Advanced Cathodes for Next Generation Electric Propulsion Technology

The research presented here investigated the feasibility of 6.4 mm Lanthanum Hexaboride (LaB6) and Cerium Hexaboride (CeB6) hollow cathodes for low power electric propulsion applications (100-300W). Two orifice geometries, one anode configuration, several anode and keeper currents, and a range of xenon flow rates were tested for the LaB6 cathode. The CeB6 cathode underwent the same tests, with the exception of the second orifice geometry due to time constraints. An oscilloscope measured waveform behavior and a single Langmuir probe for plasma properties. Infrared imaging studied the thermal characteristics of both cathodes and electron microscopy for surface contaminant analysis. High-speed imaging provided visual data for coupling plasma observations. The CeB6 cathode operated in spot mode as low as 1.5 A and 1.5 sccm with no heater or keeper power, and as high as 6 A, 1.5 sccm with 1 A keeper current. The CeB6 cathode was more susceptible to poisoning than the LaB6 cathode. It also operated at slightly higher temperatures. The LaB6 cathode was not affected by poisoning and ran in spot mode as low as 2.5 A, at 1.5 sccm with no heater or keeper power. When the aspect ratio was reduced to 0.25, the cathode operated as low as 1.4 A, with 1.5 sccm. The same spot/plume mode characteristics were observed for LaB6 as CeB6. The study of both cathodes is presented here including suggestions for a 3 mm LaB6 cathode.