ABSTRACT
Ultrahigh-vacuum techniques and system components have evolved together with special pumping methods uniquely adapted to the requirements of extreme cleanliness, bakeability, and pumping speed. The general pumping speed characteristics of sputter-ion pumps are similar to other vacuum pumps. There is a more-or-less constant-speed region at intermediate pressures, the net pumping speed is reduced to zero at low pressure, and it decreases to very low values at higher pressures. Ion-getter pumps are capable of pumping any gas, including noble gases and hydrocarbons. Due to the differences in molecular weight and chemical activity, the pumping mechanisms and the associated pumping speeds are different for different gases. Sputter-ion pumps are normally shipped to the user after evacuation, degassing, and sealing under vacuum. This keeps the pump surfaces clean, unsaturated with adsorbed gases, and makes it easier to start the pump. Nonevaporated getter pumps can be incorporated into ion-getter pumps to provide a higher pumping speed for hydrogen.
