The superconducting separation dipoles MBRD for the High Luminosity upgrade of LHC: From short model to prototype

A new recombination dipole D2 for the luminosity upgrade of the Large Hadron Collider at CERN (LHC) is under development since 2016 at INFN in a collaboration framework with CERN. These twin aperture magnets will be installed on both sides of LHC main multipurpose experiments, ATLAS and CMS, interaction points. The target integral magnetic field in an aperture of 105 mm is 35 T m, obtained with a magnetic field of 4.5 T and a magnetic length of 7.78 m. The coils in both apertures are asymmetric for canceling the unwanted multipoles caused by the magnetic field cross-talk. The asymmetric design and the demanding requirements on the field quality made preferable an independent collaring, which allows for a more accurate assembly: the mechanical stability is ensured by a novel approach of coil integration in an Al-alloy mechanical structure. After a design phase, the construction of a short model has been planned followed by the construction of a full-length prototype. This contribution is focused on the aspects of the short model assembly and the implications on the prototype design in terms of mechanical tolerances, manufacturing processes, and materials involved in the construction.