Determination of a high-precision gravity field model for the Future Circular Collider region

The Large Hadron Collider (LHC), the biggest collider of its type, is reaching its conclusion by 2040. In the scope of initial studies for a post-LHC particle accelerator, the design and feasibility of the Future Circular Collider (FCC) at CERN, with a circumference of around 100 km, are investigated until 2025/2026. In the FCC-Geodesy project funded by CHART (Swiss Accelerator Research and Technology) the reference network on the surface and in the tunnel is under development and a new high-precision geoid model for the significantly larger FCC area will be computed. For the so-called pre-alignment of the magnets and thrusters in the tunnel, a hydrostatic levelling system is used, which is influenced by the changing geoid heights due to the topography on the Earth's surface and density variations within the Earth's interior. Since the particle accelerator is designed to be a perfect straight line, the influence of the geoid must be known with an accuracy of up to 30 \(\mu m\) over 225 m in the region.