Particle physics research at renowned universities and institutes, such as that conducted at CERN in Geneva, the MPI in Greifswald or DESY in Hamburg, requires low-temperature cooling that can only be delivered by large cryogenic refrigeration Units.

A helium refrigerator is a closed system in which the same quantity of helium constantly circulates. In contrast to the liquefier, the mass flow rates are symmetric. The required low-temperature cooling is assisted by two or more gas-bearing expansion turbines and can be enhanced by precooling to 80 K with liquid nitrogen.

Research applications, cooling of cavities or superconducting magnets require hundreds of watts refrigeration capacity at liquid helium temperature. For these applications Linde Kryotechnik has developed refrigeration systems on the basis of the L-series standard units. The wide range of performance ratings is achieved by different compressors and precooling with or without liquid nitrogen.

Refrigeration below 4.5 K requires cold ejectors or cold compressors to reduce the pressure in the experiments.

Adsorbers are integrated into the cold box at 80 and 20 K to remove any residual contaminants from the helium. Like the standard systems, the refrigerator is fitted with a Siemens S-7 automatic control and monitoring system. A PC system is offered for visualization; it can be fitted with online access for remote monitoring and support.

Particle physics research at renowned universities and institutes, such as that conducted at CERN in Geneva or DESY in Hamburg, requires low-temperature cooling that can only be delivered by large cryogenic refrigeration units. Linde Kryotechnik AG develops and builds refrigeration systems to fit customers’ requirements. Efficiency, punctuality and reliability are our watchwords. Our credentials are represented by special helium refrigeration systems with a performance rating that ranges from several hundred to well over 18,000 W at a mean temperature of 4.5 K, with an open-ended upper limit.

Other special refrigerators work with cold compressors, warm screw compressors, vacuum pumps or a combination of these, and deliver cooling power at temperatures down to and below 1.5 K.

Through its projects in the USA and worldwide, Linde Kryotechnik has accumulated a rich fund of experience in cooling high-temperature superconductors (HTS) in the 30 to 80 K range, as well as refrigeration of cold neutron sources or cryo pumps for space simulation chambers in the 20 K temperature range.

The thermodynamic process in a refrigeration system is similar to that in a liquefier, which is why the system uses the same components.

The main components of a helium refrigerator are:

• oil-injected screw compressors and oil removal systems

• vacuum-insulated cold box

• aluminium-plate heat exchanger

• TED expansion turbines with dynamic gas bearings

• control system

Further system components such as:

• transfer lines

• valve boxes

• distribution systems

are designed, supplied and installed by Linde Kryotechnik.