Two-scale structure of the electron diffusion region during magnetic reconnection: Implications for reconnection rate and experimental observations

Details Two-scale structure of the electron diffusion region during magnetic reconnection: Implications for reconnection rate and experimental observations Two-scale structure of the electron diffusion region during magnetic reconnection: Implications for reconnection rate and experimental observations

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsh43a..04s&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SH43A-04

Physics

2723 Magnetic Reconnection (7526, 7835), 7526 Magnetic Reconnection (2723, 7835), 7835 Magnetic Reconnection (2723, 7526)

Scientific paper

Particle in cell (PIC) simulations of collisionless magnetic reconnection are presented which demonstrate that the electron diffusion region develops a distinct two-scale structure along the outflow direction, extending large distances (10s of ion inertial lengths) downstream from the X-line[1]. This surprising finding that the electron diffusion region can be macroscopic has significant implications for satellite missions such as the Magnetospheric Multiscale Mission (MMS) whose goal is to observe the regions where electrons are not frozen-in. In addition, it is at odds with past two-fluid and hybrid simulation studies of reconnection because it requires a kinetic description of the electrons. In this two-scale structure, the inner electron diffusion region is the typical electron diffusion region with a strong out-of-plane current. The length of this inner region is found to decrease with decreasing electron mass, approaching the ion inertial length for a proton-electron plasma. Due to the microscopic nature of this inner region, the rate of reconnection remains fast in very large systems, independent of boundary conditions and the mass of the electrons. A surprise is the existence of an outer electron diffusion region downstream of the inner one. This outer region extends very large distances downstream from the x-line (40 ion inertial lengths in the largest simulations) and consists of a super-Alfvenic outflowing jet of electrons which are decoupled from the magnetic field. This non-frozen-in jet is supported by electron momentum transport, which manifests itself in Ohm's law as an off-diagnoal electron pressure force. The fast electron jet creates a quadrupolar Hall magnetic field which is not localized near the separatrices, different from previous hybrid and two-fluid simulations. Signatures of this two-scale electron diffusion region and its implications for satellite and laboratory observations will be discussed. [1]Shay, M. A., J. F. Drake, and M. Swisdak, "Two-scale structure of the electron dissipation region during collisionless magnetic reconnection," Physical Review Letters, In Press, also available

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