Feasibility study on quench detection methods of Raman and Rayleigh scattering techniques in optical fiber encapsulated HTS coils

Quench detection is a key issue to be solved for safe operation of high temperature superconducting (HTS) magnets. Recently, distributed optical fiber sensors based on Raman and Rayleigh scattering techniques are proposed for quench detection in HTS applications. However, sensing and demodulating principles of these two techniques are different, and they may show different performances in quench detection. In this paper, a 13 m long optical fiber encapsulated HTS coil (OF-coil) was fabricated. Two sensing devices based on Raman and Rayleigh techniques, which are named Raman-device and Rayleigh-device, were prepared. Overcurrent and heater induced quench detection experiments in the OF-coil were carried out and the above two devices were used for quench detection. The results show that both Raman-device and Rayleigh-device can measure temperature changes of the OF-coil in the overcurrent experiment. And their quench response time is 36 s and 14 s, respectively. In heater induced quench detection experiment, Rayleigh-device can successfully acquire local temperature rise of the OF-coil, and the quench response time is 1.7 s. For Raman-device, its spatial resolution is too large to realize local quench detection.