Application of prebending effect to high strength Nb3 Sn strands

It is reported that the repeated bending loads at room temperature for Nb3 Sn wires, which show the strain dependence of superconducting properties, cause the large enhancement of a critical current, an upper critical field and a critical temperature. Those phenomena are so called “prebending effect”. It is considered that the enhancement effect is associated with the reduction of the residual strain state for Nb3 Sn wires. In order to apply the prebending treatment to a react-and-wind processed Nb3 Sn superconducting magnet, repeatedly bent Nb3 Sn wires with bending strains up to 1.0% were fabricated by using pulleys, and were confirmed to demonstrate the large enhancement of the critical current in spite of the bending strain of 0.5%. From these experimental results, we intended to fabricate the high strength Nb3 Sn strands applying the prebending effect for the cabling conductor. As a first step, we prepared triplet cables using prebent CuNb/Nb3 Sn and Cu/Nb3 Sn strands and evaluated critical currents and n-values of each strand. The prebent Nb3 Sn strands show the large enhancement of critical current I c even after the cabling process. Hence, it is expected that the prebent high strength Nb3 Sn strands may be useful for the cabling conductors.