Nongyrotropy in magnetoplasmas: simulation of wave excitation and phase space diffusion

Abstract

Nongyrotropic (gyrophase bunched) ion distributions in a magnetoplasma are studied by analytical methods and by 2-dimensional hybrid code simulations. Nongyrotropy may not occur in a plasma being simultaneously homogenous, stationary, and solenoidal in phase space. A detailed study is performed for a homogeneous and stationary plasma with sources and sinks in pase space. The analytical investigation cast in the framework of linearized Maxwell-Vlasov Theory yields a coupling of low frequeny lefthanded, righthanded, and longitudinal modes. Nongyrotropic ion distributions are unstable; they excite lefthanded waves. The growth rate is comparable to that of the iron ring instability. The hybrid code simulation stufy vonfirms the expected propagation direction parallelto the background magnetic field. Three diffusion processes are studied; arc lengthening, arc broadening, and arc radius decreasing corresponding to particle energy diffusion. the characteristic diffusion time scales are found to be of the order of 10_1 wave cycles.