diffusion pump


Diffusion pumps have been the first generation of pumps used to achieve high-vacuum or ultra high vacuum. The operating idea is similar as in a turbomolecular pump. The pump is connected with a large cross section to the UHV recipient in order to increase the likelihood for molecules to enter the pump. These molecules are then given some momentum in the direction of the pump exhaust. The way this momentum is transferred is by a stream of oil vapour. The oil is heated in the base of the pump, streams to the top, condenses again at the cooled walls and flows to the heater. It is, of course, important that this oil has a sufficiently low vapour pressure.

A diffusion pump needs a roughing pump in a first pumping stage. It cannot operate against ambient pressure. Compared to turbomolecular pumps, diffusion pumps have the advantage of reliability (no moving parts) and low cost. There is, however, the danger of the pump oil getting into the UHV system.

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