Improvement of the Geometrical Stability of the LHC cryodipoles when Blocking the Central Support Post

The LHC will be equipped with 1232 horizontally curved 16 meter long super-conducting dipole magnets cooled at 1.9 K, supported within their vacuum vessel by three Glass Fiber Resin Epoxy (GFRE) support posts. The two support posts at the dipole extremities were initially designed free to slide longitudinally with respect to the vacuum vessel and the central support post free to slide transversely. However the magnet shape did not retain the tight geometrical tolerances, of the order of fractions of mm, imposed by machine aperture and magnetic corrector centering requirements. Thereafter a modification to the supporting system, removing the initial transversal degree of freedom of the lower flange of the central support post with respect to the vacuum vessel, was designed and implemented. This paper describes the design of the magnet/cryostat interface with and without blockage of the central support post, analyzes the additional mechanical loads related to the modification and reviews the experimental results with respect to the requirements for beam aperture and magnetic corrector centering.