Mechanical Behaviour of the LHC Cryodipoles

The LHC cryodipoles are slender and heavy objects more than 15-m long. The major components of the cryodipole assembly are the 28-tonne cold mass, supported on its three Glass-Fibre-Reinforced-Epoxy support posts and the 4-tonne vacuum vessel. The performance of the LHC depends very much upon the accurate positioning of the dipoles and the beam tubes, in particular to maximise the useful beam apertures. The cryodipoles will be conditioned and measured in surface assembly buildings, then handled and transported to their positions in the tunnel and, finally, aligned. This paper presents the static and dynamic studies of the cryodipole in different configurations. The tests and analyses carried out have led to a thorough understanding of the mechanical behaviour of the cryodipoles. From the static analysis, an hyperstatic supporting system is proposed in order to minimise the systematic deflections and the effects due to changing temperature conditions in the tunnel. The dynamic analysis has shown that the cryodipole resonates at a series of very low natural frequencies and, moreover, shows a low damping value. Since the dynamic loads during transport and handling are in the low frequency range, the cryodipole components are potentially susceptible to damage. Simulations have included the truck suspension for road transport and the lifting device for handling with a crane. Solutions coping with the transport and handling conditions are presented.