Acoustic emission induced from an alternating current superconducting coiland quenching patterns

Acoustic emission (AE) signals induced from an alternating current (ac) NbT i superconducting coil were studied to observe the relationship between AE signals and the superconducting states of the winding of the ae coil, aroun d the time of quenching initiation during operation at a commercial frequen cy of 50 Hz. The envelopes of the AE signals induced at quenching initiatio n were analyzed using information from operating currents and voltages in t he coil. The AE signals rose and increased in accordance with the appearanc e and enhancement of the normal components for most cases in a series of qu enching tests, where the quenching was initiated at the coil ends. In the c ase that the quenching was initiated by a different cause, the AE waveform had a different pattern, in which the AE signals started like a impulsive s ignal having slow decay,and normal zone propagation was not initiated at th e moment when the AE signal started. Those differences are compared and dis cussed.