Instabilities due to mechanical strain energy in superconducting magnets

In order to investigate fundamental mechanisms of winding motions during charging superconducting magnets, single layer, 2- layer and multilayer (10 turns, 29 turns) test magnets were used. The winding motion was detected as mechanical strains and acoustic emission (AE). Compressive strains which appeared in the axial direction of the magnet showed large hysteresis when it was charging and discharging. It was clarified that the hysteresis directly resulted in frictional losses and the AE signal. Microslips (0.36 μm ∼ 0.5 μm) and dissipation energies were estimated by the hysteresis curves and were compared with the AE energy. It was also suggested that the magnet instability tends to increase in the vicinity of its ends, because the microslips are accumulated toward the center of the magnet.