High power millimeter wave experiment of torus diamond window prototype for ITER EC H&CD system

The design of the torus diamond window for the ITER electron cyclotron heating and current drive (EC H&CD) system has advanced considering a reliable and manufacturable structure. The diamond window prototype was fabricated based on the design and the high power experiment was carried out to verify the millimeter wave transmission capability. Transmission of 740 kW-100 s was demonstrated and no significant temperature increase of the window structure and no damage on the diamond disk were obtained. The temperature saturation of the cooling water for the window was observed and loss tangent of 7.8 × 10−6, which was the lowest value that we had ever obtained at JAEA, was evaluated. This result indicates that the diamond window design is feasible and promising the high power more than 1 MW transmission.