Nondestructive Analysis of Nb3Sn CICC and Strand by X-Ray Tomography

The Nb
₃
Sn cable-in-conduit conductors (CICCs) have a multistage twisted configuration. The inner structure of the CICC, such as the twist pitch and void fraction, has a substantial impact on the superconductive cable performances. X-ray tomography is a powerful nondestructive technique that can provide 3-D images of strands' configuration. Therefore, this technique is used to determine the internal structure of the cables, which, in turn, can be used to verify the cabling process and even further for modeling purposes. Additionally, scanning electron microscopy analysis has been carried out to show the interaction between strands and to characterize the filaments of the superconductive compound. Through an energy-dispersive X-ray spectroscopy analysis, a chemical characterization of the superconductive filaments was performed. The trajectory of the strands was defined by analysis of the X-ray tomography. Contacts between strands produce detachments between the central zone and the outer ring of pure copper. Regarding the superconductive filaments, the solid-state reaction performed to obtain the superconductive compound was not fully completed, and an inner central core composed of pure Nb was obtained in several filaments. In addition, a tendency of the Nb filaments to bridge together could be observed, and some cracks were seen, specially in those with an inner central core of pure Nb.