Particle simulation of the kinetic Kelvin–Helmholtz instability in a magnetoplasma

Abstract

The kinetic Kelvin–Helmholtz instability in a collisionless magnetoplasma is simulated numerically in cases where the ion gyroradius is comparable with or larger than the spatial scale of the cross-field shear. The approach consists of starting the simulation from a state close to equilibrium, then observing the linear growth of instabilities and their ultimate saturation. The initial quasiequilibrium state is set up by a newly developed particle loading method; the instabilities are excited by numerical noise. The simulation is performed in two dimensions, in the plane perpendicular to the magnetic field, using an electrostatic particle code. The results for the kinetic Kelvin–Helmholtz instability are similar to those predicted by a hydromagnetic model, except that they depend slightly on the sign of the shear. Other instabilities are observed also: when the ion gyroradius is small on the scale of the shear, there is an unidentified short-wavelength instability characterized by k Δx≥1, where k is the wave number in the flow direction and Δx is the spatial scale of the shear; when the ion gyroradius is large, Bernstein waves, both ionic and electronic, are excited in the flow direction.