I. Introduction
Conduction cooling is an attractive design approach for superconducting magnets due to its compactness, easy and safe handling, and low running cost [1]–[5]. In a conduction-cooled superconducting magnet system, a 4 K Gifford-McMahon (GM) or Pulse-tube cryocooler is employed as a heat sink to cool the magnet down to the operating temperature. Since the cold head of a cryocooler has a positional restriction [6], it should be located far from the magnet in order to avoid the degradation of cooling performance. Also, heat transfer is poor in the conduction cooling system because of the difficulty in thermal contact between the magnet and the cryocooler. Therefore, the cooling medium between the magnet and the cryocooler is crucial in developing the conduction-cooled superconducting magnet system.