Design Consideration of Cavity and MIG of a 170/230-GHz Dual-Frequency Megawatt-Class Gyrotron for CFETR

In this article, a dual-frequency, megawatt-class (MW-class) gyrotron for Chinese Fusion Engineering Testing Reactor (CFETR) is analyzed, which can operate individually at frequencies of 170 and 230 GHz with the operating modes of TE+33,12 and TE+44,16, respectively. A triode-magnetic injection gun (MIG) is investigated for this dual-frequency gyrotron. With the help of the time-dependent, multimode, self-consistent code, the startup scenarios are investigated with considering the realistic electron beams. The results show that the gyrotron can steadily operate at the operating modes with MW-class under the transverse velocity spreads from 3% to 7% together with the beamwidth from 3 to 5 times Larmor radii. When considering the velocity spreads of 7% and the electron radial thickness of 4 times Larmor radii, the output power of TE+33,12 mode can reach 875 kW with a beam voltage of 70 kV and a current of 48 A, and the output power of TE+44,16 mode can reach 805 kW with a beam voltage of 65 kV and a current of 45 A.