JPS5524511A - Cold trap - Google Patents

Abstract

PURPOSE: To provide a cold trap which prevents restriction due to difference between the axial thermal expansion of inner and outer walls of an insulating gas layer, by forming an annulus structure of insulating gas layer, which caused no restriction to the outer and inner walls, between a cooling section and an impurity collecting section.

CONSTITUTION: A cold trap has a cooling section 11 installed side by side with an impurity collecting section 7, both the sections being separated within a liq. An outer wall 4 of a thermally insulating gas layer is installed along the inner wall 5 of the thermally insulating gas layer, an outlet nozzle 2 being used simultaneously for the upper parts of both the walls, and the upper end of the outer wall 4 is opened to the gas layer of the cold trap. The distance of the upper end of the outer wall 4 from the upper end surface 15 of the cold trap is made larger than the maximum difference between the thermal expansions of the inner and outer walls 4, 5 which is developed during the service life of the cold trap. Spacers 14 are attached between the inner wall 5 and the outer wall 4 to prevent the decrease in thickness of the thermally insulating gas layer 12 due to external force. The lower end of the gas layer is sealed by welding. A plate 13, which prevents liq. from flowing in, is attached around the upper end of the outer wall 4 in order to prevent the fluid formed by condensation at the upper end plate 15 from flowing into the gas layer 12.

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