Kevin B. Quest

Nonlinear evolution of the lower‐hybrid drift instability

The results of simulations of the lower‐hybrid drift instability in a neutral sheet configuration are described. The simulations use an implicit formulation to relax the usual time step limitations and thus extend previous explicit calculations to weaker gradients, larger mass ratios, and long times compared with the linear growth time. The numerical results give the scaling of the saturation level, heating rates, resistivity, and cross‐field diffusion and a demonstration by comparison with a fluid electron model that dissipation in the lower‐hybrid drift instability is caused by electron kinetic effects.

Electron heating by ion acoustic turbulence in simulated low Mach number shocks

Explicit and fully electromagnetic particle‐in‐cell simulations of perpendicular, collisionless, and nominally subcritical shocks are performed in one and two spatial dimensions using the code wave [Phys. Fluids 14, 830 (1971)]. Shock parameters are chosen to maximize the growth rates of the current driven ion acoustic instability in the shock. Electron heating by ion acoustic turbulence is observed at the shocks, at rates in agreement with second‐order Vlasov theory predictions. However, the amount of resistive electron heating is small and ion reflection provides the major source of dissipation. Strictly resistive shocks do not exist for the parameters suitable for explicit particle codes running on today’s supercomputers, because the plasma convects through these shocks so quickly that current driven instabilities have little time to be amplified and to heat the electrons resistively. This effect is primarily a result of the relatively small values of ωpe/ωce that can be analyzed.

Very high Mach number shocks: Theory

Abstract The theory and simulation of collisionless perpendicular supercritical shock structure is reviewed, with major emphasis on recent research results. The primary tool of investigation is the hybrid simulation method, in which the Newtonian orbits of a large number of ion macroparticles are followed numerically, and in which the electrons are treated as a charge neutralizing fluid. The principal results to be presented are (1) electron resistivity is not required to explain the observed quasi-stationarity of the earths bow shock, (2) the structure of the perpendicular shock at very high Mach numbers ( M A ⋍ 15 – 20 and β ⋍ 1, where M A is the Alfven Mach number of the shock and β is the ratio of the thermal to magnetic pressure) depends sensitively on the upstream β and electron resistivity, (3) two-dimensional turbulence will become increasingly important as the Mach number is increased, and (4) non-adiabatic bulk electron heating will result when a thermal electron cannot complete a gyro-orbit while transiting the shock.

Simulation and non-linear stage of the electrostatic waves observed during the AMPTE lithium release in the solar wind

Abstract During the AMPTE lithium releases in the solar wind intense electrostatic waves with frequencies between a few tens of Hz to several kHz were observed outside the diamagnetic cavity. The results of linear Vlasov theory have suggested that these waves may be generated through two types of instabilities. One is the ion-ion instability associated with the relative drift between the lithium ions and the solar wind protons, and the other is the ion-acoustic instability due to the relative drift between the electrons and the ions. In order to look at the non-linear behavior of the wave-particle interactions, and discern the effect of waves on the particles, full particle electrostatic simulations have been performed, and the results are presented here. It is shown that the ion-ion instability whose phase velocity is oblique to the solar wind velocity can cause considerable anisotropic “heating” of both the lithium ions and the solar wind protons.