A one-week conference dedicated to CERN’s proposed Future Circular Collider (FCC) has brought together over 600 international experts from around the world to discuss several aspects of the project, such as scientific advancements, construction and infrastructure, the societal impact of big science and public outreach. FCC Week 2025, which took place in Vienna, Austria, from 19 to 23 May, comes after the completion of the FCC Feasibility Study Report in March 2025 and provided a timely opportunity to review the project’s scientific and technical progress, and the next phase of design and development.
Expert talks throughout the week covered a wide range of topics, which included breakthroughs in the science behind the proposed new accelerator, studies into the technical infrastructure, the role early career researchers can play in shaping the future of particle physics, and how the public can benefit.
FCC feasibility and growing international collaboration
The FCC integrated programme foresees a two-stage collider hosted in a new 90.7 km tunnel in the Geneva basin. In its first phase, the FCC-ee would serve as a precision electron-positron collider operating as a Higgs, electroweak and top factory. It would later be succeeded by the FCC-hh, a 100 TeV hadron collider, extending the reach of the LHC by an order of magnitude in energy.
The recently published FCC Feasibility Study Report provided the most detailed and comprehensive analysis to date of such a facility. Submitted as input to the ongoing update of the European Strategy for Particle Physics, the report comprises three volumes: physics and detectors, accelerators and infrastructure, and civil engineering and sustainability, respectively.
Fabiola Gianotti, CERN Director-General, reflected on the project at the FCC Week conference, saying “the FCC integrated programme promises unparalleled reach for the exploration of physics at the shortest distances.
“The recently completed Feasibility Study is a key milestone for the future of the field, and we are pleased to see the growing support and enthusiasm of the community,” she said.
Michael Benedikt, FCC Project Leader, summarising the status and next steps after the Feasibility Study, noted: “With the completion of the Feasibility Study, we now have a technically mature, globally supported vision for the FCC. The focus is shifting to prepare a robust implementation strategy, continuing the design effort, and deepening our engagement with partners around the world.”
The collaboration behind the FCC has significantly expanded, now comprising 162 institutes hailing from 38 countries. In the past year alone, 28 new Memoranda of Understanding have been signed, including a special agreement with several Ukrainian institutions.
The collaboration has benefited from new partnerships in Latin America and Asia and is deepening its dialogue with industry. Statements of intent signed by the United States and Canada signal growing global alignment around the FCC vision, and the project has been explicitly referenced in high-level policy discussions, such as the Draghi report on European competitiveness.
Costas Fountas, professor at the University of Ioannina and President of CERN’s Council, underlined the broader impact:
"The CERN Council is committed to maintaining CERN's role as a global leader while preserving its European character,” he said during a talk at FCC week.
“Member states continue to support this mission, recognising its value not only for science but also for innovation. The Future Circular Collider, if approved, represents a significant step forward in this vision, strengthening the Organization’s contribution to scientific progress and technological development in the years to come."
Scientific developments behind the FCC
FCC Week 2025 offered a comprehensive overview of the scientific motivation underpinning the FCC programme.
In dedicated plenary and parallel sessions, researchers shared updates on theoretical frameworks and simulations that inform the design and physics goals of the FCC. Talks spanned from precision studies of the Higgs boson to rare processes and searches for new physics phenomena beyond the Standard Model.
The key technology for the FCC-ee is the superconducting radiofrequency system, consisting of 2-cell 400 MHz Nb/Cu cavities in the collider for the lowest three energies (Z, WW and ZH running), and of 6-cell 800 MHz bulk Nb cavities for the booster ring, and, additionally, for the highest energy mode (top quark pair production) of the collider. Cryomodule designs for both types of cavities are complete. The recent introduction of reverse phase operation allows for the same radiofrequency (RF) installation from Z to ZH, and great flexibility in the order and sequence of operation modes, which is a major breakthrough. So far, high-efficiency klystrons had been considered for the RF power source, with efficiencies up to 80%. Now an even more promising source concept was introduced. The tristron could reach an energy efficiency above
90% and is only a third of the size of a klystron. The collider vacuum system relies on ultrathin NEG coating and discrete photons stops. Industrialisation and cost reduction are among the next R&D tasks.
The detector R&D community presented major progress in the design of detector concepts for both FCC-ee and FCC-hh, with prototypes under development and software frameworks advancing rapidly. Simulation campaigns, increasingly integrated with AI-based tools, are laying the groundwork for exploiting the full potential of the FCC, while theoretical studies continue to refine the precision goals and search strategies of future experiments.
Significant progress was also presented on the accelerator design, accelerator technologies, and technical infrastructure aspects of the FCC project. On the accelerator front, updated lattice designs and optics concepts were discussed, with advances in beam dynamics simulations, injection schemes, and collimation systems. Both the Global Head-on Collision and Local Crab Crossing optics approaches were refined, with a coordinated roadmap toward final down selection. Studies on impedance budgets, instabilities, and mitigation strategies – such as the use of chromaticity and filling schemes – demonstrated the level of technical maturity needed for the next design phase.
The progress in the development and deployment of the Xsuite simulation platform was highlighted. Xsuite serves as a central tool for evaluating dynamic aperture, collective effects, beam-beam interaction, etc. Recently, spin tracking has also been available in Xsuite, thanks to a collaborative effort with Brookhaven National Laboratory. Since fall 2024, a complete Xsuite model of the SuperKEKB collider in Japan exists, which has already allowed valuable benchmarking of the Xsuite simulation tools, e.g., by modelling the Belle II detector background due to beam-gas collision and Touschek scattering as a function of collimator settings.
For the challenging high-field magnets required for the FCC second stage, namely the FCC-hh, a two-pronged approach is followed: on one hand, building Nb₃Sn model magnets and short prototypes; on the other, advancing magnet technology based on high-temperature superconductors through activities such as cable development, test coils, and other related R&D efforts.
FCC Infrastructure
On the technical infrastructure side, sessions covered a broad range of topics including electrical grid design, cryogenics, safety systems, ventilation, and transport and logistics.
Innovative concepts such as the integration of renewable energy and hydrogen storage were discussed, alongside updates on RF power delivery, cryogenic layouts for FCC-ee and FCC-hh, and arc half-cell mock-up developments. Robotics, installation planning, and heat recovery were also featured, illustrating a holistic approach to sustainable and resilient infrastructure. These updates reflect how the FCC project is progressing as a complex, interdisciplinary engineering endeavour that reaches far beyond conventional accelerator design.
Early career researchers and the FCC
A standout feature of the week was the FCC Early Career Researchers (ECR) session, which drew nearly a hundred participants and served as a dynamic forum.
Organised by a dedicated team of early-career scientists, the session featured parallel and plenary discussions on key issues including the environmental, economic, and social sustainability of large-scale research infrastructures, strategies for communicating societal benefits, and the challenges in building and operating the FCC.
Topics ranged from governance models and career trajectories within long-term projects to public engagement. The session concluded with a shared commitment to inclusive and open collaboration, echoing the words of Austrian artist Friedensreich Hundertwasser: "Those who do not honor the past lose the future. Those who destroy their roots cannot grow."
The forum showcased the FCC community’s commitment to empowering the next generation and integrating their insights into the project's future.
Big science’s impact on society
Beyond science and strategy, the FCC Week 2025 was a chance to show how big science reaches outside the laboratory walls.
A special event, "CERN Technology & Industry Days", held in collaboration with the Austrian Federal Economic Chamber (WKO), brought together leading voices from economics, industry, and research policy.
Daniel Pawel Zawarczynski from WKO pointed out that Austrian industry is already benefitting from participation in CERN programmes: a local SME working on cryogenic insulation doubled its revenue after being selected as a supplier for CERN, later winning contracts in the space sector.
Zawarczynski also drew attention to the multiplier effect of big science on education and employment, noting that 11% of CERN alumni create startups and that training the next generation of engineers and physicists is key to Europe’s technological leadership.
Gabriel Felbermayr, president of the Austrian Institute of Economic Research (WIFO), highlighted the economic rationale for large-scale scientific projects, noting that big science generates public goods, industrial spillovers, and regional development.
His economic analysis of the FCC infrastructure indicated a benefit-to-cost ratio greater than 1.2, even under the most conservative assumptions.
FCC and public engagement
Public engagement featured prominently during the week.
More than 750 curious members of the public – primarily students – participated in the "Wheel of Science" event at the iconic Wiener Riesenrad and the Vienna Planetarium. Through talks and interactive installations, researchers introduced audiences to particle physics, the Large Hadron Collider, and the FCC. The event was co-organised by CERN, TU Wien, the University of Natural Resources and Life Sciences, and the Institute of High Energy Physics of the Austrian Academy of Sciences.
Another highlight was the public evening event "The Higgs Boson and our Life" at the Austrian National Library. With more than 350 attendees, the discussion featured Fabiola Gianotti, Ulrike Diebold (vice president of the Austrian Academy of Sciences), and governance expert Verena Ringler, moderated by physicist and science communicator Florian Aigner. The conversation extended beyond particle physics to consider how curiosity-driven research helps shape democratic societies. The outdoor exhibition "Code of the Universe: The Journey of Discovery," which opened the same evening, invited passers-by to explore the visual poetry of physics and remains on display through early June.
Diversity and international reach were also defining features of FCC Week 2025. The event welcomed 614 participants from 34 countries, with 557 attending on site and 58 remotely. Nearly 13% of the on-site participants were students, and a wide range of age groups and career stages were represented – from young researchers to seasoned experts. The distribution of attendees by gender and age underscored the growing inclusivity of the particle physics community and its commitment to generational renewal. Austria, France, Germany, Italy, Switzerland, and the United States were among the most strongly represented countries, testifying to the broad interest in the FCC vision.
The event closed with the presentation of this year’s FCC Awards ceremony, honouring outstanding contributions from early-career researchers. Poster prizes went to Tsz Hong Kwok (University of Zürich), for his work on time-dependent precision measurements in flavour physics, and Audrey Piccini (CERN), for a detailed study on vibrational stability in FCC infrastructure.
Innovation awards were presented to Sara Aumiller (TU München), for groundbreaking developments in jet flavour tagging and Higgs studies, and Elaf Musa (DESY), for her successful correction of beam optics in challenging alignment conditions.
In partnership with Physical Review Accelerators and Beams (PRAB), the paper awards recognised Ivan Karpov (CERN) and Nicolas Vallis (Paul Scherrer Institute) for their impactful and innovative publications. These recognitions underscored the depth of emerging talent and the vitality of the FCC community.