Tearing instability, flux ropes, and the kinetic current sheet kink instability in the Earth's magnetotail: A three-dimensional perspective from particle simulations

In this paper the tail current sheet is shown to be unstable to the kinetic current sheet kink instability (or simply the kinetic kink instability) in the cross-tail plane (y-z plane) and under similar conditions that drive the tearing instability in the noon-midnight meridional plane (x-z plane). The tail current sheet is assumed to be a thin Harris current sheet (rho(i)/L(c) similar to 1) with equal ion and electron temperature. The kinetic kink instability develops due to the bending of the tail current sheet and the resulting pressure imbalance. The development of the kinetic kink instability including its growth rate and resultant distortion of the current sheet, is first examined using two-dimensional electromagnetic particle simulations. The coupling between the kinetic kink and tearing instabilities is then investigated via three-dimensional electromagnetic particle simulations. The results show that the tearing instability and the kinetic kink instability occur on the same timescale as what we expected from the two-dimensional simulations and that the projection of the field lines in the x-z plane reproduces a standard plasmoid shape. However, the three-dimensional plasmoid produced by the tearing instability is shown to consist of a series of flux ropes where the magnetic field Lines are tightly wound as they cross the center of the current sheet. The entry and exit points of the field lines of the flux ropes are displaced in the dawn-dusk direction. Twist and displacement of the magnetic field Lines arise from the magnetic field component B-y generated by a plasma current due to the differential motion between electrons and ions. This current and the associated flux ropes result from intrinsic particle effects. The kinetic kink instability bends the current sheet and the flux ropes along the y direction and generates large-scale cross-tail. wavy structures. The wave fronts may eventually collide, causing a total distortion of the current sheet configuration and strong electron heating, while the tearing accounts for most of the ion heating.