Development of Double-pancake for ITER Toroidal Field Coil

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.

Lessons learned from European and Japanese production of ITER toroidal field coils

“…The TF coil manufacturing is described in [9][10][11][12]. The major technical challenges of TF coil manufacturing were (1) wind, react and transfer technology to insert the conductor into the RP [10,12,13], (2) development of electrical insulating performance with high radiation condition [10,14], (3) accuracy of the CCL positioning to minimize the error magnetic field [9,10,15,16], (4) welding and machining technology within severe tolerances for the huge structures [9,11,[15][16][17][18].…”