Mode competition between fundamental and second-harmonic modes in 0.4 THz gyrotron with gradually tapered complex cavity

The gyrotron has been demonstrated to be an efficient, high power source of terahertz radiation. However, one of the main obstacles in achieving stable, efficient operation at the cyclotron harmonics in a gyrotron is mode competition with lower harmonic modes. Therefore a theoretical investigation of mode competition is an essential first step to the implementation of gyrotron. In this article, the nonlinear dynamics of mode competition in 0.4 THz gyrotron with gradually tapered complex cavity are studied by using multifrequency, time-dependent theory. The results show that the operating modes TE_17.3-TE_17.4 can be stably excited and the output power can reach over 130 kW.