The Influence of Metal Plates on Quench Protection of High Temperature Superconducting Pancake Coils

Quench has always been an urgent problem for high temperature superconductor (HTS) magnets. Fast discharge of the coil current is an effective method to protect the HTS magnet from quenching. In HTS magnets, metal plates are originally used to provide conduction cooling and mechanical support for the coil. During fast discharging operations, the metal plates can rapidly absorb part of the magnetic energy stored in the HTS coils through electromagnetic coupling. Previous studies are based on copper plates. This paper studies the influence of several promising metal materials on the discharging process of the HTS coils coupled with metal plates by experiments and simulations. The results show that in the explored resistance range, the higher the electrical conductivity of the metal plates, the better the acceleration of the current attenuation of coil at the early stage of discharging process. The effects of different metal plates on accelerating current attenuation of the coil are ranked as follows: SS 304L < Al 6061-T6 < Al (RRR = 30) < Cu (RRR = 30) < Au < Cu (RRR = 300) < Ag. However, Cu (RRR = 300) plates can absorb more energy from the HTS coil than the Ag plates during the discharging process. Copper with higher purity (Cu (RRR = 300)) and silver are promising alternatives for metal plates of HTS magnets. Generally, a fast current drop is always the most effective method for avoiding tape turn-out during a local quench; therefore, silver with the highest electrical conductivity is the best choice in view of quench protection.