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 750 degrees C-800 degrees C 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)(3)Sn 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)(3)Sn 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)(3)Sn 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 similar to 150 A/mm(2) has been obtained at 22 T and 4.2 K in the wires with different sheet composition after the heat treatment at 725 degrees-750 degrees C.