Development of a LaB6 cathode for high-power Hall thrusters

High-power Hall eect thrusters represent attractive propulsion systems to perform thrust-intensive and deep-space missions. For this class of thrusters the cathodes must be able to sustain operating currents up to several tens of amperes. To this purpose, a heaterless lanthanum hexaboride (LaB6) cathode for 5-kW-class Hall eect thrusters has been developed and tested at SITAEL S.p.A. (formerly Alta S.p.A.). The boride compound has been selected for the longer expected lifetime at the required discharge current, despite the higher work function as compared to the traditional dispenser emitters. In addition, a LaB6 cathode relaxes the gas purity requirements due to a reduced sensitivity to contaminants and does not require a lengthy conditioning process to initiate the electron emission. The cathode design features a refractory metal tube and a graphite keeper to limit the eect of sputtering by ion bombardment on this electrode. A laboratory model of the cathode was experimentally characterized using both xenon and krypton as propellants. The cathode was tested at current levels as high as 18 A for a total of about 340 hours of continuous operation and more than 100 cold ignitions. The cathode was also coupled with the 5-kW HT5k Hall thruster, showing a successful operation and good performance. The experimental results will be presented and compared with the predictions from a previously developed model describing the operation of thermionic hollow cathodes, showing a good agreement between empirical and theoretical data.