The Effect of Background Pressure on SPT-100 Hall Thruster Performance

Abstract

A flight-model SPT-100 Hall thruster from the Fakel Experimental and Design Bureau was characterized with respect to performance and plume properties at The Aerospace Corporation and at L-3 Electron Technologies, Inc. over vacuum facility background pressures ranging from 2.3×10 -4 to 9.5×10 -3 Pa (1.7×10 -6 to 7.1×10 -5 Torr). Thrust and xenon mass flow rate measured at both facilities agreed to within the measurement uncertainties. Thrust decayed exponentially, while flow rate increased linearly with decreasing pressure. Using simple curve-fits for extrapolation, thrust, specific impulse, efficiency, and flow rate were projected to change by -4, -10, -14, and 7% respectively at zero pressure relative to 6.7×10 -3 Pa (5.0×10 -5 Torr). A decrease in net ion accelerating voltage and an increase in plume divergence were identified as contributors to decreased thrust with decreasing pressure. The amplitude of discharge current oscillations decreased linearly with decreasing background pressure, while the center frequency of the oscillations also decreased, from 26 to 16.5 kHz, but in non-linear fashion. Neutral density near the exit plane of Hall thrusters can be quite low, O(10 18 ) m -3 , such that background neutrals from the residual gas in the vacuum chamber may significantly influence ionization and conduction there.