Life prediction model for vacuum electron devices using barium calcium aluminate impregnated tungsten cathodes as electron sources

Operational life of most Vacuum Electron Devices (VEDs) is dependent on the function of the electron source used. In most Klystrons and TWTs dispenser cathodes, which are made of porous tungsten impregnated with Barium calcium aluminate, are used as the electron source. Often these are over-coated with osmium ruthenium. The mechanisms involved in these electron sources are rather complex. When heated the impregnant reacts with the tungsten in the pores releasing Barium which must migrate through the pores to the surface of the cathode. Once there the Barium, through surface migration, uniformly covers the surface up to a monolayer. This coverage plus and the metal substrate composition determine the surface work-function. All of these factors change with time, operating temperature and measurement temperature. Earlier models did not consider the effect of decreasing coverage between pores. The model described takes all this factor into consideration.