Finite-element modelling of no-insulation HTS coils using rotated anisotropic resistivity

The no-insulation (NI) winding method is an effective technique for winding coils from high-T-c superconductors (HTS). NI coils are electrically and thermally robust due to their ability to radially bypass current away from the fragile superconducting path when necessary. This avoids stored magnetic energy being entirely discharged on local defects in the HTS tape. However, the increased degrees of freedom for the current distribution makes finite-element modelling of these coils a complicated and multi-level problem. Here we present and validate a 2D axially symmetric model of an NI (or partially insulated) coli that captures all the inherent electromagnetic properties of these coils, including axial vs radial current flow and critical current suppression, and also reproduces the well-known charging and discharging characteristics. The model is validated against previously reported discharge measurements, and is shown to produce results consistent with the expected equivalent-circuit behaviour. Only by solving the NI coli problem with both axial and radial fidelity can the interplay of critical current anisotropy and turn-to-turn current be properly accounted for. The reported FE model will now enable coli designers to simulate key complex behaviours observed in NI coils, such as shielding currents, magnetic field inhomogeneity and remnant field effects.