Abstract
A beam optics scheme has been designed for the Future Circular Collider-e+e- (FCC-ee). The main characteristics of the design are: beam energy 45 to 175 GeV, 100 km circumference with two interaction points (IPs) per ring, horizontal crossing angle of 30 mrad at the IP and the crab-waist scheme [1] with local chromaticity correction. The crab-waist scheme is implemented within the local chromaticity correction system without additional sextupoles, by reducing the strength of one of the two sextupoles for vertical chromatic correction at each side of the IP. So-called "tapering" of the magnets is applied, which scales all fields of the magnets according to the local beam energy to compensate for the effect of synchrotron radiation (SR) loss along the ring. An asymmetric layout near the interaction region reduces the critical energy of SR photons on the incoming side of the IP to values below 100 keV, while matching the geometry to the beam line of the FCC proton collider (FCC-hh) [2] as closely as possible. Sufficient transverse/longitudinal dynamic aperture (DA) has been obtained, including major dynamical effects, to assure an adequate beam lifetime in the presence of beamstrahlung and top-up injection. In particular, a momentum acceptance larger than +/-2% has been obtained, which is better than the momentum acceptance of typical collider rings by about a factor of 2. The effects of the detector solenoids including their compensation elements are taken into account as well as synchrotron radiation in all magnets. The optics presented in this paper is a step toward a full conceptual design for the collider. A number of issues have been identified for further study.
Highlights
REQUIREMENTS AND PARAMETERSThe future circular collider-eþe− (FCC-ee) is a double-ring collider to be installed in a common tunnel of ∼100 km circumference, as a potential first step before the FCC-hh hadron collider
A beam optics scheme has been designed for the future circular collider-eþe− (FCC-ee)
The crab-waist scheme is implemented within the local chromaticity correction system without additional sextupoles, by reducing the strength of one of the two sextupoles for vertical chromatic correction at each side of the interaction points (IPs)
Summary
The FCC-ee is a double-ring collider to be installed in a common tunnel of ∼100 km circumference, as a potential first step before the FCC-hh hadron collider. Finished, at this stage we assume similar levels as what was experienced at LEP2, where the critical energy toward the IP was ∼80 keV from the last dipole [2]. This FCC-ee collider ring must have enough DA to store the colliding beam, whose energy spread is drastically increased by beamstrahlung [3,4], and to maintain the beam current considering the beam lifetime and the ability of the top-up injection scheme [5]. Compared to (1 m, 2 mm) is estimated to be small at tt as shown in Table I, and βÃx;y 1⁄4 ð1 m; 2 mmÞ is considered to be the baseline at tt
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