YBCO Coated Conductor with an Integrated Optical Fiber Sensors

Advanced magnet systems being designed for fusion devices and other applications would greatly benefit from the use of high-temperature superconductors (HTS). However, the HTS magnet designs currently suffer from the inability to rapidly detect a quench, raising the possibility that the magnet and associated systems can be damaged if preventative action is not takes fast enough. Most efforts to address this challenge have focused on developing fast respond sensors that can be incorporated into the magnets. The ideal approach, however, is to develop a self-monitoring HTS wire that instantly responds to stress changes occurring at the beginning of a quench condition. This advance self-monitoring wire would provide a level of quench protection not available with existing systems and ensure the reliable operation of critical and costly magnet systems. American Superconductor Corporation (AMSC) and collaborators at North Carolina State University (NCSU) propose to develop and demonstrate the feasibility of a self- monitoring 2G HTS wire incorporating an embedded optical fiber sensor in the wire. The optical fiber, which will be an integral component in the AMSC's laminated 2G composite wire, will allow the continual, real time monitoring of local temperature variations (stress) throughout the length of the wire in the magnet. Temperature increases signal the initiation of a potential quench and will be detected using a novel Rayleigh scattering technique developed at NCSU which overcomes the lack of spatial resolution encountered with conventional optical measurement techniques. The Rayleigh technique will also provide the ability to identify the position of the quench within the wire. It is expected that this self-monitoring capability will add minimal cost to the 2G coil wire manufacturing and can utilize commercially available optical sources and equipment for the detection system. In Phase I we will fabricate short length lengths of the self-monitoring 2G wire and conduct a series of mechanical and electrical test to ensure that the mechanical and electrical integrity of the 2G coil wire and optical fiber are not affected by the manufacturing process. Meter length wires using the optimal design and optical fibers will be produced and the quench detection will be tested in small coils. In Phase II we will develop a reel-to-reel system for incorporating the optical fiber into AMSC's 2G coil wire. The goal will be the production of self-monitoring wire with lengths exceeding 500 meters. The long length wire will be used in coils that will be subjected to extensive testing to confirm the mechanical integrity and the rapid quench detection. The Phase II project will also focus on manufacturing yield and the fabrication of electrical and optical splices.

The self-monitoring 2G HTS wire technology will significantly increase the reliability of advanced magnet systems needed for fusion devices and motors and generators being planned for critical energy, defense, medical and other commercial applications. The proposed quench detection technology will provide an unsurpassed level of protection for these critical and expensive systems. This increased reliability will enable the use of HTS wire in these applications, protect the systems from failure and extend the lifetime of the systems, ultimately leading to lower costs for both the advanced magnets and systems.