Effect of Applied Pure Bending Strain on Critical Current for CuNb/Nb3Sn Superconducting Wires

We have developed a CuNb-reinforced Nb
₃
Sn (CuNb/Nb
₃
Sn) wire. Critical current (I
_c
) of prebent CuNb/Nb
₃
Sn coils with various diameters was investigated in order to develop a Nb
₃
Sn superconducting magnet by a react-and-wind (R&W) method. It was found that the prebending treatment enhances I
_c
of the small pure bending coil. In the small pure bending strain region, I
_c
of the prebent coil with over 96-mm outer diameter is larger than that of the as-reacted coil. However, the as-reacted coils exhibited large I
_c
in the large pure bending strain region. Calculated results on the basis of the perfect current transfer model with a neutral axis shift successfully indicated the enhancement behavior of I
_c
by pure bending strains. Hence, we can understand the relationship between coil diameter and prebending treatment for the R&W method using CuNb/Nb
₃
Sn wires.