Quasi 3-D Model for Numerical Computations of Screening Currents in ReBCO Coils

Screening currents are a major drawback in the context of rare-earth-barium- copper-oxide (ReBCO) magnets because their parasitic effects on the generated field are exacerbated by the particular shape of the conductors. Previously, we have developed numerical tools for the computation of screening currents and their effects in the cases of systems featuring two-dimensional (2-D) symmetries, axial or longitudinal. Nevertheless, 2-D models are not always adequate for every three-dimensional (3-D) shape or alternative winding configuration such as layer-wound ones. Therefore, a quasi 3-D model has been implemented in the in-house CAST3M finite-element code, using the current function T formulation. We developed CAST3M operators to take into account the superconducting behavior of the material and the anisotropic dependence of the current density on the magnetic induction. Simple scenarios, especially one solved with analytical formulations, have been defined to benchmark codes; CASTEM was successfully benchmarked against them. Finally, we compared the generation of screening currents within a small solenoid depending on the type of winding, made either of layers or pancakes. We also compared these results with a simple 2-D model made of nested turns.