Performance and pulse shortening effects in a 200-kV PASOTRON/sup TM/ HPM source

The PASOTRON/sup TM/ is a unique, high-power microwave source that uses a long-pulse (/spl les/100 /spl mu/s) plasma-cathode electron-gun and plasma-filled slow-wave structure (SWS) to produce high-energy microwave pulses. The device utilizes no externally-produced magnetic fields; relying on a beam-generated plasma channel in the SWS to transport the beam. Peak powers of up to 5 MW were previously reported in C-band using a rippled-wall waveguide SWS. Scaling experiments indicated that increasing the beam voltage above the 90 kV C-band operation produces significantly higher peak powers. We report results from an L-band PASOTRON/sup TM/ BWO designed to operate at 200 kV. The plasma-cathode E-gun built for this device generated beams with voltages of up to 225 kV and currents in excess of 1 kA for pulse lengths of up to 200 /spl mu/s. The L-band PASOTRON/sup TM/ BWO produced 10-20 MW of peak power in the TM/sub 01/ mode, which was converted in the output to a TE/sub 11/ mode with fixed polarization. The PASOTRON/sup TM/ also directly produced TE-mode radiation in the 5-10 MW power range with a rotating output polarization, the rate of which can be controlled externally. The peak power and poise width was limited by the stability of the plasma channel at high peak powers and excessive plasma generation in the SWS during the long pulse length.