Stability properties of a field-reversed ion layer in a background plasma

Abstract

Stability properties of an intense proton layer (P layer) immersed in a background plasma are investigated within the framework of a hybrid model in which the layer ions are described by the Vlasov equation, and the background plasma electrons and ions are described as macroscopic, cold fluids. Moreover, the stability analysis is carried out for frequencies near multiples of the mean rotational frequency of the layer. It is assumed that the layer is thin, with radial thickness (2a) much smaller than the mean radius (R0). Electromagnetic stability properties are calculated for flute perturbations (∂/∂z=0) about a P layer with rectangular density profile, described by the rigid-rotor equilibrium distribution function f0b= (minb/2π) δ (U−T̂) G (vz), where nb and T̂ are constants, mi is the mass of the layer ions, G (vz) is the parallel velocity distribution, and U is an effective perpendicular energy variable. Stability properties are investigated including the effects of (a) the equilibrium magnetic field depression produced by the P layer, (b) transverse magnetic perturbations (δB≠0), (c) small (but finite) transverse temperature of the layer ions, and (d) the dielectric properties of the background plasma. All of these effects are shown to have an important influence on stability behavior. For example, for a dense background plasma, the system can be easily stabilized by a sufficiently large transverse temperature of the layer ions.