Nb3Sn wire shape and cross sectional area inhomogeneity in Rutherford cables

TL;DR

This study uses advanced X-ray tomography to analyze shape and cross-sectional inhomogeneity in Nb3Sn Rutherford cables, revealing oscillations and variations caused by manufacturing deformation.

Contribution

It introduces a novel application of 3D imaging and image processing to quantify wire shape and area variations in Rutherford cables.

Findings

Cable cross section oscillates by 2% with a 1.24 mm frequency.

Stronger cross-sectional area variation occurs at the keystoned cable edges.

Shape and area inhomogeneities are linked to manufacturing deformation effects.

Abstract

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 3D 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 artefacts 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.