New high-field Nb/sub 3/Sn conductors prepared from Ta-Sn compound powder

New Nb/sub 3/Sn conductors with excellent high-field performance have been fabricated using Ta-Sn powder as a core material. The powder was easily synthesized by the melt diffusion reaction between Ta and Sn powders. The Ta-Sn powder was encased in a Nb or Nb-Ta alloy sheath to form a composite. The composite was fabricated into tape and wire specimens without intermediate annealing. The specimens were then reacted at 800-925/spl deg/C in vacuum. After the reaction a thick Nb/sub 3/Sn layer, several tens of micrometers in thickness, is formed between the sheath and the core. No void is formed in the core after the reaction. Ta is incorporated into the Nb/sub 3/Sn layer from both the core and the Nb-Ta sheath. The J/sub c/ of the Nb/sub 3/Sn layer reaches 5 /spl times/10/sup 4/ A/cm/sup 2/ at 23 T and 4.2 K. The tape specimens show large critical current at 23 T due to the large thickness of the Nb/sub 3/Sn layer. The optimum reaction temperature can be decreased by the small amount of Cu addition.