Analysis And Simulation Of Vircators With Step Circular Waveguides

Abstract

It has been previously shown that higher-power microwaves can be generated from vircators with an abrupt discontinuity in circular waveguides. In this paper the authors investigate the effects of the distance of the waveguide step from the anode on the microwave output and the dominant microwave frequency via the two-dimensional, relativistic, electromagnetic, particle-in-cell code. The parameters of the vircator in this simulation study are: a negative constant voltage of 270 kV applied to the cathode, a constant injection current of 7.3 kA at the cathode surface, 0.46 cm for the cathode to anode distance, 1.3 cm cathode radius, 12.5 cm for the drift tube length, and the radii of the front and the rear section of the drift tube are 4 and 5 cm, respectively. Simulation results show that the dominant microwave frequencies are concentrated in two bands centered roughly at 8.24 and 11 GHz. As the distance of the waveguide step from the anode increases from 0 to 7 cm, the dominant microwave frequency hops between lower- and higher-frequency bands. Among each band, the frequency gradually decreases with increasing distance of the waveguide step. They have demonstrated qualitatively, through time-domain analysis of open cavities containing no sources, the dependencemore » of the dominant microwave frequency on the distance of the waveguide step. The output powers observed in the simulation are greatly enhanced at the waveguide steps of, roughly, 0.8, 1.7, 3.7--4.3, and 7.0 cm from the anode with respective dominant-mode excitation of TM{sub 01}, TM{sub 02}, TM{sub 03}, and TM{sub 04}.« less