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

A model is developed for electrostatic drift instabilities which arise in inhomogeneous electron-hole plasmas subject to crossed fieldsE₀B₀. The instabilities are initiated by gradients in the equilibrium plasma densityn₀. 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 wheren₀B₀ andn₀⁺n₀^- it is found that the propagation direction of maximal gain,, is the bisectrix of the angle between (–n₀) and (E₀ ×B₀) and that stable and unstable configurations are distinguished by the angle between₀ andn₀. A local density perturbation built by superpositions of the plane waves, and initially chosen radially symmetric, broadens unisotropically. In the direction transverse to 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].