Computer simulations of electromagnetic ion instabilities in the plasma sheet boundary layer

Linear Vlasov dispersion theory and one-dimensional hybrid computer simulations are used to study electromagnetic instabilities driven by hot, anisotropic counterstreaming proton components which model those observed from ISEE in the plasma sheet boundary layer of the near-Earth magnetotail. The proton anisotropies lead to the ion cyclotron anisotropy instability, which saturates at a low level of fluctuating fields and yields only weak proton scattering. Modest increases of the proton/proton relative drift, which might correspond to deeper tail conditions, excite the proton/proton nonresistant instability which attains larger fluctuation levels and more strongly heats the protons. If a relatively dense oxygen ion component is also introduced, the ion/ion right-hand resonant instability is excited; the consequent pitch-angle scattering of the protons resembles that indicated in the ISEE data. 6 refs., 5 figs