Studies on Jelly Roll Processed Nb3Sn Superconducting Wires Using Sn-Ta and Sn-Ti Based Alloy Sheets

Sn-Ta based alloy buttons of different compositions were prepared by the melt diffusion process among constituent metal powders at ∼780°C. The buttons were then pressed into plates. Sn-Ti based alloy plates were sliced from the melt and cast ingot. Resulting Sn-based alloy plates were rolled into thin sheets. The Sn-based alloy sheet was laminated with a commercial Nb sheet, and wound into a Jelly Roll (JR) composite. The composite was encased in a Nb-3.3 at% Ta sheath, and fabricated into a thin wire followed by the heat treatment at 700-775°C. The application of hydrostatic extrusion was useful for the fabrication of JR processed wires. The JR wires using Sn-Ta and Sn-Ti based alloy sheets show a non-Cu Jc of ∼250 A/mm2 at 20 T and 4.2 K, which is considerably higher than that of 16 wt% Sn bronze processed Nb3Sn wires. In the Sn-Ta based alloy sheet the dispersion of Ta powders improves mechanical strength of the sheet. Furthermore, it has been found that the Nb impregnates into the Sn-Ta based alloy layers, and Nb3Sn layers are synthesized by the mutual diffusion between the Nb and Sn-Ta based alloy sheets. Meanwhile, Sn-Ti based alloy sheet is attractive due to its easiness of mass production. Structure and performance of JR processed Nb3Sn wires prepared from Sn-based alloy sheets with different composition are compared.