Comparative Study on Distributed Fiber Optic–Based Quench Detection Schemes for HTS Cables for Fusion Magnets

Distributed Fiber Optic Sensors (DFOS) are being considered as an alternative solution for Quench Detection in HTS fusion magnets. Their successful application is not straightforward due to the simultaneous need for high spatial and temporal resolution over long-length conductors operating in demanding cryogenic environments. In this work, we explore the potential of two different commercially available distributed sensing technologies, respectively based on the analysis of Rayleigh-backscattering through Optical Time Domain Reflectometry (OTDR) and Optical Frequency Domain Reflectometry (OFDR). The two techniques were used first to characterize the cryogenic temperature response of similar fibers between room temperature and 4 K. The temperature sensitivities were computed and compared to those of Fiber Bragg Grating sensors, showing comparable results. The performance of the investigated techniques in detecting local quenches was then experimentally assessed in operating conditions on a 2-meter-long, aluminum-stabilized HTS sample cooled by Liquid Nitrogen flow. While OFDR needs improvements in temporal resolution, the limited scale of the hot spot represents a challenge for the OTDR technique due to its lower spatial resolution.