Fabrication of High-Field (Nb,Ta)3Sn Conductors Through a Jelly Roll Process

Abstract

Fabrication and high‐field performance of (Nb,Ta)3Sn conductors through a new Jelly Roll process using Sn‐Ta sheet are reported. A mixed powder of Sn and Ta (Ta/Sn ratio=3/7 and 1/3) with or without a small amount of Cu addition was melted at 800°C in vacuum. The resulting Sn‐Ta alloy was rolled into sheets 100 and 200μm in thickness. The Sn‐Ta sheet was laminated with a Nb foil of the same thickness, and wound around a Nb‐4at%Ta rod forming a Jelly Roll composite. The composite was encased in a Nb‐4at%Ta tube, and then fabricated into a wire without intermediate annealing. The wire with no Cu addition to the Sn‐Ta sheet and reacted at 900°C showed a non‐Cu Jc of 100–120A/mm2 at 23T and 4.2K. The non‐Cu Jc of the wire at 2.1K and 25T reached 100A/mm2, the upper critical field of the wire being 28.4T. A small amount of Cu addition to the Sn‐Ta sheet significantly reduced the reaction temperature, and produced a non‐Cu Jc of 100–120A/mm2 at 22T and 4.2K after the reaction at 775°C. Structure characterization of the new Jelly Roll‐processed (Nb,Ta)3Sn wire is also described.