Mode competition in a high current, high voltage gyro-BWO experiment

Abstract

Summary form only given, as follows. The Air Force Phillips Laboratory Gyro-BWO experiment is utilizing the RAMBO pulser, with electron beam parameters of: V/sub D/=300-800 kV; I/sub D/=1-50 kA; pulselength=1-3 /spl mu/s. An annular electron beam of /spl sim/1-3 kA is produced by an annular aluminum cathode. The interaction cavity is designed to radiate in the frequency range of 4.2-5.5 GHz in a TE/sub 01/ mode. The interaction cavity has a radius of 4.37 cm and a length of 15 cm. A diode magnetic field is used for a field immersed diode, and is tunable from 0-2 kG. The interaction region magnetic field is tunable from 2-7 kG. The diode and interaction magnetic fields are used together to provide a magnetic compression of the electron beam. C-Band bevel-cut antennas located at the diode end of the experiment are used to extract the backward wave. Experiments have given microwave output pulselengths of 40-500 ns, on a voltage pulselength of 200-1400 ns. Extracted power range from 0.1 to 4 MW, and is voltage dependent. Nearly constant rf power can be extracted from 4.2-5.0 GHz in small passband filters. Breakdown of the air in the C-Band waveguide has been observed during operation in the TE/sub 21/ mode. Evidence of mode competition exists in the form of two different frequency values appearing at the same time. A /spl lambda//4 slotted cavity has been designed,as well as a helical slotted cavity, in an effort to suppress the TE/sub n1/ modes, n=0. Analysis and numerical simulations from the 2 1/2-D PIC code MAGIC will be presented, as well as the latest experimental results.