Simulation of collisionless electrostatic velocity-shear-driven instabilities

The properties of electrostatic instabilities in velocity shear layers in collisionless plasmas are investigated by means of two-dimensional particle simulations for the case where the ion gyroradius is comparable to the scale length of the velocity shear. For modes exactly perpendicular to the magnetic field, the Kelvin--Helmholtz instability dominates the evolution of the system producing eφ/Te>1; the observed growth rates show no reduction compared to the hydromagnetic limit. To obtain this result for the case of negative shear (v0y'/Ωi<0), it is necessary to include the kinetic modifications to the structure of the shear layer equilibrium. For finite kparallel in the range 0<kparallel/k<0.04, the shorter-wavelength inhomogeneous-energy-density-driven instability cannot be identified in the simulations, and the upper limit on its excitation is eφ/Te approx-lt 2x10-3