Effect of Induced Hall Thruster Discharge Current Oscillations on External Cathode Plume Ion Population

Spatial high-speed ion saturation probe measurements were performed on an independent cathode setup with a magnetic field simulator that matches the magnetic field topography of the HERMeS thruster. These data were directly compared to similar maps generated with the HERMeS thruster. Discharge signals from different HERMeS throttle conditions were digitized and injected on the anode signal in the lone cathode setup. Generally, inducing oscillations on the anode resulted in closer matched high-frequency wave energy to what was observed during thruster operation. Increasing the background pressure resulted in a decrease in the spatial wave energy. Alternatively, decreasing the flow rate resulted in a higher wave energy spatial profile. This suggests a high local neutral pressure near the cathode exit contributes to the neutral damping of turbulent waves in the cathode plume that are existent in the thruster plume. Matching the wave profile between lone cathode and full thruster operation is important because these waves are known to generate high-energy ions that can lead to erosion of thruster surfaces. Achieving similar wave profiles ensures an accurate representation of energetic ion production in lone cathode setups for life-time erosion testing and model verification.