Plasma Electromagnetic Instabilities

Abstract

A gyrotropic plasma with T_∥/T_⊥ ≡ γ < 1, where T_⊥ and T_∥ are the transverse and longitudinal temperatures, is shown to be unstable to a perturbation in the form of a transverse wave with a wave vector k such that k² < k₀² = {ω_c²(1−γ)² + ω_p²(1−γ)/γ}/c², ω_c and ω_p are the gyro and plasma frequencies. For T_∥ > T_⊥ such an instability arises only if ω_c²/ω_p² > 1/γ(γ−1) and then only for k² < k₀². However, in the latter case, the phase velocity of the instability exceeds c and the growth rate must be made to vanish because of relativistic considerations. No such instability arises for complete isotropy T_⊥ = T_∥.