Electromagnetic–Mechanical Coupling Analysis of Nb3Sn Superconducting Strand

The transport performance of Nb 3 Sn cable-in-conduit conductors (CICCs) depends on the strain distribution along the superconducting filaments determined by the combination of electromagnetic and mechanical forces applied to the strands. The aim of this paper is to analyze the electromagnetic-mechanical coupling behavior of Nb 3 Sn strand by establishing a 3-D finite-element model. This model contains subdomains, which are air region, superconducting filaments, and metal matrix. The mechanical constitutive relations of superconducting filaments and metal matrix are described with elastic and elasto-plastic strain-stress experimental curve, respectively. For the voltage-current (V-I) characteristic, metal matrix elements follow the Ohmic law, and superconducting filaments are modeled with the n-power relation. Lorentz force in three directions (x, y, and z) caused by the external magnetic field and induced current are calculated. The current density and magnetic field distribution of strand are also computed, and the results show the filaments prevent a further field penetration from the outer into the interior matrix. The combination effect of the tensile force and Lorentz force on the strand is discussed. It can be found that Lorentz force combined with the tensile force makes the degradation obvious. The model provides a basis to analyze the electromagnetic-mechanical coupling behavior of the Nb 3 Sn strand and be able to predict the current flow patterns and magnetic field distribution.