The Future Circular Collider (FCC) study was launched as a worldwide international collaboration hosted by CERN with the ultimate goal of pushing the energy frontier far beyond the LHC. FCC covers two accelerators, namely an energy-frontier hadron collider (FCC-hh) and a highest luminosity, high-energy lepton collider (FCC-ee) serving as electroweak Higgs factory, as a possible first stage. The mass of particles that could be either directly produced at FCC-hh or indirectly detected at FCC-ee is increased by an order of magnitude, relative to today's reach, and the subatomic distances that can be resolved are decreased in the same proportion. Importantly, FCC-hh and FCC-ee share the same ~100 km tunnel infrastructure. This paper focuses on the FCC-hh, summarising its key features, such as accelerator design, performance reach, and underlying technologies. The discussion is based on the 2019 conceptual design report (CDR) [1], which represents a study milestone, but also describes more recent design activities and indicates future directions.

The systematic dodecapole component in the Main Quadrupoles of the LHC lattice has a strong influence on the machine dynamic aperture at injection. In this paper we quantify this effect with the help of tracking studies, explain the mechanism for the loss in dynamic aperture and look into potential correction schemes. Finally, we provide an estimate for the maximum allowed systematic dodecapole component in the MQ.

Recent developments on the CLIC collimation and final focus are described. The combination of a shortened linear, or alternative nonlinear, collimation section and a compact final focus substantially reduces the overall system length at 3 TeV centre-or-mass energy to less than 3 km. A beam- delivery system (BDS) for 500 GeV centre-of-mass energy is obtained by relatively minor optics modifications of the 3-TeV system . It promises a satisfactory performance. The attainable luminosity can be raised, at both energies, by decreasing the beta functions at the collision point. We also discuss field errors, gas scattering and wake fields in the final quadrupoles, and the collimation parameters.