Improvement of the Circuit Analyzer Problem Solver CALYPSO

The no-insulation high-temperature superconducting (NI-HTS) coil technology is a promising field of application of HTS tapes, which has gained popularity in recent years. Compared to conventional insulated coils, NI-HTS coils have a better ability to cope with quenches, given the possibility for current and heat to redistribute towards adjacent turns in presence of a hot-spot. In recent years, the authors developed a nonlinear circuit model to compute current distribution and AC losses in NI-HTS coils (named CALYPSO). This model describes the currents flowing from turn to turn due to the NI configuration, as well as the magnetization currents arising in each tape. However, applying this model to coils composed of a large number of turns results in a high computational burden. This work presents an in-depth discussion of the reasons for the long computation time and the solutions and code improvements implemented to tackle this issue. Additionally, a comparison between the losses predicted by the code and those measured on straight REBCO tapes is presented. The model is then applied to investigate the electrodynamics of a NI pancake coil including both magnetization currents and radial currents. The impact of surface contact resistivity between turns on the delay between the magnetic field along the coil axis and the transport current is analyzed, showing the details of the current distribution between turns and inside individual tapes.