Cold storage characteristics of mobile HTS magnet

An apparatus was constructed to evaluate the possibility of using cold storage systems in maglev vehicles. The thermal characteristic of this apparatus was based on a magnet for previous maglev test vehicles [1]. The operational temperature range of the magnet was assumed from 20 K to 50 K. Some experiments indicated that heat conduction by residual gas was not negligible. Especially over 30 K, gas conduction took a large part of heat input. This phenomenon is attributable to reduction of cryopumping effect. However, activated carbon in the apparatus compensates cryopumping effect. A unique heat capacitor was also used to enhance the cold storage effect. Water ice was chosen as a heat capacitor because water ice has a higher heat capacity than metallic materials at cryogenic temperatures. A small amount of water ice also prolonged cryogenic temperature condition. These results indicate 1 day of cold storage is probable in a magnet for maglev vehicles.