Buckling Analysis of $\hbox {Nb}_{3}\hbox {Sn}$ Strand for Large-Scale Cable-In-Conduit Conductor

Nb₃Sn strand buckling and crack has been observed on the surface of a cable-in-conduit conductor, and it definitely degrades the performance such as critical current density. The strand bending or large deformation, which leads to macroscopic cracks, is not explained by the transverse loading because the direction is completely perpendicular to the electromagnetic force. The most likely explanation is due to the compressive force originating from the difference in coefficient of thermal expansion between strands and steel jacket. Once the load pushes the cable away to one side of the inner wall of the jacket, there would appear a large void on the other side (low transverse load side). It is expected that the strands on the surface of the low transverse load side would free from the frictional force (apart from the jacket wall) and eventually they would start shrinking. In order to analyze the situation which leads to the Tcs degradation, we developed a simulation model based on the structural mechanics by which the strand is divided into discrete elements along centroidal lines. Our simulation results indicate that the displacement would be up to 2 mm, and maximum curvature of the trace 10 %, which is enough for cracks to form as observed in the visual inspection.