Research Of Self-Feedback Vircator With Quasi-Optical Resonator

The virtual cathode oscillator (vircator) is one of the most promising high-power microwave sources due to its conceptual simplicity, high-output power capability, and tunability. The drawbacks of vircators are their low efficiency (~1% as measured in the majority of experiments) and poor frequency stability.As a solution, we propose a new type of vircator with a quasi-optical cavity surrounding the virtual cathode (VC). The cavity can be seen as a resonator to offer self-consistent feedback mechanism and frequency selectivity. It serves the purpose of enhancing the efficiency, shortening the saturated time and achieving both stable frequency and narrow bandwidth. Moreover, the output microwave with Gauss mode is apt to focus and radiate.In this thesis, the property of the resonating system is analyzed by means of the scalar potential theory. The distribution of electromagnetic field, the energy in propagation wave and the oscillation frequency of the resonator are obtained with the method of numerical calculation. In addition, our purpose is confirmed by the theoretical analysis. Results of 2.5-D numerical simulation of the device are presented with the fully electromagnetic and relativistic particle-in-cell code. A powerful microwave with quasi-Gauss mode is obtained at 7.0GHz, Xc band. The electromagnetic field is the eigen mode of the cavity, which is indicated by code of Superfish and HFSS (two professional electromagnetic analysis soft). On the other hand, the time average power of output microwave is 1.34GW and peak power overtakes 2.5GW, while the average and rms efficiency approximates to 10% and 17%, respectively. Furthermore, we find that the frequency selective property of the resonator can also narrow the bandwidth, while the high-Q and large cavity makes it possible to increase the output power and avoid the rf breakdown. In the end, we design a quasi-optical reflect system, which can focus the microwave from the resonator and radiate it effectively.In short, the simulation confirms the conclusion of the theoretic analysis. And we can believe that this new device is a useful high-power microwave generation source.