<title>Pasotron high-power microwave source performance</title>

The PASOTRON (Plasma Assisted Slow-wave Oscillator) high- power microwave source utilizes a unique plasma-cathode electron gun and self-generated plasma channel to inject a long-pulse electron beam into a variety of slow-wave structures for microwave generation. The plasma-channel beam transport eliminates the need for an externally-applied axial magnetic field to confine the beam, which results in a very compact, low weight HPM source compared to conventional technologies. The Pasotron has been configured as both a backward-wave oscillator (BWO) and a traveling-wave amplifier, and has produced up to 20-MW of peak power and >= 500 Joules per pulse during operation as a BWO. In this paper, we will present the performance of the Pasotron device for a variety of rippled-wall and helix slow-wave structures. The advantages of each slow-wave structure will be discussed, and the output couplers and mode-converters used with each structure to obtain TE-mode outputs are described. The device configurations used for operation in C-band and in L-band will be shown. Long-pulse (approximately equals 100 microsecond(s) ec), plasma-cathode electron-guns operating at 30-to- 200 kV and currents of 50-to-1000 A will also be described. Finally, we will present and discuss pulse shortening that has been observed in these plasma-filled devices.