Commissioning of the Helium Refrigerator System for the Compact Muon Solenoid (CMS) Detector of LHC

At CERN a new helium refrigeration plant specified for a cooling capacity of 800 W at 4.45 K, 4500 W between 60 K and 80 K and 4 g/s liquefaction simultaneously has been installed and commissioned. In a first operation phase, the plant will provide the refrigeration capacity for the cool down and the operation of the superconducting solenoid of the CMS experiment during the magnet tests at the surface of the LHC interaction point 5. On completion of the tests a part of the refrigeration plant will be dismantled and moved to its final underground position next to the CMS experimental cavern. This paper compiles the commissioning activities starting from the compressor station up to the intermediate cryostat interfacing the refrigerator cold box with the magnet thermosiphon cooling system. It reports the problems encountered and the lessons learned during the commissioning phase and summarizes the results of the refrigeration power measurements in the transient cool-down and the steady-state operation modes.