CERN, the European Organization for Nuclear Research near Geneva, conducts important basic physical research on the structure of matter. Since 2008 the acclaimed research institute has been using the Large Hadron Collider (LHC), at 27 kilometres in length the largest particle accelerator in the world, for this research. Now, under the ‘European Strategy for Particle Physics’, a feasibility study is to be carried out on the successor model of CERN’s current centrepiece. This new model is the Future Circular Collider, abbreviated FCC. The FCC is to be three times larger than its predecessor, enabling it to develop much greater energy for the collision of the particles.

How does a particle accelerator work?

In a particle accelerator, particles – in the case of the LHC, these are protons or lead ions – circulate in a vacuum tube. Inside this tube, electric fields are used to accelerate the particles. They are acted on by magnetic coils, which control their direction. These magnetic coils need to be very precisely aligned. The measurement department at CERN carries out an initial alignment that is accurate to the millimetre. An extremely accurate model of the earth’s gravitational field is required for this purpose. This model is known as a geoid model, and it is used, among other things, to correct the measurements. The geoid model is worked out on the basis of various measurements, such as measurements of gravity and GNSS levelling, a combination of GNSS measurements with levelling.

One essential prerequisite for implementing the project, therefore, is a very accurate geodetic basis. This is necessary for the planning, and for the construction and subsequently the operation of the futuristic particle accelerator. Existing models are not adequate for this. Instead, the partnership between CERN, ETH Zurich, the School of Business and Engineering Vaud (Hochschule für Wirtschaft und Ingenieurwissenschaften des Kantons Waadt, HEIG-VD) and swisstopo aims to provide very precise geodetic survey readings for the project. One anticipated result of this collaboration is a highly accurate gravity field model for the area surrounding the FCC. swisstopo is supporting the project, firstly, with practical aspects such as taking new measurements, and making available existing measurements or equipment. In addition, swisstopo is supporting the project with its expert knowledge. 

As a first step a 50 km long geodetic profile, running from Geneva to Annecy, will be created. Firstly, existing level measurements by both the IGN (French counterpart of the Swiss Federal Office of Topography) and swisstopo were integrated. A section of 8 km through CERN was re-levelled. swisstopo then carried out a vertical deflection measurement approximately every 800 m along the profile, using a zenith camera. The zenith camera used for this was developed at the Institute of Geodesy and Photogrammetry at ETH Zurich. In addition, as part of a major, one-week GNSS campaign with the involvement of all project partners, 50 survey points have been mapped using high-precision, static GNSS in the autumn of 2021.  

All these measurements will be used to generate a very precise geoid profile (in effect, a section of the geoid along the profile), which can be used for validation and comparison purposes. This is the basis for assessing the precision of the future geoid models. The calculation of the new geoid models will be commenced after the work on the profile has been completed. Some compaction measurements are also necessary for this.

This partnership with CERN is nothing new for swisstopo. The research institute, based in Geneva, has already collaborated with the Federal Office of Topography on a number of occasions. The collaborative research is useful for swisstopo because new methods and software are used in the project which can also be of use in the future for normal land surveying.