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The 110 GHz system on the DIII-D tokamak comprises three Gycom Centaur class gyrotrons producing 750 kW for 2.0 sec pulses and one CPI VGT8110 series gyrotron producing 800 kW for 2.0 ec pulses. Total injected power is in excess of 2 MW. An additional two CPI gyrotrons are being prepared for operation following failure of their diamond output windows and these failures have resulted in operational limits on power and pulse length for the operating CPI gyrotron. The system has poloidally steerable launchers for four gyrotrons, two with oblique launch for current drive and two with perpendicular launch for heating only. A fully articulating launcher with poloidal scan and ±19 deg toroidal scan is also operational. Radiatively cooled mirrors capable of 1 MW for 10 s pulses at 1% duty cycle are being tested on the oblique launcher. New dummy loads based on conversion of the HE[sub 1,1] fundamental mode to surface modes and having fast time response and 80% absorption of the incident rf are now in service. A new single mirror coupling scheme for the diamond window gyrotrons has cut losses in the wave coupling process in half to about 6% of the generated power for focused Gaussian beams. The evacuated windowless waveguide lines are up to 100 m in length and are greater than 90% efficient. The performance of the dummy loads, output power modulation, polarization control and the transmission line will be presented. The history and analysis of the failures of the diamond windows will also be discussed. [ABSTRACT FROM AUTHOR]

Artificially grown diamond has extremely low absorption for microwaves in the millimeter wave range, making this material an attractive candidate for output windows on high power gyrotrons. Several windows have failed in this application due to higher than expected losses. Infrared measurements of the window temperature on a high power gyrotron operating at 110 GHz have been performed. The peak central temperature and time to equilibrium during the rf pulse were consistent with the low loss properties of the material determined from low power cavity measurements. [ABSTRACT FROM AUTHOR]