On wave generation by perpendicular currents

Abstract

Previous assessment of the stability of perpendicular particle drifts in cold magnetoplasmas showed that their free energy could stimulate wave activity under various circumstances that included nonoscillatory (aperiodic, purely growing) instabilities and growth with zero-drift thresholds. Here, the influence of finite temperatures is studied. The theoretical model, as in the cold plasma case, uses gravity to bring about the perpendicular currents but is applicable to other drift-generating mechanisms and arbitrary drift velocities, and is not concerned with the stability of the macroscopic plasma-gravity system. The zero-order medium is a homogeneous equatorial-plane configuration with the gravity force perpendicular to the background magnetic field, and the validity of neglecting the magnetic field generated by the drift currents is discussed. The kinetic electromagnetic wave matrix and dispersion equations are analytically derived for arbitrary directions of propagation and magnetized (nonrelativistic) plasma populations without further restrictive assumptions, and algorithms for their numerical evaluation are provided. Allowance for finite temperature plasmas does, in general, mitigate the cold plasma growth rates and instability bandwidths albeit introducing new modes that are fed by the free energy of the perpendicular drifts. Application of the developed tools can yield insight to the phenomenology encountered in space environments whose perpendicular currents and particle drifts arise from alternative generating mechanisms, namely, to the properties of the magnetotail current sheet and the possible stimulation of cyclotron harmonic wave activity.