CERN Accelerating science

Designing an elevator system for FCC
by Panos Charitos (CERN)

Designing an elevator system for a 300 underground tunnel that could host a future circular collider (Image: CERN - FCC Collaboration)

CERN has come a long way since its foundation in 1954 in advancing our knowledge about the basic components of the Universe. This was made possible due to the advancements in technologies and the building of more complex accelerators and detectors that significantly push the limit of our knowledge. This complexity calls for long-term planning of any future development.

Building a larger and more powerful accelerator sets a number of challenges related to physics and accelerator parameters but also to civil engineering and day-to-day operations. A future collider like those explored under the FCC study will not merely be a scaled-up version of the LHC but a totally new machine. Scientists and engineers are working to develop new technologies and concepts for building and running such a large-scale research infrastructure.

Designing a 100 km tunnel, lying in an average depth of 300 meters that could host a future collider and the experimental detectors is not a trivial task.

First of all, one needs to face open issues related to the installation of the different accelerator parts, including the high-field magnets, the commissioning of the detectors and the need to transfer equipment between the tunnel and surface facilities. There are many more questions when designing such a system like: "How many people will move within such a large underground facility? How often they will need to access the tunnel and from which points? How quickly will the tunnel be evacuated to ensure safety for the personnel?

Volker Mertens, who is in charge of the Infrastructure and Operation studies for the FCC study, notes: "answering these questions becomes more challenging as the answers depend on the available state-of-the-art technologies and a possible project on how they could evolve within the next 20 years."

A key aspect of the construction and operation phase linked to the above questions is the elevator system that will be installed. Engineers are working to design a number of elevators that will efficiently connect the tunnel with the surface giving access to the engineers and technicians that will work in this project. Damien Lafarge, section leader at CERN responsible for lift operation explains: "lifts that give access to underground part are one of the most vital parts in designing a post-LHC collider. They must be operational all time, with an availability rate of 99.6% as any failure can be very costly in the operation of such a large-scale infrastructure".

An overview of the cavern and the elevator system (Image: CERN - FCC Collaboration)

At this early stage engineers are looking nominally at 12 deep access shafts, where approximately 24 lifts could be located at significant locations intervals along the collider ring. Volker notes that: "to ensure quick and successful intervention in the tunnel, the number of shafts around the tunnel, the number of lifts in each shaft and their capacity are key elements". Presently at the LHC sixteen elevators are used to connect the surface to the LHC and its experiments. The one-stop ride between the surface and the tunnel last about one minute while the cabins of these lifts can carry loads from 1 to 3 tons up to a speed of 2.5 m/s.

For FCC a slightly higher speed of 4-6 m/s to keep the duration of the ride to two minutes and a similar load of 3 tons are discussed as baseline parameters. However the greater depth of the tunnel means that one needs larger cables and thus the total weight of the cables becomes a critical issue. In fact, it turns out that the cables weigh much more than the actual cabin load as Lafarge explains. To address this issue we discuss with our industrial partners different scenarios; from using different materials to a more clever design for the elevator system.

The LHC lifts have made nearly 9'140'000 races ranging from 45.35 to 143.54m, over the LEP and LHC run 1 operation periods. You can multiply this by a factor of 2 or 3 based on the depth and number of components of a future collider (3 times bigger than the LHC) to get a rough idea of the wear and tear that the elevator system will be exposed to. That's why a key idea is now to get a redundancy with 2 lifts per shaft in order to reduce constraints on each lift, therefore maintenance costs, and increase the reliability of the function "access to the underground" at the same time!

Ingo Ruehl, an expert in CERN's Handling Engineering (HE) Group comments: "the earliest stages of any construction project offer the most opportunity for maximising quality and reducing total project costs. With this in mind, we are working in partnership with world leading engineering consultancies to utilise the latest methods and technology to ensure the best possible outcome from the first stages of design."

Thinking and designing the next generation of elevators that will be used for FCC, reliability and availability are realized to be key factors in future large and high-performance colliders as they can guarantee an efficient operation. CERN is working closely with its industrial partners to explore the latest generation of monitoring system for elevators, allowing to anticipate failures, an essential element to ensure the reliability of our facilities. 

In the next years, a detailed presentation of the available technical options for the elevator system of the FCC will be prepared. This will be included in the FCC conceptual design report that will cover every aspect of building and operating such a future large-scale infrastructure. FCC offers a unique opportunity for experts in elevator engineering to think of novel solutions in order to address the unprecedented challenges posed by such a large underground facility. 

Designing an efficient elevator is important to guarantee the safety for the people installing, maintaining and operating a future more powerful collider and running new experiments that will allow to go deeper in our understanding of our Universe!