Understanding the discharge current distribution and upper operational limit of a high power, gridded ion thruster

Summary form only given. Past studies suggest that for a given ion thruster magnetic circuit configuration, there exists an upper discharge operational limit, above which the discharge is either unstable or operates in a reduced efficiency mode. A 50 cm, ring cusp ion thruster discharge chamber was operated at elevated discharge currents in an attempt to identify its operational upper limit. The discharge plasma properties near the anode and in the bulk of the discharge were monitored using Langmuir probes as a function of discharge current for currents up to 85 A. The current distribution to the magnet rings and the intervening anode shell was also monitored. It was found that the discharge was essentially resistive up to 85 A. The limits of the ring cusp magnetic circuit was also probed by floating collection electrodes placed at the various magnet rings. By floating various magnet rings, operational upper limits for a given collection electrode combination could be determined. Finally it should be pointed out that discharge operation without collection at any magnet ring was demonstrated. Variation in discharge efficiency for the various ring configurations is also reported.