Mechanical Modeling of Low Temperature Superconducting Cables at the Strand Level

Low-temperature superconductors such as NbTi are widely used in high field magnets. The run for higher fields leads to greater forces on the conductor, which is pushed closer to its mechanical limit. Managing the higher stresses on the conductor supposes accurate mechanical models: it becomes necessary to simulate local peak stresses and strains, especially with conductors, which are mechanically brittle and strain-sensitive. Superconducting cables are anisotropic composite structures that can comprise superconducting strands, insulation materials and stabilizing parts. This paper presents a convenient method for the geometrical modeling of composite superconducting Rutherford cables at the level of the strand. It is applied on the example of a cable-in-channel NbTi conductor. Our goal is to obtain a mesh of a cable sample that is suitable for Finite Elements (FE) Analysis, at the scale of the strand (around one millimeter), with a true-to-life contact configuration. Different methods and tools are discussed. Computed geometries are compared to tomographic data. Preliminary mechanical simulations with simplified parameters are done to verify the model convergence. The ultimate goal of these explorations is to correlate the model results at the scale of the strand with experimental results at the scale of the cable, in order to identify the critical parameters that describe the best the conductor performance under mechanical solicitation.