Mode selection and interaction structure design of a megawatt class, sub-THz wave coaxial cavity gyrotron

In this paper, mode selection procedure leading to interaction circuit design of a 2 MW, 204 GHz coaxial cavity gyrotron suitable for Electron Cyclotron Resonance Heating of plasmas in future fusion experimental reactor DEMO tokamak is presented. By considering all design constraints, operating mode is selected as TE44,26. Diffractive quality factor, ohmic wall losses and coupling coefficient are calculated for the desired mode and competing modes of the designed structure. Surface Impedance Model (SIM) has been used for the calculation of the ohmic losses.