The construction of the modules composing the CMS superconducting coil

CMS (compact muon solenoid) is a general-purpose detector designed to run at the highest luminosity at the CERN large hadron collider (LHC). Its distinctive features include a 4 T superconducting solenoid 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 is presently under way. The methods for constructing large aluminum alloy mandrels, for winding the reinforced conductor with high accuracy of the winding pack and for impregnating the single large modules (50 t) have been assessed through the construction of a module prototype. The prototype has the same radius as a CMS module (6900 mm outer diameter), but a shorter axial length (670 mm against 2500 for the module). The relevant technological result was the understanding of the methods for obtaining a large coil with a very limited shape deformation (±2.5 mm on diameter) for allowing the precise mounting of the modules. This paper describes the main technical issues of the prototype and of the construction of the first modules, the geometrical and RT tests performed on them and the common problems related to the series construction of large superconducting coils.