Time-frequency distribution of acoustic emission signals induced from a rotating NbTi superconducting winding

Experimental analyses using the time-frequency distribution of acoustic emi ssion (AE) signals were studied in terms of quench propagation along a NbTi superconducting winding in a rotor cooled by liquid helium, Data acquisiti on of the AE signals was carried out with a sampling frequency of 2 MHz to cover almost the full frequency range of the signals. Short-time spectrum a nalyses were performed for the AE signals when the voltage between taps at the superconducting winding rose after applying heat energy to the winding. A similar test with a heat pulse of lower energy, which did not cause quen ch propagation, were also carried out. The spectra in this case are equival ent to the background noise of the AE signals in the quench case, and so th e AE components resulting from the quench propagation can be estimated.