Propagation and spreading of unstable perturbations in electron-hole plasmas subject to crossed fields

Abstract

A model is developed for electrostatic drift instabilities which arise in inhomogeneous electron-hole plasmas subject to crossed fieldsE 0⊥B 0. The instabilities are initiated by gradients in the equilibrium plasma densityn 0. Using two-fluid magnetohydrodynamics and linear perturbation theory the dispersion relation of local density oscillations is calculated for arbitrary inhomogeneous equilibrium distributions and plasma densities. For cases where∇n 0⊥B 0 andn 0 + ≪n 0 - it is found that the propagation direction of maximal gain, $$\hat k_m $$ , is the bisectrix of the angle between (−∇n 0) and (E 0 ×B 0) and that stable and unstable configurations are distinguished by the angle between∇Φ 0 and∇n 0. A local density perturbation built by superpositions of the plane waves, and initially chosen radially symmetric, broadens unisotropically. In the direction transverse to $$\hat k_m $$ the broadening is anomaleously enhanced, as compared to the broadening by diffusion in the stable case. The results are referred to experimental observations of low-frequency instabilities reported in [1].