Coupled Thermal and Electromagnetic Analysis of the NAFASSY Magnet

The paper presents an analysis of the current distribution and electromagnetic losses in the NAFASSY magnet carried out with the THELMA code, thanks to a brand-new thermal module coupled with the pre-existing electromagnetic module. The non-linear thermal and electrical properties of both superconducting and copper strands, depending on the local temperature, current density and magnetic field, are taken into account. The model analyses a single turn of the magnet, located in the highest field zone, focusing on the current distribution in the cable, the coupling AC and DC losses during ramped waveforms. The results are then extrapolated to estimate the behaviour of the overall magnet. A description of the models is given, together with a parametric analysis of different boundary conditions and cable discretizations. The analysis shows that, in nominal working conditions, no thermal instability should take place. However, local current redistribution among the strands may occur, mainly driven by the interstrand contact pattern, the local magnetic field and the strand current density.