The turbomolecular pump, or turbo pump for short, is an ultra-high vacuum pump for extremely low end pressures of up to 10-10 mbar). The pressure which can be actually achieved in a system depends upon the leak rate of the components and their gassing in the vacuum chamber. A turbomolecular pump consists of series of stators and rotors arranged one behind the other, comparable to a jet engine. The speeds of turbomolecular pumps are several 10000 rpm. Since the capacity of turbo pumps decreases with increasing pressure, they can only be operated in connection with a pre-pump, e.g. a rotary vane pump. Turbomolecular pumps are used in plasma systems whenever very low pressures are required that cannot be achieved by other types of pumps (rotary vane, roots pump).