First tests of a 117.5 GHz 1.8 Megawatt gyrotron for plasma heating and current drive

A gyrotron operating in the TE_{20, 9} interaction mode at 117.5 GHz has been developed. Communications and Power Industries (CPI) has designed, fabricated, and conducted initial testing of this device. Short pulse testing demonstrates output power levels up to 1.8 MW, with electrical efficiencies of up to 42% (including the effect of a single-stage depressed collector), for an accelerating voltage of 98 kV and a beam current of 60 A. The output power is delivered in the form of a high-quality Gaussian (TEM₀₀) beam. The prototype gyrotron exhibits low internal RF losses and shows no evidence of parasitic beam tunnel oscillations, for beam currents up to the full-rated 60A. A combination of magnetic shielding and dynamic beam sweeping ensures that the residual electron beam power is safely dissipated in the collector. An overview of the gyrotron design, available test results, and current status will be provided.