Efficiency Analysis of a High-Specific Impulse Hall Thruster

Performance and plasma measurements of the high-specific impulse NASA-173Mv2 Hall thruster were analyzed using a phenomenological performance model that accounts for a partially-ionized plasma containing multiply-charged ions. Between discharge voltages of 300-900 V, the results showed that although the net decrease of efficiency due to multiplycharged ions was only 1.5-3.0%, the effects of multiply-charged ions on the ion and electron currents could not be neglected. Between 300-900 V, the increase of the discharge current was attributed to the increasing fraction of multiply-charged ions, while the maximum deviation of the electron current from its average value was only +5/-14%. These findings revealed how efficient operation at high-specific impulse was enabled through the regulation of the electron current with the applied magnetic field. Between 300-900 V, the voltage utilization ranged from 89-97%, the mass utilization from 86-90%, and the current utilization from 77-81%. Therefore, the anode efficiency was largely determined by the current utilization. The electron Hall parameter was nearly constant with voltage, decreasing from an average of 210 at 300 V to an average of 160 between 400-900 V. These results confirmed our claim that efficient operation can be achieved only over a limited range of Hall parameters.