Nonlinear simulation of multimode startup in the high-order-mode coaxial-cavity gyrotron oscillator

A model of multimode startup in the coaxial-cavity gyrotron operating at higher-order mode with mode competition taken into account is presented in this paper, the detailed numerical calculation method is also given. By the use of the code based on this model, the nonlinear multimode simulations on a coaxial-cavity gyrotron with the high-order mode TE42, 22 at a frequency of 0.22 THz are performed. The results show that with proper cavity parameters and considering the ohmic losses on the wall, the competing modes can be effectively suppressed, this resonator can operate stably at a single mode with the output power of 0.87 MW and corresponding efficiency of 22.8%, and the maximum density of ohmic losses on the wall is below the constraint.