Hundreds of scientists met in London early in June for the ninth edition of the Future Circular Collider (FCC) Week. The scientific value of the FCC was confirmed by the European Strategy for Particle Physics, which was updated in 2020, as the most suitable option for the post-LHC era. 

FCC would offer a multi-stage facility with an immense physics potential until the end of the 21st century. The first step, aimed to start operation right after the end of the HL-LHC programme, is a lepton collider (FCC-ee) that could provide the highest luminosity of all proposed higgs and electroweak factories and indirect discovery potential up to the area of ~ 70 TeV. The second step of a hadron collider (FCC-hh), would reach energies up to eight times those of the LHC and allow direct exploration of the next energy frontier. The combined programme of FCCs would allow for unparalleled measurements of low-rate and “heavy” Higgs couplings as well as of other Standard Model parameters while the two machines could be housed subsequently in the same tunnel, thus largely profiting from CERN’s existing infrastructure and expertise. In addition, the FCC design foresees the possibility of colliding heavier ions as well as asymmetric collisions between electrons and protons. The full FCC programme would offer 100 years of trailblazing physics at both the energy and intensity frontiers, while the first stage of FCC-ee could begin operations within a few years of the end of the HL-LHC – a crucial step in keeping the community engaged across different generations.

Designing a new particle accelerator infrastructures sets a number of challenges in different areas; from civil engineering and geodesy to the development of accelerator technologies and detector concepts to meet the scientific goals. To understand the technical and financial feasibility of the proposed infrastructure, CERN together with its international partners have launched a feasibility study that shall be completed in time for the next Strategy update. FCC Week 2023 offered an excellent opportunity to strengthen the bonds between the FCC collaborating institutes, discuss the  technological and scientific opportunities on offer and plan the submission of the FCC mid-term review to the CERN's Council later this year. From the beginning onwards the FCC feasibility study, with the support of the H2020 FCCIS project, aims to build an ecosystem of science and technology involving fundamental research, computing, engineering, and skills for the next generation. An encouraging sign from the FCC Week 2023, is the participation of young researchers (about 40% of the participants belonging to an age group under 40ies) sharing the vision of getting deeply involved as they see the wider benefits of designing the next-generation of particle colliders. 

In his welcome speech, Executive Chair of the UK’s Science and Technology Facilities Council (STFC), Mark Thomson, stressed the value of a next-generation Higgs factory as the next tool in exploring the universe at a very fundamental level. In this endeavour, he stressed the support of UK physicists and laboratories while also reflecting on the encouraging progress of the FCC feasibility study. In closing his talk, he expressed his hope that the meeting in London would mark an important milestone towards the success of the project. In her plenary address, CERN’s director-general Fabiola Gianotti confirmed that the current schedule for the completion of the FCC feasibility study is on track. As mentioned in her presentation, FCC is the only facility commensurate with the present size of CERN’s community providing up to four experimental points. “I believe FCC is the best project for CERN’s future” noted Gianotti. “We need to work together to make it happen”. Michael Benedikt, FCC Study Leader presented the progress in the different domains of the FCC feasibility study and verified that the project is on track to deliver its mid-term review later this year “the FCC integrated project allows the start of a new, major facility at CERN within a few years of the end of HL-LHC”. Moreover, speakers of the plenary sessions stressed that FCC-ee offers a reliable and cost-efficient path towards an energy-frontier machine. The project would allow the reuse of large parts of the same infrastructure while also offering two decades for intensive R&D on innovative technologies for superconducting magnets that would provide the highest achievable fields.

One of the major achievements of the feasibility study is the development of a new FCC layout and placement scenario thanks to the close collaboration with CERN’s host states and external consultants (CERN Courier May/June 2022). This is based on a 90.7km ring with eight surface points, presenting a 4-fold symmetry that offers the possibility for 2 or 4 experiments. As CERN’s Johannes Gutleber showed in his presentation, the baseline scenario is presently communicated to the respective communes while preliminary work is ongoing to analyse some of the environmental aspects at the surface site locations. The goal over the next couple of years is to develop synergies with the local communes while also progressions with the authorisation process to launch the first geophysical investigations around 2024; a valuable step to collect more information on the underlying geology. Identifying the best placement and layout and adapting the entire project parameters to the new placement was one of the main focal points of the feasibility study that was achieved in a very fruitful collaboration between all scientific and technical actors in the feasibility study and in close cooperation with the host state services concerned.

The FCC Week 2023 also saw significant work on the optimization of the design of FCC-ee and FCC-hh colliders and their injector chains. Transfer lines have been optimised for re-using existing tunnels as much as possible and for compatibility between the lepton and hadrons phase of FCC-ee. Further work will consolidate the option of using the SPS as the FCC-ee pre-boosted. This work respects the layout and placement scenario while also considering CERN’s versatile experimental programme.

Designing a research infrastructure for the 21st century, means addressing questions of sustainability and efficiency. The goal is to reduce the environmental impact while also investing relevant technologies that could find applications beyond particle physics. This informs ongoing RnD efforts in the framework of the feasibility study. One of them are the high-efficiency klystrons to power the RF cavities. Profiting from a previous R&D programme on High-Efficiency Klystron for CLIC, the goal is to increase their efficiency from 50% to 80%, resulting in a 300GWh/y of energy saving - without considering the impact that this development could have for other industries. Other accelerator components where work is ongoing to minimise their energy consumption include low-loss magnets, SRF cavities and high-efficiency cryogenics compressors. The FCC collaboration is also working to demonstrate the large re-use of excavated materials including carbon capture potentials. This work builds on the results of the EU-funded “Mining the Future” competition that was launched in 2020 and identified a number of relevant technologies. The aim of these efforts is to re-use the excavated material locally, minimising the global nuisances (transport) and using soil for agriculture and reforestation as part of the Avoid - Reduce - Compensate principle. This work has culminated in the establishment of the framework for building a real-scale demonstration of the innovative solutions at CERN together with local industries and partners. Last but not least, during the FCC Week discussions focused on solutions related to the energy supply for FCC-ee and the development of a concept for the renewable energy supply along with relevant energy storage technologies. Work in this field could also enable partnerships with other Research Infrastructures facing similar challenges. 

If the FCC project is approved, a new generation of young researchers will need to take the reins to deliver it and exploit the physics opportunities offered by this research infrastructure. This motivated the organisation of a dedicated Early Career Researchers (ECRs) session at CERN FCC Week. Hosted by Dr Sarah Williams it gave the panel of ECRs, including: Abraham Tishelman-Charny (Brookhaven National Laboratory), Andrey Abramov (CERN), Armin Ilg (University of Zurich), Emily Howling (Univ. of Oxford University College), Julia Gonski (Columbia University), and Tevong You (King’s College London), the chance to discuss their hopes, fears and experiences to date with the FCC project.

The FCC Week’s public event “Giant Experiments, Cosmic Questions” held on the 8th June at The Royal Society, highlighted some of the big questions that particle colliders as well as other Big Science facilities aim to address. The panel featured fellow particle physicists Dr Sarah Williams, Prof. Jon Butterworth alongside radio astronomer Professor Anna Scaife and gravitational wave astronomer Dr Laura Nuttall, and was hosted by the brilliant BBC’s Robin Ince. You can watch the recording of this event: 

Following FCC Week 2023, the coming months will keep the FCC team very busy, with hopefully new institutes formalising their accession to the FCC collaboration and the expected submission of the FCC Midterm review to CERN’s Council; a key milestone towards the completion of the FCC feasibility study in 2025.