Effect of Prebending Strain on$rm CuNb/Nb_3rm Sn$Superconducting Coils Using a React and Wind Method

We have found that superconducting properties such as a critical current for bronze route Nb
₃
Sn superconducting wires were enhanced by prebending strain (epsiv
_pb
), which is the repeated bending strain at room temperature. In this study, four kinds of react and wind (R&W) processed CuNb reinforced bronze route Nb
₃
Sn coils with epsiv
_pb
=1.0, 0.8, 0.5 and 0% were prepared. We investigated the effect of prebending strain for the coils. In the electromagnetic compressive stress condition, a critical current (I
_c
) of the R&W processed coil was enhanced by the prebending strain. These I
_c
values are larger than those of a short sample wire without prebending strain. In the hoop stress condition, the I
_c
of four coils revealed a similar value. Therefore, it is considered that the I
_c
was limited by the large tensile stress for all coils in the hoop stress states. These results suggest that the I
_c
enhanced by the effect of prebending strain is applicable for the R&W coil design without degradation in large stress and strain states