Cryogenic refrigerator, and method for cooling down cryogenic refrigerator

A cryocooler comprising:

• a cold head including a first cooling stage and a second cooling stage cooled to a lower temperature than the first cooling stage;
• a heater thermally coupled to the first cooling stage;
• a first temperature sensor that measures a first temperature of the first cooling stage;
• and
• a controller configured to perform a cool-down operation of the cold head to cool the first cooling stage from an initial temperature to a first final target temperature and to cool the second cooling stage from the initial temperature to a second final target temperature which is lower than the first final target temperature,
• wherein the controller is configured to, during the cool-down operation,
• acquire the first temperature of the first cooling stage from the first temperature sensor, and
• control the heater such that the first temperature of the first cooling stage follows an intermediate target temperature which is lower than the initial temperature and higher than the first final target temperature.