A partially-insulated cathode for exciting plasma in a plasma chamber is provided. The partially-insulated cathode includes a conductive structure enclosing a cavity having a cavity surface and an insulating material contiguously covering a portion of the cavity surface from the cavity opening up to an insulation height that is less than a cavity height. Cross-sections of the cavity in X-Y planes have at least one respective cavity-width. A cavity opening has a diameter less than a minimum cavity-width of the at least one cavity-width.

An electron gun may include a cathode with an emitting surface configured to emit electrons. The cathode may include a through hole that goes through the emitting surface and is configured to allow back-streaming electrons of the emitted electrons to pass through. The electron gun may also include an anode configured to attract the emitted electrons from the cathode to the anode and focus the emitted electrons into an electron beam. The electron gun may also include a grid structure configured to facilitate the focusing of the emitted electrons, the grid structure being positioned corresponding to the through hole.

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.