Acoustic Emission Measurement and Location Analysis of Acoustic Emission Source for Superconducting Coil Quench During Training

Acoustic emission (AE) measurement is a non-destructive testing method that can detect high-frequency elastic waves generated by mechanical events inside an object, and is able to localize the wave source by using multiple sensors. In order to determine the mechanism causing the quench phenomenon in superconducting coil, we applied the AE method to a small ellipse-shaped coil in a training experiment. Six AE sensors were installed on the coil surface before the coil was cooled to 4 K in a vacuum vessel and excited. The current to the coil was controlled to produce a gradual increase until the quench occurred. The entire training experiment ended after over 10 quenches and all AE events that occurred in each training cycle were measured. The location of the AE source inside the coil was calculated from the difference in arrival time between sensors, and the results were plotted on an expansion plan of the coil. High-amplitude AE events appeared in areas assumed to have sufficiently high internal stress to cause concentration of strain energy.