Development of RHQ-processed Nb3Ga wire

Nb₃Ga wires fabricated by using RHQ (rapidly heating and quenching) treatment show T_c = 29.7 K and B_c2 (4.2 K) = 32 T. In addition J_c of the Nb₃Ga phase is very high, comparable to those of practical (Nb, Ti)₃Sn wire and RHQT-processed Nb₃Al wire. However we cannot obtain the large overall J_c for the wire, because of small volume fraction of Nb₃Ga in the wire. By using Ta-matrix Nb₃Ga precursor wire, we performed the RHQ treatment at higher temperatures, resulting in two-times improvement of overall J_c and a little improvement in J_c. We measured temperature dependence of J_c vs. B curve for the Nb₃Ga wire. The pinning force vs. B curves did not show any agreement with Kramer´s scaling law. TEM observations clarified that the composition of Nb₃Ga varies from near-stoichiometry (24at%Ga) nearby the Nb₅Ga₃ phase to Ga-poor composition (21.8at%) nearby the Nb-Ga bcc phase. We also measured the tensile strain effect on the superconducting properties of Nb₃Ga wire. The strain effect of Nb₃Ga wire is as large as that of Nb₃Sn wire.