Acoustic emission induced from alternating current superconducting coils resulting from vibration of windings

Acoustic emission (AE) induced from alternating current (AC) superconducting coils was studied in terms of the vibration of the superconducting windings caused by the interaction between self-magnetic fields and operating currents. The AE signals were analyzed regarding two types of epoxy-impregnated NbTi coils having different tension at their winding ends. The AE pulses from vibrations appear at the time of zero-crossings of the operating currents as well as at the time of peaks of the currents, where the former AE signals resulted from the electromagnetic force in the axial direction combined with that in the radial direction. The waveforms of AE envelopes that depended on the tension and the amplitude of operating current were also described. Those data are considered to contribute to understanding of AE signals, for example, for detecting vibration that suddenly appears during operation or for discriminating between the vibration-induced AE components and other components.