1 MW and long pulse operation of Gaussian beam output gyrotron with CVD diamond window for fusion devices

A 110 GHz-Gaussian beam output gyrotron with chemical vapor deposition (CVD ) diamond window was developed for electron cyclotron heating and current d rive on JT-60U. A stable Gaussian output beam power of 1.0 MW for 2 s was o btained with depressed collector operation. The temperature at the center o f the diamond window was stabilized at the DeltaT similar to 25 K. Gaussian beam output from the gyrotron remarkably improved the coupling efficiency to the HE11 mode in the transmission waveguide. 94% of the gyrotron output power was coupled to the corrugated waveguide of 31.75 mm in diameter, via a matching optics unit with two mirrors. A combination of the Gaussian outp ut and the diamond window are indispensable for high power gyrotron operati on at more than 1 MW and efficient coupling to the transmission line. (C) 2 001 Elsevier Science B.V. All rights reserved.