Russian superconducting materials for magnet systems of fusion reactors

A survey is given of the Russian superconducting materials for the magnet systems of fusion reactors such as `Tokamak-7ʹ, `Tokamak-15ʹ and ITER. In total, approximately 10 t of superconductors based on Nb–Ti for Tokamak-7 and 26 t of superconductors based on Nb3Sn (25 t for Tokamak-15 and 1 t for ITER) have been produced. Also reported here are test results of strands produced for the coil-insert conductor for the central solenoid of magnet coils for ITER. The results show small variation in values of critical current, hysteresis losses, residual resistance ratio, and others, which meet the ITER high performance specifications (HP-II). The possibilities of improving critical characteristics by optimization of strand design produced by the bronze and internal-tin process and by processing composite superconductors based on HTSC-compounds have been also considered.