Operating Thermal Characteristics of REBCO Magnet for Maglev Train Using Detachable Cooling System

Recently, high speed trains over 1000 km/h have been proposed in an evacuated tunnel and a Maglev train using REBCO magnets can be considered as a feasible option due to their excellent mechanical and electromagnetic characteristics. A cryogenic cooling system for REBCO magnet occupies an installation space and burdens system weight. For a Maglev train with a limited space, it is important to minimize the installation space and reduce the system weight. The electric power is also limited while the magnet is running. This paper describes thermal characteristics of a prototype REBCO magnet with a solid nitrogen vessel as a thermal battery, a detachable cryocooler, and a quasi-persistent current switch to reduce the installation space and system weight. Solid nitrogen vessel, attached on the magnet bobbin, is designed to maintain the magnet temperature below an operation limit without an on-board cryocooler, which simulates an external cryogenic refrigeration system that periodically cools the magnet at stations. Heat capacity of the solid nitrogen, which includes a solid phase change at 35.6 K, is used to maintain the magnet temperature. The experimental results with solid nitrogen are compared with a design and simulation results. The result shows the possible application of external cooling system and the quasi-persistent current mode of the REBCO magnet for a high-speed maglev train.