Stress Analysis of an Insulated Superconducting Magnet Winding Pack Under Torsion

Electrical insulation of superconducting magnets represents one of the most critical aspects in the manufacturing and operation of these devices. Accidents during manufacturing or severe out-of-design loadings in operations could compromise the design life of the component. In this respect, since they do not present a ductile behavior, when elastic limits are exceeded, insulating materials could be irreversibly damaged. Damages could be cracks or delaminations producing different effects in terms of operational life of the magnets. While a crack could give rise to electrical breakdown during fast discharge after a quench, delaminations might produce local heating due to friction that might induce superconducting quench. This paper shows the results obtained with two finite element models of a winding pack mock-up of a superconducting magnet for fusion applications subject to off-normal torsion conditions. The mockup is supposed to be made of a matrix of superconducting cable-in-conduit-conductors wrapped by 1 mm thick glass fiber resin composites. Through a detailed analysis of stress-strain properties of the insulation and a comparison with available experimental results, the authors give a threshold to the off-normal loading conditions under which the magnet could be safely operated.