Evacuation Characteristics of Screw-Grooved Molecular Pump

Axial pressure distributions in a screw-grooved molecular pump were analyzed, using the pressure-smoothing theory applying numerical solutions of the BoltzmannKrook equation for flow of a rarefied gas in a rectangular groove faced with a moving plate, and relations among attainable pressure, evacuation speed, and rota rotation speed were made clear. A screw-grooved pump was designed for tests to investigate the evacuation characteristics. Attainable pressures and evacuation speeds at some typical rough pressures were measured against rota rotation speed, and their results were compared with numerical ones from the theory. Dependencies of gas species on evacuation characteristics were also made clear.