Method for maintaining refrigeration unit and refrigeration unit

A method for maintaining a refrigeration unit used for a superconducting magnet device including a superconducting coil, a radiation shield housing the superconducting coil, and a vacuum case housing the radiation shield, the refrigeration unit including a first cooling stage for cooling the radiation shield, a second cooling stage for cooling the superconducting coil, and a refrigerator body attachable to the vacuum case, the method comprising:

• a connecting step of connecting the refrigerator body to the vacuum case with the first cooling stage in thermal contact with the radiation shield, using a fastener fixing the refrigerator body to the vacuum case, the fastener being configured to be able to adjust, through adjustment of the fastening force of the fastener, a contact pressure of the first cooling stage to the radiation shield or a heat conductor in thermal contact with the radiation shield;
• and
• in the connecting step:
• determining a target temperature for the first cooling stage,
• detecting a temperature of the first cooling stage, and
• adjusting a fastening force of the fastener such that the detected temperature of the first cooling stage in thermal contact with the radiation shield becomes the target temperature, and if the detected temperature of the first cooling stage is lower than the target temperature, the fastening force of the fastener is increased, wherein
• in the connecting step, the target temperature is a temperature calculated by subtracting a predetermined value from a temperature of the radiation shield.