Gas poisoning investigations of scandate and M-type dispenser cathodes

Gas poisoning tests of cathode emission were carried out with four kinds of thermal cathodes: W+Sc2O3 mixed matrix cathode, impregnated scandate cathode, Ir-coated cathode, Os-coated cathode. As a result, M-type cathodes are more sensitive to O2, but can recover absolutely in a short time; scandate-type cathodes react slowly and recover partly after a long time. Compared to O2, ambient air leaked into the vacuum chamber has a smaller influence on the cathode emission; H2 has a little effect of activation on the four cathodes, especially on the Os-coated cathode.