Ion Energy Diagnostics in the Far-Field Plume of a High-Specific Impulse Hall Thruster
AIR FORCE RESEARCH LAB EDWARDS AFB CA
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Retarding potential analyzer and cylindrical Langmuir probe measurements were taken on the laboratory model NASA-173Mv2 to improve understanding of the physical processes affecting Hall thruster performance at high specific impulse. A retarding potential analyzer was used to measure the ion voltage distribution at voltages of 300-800 V. A cylindrical Langmuir probe was also used to obtain the local plasma potential so that the true ion voltage was obtained. The goal of the experiments was to provide information on the ionization and acceleration processes internal to the thruster as a function of discharge voltage and magnetic field. The results have shown that the ratio of ion energy to discharge voltage and the width of the ion voltage distribution both increased with discharge voltage. This implied that the primary ionization zone was growing in axial extent and moving closer to the anode as the discharge voltage increased.
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