Chromaticity Compensation Schemes for the Arc Lattice of the FCC-ee Collider

FCC-ee is an 100 km e⁺/e⁻ collider that is being designed within the Future Circular Collider Study organised by CERN. It's layout is optimised for precision studies and rare decay observations in the range of 90 to 350 GeV center of mass energy with luminosities in the order of 10³⁵ cm⁻²s⁻¹. Extremely small vertical beta functions of 1 - 2 mm are required at the two interaction points to reach this goal. The strong focusing required in the final doublet quadrupoles drives the chromaticity to more than -2000 units, far beyond the values that had been achieved in previous storage rings. As a consequence a pure linear chromaticity compensation scheme will not be sufficient to obtain the required ± 2 % energy acceptance. A state of the art multi-family sextupole scheme will have to be combined with a local chromaticity correction. This paper presents the design of the arc lattice, optimised for highest momentum acceptance and the results of systematic studies of the sextupole scheme in the arcs in order to gain highest chromaticity performance.