Yoshinori Nagasu

(Nb,Ti)/sub 3/Sn superconducting wire with CuNb reinforcing stabilizer

An in-situ CuNb composite shows a high strength and a high electrical conductivity. Therefore, it is a suitable material for the reinforcement of Nb/sub 3/Sn superconducting wire. Many studies about mechanical and electrical properties of Nb/sub 3/Sn wire with CuNb reinforcing stabilizer have been carried out, but a fabricability of the long-length wire was not confirmed. In this study, 1 mm-diameter (Nb,Ti)/sub 3/Sn superconducting wire with Cu-20 wt%Nb reinforcing stabilizer was fabricated 22 km in length. The wire showed a good fabricability throughout the production. Mechanical properties and critical currents are evaluated in comparison with un-reinforced one.

(Nb,Ti)/sub 3/Sn superconducting wire reinforced with Nb-Ti-Cu compound

Reinforcement of Nb/sub 3/Sn wires is required for high field superconducting magnets because the Nb/sub 3/Sn superconductor is very sensitive to mechanical strain and its critical current degrades drastically at a higher absolute strain than 0.3%. Recently, Nb/sub 3/Sn superconducting wires reinforced with tantalum, Cu-Nb alloy and Al/sub 2/O/sub 3/-dispersed copper, have been developed. But, these high-strength wires do not show very high strength at an absolute strain of 0.3% because these reinforcements have a similar Youngs modulus to copper. In addition, Nb/sub 3/Sn layers of these wires experience an additional compressive strain caused by the differences in thermal contraction between reinforcements and Nb/sub 3/Sn layers. Such a compressive strain also decreases the critical current of the wire. An intermetallic compound was selected as a reinforcement for Nb/sub 3/Sn superconducting wire because such a compound is expected to have a high Youngs modulus and a similar thermal contraction to the Nb/sub 3/Sn compound. Fortunately, the Nb-Ti-Cu compound can be formed from the Nb-Ti and copper composite during reaction heat treatment for Nb/sub 3/Sn layers. Therefore, (Nb,Ti)/sub 3/Sn superconducting wire reinforced with the Nb-Ti-Cu compound has been fabricated. The wire shows a 0.2% proof stress of 400 MPa and maintains a critical current density equal to the unreinforced wire.