A Virtual Cathode Oscillator with Double Cavities

The paper describes numerical and experimental studies of a virtual cathode oscillator (vircator) with double rectangular cavities coupled by a rectangular window. In this vircator, the virtual cathode was formed in the second cavity and the microwave generated by virtual cathode oscillation was fed back partially to the first cavity to modulate the e-beam current and so as to improve the performance of the vircator. The high frequency field structure was analyzed to find the wave mode which was fit for the interaction between the e-beam and cavity. Based on three-dimensional numerical simulations, the interaction process between the e-beam and RF field was obtained. Optimization of the device parameters was considered to obtain maximum microwave power output. A experimental device with double cavities was constructed. Experiment studies were conducted on the Spark-03 REB accelerator and microwaves of power about 220MW were measured at frequency of 2.66GHz with typical electron-beam parameters of 600 kV, 32 kA. It was observed that when the length of the couple window was changed step by step, the output microwave power changed regularly.