Fairfield Plume Measurement and Analysis on the NASA-300M and NASA-300MS

NASA is developing a 10- to 15-kW Hall thruster system to support future NASA missions. This activity is funded under the Space Technology Mission Directorate Solar Electric Propulsion Technology Demonstration Mission project. As a part of the development process, the NASA-300M, a 20-kW Hall thruster, was modified to incorporate the magnetic shielding concept and named the NASA-300MS. This activity was undertaken to assess the viability of using the magnetic shielding concept on a high-power Hall thruster to greatly reduce discharge channel erosion. This paper reports on the study to characterize the far-field plumes of the NASA-300M and NASA-300MS. Diagnostics deployed included a polarlyswept Faraday probe, a Wien filter (ExB probe), a retarding potential analyzer, and a Langmuir probe. During the study, a new, more accurate, integration method for analyzing Wien filter probe data was implemented and effect of secondary electron emission on the Faraday probe data was treated. Comparison of the diagnostic results from the two thrusters showed that the magnetically shielded version performed with ~2 percent higher voltage utilization efficiency, ~2 percent lower plume divergence efficiency, and ~2 percent lower mass utilization efficiency compared to the baseline version. The net change in efficiency is within the aggregate measurement uncertainty so the overall performance is roughly equal for the two versions of the thruster. Anode efficiency calculated from thrust stand measurement corroborates this finding.