Local chromaticity correction of the LHC

Abstract

Local chromaticity correction of a low-beta region can under certain conditions enhance the momentum acceptance of a circular accelerator. For this paper a local chromaticity scheme was explored for the LHC employing chromatic correction sextupoles in the arc cells nearest the final-focus triplet. Initially, existing optics and current sextupole locations were used to correct the natural chromaticity of the LHC Interaction Region (IR) and preliminary tracking indicated an increase in dynamic aperture. However, calculated sextupole strengths were unrealistic. Therefore, work on a specialized chromatic correction region with increased beta functions at specific sextupole locations has begun. The higher beta functions allow the strengths required for the sextupoles to be reduced and, also, more optimal sextupole phase advances for chromatic correction. Progress towards an optical model for local chromatic correction for the LHC IR is the subject of this paper.