Instability in Low-Pressure Plasma Diffusion Experiments

Abstract

We consider the stability of a weakly ionized, low-density (1010-1012) plasma in a uniform magnetic field. The plasma is in a finite conducting chamber and there is diffusion across the field lines and streaming to the conducting end walls. The stability analysis is similar to that of Kadomtsev and Nedospasov for the positive column. It is found that instability sets in above a critical field or below a critical background pressure. The driving force is the charge separation produced by the unequal streaming of ions and electrons to the end walls. The unstable mode is helical in space and rotates about the axis of symmetry. Expressions are obtained for the critical field value and for the rotational velocity. These compare favorably with the experiments of Neidigh and Weaver and those of Zharinov.