Sensitive fiber optic sensor for rapid hot-spot detection at cryogenic temperatures

The incredible current density and high magnetic field generation possible with high-temperature superconductors (HTS) have the potential to revolutionize energy generation, e.g. high-power generators, and compact fusion energy devices. However, an open issue that limits the applications of this class of superconductors is the challenge of rapidly detecting a hot spot which can lead to a quench. Owing to the inherent advantages of fibre optic sensors, they are promising candidates to be integrated in HTS magnets for hot-spot detection. In this paper, closely spaced fibre Bragg gratings (FBG) with the same Bragg wavelength are used to establish an ultra-long FBG (ULFBG) for distributed hot-spot monitoring. We investigate the capability of a 10m ULFBG to detect a small temperature rise at the end of the sensor. The results show that a 10 m long ULFBG can rapidly detect a small hot spot within 1 K temperature rise at 80 K. It is expected that ULFBG can be wavelength-division multiplexed and integrated to superconducting coils to achieve long-distance hot-spot monitoring with extremely high spatial resolution and fast response.