No abstract

Superconducting conductors are applied in the toroidal field (TF) coils, poloidal field coils, and central solenoid (CS) in the ITER. The Japan Atomic Energy Agency plans to procure 25% of the TF conductors and 100% of the CS conductors. Mass-produced Nb 3 Sn superconducting strands for TF conductors have been supplied by two manufacturers since 2008. The total length of the strands is approximately 23,000 km; thus, quality control is extremely important. A statistical process control has been adopted in order to reduce the dispersion of strand performance, and stable performance of the mass-produced strands was achieved. Both manufacturers improved the fabrication yield through mass production. Approximately 72% of the Japanese share in TF strands has been produced as of October 2011.

Cable-in-conduit conductors for ITER toroidal field (TF) coils will be operated at 68 kA and 11.8 T. The cable is composed of 1,422 strands with a diameter of 0.82 mm. There were two options for initial procurement. For option 2, the twist pitches at lower stages are longer than in option 1. Trials were performed to assess the feasibility of these options. In the trials for option 1, the nominal outer diameter of sub-cables and reduction schedule of final cables were evaluated and finalized. In the trials for option 2, problems were encountered at the third stage cabling. These problems were resolved through increasing the die size in that stage and improving the tension balance of the second-stage cables to reduce friction between the die and the cable, and also through avoiding loose twisting at both edges of the third cable. Option 2 was finally selected in 2009 based on superconducting performance enhancement of the cable. After the qualification of the fabrication procedure using fabrication of a 760-m dummy cable and a 415-m superconducting cable, mass production of the cables started in March 2010.