Scandate hollow cathode for ion thruster

A hollow cathode was fabricated from scandium oxide-doped one-micron tungsten powder. The prepared powder was pressed into a solid billet and sintered in hydrogen. The sintered billet was electron discharge machined to create the hollow emitter. A unique test vehicle was developed consisting of a central wire as anode, a glass-rodded support structure, and a glass envelope, pumped and baked at 400^o C. The cathode was tested in both vacuum and one torr of xenon. The vacuum was maintained with barium getters flashed on the internal surface of the envelope. A capsule containing xenon was enclosed in the vacuum envelope. After vacuum testing, the capsule was broken and cathode emission in a xenon discharge was measured. About 2 amps/cm² space-charge-limited emission was achieved in vacuum at 945^o C_b(W). In xenon, the current was 50 amps (17A/cm²) temperature-limited at 880^o C_b(W). By contrast, an all-tungsten emitter of the same geometry required a temperature of 1080^o C_b(W) to achieve the same current.