Influence of Electron Beam Misalignment on the Performance of a 0.24 THz, 1.5 MW Hollow-Cavity Gyrotron Design for DEMO

Abstract

After ITER, a DEMOnstration power plant (DEMO) is planned to prove technical feasibility of controlled thermonuclear fusion energy. High-frequency ( ≥ 0.2THz), high-power (2 MW) gyrotrons are planned as RF sources for Electron Cyclotron Resonance Heating and Current Drive (ECRH&CD) applications in DEMO. At such a high frequency, the effect of a possible electron beam misalignment could be critical for the gyrotron performance. For this reason, the beam misalignment tolerance has been numerically studied for a 236 GHz, 1.5 MW hollow-cavity gyrotron design using a macro-electron based simulation approach. Spread in the electron perpendicular velocity and the radial width of the electron beam are considered too. The results suggest a stable excitation of the selected TE-52,18-operating mode assuming a maximum electron beam misalignment (D) of 0.225 mm (D/1=0.18).