Derivation of Ic degradation rate for Nb3Sn coils through the react & wind technique

To estimate critical current, I_c, degradation when bending and tensile strains are applied to Nb₃Sn wires through the react & wind (R&W) process, we theoretically analyzed the degradation by considering the shift of the neutral axis when the wire was bent, taking the plastic deformation of the composite materials into account. The results were as follows. The neutral axis shifts 72 μm; from the center of the wire toward the inside. The strain range of the Nb₃Sn filaments is from 0.40% to -0.06% when the wire is wound into a coil. The strain of the filaments increases 0.14% when the coil is cooled to 4.2 K. The additional Hoop´s strain of 0.033% is applied to the wire for passing current to the coil. The I_c degradation rate based on the I_c-strain characteristics of the wire was estimated to be 8.5%. We also succeeded in generating a maximum field of 9.2 T for a commercial scale coil manufactured by the R&W process.