Kinetic theory of the drift kink instability in a current sheet

Abstract

The linear stability of a current sheet is of interest in connection with the dynamics of the magnetotail and in particular as a triggering mechanism for substorms. Until recently, most theoretical work in this area has concentrated on the collisionless tearing mode. Recent simulations suggest that for thin current sheets another long wavelength electromagnetic mode, the so‐called drift kink instability, may also be of importance. The linear stability analysis for a Harris‐type equilibrium is formulated using a kinetic description for both ions and electrons. The orbit integrals are treated numerically using the exact unperturbed particle orbits and including the global structure of the perturbation inside the integral. It is found that the drift kink has a significant electrostatic component which strongly alters the mode structure and real frequency relative to the case of a purely electromagnetic mode. The resulting growth rates, mode structure and parametric dependences are presented and compared with previous results. The effect of finite parallel wavelength is considered, and the relevance of the drift kink mode to the magnetotail is discussed.