On the stability of perpendicular particle drifts in cold magnetoplasmas

Abstract

Assessment of the stability of perpendicular particle drifts in cold magnetoplasmas shows that their free energy can stimulate wave activity under various circumstances that include nonoscillatory (aperiodic, purely growing) instabilities and growth with zero-drift thresholds. The theoretical model uses gravity as a means of originating the perpendicular drifts but does not address the stability of the macroscopic plasma-gravity system. It adopts a homogeneous zero-order equatorial-plane configuration with the gravity force perpendicular to the background magnetic field; the wave matrix and dispersion equations are derived for arbitrary directions of propagation and magnetized plasma populations, and the influence of the ignored inhomogeneity of the equilibrium medium on the discussed wave activity is shown to be negligible. Even for atomic hydrogen magnetoplasmas and low frequencies (much smaller than the upper hybrid frequency), instabilities are found for the three principal directions (magnetic field, gravity and drift), with some of them maximizing their growth rates away from these axes. The analysis, to be extended to hot plasmas, incorporates the influence of the background magnetic field on the current-carrying particles, recovers, where appropriate, classical instability results, and can also provide insight to the phenomenology encountered in space environments whose perpendicular currents and particle drifts arise from alternative generating mechanisms. Evaluation of the influence of the neglected inhomogeneity of the zero-order medium indicates that the discussed wave activity persists.