Cryogenic refrigerator

A cryogenic refrigerator, comprising:

• a regenerator filled with a regenerator material;
• a compressor connected to a first pipe for feeding a refrigerant gas of a first pressure to the regenerator, and connected to a second pipe for collecting the refrigerant gas of a second pressure lower than the first pressure from the regenerator;
• a third pipe having a first end connected to a connection of the first pipe and the second pipe and a second end connected to a high-temperature end of the regenerator;
• a buffer tank configured to store the refrigerant gas;
• a first opening and closing valve provided in the first pipe;
• a second opening and closing valve provided in the second pipe;
• a first valve provided in a first connecting pipe extending from the buffer tank to bypass the first opening and closing valve and the second opening and closing valve to connect to the third pipe;
• a second valve provided in a second connecting pipe extending from the buffer tank to connect to the first pipe;
• and
• a third valve provided in a third connecting pipe extending from the buffer tank to connect to the second pipe,
• wherein the third valve is opened at a first time and remains opened until a second time at which the third valve is closed, the first opening and closing valve remains open from the first time to the second time, and each of the first valve and the second valve remains closed from the first time to the second time.