instabilities along the separatrix were found to be viable sources of electron holes. However, long-lived coherent Buneman-driven holes only formed when the destabilizing current was restricted to a narrow channel perpendicular to the local magnetic field vector B. In this presentation we extend the 2D Vlasov study of electron holes driven by unstable distributions to include both e-e and e-i instabilities localized in the direction perpendicular to B. Emphasis will be placed on how the ion/electron mass and temperature ratios (mi/me and Ti/Te) and the magnetization ratios (Ωe/ωe and Ωi/ωi) influence the properties of the resulting electron holes, including their spatial size and aspect ratio. Distributions from recent implicit PIC reconnection simulations [2] will be used to guide the initialization of the Vlasov simulations. *Research supported by NASA, NSF, and DOE. [1] M. V. Goldman, D. L. Newman, and P. L. Pritchett, "Vlasov Simulations of Electron Holes Driven by Particle Distributions from PIC Reconnection Simulations with a Guide Field," submitted to Geophys.~Res.~Lett. (2008). [2] A. Divin, G. Lapenta, D. L. Newman and M. V. Goldman, "Implicit PIC Simulations of Guide Field Magnetic Reconnection," this meeting.

  11. Cold ion demagnetization near the X-line of magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Toledo-Redondo, Sergio; André, Mats; Khotyaintsev, Yuri V.; Vaivads, Andris; Walsh, Andrew; Li, Wenya; Graham, Daniel B.; Lavraud, Benoit; Masson, Arnaud; Aunai, Nicolas; Divin, Andrey; Dargent, Jeremy; Fuselier, Stephen; Gershman, Daniel J.; Dorelli, John; Giles, Barbara; Avanov, Levon; Pollock, Craig; Saito, Yoshifumi; Moore, Thomas E.; Coffey, Victoria; Chandler, Michael O.; Lindqvist, Per-Arne; Torbert, Roy; Russell, Christopher T.

    2016-07-01

    Although the effects of magnetic reconnection in magnetospheres can be observed at planetary scales, reconnection is initiated at electron scales in a plasma. Surrounding the electron diffusion region, there is an Ion-Decoupling Region (IDR) of the size of the ion length scales (inertial length and gyroradius). Reconnection at the Earth's magnetopause often includes cold magnetospheric (few tens of eV), hot magnetospheric (10 keV), and magnetosheath (1 keV) ions, with different gyroradius length scales. We report observations of a subregion inside the IDR of the size of the cold ion population gyroradius (˜15 km) where the cold ions are demagnetized and accelerated parallel to the Hall electric field. Outside the subregion, cold ions follow the E × B motion together with electrons, while hot ions are demagnetized. We observe a sharp cold ion density gradient separating the two regions, which we identify as the cold and hot IDRs.

  12. OBSERVATION OF SUPRATHERMAL ELECTRONS DURING MAGNETIC RECONNECTION AT THE SAWTOOTH INSTABILITY IN DIII-D TOKAMAK

    SciTech Connect

    SAVRUKHIN,RV; STRAIT,EJ

    2002-11-01

    OAK A271 OBSERVATION OF SUPRATHERMAL ELECTRONS DURING MAGNETIC RECONNECTION AT THE SAWTOOTH INSTABILITY IN DIII-D TOKAMAK. Intense bursts of x-ray and electron cyclotron emission are observed during sawtooth instabilities in high-temperature plasmas in the DIII-D tokamak. The bursts are initiated around the X-point of the m = 1, n = 1 magnetic island at the beginning of the sawtooth crash and are displaced to larger radii later during the temperature collapse. Reconstruction of the magnetic configuration using motional Stark effect (MSE) data and numerical simulations indicates that the bursts can be connected with suprathermal electrons (E{sub r} {approx} 30-40 keV) generated during reconnection of the magnetic field around the q = 1 surface.

  13. Charge-to-mass-ratio-dependent ion heating during magnetic reconnection in the MST RFP

    SciTech Connect

    Kumar, S. T. A.; Almagri, A. F.; Den Hartog, D. J.; Nornberg, M. D.; Sarff, J. S.; Terry, P. W.; Craig, D.

    2013-05-15

    Temperature evolution during magnetic reconnection has been spectroscopically measured for various ion species in a toroidal magnetized plasma. Measurements are made predominantly in the direction parallel to the equilibrium magnetic field. It is found that the increase in parallel ion temperature during magnetic reconnection events increases with the charge-to-mass ratio of the ion species. This trend can be understood if the heating mechanism is anisotropic, favoring heating in the perpendicular degree of freedom, with collisional relaxation of multiple ion species. The charge-to-mass ratio trend for the parallel temperature derives from collisional isotropization. This result emphasizes that collisional isotropization and energy transfer must be carefully modeled when analyzing ion heating measurements and comparing to theoretical predictions.

  14. Laboratory study of magnetic reconnection with a guide field and density asymmetry across the current sheet

    NASA Astrophysics Data System (ADS)

    Zhu, Hongxuan; Yoo, J.; Ji, H.; Jara-Almonte, J.; Fox, W.; Yamada, M.

    2016-10-01

    It has been known that the diamagnetic drift can stabilize the tearing mode, which is used to explain incomplete reconnection during sawtooth oscillations in Tokamaks. Swisdak et al. propose that reconnection with a strong guide field and pressure asymmetry is suppressed when the relative drift speed between ions and electrons along the outflow direction exceeds the upstream Alfvén speed. Swisdak's argument has been supported by space observations, but the exact mechanism of suppression has not been conclusively verified. We will conduct experiments in MRX to study suppression of reconnection with a strong guide field and density asymmetry. We will apply a guide field strength of about 2-3 times of the reconnecting field and achieve a density ratio up to 10. By systematically changing the guide field strength, we will investigate how the electron diamagnetic drift can affect profiles of the magnetic/electric field and patterns of the ion/electron flow. Finally, we will study how these modified field profiles and flow patterns contribute to reduction of the reconnection rate. This work is supported by DOE Contract No. DE-AC0209CH11466.

  15. IMAGING AND SPECTROSCOPIC OBSERVATIONS OF MAGNETIC RECONNECTION AND CHROMOSPHERIC EVAPORATION IN A SOLAR FLARE

    SciTech Connect

    Tian, Hui; Reeves, Katharine K.; Raymond, John C.; Chen, Bin; Murphy, Nicholas A.; Li, Gang; Guo, Fan; Liu, Wei

    2014-12-20

    Magnetic reconnection is believed to be the dominant energy release mechanism in solar flares. The standard flare model predicts both downward and upward outflow plasmas with speeds close to the coronal Alfvén speed. Yet, spectroscopic observations of such outflows, especially the downflows, are extremely rare. With observations of the newly launched Interface Region Imaging Spectrograph (IRIS), we report the detection of a greatly redshifted (∼125 km s{sup –1} along the line of sight) Fe XXI 1354.08 Å emission line with a ∼100 km s{sup –1} nonthermal width at the reconnection site of a flare. The redshifted Fe XXI feature coincides spatially with the loop-top X-ray source observed by RHESSI. We interpret this large redshift as the signature of downward-moving reconnection outflow/hot retracting loops. Imaging observations from both IRIS and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory also reveal the eruption and reconnection processes. Fast downward-propagating blobs along these loops are also found from cool emission lines (e.g., Si IV, O IV, C II, Mg II) and images of AIA and IRIS. Furthermore, the entire Fe XXI line is blueshifted by ∼260 km s{sup –1} at the loop footpoints, where the cool lines mentioned above all exhibit obvious redshift, a result that is consistent with the scenario of chromospheric evaporation induced by downward-propagating nonthermal electrons from the reconnection site.

  16. Particle acceleration during magnetic reconnection in a low-beta pair plasma

    SciTech Connect

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

    2016-04-29

    Plasma energization through magnetic reconnection in the magnetically dominated regime featured by low plasma beta (β=8πnkT0/B2 <<1) and/or high magnetization (σ=B2/(4πnmc2)>>1) is important in a series of astrophysical systems such as solar flares, pulsar wind nebula, and relativistic jets from black holes. In this paper, we review the recent progress on kinetic simulations of this process and further discuss plasma dynamics and particle acceleration in a low-β reconnection layer that consists of electron–positron pairs. We also examine the effect of different initial thermal temperatures on the resulting particle energy spectra. While earlier papers have concluded that the spectral index is smaller for higher σ, our simulations show that the spectral index approaches p = 1 for sufficiently low plasma β, even if σ~1. Since this predicted spectral index in the idealized limit is harder than most observations, it is important to consider effects that can lead to a softer spectrum such as open boundary simulations. Here, we also remark that the effects of three-dimensional reconnection physics and turbulence on reconnection need to be addressed in the future.

  17. The Rate of Flux Pile-up Magnetic Reconnection in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Litvinenko, Y. E.

    2000-05-01

    The rate of two-dimensional flux pile-up magnetic reconnection is known to be severely limited by gas pressure in a low-beta plasma of the solar corona. For a two-dimensional stagnation point flow with nonzero vorticity, for example, the rate cannot exceed the Sweet-Parker scaling. The limitation should be less restrictive, however, for three-dimensional flux pile-up. This paper examines the maximum rate of three-dimensional pile-up reconnection in the approximation of reduced magnetohydrodynamics (RMHD), which is valid in the solar coronal loops. Gas pressure effects are ignored in RMHD, but a similar limitation on the rate of magnetic merging exists. Both the magnetic energy dissipation rate and the reconnection electric field are shown to increase by several orders of magnitude in RMHD as compared with strictly two-dimensional pile-up. This is enough to explain small solar flares and slow coronal transients with energy release rates of order 1025 - 1026 erg s-1, as well as heating of quiet coronal loops. Notably, the reconnection electric field is several orders of magnitude greater than the Dreicer field, hence it can efficiently accelerate charged particles in flares. This work was supported by NSF grant ATM-9813933.

  18. Particle acceleration during magnetic reconnection in a low-beta pair plasma

    DOE PAGES

    Guo, Fan; Li, Hui; Daughton, William; ...

    2016-04-29

    Plasma energization through magnetic reconnection in the magnetically dominated regime featured by low plasma beta (β=8πnkT0/B2 <<1) and/or high magnetization (σ=B2/(4πnmc2)>>1) is important in a series of astrophysical systems such as solar flares, pulsar wind nebula, and relativistic jets from black holes. In this paper, we review the recent progress on kinetic simulations of this process and further discuss plasma dynamics and particle acceleration in a low-β reconnection layer that consists of electron–positron pairs. We also examine the effect of different initial thermal temperatures on the resulting particle energy spectra. While earlier papers have concluded that the spectral index ismore » smaller for higher σ, our simulations show that the spectral index approaches p = 1 for sufficiently low plasma β, even if σ~1. Since this predicted spectral index in the idealized limit is harder than most observations, it is important to consider effects that can lead to a softer spectrum such as open boundary simulations. Here, we also remark that the effects of three-dimensional reconnection physics and turbulence on reconnection need to be addressed in the future.« less

  19. On the occurrence of magnetic reconnection equatorward of the cusps at the Earth's magnetopause during northward IMF conditions

    NASA Astrophysics Data System (ADS)

    Trattner, K. J.; Thresher, S.; Trenchi, L.; Fuselier, S. A.; Petrinec, S. M.; Peterson, W. K.; Marcucci, M. F.

    2017-01-01

    Magnetic reconnection changes the topology of magnetic field lines. This process is most readily observable with in situ instrumentation at the Earth's magnetopause as it creates open magnetic field lines to allow energy and momentum flux to flow from the solar wind to the magnetosphere. Most models use the direction of the interplanetary magnetic field (IMF) to determine the location of these magnetopause entry points, known as reconnection lines. Dayside locations of magnetic reconnection equatorward of the cusps are generally found during sustained intervals of southward IMF, while high-latitude region regions poleward of the cusps are observed for northward IMF conditions. In this study we discuss Double Star magnetopause crossings and a conjunction with a Polar cusp crossing during northward IMF conditions with a dominant IMF BY component. During all seven dayside magnetopause crossings, Double Star detected switching ion beams, a known signature for the presence of reconnection lines. In addition, Polar observed a cusp ion-energy dispersion profile typical for a dayside equatorial reconnection line. Using the cutoff velocities for the precipitating and mirrored ion beams in the cusp, the distance to the reconnection site is calculated, and this distance is traced back to the magnetopause, to the vicinity of the Double Star satellite locations. Our analysis shows that, for this case, the predicted line of maximum magnetic shear also coincides with that dayside reconnection location.

  20. GAMMA-RAY BURSTS FROM MAGNETIC RECONNECTION: VARIABILITY AND ROBUSTNESS OF LIGHT CURVES

    SciTech Connect

    Granot, Jonathan

    2016-01-10

    The dissipation mechanism that powers gamma-ray bursts (GRBs) remains uncertain almost half a century after their discovery. The two main competing mechanisms are the extensively studied internal shocks and the less studied magnetic reconnection. Here we consider GRB emission from magnetic reconnection accounting for the relativistic bulk motions that it produces in the jet's bulk rest frame. Far from the source the magnetic field is almost exactly normal to the radial direction, suggesting locally quasi-spherical thin reconnection layers between regions of oppositely directed magnetic field. We show that if the relativistic motions in the jet's frame are confined to such a quasi-spherical uniform layer, then the resulting GRB light curves are independent of their direction distribution within this layer. This renders previous results for a delta-function velocity-direction distribution applicable to a much more general class of reconnection models, which are suggested by numerical simulations. Such models that vary in their velocity-direction distribution differ mainly in the size of the bright region that contributes most of the observed flux at a given emission radius or observed time. The more sharply peaked this distribution, the smaller this bright region, and the stronger the light curve variability that may be induced by deviations from a uniform emission over the thin reconnection layer, which may be expected in a realistic GRB outflow. This is reflected both in the observed image at a given observed time and in the observer-frame emissivity map at a given emission radius, which are calculated here for three simple velocity-direction distributions.

  1. Dayside and nightside magnetic field responses at 780 km altitude to dayside reconnection

    NASA Astrophysics Data System (ADS)

    Snekvik, K.; Østgaard, N.; Tenfjord, P.; Reistad, J. P.; Laundal, K. M.; Milan, S. E.; Haaland, S. E.

    2017-02-01

    During southward interplanetary magnetic field, dayside reconnection will drive the Dungey cycle in the magnetosphere, which is manifested as a two-cell convection pattern in the ionosphere. We address the response of the ionospheric convection to changes in the dayside reconnection rate by examining magnetic field perturbations at 780 km altitude. The Active Magnetosphere and Planetary Electrodynamics Response Experiment data products derived from the Iridium constellation provide global maps of the magnetic field perturbations. Cluster data just upstream of the Earth's bow shock have been used to estimate the dayside reconnection rate. By using a statistical model where the magnetic field can respond on several time scales, we confirm previous reports of an almost immediate response both near noon and near midnight combined with a 10-20 min reconfiguration time of the two-cell convection pattern. The response of the ionospheric convection has been associated with the expansion of the polar cap boundary in the Cowley-Lockwood paradigm. In the original formulation of this paradigm the expansion spreads from noon to midnight in 15-20 min. However, also an immediate global response has been shown to be consistent with the paradigm when the previous dayside reconnection history is considered. In this paper we present a new explanation for how the immediate response can be accommodated in the Cowley-Lockwood paradigm. The new explanation is based on how MHD waves propagate in the magnetospheric lobes when newly reconnected open flux tubes are added to the lobes, and the magnetopause flaring angle increases.

  2. ELECTRON HEATING AND ACCELERATION BY MAGNETIC RECONNECTION IN HOT ACCRETION FLOWS

    SciTech Connect

    Ding Jian; Yuan Feng; Liang, Edison

    2010-01-10

    Both analytical and numerical works show that magnetic reconnection must occur in hot accretion flows. This process will effectively heat and accelerate electrons. In this paper, we use the numerical hybrid simulation of magnetic reconnection plus the test-electron method to investigate the electron acceleration and heating due to magnetic reconnection in hot accretion flows. We consider fiducial values of density, temperature, and magnetic parameter beta{sub e} (defined as the ratio of the electron pressure to the magnetic pressure) of the accretion flow as n{sub 0} approx 10{sup 6} cm{sup -3}, T {sup 0}{sub e} approx 2 x 10{sup 9} K, and beta{sub e} = 1. We find that electrons are heated to a higher temperature T{sub e} = 5 x 10{sup 9} K, and a fraction eta approx 8% of electrons are accelerated into a broken power-law distribution, dN(gamma) propor to gamma{sup -p}, with p approx 1.5 and 4 below and above approx1 MeV, respectively. We also investigate the effect of varying beta and n{sub 0}. We find that when beta{sub e} is smaller or n{sub 0} is larger, i.e., the magnetic field is stronger, T{sub e} , eta, and p all become larger.

  3. A global magnetohydrodynamic simulation of the magnetosphere when the interplanetary magnetic field is southward: The onset of magnetotail reconnection

    SciTech Connect

    Walker, R.J.; Raeder, J.; Ashour-Abdalla, M.; Ogino, Tatsuki

    1993-10-01

    The authors have used a new high-resolution global magnetohydrodynamic simulation model to investigate the onset of reconnection in the magnetotail during intervals with southward interplanetary magnetic field (IMF). After the southward IMF reaches the dayside magnetopause, reconnection begins and magnetic flux is convected into the tail lobes. After about 35 min, reconnection begins within the plasma sheet near midnight at x = 14R{sub E}. Later the x line moves toward dawn and dusk. The reconnection occurs just tailward of the region where the tail attaches onto the dipole-dominated inner magnetosphere. The simulation shows that prior to the onset of reconnection, the Poynting flux is concentrated in this region. The time required for the start of reconnection depends on the component of the magnetic field normal to the equator (B{sub z}). Reconnection occurs only after the B{sub z} component has been reduced sufficiently for the tearing mode to grow. Later, when all the plasma sheet field lines have reconnected, a plasmoid moves down the tail. 63 refs., 15 figs.

  4. Electron and ion heating characteristics during magnetic reconnection in MAST

    NASA Astrophysics Data System (ADS)

    Tanabe, Hiroshi; Yamada, Takuma; Watanabe, Takenori; Gi, Keii; Kadowaki, Kazutake; Inomoto, Michiaki; Imazawa, Ryota; Gryaznevich, Mikhail; Michael, Clive; Conway, Neil; Scannell, Rory; Crowley, Brendan; McClements, Ken; Ono, Yasushi; MAST Team

    2015-11-01

    Localized electron heating at X point and global ion heating in the downstream during merging/reconnection startup of ST in MAST have been studied in detail using 130 channel YAG- and 300 channel Ruby-Thomson scattering measurement and a new 32 chord ion Doppler tomography diagnostics. In addition to the previously achieved record heating of ~1keV, 2D profile of electron temperature revealed highly localized heating structure at X point with the characteristic scale length of 0.02-0.05m < c /ωpi , while the ion temperature increases in the downstream of outflow jet with the width of c /ωpi ~ 0 . 1 m where reconnected field forms thick layer of closed flux surface. The effect of Ti -Te energy relaxation also affects both heating profiles in MAST, finally the formation of triple peak structure for both profiles was observed with the delay of τeiE. The toroidal guide field mostly contributes to the formation of a localized electron heating structure at the X point but not to bulk ion heating downstream. This work is supported by JSPS KAKENHI Grant Number 15H05750 and 15K20921.

  5. On the role of pseudodisk warping and reconnection in protostellar disk formation in turbulent magnetized cores

    SciTech Connect

    Li, Zhi-Yun; Zhao, Bo; Krasnopolsky, Ruben; Shang, Hsien

    2014-10-01

    The formation of rotationally supported protostellar disks is suppressed in ideal MHD in non-turbulent cores with aligned magnetic fields and rotation axes. A promising way to resolve this so-called 'magnetic braking catastrophe' is through turbulence. The reason for the turbulence-enabled disk formation is usually attributed to the turbulence-induced magnetic reconnection, which is thought to reduce the magnetic flux accumulated in the disk-forming region. We advance an alternative interpretation, based on magnetic decoupling-triggered reconnection of severely pinched field lines close to the central protostar and turbulence-induced warping of the pseudodisk of Galli and Shu. Such reconnection weakens the central split magnetic monopole that lies at the heart of the magnetic braking catastrophe under flux freezing. We show, through idealized numerical experiments, that the pseudodisk can be strongly warped, but not completely destroyed, by a subsonic or sonic turbulence. The warping decreases the rates of angular momentum removal from the pseudodisk by both magnetic torque and outflow, making it easier to form a rotationally supported disk. More importantly, the warping of the pseudodisk out of the disk-forming, equatorial plane greatly reduces the amount of magnetic flux threading the circumstellar, disk-forming region, further promoting disk formation. The beneficial effects of pseudodisk warping can also be achieved by a misalignment between the magnetic field and rotation axis. These two mechanisms of disk formation, enabled by turbulence and field-rotation misalignment respectively, are thus unified. We find that the disks formed in turbulent magnetized cores are rather thick and significantly magnetized. Implications of these findings, particularly for the thick young disk inferred in L1527, are briefly discussed.

  6. THE ROLE OF TURBULENT MAGNETIC RECONNECTION IN THE FORMATION OF ROTATIONALLY SUPPORTED PROTOSTELLAR DISKS

    SciTech Connect

    Santos-Lima, R.; De Gouveia Dal Pino, E. M.; Lazarian, A.

    2012-03-01

    The formation of protostellar disks out of molecular cloud cores is still not fully understood. Under ideal MHD conditions, the removal of angular momentum from the disk progenitor by the typically embedded magnetic field may prevent the formation of a rotationally supported disk during the main protostellar accretion phase of low-mass stars. This has been known as the magnetic braking problem and the most investigated mechanism to alleviate this problem and help remove the excess of magnetic flux during the star formation process, the so-called ambipolar diffusion (AD), has been shown to be not sufficient to weaken the magnetic braking at least at this stage of the disk formation. In this work, motivated by recent progress in the understanding of magnetic reconnection in turbulent environments, we appeal to the diffusion of magnetic field mediated by magnetic reconnection as an alternative mechanism for removing magnetic flux. We investigate numerically this mechanism during the later phases of the protostellar disk formation and show its high efficiency. By means of fully three-dimensional MHD simulations, we show that the diffusivity arising from turbulent magnetic reconnection is able to transport magnetic flux to the outskirts of the disk progenitor at timescales compatible with the collapse, allowing the formation of a rotationally supported disk around the protostar of dimensions {approx}100 AU, with a nearly Keplerian profile in the early accretion phase. Since MHD turbulence is expected to be present in protostellar disks, this is a natural mechanism for removing magnetic flux excess and allowing the formation of these disks. This mechanism dismisses the necessity of postulating a hypothetical increase of the ohmic resistivity as discussed in the literature. Together with our earlier work which showed that magnetic flux removal from molecular cloud cores is very efficient, this work calls for reconsidering the relative role of AD in the processes of star

  7. The Effect of Dissipation Mechanism and Guide Field Strength on X-line Spreading in 3D Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Shepherd, Lucas; Cassak, P.; Drake, J.; Gosling, J.; Phan, T.; Shay, M. A.

    2013-07-01

    In two-ribbon flares, the fact that the ribbons separate in time is considered evidence of magnetic reconnection. However, in addition to the ribbons separating, they can also elongate (as seen in animations of, for example, the Bastille Day flare). The elongation is undoubtedly related to the reconnection spreading in the out-of-plane direction. Indeed, naturally occurring magnetic reconnection generally begins in a spatially localized region and spreads in the direction perpendicular to the reconnection plane as time progresses. For example, it was suggested that X-line spreading is necessary to explain the observation of X-lines extending more than 390 Earth radii (Phan et al., Nature, 404, 848, 2006), and has been seen in reconnection experiments. A sizeable out-of-plane (guide) magnetic field is present at flare sites and in the solar wind. Here, we study the effect of dissipation mechanism and the strength of the guide field has on X-line spreading. We present results from three-dimensional numerical simulations of magnetic reconnection, comparing spreading with the Hall term to spreading with anomalous resistivity. Applications to solar flares and magnetic reconnection in the solar wind will be discussed.

  8. Connection between Magnetic Topology, Mixing and the Reconnection Rate in Asymmetric Layers

    NASA Astrophysics Data System (ADS)

    Daughton, W. S.; Nakamura, T.; Roytershteyn, V.; Karimabadi, H.; Hesse, M.; Loring, B.

    2013-12-01

    The entry of solar wind plasma into the magnetosphere occurs in thin boundary layers, which are typically asymmetric and have large magnetic and/or velocity shear across them. Magnetic reconnection is the dominant entry mechanism, but in regions with strong nearly perpendicular velocity shear, the Kelvin-Helmholtz instability dominates and can lead to vortex induced reconnection [1]. In both of these limits, recent fully kinetic simulations feature the development of 3D turbulence, characterized by electron-scale current sheets and interacting magnetic flux ropes. The 3D magnetic field, characterized by the Lyapunov exponent, reveals a chaotic structure within the reconnection layer in which neighboring field lines undergo rapid separation. In the presence of this complex 3D dynamics, defining and accurately computing the time evolving reconnection rate is a major challenge. One of the leading theoretical ideas [2] for computing the rate is based on integrating the parallel electric field. However, applying this approach is complicated by the chaotic magnetic field, which can lead to different answers on closely neighboring field lines. Furthermore, it is difficult to cleanly identify a transition back into an ideal region where the integration can be terminated. Here we explore a new approach that exploits the connection between the magnetic topology and the mixing of electrons that originate from separate sides of the asymmetric current layer. This idea is motivated by a clear correlation between the Lyapunov exponent for the magnetic field and the boundaries between mixed and unmixed regions. This correlation implies that mixing is a good proxy for quickly identifying 3D surfaces separating different topologies, and thus accurately measuring the time changing flux between topologies. The 3D reconnection rate obtained from this approach is contrasted with corresponding 2D simulations in the limits of both weak and strong velocity shear. [1] T.K.M Nakamura et al

  9. The inner structure of collisionless magnetic reconnection: The electron-frame dissipation measure and Hall fields

    SciTech Connect

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

    2011-12-15

    It was recently proposed that the electron-frame dissipation measure, the energy transfer from the electromagnetic field to plasmas in the electron's rest frame, identifies the dissipation region of collisionless magnetic reconnection [Zenitani et al., Phys. Rev. Lett. 106, 195003 (2011)]. The measure is further applied to the electron-scale structures of antiparallel reconnection, by using two-dimensional particle-in-cell simulations. The size of the central dissipation region is controlled by the electron-ion mass ratio, suggesting that electron physics is essential. A narrow electron jet extends along the outflow direction until it reaches an electron shock. The jet region appears to be anti-dissipative. At the shock, electron heating is relevant to a magnetic cavity signature. The results are summarized to a unified picture of the single dissipation region in a Hall magnetic geometry.

  10. Model of electron pressure anisotropy in the electron diffusion region of collisionless magnetic reconnection

    SciTech Connect

    Divin, A.; Markidis, S.; Lapenta, G.; Semenov, V. S.; Erkaev, N. V.; Biernat, H. K.

    2010-12-15

    A new model of the electron pressure anisotropy in the electron diffusion region in collisionless magnetic reconnection is presented for the case of antiparallel configuration of magnetic fields. The plasma anisotropy is investigated as source of collisionless dissipation. By separating electrons in the vicinity of the neutral line into two broad classes of inflowing and accelerating populations, it is possible to derive a simple closure for the off-diagonal electron pressure component. The appearance of these two electron populations near the neutral line is responsible for the anisotropy and collisionless dissipation in the magnetic reconnection. Particle-in-cell simulations verify the proposed model, confirming first the presence of two particle populations and second the analytical results for the off-diagonal electron pressure component. Furthermore, test-particle calculations are performed to compare our approach with the model of electron pressure anisotropy in the inner electron diffusion region by Fujimoto and Sydora [Phys. Plasmas 16, 112309 (2009)].

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

    SciTech Connect

    Li, Xiaocan

    2015-07-21

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

  12. Propagation speed of rotation signals for field lines undergoing magnetic reconnection

    SciTech Connect

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

    2013-10-15

    Reconnection is associated with two bending of the magnetic field lines. Considering the usual plane of a 2D reconnection simulation, the first bending is in-plane and produces the needed topological changes by bringing oppositely directed filed lines in proximity. The second is typical of fast reconnection and is out of plane, leading to the formation of the Hall magnetic field. This second rotation has recently been observed to proceed at superAlfvénic speeds and to carry substantial energy fluxes (Shay et al., Phys. Rev. Lett. 107, 065001 (2011)). We revisit these rotations with a new diagnostics based on dispersing a multitude of virtual probes into a kinetic simulation, akin the approach of multi spacecraft missions. The results of the new diagnostics are compared with the theory of characteristics applied to the two fluid model. The comparison of virtual probes and the method of characteristics confirm the findings relative to the out of plane rotation and uncover the existence of two families of characteristics. Both are observed in the simulation. The early stage of reconnection develops on the slower compressional branch and the later faster phase develops on the faster torsional branch. The superAlfvénic signal is only relevant in the second phase.

  13. Kinetic PIC simulations of reconnection signal propagation parallel to magnetic field lines: Implifications for substorms

    NASA Astrophysics Data System (ADS)

    Shay, M. A.; Drake, J. F.

    2009-12-01

    In a recent substorm case study using THEMIS data [1], it was inferred that auroral intensification occurred 96 seconds after reconnection onset initiated a substorm in the magnetotail. These conclusions have been the subject of some controversy [2,3]. The time delay between reconnection and auroral intensification requires a propagation speed significantly faster than can be explained by Alfvén waves. Kinetic Alfvén waves, however, can be much faster and could possibly explain the time lag. To test this possiblity, we simulate large scale reconnection events with the kinetic PIC code P3D and examine the disturbances on a magnetic field line as it propagates through a reconnection region. In the regions near the separatrices but relatively far from the x-line, the propagation physics is expected to be governed by the physics of kinetic Alfvén waves. Indeed, we find that the propagation speed of the magnetic disturbance roughly scales with kinetic Alfvén speeds. We also examine energization of electrons due to this disturbance. Consequences for our understanding of substorms will be discussed. [1] Angelopoulos, V. et al., Science, 321, 931, 2008. [2] Lui, A. T. Y., Science, 324, 1391-b, 2009. [3] Angelopoulos, V. et al., Science, 324, 1391-c, 2009.

  14. Development of a fast EUV movie camera for study of magnetic reconnection in magnetically driven plasma jets

    NASA Astrophysics Data System (ADS)

    Chai, Kil-Byoung; Bellan, Paul

    2012-10-01

    The Caltech MHD driven jet experiment involves a low temperature (˜5 eV) and high density (˜10^21 m-3) plasma that travels at 10's of km/s. During and after formation, magnetic reconnections are observed together with kink and Rayleigh-Taylor instabilities [1]. It has also been observed that there are highly transient EUV emissions when there is magnetic reconnection. The first EUV peak occurs when flux tubes merge during formation and the second one occurs when a Rayleigh-Taylor instability causes the jet to break off from its source electrode. It would be helpful for understanding magnetic reconnection to investigate the spatial and temporal behaviors of these EUV bursts associated with magnetic reconnection. In order to achieve this, we are developing a high speed EUV movie camera. It consists of an Al coated YAG:Ce scintillator, an Au parabolic mirror (or a multilayer coated mirror for a specific EUV wavelength) and a fast framing camera (2x10^8 fps). We tested our system using visible light from the actual plasma jet and obtained image sequence with submicron time resolution.[4pt] [1] A. L. Moser and P. M. Bellan, Nature 482, 379 (2012).

  15. Connecting Global Measures of 3D Magnetic Reconnection to Local Kinetic Physics

    SciTech Connect

    Daughton, William Scott

    2015-07-16

    After giving the motivation for the work, slides present the topic under the following headings: Description of LAPD experiment; Actual simulation setup; Simple kinetic theory of ined-tied tearing; Diagnostics to characterizing 3D reconnection; Example #1 - short-tied system; and Example #2 - long line-tied system. Colorful simulations are shown for quasipotential vs field line exponentiation, field line integrated Ohms Law, and correlation with agyrotopy & energy conversion for example #1; and evolution of current density for largest case, field exponentiation vs quasi-potential, and time evolution of magnetic field lines for example #2. To satisfy line-tied boundary conditions, there is need for superposition of oblique modes--the simple two-mode approximation works surprisingly well. For force-free layers with bg >1, the fastest growing periodic modes are oblique with kxλ ~0.5. This implies a minimum length of Ly > 2πλbg. There are strong correlations between σ → Ξ → A0e (observable with spacecraft). Electron pressure tensor is the dominant non-ideal term.

  16. Ellerman bombs—evidence for magnetic reconnection in the lower solar atmosphere

    SciTech Connect

    Nelson, C. J.; Doyle, J. G.; Madjarska, M. S.; Shelyag, S.; Mathioudakis, M.; Uitenbroek, H.; Erdélyi, R.

    2013-12-20

    The presence of photospheric magnetic reconnection has long been thought to give rise to short and impulsive events, such as Ellerman bombs (EBs) and Type II spicules. In this article, we combine high-resolution, high-cadence observations from the Interferometric BIdimensional Spectrometer and Rapid Oscillations in the Solar Atmosphere instruments at the Dunn Solar Telescope, National Solar Observatory, New Mexico, with co-aligned Solar Dynamics Observatory Atmospheric Imaging Assembly and Hinode Solar Optical Telescope (SOT) data to observe small-scale events situated within an active region. These data are then compared with state-of-the-art numerical simulations of the lower atmosphere made using the MURaM code. It is found that brightenings, in both the observations and the simulations, of the wings of the Hα line profile, interpreted as EBs, are often spatially correlated with increases in the intensity of the Fe I λ6302.5 line core. Bipolar regions inferred from Hinode/SOT magnetic field data show evidence of flux cancellation associated, co-spatially, with these EBs, suggesting that magnetic reconnection could be a driver of these high-energy events. Through the analysis of similar events in the simulated lower atmosphere, we are able to infer that line profiles analogous to the observations occur co-spatially with regions of strong opposite-polarity magnetic flux. These observed events and their simulated counterparts are interpreted as evidence of photospheric magnetic reconnection at scales observable using current observational instrumentation.

  17. Local properties of magnetic reconnection in nonlinear resistive- and extended-magnetohydrodynamic toroidal simulations of the sawtooth crash

    DOE PAGES

    Beidler, M. T.; Cassak, P. A.; Jardin, S. C.; ...

    2016-12-15

    We diagnose local properties of magnetic reconnection during a sawtooth crash employing the three-dimensional toroidal, extended-magnetohydrodynamic (MHD) code M3D-C1. To do so, we sample simulation data in the plane in which reconnection occurs, the plane perpendicular to the helical (m, n) = (1, 1) mode at the q = 1 surface, where m and n are the poloidal and toroidal mode numbers and q is the safety factor. We study the nonlinear evolution of a particular test equilibrium in a non-reduced field representation using both resistive-MHD and extended-MHD models. We find growth rates for the extended-MHD reconnection process exhibit amore » nonlinear acceleration and greatly exceed that of the resistive-MHD model, as is expected from previous experimental, theoretical, and computational work. We compare the properties of reconnection in the two simulations, revealing the reconnecting current sheets are locally different in the two models and we present the first observation of the quadrupole out-of-plane Hall magnetic field that appears during extended-MHD reconnection in a 3D toroidal simulation (but not in resistive-MHD). We also explore the dependence on toroidal angle of the properties of reconnection as viewed in the plane perpendicular to the helical magnetic field, finding qualitative and quantitative effects due to changes in the symmetry of the reconnection process. Furthermore, this study is potentially important for a wide range of magnetically confined fusion applications, from confirming simulations with extended-MHD effects are sufficiently resolved to describe reconnection, to quantifying local reconnection rates for purposes of understanding and predicting transport, not only at the q = 1 rational surface for sawteeth, but also at higher order rational surfaces that play a role in disruptions and edge-confinement degradation.« less

  18. Local properties of magnetic reconnection in nonlinear resistive- and extended-magnetohydrodynamic toroidal simulations of the sawtooth crash

    SciTech Connect

    Beidler, M. T.; Cassak, P. A.; Jardin, S. C.; Ferraro, N. M.

    2016-12-15

    We diagnose local properties of magnetic reconnection during a sawtooth crash employing the three-dimensional toroidal, extended-magnetohydrodynamic (MHD) code M3D-C1. To do so, we sample simulation data in the plane in which reconnection occurs, the plane perpendicular to the helical (m, n) = (1, 1) mode at the q = 1 surface, where m and n are the poloidal and toroidal mode numbers and q is the safety factor. We study the nonlinear evolution of a particular test equilibrium in a non-reduced field representation using both resistive-MHD and extended-MHD models. We find growth rates for the extended-MHD reconnection process exhibit a nonlinear acceleration and greatly exceed that of the resistive-MHD model, as is expected from previous experimental, theoretical, and computational work. We compare the properties of reconnection in the two simulations, revealing the reconnecting current sheets are locally different in the two models and we present the first observation of the quadrupole out-of-plane Hall magnetic field that appears during extended-MHD reconnection in a 3D toroidal simulation (but not in resistive-MHD). We also explore the dependence on toroidal angle of the properties of reconnection as viewed in the plane perpendicular to the helical magnetic field, finding qualitative and quantitative effects due to changes in the symmetry of the reconnection process. Furthermore, this study is potentially important for a wide range of magnetically confined fusion applications, from confirming simulations with extended-MHD effects are sufficiently resolved to describe reconnection, to quantifying local reconnection rates for purposes of understanding and predicting transport, not only at the q = 1 rational surface for sawteeth, but also at higher order rational surfaces that play a role in disruptions and edge-confinement degradation.

  19. Local properties of magnetic reconnection in nonlinear resistive- and extended-magnetohydrodynamic toroidal simulations of the sawtooth crash

    NASA Astrophysics Data System (ADS)

    Beidler, M. T.; Cassak, P. A.; Jardin, S. C.; Ferraro, N. M.

    2017-02-01

    We diagnose local properties of magnetic reconnection during a sawtooth crash employing the three-dimensional toroidal, extended-magnetohydrodynamic (MHD) code M3D-C1. To do so, we sample simulation data in the plane in which reconnection occurs, the plane perpendicular to the helical (m,n)=(1,1) mode at the q = 1 surface, where m and n are the poloidal and toroidal mode numbers and q is the safety factor. We study the nonlinear evolution of a particular test equilibrium in a non-reduced field representation using both resistive-MHD and extended-MHD models. We find growth rates for the extended-MHD reconnection process exhibit a nonlinear acceleration and greatly exceed that of the resistive-MHD model, as is expected from previous experimental, theoretical, and computational work. We compare the properties of reconnection in the two simulations, revealing the reconnecting current sheets are locally different in the two models and we present the first observation of the quadrupole out-of-plane Hall magnetic field that appears during extended-MHD reconnection in a 3D toroidal simulation (but not in resistive-MHD). We also explore the dependence on toroidal angle of the properties of reconnection as viewed in the plane perpendicular to the helical magnetic field, finding qualitative and quantitative effects due to changes in the symmetry of the reconnection process. This study is potentially important for a wide range of magnetically confined fusion applications, from confirming simulations with extended-MHD effects are sufficiently resolved to describe reconnection, to quantifying local reconnection rates for purposes of understanding and predicting transport, not only at the q = 1 rational surface for sawteeth, but also at higher order rational surfaces that play a role in disruptions and edge-confinement degradation.

  20. NUMERICAL SIMULATIONS OF THE MAGNETIC RAYLEIGH-TAYLOR INSTABILITY IN THE KIPPENHAHN-SCHLUeTER PROMINENCE MODEL. II. RECONNECTION-TRIGGERED DOWNFLOWS

    SciTech Connect

    Hillier, Andrew; Isobe, Hiroaki; Shibata, Kazunari; Berger, Thomas

    2012-09-10

    The launch of the Hinode satellite has allowed high-resolution observations of supersonic bright downflows in quiescent prominences, known as prominence knots. We present observations in the Ca II H spectral line using the Solar Optical Telescope on board the Hinode satellite of a descending plasma knot of size {approx}900 km. The knot initially undergoes ballistic motion before undergoing impulsive accelerations at the same time as experiencing increases in intensity. We also present a subset of our three-dimensional magnetohydrodynamic simulations, performed to investigate the nonlinear stability of the Kippenhahn-Shlueter prominence model to the magnetic Rayleigh-Taylor instability in which interchange reconnection occurs. The interchange reconnection in the model breaks the force balance along the field lines which initiates the downflows. The downflows propagate with a downward fluid velocity of {approx}15 km s{sup -1} and a characteristic size of {approx}700 km. We conclude that the observed plasma blob and the simulated downflow are driven by the breaking of the force balance along the magnetic field as a result of a change in magnetic topology caused by reconnection of the magnetic field.

  1. Electrostatic and electromagnetic fluctuations detected inside magnetic flux ropes during magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Wang, Rongsheng; Lu, Quanming; Nakamura, Rumi; Huang, Can; Li, Xing; Wu, Mingyu; Du, Aimin; Gao, Xinliang; Wang, Shui

    2016-10-01

    A series of magnetic flux ropes embedded in the ion diffusion region of a magnetotail magnetic reconnection event were investigated in this paper. Waves near the lower hybrid frequency were measured within each of the flux ropes and can be associated with the enhancements of energetic electrons in some of the flux ropes. The waves in the largest flux ropes were further explored in more detail. The electrostatic lower hybrid frequency range waves are detected at the edge, while electromagnetic lower hybrid frequency range waves are observed at the center of the flux rope. The electromagnetic waves are right-hand polarized and propagated nearly perpendicular to magnetic field lines, with a wavelength of ion-electron hybrid scale. The observations are analogous to simulations in which the electrostatic lower hybrid waves are confined to the edge of current sheet but can directly penetrate into the current sheet center in the form of the electromagnetic mode. The observations indicate that the electromagnetic lower hybrid frequency range waves can be excited inside magnetic flux ropes.

  2. Magnetic Force Microscopy in Liquids.

    PubMed

    Ares, Pablo; Jaafar, Miriam; Gil, Adriana; Gómez-Herrero, Julio; Asenjo, Agustina

    2015-09-01

    In this work, the use of magnetic force microscopy (MFM) to acquire images of magnetic nanostructures in liquid environments is presented. Optimization of the MFM signal acquisition in liquid media is performed and it is applied to characterize the magnetic signal of magnetite nanoparticles. The ability for detecting magnetic nanostructures along with the well-known capabilities of atomic force microscopy in liquids suggests potential applications in fields such as nanomedicine, nanobiotechnology, or nanocatalysis.

  3. MULTIWAVELENGTH OBSERVATIONS OF SMALL-SCALE RECONNECTION EVENTS TRIGGERED BY MAGNETIC FLUX EMERGENCE IN THE SOLAR ATMOSPHERE

    SciTech Connect

    Guglielmino, S. L.; Zuccarello, F.; Bellot Rubio, L. R.; Aulanier, G.; Vargas DomInguez, S.; Kamio, S.

    2010-12-01

    The interaction between emerging magnetic flux and the pre-existing ambient field has become a 'hot' topic for both numerical simulations and high-resolution observations of the solar atmosphere. The appearance of brightenings and surges during episodes of flux emergence is believed to be a signature of magnetic reconnection processes. We present an analysis of a small-scale flux emergence event in NOAA 10971, observed simultaneously with the Swedish 1 m Solar Telescope on La Palma and the Hinode satellite during a joint campaign in 2007 September. Extremely high-resolution G-band, H{alpha}, and Ca II H filtergrams, Fe I and Na I magnetograms, EUV raster scans, and X-ray images show that the emerging region was associated with chromospheric, transition region and coronal brightenings, as well as with chromospheric surges. We suggest that these features were caused by magnetic reconnection at low altitude in the atmosphere. To support this idea, we perform potential and linear force-free field extrapolations using the FROMAGE service. The extrapolations show that the emergence site is cospatial with a three-dimensional null point, from which a spine originates. This magnetic configuration and the overall orientation of the field lines above the emerging flux region are compatible with the structures observed in the different atmospheric layers and remain stable against variations of the force-free field parameter. Our analysis supports the predictions of recent three-dimensional numerical simulations that energetic phenomena may result from the interaction between emerging flux and the pre-existing chromospheric and coronal field.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  5. Impulsive magnetic pulsations and electrojets in the loop footpoint driven by the fast reconnection jet

    SciTech Connect

    Ugai, M.

    2009-11-15

    It is well known that magnetic pulsations of long periods impulsively occur in accordance with the sudden onset of geomagnetic substorms and drastic enhancement of electrojets in the ionosphere. On the basis of the spontaneous fast reconnection model, the present paper examines the physical mechanism by which both magnetic pulsations and strong electrojets are impulsively driven by the fast (Alfvenic) reconnection jet. When a large-scale plasmoid [or traveling compression region (TCR)], directly caused by the fast reconnection jet, collides with the magnetic loop footpoint, strong electrojets are impulsively driven in a finite extent in the loop footpoint in accordance with the evolution of the current wedge and the generator current circuit. Simultaneously, magnetohydrodynamic (Alfven) waves, accompanied by the TCR, are reflected from the electrojet layer, leading to impulsive magnetic pulsations ahead of the loop footpoint because of the interaction (or resonance) between the reflected waves and the waves traveling toward the footpoint. The pulsations propagate outward in all directions from the source region of the wave reflection, and the pulsation periods are typically estimated to be of several tens of seconds.

  6. Kinetic Alfvén wave explanation of the Hall fields in magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Dai, Lei; Wang, Chi; Zhang, Yongcun; Lavraud, Benoit; Burch, James; Pollock, Craig; Torbert, Roy B.

    2017-01-01

    Magnetic reconnection is initiated in a small diffusion region but can drive global-scale dynamics in Earth's magnetosphere, solar flares, and astrophysical systems. Understanding the processes at work in the diffusion region remains a main challenge in space plasma physics. Recent in situ observations from Magnetospheric Multiscale and Time History of Events and Macroscale Interactions during Substorms reveal that the electric field normal to the reconnection current layer, often called the Hall electric field (En), is mainly balanced by the ion pressure gradient. Here we present theoretical explanations indicating that this observation fact is a manifestation of kinetic Alfvén waves (KAWs) physics. The ion pressure gradient represents the finite gyroradius effect of KAW, leading to ion intrusion across the magnetic field lines. Electrons stream along the magnetic field lines to track ions, resulting in field-aligned currents and the associated pattern of the out-of-plane Hall magnetic field (Bm). The ratio ΔEn/ΔBm is on the order of the Alfvén speed, as predicted by the KAW theory. The KAW physics further provides new perspectives on how ion intrusion may trigger electric fields suitable for reconnection to occur.

  7. The reconnection of magnetic fields between plasmas with different densities: Scaling relations

    SciTech Connect

    Borovsky, Joseph E.; Hesse, Michael

    2007-10-15

    Using two-dimensional compressible-magnetohydrodynamic computer simulations, the reconnection of magnetic fields between two plasmas with different mass densities is examined. Antiparallel, undriven merging is studied from a Harris-sheet initial condition with the sheet separating the two different plasmas. Reconnection is initiated with a resistive spot in the center of the Harris sheet. Density ratios from 1 to 320 are simulated. It is found that the rate of magnetic-field reconnection R is give approximately as R=0.07v{sub Ah}, where v{sub Ah}=B/[4{pi}(0.5{rho}{sub 1}+0.5{rho}{sub 1})]{sup 1/2} is a hybrid Alfven speed constructed by averaging the densities of the two plasmas. In the symmetric-density case, plasma jetting speeds are equal to the local E lowbar xB lowbar velocity; in the asymmetric-density cases, the plasma jetting speeds exceed the local E lowbar xB lowbar velocity. In the asymmetric cases, plasma jetting tends to be parallel to the local magnetic field. In the symmetric-density case the plasma jetting arises from the site of the X-line and resides in the region of magnetic-field reversal; in the asymmetric case, jetting tends to reside in the lower-density plasma.

  8. Electron Heating Characteristics of Magnetic Reconnection in UTST Merging Tokamak Experiment

    NASA Astrophysics Data System (ADS)

    Guo, Xuehan; Sugawara, Takamichi; Inomoto, Michiaki; Ono, Yasushi; UTST Team

    2014-10-01

    Localized electron heating from 10 eV to 30 eV was documented around the X-point during strong guide field (typically Bt ~ 15Bp) magnetic reconnection in the UTST tokamak merging experiment. We developed a novel two-dimensional Thomson scattering measurement system by sliding radially the whole 1D system that can measure an axial profile of electron temperature and density in a single discharge. The high electron temperature area was found to have a round shape with radius of 2 cm, in sharp contrast with high current density area. This scale length 2 cm is close to the orbit amplitude of an ion meandering motion 1.5-2 cm but 3 times longer than the ion gyroradius 0.6 cm.The electron heating power is about 12 MW/m3 which is an order of magnitude larger than heating power calculated from the Splitzer resistivity. The increment in electron thermal energy is about 2.2 J, which is about 15% of the dissipated magnetic energy of 14 J measured by 2D magnetic probe array. This conversion ratio in the strong guide field magnetic reconnection is higher than that in the weak guide field (typically Bt ~ 5Bp) experiment in MAST and TS-3 devices, suggesting that the electrons are accelerated toroidally toroidally by reconnection electric field and thermalized around X-point.

  9. IRIS Si iv LINE PROFILES: AN INDICATION FOR THE PLASMOID INSTABILITY DURING SMALL-SCALE MAGNETIC RECONNECTION ON THE SUN

    SciTech Connect

    Innes, D. E.; Guo, L.-J.; Huang, Y.-M.; Bhattacharjee, A.

    2015-11-10

    Our understanding of the process of fast reconnection has undergone a dramatic change in the last 10 years driven, in part, by the availability of high-resolution numerical simulations that have consistently demonstrated the break-up of current sheets into magnetic islands, with reconnection rates that become independent of Lundquist number, challenging the belief that fast magnetic reconnection in flares proceeds via the Petschek mechanism which invokes pairs of slow-mode shocks connected to a compact diffusion region. The reconnection sites are too small to be resolved with images, but these reconnection mechanisms, Petschek and the plasmoid instability, have reconnection sites with very different density and velocity structures and so can be distinguished by high-resolution line-profile observations. Using IRIS spectroscopic observations we obtain a survey of typical line profiles produced by small-scale events thought to be reconnection sites on the Sun. Slit-jaw images are used to investigate the plasma heating and re-configuration at the sites. A sample of 15 events from 2 active regions is presented. The line profiles are complex with bright cores and broad wings extending to over 300 km s{sup −1}. The profiles can be reproduced with the multiple magnetic islands and acceleration sites that characterize the plasmoid instability but not by bi-directional jets that characterize the Petschek mechanism. This result suggests that if these small-scale events are reconnection sites, then fast reconnection proceeds via the plasmoid instability, rather than the Petschek mechanism during small-scale reconnection on the Sun.

  10. IRIS Si IV Line Profiles: An Indication for the Plasmoid Instability during Small-scale Magnetic Reconnection on the Sun

    NASA Astrophysics Data System (ADS)

    Innes, D. E.; Guo, L.-J.; Huang, Y.-M.; Bhattacharjee, A.

    2015-11-01

    Our understanding of the process of fast reconnection has undergone a dramatic change in the last 10 years driven, in part, by the availability of high-resolution numerical simulations that have consistently demonstrated the break-up of current sheets into magnetic islands, with reconnection rates that become independent of Lundquist number, challenging the belief that fast magnetic reconnection in flares proceeds via the Petschek mechanism which invokes pairs of slow-mode shocks connected to a compact diffusion region. The reconnection sites are too small to be resolved with images, but these reconnection mechanisms, Petschek and the plasmoid instability, have reconnection sites with very different density and velocity structures and so can be distinguished by high-resolution line-profile observations. Using IRIS spectroscopic observations we obtain a survey of typical line profiles produced by small-scale events thought to be reconnection sites on the Sun. Slit-jaw images are used to investigate the plasma heating and re-configuration at the sites. A sample of 15 events from 2 active regions is presented. The line profiles are complex with bright cores and broad wings extending to over 300 km s-1. The profiles can be reproduced with the multiple magnetic islands and acceleration sites that characterize the plasmoid instability but not by bi-directional jets that characterize the Petschek mechanism. This result suggests that if these small-scale events are reconnection sites, then fast reconnection proceeds via the plasmoid instability, rather than the Petschek mechanism during small-scale reconnection on the Sun.

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

    NASA Astrophysics Data System (ADS)

    Li, Shiyou; Chen, Xiaoqian; Guo, Jianming

    2016-07-01

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

  12. Modeling of magnetic reconnection in the magnetotail using global MHD simulation with an effective resistivity model

    NASA Astrophysics Data System (ADS)

    Den, M.; Horiuchi, R.; Fujita, S.; Tanaka, T.

    2011-12-01

    Magnetic reconnection is considered to play an important role in space phenomena such as substorm in the Earth's magnetosphere. Tanaka and Fujita reproduced substorm evolution process by numerical simulation with the global MHD code [1]. In the MHD framework, the dissipation model is introduced for modeling of the kinetic effects. They found that the normalized reconnection viscosity, one of the dissipation model employed there, gave a large effect for the dipolarization, central phenomenon in the substorm development process, though that viscosity was assumed to be a constant parameter. It is well known that magnetic reconnection is controlled by microscopic kinetic mechanism. Frozen-in condition is broken due to particle kinetic effects and collisionless reconnection is triggered when current sheet is compressed as thin as ion kinetic scales under the influence of external driving flow [2, 3]. Horiuchi and his collaborators showed that reconnection electric field generated by microscopic physics evolves inside ion meandering scale so as to balance the flux inflow rate at the inflow boundary, which is controlled by macroscopic physics [2]. That is, effective resistivity generated through this process can be expressed by balance equation between micro and macro physics. In this paper, we perform substorm simulation by using the global MHD code developed by Tanaka [3] with this effective resistivity instead of the empirical resistivity model. We obtain the AE indices from simulation data, in which substorm onset can be seen clearly, and investigate the relationship between the substorm development and the effective resistivity model. [1] T. Tanaka, A, Nakamizo, A. Yoshikawa, S. Fujita, H. Shinagawa, H. Shimazu, T. Kikuchi, and K. K. Hashimoto, J. Geophys. Res. 115 (2010) A05220,doi:10.1029/2009JA014676. [2] W. Pei, R. Horiuchi, and T. Sato, Physics of Plasmas,Vol. 8 (2001), pp. 3251-3257. [3] A. Ishizawa, and R. Horiuchi, Phys. Rev. Lett., Vol. 95, 045003 (2005). [4

  13. DIRECT OBSERVATIONS OF MAGNETIC RECONNECTION OUTFLOW AND CME TRIGGERING IN A SMALL ERUPTING SOLAR PROMINENCE

    SciTech Connect

    Reeves, Katharine K.; McCauley, Patrick I.; Tian, Hui

    2015-07-01

    We examine a small prominence eruption that occurred on 2014 May 1 at 01:35 UT and was observed by the Interface Region Imaging Spectrometer (IRIS) and the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory. Pre- and post-eruption images were taken by the X-ray Telescope (XRT) on Hinode. Pre-eruption, a dome-like structure exists above the prominence, as demarcated by coronal rain. As the eruption progresses, we find evidence for reconnection between the prominence magnetic field and the overlying field. Fast flows are seen in AIA and IRIS, indicating reconnection outflows. Plane-of-sky flows of 300 km s{sup −1} are observed in the AIA 171 A channel along a potentially reconnected field line. IRIS detects intermittent fast line of sight flows of 200 km s{sup −1} coincident with the AIA flows. Differential emission measure calculations show heating at the origin of the fast flows. Post-eruption XRT images show hot loops probably due to reconfiguration of magnetic fields during the eruption and subsequent heating of plasma in these loops. Although there is evidence for reconnection above the prominence during the eruption, high spatial resolution images from IRIS reveal potential reconnection sites below the prominence. A height–time analysis of the erupting prominence shows a slow initial rise with a velocity of 0.4 km s{sup −1} followed by a rapid acceleration with a final velocity of 250 km s{sup −1}. Brightenings in IRIS during the transition between these two phases indicate the eruption trigger for the fast part of the eruption is likely a tether-cutting mechanism rather than a break-out mechanism.

  14. The role of Magnetic Reconnection in Compact Sources and Jet Acceleration

    NASA Astrophysics Data System (ADS)

    Singh, Chandra Bahadur; De Gouveia Dal Pino, Elisabete; Kadowaki, Luis H. S.

    Almost a decade ago de Gouveia Dal Pino and Lazarian (2005) proposed a model for producing jet plasmons and particle acceleration by magnetic reconnection events in the surrounds of accretion disks around black holes with magnetospheres. Although this model predicts that the amount of magnetic power released by reconnection is more than sufficient to explain observed flares from black hole mass sources in different scales (from microquasars to low luminous active galactic nuclei; see de Gouveia Dal Pino et al. 2010), it still requires refinement and numerical testing. In this work, we take into account relativistic effects by introducing a Pseudo Newtonian approach to the model and also present the results of 2D MHD numerical simulations under this approach.

  15. Anomalous heating and plasmoid formation in a driven magnetic reconnection experiment

    DOE PAGES

    Hare, J. D.; Suttle, L.; Lebedev, S. V.; ...

    2017-02-21

    We present a detailed study of magnetic reconnection in a quasi-two-dimensional pulsed-power driven laboratory experiment. Oppositely directed magnetic fields (B=3 T), advected by supersonic, sub-Alfvénic carbon plasma flows (Vin = 50 km/s), are brought together and mutually annihilate inside a thin current layer (δ = 0.6 mm). Temporally and spatially resolved optical diagnostics, including interferometry, Faraday rotation imaging, and Thomson scattering, allow us to determine the structure and dynamics of this layer, the nature of the inflows and outflows, and the detailed energy partition during the reconnection process. We measure high electron and ion temperatures (Te = 100 eV, Timore » = 600 eV), far in excess of what can be attributed to classical (Spitzer) resistive and viscous dissipation. Finally, we observe the repeated formation and ejection of plasmoids, consistent with the predictions from semicollisional plasmoid theory.« less

  16. Anomalous Heating and Plasmoid Formation in a Driven Magnetic Reconnection Experiment

    NASA Astrophysics Data System (ADS)

    Hare, J. D.; Suttle, L.; Lebedev, S. V.; Loureiro, N. F.; Ciardi, A.; Burdiak, G. C.; Chittenden, J. P.; Clayson, T.; Garcia, C.; Niasse, N.; Robinson, T.; Smith, R. A.; Stuart, N.; Suzuki-Vidal, F.; Swadling, G. F.; Ma, J.; Wu, J.; Yang, Q.

    2017-02-01

    We present a detailed study of magnetic reconnection in a quasi-two-dimensional pulsed-power driven laboratory experiment. Oppositely directed magnetic fields (B =3 T ), advected by supersonic, sub-Alfvénic carbon plasma flows (Vin=50 km /s ), are brought together and mutually annihilate inside a thin current layer (δ =0.6 mm ). Temporally and spatially resolved optical diagnostics, including interferometry, Faraday rotation imaging, and Thomson scattering, allow us to determine the structure and dynamics of this layer, the nature of the inflows and outflows, and the detailed energy partition during the reconnection process. We measure high electron and ion temperatures (Te=100 eV , Ti=600 eV ), far in excess of what can be attributed to classical (Spitzer) resistive and viscous dissipation. We observe the repeated formation and ejection of plasmoids, consistent with the predictions from semicollisional plasmoid theory.

  17. Magnetic reconnection and modification of the Hall physics due to cold ions at the magnetopause

    NASA Astrophysics Data System (ADS)

    André, M.; Li, W.; Toledo-Redondo, S.; Khotyaintsev, Yu. V.; Vaivads, A.; Graham, D. B.; Norgren, C.; Burch, J.; Lindqvist, P.-A.; Marklund, G.; Ergun, R.; Torbert, R.; Magnes, W.; Russell, C. T.; Giles, B.; Moore, T. E.; Chandler, M. O.; Pollock, C.; Young, D. T.; Avanov, L. A.; Dorelli, J. C.; Gershman, D. J.; Paterson, W. R.; Lavraud, B.; Saito, Y.

    2016-07-01

    Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and strong normal electric fields, cold (eV) ions of ionospheric origin can remain frozen-in together with the electrons. The cold ions reduce the Hall current. Using a generalized Ohm's law, the electric field is balanced by the sum of the terms corresponding to the Hall current, the v × B drifting cold ions, and the divergence of the electron pressure tensor. A mixture of hot and cold ions is common at the subsolar magnetopause. A mixture of length scales caused by a mixture of ion temperatures has significant effects on the Hall physics of magnetic reconnection.

  18. Electron acceleration in three-dimensional magnetic reconnection with a guide field

    SciTech Connect

    Dahlin, J. T. Swisdak, M.; Drake, J. F.

    2015-10-15

    Kinetic simulations of 3D collisionless magnetic reconnection with a guide field show a dramatic enhancement of energetic electron production when compared with 2D systems. In the 2D systems, electrons are trapped in magnetic islands that limit their energy gain, whereas in the 3D systems the filamentation of the current layer leads to a stochastic magnetic field that enables the electrons to access volume-filling acceleration regions. The dominant accelerator of the most energetic electrons is a Fermi-like mechanism associated with reflection of charged particles from contracting field lines.

  19. Three-dimensional Transient Magnetic Reconnection and Dipolarization Fronts in the Terrestrial Magnetotail

    NASA Astrophysics Data System (ADS)

    Zhou, M.; Deng, X.; Ashour-Abdalla, M.; Pang, Y.; Lapenta, G.; Fu, H.; Walker, R. J.; Huang, S.; Tang, R.

    2015-12-01

    We report a Cluster observation of transient magnetic reconnection in the Earth's magnetotail at the location of [Xgsm ~ -17.2 RE, Ygsm ~ -4.5 RE and Zgsm ~ 0]. The reconnection X-line retreated tailward with a speed of 34 km/s. An ion diffusion region with a weak guide field (~10% of the lobe field) was encountered during the flow reversal. Transient energetic electron beams, which directed away from the X-line, were detected repeatedly around the current sheet boundary layer with periods of about 60s during the tailward flow burst. On the earthward side of X-line, multiple earthward-propagating dipolarization fronts were observed quasi-periodically with time period of 60s-90s. Surprisingly the cross-tail sizes of some observed dipolarization fronts are only 1-2 ion inertial lengths. The X-line expanded across the tail in the electron flow direction with a speed about 0.03VA, here VA is the Alfven speed. Two spacecraft, which were separated in the cross-tail direction by 1 RE, observed distinct structures and different tones of reconnection, which implies that reconnection proceeds drastically different in different segments of X-line.

  20. Spacecraft observations of a Maxwell Demon coating the separatrix of asymmetric magnetic reconnection with crescent-shaped electron distributions

    NASA Astrophysics Data System (ADS)

    Egedal, J.; Le, A.; Daughton, W.; Wetherton, B.; Cassak, Pa; Chen, Lj; Lavraud, B.; Dorell, J.; Avanov, L.; Gershman, D.

    2016-10-01

    During asymmetric magnetic reconnection in the dayside magnetopause in situ spacecraft mea- surements show that electrons from the high density inflow penetrate some distance into the low density inflow. Supported by a kinetic simulation, we present a general derivation of an exclusion energy parameter, which provides a lower kinetic energy bound for an electron to jump across the reconnection region from one inflow region to the other. As by a Maxwell Demon, only high energy electrons are permitted to cross the inner reconnection region, strongly impacting the form of the electron distribution function observed along the low density side separatrix. The dynamics produce two distinct flavors of crescent-shaped electron distributions in a thin boundary layer along the separatrix between the magnetospheric inflow and the reconnection exhaust. The analytical model presented relates these salient details of the distribution function to the electron dynamics in the inner reconnection region.

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

    PubMed

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

    2012-06-22

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