Distributed Rayleigh Sensing in Superconducting Magnets

Superconducting magnets have a variety of applications, including medical imaging, magnetic levitation transport, novel computing hardware, and plasma fusion confinement systems. Precise control of superconducting magnet systems is key to ensuring safe, stable operation. Control devices need to be immune to the large electromagnetic fields present to optimally control operations and prevent damage to the systems. Current monitoring of superconducting systems is often hindered by electromagnetic noise due to high magnetic field strength, strong radiation, and low temperatures. Measurement solutions have begun to utilize embedded optical fibers which are immune to electromagnetic noise. These techniques (OFDR) rely on tracking the spectral change of a light signal within the fiber. They offer high spatial resolution but have limited range and poor temporal resolution. Temporal resolution, enabling control systems to respond quickly, is key to controlling superconducting magnets in real time. We will develop a system for continuous fiber optic monitoring of superconducting devices using a distributed Rayleigh sensing technique that employs coherent-phase optical time domain reflectometry (cpOTDR), which is capable of sampling much more rapidly, in the kHz frequency range. The system will use a fiber optic cable that is purpose-designed for strain and temperature separation, allowing us to track minute temperature and strain changes in time and space. The high temporal sampling of cpOTDR offers the potential to detect quench events in fusion reactors much more quickly than other systems, and the ability to sense a long fiber optic cable means that the fiber can monitor not only magnetic coils but other components such as pipes, power lines and many auxiliary devices in the overall system. During Phase I, we will demonstrate the viability of cpOTDR to detect thermal transients at cryogenic temperatures via experiments and simulations. We will design and model various cable alternatives that will be performance tested in high-temperature superconductor systems in Phase II. This project will provide a novel distributed fiber optic monitoring system for control of superconducting magnet systems using purpose-designed embedded fiber optic cables. The system will be immune to electromagnetic noise. It will observe anomalous events (caused by field disturbances, coolant flow instabilities or other adverse physical parameter changes in superconducting system) at very high temporal sampling rates, enabling rapid response to such disturbances, to keep the system operating and prevent damage. The long-term goal is to provide enhanced methods to optimally monitor and control a superconducting environment. The technology will ultimately be transitioned into the commercial market through Luna equipment sales and services. The integration and adoption of the technology will improve the efficiency and economics of superconducting operations.