Experience Gained From the Construction, Test and Operation of the Large 4-T CMS Coil

The 4-T, 6-m free bore CMS solenoid has been successfully tested, operated and mapped at CERN during the autumn of 2006; R&D studies started in 1993 and the construction proper in 1997. The main parameters of this 100 MUS$ project (including yoke) were then considered beyond what was thought possible, as the total stored magnetic energy reaches 2.6 GJ for a specific magnetic energy density exceeding 11 kJ/kg of cold mass. During this period, the international design and construction team had to make several important technical choices, in particular mechanical, to maximize the chances of reaching the nominal induction of 4 Tesla. The paper will review these choices in the light of what is presently known and examine if better solutions would be possible today for constructing a new large high-field thin solenoid for a future detector magnet.