Real Time and Distributed Temperature Sensing and Quench Detection Via Multi-Functional Fiber Optic Sensors

The real-time detection of thermal instabilities, i.e. “quench detection” is critically important to the protection of superconducting magnetics. Undetected “hot spots” where local temperature increase arises, due to the transition to the normal state (irreversible loss of superconductivity, is the primary failure mechanism in superconducting magnets. Rapid detection is necessary to avoid material degradation and damage to the magnetic by quickly eliminating the stored energy. Quenches are often detected electromagnetically: by using voltage taps to detect a resistive voltage or by detecting a loss of superconducting diamagnetism. Voltage taps can work well for DC superconducting magnets but those with high terminal voltages and large unpredictable voltage transients demand other solutions. Thus, there is a need for a reliable quench detection technology for the next generation of superconducting magnets. The objective of the project is to develop a first-of-its-kind distributed fiber optic sensing system for rapid and real-time cryogenic temperature sensing of superconducting magnets. Development of this unique technology will rely on the design and fabrication of multi-material optical sensing fiber to provide localized temperature measurements in liquid nitrogen (77 K) and liquid helium (4 K) environments. The multi-material sensing fiber will include high thermal expansion materials and integrated with fiber Bragg grating sensors will yield a simple, yet transformative approach to cryogenic sensing. In this Phase I effort, a first-of-its-kind distributed fiber optic sensing system will be designed and developed for rapid and real-time cryogenic temperature sensing of superconducting magnets. This unique technology will rely on a high thermal expansion optical sensing fiber to provide localized temperature measurements at in liquid nitrogen (77 K) and liquid helium (4 K) environments. Integration of mature fiber optic sensing schemes, such as those based on fiber Bragg gratings, with a special optical sensing fiber produced on a commercial optical fiber draw tower is well positioned for near-term commercial viability. The inclusion of materials, such as indium or lead, with a relatively high coefficient of thermal expansion directly into the silica glass cladding will enhance the sensor response, limit the size, and assure reliability. The cryogenic temperature sensing system will be fully integrated and fit for use upon project completion. The proposed sensing technology will not only provide end users with a critical diagnostic tool but will also serve as a platform for the development of additional sensor types. The successful development of the proposed sensing system that can provide real-time temperature measurements down to <10 K will fill the technology gap that is required for reliable quench detection for superconducting magnets. The unique high thermal expansion sensing fiber will become a platform for cryogenic sensing via other fiber optic sensing techniques such as those based on Rayleigh and Brillouin backscatter. The demonstrated ability to fabricate optical fibers and sensors designed specifically for operation in cryogenic environments will immediately benefit the scientific community by providing a means to develop new technologies and/or realize the potential of current innovations whose development has stalled and never “made it out of the lab”. If successful, the temperature sensing system will find immediate application for real-time temperature monitoring of superconducting transmission cables and has the potential to enable the development of long span, distributed temperature sensing systems for superconducting magnets.