Ic Enhancement Effect in Nb3Sn Coils Fabricated by the React‐and‐Wind Method

We found that critical current Ic, upper critical field Bc2 and critical temperature Tc are greatly enhanced by pre‐bending treatment for bronze route Nb3Sn superconductors, called the pre‐bending effect. The superconducting properties of Nb3Sn superconductor are sensitive to strain. However, a pre‐bending treatment of the Nb3Sn wire enhances the properties. This is because the treatment causes relaxation of the residual strain in the Nb3Sn layer in the wire.Interestingly, the pre‐bending effect also makes the Nb3Sn wire stronger against strain. By using this effect, the react‐and‐wind (R&W) method is expected to be applicable for the fabrication of the Nb3Sn superconducting coil. In this paper, the development of Nb3Sn coils made by the R&W method with the pre‐bending effect is described, and the efficiency of the cable assembled by the reacted Nb3Sn strands is discussed.