In-vacuo work function measurement of dispenser cathodes

A novel experimental technique was used for direct measurement of cathode material work function at elevated temperature. Dispenser cathodes were activated in a vacuum chamber and the work function determined from the contact potential difference between the cathode and a precisely calibrated probe tip. The experimental test setup allowed for cathodes to be activated and the work function measured without breaking vacuum. B-Type, M-Type, and other cathodes were activated and their work function tracked during the initial heating stage and during cooling after activation. The various cathode types showed a smooth increase in work function as the cathode cooled, but the B-Type had a lower room temperature work function than other cathodes. It is suggested that residual gas in the chamber may have caused the rise in work function during cooling.