Life test performance of thermionic cathodes

To ascertain the electron emission properties of impregnated M-type cathodes long term life tests in diodes have been performed. The evolution of the zero field current density and the emitted current during more than 100,000 h has been determined. The evolution of the emitted current in travelling wave tubes (TWT) has also been measured and compared with the results obtained in diodes. Two mathematical models have been developed and calibrated to get long term evolution of the cathodes current in diodes and TWTʹs. From the results the life time (to 10% of current loss) in TWTʹs is estimated at 200,000 h, 170,000 h and 150,000 h for a load of 0.5, 1.5 and 2 A/cm2, respectively at temperature of 985°Cb.