Preliminary Design Study of a Pre-booster Damping Ring for the FCC e+e− Injector

The aim of the FCC e+e− lepton collider is to collide particles in the energy range 40–175 GeV. The FCC e+e− injector complex needs to produce and transport high-intensity e+e− beams at a fast repetition rate of about 0.1 Hz to top up the collider at its collision energy. A basic parameter set exists for all collider energies, assuming a 10 GeV linac operating with a large number of bunches accumulating in the existing SPS, which serves as pre-accelerator and damping ring before the bunches are transferred to the high-energy booster. The purpose of this study is to provide the conceptual design of an alternative damping and accelerator ring, replacing the SPS in the current scheme. This ring will have an injection energy of around 6 GeV and an extraction energy of around 20 GeV. Apart from establishing the basic ring parameters, the final study will include the optics design and layout, and single particle linear and non-linear dynamics optimization, including magnetic and alignment error tolerances. The study will also involve some basic estimation of collective effects, including intrabeam scattering, single and multibunch instabilities and impedances, two-stream effects (e-cloud and ion instabilities) and address the issue of synchrotron radiation handling. In this document, as part of these studies, basic ring parameters, first results of optical design after some analytical calculations, and layout studies are presented.