High Current Lanthanum Hexaboride Hollow Cathode for 20-to-100 kW Class Hall Thrusters

Abstract

NASA is continuing to develop high power Hall thrusters in the range of 20 to 100 kW for future cargo and manned-missions. The cathodes for these thrusters will be required to produce discharge currents in the 50 to likely over 300 A range with lifetimes in excess of 10 khrs. A prototype high current hollow cathode with a 2-cm-dia lanthanum hexaboride (LaB 6 ) insert was previously developed for these applications. The original design featured a graphite cathode tube to interface with the LaB 6 insert and an Al 2 O 3 insulated sheath heater capable of heating the higher temperature emitter to ignition temperatures. A new version of this cathode has been designed and built that uses a refractory metal cathode tube and features a robust design similar to the small LaB 6 cathode used for the H6 Hall thruster. The cathode has been successfully tested at steady-state discharge currents from 25 A to 300 A. This cathode is intended to be used in the X3/80 80-kW Nested Hall thruster being built at the University of Michigan at discharge currents over 250 A.