Status report on the CMS superconducting solenoid for LHC

The CMS (Compact Muon Solenoid) experiment is one of the two large experiments approved to be installed on the Large Hadron Collider (LHC) at CERN, and is now at an early stage of construction. For good momentum resolution, a $9 superconducting solenoid is needed, the main characteristic of which is a nominal magnetic field of 4 T in a 5.9 m diameter and 12.5 m long warm bore, leading to a stored energy of 2.7 GJ. These characteristics make this $9 superconducting solenoid the largest and most powerful one ever designed. The main technical choices are: the use of a mechanically reinforced Al-stabilized conductor, the subdivision of the coil in five modules, each internally $9 wound and vacuum impregnated before final assembly, the use of indirect cooling with circulation of liquid helium in a thermosyphon mode and quench back protection process to enhance the energy dump. All these choices need $9 developments which will be reported together with the detailed description and the status of each main component of the cold mass of the solenoid. (9 refs)