Performance and experience of a 110 GHz gyrotron operation on the JT-60U ECH system

Takahashi, Masami*; Seki, Masami; Shimono, Mitsugu; Terakado, Masayuki; Igarashi, Koichi*; Ishii, Kazuhiro*; Kasugai, Atsushi

The JT-60U electron cyclotron heating (ECH) system has been introduced to suppress MHD instabilities via a current profile control by local heating or current drive. The ECH system consists of four 1MW-110GHz gyrotrons, four 60m transmission lines composed of a corrugated waveguide with a diameter of 31.75mm and two steerable type mirror antennas. Recently, a gyrotron developed for ITER has realized high power in an extremely high frequency range of millimeter waves although there was no high power source around 110GHz ten years ago. Therefore, it requires many techniques to operate the gyrotoron. The oscillation conditions had to be found at output power 1MW by adjusting the magnetic field parameters and anode voltage after heater aging. Then conditioning of the gyrotoron was done, where the pulse length is gradually extended in order to operate for 1sec level of pulse length. Consequently, 1MW-5sec of the designed value was achieved and the ECH system with four gyrotrons successfully injected the millimeter wave energy of 10MJ into plasmas, which is the world record.