Large Cryogenic Helium Refrigeration System for the LHC

In the framework of the Large Hadron Collider (LHC) project, CERN is presently building a large distributed cryogenic system to operate the high-field superconducting magnets of the 26.7 km accelerator in superfluid helium at 1.9 K. Refrigeration will be produced at several temperature levels down to 1.8 K, by eight cryogenic plants with a capacity of 18 kW @ 4.5 K (four of which recovered from the former LEP collider and suitably upgraded), feeding eight 2.4 kW @ 1.8 K refrigeration units using several stages of cold hydrodynamic compressors. After recalling the basics of LHC cryogenics, this paper gives an overview of the refrigeration system, from specification to design and production in industry, as well as status of the project.