Inter-Layer Joint for the TF Coils of DEMO—Design and Test Results

Abstract

In summer 2015, a new reference baseline is issued for the DEMO EUROfusion tokamak. Thereafter, the toroidal field (TF) coils have been updated with the new layout of the react-and-wind conductor proposed by the Swiss Plasma Center (SPC). Each TF coil consists of 12 single layers of graded Nb3Sn conductors connected in series by “invisible” inter-layer joints fully embedded in the winding pack. The high-grade Nb3Sn conductor operates at 63 kA, 12.2 T with Tcs > 6.5 K. The new prototype of the high-grade cable had been manufactured by ENEA at TRATOS, Italy, and delivered to SPC: 20 m of Nb3Sn and about 10 m of copper dummy conductor. The SULTAN conductor sample consisting of two identical, beforehand heat-treated conductors was prepared and tested at SPC in May–June 2017. Upon the completion of comprehensive conductor tests, the one of those conductors was used for manufacturing of the designed at SPC potentially applicable inter-layer TF joint. The conductor was cut, and then, joined again in accordance with the developed at SPC design of inter-layer joint. The SULTAN sample comprising the earlier tested non-destroyed conductor and the earlier tested, but then cut and joined conductor was re-assembled and tested in the SULTAN test facility at SPC in August 2017.