Large Tc, Bc2 and Ic enhancement effect due to the prebending treatment for bronze route Nb3Sn wires

In order to develop a react-and-wind (R&W) processed Nb₃Sn superconducting magnet, we investigated the influence on the superconducting properties due to the prebending treatment. Since a reacted Nb₃Sn superconducting wire reveals a very sensitive response from stress and strain, we focus on the prebending treatment which is repeatedly applied to the Nb₃Sn wire through several pulleys in the R&W coil winding process. We found that the prebending treatment doubles the I_c value at 20 T and 4.2 K for bronze route Nb₃Sn wires. This I_c enhancement effect comes from the T_c and B_c2 enhancement. It turned out that T_c increases from 17.4 to 17.9 K and as a result B_c2 also increases from 23.7 to 25.2 T at 4.5 K for bronze route multifilamentary Nb₃Sn wires prebent at bending strain of 1.0% and at 5 repeated times.