Electrical Facility Effects on Faraday Probe Measurements

摘要

This work empirically investigated electrical facility effects on Faraday probe measurements. It was shown that the changes in plasma potential associated with biasing of the axial witness plate impacted the current collection characteristics of Faraday probes. Specifically, it was shown that increases in plasma potential with axial plate bias led to artificial increases in the measured divergence half-angle. This observed distortion indicates that electrical facility effects may influence terrestrial Hall effect thruster (HET) efficiency analyses. Specifically, the observed artificial changes in divergence half-angle could lead to overestimation of the power losses associated with radial plume acceleration and, consequently, for a fixed overall efficiency, underestimation of losses associated with other processes such as thruster heating as compared to what would otherwise be found in the absence of the conductive facility walls. Unless accounted for, this misallocation of power losses could cause ground tests to misrepresent the various efficiencies of a given HET during design and testing. To eliminate these effects, the process for selecting probe bias detailed in the Faraday probe measurement recommended practices should be repeated any time the electrical boundary conditions are altered.