Abstract
The influence of the amount of outgassing from a turbomolecular pump (TMP) on pumping speed was investigated experimentally. The amount of TMP outgassing was calculated using the results of experiments for measurement of outgassing from a stainless steel vessel. The calculation method is based on a new formulation for pressure estimation in which intrinsic pumping speed and the amount of TMP outgassing are considered. The amount of TMP outgassing was found to be much greater than that from the vessel, and the ratio of the two reaches more than twenty after baking, having being four before baking. This makes the ratio of the effective pumping speed to the nominal one about 0.03 after baking, and 0.2 before baking. These results clarify that the amount of TMP outgassing plays quite an important role in pressure determination in the vacuum system. The high accuracy of pressure estimation by the new method facilitated selection of the appropriate size of pump for a vacuum system. The new formulation can also be used for quantitative evaluation of the influence of materials, surface treatments, and configuration of the TMP on the pumping speed.
