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

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 T-cs > 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.