Analysis of nonlinear rigidity for superconducting coil pack experiments

Several experiments of coil packs simulating superconducting coils in the large helical device (LHD) were carried out to evaluate rigidity of coils at cryogenic temperature. In these experimental results, nonlinear behavior was apparent in relations of load versus displacement. In the supplemental measurements, there was a gap between the superconductor and electrical insulators. Nonlinearity as a contact problem was considered and some analytical models using the finite element method were devised. The gap was modeled using the general contact element in a finite element model. Assuming the number of conductors contacting the insulator was increased gradually, the analytical results showed good correlation with the experimental findings.