C12A7 Electride Hollow Cathode
AIR FORCE RESEARCH LAB EDWARDS AFB CA
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Hollow cathodes featuring C12A7 electride as a low work function thermionic emitter are hypothesized to have faster start-up times and lower operating temperatures than conventional hollow cathodes. C12A7 electride is a crystalline ceramic in which electrons clathrated in subnanometer sized cages act as a conductive medium. This unique structure leads to an extremely low work function. Calculations predict equivalent levels of current emission as LaB6 or CeB6 hollow cathode inserts, but at a much lower temperature. C12A7 electride is stable at temperatures below its re-crystallization temperature 1000 61616C and is not consumed during operation. C12A7 electride has been fabricated at CSU using a simplified, one-step approach that results in a more conductive material than previously reported. Hollow cathodes have been designed at CSU that take advantage of the unique properties of C12A7 electride, and are capable of starting at room temperature without the benefit of a heater. The C12A7 electride hollow cathodes have been shown to run stably in a diode configuration at low flow rates. In addition, a C12A7 electride hollow cathode successfully operated with a 6 kW hall thruster, producing an efficiency comparable with that of a traditional LaB6 hollow cathode. Our paper will present the results obtained from these recent tests. In addition, surface studies analyzing the effect of cathode operation on the C12A7 electride surface will be discussed.
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