The largest superconducting solenoid ever built in the world is finally completed. It is formed by five huge modules connected each other and will generate a magnetic field of 4 Tesla, equal to 100.000 times the Earth magnetic field. This extraordinary system will be dedicated to Cms (Compact Muon Solenoid) experiment at Lhc accelerator at Cern.
Cms magnet is the result of a large international collaboration among Italian Institute of Nuclear Physics, Cern, Commissariat pour l'Energie Atomic (Cea) in Saclay (France) the Eth-Z (Polytechnic of Zurich) and the best industries in this field in Italy, France, Switzerland, Germany, Russia and many other member countries of the collaboration. The consignment of the last module of Cms solenoid will take place officially during a ceremony at Cern, Tuesday, March 1.
Cms experiment will study the characteristics of particles produced in the collisions between proton beams moving into Lhc accelerator. The main aim of the experiment is identifying the Higgs boson, the most elusive particle of modern subnuclear physics. The Higgs boson, indeed, has not been directly observed yet. Although it is predicted by theoretical models, that assume its existence to explain why some particles own the essential characteristic named mass.
Cms will allow the study of different types of particles produced through proton collisions. Cms will separate them thanks to a very strong magnetic field that will deflect their tracks according to their electric charge and impulse. The five modules forming the solenoid will generate the magnetic field. Every module is 6 metres diameter, 2.5 metres length and 50 tonnes weight. Thanks to a sophisticated liquid Helium cooling system, modules will be kept to the low temperature of –269 C°, so that they become superconducting (superconductivity allows, without waste, circulation of huge currents that produce the powerful magnetic field). The whole solenoid will be contained in an enormous vacuum cylinder the will isolate it from the external environment. Finally a structure composed by 12.000 tonnes of iron will "bridle" the lines of the magnetic field that otherwise would be get lost causing disturbs. Cms will be an enormous system of 16 metres of diameter and 22 metres length: measures of a five level building!
"Italy has an essential role in Cms construction: Cms-Italy is indeed one of the main collaborations between high energy physicists in the world and counts among the others, 235 researchers, physicists and engineers belonging to 14 Infn sections and laboratories and to 13 Italian Universities. Italy has participated in the global planning of the system. Moreover the delicate phases of the winding of the conducting cable that form the modules and the realization of the refrigerating cylinders that contain them have been carried out in Italy thanks to the collaboration between Infn Section in Genoa and Ansaldo Superconductors industry. The same collaboration allowed to carry out other delicate phases, such as the final potting of the modules in epoxy resin through vacuum diving. This operation was necessary to fill with a solid matrix even the smallest interspaces. In this way it was possible to block the conducting cable and prevent even the smallest vibration, that could cause heat, modifying the very low temperatures necessary for the superconductivity" explains Guido Tonelli, Cms Italy national spokesman, professor of General Physics at Pisa University and collaborator of Infn.
The difficult and delicate work realized by physicists and engineers of Infn for the realization of the modules of Cms solenoid required the development of innovative technological solutions and a lot of precision. "In order to avoid imperfections in the conducting cable, new welding techniques have been carried out and proper equipment were invented to assure the perfect winding and the potting in epoxy resin of kilometres of conducting cable.
Moreover it was necessary to plan and to realize special equipments, able to guarantee mechanical precision equal to fractions of millimetres on dimensions of some metres. On the whole, the realization of the big solenoid was one of the main technological challenge of Cms: it took us about 10 years of work and an investment of about 80 millions of Euros. Superconductivity plays an always more important role in society: for instance all solenoids used for Nuclear Magnetic Resonance are superconducting. It is also essential that there are in Italy industrial top competences in this field. Infn was, with the Italian industry, among the forerunners for the development of this technology" remarks Pasquale Fabbricatore, manager of Infn of Genoa, and Italian spokesman of Cms-Solenoid Italy.
Even the transportation of the modules that form the solenoid of Cms from Genoa, where it was realized, to Geneva, was in a certain sense a delicate operation. The single huge modules were transported to Cern leaving from Genoa port and going up the Rhone up to Macon, in order to reduce the passage on road. The first of the five modules was consigned in February 2004. The fitting of Cms solenoid is foreseen by next summer, while the final test will take place by the end of the year.