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

Summary form only given, as follows. It has been a tradition for pulsed power-driven intense high power microwave (HPM) sources utilizing annular electron beams to generate such beams from a "cookie cutter" geometry cathode made from typically 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 BWO. Work by Loza and colleagues (2000) have demonstrated the ability to generate intense annular electron beams of 1 microsecond 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. We present results from both experiments and MAGIC simulations that describe the advantages of using disk cathodes in this application.