Mass Production and Quality Control of Nb3Sn Superconducting Strands for ITER Toroidal Field Coils

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 3Sn 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.