Bruker Ost LLC

Hanping Miao

Michael Field

Carlos Sanabria

Jeffrey Parrell

A new heat treatment for Internal-Tin NbSn strands is described. The heat treatment uses Nausite membranes to decrease the volume fraction of the &#x3b7; phase and therefore minimize its liquefaction&#x2014;ultimately resulting in better connected NbSn. The heat treatment requires only one stage aside from the final NbSn reaction stage. This heat treatment enables an increase in critical current density (at 16 T) of 28%.

Strand critical current density in NbSn superconducting strands via a novel heat treatment

Methods for producing a multifilament NbSn superconducting wire having a Jc value of at least 2000 A/mmat 4.2 K and 12 T by a) packing a plurality of Cu encased Nb rods within a first matrix which is surrounded by an intervening Nb diffusion barrier and a second matrix on the other side of the barrier remote from the rods thereby forming a packed subelement for the superconducting wire; b) providing a source of Sn within the subelement; c) assembling the metals within the subelement, the relative sizes and ratios of Nb, Cu and Sn being selected such that (i) the Nb fraction of the subelement cross section including and within the diffusion barrier is from 50 to 65% by area; (ii) the atomic ratio of the Nb to Sn including and within the diffusion barrier of the subelement is from 2.7 to 3.7; (iii) the ratio of the Sn to Cu within the diffusion barrier of the subelement is such that the Sn wt %/(Sn wt %+Cu wt %) is 45%-65%; (iv) the Cu to Nb local area ratio (LAR) of the Cu-encased Nb rods is from 0.10 to 0.30; (v) the Nb diffusion barrier being fully or partially converted to NbSn by subsequent heat treatment; and (vi) the thickness of the Nb diffusion barrier is greater than the radius of the Nb portions of the Cu encased Nb rods; and d) assembling the subelements in a further matrix and reducing the assemblage to wire form such that (i) the multifilamentary NbSn superconducting wire is formed of a plurality of the subelements, each having a Nb diffusion barrier to thereby form a wire having a distributed barrier design; (ii) the Nb portions of the copper encased Nb rods in the final wire are of diameter from 0.5 to 7 &#x3bc;m before reaction, and (iii) the Nb diffusion barrier that is fully or partially converted to NbSn by heat treatment is from 0.8 to 11 &#x3bc;m thickness before reaction; and e) heat treating the final size wire from step d) to form the NbSn superconducting phases, and multifilament NbSn superconducting wires made thereby are described herein.

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Edison, NJ, United States of America

Hanping Miao