Magnetic confinement in a ring-cusp ion thruster discharge plasma

摘要

An experimental investigation, in conjunction with a volume averaged analytical model, has been developed to improve the confinement and production of the discharge plasma for plasma thrusters and ion sources. The research conducted explores the discharge performance of a ring-cusp ion source based on the magnetic field configuration, geometry, and power level. Analytical formulations for electron and ion confinement are developed to predict the ionization efficiency for a given discharge chamber design. Explicit determination of discharge loss and volume averaged plasma parameters are- obtained via a series of experimental measurements on a ring-cusp NASA Solar Technology Application Readiness (NSTAR) ion thruster to assess the validity of the analytical model. Measurements of the discharge loss with multiple magnetic field configurations compare well with plasma parameter predictions for propellant utilizations between 80% and 95%. The results indicate that increasing the magnetic strength of the first rnclosed magnetic contour line reduces Maxwellian electron diffusion and electrostatically confines the ion population and subsequent loss to the anode wall. The results also indicate that increasing the strength and minimizing the area of the magnetic cusps improves primary electron confinement, increasing the probability of an ionization collision prior to loss at the cusp.