Development of improved cathodes for high power RF sources

All high power RF sources start with an electron beam generated by a cathode. The quality of this cathode directly impacts the performance of the RF device. Typically, dispenser cathodes heated to approximately 1000 C provide the electrons constituting the electron beam that is subsequently used to drive an RF circuit. A number of high power devices recently suffered significant performance degradation due to nonuniform emission from the cathode surface. Nonuniform emission can be caused by variations in temperature or work function across the cathode surface. Research is underway to determine the causes of both temperature and work function nonuniformity and derive improved construction and processing techniques and procedures to reduce of eliminate the problems. This information will be provided to cathode vendors and users to improve the future performance of these devices. This paper presents results of research to date as well as experimental measurements of cathode performance.