CORC® wires containing integrated optical fibers for temperature and strain monitoring and voltage wires for reliable quench detection

Safe operation of large superconducting magnets wound from high-temperature superconductors (HTS) requires reliable detection of the onset of a quench. A novel method to integrate optical fibers and voltage wires within the core of multi-tape HTS CORC(R)wires has been developed that allows real time monitoring of local changes in strain, temperature and of the superconducting state of the magnet windings. The ability to detect highly localized changes in temperature with Rayleigh scattering in the embedded optical fibers provides invaluable information about local heating at hot spots from which a quench may originate. Integrated voltage contacts allow accurate voltage measurements in long CORC(R)wires without being affected by high current ramp rates or electromagnetic interference. They also allow detection of inductively driven redistribution of current between tapes in CORC(R)wires that may occur at high current ramp rates. Continuous monitoring of temperature and voltage was used to detect the formation of local hot spots induced by a heater or by operating the CORC(R)wire above its critical current. The results show that, within the boundary conditions of the experiment and the method by which the optical fibers were integrated into the CORC(R)wire in this study, the speed and resolution with which hot spots can be detected with optical fibers lagged that of the integrated voltage wires. This study also shows that integrated voltage wires reliably detected the formation of a local hot spot in a 5.1 meter long coiled CORC(R)wire, down to a hot spot size covering 0.1% of the conductor length and at current ramp rates as high as 2000 A s(-1). Voltage measurements thus remain an effective option for quench detection in magnets wound with HTS conductors for which current sharing between tapes allows for operation within the flux flow regime.