Investigation of lower order mode suppression in a high current, high voltage gyro-BWO experiment

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. 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 shown evidence of mode competition existing as two different frequency values appearing at the same time. A helical slotted cavity has been designed, in an effort to suppress the TE/sub n1n1/ modes, n/spl ne/0. Analysis and numerical simulations from the 3-D code HFSS will be presented, as well as the latest experimental results.