The use of the electride form of 12CaO-7Al.sub.2O.sub.3, or C12A7, as a low work function electron emitter in a hollow cathode discharge apparatus is described. No heater is required to initiate operation of the present cathode, as is necessary for traditional hollow cathode devices. Because C12A7 has a fully oxidized lattice structure, exposure to oxygen does not degrade the electride. The electride was surrounded by a graphite liner since it was found that the C12A7 electride converts to it's eutectic (CA+C3A) form when heated (through natural hollow cathode operation) in a metal tube.

The use of the electride form of 12CaO-7Al.sub.2O.sub.3, or C12A7, as a low work function electron emitter in a hollow cathode discharge apparatus is described. No heater is required to initiate operation of the present cathode, as is necessary for traditional hollow cathode devices. Because C12A7 has a fully oxidized lattice structure, exposure to oxygen does not degrade the electride. The electride was surrounded by a graphite liner since it was found that the C12A7 electride converts to it's eutectic (CA+C3A) form when heated (through natural hollow cathode operation) in a metal tube.

Current sharing in a power system having multiple PSUs comprises generating and supplying a first power and a second power to a load, and sensing a remote voltage value received by the load based on an accumulation of the first and second powers. The method further comprises determining, by the first PSU, local voltage and current values of the first power, a real impedance value of the first PSU based on the remote voltage value and the local voltage and current values of the first power, and a virtual impedance value of the first PSU based on the real impedance value of the first PSU and a reference impedance value. The method further comprises controlling generation of the first power by the first PSU based on the virtual impedance value of the first PSU.