Design and Nonlinear Theoretical Investigations on a 250 GHz MW-Level CW Demo Gyrotron With Realistic Electron Beam

This article presents a study for a 250 GHz MW-level continuous mode gyrotron to satisfy the demand of DEMO for over 200 GHz high-power microwave sources. Through careful analysis, the new high-order mode TE 45,18 is chosen as the operation mode. Simultaneously, the magnetic injection electron gun is researched to meet the operation requirement of the gyrotron. A novel curved gradient structure is proposed instead of the traditional linear folding structure for obtaining high-quality electronic beams. Through the linear theory and the time-dependent multimode self-consistent nonlinear theory of gyrotron, the detailed study of mode competition is conducted in the resonator cavity. The TE 45,18 mode can maintain operational stability while suppressing other competition modes at the magnetic field of 9.9600 T, the operation voltage of 80 kV, and the beam current of 35 A. When considering the ideal electron beam, the output power is 1070 kW and the operation efficiency is 38.21%. The output power and operation efficiency are reduced to 1041 kW, and 37.17%, respectively, when considering the realistic electron beam from the magnetic injection gun (MIG) electron gun.