Application of Fiber Bragg Grating Sensors in Quench Detection for HTS BRAST-based Cables in Fusion Magnets

This thesis explores the integration of Fiber Bragg Grating (FBG) optical fibers as an innovative solution for quench detection in high-temperature superconducting (HTS) cables, specifically within a 6-slot aluminum core design for fusion applications developed at ENEA. HTS materials, such as REBCO, are known for their high critical parameters but present challenges in quench detection due to their low normal zone propagation velocity (NZPV). Traditional voltage-based quench detection methods are less effective under these conditions, necessitating alternative solutions. In this study, an HTS cable utilizing a BRAided STack (BRAST) of YBCO tapes was fabricated and tested, incorporating FBG sensors within steel capillaries placed directly onto the stack. Experiments were conducted in both liquid nitrogen bath and flow at 77 K to simulate quench conditions and assess the performance of FBG-based detection in comparison to conventional voltage taps and thermocouples. Results demonstrate that the FBG sensors provide rapid and accurate thermal response detection, allowing real-time monitoring of temperature variations within the stack, even in the presence of electromagnetic noise. Furthermore, the study underscores the practical benefits and challenges of optical fiber integration, which is critical for durability in high-current HTS applications. The findings support the viability of FBG-based quench detection in HTS cables for fusion applications, offering enhanced detection sensitivity, reduced electromagnetic interference, and valuable insights into future development of robust, high-performance superconducting magnet systems.