DRIFT-ALFVEN INSTABILITY IN A 2D MAGNETOTAIL CONFIGURATION – THE ADDITION OF BOUNCING ELECTRONS

Abstract

To explain the possible destabilization of a 2D magnetic equilibrium such as the Near-Earth magnetotail, we developed a kinetic model describing the resonant interaction of electromagnetic fluctuations and bouncing electrons trapped in the magnetosphere, characterized by a high plasma density gradient. A small-β approximation is used in agreement with a small field line curvature. It has been found that for a quasi-dipole configuration, unstable electromagnetic modes may develop in the current sheet in westward direction with a growth rate of the order of a few tenth of seconds provided that the typical scale of density gradient slope responsible for the diamagnetic drift effects is over one Earth radius or less. This instability growth rate is large enough to destabilise the current sheet on time scales often observed during substorm onset.