The status of thermionic cathodes: theory and practice

Summary form only given. Most practical devices rely on the measurement of emission current as the only practical means of evaluating the adequacy of cathode emission. A complete theory of emission is essential for evaluating cathode efficiency. The theories of thermionic emission developed shortly after the discovery of the emission phenomena are incomplete. Part of this paper addresses the inconsistencies of existing theories and shows that these theories can be used to produce a coherent and unified emission theory. Certain vacuum electron devices (VEDs) such as multiple beam klystrons (MBKs) and millimeter wave devices place a demand on electron sources to provide higher current densities. This paper also describes various cathode materials and structures for these high power devices.