Instabilities of impregnated windings induced by epoxy cracking

Changes in the mechanical behaviour and the instabilities of impregnated windings induced by epoxy cracking have been studied in order to establish a methodology for constructing a superconducting magnet. Epoxy cracks are inevitably induced in the process of training. The cracks degrade the rigidity of the superconducting windings, hence the evaluation of epoxy cracks in impregnated windings is important in analyzing the stability of the windings. Test windings in which epoxy cracks were purposely introduced were used, and the degradation and the training behavior were measured before and after crack introduction. Before crack introduction the winding showed training, that is, the quench current increased with quench number. After crack introduction the quench current did not increase with quench number