Cryopumps are gas entrapment vacuum pumps for the pressure range from 10-3 to < 10-11 mbar (0.75 x 10-3 to ≤ 0.75 x 10-11 Torr). The principle of operation is that gaseous substances are bound to the cold surfaces within the pump by means of cryocondensation, cryosorption or cryotrapping.
In order to be able to produce a high or ultra high vacuum the cold surfaces (cryopanels) must be cooled to a sufficiently low temperature. Depending on the type of cooling system used a difference is made between refrigerator cryopumps, bath cryopumps and evaporator cryopumps. Leybold manufactures only cryopumps which are cooled by means of a refrigerator.
Advantages to the User
Advantages offered by the Pumping Principle
High effective pumping speed for all gases
Extremely high pumping speed for water vapor
For a given diameter of the high vacuum flange, the cryopump offers the highest pumping speed of all high vacuum pumps.
Advantages offered by Design
In contrast to gas transfer high vacuum pumps (mechanically suspended turbomolecular pumps, for example), cryopumps do not have any mechanically moving, oil, or grease lubricated parts on the vacuum side.
The following advantages are a direct result of this design characteristic:
Hydrocarbon-free vacuum in the pressure range from 10-3 to < 10-11 mbar (0.75 x 10-3 to ≤ 0.75 x 10-11 Torr).
Insensitivity to mechanical disturbances from particles coming from the process or external vibrations.
Further Advantages
Much more compact than comparable pump systems offering a pumping speed of over 1500 l x s-1
Backing pump is only required during start-up and during regeneration
Easy process control and pump control via computer
Favourable price-to-performance ratio and low running costs especially at higher pumping speeds
The cryopumps are cooled by the well-proven two-stage cold heads from Leybold’s COOLPOWER line (Gifford/McMahon principle). The design of a refrigerator cryopump from the COOLVAC range is shown schematically in the figure below.
The first stage of the cold head (9) cools the thermal radiation shield (5) and the baffle (6) of the pump. Depending on the type of pump and the operating conditions operating temperatures of 45 to 80 K are attained. Correspondingly water vapor condenses at this temperature.
The thermal shield and baffle are made of copper which conducts heat very well so as to optimally utilize the refrigerating capacity which is available.
Moreover, the thermal shield is metallized so that reflective losses will be minimal.
The second stage of the cold head (7) is used to cool the cryopanels (8). Depending on the operating conditions, operating temperatures of 10 to 20 K are attained. Here the process of cryocondensation of N2, O2 and argon will take place.
The active pumping surfaces are made of copper of high thermal conductivity and they are tightly linked thermally to the second stage of the cold head. H2, Ne and He are also adsorbed on to these surfaces which are partly covered with activated charcoal.
All cryopumps from the COOLVAC range are equipped with a safety valve (respectively with a bursting disk in the case of the UHV variants) which is set in the factory so that it will open at an overpressure of 150 mbar (113 Torr). In order to be able to safely remove any gases which may present a health hazard when the safety valve responds, the valve is equipped with an additional DN 40 KF flange where an exhaust line is connected. The pump’s body, all flanges and the safety valve are made of high-quality stainless steel. Upon request we will be pleased to mail you our special publication SO 182.04.02 “Benefits of modern refrigerator cryopumps in industrial processes and research”.
Multiple Operation of Refrigerator Cryopumps
The powerful Leybold compressor units COOLPAK 4000 D and 6000 D open up the possibility of operating two cold heads or refrigerator cryopumps simultaneously.
Advantages to the User
Significantly reduced investment and operating costs
Small footprint
Regenerating Cryopumps
An important aspect in the operation of cryopumps is that of regeneration. Since a cryopump is a gas entrapment pump, the gasses which have accumulated in the pump during the “pumping” mode must from time to time be removed from the pump. This is done by switching the compressor unit off and by warming up the cryopanels to room temperature or sightly higher so that the released substances can be pumped out by a forevacuum pump.
Cryopumps without Electric Regeneration System
The cryopump is warmed up to room temperature by purging the inside of the pump with a dry, pre-warmed inert gas (such as nitrogen). In this case it is not possible to set up defined and controlled temperatures within the cryopump. Thus the simultaneous presence of gases such as hydrogen and oxygen in the pump can not be entirely excluded. The formation of ignitable gas mixtures is only prevented by the diluting effect of the dry inert gas.
Cryopumps with Fully Automatic Electric Regeneration System from Leybold
The cryopump is warmed up to room temperature by heating the 1st and 2nd stages of the cold head with electric heaters. In this case, a defined and controlled temperature distribution within the cryopump can be set up. This controlled warming process ensures that the pumped gases are removed sequentially, i.e. the pumped gases are released one after the other in the following sequence:
Gases adsorbed at the cryopanels (e.g. hydrogen, helium, neon),
Gases condensed at the cryopanels (e.g. nitrogen, oxygen, argon),
Gases and vapors which have condensed on to the baffle and thermal radiation shield (e.g. water vapor).
The electric method of regeneration from Leybold prevents gases such as hydrogen and oxygen from being present in the pump at the same time. This excludes the formation of ignitable gas mixtures right from the start.
Cryopumps without fully automatic control and without electric regeneration system belong to the BasicLine (BL), like the COOLVAC 800 BL, for example.
The warming up process is fully automatic. Pressure and temperature distribution within the pump are set up and controlled by the control system at all times. The sequential regeneration of pumped gases prevents the formation of ignitable gases right from the start. This ensures the utmost safety during the regeneration of cryopumps from Leybold.
In the case of cryogenic pumps with fully automatic control there exist two cryo pump lines.
1. The COOLVAC BasicLine (COOLVAC BL) offering the following pumping speed class for Nitrogen in l/s: 800; COOLVAC 800 BL, for example. Other pumping speed classes from 1 500 to 18 000 l/s are available on request. For more information please contact your local Leybold Vacuum representative.
2. The COOLVAC ClassicLine (COOLVAC CL) offering the following pumping speed classes for nitrogen in l/s: 800, 1 500, 2 000, 3 000, 5 000, 10 000 and 18 000; COOLVAC 1500 CL, for example.
In the price list the designators “V” appears in connection with the pump designations. “V”: The high-vacuum flange is located at the top and the cold head below, as is the case for the COOLVAC 1500 CL-V, DN 200 CF. Leybold Vacuum Full Line Catalog 2005
