RF Behavior of a Coaxial Interaction Structure for 0.24-THz, 2-MW Gyrotron

The coaxial interaction structure for a 0.24-THz, 2-MW gyrotron is designed, and its RF behavior is analyzed for the beam current of 60 A and the beam voltage of 90 kV. The searching of a suitable, very high-order TE mode, which satisfies all the technical conditions required to generate 2-MW RF power, is an important and critical step in the development of a coaxial-cavity (COCA) gyrotron. The detailed analysis of mode selection is described in this article. The geometry of the axially corrugated insert is optimized using an in-house code COCA. Based on the optimized geometry of the coaxial insert and the cylindrical cavity, the coupling coefficient and the start oscillation current are computed to analyze the mode competition for the operating mode TE42,28. The particle-in-cell (PIC) algorithm-based simulation tool is used for the beam-wave interaction computation. Very fine meshing is implemented in the simulations, considering the high frequency and fine geometry of the coaxial insert. The electron beam parameters and the cavity magnetic field are optimized first aiming at the RF power >= 2 MW and frequency 240 GHz. The final results of the cavity design confirm 2.2-MW RF power and 239.975-GHz frequency at 9.74-T magnetic field.