Magnetically Shielded Miniature Hall Thruster: Performance Assessment and Status Update

The magnetically shielded miniature Hall thruster, originally tested at the University of California, Los Angeles, underwent performance validation experiments at the Jet Propulsion Laboratory. The thruster was operated over a range of discharge voltages, from 150 V – 300V, and currents, from 1 A – 2.3 A. It was discovered that the thruster operated in two distinct modes which were dependent on the thruster’s temperature: a “jet” mode and a “diffuse” mode. At the nominal condition of 275 V and 1.2 A in the jet mode, a thrust of approximately 12 – 13 mN was measured by a thrust stand with an anode efficiency of approximately24%. At the same nominal conditions, the diffuse mode showed a thrust of 11 – 12 mN and an anode efficiency of approximately 21%. Characterization of the plume in both operating modes was accomplished using a shielded Faraday probe, a retarding potential analyzer, and an ExB probe. Discharge current oscillations on the order of 2.5 – 4 times the mean current were observed during jet mode operation, while the oscillations in the diffuse mode were on the order of 20% of the mean current. Results from the plume characterization, post-operation discharge channel inspection, and discharge oscillations, combined with the temperature-dependent mode shift, suggest that changes to the magnetic field strength and topology caused by saturation of the thruster’s magnetic circuit may be occurring at elevated operating temperatures.