Operational progress of the 110GHz-4MW ECRF heating system in JT-60U

The JT-60U electron cyclotron range of frequency (ECRF) heating system is utilized to realize high performance plasma. Its output power is 4 MW at 110 GHz. The output power of the gyrotron used in the heating system can be controlled by changing its anode voltage. Then, a compact anode voltage controller was developed to modulate the injected power into plasmas. This controller achieved the modulation frequency of 12 - 500 Hz with modulation factor of 80 % at 0.7 MW of output power. Additional function of this controller also could make the pulse duration longer from 5 s to 16 s at 0.5 MW. For the long pulse operation, temperature rise of the DC break made of Alumina ceramics in the gyrotron was estimated from the measured temperature rise of the coolant and its maximum temperature was about 140 deg. From the analysis of this temperature rise, DC break materials should be changed to low-loss materials for extending to 30 s of the pulse duration. The stabilization of neoclassical tearing mode (NTM) was demonstrated by ECRF heating using the real-time system in which ECRF beams were injected to the NTM location predicted from ECE measurement every 10 ms. The ECRF beams were scanned poloidally with the steering mirrors of the antennas.