The 6 MW, 110 GHz ECH system for the DIII-D tokamak

Summary form only given. Six 110 GHz gyrotrons have been installed and are operational on the DIII-D tokamak. Three gyrotrons are built by Gycom and have a nominal rating of 750 kW and a 2 s pulse length, with the pulse length being determined by the maximum temperature allowed on the edge cooled Boron Nitride window. The other three gyrotrons were built by Communications and Power Industries (CPI) and are rated at 1.0 MW for 10 s pulses. The CPI gyrotrons use a single disc CVD (chemical vapor deposition) diamond window, that employs water cooling around the edge of the disc. Calculation predict that the CVD diamond window should be capable of full 1 MW CW operation, which is confirmed by IR measurements which shows the window temperature stabilizing after 2 s. All gyrotrons are connected to the tokamak by a low-loss-windowless, 31.75 mm diameter, evacuated transmission line using circular corrugated waveguide for propagation in the HE,, mode. Each waveguide system incorporates a two mirror launcher which can steer the RF beam poloidally from the center to the outer edge of the plasma, and can steer toroidally for either co- or counter-current drive coupling. Central current drive experiments with four gyrotrons and 2.1 MW of injected power drove about 0.17 MA. Results from using the six gyrotron systems will be reported as well as the plans to upgrade the system to eight gyrotrons.