AVS2001 Session VST-TuM: Turbomolecular, Molecular Drag and Similar Pumps

Tuesday, October 30, 2001 8:20 AM in Room 125

Tuesday Morning

Start	Invited?	Item
8:20 AM	Invited	VST-TuM-1 History of Alcatel Turbomolecular Pump Development R. Mathes, O. Boulon (Alcatel Vacuum Technology, France) This article describes the development of turbomolecular pumps at Alcatel over more than 20 years. It shows the changes from the initial molecular pumps and turbomolecular pumps to the present technology of hybrid turbomolecular pumps. The different bearing technologies used in pumps such as ball bearing, gas bearing and maglev bearing technologies are described. The changes in the rotor design of MDP and TMP are explained by the improvement of calculation methods such as analytical calculation for molecular and viscous flow, Monte Carlo simulation for the molecular flow, direct Monte Carlo simulation for transition flow and simulation with CFD codes for viscous flows in 2D and 3D.
9:00 AM		VST-TuM-3 Effects of Surface Roughness of Blades on the Pumping Performance of a Turbomolecular Pump M. Yabuki, T. Sawada, W. Sugiyama (Akita University, Japan); M. Watanabe (Osaka Vacuum Ltd., Japan) Turbomolecular pumps (TMPs) are widely used in the semiconductor and other thin film industries. Some semiconductor processes form corrosive gases such as HCl or HF as byproducts. The elements of a TMP are sometimes coated with ceramic (SiO ₂) film for the purpose of preventing corrosion on the TMP. The blades coated with SiO₂ have relatively rough surfaces and may change the pumping performance. The effects of the surface roughness of the blades on the pumping performance were studied experimentally and theoretically. First, the maximum-compression ratio was measured for the non-coated TMP that had two rotor discs and one stator disc. Next, the pump that had been tested was disassembled and the elements were coated with SiO₂. Then the maximum-compression ratio was measured for the reassembled-coated pump. The compression ratio attained by the coated pump was compared with the one attained by the non-coated pump. The effects of the surface roughness were also estimated by a two dimensional calculation. Both the experimental and calculated results show that the TMP coated with SiO₂ film gives about a 13% higher maximum-compression ratio than that of the non-coated TMP when the blade speed ratio is 0.47.
9:20 AM		VST-TuM-4 Power Optimisation of a Hybrid Turbomolecular-drag Vacuum Pump S. Giors, R. Cerruti, J.C. Helmer (Varian Vacuum Technologies, Italy) Varian has specialised in the development of Gaede stages for extending the tolerable fore pressure of hybrid turbomolecular-drag vacuum pumps. The design of the first hybrid turbomolecular pumps was focused to the optimisation of their vacuum performances, disregarding the power dissipated to get them. The power dissipated by the pump was just a consequence of a given vacuum optimisation, normally resulting in high power dissipation rates. Nowadays, this approach is no more acceptable, as a consequence of our need to build pumps able to reach higher and higher fore pressures. Today the optimisation has to be carried out, taking into account both power dissipation and performance, stage by stage. In a previous paper¹ we presented a model able to predict power consumption of a single Gaede stage. Now that model is extended to a cascade of Gaede stages and applied to the optimisation of a full commercial pump. The drag stages of a 250 L/s pump have been redesigned according to that model in order to heavily reduce its power consumption without compromising its vacuum performance and without affecting the production process. Measurements show about 50% in power reduction with respect to the old pump without any loss in pumping speed, compression ratio or high throughput characteristics. This work demonstrates that further improvement is possible in the design of commercial hybrid turbomolecular-drag pumps, in order to reduce power dissipation, and hence cooling requirements, rotor working temperature and reliability. ¹ R. Cerruti, M. Spagnol, J. C. Helmer, "Power dissipation in turbomolecular pumps at high pressure", J. Vac. Sci. Technol. A 17(5), 3096-3102, Sept/Oct 1999.
9:40 AM		VST-TuM-5 Study on the Performance Prediction of Turbine Blade under Low Vacuum M. Watanabe (Osaka Vacuum, Ltd., Japan); T. Sawada (Akita University, Japan); T. Ohbayashi, M. Iguchi (Osaka Vacuum, Ltd., Japan) A turbo molecular pump with the ability to pump a large quantity of gas under a low vacuum is required in the fields of semiconductor and liquid-crystal device manufacturing. In this study, we propose the method of performance prediction for a turbine blade under a low vacuum, which enables the design of high throughput pump. The performance was analyzed with Stokes equation, which governs the low vacuum flow between the turbine blades with small Reynolds numbers. Experiments were carried out with conventional and optimized blade pumps under a low vacuum; throughputs were measured. The comparison between the measurements and the predicted values showed that the present method predicts the performance of the turbo molecular pump in the pressure range under 10 Pa with a sufficient accuracy for practical applications.
10:20 AM	Invited	VST-TuM-7 Turbine-type Pumps in High-vacuum Technology M.H. Hablanian (Consultant) High-vacuum pumping technology has undergone a very significant transformation during the last 45 years: from oil vapor-jet pumps (so-called diffusion pumps) and oil-sealed mechanical pumps to a variety of oil-free technologies. The major trend has been the demand for improved cleanliness. Ultrahigh vacuum techniques, ion-getter pumping, cryogenic pumps, turbomolecular pumps, and oil-free roughing pumps are part of the trend. Turbomolecular pumps, or turbopumps, of various designs have become one of the major means of obtaining high vacuum. Their relative simplicity of operation, an advantage of a single rotor, a possibility of use in a remarkably wide range of pressure, and the convenience of multi-staging in a compact body to achieve high compression ratios, combine to provide a design flexibility unrivaled by other types of pumps. The design variations are still in process. Articles describing new designs are appearing in technical journals and patent literature. These include compound pumps, hybrid pumps, pumps with multiple inlets and exhausts, miniature pumps, and finally, pumps that are capable of exhausting directly into atmosphere. The latest addition to the variety of pumping disks, attached to the same shaft, are regenerative-centrifugal impellers. The proper selection and design of such pumping disks has a significant impact on performance and power consumption. We should expect that in the next 10 or 20 years the potential product possibilities should be sorted out.