Detection of temperature rise in YBCO coil by time-frequency visualization of AE signals

The normal zone propagation velocities in the high T_C superconductors are slow at the high operation temperature and therefore the local and excessive temperature rise generates when the superconducting-to-normal transition occurs, and then the superconductors are degraded or burned. Therefore it is essential to detect the temperature rise in the high T_C superconducting coils as soon as possible to protect the coils. In general, the temperature rise can be detected by many voltage taps and thermocouples, however, the taps and thermocouples make the electric insulation of the windings degraded. The author has presented the time-frequency visualization of AE signals as a method to detect the temperature rise with non electric contact and the usefulness for Bi₂Sr₂Ca₂Cu₃O_x (Bi2223) superconductors has been presented. In this paper, the usefulness of the proposed method for YBa₂Cu₃O_x (YBCO) superconductors is verified and the experimental results show that the proposed method can detect the temperature rise in a YBCO coil.