Chapter 2.6 - Turbomolecular Pumps

Abstract

This chapter provides an overview of the turbomolecular pump (TMP)—only mechanical vacuum pump that together with a roughing pump can attain ultimate pressures in the range below 10–10 torr. The pumping speed and the compression of a TMP depend strongly on the rotor geometry and rotational speed. The gas throughput is constant in each stage, so the blades nearest to the inlet of the TMP are designed to have a high pumping speed and a low compression, whereas the blades nearest to the foreline port are designed for high compression and low pumping speed. TMPs are equipped with lubricated mechanical rotor bearings, or by a combination of permanent magnet bearing at the high-vacuum side with a lubricated mechanical bearing at the forevacuum side. Depending on the disk diameter, the rotational speed of the rotor goes up to 90,000 rpm. The dynamic balancing of the rotor of a TMP is very important for minimizing vibration and noise levels, which are related to the mechanical bearing lifetime. Due to the high rotational speed of TMP rotors, the centrifugal forces associated with the residual imbalance attain considerable values and transmit vibrations to the body of the pump.