Analysis of Strain Distribution in A15-Type Superconducting Coils Under Compressive Stress

The A15-type superconductors (Nb₃Sn, Nb₃Al) have been used to fabricate the 10 -15-T high-field superconducting magnets. Due to the strain sensitivity of this type of conductors, minimization of the strain in conductors is an important issue to realize the highest critical current density during operation. It is also known that the superconductors in epoxy-impregnated coils exhibit much less critical current degradation than wire samples when subjected to transverse compressive stress, due to the stress buffer effect of the epoxy and insulation materials among strands. This paper presents analytical and numerical investigation of the stress and strain distributions in A15-type superconducting coils, which are usually wound with copper-stabilized Rutherford cable and are epoxy impregnated. Analytical formulas have been derived to calculate the strain in superconductors from the average strain in coils. In addition, a FEM simulation model has been built to get a clear view of the strain distribution between superconductors and the surrounding insulation materials.