Design and Implementation of an Acoustic Waveguide Quench Detection and Localization Sensor for the HTS Uni-Layer Magnet Prototype

Detection and localization of quench events are essential to protect superconducting magnets for particle accelerators. Voltage taps are widely adopted for low-temperature superconductors (LTS), but they do not ensure reliable quench detection for high temperature superconducting (HTS) magnets. The propagation velocity of the normal conducting zone is in the order of m/s for LTS, compared to cm/s for HTS, leading to a higher risk of irreversible conductor degradation before any voltage can be detected. As an alternative solution, non-leaky ultrasonic waveguides have been proposed as a diagnostic option to monitor hot-spots by tracking thermally induced sound velocity variations. A first practical implementation of this concept has been developed and tested for a Uni-layer winding prototype at Lawrence Berkeley National Laboratory (LBNL). In this work, we present the practical design of a non-leaky acoustic waveguide tailored for this magnet. We also show the results of an experimental campaign conducted to assess hot-spot detection and localization for the ultrasonic waveguide sensor, both in a straight and a configuration representing the magnet real geometry. Finally, the application of this technique is presented over a Uni-Layer winding prototype copper mock-up. The results of the tests at room temperature and liquid nitrogen temperature are discussed.