Simulation of a High-power V-band Transit-time Oscillator under a Low Magnetic Field

With the development of high-power microwave technology, the study of high-power microwave sources is moving towards higher frequencies. However, when the frequency band expands to the millimeter band, the instability of the electron beam is very strong, which makes the guiding magnetic field of the device high and the resultant bulky and heavy solenoid system. Among all the high-power microwave generators, the transit-time oscillator is one form of a slow-wave device that converts the kinetic energy of an electron beam into microwave radiation. Due to the potential significance of millimeter wave V-band application and the sake of compactness and miniaturization, a V-band low magnetic field high-efficiency transit-time oscillator is studied in this paper. By using TM
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mode, the volume wave property of the generator is enhanced to avoid the high energy electron beam diffusion bombardment on the device surface under a low magnetic field. Furthermore, the maximum surface field of the device can be reduced by using a positive conductance modulation cavity and a traveling-wave extraction cavity, what’s more, the power capacity and fundamental harmonic current modulation coefficient can be also increased. With the improvement of the fundamental harmonic current modulation coefficient, the beam-wave interaction can be further promoted so that the efficiency of the device can be enhanced. The particle-in-cell code is used to simulate the working state of the model, and the results are as follows when the guiding magnetic field of 0.7 T, the electron beam voltage of 393 kV, and the current of 5.2 kA, the microwave output power of the device is 491.3 MW with the corresponding conversion efficiency is 24%, and the frequency of the output microwave is 59.76 GHz.