Cryogenic refrigerator and rotary joint

A cryogenic refrigerator for installation on an apparatus including a stationary portion and a rotating portion axially rotatably supported by the stationary portion, the refrigerator comprising:

• a compressor installed on the stationary portion;
• an expander installed on the rotating portion;
• and
• a rotary joint fluidly coupling the compressor with the expander, the rotary joint including
• a rotor fixed to the rotating portion and coaxial with the rotating portion's rotational axis,
• a stator disposed adjacent to the rotor to form a clearance between the rotor and the stator, and fixed to the stationary portion,
• a first high-pressure flowpath, being a flowpath for a first high-pressure working gas having a first high pressure that is higher than ambient pressure of the cryogenic refrigerator, and extending from the stator through the clearance to the rotor,
• a second high-pressure flowpath, being a flowpath for a second high-pressure working gas having a second high pressure that is higher than ambient pressure and is lower than the first high pressure, and extending from the rotor through the clearance to the stator, and
• a working-gas sealing area dividing the clearance into a first high-pressure section communicating with the first high pressure flowpath, and a second high-pressure section communicating with the second high-pressure flowpath;
• wherein
• the rotor includes a rotor base portion fixed to the rotating portion, and a rotor axial end located on the rotor's axially opposite side from the rotor base portion, and where between the stator and the rotor axial end the first high-pressure section is formed, and
• the stator includes a stator bottom wall portion forming a semi-enclosed section surrounding the rotor axial end.