High-field performance and structure of (Nb,Ta)3Sn wires prepared from Sn-Ta matrix

Sn-Ta-Cu buttons with enough ductility to be fabricated into thin sheets were synthesized by melting a mixture of Sn+Ta+(Cu) powder. (Nb,Ta)₃Sn wires have been prepared by a Jelly Roll (JR) process and a filamentary process. In the JR process a Sn-Ta(-Cu) sheet was laminated with a Nb sheet forming a JR composite. In the filamentary process a Sn-Ta(-Cu) sheet was wrapped around thirteen Nb-1.0 at%Ta rods forming a filamentary composite. Both composites were fabricated into wires without intermediate annealing, and then heat treated. The effect of Ge and Ti addition to the Sn-Ta-Cu sheet has been studied in the JR wires. A small amount of Ge addition improves the workability of the sheet, while that of Ti addition enhances appreciably the J_c of the JR wires. Meanwhile, the 13-core filamentary wires exhibit equivalent high-field performance as that of the JR wires. Present new (Nb,Ta)₃Sn wires can be fabricated through a relatively easy process, and show attractive J_c in the field range of 22-23 T at 4.2 K and that of 24-25 T at 2.1 K.