Life test results of various impregnated cathode types

To ascertain the electron emission properties of impregnated cathodes, long-term tests in diodes at various loads and temperatures are performed. A test program of S, M, mixed matrix, coated mixed matrix and reservoir type cathodes was started in 1980. A test vehicle was developped which consists of a closely-spaced space gridded anode diode allowing the measure at regular intervals of time, JN, Joand φo. More than 2,000,000 hours of cumulated life test results have been obtained with an average of 20,000 hours for the latest diodes and more than 60,000 hours for the oldest ones.