High vacuum pumps cryopump

Efficient high-vacuum pumps generally do not operate well near atmospheric pressure. Thus the vacuum system must have a mechanical vacuum pump to evacuate the system to a pressure where the high-vacuum pumps are effective. Mechanical pumps require routine maintenance, such as ballasting and replacing the pump oil. The diffusion pump is the least expensive and most reliable high-vacuum pump. Turbomolecular pumps and cryopumps are also used on mass analyzers. The high-vacuum pumps also require... 

From the operational point of view, reliable vacuum systems are a prerequisite for mass spectral measurements. In most cases, manufacturers apply differential stage pumping to achieve the required pressure range(s). Rotary pumps are used to provide an initial vacuum of approximately 10 to 10 Torr. High-vacuum pumps such as diffusion pumps (10 to 10 Torr), turbomolecular pumps (10 to 10 Torr), and cryopumps (10 to 10 Torr) are used to reduce pressure ftorther. Adequate knowledge in vacuum technology is essential in instrument design however, this is also beyond the scope of this chapter. 

Cryopumps adsorb (freeze) residual gas to a surface cooled to the temperature of liquid nitrogen. They are highly efficient and silent and provide clean vacuum, but cannot be operated without interruptions to recover the adsorber. Cryopumps are typically operated in combination with turbo pumps because they are only started after high vacuum conditions are reached. Otherwise, the adsorber would soon be saturated. 

It is now increasingly common to have high-vacuum systems based on turbomolecular pumps (TMPs), turbomolecular pumps + cryo-surfaces, or cryopumps. Diffusion pumps were extensively used in the past and remain fairly widespread in laboratory applications. However, for industrial purposes their use appears to be restricted to systems requiring very high pumping speeds (5o= thousands of Ls ), particularly where substantial amounts of particulates are handled. 

In space simulation, environmental testing, and other related fields there is a need for compact, high-speed vacuum pumps capable of operation over a wide span of subatmospheric pressure. The cryopump can fulfill these requirements. 

The student should be aware that it takes special vacuum equipment to maintain an ultrahigh vacuum. First, a clean surface must be inside a special vacuum chamber that has no leaks—which is easier said than done. In addition, special vacuum pumps must be used to get to such high vacuums and stay there. The normal oil-filled rotary vacuum pump can only maintain a vacuum of about 10 torr or so, a full five orders of magnitude higher than what is necessary for ultrahigh vacuum. Special vacuum pumps (like turbomolecular pumps, titanium sublimation pumps, or liquid-helium-based cryopumps) are needed and can be extremely expensive. 

YAG laser. Helium typically flows into the cell at 1 x 10 to 8 x 10 atom/sec. Despite the large He gas flow, the vacuum in the beam region is maintained at a low 3x10 torr by two stages of differential pumping with high speed cryopumps made of activated charcoal. 

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