Theoretical Study on a 0.4-THz Second Harmonic Gyrotron

In this paper, the results of theoretical study on a 0.4-THz second harmonic gyrotron operating at TE_19.3 are presented. A gradually tapered cavity is adopted to alleviate the problem of parasitic mode competition. It is proved that the amplitudes of spurious modes in the gradually tapered cavity could be kept lower than that in the line-joint cavity, especially that in the line-joint cavity with large angle. Based on the self-consistent nonlinear theory, a code is written to simulate the process of beam-wave interaction. Through optimizing the operating parameters, the beam-wave interaction efficiency can reach 35% and an output power of 100 kW can be obtained. In addition, the mode competition in the designed gyrotron is studied using multifrequency time-dependent nonlinear theory. Simulations tracking five competition modes show that stable excitation of the desired operating mode TE_19.3 at 100 kW level can be realized with proper choice of operating parameters.