Institut de recherche sur les lois fondamentales de l'Univers

CMS (Compact Muon Solenoid) is a generalpurpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T superconducting solenoid, composed of five modules, with a 6 m diameter by 12.5 m long free bore, enclosed inside a 10,000-ton return yoke. The construction of the five modules composing the coil was a very challenging task due to the large dimensions and weight of each module (50 t) and to the severe requirements on tolerances. This paper describes the main technical issues related to the module construction, namely the winding, the vacuum impregnation (requiring 1100 l of epoxy resin for each module), the machining operations (to get the proper tolerances on dimensions), the hydraulic circuit connections and the blank module-to-module mechanical coupling. Despite the limited number of modules, the manufacture was arranged as a series construction in a single large area. This area was subdivided in sectors for winding, impregnation, mounting and machining operations and equipped with the required large tools such as two 100 t cranes, a huge lathe and an autoclave suitable for hosting a single module enclosed in its impregnation mold.