Instability of a Plasma Drifting across a Magnetic Field

Abstract

Longitudinal waves propagating across a magnetic field are studied theoretically. It is assumed that electrons and ions of the plasma have shifted Maxwellian velocity distributions with mean velocities perpendicular to the magnetic field and different from each other. The minimum relative velocity between electrons and ions for the onset of an instability is obtained in terms of collision frequencies and other parameters. The wave number k of the wave excited at the minimum relative velocity V_min is given by kV_min≈ω_ce(electron cyclotron frequency) and the corresponding frequency is ω≈kv_iT(v_iT is ion thermal velocity) in the rest frame of ions. Some numerical analyses are made to confirm the conclusions and to show the characteristic harmonic structure of frequency spectra.