Final design of the CMS solenoid cold mass

The 4 T, 12.5 m long, 6 m bore diameter superconducting solenoid for the CMS (Compact Muon Solenoid) experiment at LHC will be the largest and the most powerful superconducting solenoid ever built. Part of the CMS design is based on that of previous large superconducting solenoids-the use of a high purity aluminium stabilized conductor, a compact impregnated winding with indirect cooling and quench back protection process. However, the dimensions and the performances of this solenoid have imposed solutions which are more than extrapolations of the previous ones : the use of a mechanically reinforced conductor and a five module winding, each module being made of four layers, internally wound. This design, which is now frozen, relies on numerous magnetic, mechanical and thermal calculations, on various experimental tests (characterization of structural and insulating materials, electrical joints...) and specific mock-ups. Two pre-industrialization programs, concerning the conductor and the winding process have also been carried out with industrial partners to support the foreseen solutions. Both the final design and the experimental results obtained to validate this design are presented in this paper.