Optics Challenges and Solutions for the LHC Insertion Upgrade Phase I

The goal of the LHC Insertion (IR) Upgrade Phase-I is to enable a reliable operation of the machine with a performance at least doubled with respect to its design luminosity. One key ingredient is ideally a reduction of Beta* down to 25 cm, using a new inner triplet (IT) with longer Nb-Ti quadrupoles operating at a lower gradient (~ 120 T/m) and therefore offering a larger aperture (120 mm). Reducing Beta*, but also operating at a lower IT gradient (which, at a given Beta*, further increases the size of the Beta-functions all over the long straight section), has however a certain number of drawbacks which cannot be solved by only increasing the aperture of the new low-beta quadrupoles. Without modifying the current layout of the matching section (MS) and assuming that the arc sextupoles cannot safely operate above nominal current (550A), optics solutions with a Beta* of 30 cm are already at the edge of feasibility, both in terms of mechanical aperture in the MS and new IT (assuming 120 mm aperture), in terms of gradients for some MS and DS quadrupoles and in terms of chromatic correction. These limitations will be analyzed in detail, in particular concerning the chromatic correction of the new inner triplet which requires a global modification of the present LHC optics. Concerning the high luminosity insertions, the layout of the new IT and the corresponding injection and collision optics (with Beta* ≥ 30 cm) will be present ed and studied in detail both in terms of mechanical aperture, chromatic correction, squeeze-ability, dynamic aperture and beam-beam effects