Effect of mechanical disturbances on stability of impregnated windings

The impregnation of magnet windings with epoxy resin is widely used in developing high-performance superconducting magnets. The purpose of the epoxy impregnation is to prevent wire motion, to enhance the rigidity of the windings, and to assemble the windings in one body. Composite beams simulating an impregnated coil have been examined in order to investigate the effect of mechanical disturbances such as bond failures or epoxy cracks on the stabilities. Since the elastic energy stored in impregnated coil could be released as heat, the sudden change of rigidity during deformation would induce the mechanical disturbances which could quench the superconducting windings. Mechanical disturbances simultaneously release acoustic emissions, hence, the disturbances were monitored by thermocouples together with an acoustic-emission measuring apparatus. The change of macroscopic mechanical properties was measured in terms to the load-displacement curve of the windings. The stress analysis was made using the finite-element method (FEM). It was confirmed experimentally that the epoxy crackings and bond failures could induce the rigidity degradation and cause the heat generation which could result in a premature quench. Such disturbances were successfully estimated by the FEM analysis.