Improved fabrication process for Nb3Sn superconductors with Ta-Sn powder core

Nb₃Sn superconductors made by the powder-in-tube (PIT) process have been developed for application to particle accelerator magnets, high field magnets and many other fields. Recently, newly developed PIT process wires having the Ta-Sn core/Nb(Nb-Ta) sheath composite have aroused interest since these wires show excellent high field performance up to 23 T at 4.2 K. We found that the superconducting characteristics of the PIT process wires were improved by locating Nb-Ta rods in the Ta-Sn core. It is known as the RIC (rod-in-core) process. Multifilamentary wires fabricated by the RIC process using a Cu stabilizer were studied. To improve critical current density (J_c) in RIC wires, different sheath materials were studied. The wires using Ta sheath and Cu stabilizer have shown the highest J_c performance, though no reacted superconducting layer existed at the interface between the core and the sheath. We investigated the composition and the microstructure of Nb₃Sn layer in the wires with Nb and Ta sheath. In this report we discuss the origin of high J_c in the Ta sheathed RIC wires through the composition and microstructure analysis.