Excellent performance of a C12A7:e- cold cathode based on charge coupling techniques

Abstract

Abstract This work, based on the EU-funded project NEMESIS, is aiming at developing electride-based new cathode technology which is compatible with all kinds of electric propulsion systems requiring neutralization. In last years, the novel material C12A7:e- electride has been investigated for neutralization applications due to its adequate characteristics as thermionic emitter: low effective work function of 2.4 eV, lower operational temperatures than traditional emitters as LaB6, BaO or Thoriated-W, stability at room temperature and chemical inertness. Additionally, the electride can be used as cathode material to provide electrons in low pressure discharges where the operation temperatures are much lower than for electron thermionic emission. Nevertheless, some of the most common issues described in literature about C12A7:e- based cathodes are the emission instabilities, which in some cases derive into degradation, sputtering or even melting of the electride material. A new developed technique based on charge coupling showed a remarkable performance up to five times better than other typical emitter material in terms of current emission and power consumption. In this work, the performance improvements reached when using this technique in the operation of C12A7:e- based cathodes when using Argon, Xenon or Ammonia (NH3) as propellants will be described. NH3 is incorporated in this work because it is one of the best mass storage compounds in liquid state at very low pressures and/or temperatures (10bar@25ºC, 1bar@-33ºC) with an easy and direct gas usage as propellant in space propulsion. It is also an excellent H2 carrier (4 KWh/Liter), which makes it an appropriate H2 carrier for future use by H2 Fuel Cells or even NH3 direct Fuel Cells in space.