Optimization of the Sn-Ta Sheet Composition in Jelly Roll Processed (Nb,Ta)3Sn Wires

Tightly shrunk Sn-Ta ingots with good workability were prepared by the reaction at 750degC-800degC from the mixed powder of Sn and Ta containing 25-30at%Ta. Then jelly roll processed wires were fabricated starting from Sn-Ta/Nb composites in which thick (Nb, Ta)₃Sn layers were produced after the heat treatment. A few wt% Cu addition to the Sn-Ta mixed powder reduces the heat treatment temperature. Moreover, a few at% Ti substitution for Sn + Ta enhances the formation of (Nb, Ta)₃Sn layer, and improves the non-Cu J_c of the wire. In the present study, effect of the Sn-Ta-Ti-Cu sheet composition on the structure and high-field performance of the wire has been studied. It has been found that a small amount of Ti and Cu addition decreases the amount of Ta in the sheet from 25-30at% to 10at%, which is favorable for the material cost reduction. Moreover, it has been revealed that thick (Nb, Ta)₃Sn layers are synthesized even if the Cu concentration in the sheet is decreased less than 1wt% when a few at% Ti is substituted. A non-Cu J_c of ~ 150 A/mm² has been obtained at 22 T and 4.2 K in the wires with different sheet composition after the heat treatment at 725deg-750degC.