The LHC as FCC injectors

The re-use of the modified LHC is presently the reference baseline for the High Energy Booster (HEB) injector into the FCC-hh hadron collider, although a number of other promising options exist. As part of the FCC study, the transformation of the LHC into the last acceleration stage into the new collider has been investigated in some detail, including the key aspects of new insertion designs and faster ramping. Performance aspects including energy reach, flexibility and filling time of the collider have been considered, and the transfer lines linking the HEB to the FCC have been defined. This chapter describes the required performance, the required changes which would be needed to the existing LHC machine and discusses the remaining challenges for LHC operation as FCC-hh injector. The study was based on the FCC-hh machine layout defined in the Conceptual Design Report in 2018: the design continues to evolve, which could have an impact on the changes needed in specific LHC straight sections, but the main considerations on the feasibility of reuse of LHC remain valid.