Mechanical performance at cryogenic temperature of the modules of the external cylinder of CMS and quality controls applied during their fabrication

The CMS experiment (Compact Muon Solenoid) is a general-purpose proton-proton detector designed to run at the highest luminosity at the Large Hadron Collider (LHC). Distinctive features of the CMS detector include a high-magnetic-field solenoid (4 T) coupled with a multilayer muon system, a fully active scintillating-crystal electromagnetic calorimeter, a tile hadronic calorimeter, and a powerful inner tracking system. The superconducting solenoid (6 m diameter by 12.5 m long free bore) is enclosed inside a 10,000 t return yoke. The external cylinder of the CMS coil consists of five modules having an inner diameter of 6.8 m, a thickness of 50 mm and an individual length of 2.5 m. The cylinder shall feature a yield strength of 209 MPa at its working temperature of 4.5 K. The structural material selected for the components of the cylinders is the non heat-treatable aluminum alloy EN AW-5083. Each module of the cylinder is composed of a 50 mm thick shell, manufactured by bending and welding thick plates of strain hardened EN AW-5083-H321, of two 130 mm thick end flanges fabricated as seamless rolled rings and circumferentially welded to the shells, and of radial shoulders of the same alloy, to which the coil support system is attached through tie-rods. The components (seamless rings, plates, shoulders) and the manufacturing methods have been fully validated by a systematic assessment down to cryogenic temperature of the mechanical properties on samples issued from full scale parts, and by a rigorous qualification of the fabrication welds, performed on weld extra-lengths issued from each one of the modules.