Design of Beam Optics for the FCC-ee Collider Ring

A design of beam optics is made for the FCC-ee doublering e + e − collider. The main characteristics of the design are: 45 to 175 GeV beam energy, 100 km circumference withtwointeractionpoints(IPs)perring, horizontalcrossing angle of 30 mrad at the IP, and the crab-waist scheme with local chromaticity correction system. A so-called “tapering" of the magnets is applied, which scales all fields of magnets with the local beam energy to compensate the synchrotron radiation (SR) loss along the ring. An asymmetric layout near the interaction region suppresses the critical energy of SR incoming to the detector at the IP below 100 keV, while matching the geometry to the beam line of the FCC proton collider (FCC-hh) [1] as close as possible. Sufficient transverse/longitudinal dynamic apertures (DAs) have been obtained to assure the beam lifetime with beamstrahlung and top-up injection. The synchrotron radiation loss in all magnets as well as the IP solenoids with compensation are taken into account.