Fabrication of high-field (Nb,Ta)3Sn conductors through a jelly roll process

Fabrication and high-field performance of (Nb,Ta)(3)Sn 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 800degreesC in vacuum. The resulting Sn-Ta alloy was rolled into sheets 100 and 200mum 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 900degreesC showed a non-Cu J(c) of 100-120A/mm(2) at 23T and 4.2K. The non-Cu J(c) of the wire at 2.1K and 25T reached 100A/mm(2), 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 J(c) of 100-120A/mm(2) at 22T and 4.2K after the reaction at 775degreesC. Structure characterization of the new Jelly Roll-processed (Nb,Ta)(3)Sn wire is also described.