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The thermal performance of three different designs for the steerable mirrors on the ECH launchers installed in the DIII-D tokamak has been evaluated theoretically and experimentally. In each case the disruption forces must be minimized while providing a low loss reflecting surface. One design uses all Glidcop® material, but shaped so that the center is appreciably thicker than the edge. A second design is graphite with a molybdenum surface brazed to the graphite. The latest design is laminated copper/stainless steel construction with a thin copper reflecting surface. All three mirrors employ passive radiative cooling. The mirror temperatures are measured by resistance temperature devices (RTDs) which are attached at the back surfaces of the mirrors. The temperature increases are moderate for the laminated mirror, which has the best overall performance. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Six 110 GHz gyrotrons in the 1 MW class are operational on DIII-D. Source power is >4.0 MW for pulse lengths ≤2.1 s and ∼2.8 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 ±20°. Measured transmission line loss is about -1 dB for the longest line, which is 92 m long with 11 miter bends. Coupling efficiency into the waveguide is ∼93% 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 <180°C at equilibrium. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]