Critical current densities in multifilamentary Nb3Sn composite conductors for AC use

Three types of multifilamentary Nb3Sn composite conductors have been fabricated by the internal tin-core method. One type of conductor has a bundle of copper-clad tin-cores of 85 in the center, around which copper-clad Nb filaments of ∼1.6 x 106 are arranged. In the other two types, the tin-cores are dispersed throughout the conductor. A ratio of Cu/Nb/Sn is 15/1/0.6 and the Nb filament diameter 51 nm. At first, the conductors were heat-treated at 345 to 410 degrees for 26 to 52 days to homogenize tin concentration in the matrix, and then reacted at 450 to 500 degrees for 1 to 42 days. It has been found the tin-homogenization treatment and the reaction at low temperature for long time are effective for the enhancement of critical current density JC. The highest JC of 2.5 x 1010 A/m2 at 1.5 T has been obtained in the conductor with uniformly dispersed tin-cores