Design of disk molecular pumps for hybrid molecular pumps*

Abstract

In recent years, the various types of hybrid molecular pumps combining a molecular drag pump (MDP) with a turbomolecular pump (TMP) have been developed in order to raise their pumping throughput and operating pressure. Some of them have been put on the market. In this article the pumping performances of the disk MDP, whose pumping channels are cut on a rotating disk, were calculated using a new model based on the Monte Carlo method. The relationship between the pump performance to the structural parameters was studied. The above pumping performance is also compared with that of the pumps having channels on stationary disks. When a pump is constructed in a series of two stages, the pumping speed and the compression ratio of the present pump for nitrogen gas increases by 35% and 64%, respectively, as compared with the previous type. It is believed that the pump having channels on the rotating disk has both kinds of pumping actions. Hence, it possesses the advantages of both MDP and TMP.