SBIR-STTR Award

The particle accelerators and detectors needed for future high energy physics devices require magnetic fields higher than those that can be produced by the low-temperature superconductor (LTS) technologies used in present-day superconducting magnets (SCMs). High temperature superconductor (HTS) materials, however, have the potential to generate very high magnetic fields, offering a technological pathway to next-generation devices. One important technological difference between LTS and HTS magnets is that the normal zone propagation in HTS conductors is 1-2 orders-of-magnitude slower than in LTS conductors. Thus, one of the key limiting factors for the implementation of HTS SCMs is the quench detection challenge. Here we propose a solution to this long-standing problem: a fast and effective quench detection system based on Rayleigh-scattering interrogated optical fibers (RIOFs), enabling the further advancement of HTS SCMs for high energy physics applications. Research at North Carolina State University (NCSU), our partner in this STTR proposal, has shown that RIOF has great promise as the primary sensing element in a fast, distributed quench detection system. Optical fibers can be integrated in conductors and cables, allowing a distributed sensor for temperature and strain with extremely high spatial and temporal resolution. Here we propose to expand the RIOF operational window to 4.2 K when integrated into (RE)Ba2Cu3Ox (REBCO) and Bi2Sr2CaCu2Oy (Bi2212) SCMs. Note that RIOF integration into Bi2212 coils has an added challenge as compared to REBCO due to the issues associated with the wind & react magnet fabrication and the final high-temperature heat treatment. During Phase I, the quench detection properties of RIOF integrated into REBCO and Bi2212 coils will be characterized at 4.2 K and the viability of RIOF in Bi2212 coils will be assessed. In Phase II we will focus on scale-up into larger REBCO and Bi2212 coils that are meaningful to the high energy physics community, including consideration of HTS cables and Bi2212 coils heat-treated with over-pressure processing. Furthermore, in Phase II, the possibility of using RIOF as a heat treatment monitor in Bi2212 coils will be investigated, along with any other scale-up issues emerging from Phase I. Key Words: Optical fiber sensors, superconducting magnets, quench detection

High-temperature superconductors (HTS) are a vital technology for future particle accelerators, motors, generators and other electric power systems, fusion reactors, and many other medical and defense applications requiring high magnetic fields. One remaining limiting factor limiting to the implementation of HTS systems is the lack of adequate sensors to monitor the temperature and strain states of the superconducting magnets (SCMs), and in particular for rapid and early quench detection, as the slow normal zone propagation velocity of HTS conductors results in a particularly difficult quench protection challenge. Without effective quench protection, HTS magnets are likely to fail catastrophically, so addressing this challenge is critical to technological success. Previously, it has been shown that the quench detection challenge may be addressed by integrating optical fibers interrogated by Rayleigh scattering into HTS SCMs, providing a novel, fast quench detection system which is particularly impactful on but not limited to HTS SCMs. Optical fibers can be integrated with conductor or cables providing a distributed measurement of temperature and strain with very high spatial and temporal resolutions. Many key questions remain, however, for Rayleigh-interrogated optical fiber (RIOF) quench detection to become an accepted sensor within SCMs. One of these questions was whether RIOF would provide sufficient sensitivity at very low temperature (4.2 K); this was successfully addressed in Phase I. In Phase I, we integrated optical fibers into HTS coils and demonstrated effective quench detection at 4.2