Abstract
An S-type impregnated cathode depends on the Ba consumption for its life time, whereas an M-type the composition change of the coating film as well as the Ba consumption. For the latter cathode, the factor which ends the cathode life is determined by the cathode operation temperature. The lifetime determination factor for an M-type cathode, operating at 1000℃, is the Ba consumption rate. Activation energy of Ba evaporation process undergoes three stages during the cathode life. In the first stage, the energy increases from early 〜3eV to 〜4eV. Second stage is a stable period maintaining the activation energy of 〜4eV. Finally the energy rapidly increases and the cathode life comes to an end.
