A High-Efficiency Protecting Scheme for HTS Inserts in Case of Background Magnet Quenches

For extremely high field magnets, the low-temperature superconducting/high-temperature superconducting (LTS/HTS) structure is an efficient and economical solution. In an LTS/HTS magnet system, the LTS background field magnet is deeply mutual inductance coupled with the HTS insert magnet. A sudden background LTS magnet quench may potentially destroy the double pancakes (DPs) of the insert HTS magnet because of the induced current and the resulting additional electromagnetic stress. To improve the safety and stability of the LTS/HTS magnet system, this article proposed a new passive protecting scheme of the LTS/HTS system. In this scheme, a magnetic dam is arranged between the insert magnet and the background field magnet. When the background field magnet quenches, the magnetic dam can help to slow down the magnetic flux variation in the insert magnet. According to the simulation results, a magnetic dam can significantly reduce the instantaneous stress rise of the insert magnet by 65.3%. The protective effect of the magnetic dam was also verified by the experiments with a Bi-2223 insulating coil magnet. The structural parameters affecting the isolating effect of the magnetic dam were also discussed. Based on this work, researchers can further improve the safety and stability of the LTS/HTS magnet system.