High-field superconducting critical values of titanium bronze multifilamentary Nb3Sn conductors

Multifilamentary Nb/Cu-7.5at%Sn-0.4at%Ti wires with two kinds of configurations were fabricated and their superconducting properties were evaluated. One kind of wires contain m-diam 31 × 361-Nb cores. These wires composed of our typical configuration with each 361-Nb cores embedded in a Cu-7.5Sn-0.4Ti matrix inside a Nb barrier, surrounded by a stabilizing Cu. The other kind of wire contains 4.7μm-diam 721-Nb cores in a Cu-7.5Sn-0.4Ti matrix inside a Nb barrier surrounded by a stabilizing Cu. The latter wire showed higher Jc(overall) than the wire with the former configuration of about the same core diameter. The Jc(overall) at 15 T exceeded 400 A/mm²at 4.2 K and reached to 570 A/mm²at 1.8 K for the latter wire heat treated at 650°C for 200 hr. While the 4.6μm-diam core wire with the former configuration showed a Jc(overall) of 350 A/mm²at 15 T, 4.2 K after the heat treatment at 660°C for 200 hr, it also reached to 400 A/mm²at 15 T, 4.2 K when the core diameter was reduced to 2.7μm and heat treated at comparatively low temperature of 640°C for 200 hr. The Hc2\´s at 4.2 K were extrapolated to about 25 T for both kinds of wires. Since the Tc\´s were measured to be 16.8 K for these two kinds of wires, this Hc2 enhancement may be attributed to the ρn increase as a result of Ti incorporation into the Nb3Sn layer in the same way as that for Nb-Ti core Nb3Sn wires.