Long-pulse relativistic backward wave oscillator operation utilizing a disk cathode

It has been a tradition for pulsed power-driven intense high power microwave (HPM) sources utilizing thin-walled annular electron beams to generate such beams from a "cookie cutter" geometry cathode made from either graphite or stainless steel. When such beams are produced for pulse durations exceeding 100 ns, the accompanying microwave generation process terminates much earlier in time than the electron beam current pulse. It has been postulated that the electron beam halo caused by radial expansion of the beam is the cause of pulse shortening in the University of New Mexico (UNM) long-pulse backward wave oscillator (BWO). Recent work by Loza and colleagues has demonstrated the ability to generate intense annular electron beams of 1 /spl mu/s duration without any radial beam expansion. This was accomplished utilizing a solid disk cathode. At UNM we have integrated a disk cathode in our long-pulse BWO and have demonstrated significant lengthening of the HPM pulse.