Operation experience and development status of ECRF system in JT-60U

Moriyama, Shinichi; Kobayashi, Takayuki; Isayama, Akihiko; Yokokura, Kenji; Shimono, Mitsugu; Hasegawa, Koichi; Sawahata, Masayuki; Suzuki, Sadaaki; Terakado, Masayuki; Hiranai, Shinichi; Igarashi, Koichi; Sato, Fumiaki; Wada, Kenji; Shibayama, Minoru; Hinata, Jun

Full specification of 4 MW for 5s was achieved by simultaneous operation of 4 gyrotrons, and 3 MW was injected to the JT-60U plasma by the completion of experiments in August 2008. In the inspection of the antenna after the operation, there were no large damages but the color of the mirror surfaces were slightly changed and some evidences of arcing were found. In the statistical analysis of operation, the rate of successful shots to the plasma was higher than 85% in the last 3 years. Development of long-pulse gyrotron with improved mode converter is on going and the conditioning was started in the end of 2008 aiming at 1 MW, 100s for JT-60SA. It was confirmed that the diffraction loss was remarkably decreased and the pulse length reached 1 MW 17s so far. A new operation technique of active anode voltage control was developed to obtain high efficiency, and the pulse length for 1.5 MW oscillation was extended from 1s to 4s.