L05-Vacuum_Technology

L05-Vacuum_Technology - Vacuum Technology Vacuum Pumps Two...

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Vacuum Technology
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Vacuum Pumps Two general classes exist: Gas transfer – physical removal of matter Mechanical, diffusion, turbomolecular Adsorption – entrapment of matter Cryo, sublimation, ion
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Mechanical Pumps High flow rates, mechanical vibrations are a problem. Rotary Vane Pumps Spring loaded on a rotor confine, compress and discharge gas. Good workhorse pump, used as fore pumps for high vacuum pumps like diffusion pumps. Works from atmospheric pressure to ~ 10 mT (0.1 mT for two-stage versions) Uses oil. Roots Pumps Two figure-8 lobes rotate in opposite directions for pumping. Close tolerances eliminate the need for oil. Used to maintain a low vacuum (~ 1 T) in high volume LPCVD systems but can go down to 10 -5 T with the assistance of a rotary vane pump.
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Diffusion Pumps Si oil is boiled and vaporized in a multistage jet assembly. Oil vapors emerging from the nozzles impart momentum on the residual gas molecules and drive them towards the bottom of the pump. The molecules are compressed and exhausted. No vibrations. From 1 mT to 10 -10 T with LN cooling (works in the molecular flow regime). Wide range of flow rates. Requires mechanical pump. Backstreaming of the vapors are a problem and can be minimized with cooling coils are used to condense the oil before it enters the vacuum chamber.
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Turbo Molecular Pumps High rpm (20-30K) rotor blades impart momentum to molecules Can go from 1 mT to 10 -10 T Can have vibrations Needs mechanical pump. Not good for H 2 pumping.
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Ion Pumps A cold cathode electrical discharge creates an electron gas which is trapped by a small magnetic field.
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L05-Vacuum_Technology - Vacuum Technology Vacuum Pumps Two...

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