High field applications such as magnetic fusion devices have the opportunity to utilize the high performance capabilities of high temperature superconductors (HTS) with higher operating current densities, temperatures, and fields compared to low temperature superconducting (LTS) magnets. However, insulated HTS magnets introduce new challenges such as slow quench propagation velocities (orders of magnitude slower than LTS) that are harder to detect and can lead to high temperatures that can permanently damage the magnet if undetected. A quench test campaign was performed on the VIPER HTS Delta cable, a prototype of the VIPER HTS cable designed in collaboration between MIT-PSFC and Commonwealth Fusion Systems, in order to experimentally measure the quench propagation velocities, cryostability limits, and determine the quench temperature thresholds of a high field and high-current carrying HTS cable across a range of operating conditions (an external background field of 10.9 T, operating temperatures ranging from 6 – 20 K, and operating currents up to 50 kA). The quench tests were performed at the SULTAN magnet test facility in Switzerland. The measured propagation velocities varied from 0.05 – 0.25 m/s and the VIPER Delta cable was cryostable in the presence of localized thermal disturbances up to 0.9 Iop/Ic in 10 K conditions and up to 1.0 Iop/Ic in 20 K conditions. Additionally, novel temperature-based optical fiber technologies (fiber Bragg gratings and ultra-long fiber Bragg gratings) through collaborations with Robinson Research Institute and CERN were tested during the quench test campaign and validated as a robust quench detection technology that is immune to electromagnetically induced signals that affects conventional voltage-based quench detection systems. The quench temperature thresholds in combination with the temperature-based fiber optic quench detection technology enable a robust quench detection system that can detect the initiation of a quench event before it is fully developed. Although the measured propagation velocities of the VIPER Delta cable are significantly slower than LTS cables of similar current-carrying capacity, VIPER’s high cryostable performance against localized thermal disturbances at Iop/Ic above 0.9 in combination with the novel optical fiber quench detection technology (which can detect the initiation of slowly propagating quench events) enables the design and operation of high performing HTS cables, such as the VIPER cable.

This research work was sponsored by Commonwealth Fusion Systems. The optical fiber research was done in collaboration with the Robinson Research Institute and CERN.

Keywords: HTS, Quench Detection, Optical Fiber, Cables