| 摘要 |
PROBLEM TO BE SOLVED: To output stable temperature by reducing a leakage gas from the gap between the outer circumferential surface of a displacer and the circumferential surface of a cylinder in operation by forming the dispenser with plastic having a negative coefficient of linear expansion so as to not to shrink radially against the cylinder. SOLUTION: A cylinder part 4 comprises a first stage cylinder 6 made of stainless steel and a second stage cylinder 18, and each inside of which is inserted with a first stage displacer 7 and a second stage displacer 19, which slide reciprocally. When a cryogenic freezer is operated, each displacer moves reciprocally and when temperature drops by the adiabatic expansion of a coolant gas, the temperature of the cylinder and the displacer drops. The diameter of the cylinder, having a positive coefficient of linear expansion, changes in the shrinking direction and the diameter of the dispenser, having the negative coefficient of linear expansion, changes in the expanding direction. Therefore, the gap between the cylinder and the dispenser is reduced and the leakage of the gas can be reduced.
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