Patent ID: 7585377

Claim:
A method for producing a multifilament Nb 3 Sn superconducting wire having a J c values of at least 2000 A/mm 2 at 4.2 K and 12 T, comprising the steps of: a) packing a plurality of Cu encased Nb rods within a first Cu containing matrix which is surrounded by an intervening Nb diffusion barrier and a second Cu containing matrix on the other side of the barrier remote from said rods, to thereby form a packed subelement for said superconducting wire; b) providing a source of Sn within said subelement; c) assembling said metals within the subelement, the relative sizes and ratios of Nb, Cu and Sn being selected such that (1) the Nb fraction of the subelement cross section including and within the said diffusion barrier is from 50 to 65% by area; (2) the atomic ratio of the Nb to Sn including and within the said diffusion barrier of the subelement is from 2.7 to 3.7; (3) the ratio of the Sn to Cu within the said diffusion barrier of the subelement is such that the Sn wt %/(Sn wt %+Cu wt %) is 45%-65%; (4) the Cu to Nb local area ratio (LAR) of the said Cu-encased Nb rods is from 0.10 to 0.30; (5) the said Nb diffusion barrier being fully or partially converted to Nb 3 Sn by subsequent heat treatment; and (6) the thickness of said Nb diffusion barrier is greater than the radius of the Nb portions of said Cu encased Nb rods; and d) assembling said subelements in a further matrix of Cu and reducing said assemblage to wire form such that (1) said multifilamentary Nb 3 Sn superconducting wire is comprised of a plurality of said subelements, each having a Nb diffusion barrier to thereby form a wire having a distributed barrier design; (2) the Nb portions of the said copper encased Nb rods in the final wire are of diameter from 0.5 to 7 μm before reaction, and (3) said Nb diffusion barrier that is fully or partially converted to Nb 3 Sn by heat treatment is from 0.8 to 11 μm thickness before reaction; and e) heat treating the final size wire from step d) to form the Nb 3 Sn superconducting phases.