Magnetization and critical currents of tin-core multifilamentary Nb 3Sn conductors

Critical current and magnetization data are presented for some multifilamentary Nb₃Sn wires that have been produced by the internal-tin method. A comparison of magnetization and transport critical current measurements shows that filament bridging during heat treatment is a common occurrence leading to effective filament diameters that are sometimes an order of magnitude larger than the geometrical filament size. At present J_c´s (in the noncopper region) greater than 1300 A/mm² at 10 T have been achieved in some conductors, which also exhibit high losses. Low losses have only been seen in conductors with a high local ratio of copper to niobium. The use of (Nb-1%Ti) alloy instead of pure Nb helps to reduce low-field loss and increase high-field J_c. Measurements of the temperature dependence of hysteretic loss to 5 T indicate that loss decreases linearly with increasing temperature