Design, construction and start up by Air Liquide of two 18 kW at 45 K helium refrigerators for the new CERN accelerator (LHC)

CERN in Switzerland is presently building a new particle accelerator labeled as the LHC. This 27 km accelerator will, for the first time at such a large scale, operate at cryogenic temperatures with superconducting magnets and radio-frequency cavities. For that purpose, Air Liquide has designed, constructed and started up two custom designed refrigerators. The cryogenic power of each of these refrigerators is equivalent to 18 kW at 4.5 K. In order to produce the cryogenic power requested by the LHC accelerator at the different temperature levels with a very high efficiency, a custom design thermodynamic cycle has been chosen. This cycle, the major components of the refrigerators and the results obtained during the reception tests of the refrigerators are presented in this paper