Ignition and Early Operating Characteristics of a Low- Current C12A7 Hollow Cathode

Calcium aluminate electride 12CaO-7Al2O3:4e(e.g., C12A7:e-) shows promise as a low temperature electron emitter for hollow cathodes in spacecraft electric propulsion, but the material’s basic performance limits remain poorly understood, including an exact value for work function. As a supplement to a companion paper examining C12A7:eemission in a planar close-spaced diode configuration in vacuum, this paper examines operation of C12A7:etubular inserts in the plasma environment of a gas-fed hollow cathode. The inserts are sized for a lanthanum hexaboride (LaB6) 20-ampere class cathode normally used in a Hall thruster, but are here operated at greatly reduced currents of 30-150 mA due to early experiences with insert overheating and degradation. Nevertheless, the low sustainable operating powers demonstrated in these low-current operating modes suggest that C12A7 cathodes merit further investigation and improved thermal and plasma design.