| 摘要 |
PURPOSE:To improve the exhaust characteristics of gas having a low molecular weight, especially a water molecule by a method wherein a heat exchanger cooled by a helium freezer to freeze and collect gas molecules is disposed on the suction port side of a turbomolecular pump. CONSTITUTION:When vacuum exhaust is effected with the aid of only a turbomolecular pump 26, residual gas in a vacuum vessel 21 contains quantities of light gas. Therefore, by freezing and collecting water molecules by a heat exchanger 25 cooled by a helium freezer 24 on the suction side of a turbomolecular pump 26, exhaust performance is improved, and vacuum having good quality and the high degree of vacuum can be generated. By also cooling small gas, e.g. hydrogen, helium, having a molecular weight not frozen and collected by means of the heat exchanger 25, temperature is reduced and a gas molecular speed is decreased. As a result, a blade velocity ratio is increased, and exhaust performance of the turbomolecular pump 26 is improved. Conventional poor exhaust performance for gas having a small molecule, especially a water molecule can be eliminated.
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