High current density operation of a 4.5-kW Hall effect thruster on krypton

The high current density operation of the 4.5-kW T-140 Hall effect thruster, is characterized on krypton at operating powers up to approximately 2.5x the nominal power. Nominal operating setpoints are identified and characterized at discharge currents of 8 to 10 A and discharge voltage of 300 V, 2.4–4.5 kW. The thruster performance is characterized at high current density operation varying the discharge current from 10 to 20 A in 2-A steps at three different discharge voltages: 300, 400, and 500 V. The global performance is characterized, with a specific focus on the anode efficiency, for high current density operation and to understand the effect of varying discharge voltage on the operating conditions. The 300 V condition exhibits a peak anode efficiency of 49% at 14 A. The 400 and 500 V conditions demonstrate increasing anode efficiency with discharge current that approaches an asymptote of approximately 56% and 60% respectively. The anode efficiency is decomposed into constituent efficiencies, individually characterized based on plasma properties measured in the plume in order to gain a better understanding of the physics underlying the measured behavior. The current utilization efficiency is the lowest efficiency and the observed trends match those seen in the overall anode efficiency, suggesting that it has the greatest effect on the measured efficiency behavior. The mass utilization and divergence efficiencies also vary significantly with both discharge voltage and current, with a peak difference of 13% and 7%, respectively, across the tested range. Meanwhile, the voltage utilization shows small increases with discharge voltage and no discernible pattern with discharge current. The uncertainty in the total anode efficiency was calculated to be $$\pm$$ 5–7% of the reported value. Neglecting multiply-charged ions is a potential source of error, but a comparison between the anode efficiency measurements based on thrust and the anode efficiency estimates based on plume measurements shows that the difference between the two methods is within the aforementioned uncertainty of the anode efficiency for all setpoints giving confidence in the analysis methods employed.