The first of five modules that will form the superconducting solenoid magnet for the CMS experiment at CERN was ready to leave the Italian port of Genova at the end of January, subject to good weather conditions. The magnet, which has an inside diameter of 6.3 m and a length of 12.5 m, has required a modular construction to allow transportation from the fabrication site in Italy to CERN. The five modules, each 2.5 m long and weighing 45 tonnes, are being transported one by one to CERN, where they will be assembled into the final solenoid.
The solenoid, which represents the “S” in CMS (Compact Muon Solenoid), is the product of an international collaboration between the French Commissariat á l’Energie Atomique (CEA), CERN, the Italian National Institute for Nuclear Physics (INFN), ETH (Polytechnic of Zürich) and Ansaldo Superconductors of Genova. Ansaldo was entrusted with the construction of the five modules constituting the magnet, which generates a magnetic field of 4 T. Once completed, the superconducting solenoid will boast a notable record: with its 2.6 Gigajoule of energy it will hold the world record for energy stored in a magnet.
INFN has been responsible for the design and construction of the so-called cold mass, i.e. the coil and mechanical structures that will be cooled to 4.2 K. Construction of the coil has required the development of some innovative technologies. Since the magnetic field is so high and the device so big, large electromagnetic forces are generated inside the solenoid causing mechanical deformation that could prevent it from working. The standard solution for such problems is to use a reinforcing mechanical structure to contain the solenoid, but this would not have been sufficient in this case. To avoid the smallest deformation, which would make the cables lose their superconducting properties, the reinforcement has been inserted directly inside the cables. This innovative solution required remarkable technical skills. It was also necessary to develop a sophisticated automated winding system to form the solenoid coils with high geometrical precision.
