Dynamic aperture studies and field quality specifications for the triplet quadrupoles of the LHC phase 1 upgrade

The layout of the interaction region for the LHC upgrade project is based on a number of new magnets that will provide the required strengths to focus the colliding beams as well as to separate them after the collision. As in the nominal LHC, a triplet of quadrupole magnets is foreseen for the upgrade optics and in addition a separation dipole to limit the parasitic bunch crossings of the two counter-rotating bunch trains. Due to the smaller beta function at the IP however, the requirements for the free aperture of these IR magnets are more demanding and the effect of the higher order multipoles is more severe than under the nominal LHC conditions. Using tracking simulations to study these effects, target values for the multipole coefficients of the new magnets have been defined as well as a multipole correction scheme that will be used to compensate those field errors which cannot be avoided due to design and construction tolerances. Based on these considerations, specifications are defined for the multipole coefficients of the new MQXC triplet that will act as guideline for the LHC upgrade magnet design.