Cern entices authorities over gigantic collider with green arguments

Spanning the border between Geneva and France, and running deep below the Rhone and Arve valleys and Lake Geneva, the next-generation accelerator will be three times larger than the current Large Hadron Collider (LHC), at 100 km in circumference. After a feasibility study for the Future Circular Collider (FCC) was launched in 2020, the project is now aiming to be readied for 2040. But first, member states will have to greenlight the project by 2025. The biggest challenge Cern faces at this stage is the environment.

Why it's sensitive. Cern has already charted a possible path for the particle collider tunnel, But the test will be to achieve certain scientific targets while avoiding geological constraints and having the least possible environmental impact. Its member states, as well as local authorities, will have to be swayed.

Among the arguments the organisation is presenting are that heat released by FCC magnets may be used to heat entire neighbourhoods, and the dug-up earth could be redeployed locally.

For Europe, the FCC would represent a key move to consolidate its leadership position on particle research. But questions remain on whether Cern's member states are ready to foot the bill. According to initial estimates, the total construction cost may amount to CHF20 billion, a figure that will have to be refined by the feasibility study, which alone will cost a whopping CHF100 million.

From one collider to the next. The future project is expected to have two operating phases. Between 2045 and 2060, it would be an electron-positron accelerator. After 2065, it would become a hadron collider, with the LHC serving as a particle “injector” or a pre-accelerator.

“The goal is for the FCC to be able to start operating by 2040 to 2045 because the LHC will stop during 2040 to 2041, and it is important for Europe to maintain its status as the world leader,” said Michael Benedikt, who has been coordinating preliminary work on the FCC since 2014.

Patrick Janot, a physicist at Cern, explained why the LHC is doomed to end: “When you accumulate the data produced by accelerators, in the end, you hit a wall in terms of the system and statistical rules. By 2040, we will have collected enough data to have reached the end of the machine's statistical and systemic power – using it any longer than that would be a waste of money.”

Clearing the ground. The feasibility study has examined more than 100 scenarios for the collider's trajectory, with a front-runner mapped below. Next, the field phase should identify areas with technical or territorial challenges.

The field stage of the study aims to better understand the selected sites' challenges in terms of surface and below-ground biodiversity. “We will conduct geophysical measurements to understand the nature of the subsoil, followed by tests to verify the models,” said  Antoine Mayoux, a civil engineer involved in the feasibility study.

The challenge will be to dodge limestone and karst zones, which are too unstable, as well as avoid having to dig more than 50 metres below Lake Geneva for cost reasons, Benedikt added.

According to Mayoux, technically, this may be done, noting that the tunnel’s roughly eight-metre diameter is much narrower than other civil engineering projects.

“It's actually easier, from a civil engineering point of view, than the Mont Blanc tunnel. What is atypical here is the length of the tunnel,” he said.

Meanwhile, politics represent another issue in the equation, with the FCC transiting through two countries and a number of municipalities. “We have a participatory approach with the local authorities, who will examine the project if approved,” Mayoux said. Several members of the feasibility study team affirm that relations with the authorities are good.

Aware of such issues, Cern appointed its former director of relations with France and Switzerland to the team overseeing the study to address these questions.

Heating with particles. To plead its case, Cern is focusing its argument on energy. A system is already in place to retrieve heat released by the LHC magnets and warm an entire neighbourhood in Ferney-Voltaire, in France, not far from Cern. This could be replicated on a larger scale at several sites above the future FCC tunnel.

Serge Claudet, Cern’s energy coordinator, said the heating network system in Ferney-Voltaire produces in energy the equivalent of 400 geothermal probes, which would have cost several million euros to install.

“We don’t intend to become an energy supplier. The aim is to identify synergies with public authorities. To be worthwhile, you need to have a site requiring an urban heating network that is between one to three kilometres away,” he said.

The model is soon to be extended to Prevessin in France, where Cern’s data centre is hosted, as well as Meyrin, on the Swiss side. “The expected natural gas savings are 80 per cent for the Prevessin site and 30 per cent for the Meyrin site,” said Claudet. He added that the villages of Gex and Saint-Genis-Pouilly in France have also shown interest in this type of project.

Greening the LHC. Since the LHC was built in the late 1990s, the public’s concerns over Cern’s operation have moved on. “During the preliminary studies for the collider, the main challenge back then was developing suitable magnets,” Benedikt recalled. “Now the main issue is sustainability, where we seek to improve the energy efficiency of all systems.”

This issue already emerged during the LHC’s technical developments. Malika Meddahi, Cern’s deputy director of colliders and technology, said: “Currently, the LHC consumes 10 gigawatt hours per unit of secondary particles). In 2030, thanks to improvements underway, the LHC will consume only 2.4 gigawatt hours.”

The FCC will nevertheless have a heftier electricity bill, burning through seven times more energy than its predecessor. The challenge is making the most of this energy to produce a maximum amount of scientific data.

In spite of its gigantic scale, the FCC’s carbon footprint will only be a fraction of that of rival projects, such as the planned International Linear Collider (ILC) in Japan or the Circular Electron-Positron Collider (CEPC), currently under consideration in China. According to a scientific study published last October cited by Nature, 90 per cent of Cern’s electricity comes from renewable sources.

China’s future plans. The proposed CEPC, similar in characteristics to the FCC, including its 100km-circumference and production of electrons and positrons, may overshadow Cern’s plans. For now, the Chinese project is also at the site selection stage.

"There is no need for two projects of this type on the planet. We must move forward together," Cern’s Meddahi said. When the LHC was built, the United States obtained observer status at Cern and footed $531 million for the construction of the LHC – in exchange for the promise that Cern’s scientists would use its installations to conduct their research on neutrinos.

Meddahi admitted: “China is stating its ambition, so let's be cautious and watch for a change in leadership.”

However, if China chooses to build its collider before Cern, it will face fewer social constraints and may have it up and running as early as 2030, according to the latest updates from China.