RF Behavior of a 220/251.5-GHz, 2-MW, Triangular Corrugated Coaxial Cavity Gyrotron

In this paper, RF behavior studies of a dual regime coaxial cavity gyrotron designed for electron cyclotron resonance heating and current drive of magnetically confined plasmas in the future fusion reactors are presented. Considering all the design constraints, the mode pair is chosen as TE48,30 and TE55,34 for operation at 220 and 251.5 GHz, respectively. The interaction circuit is initially designed through the cold cavity design. A triangular corrugated insert offers good mode selection and also reduces the localized heating problem. Single mode computations are carried out to optimize the beam parameters for the maximum efficiency of the chosen mode pair. Time-dependent multimode simulations are carried out to conform the power in the desired mode pair and the possibility of power in the competing modes. Start-up analyses are performed before and after space-charge neutralization with nonuniform magnetic field using nominal electron beam parameters obtained from magnetron injection gun calculations. These studies ensure that the continuous wave operation of a coaxial cavity gyrotron is possible with the output power of ≈2 MW with the chosen mode pair.