Particle simulation of magnetic reconnection in the magnetotail configuration

Abstract

We investigate the time development of a magnetotail like plasma sheet equilibrium, using the two‐dimensional implicit electromagnetic particle code VENUS. As a starting point, we treat the simplified case of equal ion and electron masses. It is shown that a tearing instability develops if the magnetic field component perpendicular to the sheet is small enough and if the ion gyroradius is comparable to the plasma sheet thickness. An earlier estimate of the stability criterion has been confirmed approximately. In contrast to the case of a one‐dimensional sheet equilibrium, the instability does not saturate. Instead, the unstable dynamics continues to evolve by formation, acceleration, and ejection of a plasmoid structure. The analysis of the distribution function in the nonlinear stage shows anisotropic heating and the generation of a bulk flow in the tail direction, caused by the development of the plasmoid structure. There is a local enhancement of the drift velocity in the cross‐tail direction in the vicinity of the neutral line. Detailed investigation of the particles at the neutral line presents evidence that the current is significantly carried by resonant particles, which is typical for a kinetic tearing instability. We briefly address the case of an ion to electron mass ratio of 10, where the ion tearing instability still develops. Compared to the case of equal masses, electron stabilization leads to smaller growth rate and to an enhanced wavelength, according to theory.