The 110 Ghz Microwave Heating System On The Diii-D Tokamak

Six I 10 GHz gyrotrons in the I MW class are operational on DIII-D. Source power is >4.0 MW for pulse lengths less than or equal to2.1 s and similar to2.8 MW for 5.0 s. The rf beams can be steered poloidally across the tokamak upper half plane at off-perpendicular injection angles in the toroidal direction up to +/-20degrees. Measured transmission line loss is about similar to1 dB for the longest line, which is 92 m long with I I miter bends. Coupling efficiency into the waveguide is similar to93% for the Gaussian rf beams. The transmission lines are evacuated and windowless except for the gyrotron output window and include flexible control of the elliptical polarization of the injected rf beam with remote controlled grooved mirrors in two of the miter bends on each line. The injected power can be modulated according to a predetermined program or controlled by the DIII-D plasma control system using real time feedback based on diagnostic signals obtained during the plasma pulse. Three gyrotrons have operated at 1.0 MW output power for 5.0 s. Peak central temperatures of the artificially grown diamond gyrotron output windows are <180degreesC at equilibrium.