Earlier this month, the European Organization for Nuclear Research (CERN) released a first view of its proposed particle accelerator, which, as currently envisioned, would be one of the most massive science facilities ever built: the Future Giant Circular Collider (FCC).
The last time the European Organization for Nuclear Research (CERN) undertook a project of the size of the FCC was in the 1980s, and the target was the Large Electron-Positron Collider (LEP): sometimes described as the largest civil engineering project in Europe up to that time . In the 21st century, engineers modified the LEP tunnel into today's Large Hadron Collider (LHC). By smashing atomic nuclei, or subatomic particles, together at near-light speeds, accelerators like the LHC have dramatically helped push the boundaries of physics and technology.
“We have to distribute all this power through underground substations. … We are playing with big numbers.” —Jean-Paul Burnet, CERN
Building the Large Hadron Collider (LHC) was certainly a massive undertaking, but it was nothing compared to the challenges that building the FCC would bring. “What changed with the FCC is that we have to build new infrastructure in places that are not on CERN land,” says Jean-Paul Burnet, an electrical engineer at CERN. But despite its size and cost, the FCC represents an evolution of existing technology.
Planning and drilling
Detailed conceptual treatments of the FCC giant date back to at least 2014. Over the decade since then, engineers and scientists have studied these proposals, trying to find a suitable alignment for a ring more than three times the length of the LHC. Now, finally, they have a loop of their own: a 91-kilometre-long close-in circuit, south of the existing loop at the LHC, and studded with eight access columns connecting the tunnel to the surface above. Timothy Watson, a civil engineer at the European Organization for Nuclear Research (CERN), calls its design “LHC on steroids.”
“It's very similar in terms of its design and the engineering input that would be necessary to design and build it, but it's obviously much larger,” he says.
In fact, if we focus on the FCC's design rather than its sheer size, the FCC's infrastructure may not look much different from its predecessors. The FCC tunnel and access shafts are not much wider than the Large Hadron Collider (LHC). The most technically demanding structures will be the collider caverns, where the tunnel explodes into larger spaces containing particle detectors. Even then, Watson says, the FCC caverns are likely to be similar to those that host LHC experiments like CMS and ATLAS.
However, some crucial and difficult differences remain. For example, the FCC tunnel – which averages 200 meters below the surface – will be much deeper than the LHC tunnel and, in fact, several times deeper than most underground metro systems.
Additionally, the FCC's proposed training course will take builders through unfamiliar geological conditions. In particular, the FCC will need to traverse major bodies of water – specifically Lake Geneva and the Rhone River – challenges of the kind that no previous CERN collider has done.
However, Watson is confident that current construction technology – eight tunneling machines, one for every eighth of the ring – will be up to the task. “We think these are things the industry can do,” he says.
Wiring it
To keep the particles at close to the speed of light, the FCC tunnel would need all sorts of high-tech gadgets, like cryogenics and high-powered electromagnets. All of this equipment comes at an energy cost. When FCC operators first turn it on, it's expected to consume about 1.4 terawatt-hours of electricity for the FCC First Stage Lepton Collider (FCC-ee), which would accelerate electrons to fractions below the speed of light.
By comparison, today all of CERN—including the Large Hadron Collider itself, other colliders at the facility, its computers and data centers, and its infrastructure—uses 1.3 terawatt-hours per year. Then, as scientists anticipate future upgrades, including next-generation lepton-hadron and photon-hadron colliders, the FCC's demand for power will only rise from a baseline figure of 1.4 terawatt-hours.
Today, CERN derives its electrical power from a single 400 kV connection to the French grid. Plans call for two additional connections: one 400 kV, the other 225 kV. From these three sources, the collider's infrastructure will distribute power to the mine's eight access shafts; From there, it will be distributed to the rest of the collider.
Unlike previous colliders, which generally sought to minimize the amount of underground electrical engineering work, the FCC's initial designs anticipate that most of the electricity will be distributed within the tunnel systems themselves. “We have to distribute all this power through underground substations,” Burnett says.
No matter how the electrons actually move, they add up to a lot of energy: an estimated 350 megawatts. The long-term goal of CERN's electrical engineers is to conserve energy, Burnett says. For example, one of the largest sources of energy for any particle accelerator is the radio frequency system, which is necessary to actually accelerate the particles. Electrical engineers estimate that by improving the efficiency of klystrons in an RF system, the FCC could save 50 megawatts.
“We play with big numbers,” Burnett says. “We are trying to focus our R&D on this aspect.”
Walk before running
After CERN is expected to publish more detailed plans next year, CERN member states will determine whether they want to fund the $17 billion first phase. But even if the FCC gets the green light, the construction phase won't begin for at least the better part of a decade.
So what's happening now are important first steps. For engineers, the task at hand is to begin examining sites along the path charted by the FCC: testing all aspects of the plans and determining whether any need to be changed.
This, again, is just the beginning. “If the project is approved, we will need to investigate the site more than we plan to do in the next two years,” Watson says.
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