Discharge Plasma Parameters of a 30-cm Ion Thruster Measured without Beam Extraction using a High-Speed Probe Positioning System

* Presented as Paper IEPC-03-0069 at the 28 International Electric Propulsion Conference, Toulouse, France, March 17 – 21, 2003. Published by the Electric Rocket Propulsion Society with permission. † Graduate Student, Aerospace Engineering, [email protected]. ‡ Graduate Student, Aerospace Engineering. § Associate Professor and Laboratory Director. A method for delivering a symmetric double probe into the discharge chamber of a 30-cm diameter ringcusped ion thruster is demonstrated. Motivation for direct access of the electrostatic probe to the discharge chamber stems from the need to characterize the discharge plasma to better understand the possible cause of discharge cathode assembly (DCA) erosion. A symmetric double probe allows electron temperature and number density measurements with minimal perturbation to the discharge plasma and thruster operation. The High-speed Axial Reciprocating Probe positioning system (HARP) was used to further minimize thruster perturbation during probe insertion. Internal mechanism problems restricted previous double probe measurements to one axial location. A new, slightly modified setup allowed a complete two-dimensional mapping of the discharge plasma parameters at one thruster operating condition without beam extraction. The electron number density was found to range from 1x10 – 2x10 cm inside the discharge chamber with the maximum occurring at DCA centerline, which is consistent with other results. Electron temperature ranged from 2 – 3.3 eV, which is consistent with predictions for ion thrusters incorporating a ring-cusped design. The appearance of an off-axis maximum in electron temperature necessitates further testing to confirm and explain.