The use of electrostatic probes to measure local plasma parameters inside the discharge chamber of a Hall thruster presents significant difficulties. The high-temperature, dense plasma, and Hall current in the accelerating channel heat the probe rapidly causing ablation of probe material, which perturbs thruster operation and reduces probe lifetime. Results are presented which show the extent of perturbation to discharge current, cathode potential, and thrust for the case where probe material is ablated. A simple thermal model of probe material heating is developed and ablation times for a typical probe configuration are presented. Using the results of the thermal model, a high-speed axial reciprocating probe ͑HARP͒ system was developed to enable probe survival and reduce thruster perturbations during interrogation of the discharge chamber of a Hall thruster. Results using the HARP system are presented showing a significant reduction in thruster perturbation. The results also indicate that a mechanism other than material ablation is contributing to perturbation of the thruster. Based on emissive probe data, the tungsten conductor appears to provide a low impedance path between magnetic field lines, enhancing electron transport to the anode.
Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruction%, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or ant other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Propellant inefficiency material in particulate form is characterized in a laboratory pulsed plasma thruster (PPT) operating at 1 Hz with a 20-J discharge energy (20 W). Exhaust deposits are collected and analyzed using a combination of a scanning electron microscope with energy dispersive x-ray analysis and microscopic imaging. Teflon® particulates are observed with characteristic diameters ranging from over 10O rius down to less Mhan 1 11111. Estimates show that the particulate emission consumes 40 .t 3 % of total propellant mass while contributing less than 1% to the total thrust. If PPT modifications can be developed that eliminate this propellant loss mechanism, 'without affecting the PPT thrust, the potential exists to increase PPT efficiency by a factor of 1.7.
Public reporting burden for this collection of information Is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of Information. Send comments regarding this burden estimate or any other aspect of this collection of Information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188),
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