Nb₃Sn Wire Shape and Cross-Sectional Area Inhomogeneity in Rutherford Cables

During Rutherford cable production, the wires are plastically deformed and their initially round shape is distorted. Using X-ray absorption tomography, we have determined the three-dimensional shape of an unreacted Nb₃Sn 11-T dipole Rutherford cable and of a reacted and impregnated Nb₃Sn cable double stack. State-of-the-art image processing was applied to correct for tomographic artifacts caused by the large cable aspect ratio, for the segmentation of the individual wires and subelement bundles inside the wires, and for the calculation of the wire cross-sectional area and shape variations. The 11-T dipole cable cross section oscillates by 2% with a frequency of 1.24 mm (1/80 of the transposition pitch length of the 40 wire cable). A comparatively stronger cross-sectional area variation is observed in the individual wires at the thin edge of the keystoned cable where the wire aspect ratio is largest.