Effects of Reaction Temperature and Alloying on Performance of Restack-Rod-Process Nb₃ Sn

Final reactions of 48 or 50 hours were given in a range of temperature from 635oC to 695oC to high-JcTa- and Ti-alloyed Restack-Rod-Process Nb3Sn strands to investigate the changes in critical current density and the superconducting properties. Jcis the current density in the non-copper region of the wire. Measurements of Jcwere made at 4.2 K temperature and from 8 to 11.5 T field at BNL and from 12 to 16 T at OST, and these data were fitted to the Summers expression for Jcto extrapolate the scaling field . Bc2*ldr All three(Nb, Ta)3Sn strand designs investigated displayed peak Jcvalues of ~3000 A/mm2at 12 T and ~at 1500 A/mm2at 15 T for 665 and 680oC reactions. Bc2*increased monotonically with increasing reaction temperature, a (Nb, Ti)3, By comparison, at each reaction temperature, a strand under development had a Bc2*higher than any of the Ta-alloyed strands. This suggests that Ti-alloyed strands could improve high-field performance if further development can bring their Jcvalues closer to those of the Ta-alloyed strands. Other implications are also discussed.