Performance analysis of a low-power magnetically shielded hall thruster: Computational modeling

摘要

The applicability of a fully shielding magnetic field topology to a low-power xenon Hall thruster was demonstrated through testing of the MaSMi-60. Although the discharge channel lifetime was significantly increased, performance testing of the device revealed a peak anode efficiency of under 30%, which was lower than expected given the available data on high-power magnetically shielded Hall thrusters. Experimental measurements in a vacuum facility with operating pressures of <5 × 10~6torr suggest that the MaSMi-60's current utilization, mass utilization, and beam divergence efficiencies were the key contributors to its moderate performance. To better understand the physics causing these performance deficiencies, a computational analysis including2Dplasma modeling of the MaSMi-60 was conducted. Results from the 2D numerical models confirmed that the MaSMi-60 achieved the parameters necessary for magnetic shielding. The physics governing the low mass utilization, current utilization, and beam divergence efficiencies were then identified and described using the computational model results. The low mass utilization is attributed to a long ionization mean free path in the discharge channel caused by the predominantly axial trajectory of the injected propellant. Insufficient magnetic field strength enabling excessive electron current to the anode was the primary cause for the poor current utilization. Lastly, the high beam divergence was due to an overly shielding magnetic field topology that promoted high-energy ions to be accelerated far off the thruster's axis.