Predicting cathode life expectancy and emission quality from PWFD measurements

An objective measure is needed to assess cathode emission quality and life expectancy both for real-life applications and for cathode improvement research. The PWFD (practical work function distribution) is introduced as a convenient and simple method for representing measured cathode emission data. The PWFD is a sensitive and objective measure of emission quality useful for routine diagnosis of operating cathodes or for performance characterization and ranking of experimental cathodes. ‘Best of Class’ performance (best observed emission performance) has been identified from an extensive life test database for various cathode types and presented as a ‘Best of Class’ PWFD standard benchmark. Cathode life expectancy can be estimated from life test data for cathodes with similar PWFD characteristics. Most important, cathodes exhibiting ‘Best of Class’ PWFD performance typically exhibit ‘Best of Class’ life expectancy. The PWFD from low voltage measurements can also be used to project cathode performance to high voltage operation.