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 ephi/T(e)>1; the observed growth rates show no reduction compared to the hydromagnetic limit. To obtain this result for the case of negative shear (upsilon0y'/OMEGA(i) < 0), it is necessary to include the kinetic modifications to the structure of the shear layer equilibrium. For finite k parallel-to in the range 0 < k parallel-to/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 ephi/T(e) less than or similar to 2 X 10(3).