Abstract
The FCC-ee project studies the design of a future 100 km e+/e circular collider 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–2 s–1. In order to reach these luminosity requirements, strong focusing is needed in the interaction regions. Large maximum beta values (of 7736 m for the Z energy) and the small beta star values, make the FCC-ee lattices particularly susceptible to misalignments and field errors. FCC-ee therefore presents an appreciable challenge for emittance tuning. In this paper, we describe a comprehensive correction strategy used for the low emittance tuning. The strategy includes programs that have been developed to optimise the lattice based on Dispersion Free Steering, linear coupling compensation based on Resonant Driving Terms and beta beat correction utilising response matrices. One hundred misalignment and field error random seeds were introduced in MAD-X simulations and the final corrected lattices are presented.
Highlights
The e+/e- Future Circular Collider (FCC-ee) will provide unprecedented sensitivity [1]
A complete list of parameters can be found in the Conceptual Design Report (CDR) [2]
The betatron coupling poses a large threat due to the small required emittance ratio, which is limited to εy/εx = 0.1 %. This constraint on the coupling ratio is to ensure the small vertical emittance growth, and to reduce beam-beam blow up, which is thought to increase when the coupling ratio is greater than 0.1 % [5]
Summary
The e+/e- Future Circular Collider (FCC-ee) will provide unprecedented sensitivity [1]. The maximum beta function values in the horizontal and vertical planes for the ttbar lattice are βx,max = 1625.10 m and βy,max = 6958.63 m. Due to the differing maximum beta values and the different phase advance in the arcs (resulting in different values of the beta function at the quadrupoles), the Z and ttbar lattices respond differently to misalignments of quadrupole magnets. This is demonstrated, which shows the maximum vertical dispersion introduced by a 2 μm RMS vertical offset of the quadrupoles for 100 random seeds. This constraint on the coupling ratio is to ensure the small vertical emittance growth, and to reduce beam-beam blow up, which is thought to increase when the coupling ratio is greater than 0.1 % [5]
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