A calcium aluminate electride hollow cathode
Date
2014
Authors
Rand, Lauren Paula, author
Williams, John, advisor
Reynolds, Melissa, committee member
Sampath, Walajabad, committee member
Yalin, Azer, committee member
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Abstract
The development and testing of a hollow cathode utilizing C12A7 (12CaO.Al2O3) electride as an insert are presented. Hollow cathodes are an integral part of electric propulsion thrusters on satellites and ground-based plasma sources for materials engineering. The power efficiency and durability of these components are critical, especially when used in flight applications. A low work function material internal to the cathode supplies the electrons needed to create the cathode plasma. Current state-of-the- art insert materials are either susceptible to poisoning or need to be heated to temperatures that result in a shortened cathode lifetime. C12A7 electride is a ceramic in which electrons contained in sub-nanometer sized lattice cages act as a conductive medium. Due to its unique atomic structure and large size, C12A7 electride has a predicted work function much lower than traditional insert materials. A novel, one-step fabrication process was developed that produced an amorphous form of C12A7 electride that had a measured work function 0.76 eV. A single electride hollow cathode was operated on xenon for over 60 hours over a two-month period that included 20 restarts and 11 chamber vent pump-down sequences with no sign of degradation, and on iodine for over 20 hours with no apparent reactivity issues. The operations of cathodes with three different orifice sizes were compared, and their effects on the interior cathode plasma modeled in a zero- dimensional phenomenological model.
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Subject
electride
hollow cathode
electron emission