100 W Operation of a Cold Cathode TWT

Recent demonstration of low-voltage high-transconductance field emitter array operation holds promise for the successful development of reliable cold cathode vacuum electronics device technologies. This paper reports on the experimental studies of implementation of such field emitter arrays as the electron source for a moderate power traveling wave tube (TWT) operating in the C-band frequency regime. The cold cathode TWT has operated for over 150 h at duty factors up to 10%, beam currents up to 121 mA, and RF powers up to 100 W at 5 GHz. High cathode current densities of 15.4 A/cm² were achieved concurrent with excellent beam control, resulting in 99.4% beam transmission under zero-RF-drive operating conditions and 97.3% transmission at maximum RF output power. The cathode is shown to operate with a 72% reduction in the operating voltage from the previous generation of emitters fabricated by SRI International, bringing the operating voltage for full current operation well below 100 V. Extensive device characterization and life testing has been performed, and interesting variation in cathode performance was observed during the high-duty high-current portion of the testing program. The results presented here represent the highest current, highest power, and highest duty factor ever reported for an RF vacuum device employing a field emission cold cathode electron source.