Editing Diffusion pump (section)

{{Short description|High vacuum pump}}
[[Image:M6 Diffusion Pump.jpg|right|250 px|thumb|Six inch oil diffusion pump.]]
[[File:Ulvac oil diffusion pump ULK-04 cutaway.JPG|thumb|Ulvac oil diffusion pump cutaway]]
'''Diffusion pumps''' use a high speed jet of vapor to direct gas [[molecule]]s in the pump throat down into the bottom of the pump and out the exhaust. They were the first type of high [[vacuum pump]]s operating in the regime of [[free molecular flow]], where the movement of the gas molecules can be better understood as [[diffusion]] than by conventional [[fluid dynamics]]. Invented in 1915 by [[Wolfgang Gaede]], he named it a ''diffusion pump'' since his design was based on the finding that gas cannot diffuse against the vapor stream, but will be carried with it to the exhaust.<ref>{{cite journal | author = D. G. Avery and R. Witty | title = Diffusion pumps: a critical discussion of existing theories| journal = [[Proc. Phys. Soc.]] | volume = 59 | year = 1947 | pages = 1016–1030 | doi =  10.1088/0959-5309/59/6/313 | issue = 6|bibcode = 1947PPS....59.1016A }}</ref> However, the principle of operation might be more precisely described as '''gas-jet pump''', since diffusion also plays a role in other types of high vacuum pumps. In modern textbooks, the diffusion pump is categorized as a [[vacuum pump#Momentum transfer|momentum transfer]] pump.

The diffusion pump is widely used in both industrial and research applications. Most modern diffusion pumps use [[silicone oil]] or [[polyphenyl ether]]s as the working fluid.