Abstract
Nb3Sn superconducting wires reinforced with a Cu-NbTi compound have been developed. In laboratory-scale (2 kg) fabrication of the Nb3Sn superconducting wire with a Cu-NbTi reinforcer (Cu-NbTi/Nb3Sn), its critical current density is the same as conventional Nb3Sn wire without any reinforcer, but 0.2% proof stress is two times higher than the conventional one. The influence of the copper fraction on the strength of Cu-NbTi/Nb3Sn wires was also investigated. The strength of the wires is proportionally inverse to the copper fraction of the wire, and there are no significant effects on critical current density caused by the difference in copper fraction. According to these laboratory-scale developments, an industrial-scale Cu-NbTi/Nb3Sn wire was successfully fabricated up to a length of 13 km. The critical current density and 0.2% proof stress at room temperature of the industrial-scale wire was 604 A/mm2 at 12 T and 350 MPa, respectively. These values are the same as the laboratory-scale case. The high-strength Nb3Sn wires are going to be applied for the cryocooler-cooled hybrid magnets at Tohoku University and other high-field magnets.
