Lifetime experience with low temperature cathodes equipped in super power klystrons

When Philips started the production of super power klystrons in 1976 the electron emitter was a tungsten dispenser cathode of the well-known Philips “B” type. One disadvantage of this cathode type is the relative high cathode temperature. Many efforts have been spent from researchers world-wide to decrease the operating temperature of the dispenser cathode. Since 1990 we have tested several sputter coated Os/Ru cathodes in cw super power klystrons. The expected decrease of the temperature has been entirely confirmed. Measured emission data compared to “B” cathodes during factory acceptance test are presented. Positive experience concerning lifetime under real operation conditions has been gained at different international accelerator centers and will be reported