With a circumference of approximately 91 km, the Future Circular electron-positron Collider, FCC-ee, aims for unprecedented luminosities at beam energies from 45.6 to 182.5 GeV. A major challenge is reaching its design performance in the presence of magnet misalignments and field errors. The FCC-ee optics tuning working group studies all related aspects, and applies state-of-the-art techniques for beam-based alignment, commissioning simulations, beam threading, optics measurements and corrections, which are probed at numerous world-leading accelerator physics facilities. Advanced optics correction simulations include interaction-point tuning, magnetic tolerances are studied, and a new optics is under scrutiny. The current status of tuning simulations for different FCC-ee lattices is presented.

Circular muon colliders provide the potential to explore center-of-mass energies at the multi-TeV scale within a relatively compact footprint. Because of the short muon lifetime, only a small fraction of stored beam particles will contribute to the physics output, while most of the muons will decay in the collider ring. The resulting power carried by decay electrons and positrons can amount to hundreds of Watt per meter. Dedicated shielding configurations are needed for protecting the superconducting magnets against the decay-induced heat and radiation damage. In this paper, we present generic shielding studies for two different collider options (3 TeV and 10 TeV), which are presently being explored by the International Muon Collider Collaboration. We show that the key parameter for the shielding design is the heat deposition in the magnet cold mass, which will be an important cost factor for facility operation due to the associated power consumption.

During the operation of a muon collider in an underground tunnel, most circulating muons decay into an electron (or positron) and a neutrino-antineutrino pair, resulting in a narrow disk of high-energy neutrinos emitted radially in the collider plane and emerging on the Earth’s surface at distances of several km. Thus, dedicated studies are required to assess any potential radiation protection risks to the public due to the interaction of such neutrinos near the surface. This work presents a set of FLUKA Monte Carlo simulations aimed at characterizing the radiation showers generated by the interactions of high-energy neutrinos from TeV-scale muon decays in a reference sample of soil. The results are expressed in terms of effective dose in soil at different distances from the muon decay, quantifying the peak dose and the width of the radiation cone, for beam energies of 1.5 TeV and 5 TeV. The implications of these results for realistic muon collider scenarios are discussed, along with possible methods to mitigate the local neutrino flux.