Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session GO7: Magnetic Reconnection |
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Chair: Jan Egedal, Massachusetts Institute of Technology Room: 556AB |
Tuesday, October 30, 2012 9:30AM - 9:42AM |
GO7.00001: Energy Transport during Magnetotail Reconnection M.V. Goldman, D.L. Newman, J.T. Gosling, L. Andersson, S. Eriksson, G. Lapenta, S. Markidis A fundamental issue in magnetic reconnection concerns the magnetic energy stored in a reversed-field configuration: how much magnetic energy is lost as spontaneous reconnection develops and where does it go? This question is addressed using implicit 2D PIC simulations together with the theory of energy transport of waves and particles. The primary initial condition in these studies, relevant to Earth's magnetotail, is a Harris equilibrium with maximum density ten times the background density. These simulations show that space-integrated magnetic energy is converted into ion energy at an increasing rate, even well after the reconnection rate has leveled off. The partition of ion energy between thermal and coherent flow energy and between Harris and background particles is also studied. Examination of the spatial transport of particle and field energy at a late time reveals that little work is performed on ions at the x-point, where \textit{topological} reconnection occurs. The peak work on ions is instead performed by the reconnection electric field in the magnetic \textit{pile-up region} of the exhaust. The dominant outflowing Poynting flux is also in the pile-up region and associated with the reconnection \textbf{E}. The peak Poynting flux, \textbf{S}$_{H}$ associated with the Hall fields, \textbf{E}$_{H}$ and \textbf{B}$_{H}$ is weaker. However, additional simulations performed with a non-Harris initial condition show no pile-up and only \textbf{S}$_{H}$. [Preview Abstract] |
Tuesday, October 30, 2012 9:42AM - 9:54AM |
GO7.00002: Reconnection: where is the party? Giovanni Lapenta, Stefano Markidis, Alex Vapirev, Martin Goldman, David Newman Kinetic reconnection is often described in the form of two concentric boxes, the inner electron diffusion region and an outer ion diffusion regions. The meaning is the electrons become decoupled in the inner regions and the ions in the outer region. But is it true that all electrons and all ions involved in the process of kinetic reconnection have to go through those two regions? Or the more fluid-like point of view of Petscheck that reconneciton might be on a much larger area where most particles do not even have to go through the central part is in some form revitalised in the kinetic picture? We present evidence to the latter: a small fraction of electrons go through their little central box, or even through the extended jets frm it more recently discovered. Most cross the separatrices at far more distant regions. There is the party: a localised strong field deflects, energises and radnomises the electrons conveying them toward an outflowing plasma region charactereised by very different energetics and turbulence. [Preview Abstract] |
Tuesday, October 30, 2012 9:54AM - 10:06AM |
GO7.00003: In-plane electric fields in magnetic islands during collisionless magnetic reconnection Li-Jen Chen, William Daughton, Naoki Bessho, Amitava Bhattacharjee, Roy Torbert, Vadim Roytershteyn Magnetic islands are a common feature in both the onset and nonlinear evolution of magnetic reconnection. In collisionless regimes, the onset typically occurs within ion-scale current layers leading to the formation of magnetic islands when multiple X lines are involved. The nonlinear evolution gives rise to extended electron current layers (ECL) which are also unstable to formation of magnetic islands. Here we show that the excess negative charge and strong out-of-plane electron velocity in the ECL are passed on to the islands generated therein, and that the corresponding observable distinguishing the islands generated in the ECL is the strongly enhanced in-plane electric fields near the island core. The islands formed in ion-scale current layers do not have these properties of the ECL-generated islands. The above result provides a way to assess the occurrence and importance of extended ECLs that are unstable to island formation in space and laboratory plasmas. [Preview Abstract] |
Tuesday, October 30, 2012 10:06AM - 10:18AM |
GO7.00004: ABSTRACT WITHDRAWN |
Tuesday, October 30, 2012 10:18AM - 10:30AM |
GO7.00005: Roles of magnetic reconnection and buoyancy in the formation and evolution of dipolarization fronts in the magnetotail Mikhail Sitnov, Marc Swisdak, Natalia Buzulukova, Kalman Knizhnik Dipolarization fronts (DFs) are sharp magnetic pileup structures, moving with plasma in the direction opposite to the initial magnetic field stretching with the speed comparable to the Alfven speed in the terrestrial magnetotail. Being one of the main sources of hot plasma injections and magnetic field dipolarization during magnetospheric substorms and storms, DF have recently become very popular due to their observations by multi-spacecraft missions Cluster and THEMIS with unprecedented spatio-temporal resolution and global coverage. Recent kinetic theory and PIC simulations of 2D magnetotail equilibria revealed two possible mechanisms of the DF formation, mutual attraction of parallel current filaments in thin current sheets providing magnetic reconnection via the tearing instability and magnetic buoyancy resulting in the ballooning-interchange instability. Both mechanisms are most efficient in the geometries with accumulation of magnetic flux at the tailward end of a thin current sheet. To understand roles of magnetic reconnection and buoyancy effects in the formation and evolution of DFs we consider the linear stability of the corresponding magnetotail equilibria and the results of 2D and 3D PIC simulations of DFs. The theory and simulations are also compared with recent THEMIS observations of DFs and ballooning-interchange oscillations in the magnetotail. [Preview Abstract] |
Tuesday, October 30, 2012 10:30AM - 10:42AM |
GO7.00006: Impulsively Fast Magnetic Reconnection in Solar Flares and Coronal Mass Ejections and in Laboratory Plasma Merging Experiments Chio Z. Cheng, Yasushi Ono, Ya-Hui Yang, Gwangson Choe Impulsively fast magnetic reconnection has been shown to be the major mechanism responsible for explosive flare non-thermal energy release and acceleration of coronal mass ejection (CME) motion. It has been observed that for most large solar flares non-thermal emissions in hard X-rays (HXR) and millimeter/submillimeter waves impulsively rise and decade during the soft X-ray (SXR) emission rise phase. Moreover, the filament/CME upward motion is accelerated temporally in correlation with the impulsive enhancement of flare non-thermal emission and reconnection electric field in the current sheet in both simulations and observations. The peak reconnection electric field during flare impulsive phase is on the order of a few kV/m for X-class flares. Here, we demonstrated for the first time in laboratory plasma merging experiments the correlation of the magnetic reconnection rate with the acceleration of plasmoid ejected from the current sheet using the TS-4 device of the Tokyo University. Moreover, we have also found that the electron heating occurs in the current sheet and the ion heating occurs in the down-stream outflow region. Thus, we conclude that the plasmoid/CME acceleration is a key mechanism for the impulsive enhancement of magnetic reconnection rate (electric field). [Preview Abstract] |
Tuesday, October 30, 2012 10:42AM - 10:54AM |
GO7.00007: Pronounced energy-dependent anisotropy of particle acceleration and associated radiation in relativistic pair reconnection Gregory Werner, Benoit Cerutti, Dmitri Uzdensky, Mitchell Begelman Magnetic reconnection is one of a few astrophysical mechanisms that can accelerate particles to energies sufficient to emit observable high-energy radiation. This work reports on 2D simulations of reconnection in relativistic electron-positron pair plasmas, which may power gamma-ray emission from pulsar wind nebulae (PWNe), Gamma-Ray Bursts (GRBs), and blazar jets. The most important new discovery is the strong, energy-dependent angular anisotropy and spatial inhomogeneity of accelerated particles: high-energy particles are bunched in space and focused into beams mostly confined to the reconnection layer midplane. Another important advance is the calculation of the associated radiative signatures (spectra and light curves) seen by a distant observer. The synchrotron and inverse Compton radiation from the high-energy particles is likewise focused in narrow beams. The beams sweep back and forth within the midplane, so that an observer sees intense bursts (only) when a beam crosses the line of sight. The resulting rapid variability, on timescales much shorter than the light-crossing time of the reconnection region, could explain the short, intense gamma-ray flares observed in blazar jets and PWNe, including the GeV flares recently discovered in the Crab nebula. [Preview Abstract] |
Tuesday, October 30, 2012 10:54AM - 11:06AM |
GO7.00008: Magnetic Reconnection with Strong Synchrotron Cooling in Pulsar Magnetospheres Dmitri Uzdensky, Anatoly Spitkovsky 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 ($\sim$ 100 GeV) radiation, respectively. The motions of the secondary plasmoids may contribute to the pulsar's radio emission. [Preview Abstract] |
Tuesday, October 30, 2012 11:06AM - 11:18AM |
GO7.00009: Magnetic reconnection in plasma under inertial confinement fusion conditions driven by heat flux effects in Ohm's law Archis Joglekar, Alec Thomas, Will Fox, Amitava Bhattacharjee In the interaction of high power laser beams with solid density plasma, there are a number of generating mechanisms that result in very strong magnetic fields. Such fields can subsequently inhibit or redirect energy transport. Here, we present 2D numerical modeling of near critical density plasma using a fully implicit Vlasov-Fokker-Planck code, IMPACTA, which includes self-consistent magnetic fields as well as anisotropic electron pressure terms in the expansion of the distribution function. Magnetic field generation and advection by different mechanisms are studied in the context of heating by multiple laser spots, between which reconnection of magnetic field lines may occur. In particular, we compare the relative importance of Hall, resistivity, and heat flux effects in the magnetic field dynamics of MG strength, oppositely aligned magnetic fields interacting in a plasma under conditions relevant to the wall of a hohlraum. [Preview Abstract] |
Tuesday, October 30, 2012 11:18AM - 11:30AM |
GO7.00010: Measurements of Asymmetric Magnetic Reconnection in Laser-Produced Plasmas M. Rosenberg, C. Li, F. Seguin, J. Frenje, M. Manuel, A. Zylstra, R. Petrasso, C. Stoeckl, V. Glebov, W. Fox, A. Nikroo Magnetic topology changes due to reconnection of magnetic fields is of interest both in the context of basic plasma physics and in inertial confinement fusion (ICF), where laser-generated magnetic fields can affect energy transport in hohlraums and in ICF implosions. Face-on, monoenergetic proton radiography has been used to image and measure reconnection of $\sim $MG magnetic fields in colliding laser-produced plasma bubbles. The timing of the interaction beams with respect to each other and to the backlighter was varied to provide snapshots of both symmetric and asymmetric reconnection at different stages in the plasma bubble evolution and between bubbles of different size and magnetic field strength. While symmetric reconnection produces near complete cancellation of the interacting magnetic fields, the asymmetric case produces only partial field cancellation. The results are presented and compared to 2-D PIC simulations. This work was performed at the LLE NLUF and was supported in part by SNL, DOE, LLE and LLNL. [Preview Abstract] |
Tuesday, October 30, 2012 11:30AM - 11:42AM |
GO7.00011: Critical Turbulent Energies for Magnetic Reconnection Events in RFP Plasmas J.A. Johnson III, C.A. Weatherford, E.D. Mezonlin, J. Titus An approximation for the nonlinear Schroedinger equation, which applies to turbulent MHD flow, is solved. These solutions are applicable to both fusion and astrophysical plasmas. These results are used to interpret new data on magnetic reconnection events at the Madison Symmetrical Torus using the interpretation of transition to turbulence as a second order Landau-Ginzburg event. We find that the critical turbulent energies from edge magnetic field fluctuations are manipulated by changes in the fusion plasma current. Further, the transport properties can be controlled as well by changing the critical turbulent energies. [Preview Abstract] |
Tuesday, October 30, 2012 11:42AM - 11:54AM |
GO7.00012: ABSTRACT WITHDRAWN |
Tuesday, October 30, 2012 11:54AM - 12:06PM |
GO7.00013: ABSTRACT WITHDRAWN |
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