Instabilities in E × B Discharges Relevant to Electric Propulsion Plasmas

Investigation of instabilities in E x B plasmas of electric propulsion (EP) devices is crucial to estimate their performances and operation lifetimes [1] , [2] . High-speed imaging and measurement of magnetic-field using B-dot probe arrays have demonstrated the presence of azimuthal spoke modes in Inductive Pulsed Plasma Thrusters (IPPT). The presence of spokes in IPPTs as well as the high spoke mode numbers observed represent as yet unexplored areas of study for these E x B instabilities. The image analysis involved the development of novel techniques to track spokes in a rapidly evolving plasma discharge. Spoke surfaces [3] were generated from high-speed images and the spoke rotation was measured using Radon transform of segments of the spoke surface. The results show the dependence of spoke formation on the background pressure and the discharge voltage. The spokes also show evidence of self-organization into large-scale structures. The image analysis and signal processing methods will be applied to other EP systems of interest, mainly Hall thrusters and Electron Cyclotron Resonance thrusters.