Comparative Study of Different Designs of the Mechanical Structure for the LHC Main Dipoles

This work was carried out about two years ago to choose a robust and structurally sound structure before launching the dipole series production. First we define the requirements to be satisfied in order to have a stable structure. Then the mechanical behaviour of several possible cross sections for the LHC main dipoles is assessed and compared. Each structure is first optimised in terms of performances. Then the sensitivity of the structure to variations of key parameters due to tolerances is analysed. As a conclusion we can say that the choice of the collar material clearly influences the sensitivity to dimensional tolerances of components and to variation of coil pre-stress.