Improvement and development of ECRF equipment transmission system for JT-60SA

Electron cyclotron range of frequency (ECRF) heating system for the Tokamak type fusion experiment equipment (JT-60SA) currently under construction requires high output and long pulse operation of 1 MW - 100 seconds per gyrotron unit. In this device, development operation and conditioning operation to meet the required specifications were performed, and the output of record-high 1 MW - 70 seconds has been achieved so far using a gyrotron with a frequency of 110 GHz. In the long pulse test using a newly designed and manufactured two-frequency (110, 138 GHz) gyrotron, the transmission system was improved and developed, and at 0.5 MW of output, 100 MJ (pulse width approx. 200 seconds) of energy equivalent to the required specifications was achieved. In order to realize high output and long pulse operation with this device, it is an important issue to suppress high frequency discharge in the transmission device, transmit with high frequency efficiency, and to suppress heat generation of the device. In addition, heat-generated equipment must be cooled efficiently. The transmission system of ECRF equipment for JT-60SA will use the transmission devices of 1 MW - 5 seconds specifications used in JT-60U, so it is necessary to improve them. In this development operation, the authors acquired data on the heat generation of equipment and changes in vacuum degree that were required for improvement, and made the following improvement and development. (1) The authors improved the interlock system that shuts off the high frequency via arc light and pressure rise during high frequency discharge, and constructed the control system that can change the interlock setting signal level during the shot. This substantially improved the aging efficiency. (2) The authors strengthened the cooling of matching unit and waveguide which used to have large temperature rise, and thus succeeded in cooling between shots. (3) In the gap type vacuum exhaust waveguide, the temperature rise of the vacuum exhaust facility/equipment due to the leaked high frequency waves from the gap became a problem. The authors fabricated a leaked high frequency wave absorption tube to solve this. (4) The authors developed a device to measure the power density space distribution of high frequency waves transmitting in the waveguide to improve transmission efficiency, and succeeded in confirming changes in the waveguide transmission mode in high output test. (A.O.)