A universal multi-mode filament regulator for hard tubes

High power RF triodes used to power the injector linac cavities on the ISIS spallation neutron source at RAL tended to fail prematurely through low emission. The implication of this was a tube temperature problem. The tube manufacturer was consulted and in parallel a review instigated of the heater control system. A direct relationship between applied power and filament temperature exists and the Richardson-Dushman equation shows that for a small increase in filament temperature, a significant increase in the availability of electron emission occurs. The resulting increased depletion of filament carburization shortens the lifetime of the tube. Development and installation of a universal filament management system to replace obsolete equipment and simultaneously improve the operational stability has resulted in significantly extended tube service life. Reductions in capital costs and the ability to predict RF tube life has become possible, promoting the establishment of an effective tube replacement strategy. Actual filament lifetime data, accumulated over several years, is presented