Millimeter Wave Cyclotron Superradiant Mechanism

In recent years much attention has been paid to Superradiance(SR) because of its high peak power conversion efficiency, so far the devices based on Cherenkov SR regime have been well developed while the research on Cyclotron SR is still in the initial stage. In fact because the cyclotron has its inherent merits on the generation of high frequency band HPM, and it can effectively reduce the requirement of high magnetic field by higher harmonic operation, the Cyclotron SR has a potential advantage in developing superradiant HPM sources operating under millimeter and submillimeter waveband.The Cyclotron SR was systematically studied by association of theoretical analysis, particle simulation and experiment in this dissertation.A distributed feedback model was introduced to analyze the physical process of SR in devices based on traveling wave interaction. The calculation indicated that SR was a specific phenomenon which arose when the group velocity of the wave and the moving velocity of the maximum modulated current in the interaction space obtained well synchronous effect in the non-stationary processes, and lengthening the interaction space as well as the enhancement of coupling between the electrons and the wave were favorable for the SR in certain range.The non-stationary equations for low-Q gyrotrons were used under a predigested model to calculate the characteristics of the Cyclotron SR. With the beam voltage 210kV, beam current 250A and the guiding magnetic field 1.73T,a square relation between the beam pulse width and the peak power was acquired, which was generally considered as a typical character of SR. The operating range of the magnetic field was also given.Then a combination of 2-D and 3-D PIC simulation was used to design and optimize the structure and parameters for Cyclotron SR. The simulation acquired microwave pulses with output peak power -7.1MW, the peak power conversion efficiency 13.5%,frequency -39.1 GHz and mode TE₀₁ while the beam parameters were 210 kV, 250 A and the guiding magnetic field was 1.73 T. A square relation between the beam pulse width and the peak power was given again which proved that the system worked under SR regime. The operating characteristics were in accordance with the results of the theoretical calculations too.Finally the Cyclotron SR was studied by experiment, when the beam parameters were 210 kV,250 A and the guiding magnetic field was 1.73 T ,microwave pulses with peak power 6MW, the peak power conversion efficiency 11.4%,frequency 37.2 GHz and output mode were acquired. The experimental results were in accordance with the simulation.