206 GHz gyrotron with photonic-band-gap cavity

A gyrotron oscillator with effective interaction between high-order electromagnetic mode and high electron cyclotron mode is achieved through the analysis on mode selectivity of photonic-band-gap cavity(PBGC). By analyzing the characteristics of PBGC, TE23 is selected as the operating mode. The concept of equivalent radius for PBGC gyrotron is established and the self-consistent nonlinear theory and related numerical program are completed. The studies show that TE23 mode can interact with second-electronic cyclotron harmonics effectively with the coupling frequency of 206 GHz, and meanwhile reduces the required magnetic field significantly. With the oscillator parameters being optimized accordingly, a second-harmonic PBGC gyrotron oscillator with the wave-beam interaction efficiency of 21% is obtained, when the voltage, current and guiding magnetic field are 40 kV, 4.2 A and 3.925 T, respectively.