曲げと引張り歪印加時におけるＮｂ３Ｓｎ線材のＩｃ劣化率の導出

Abstract

Because Nb3Sn superconducting wires have strong strain-sensitivity, it is desired that we can grasp Ic degradation rate analytically when bending and tensile strains are applied to these wires. We fabricated Nb3Sn coils through the react and wind technique in which the wires, processed by our internal-tin method, were primarily reacted, then coated with formal insulation and finally wound to a coil, and we also succeeded in passing the current, which is equivalent to the case of short length wires. An estimate of the Ic degradation rate is needed when bending and tensile strains are applied to the wire for examining the above-mentioned experimental result. Therefore we theoretically analyzed it by considering the shift of neutral axis when the wire was bended, taking the plastic deformation of composite materials into account, and also numerically calculated it. The results were that the neutral axis shifts from the center of the wire toward 72μm inside; the strain range of the Nb3Sn filaments are from 0.40% of maximum value to -0.06% of minimum one when winding the coil; the strain of the filaments increases 0.14% when the coil is cooled to 4.2K; and the additional Hoop's strain of 0.033% is applied to the wire for passing current to the coil. It was estimated that the Ic degradation rate based on the Ic-strain characteristics of the wire becomes 8.5%. This value agrees substantially with the experimental data of our small-scale coil; thus the validity of the calculation on Ic degradation rate can be verified.