Hall Thruster Plume Characterization with Spatially Resolved Ion Energy Distribution Measurements

Standard methods for characterizing thruster efficiency using plume diagnostics are insufficient for electric propulsion systems with unknown or highly divergent plume structures. The standard practice of measuring a centerline ion energy distribution function is compared to spatially resolved ion energy measurements using a swept retarding potential analyzer. Using an adjustable Hall thruster, plumes ranging from highly divergent to overfocused were fully characterized and compared to the efficiency calculated using thrust stand measurements. Both centerline and spatially resolved measurements of the ion energy distribution function were sufficient to accurately characterize the efficiency for well-focused plumes. As the plume diverged, more complex plume structures were observed, and only the spatially resolved measurement maintained agreement with the thrust stand measurement.