High-temperature superconducting magnets (HTS) are an essential part of next generation tokomak nuclear fusion energy system. Stability of these superconducting magnets is crucial, and an open issue that hampers the stability of the superconducting device is a quench event which occurs when a section of the superconductor transitions into a normal state. A rapid and reliable quench detection system is necessary to prevent HTS magnets traversing into a thermal runaway and protect the system from the catastrophic failure. This necessitates the need to understand the dynamics of normal zone development.
Optical fibres with a continuous array of Bragg gratings (Ultra long fiber Bragg grating array) have been identified as a potential candidate to monitor the temporal response to the perturbations along the high temperature superconductor [1-3]. Mimicking the quench events in the fusion magnets, we created localized thermal perturbations on current carrying superconducting tapes through controlled experiment at Robinson’s facility. A high-speed interrogator along with a custom-made Bragg grating array is used in this study to investigate the normal zone development and propagation in superconducting tapes. We demonstrate the detection of localized hotspots extended over 10-15 mm along 1m HTS tape. The performance of the fiber sensor is compared to the voltage taps and the point temperature sensors distributed across the length of the superconducting tape.
[1] Salazar, E.E., Badcock, R.A., Bajko, M., Castaldo, B., Davies, M., Estrada, J., Fry, V., Gonzales, J.T., Michael, P.C., Segal, M. and Vieira, R.F., 2021. Fiber optic quench detection for large-scale HTS magnets demonstrated on VIPER cable during high-fidelity testing at the SULTAN facility. Superconductor Science and Technology, 34(3), p.035027.
[2] Ludbrook, B.M., Haneef, S.M., Huang, X., Gonzales, J., Moseley, D., Davies, M., Duke, O., Salazar, E.E. and Badcock, R.A., 2023. Continuous fiber Bragg grating optical sensors for superconducting magnet quench detection: the effects of attenuation and position in the array. IEEE Transactions on Applied Superconductivity, 33(5), pp.1-5.
[3] Huang, X., Davies, M., Moseley, D.A., Ludbrook, B.M., Salazar, E.E. and Badcock, R.A., 2023. Localized hotspot detection for quench prevention in HTS magnets using distributed fiber Bragg gratings. Journal of Lightwave Technology.
This work was supported by the New Zealand Ministry of Business, Innovation and Employment (MBIE) Strategic Science Investment Fund “Advanced Energy Technology Platforms.” This research was also supported by Commonwealth Fusion Systems (CFS).