LOW-FREQUENCY OSCILLATIONS IN A STATIONARY PLASMA THRUSTER

Stationary plasma thrusters are ion thrusters whose properties make th em especially suitable for satellite station keeping or orbit transfer . In these thrusters, a magnetic field transverse to the electron flow towards the anode increases the electron collision frequency and make s possible the generation of a plasma at relatively low gas flow and g as density. The decrease of the plasma conductivity due to the magneti c field induces a large electric field in the plasma which accelerates the quasicollisionless ions whose trajectories are not significantly affected by the magnetic field. The purpose of this article is to clar ify, using results from a simple model, the electrical properties of t hese thrusters and the low frequency oscillation regime which has been observed experimentally. The model is based on the assumption of quas ineutrality of the plasma column and on a 1D transient hybrid treatmen t of electron and ion transport in the device. Electrons are considere d as a fluid and ions are described with a collisionless kinetic equat ion. This model provides reasonable estimates of the plasma properties and is able to give a clear picture of the low frequency oscillations , qualitatively close to the experimental observations. (C) 1998 Ameri can Institute of Physics. [S0021-8979(98)07919-5].