A turbomolecular pump is a type of vacuum pump, superficially similar to a turbopump, used to obtain and maintain high vacuum.   These pumps work on the principle that gas molecules can be given momentum in a desired direction by repeated collision with a moving solid surface.   In a turbomolecular pump, a rapidly spinning turbine rotor 'hits' gas molecules from the inlet of the pump towards the exhaust in order to create or maintain a vacuum.