Suppression of Asymmetric Mode Competition in a Cross-Band Cherenkov Microwave Generator Based on Magnetic Field Tuning

A band-switching device can realize the minimization of microwave devices, saving more space than the simple combination of two devices of different bands in situations where two bands of high power microwaves (HPMs) are needed. This article presents a 3-D design and particle-in-cell (PIC) simulations of a band-switching Cherenkov microwave generator based on magnetic field tuning. Based on the cyclotron resonance absorption, the device can generate HPMs in both C- and X-bands, respectively. Mode competition is discussed and suppressed with the 3-D simulations. With the analysis of temporal growth rate in the slow wave structure (SWS), a specific method to suppress asymmetric modes is proposed. To further mimic experiment conditions, a guiding magnetic field is obtained from the magnetic coil and a voltage with a rising and falling edge is used in the simulation. In the PIC simulations, when the magnetic field is 0.67 T, an output microwave of X-band can be obtained, with a frequency of 8.4 GHz and an average power about 1.6 GW. When switching the magnetic field to 1.55 T, a C-band microwave can be obtained, with a frequency of 4.4 GHz and an average power about 1.45 GW. The simulation results indicate the device to be practical in experiments.