METHOD AND APPARATUS FOR MAKING THERMIONIC OXIDE CATHODES

摘要

A thermionic cathode and method for making same comprises depositing a thermionic oxide coating on a substrate surface. The coating comprises barium oxide, strontium oxide, or calcium oxide or a combination of these materials. An ion beam having barium, strontium, or calcium ions is directed toward the substrate surface (37). The ions (31) have a kinetic energy sufficient to cause adhesion between the ions and substrate. The substrate surface is exposed to pure oxygen gas. In a particular embodiment, the oxygen has a pressure of about 5 x 10<-6> Torr. The oxygen reacts with the deposited ions, forming the thermionic oxide coating. Preferably, the ion beam is generated by a metal vapor vacuum arc plasma gun (19). Also preferably, the ions are accelerated toward the substrate surface with an accelerating bias voltage applied to the substrate by a bias power supply (46) to help the ions adhere to the substrate surface.