Roles of ion and electron dynamics in the onset of magnetic reconnection due to current sheet instabilities

Abstract

Roles of ion and electron kinetic effects in the trigger mechanism of magnetic reconnection due to current sheet instabilities are investigated by means of (2+1∕2)D explicit particle simulation. The simulation is performed for the Harris equilibrium without guide fields in the plane perpendicular to the antiparallel magnetic fields. The instabilities excited in the vicinity of the neutral sheet are classified into two modes, i.e., one is a longer wavelength kink mode and the other is a shorter wavelength kink mode. The growth of the longer kink mode depends only on the ion mass, while the growth of the shorter one depends only on the electron mass. Before the growth of these kink modes, the lower hybrid drift instability leads to two types of plasma diffusion: diffusion at the periphery controlled by ions and diffusion in the vicinity of the neutral sheet controlled by electrons. The diffusion at the periphery affects the ion distribution function at the neutral sheet through the ion meandering motion, and the ion-ion kink mode is destabilized as the electron-independent longer kink mode. The generation of the reconnection electric field at the neutral sheet due to the longer wavelength kink mode is characterized only by the ion dynamics and can take place commonly in ion-scale current sheets observed in the magnetosphere and laboratories.