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Cryopumps & Cryogenics

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Cryogenic Pumps and Cryogenics

Cryopumps                                               

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 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.

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

Favorable 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.

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

Cold Heads

A refrigerator (cold head) is a gas cooling machine which operates on the basis of a thermodynamic cycle to produce cryogenic temperatures (T ≤ 120 K).  Refrigerators operating according to the Gifford/McMahon principle have succeeded over other methods of cooling cryopumps and cryostats.  It is thus employed exclusively by Leybold.  In order to account for individual requirements from customers, Leybold offers customized cryostats as well.

Gifford/McMahon-Refrigerators

Advantages to the User

Low temperatures on a single key press

No liquid helium and no liquid nitrogen are required

Very simple to operate 

High refrigerating capacity from a small volume

Easy process control and temperature control via a computer

Advantages by Design

No space problems since cold head and compressor unit can be installed and operated apart

Installation of the cold head basically in any orientation

High reliability

Long periods of operation without maintenance

Typical Applications

Cooling of cryopanels in cryopumps thereby producing high or ultra high vacuum

Cooling of superconducting magnets; in magnetic resonance tomographs, for example

Cooling of samples and detectors; especially for cooling of

samples for spectroscopic analysis in the areas of solid state and surface physics

high temperature superconductors

superconductors and semiconductors

infrared and gamma detectors

Calibration of sensors

Cold Heads from the COOLPOWER Range

The standard range of single-stage and two-stage cold heads matches a wide range of applications.  Leybold is offering refrigerators with usable refrigerating powers of 140 W at 80 K (COOLPOWER 140 T, single stage) and down to 3.5 W at 10 K (COOLPOWER 5/100 T; dual-stage).

The cold heads basically consist of three subassemblies:

Drive and control unit for the displacer

Displacer

First stage of the cold head (and second stage in the case of two-stage cold heads).

Pneumatically driven Cold Heads

Advantages

Simple Design - The pneumatic drive system for the displacer of these cold heads from Leybold consists of only two mechanically moving components: the rotating control valve and the synchronous motor driving the control valve.

Easy and quick maintenance - All Leybold cryopumps from the COOLVAC range are equipped with pneumatically driven Leybold cold heads.  Owing to the simple design of the built-in cold heads, maintenance is easy. Maintenance can be performed in place without detaching the cryopump from the vacuum chamber.

Mechanically driven Cold  heads

Advantages

In the case of the mechanically driven Leybold cold heads, the displacer is moved through the so called "Scotch yoke” directly by the drive motor. This elaborate mechanism allows the gas flow and the movement of the displacer to be precisely controlled through which it is possible to attain with two-stage cold heads especially high refrigerating capacities in the range of lowest temperatures (refrigerators of the COOLPOWER 10 MD line).

Advantages Through High Reliability

As to reliability, Leybold cold heads are top performers.  Especially high reliability is required for medical instrumentation, specifically in connection with nuclear spin tomographs. In this application cold heads are used to cool superconducting magnets and they are thus exposed to strong magnetic fields.  The leading manufacturers of nuclear spin tomographs have therefore decided to use Leybold cold heads to cool the superconducting magnets.

Refrigerator Cryostats (Basic Units)

Advantages to the User

Can be installed basically in any orientation thereby offering a high degree of flexibility in experimental arrangements

Can be set to any temperature between 6.5 and 320 K

High refrigerating capacity, constant temperatures

No liquid refrigerants are required 

Very simple to operate

Temperature control without problems through standardized control and connecting components

Possible high throughput of samples due to short cool down and warming-up periods

Typical Applications

Cooling of

high temperature superconductors

superconductors and semiconductors

infrared and gamma detectors

Measurement of electric and thermal transport quantities, as a function of the temperature, such as

electric and thermal conductance

electromotive force

Spectroscopic investigations in the infrared, visible and ultraviolet spectral ranges

Matrix spectroscopy

Moessbauer spectroscopy

Magneto-optic experiments

Compressor Units

COOLPAK 4000 to 6000 compressors are available for single operation of the cold heads from the COOLPOWER line as well as for multiple operation of cryopumps and cryostats.  The period during which no maintenance will be required on the Leybold compressor units depends on the service life of the adsorber.  If the values for the ambient temperature and the cooling water entry temperature remain within the specified range, Leybold guarantees a service life for the adsorber – and thus a period during which no maintenance will be required – of 18000 operating hours.

UL Approval

The Leybold refrigerators (consisting of compressor unit COOLPAK (4000/4200, 6000/6200, flexlines FL and the cold head COOLPOWER 2) meet – as complete systems – the requirements of the Underwriter Laboratories (UL) as Recognised Components (Urus) as well as the approval cUR performed through the Underwriter Laboratories for the Canadian Standards Association.

Leybold refrigerators are listed under the UL/cUL reference number SA 8676. The marks as shown on the right for the entire system can be found on the name plate of the compressor unit.

CE Approval

The Leybold compressor units RW and COOLPAK meet the basic requirements regarding safety and health of the relevant EC directives. They carry on the name plates of the compressor units the CE mark.

2 Formerly RGD

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Last Modified Friday, May 18, 2012