Status report on the CMS superconducting solenoid for LHC

The CMS (Compact Muon Solenoid) experiment is one of the two large experime nts approved to be installed on the Large Hadron Collider at CERN, and is n ow at an early stage of construction. For good momentum resolution, a super conducting solenoid is needed, the main characteristic of which is a nomina l magnetic field of 4 T in a 5.9 m diameter and 12.5 m long warm bore, lead ing to a stored energy of 2.7 GJ, These characteristics make this supercond ucting solenoid the largest and most powerful one ever designed. The main t echnical choices are the use of a mechanically reinforced Al-stabilized con ductor, the subdivision of the coil in five modules, each internally wound and vacuum impregnated before final assembly, the use of indirect cooling w ith circulation of liquid helium in a thermosiphon mode and quench back pro tection process to enhance the energy dump. All these choices need developm ents which will be reported together with the detailed description and the status of each main component of the cold mass of the solenoid.