Local electromagnetic properties and hysteresis losses in Non-Uniformly wound 2G-HTS Racetrack Coils

Abstract

A noteworthy physical dependence of the hysteresis losses with the axial winding misalignment of superconducting racetrack coils made with commercial \textcolor{black}{Second Generation High Temperature Superconducting (2G-HTS)} tapes is reported. A comprehensive study on the influence of the turn-to-turn misalignment factor on the local electromagnetic properties of individual turns, is presented by considering six different coil arrangements and ten amplitudes for the applied alternating transport current, $I_{a}$, together with an experimentally determined function for the magneto-angular anisotropy properties of the critical current density, $J_{c}(B,\theta)$, across the superconducting tape. It has been found that for moderate to low applied currents $I_{a} \leq 0.6~I_{c0}$, with $I_{c0}$ the self-field critical current of individual tapes, the resulting hysteretic losses under extreme winding deformations can lead to an increase in the energy losses of up to $25\%$ the losses generated by a perfectly wound coil. High level meshing considerations have been applied in order to get a realistic account of the local and global electromagnetic properties of racetrack coils, .... Our findings can be used as a practical benchmark to determine the relative losses for any 2G-HTS racetrack coil application, unveiling the physical fingerprints that possible coil winding misalignments could infer.