System performance and experiments with the 110 GHz microwave installation on the DIII-D tokamak

Summary form only given. A powerful microwave system operating at the second harmonic of the electron cyclotron frequency has been commissioned on the DIII-D tokamak. Two Gycom gyrotrons each of which generates about 750 kW for 1-2 s pulses, and two CPI gyrotrons with diamond windows and rated at 0.9-1.0 MW for 10 s pulses are in service. Two additional CPI 1.0 MW gyrotrons are being installed and a third Gycom gyrotron is available as a spare. The launcher system on the tokamak low field side can be scanned poloidally in the tokamak upper half plane and the launchers on two of the transmission lines can also be scanned toroidally in both the co- and counter-current drive directions. The elliptical polarization of the injected rf beam is remotely controllable. Phase retrieval and correction using a two mirror relay was employed for the Gycom gyrotrons, which generate flattened rf beam profiles, and also for one of the CPI gyrotrons with a Gaussian beam. A single ellipsoidal mirror was used to couple one of the CPI Gaussian beams to the waveguides and the beam quality for this arrangement was excellent. The primary mission of the microwave system is to permit current profile control leading to the improved performance of advanced tokamak operation in quasi-steady state. Initial experiments on current drive both near and away from the tokamak axis and on transport have been performed. The system performance and initial experimental results are presented.