Cathode Position and Orientation Effects on Cathode Coupling in a 6-kW

Cathode coupling effects in a Hall thruster are presented in an experimental study comparing operation with an external LaB6 hollow cathode at varied positions and orientations to nominal operation with a nearly identical center-mount internal cathode. The study is performed on a 6-kW laboratory model Hall thruster, a joint development effort of the Air Force Research Laboratory, the Jet Propulsion Laboratory and the University of Michigan. Testing is performed at the nominal design point of 300 volts and 20 mg/s. The plasma potential is measured via Langmuir probe in the far field plume and used with the cathode floating voltage to determine the cathode coupling voltage. Efficiency is calculated using thrust measurements from a null-type inverted pendulum thrust stand. Use of the internal cathode gives peak anode efficiency at least 3% greater than all external cases. Among the external operating cases the farthest separation distances are found to yield the best performance, including an improved cathode coupling voltage over the internal cathode