Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aps..apr.j2002d&link_type=abstract
American Physical Society, April Meeting, Jointly Sponsored with the High Energy Astrophysics Division (HEAD) of the American As
Astronomy and Astrophysics
Astrophysics
Scientific paper
Magnetic reconnection plays a fundamental role in the dynamics of astrophysical plasma systems as the driver of explosive events such as solar and stellar flares and more generally in dissipating magnetic energy as a balance to dynamo generation. Understanding the mechanisms for breaking the frozen-in condition and the associated rate of reconnection and the deposition of magnetic energy into high speed flows and energetic particles have been major issues. The failure of MHD models with classical resistivity to explain the rates of reconnection observed in nature has led to the widespread use of "anomalous resistivity" to boost reconnection rates. However, the underlying theory and observational support for anomalous resistivity has been weak. Recent kinetic models of reconnection have suggested that the coupling to dispersive waves at small scales facilitates fast reconnection even in astrophysical scale systems [1]. However, the generation of intense current layers in these models has left open the question of the role of self-generated turbulence and anomalous resistivity. A new generation of massively parallel PIC codes is facilitating the direct simulation of 3-D magnetic reconnection and the self-generation of turbulence and anomalous resistivity, opening a door to study a new class of physics. Simulations demonstrate that the electron streaming velocity in the vicinity of the x-line during reconnection can exceed by a wide margin the electron thermal velocity. The resulting Buneman instabilities grow and rapidly evolve to a nonlinear state consisting of localized regions of strongly reduced electron density with scales of 10's of Debye lengths, refered to as "electron holes". In the resulting dynamic state the formation and destruction of electron holes leads to the strong scattering of electrons by the intense, localized parallel electric fields. Particles are accelerated to relativistic velocities and the resultant distribution functions exhibit extended tails. The calculated effective resistivity is large, patchy, highly time dependent and expands like a front from the x-line out along the separatrices. In collaboration with M. Swisdak, M. Shay, B. Rogers and A. Zeiler 1. J. Birn, et al., J. Geophys. Res. 106, 3715, 2001.
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