Specification of Field Quality of the Interaction Region Magnets of the High Luminosity LHC Based on Dynamic Aperture

The high luminosity LHC upgrade (HL-LHC) requires new magnets in the low-beta interaction regions with a larger aperture than in the existing LHC. These include the Nb3Sn superconducting (SC) inner triplet quadrupoles, Nb-Ti SC separation dipoles D1 and D2, and SC matching quadrupoles Q4 and Q5. The large aperture is necessary for accommodating the increased beam size caused by significantly higher beta functions in these magnets in the collision optics. The high beta functions also enhance the effects of field errors in these magnets leading to a smaller dynamic aperture (DA). It is, therefore, critical to determine the field quality specifications for these magnets which 1) satisfy an acceptable DA, and 2) are realistically achievable. The estimates of expected field quality obtained from magnetic field calculations and measurements were used as a starting point. Then, based on the DA study, the field errors were optimized in order to reach an acceptable DA. The DA calculations were performed using SixTrack. Details of the optimization process and summary of the field quality specifications for collision and injection energies are presented.