LHC Upgrade Phase I: Preliminary Study of the Collar Structure for the New Inner Triplet Quadrupole

The LHC phase I upgrade consists of replacing the interaction region triplet with larger aperture Nb-Ti quadrupoles, in order to increase the beam focusing in the Interaction Point (IP), thus augmenting the peak luminosity. In this document we present a preliminary design of the collars and keys for a new inner triplet quadrupole. We first analytically evaluate the force needed during collaring, in order to dimension the keys used to hold the collared coils together. Though the selected aperture for the new inner triplet quadrupole is 120 mm, two other apertures - 110 and 130 mm - have been also analyzed to provide a complete comparative study. 2D FEM models have been implemented in ANSYS. in order to validate the results of the analytical approach, considering 120 and 130 mm apertures as the outcome of a former magnetic optimization. A preliminary analysis of the stress distribution inside in the collaring assembly, using different collar dimensions, is finally presented.