Abstract
Effects of titanium addition to the niobium core on the composite-processed Nb3Sn superconductor have been investigated. Composites consisting of pure niobium or Nb-0.5, 1, 2, 3, 4 at%Ti alloy core and Cu-7 at%Sn alloy matrix were fabricated into a single core and 160-core multifilamentary wires, and then heat-treated to form Nb3Sn layers. An enhanced growth rate of Nb3Sn layer with increasing titanium content has been observed, while the Nb3Sn grain size slightly increases with the titanium addition. The titanium addition of 1-2 at% to the niobium core produces a small maximum in Tc, and further titanium addition decreases it. The addition of titanium to the core increases Hc2 by ∼4 T. An Hc2 of about 25 T has been obtained at 4.2 K by the titanium addition. The Hc2 enhancement has been discussed in relation to the increases of Tc and the normal state resistivity through the titanium addition, and also to the suppression of martensitic transformation in Nb3Sn. Jc’s of Nb3Sn at high fields (H>13 T) are remarkably increased by the titanium addition, which may be due to the enhancement in Hc2. A Jc for Nb3Sn layer, 1.1×109 A/m2, and overall Jc of 2.0×108 A/m2 have been obtained at 4.2 K and 16 T for a single core wire and a 160-core multifilamentary wire, respectively. The Nb-Ti/Cu-Sn composite wire seems to be quite promising for applications in a magnetic field range of 12-16 T at 4.2 K.
