Research Of C Band New Vircator With Quasi-Optical Resonator

The virtual cathode oscillator(vircator) is one of the most promising high-power microwave sources because of its conceptual simplicity, high-output power capability, and its tenability. The disadvantages of vircators are their low efficiency, poor frequency stability and their broadband.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, shorting 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 theoretical analysis. In this cavity, the electromagnetic field is similar to the Gauss mode. The center is the strongest position of the field. And the longitudinal electric field oscillates along the axial direction periodically. At one time, the radial field attenuates rapidly. Thus, the virtual cathode oscillation will couple with the field intensively in order that the beam and field can interact efficiently. On the other hand, by using the resonator, the feedback of the electromagnetic wave is strong enough to increase the amplitude of the energy modulation and efficiency. And the frequency of the microwave can be made stable due to the frequency selectivity of the resonator.In addition, the numerical simulation is carried out with the fully electromagnetic and relativistic 2.5-D PIC particle-in-cell code to investigate the characteristics of this new configuration. Results of the numerical simulation of the device are presented. And the results of simulation are consistent with the results of theoretical analysis. A powerful microwave with TEM₁₁₆ quasi-Gauss mode is obtained at 5.0GHz, C band. And the electromagnetic field is the eigen mode of the cavity. Furthermore, the time average power of output microwave is 1.17GW and peak power overtakes 2GW, while the average and rms efficiency approximates to 8.8% and 15%, respectively. By the simulation, we also find that the frequency selective property of the resonator can also narrow the bandwidth, while the high-Q and large cavity makes it possible toincrease the output power and avoid the rf breakdown.Besides, we also investigate the device with a hollow electron beam injected into the cavity by the simulation. A powerful microwave with TEMn6 quasi-Gauss mode is obtained at 4.8GHz, C band. The time average power of the output microwave is 860MW and the peak power overtakes 1.6GW, while the average and rms efficiency approximates to 6.6% and 12%.