Cryogenic optical fiber sensors for superconducting system protection in cryo-electric aircraft

Abstract Recent advancements in high-temperature superconductors (HTSs) offer promising opportunities for cryo-electric aircraft and fusion energy systems. However, the operation of superconducting field coils, magnets and busbars in extreme environments, characterized by extreme temperatures and intense electromagnetic noise, poses significant challenges. One of the most critical threats to these devices is local heating or thermal excursions, often caused by structural impurities, which can lead to catastrophic system failures. Therefore, there is a pressing need for a fully autonomous, real-time system capable of monitoring temperature variations in such harsh environments while remaining immune to electromagnetic interference. Fiber Bragg gratings in optical fibers have emerged as a potential solution due to their ability to provide reliable, distributed sensing for quench protection in HTS systems. A numerical model based on coupled mode theory and transfer matrix formulations was developed to investigate the impact of the statistical distribution of grating parameters on the spectral response. Building on our previous work in quench detection using ultra-long Bragg grating fibers, we extend our work to a current-carrying HTS tape. Furthermore, we demonstrate fiber-optic temperature sensing of localized thermal perturbations in superconducting field windings and bus bars under operating current conditions, highlighting its applicability to real-world systems such as a homopolar motor developed for aircraft electrification.