A Study on Plasma Diffusion in a Uniform Magnetic Field

Abstract

Through gas plasmas of very low charge densities, electrons and ions diffuse freely because the space charge is negligible (free diffusion limit). On the contrary at high charge densities, the space-charge induced field saturates and causes the ambipolar diffusion which is a combination of diffusive and saturated mobility flow (ambipolar limit). The transition from the ambipolar to the free diffusion is studied for the case of magnetized slab plasmas maintained in between two plane-walls through ionization by electron collision. The basic equation is nonilnear because of the mobility flow due to the spacecharge field. A simple analytic approximation is applied to the distribution of charged particles. The amplitude of charged particle distribution and the plasma thickness are determined by an iterative numerical procedure. For typical values of the characteristic plasma parameters for magnetized hydrogen plasmas, variation of the charged particle density through the transition between both limits is investigated. Spatial distributions of electrons and ions inside the plasma slab are calculated.