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.

The ITER Toroidal Field (TF) coil is composed of a Winding Pack (WP) and a TF coil case (TFCC). In the manufacturing of a TF coil, the gap between the WP and the TFCC is filled with radiation resistant Triglycidyl-p-aminophenol (TGPAP) resin. Vacuum Pressure Impregnation (VPI) is adopted. The selected resin system displayed two potential problems: high viscosity and cracking after cure. A series of production optimizations have been performed to develop techniques to apply the selected resin for the TF coil production: crack countermeasure, narrow gap injection, and pressure control. For crack countermeasure, the addition of fiberglass tape or sheet layer was found to be effective in preventing fragmentation of cracked resin. Since the cracked resin would not harm the TF coil quality as long as it stays in the original position, addition of confining fiberglass layers solves the problem. In narrow gap qualification tests, resin injection into a 2 mm wide space was observed with proper selection of fiberglass layer addition conditions. The pressure qualification test showed that resin cured without additional pressurization can satisfy the compression strength requirements. From those results, techniques for the TF coil production have been developed, and with the implementation of those techniques the gap-filling of the first TF coil in Japan was successfully completed in 2019. Since then, two more TF coils have completed the gap-filling process with some improvements.

No abstract

Double-pancake (DP) of ITER Toroidal Field (TF) coil consists of a cable-in-conduit conductor with Nb3Sn strands and a radial plate (RP). In the TF coil winding manufacturing process, a significant technical issue that was considered is that the difference of length between the heat-treated conductor and the RP grove must be controlled within 0.023% to insert the conductor into the RP. This technical issue was solved by developing a highly accurate winding system and an RP assembly process to adjust the groove length. However, RP assembly was not able to begin before the winding is heat-treated, because the RP groove length is adjusted to the heat-treated conductor length in the assembly process developed. Therefore, it was difficult to satisfy the schedule required by ITER using this original manufacturing process. To solve this issue, an accuracy prediction method for the heat-treated conductor length was developed in which a highly accurate manufacturing process is used, and RP assembly can proceed in parallel with the winding manufacturing process. Applying this optimized process, both the required accuracy of the winding and the scheduling requirements of ITER are successfully satisfied for the series production of TF coil windings.