Recent progress of the high power ECRF system on JT-60U

The Electron Cyclotron Range of Frequency (ECRF) system having four 1 MW - gyrotrons has been successfully operated on JT-60U to locally heat a plasma and drive a plasma current. After modification by suppressing a parasitic oscillation, the gyrotron can generate ∼1.1 MW power for 3.2 s. High RF powers generated by four gyrotrons are transmitted to two independent antennas consisting of steerable mirrors via four long transmission lines with moderate transmission efficiency of 70-80 %. In 2001, injected power reaches up to ∼2.8 MW for 2.8 s after optimizing operational parameters. In such high power injection, a substantial increment in the central electron temperature from 5 keV up to ∼13 keV is observed in the Reversed-Shear (R-S) plasma with the Internal Transport Barrier (ITB). (author)