High-field performance and structure of (Nb,Ta)3Sn superconductors produced by Ta-Sn core

New (Nb,Ta)₃Sn high-field conductors have been fabricated using a Ta-Sn powder core and a Nb-Ta alloy sheath. An appropriate Ta/Sn composition ratio in the core is 6/5 to 6/4, and an optimum Ta concentration in the sheath is 3 to 4 at%. In tape specimens, relative thickness ratio of (Nb,Ta)3Sn layer increases with decreasing total thickness of the tape. The non-Cu J_c at 23 T and 4.2 K of 0.6 mm-thick tape is 1.15×10⁴ A/cm², while that of 0.3 mm-thick tape is 1.35×10⁴ A/cm² . 2 wt%Cu addition to the core decreases the optimum reaction temperature from 900°C to 800°C. More homogeneous and finer grain structure of (Nb,Ta)₃Sn is obtained in specimens with a small amount of Cu addition. 2 wt%Cu addition to the core enhances non-Cu J_c of the tape in fields lower than 22 T. Mono-core wire specimens are also easily fabricated, and show excellent non-Cu J _c values in the field range of 21 to 23 T at 4.2 K