Development of Nb3Al superconducting wire for nuclear fusion

By improving the critical current characteristic in high magnetic fields of copper-stabilized Nb3Al multi-filamentary superconducting wire using the jelly roll process, Sumitomo Electric has developed a wire with a maximum critical current density of 800 A/mm2 at 4.2 K and 12 T. The uniaxial tensile property of wire with improved current density is superior to that of Nb3Sn wire. Furthermore, copper stabilizer was placed in the center of strands which were chrome-plated to reduce coupling losses between strands, thereby suppressing the effects of chrome diffusing into copper caused by heat treatment to generate Nb3Al, and reducing residual resistivity. Using a large billet, Sumitomo Electric developed a wire with a critical current density performance of at least 600 A/mm2 at 4.2 K and 12 T for use as a strand for insert Coil of ITER/EDA. This wire was shown to have superior bending properties, and had a low hysteresis loss when a parallel fluctuating magnetic field was applied. Sumitomo Electric fabricated about 230 km of this wire, which represents the world's first mass-produced Nb3Al wire, and obtained a maximum unit length of 4600 m. (author)