Development of Double-pancake for ITER Toroidal Field Coil

Synopsis: 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.