Finite Beta Drift Cyclotron Instabilities in an Inhomogeneous Plasma

Abstract

The effect of finite beta (the ratio of plasma kinetic pressure to magnetic field pressure) on drift cyclotron instabilities for the nonresonant and ion resonant modes are investigated through numerical analysis of their dispersion relations. For the nonresonant mode, it is found that the two unstable regions are merged into one unstable region, if the steep density gradient is decreased, and there is a new mode which has approximately ion cyclotron frequency due to the effect of finite beta. For ion resonant convective modes (kz ≠ 0), finite beta greatly reduces the instability growth rates, though it does not remove instabilities completely. Furthermore, the effects of magnetic field gradient and curvature are examined. It is found for the nonresonant mode that the maximum growth rates are slightly enhanced. For the ion resonant mode, they are slightly reduced and the wave number of the fastest growing wave is increased as the gradient and curvature drift velocity are decreased.