Harness impedance effects on temporal ion energy in a low-power Hall effect thruster

Abstract

The finite length of the Hall effect thruster (HET) electrical harness has been shown to influence thruster operation by altering voltage fluctuations at the anode through changes in harness impedance. As the anode potential determines the acceleration experienced by ions, it is hypothesized that harness-induced anode-voltage fluctuations could affect ion energy within the thruster plume. To quantify the impact of HET harness inductance on discharge telemetry and plume properties, the harness inductance was varied using an air-core roller inductor. In this study, we evaluated a range of harness inductances using a 300 W HET while measuring time-resolved ion energy with a high-speed retarding potential analyzer and plasma potential with a high-speed dual Langmuir probe. Diagnostics were translated between two radial positions at 0.5 m downstream of the thruster, corresponding to a centerline and 0.2 m off-centerline location, each oriented toward the thruster. Two magnetic-field configurations were tested to verify whether harness-induced energy oscillations persisted across different discharge conditions. High-speed measurements of plasma potential showed no variation with changes in harness inductance, within measurement uncertainty. Time-resolved ion energy measurements revealed changes in oscillation amplitude and frequency at both measurement locations and operating configurations, with the ion energy peak-to-peak amplitude increasing by up to 12.5%. This work reveals that harness inductance influences ion energy populations in HET plumes, leading to energy shifts and an increased fraction of higher-energy ions at greater harness impedances, highlighting the importance of harness length and impedance in thruster–facility electrical configuration.