In an ITER toroidal field (TF) coil, tight tolerances of 1 mm in flatness and a few millimeters in profile are required to manufacture a radial plate (RP), although the height and width of the RP are 13 m and 9 m, respectively. In addition, since cover plates (CPs) should be fitted to a groove in the RP with tolerance of 0.5 mm, tight tolerances are also required for the CPs.The authors therefore performed preliminary and full-scale trials to achieve tight tolerances that meet the required RP manufacturing schedule, such as one RP every three weeks. Before the full-scale trials, preliminary trials were performed to optimize machining procedures, welding conditions and assembly procedures for the RP, and the manufacturing processes for the straight and curved CP segments. Based on these preliminary trial results, full-scale RP and CPs were fabricated. The flatness achieved for the RP is 1 mm, except at the top and bottom where gravity support is insufficient. If the gravity support is suitable, it is expected that a flatness of 1 mm is achievable. The profile of the RP was measured to be within the targeted range, better than 2 mm. In addition, most of the CPs fit the corresponding groove of the RP. Although the issue of hot-cracking in the weld still remains, the test results indicate that this problem can be prevented by improving the geometry of the welding joint.Thus, we can conclude that the manufacturing procedures for RP and CP have been demonstrated.
