Axially Extracted Vircator Research Feedback

The axially extracted virtual cathode oscillator with feedback is a promising high power microwave source. The electron beam and virtual cathode oscillation can be modulated in this type of vircator by the microwave reflected by feedback ring. This feedback device can increase the output power, stabilize the operation frequency and purify the microwave modes. In this dissertation, the axially extracted vircator with feedback is investigated by means of particle-in-cell (PIC) simulation with some of the results analysed theoretically.A 2?dimensional PIC code is employed to research into the change of themicrowave frequency, of the band width, and of the output power when the location and the size of the feedback ring changed. The output power of the feedbacked vircator can be three times that of the conventional vircator in the simulation cases, because of the number increase of the electrons oscillating in the virtual cathode, which results from the modulation of the feedbacked microwave. For example, the output power of the feedbacked vircator exceeds 330MW with diode voltage of 500kV and beam current of 40kA, while the conventional vircator generates only 94MW on the same condition. At the same time, the band width of microwaves is narrowed obviously in the former case.A axially extracted vircator with feedback is designed with the parameters optimized through PIC simulation. The average output power of this vircator is higher than 900MW, with its peak power above 2GW and operation frequency in C band.The influence of both the electron beam and the feedback ring is analysed withthe method of equivalent circuits and the perturbation theory of resonant cavity.The results show that the frequency of the microwave will increase with the feedback ring loaded in the conventional vircator, and the frequency of the resonant microwave in cavity will decrease with the electron beam injected, which are proved with PIC and SUPERFISH codes.