3D general simultaneous multi-scale homogeneous <i>T-A</i> model for electromagnetic simulations of large-scale REBCO coils with complex geometries

Abstract Electromagnetic simulations are an essential step to evaluate the performance of rare-earth–barium–copper–oxide (REBCO)-based coils, such as the effects of screening current and AC loss before magnet construction. However, the work presents challenges due to REBCO tape’s special material characteristics: the large width-to-thickness ratio of the tape’s cross-section and the nonlinear effective resistivity of superconductors. Moreover, the issues become particularly pronounced with the increasing geometric complexity of REBCO coils, such as twisting, where three-dimensional (3D) models have to be built and difficulty arises in defining variables. Thus, developing advanced numerical models is crucial for addressing electromagnetic simulations of REBCO coils with complex geometries. Here, we employ a simultaneous multi-scale homogeneous (SMSH) model based on T-A formulation (referred to as the SMSH T-A model) to successfully implement efficient 3D numerical modeling of REBCO coils wound by twisted stacked tapes. Innovatively, a general approach based on numerical solutions instead of analytical definitions is proposed to realize the data coupling between thin-strip tapes and the homogeneous bulks, which is easy to implement and suitable for models with arbitrary stacked structures. The implementation of the general SMSH T-A model is presented in detail, and the validation of its calculation accuracy is carried out by comparing AC loss of a racetrack coil and a twisted conductor obtained from numerical calculations and experimental measurements, respectively. The model is then employed for simulating a D-shaped coil wound by twisted and non-twisted REBCO tapes for the first time. The results demonstrate the feasibility of applying the proposed general SMSH T-A model to electromagnetic simulations of complex-structured REBCO-based coils, while identified issues such as current sharing by this model will be systematically addressed in future research.