Impact of dispenser cathode thickness on useful operating life

Summary form only given. Vacuum electron devices generally rely on a thermionic dispenser cathode as an electron source. Cathodes used in expendable applications that require fast warm-up are generally very thin. Recent emission testing of a quick warm-up cathode for an expendable TWT has indicated a shorter operating life than life test data and models predict. Analysis of samples indicates that there is still Ba present in the matrix at the end of life, the impregnant below the cathode surface has not receded appreciably and no discernable Ba concentration gradient seems to exist. This may indicate that very thin cathode buttons do not have sufficient impregnant to maintain surface coverage for long periods of time. There are several physical processes that impact the arrival rate of Ba to the surface of the cathode. Data from life testing a thin cathode button and a theoretical model that attempts to include button thickness and the associated Ba arrival rate processes are presented in this paper.