Abstract
The influence of outgassing from a turbomolecular pump (TMP) on the pumping speed was investigated theoretical-ly. The investigation was based on a combination of the transmission probabilities of the gas through blade rows with outgassing from every part of the TMP. A new formulation was derived for evaluating pressure from the intrinsic pumping speed and the outgassing rate of the TMP. This formulation clarified the physical meaning of the conventional pumping speed. Several of the principal quantities used in conventional methods of pumping speed evaluation can be used with the new formulation. A method was also developed for measuring outgassing rate of TMP. This method enables quantitative evaluation of the influence of materials, surface treatments, and configurations of TMP on the pumping speed. The high accuracy of pressure evaluation by the new method facilitated the selection of the appropriate size of pump for a vacuum system.
