Speaker
Stephane Fartoukh
Description
The goal of the LHC Insertions (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 b* down to 25 cm, using a new inner triplet (IT) with longer NbTi quadrupoles operating at a lower gradient (~120 T/m) and therefore offering a larger aperture (120 mm). Reducing b*, but also operating at a lower IT gradient (which further increases the size of the b-functions all over the long straight section), has however a certain number of drawbacks other than the obvious need of 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 b* 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 an overall modification of the current LHC optics. Concerning the high luminosity insertions proper, the layout of the new IT and corresponding injection and collision optics (with b*> 30 cm) will be studied both in terms of mechanical aperture, chromatic correction, squeeze-ability, dynamic aperture and beam-beam effects.
