Results of All ITER TF Full-Size Joint Sample Tests in Japan

Nine toroidal field (TF) coils have been developed in Japan for the international thermonuclear experimental reactor (ITER). The joint resistance of TF coil should satisfy the requirement of smaller than 3 nano-ohm at 2 T of external magnetic field and 68 kA of transport current. Full-size joint sample (FSJS) tests were performed for joint development and for TF coil manufacture, as part of the process control. 11 FSJS tests are conducted in total. FSJS tests were conducted with assistance from a test faculty in the National Institute for Fusion Science as reported in a previous paper. All FSJS tests successfully satisfied the requirement of resistance less than 3 nΩ at 2 T. Additionally, the TF coil joints are subjected to cyclic electromagnetic force and warm-up/cool-down during the ITER operation. The authors investigated the joint performance for the abovementioned influence. The results showed no degradation in the joint resistance. Thus, the TF joint developed in Japan was qualified successfully

Results of ITER TF coil double pancake heat treatment in Japan

In Japan, 9 ITER TF coils were manufactured for the ITER project. Each TF coil consists of seven Nb3Sn conductor double pancakes (DPs). In DP manufacturing, heat treatment is one of the most important processes, because the insertion of a heat treated conductor into the radial plate groove (i.e., transfer) is complicated owing to the elongation of the conductor under heat treatment. A critical current distribution over the DP may also occur owing to the temperature distribution and disturbance in the heat treatment process. To address these issues, this study developed a procedure wherein the conductor length elongation caused by heat treatment is precisely considered, and transfer can be successfully achieved for all the DPs. In addition, strand witness samples were simultaneously heat treated with the DPs, and their critical current (Ic) was measured. Subsequently, it was confirmed that the average Ic is equivalent to those in the strand acceptance test while the standard deviation of Ic for the witness samples is approximately 4 % larger than that for the strand acceptance test. It was also confirmed that the disturbance of the heat treatment was negligible. Related results are described herein