From drilling to dark matter
CERN in Geneva, one of the most advanced centres for research into sub-nuclear physics, is working on an even more powerful particle accelerator. However, investigating and discovering the secrets of the extremely small requires the use of gigantic equipment and systems.
Between France and Switzerland, just a few kilometres from Lake Geneva, a 27 km long circular tunnel houses the LHC (Large Hadron Collider) particle accelerator, which provides the conditions that make the main experiments carried out by CERN scientists possible. The years have gone by for it too, and it needed to be serviced. This was an opportunity to try to create a more powerful accelerator that could push research towards new frontiers and broaden the spectrum of possible particle collisions; to have new elements to analyse, to answer questions about dark matter or antimatter. The dear old LHC is almost ready to start a second life and become HiLumi. To accommodate the new parts of this technological jewel, however, it is necessary to ensure an infrastructure that protects it and connects it to the world above. This is where the Pini Group’s “made in Swiss” experience comes into play. But let’s start at the beginning: what is the HiLumi project?
The HiLumi project
A particle accelerator is basically a big torch aimed at the sub-atomic world, in particular the world of elementary particles, the building blocks of the universe. It is used to understand how they are and how they behave, to validate or not our theories about how the world is made. CERN’s LHC accelerator has done this job brilliantly, leading, among other things, to the detection of the Higgs boson. Now, the HiLumi LHC (High Luminosity LHC) project aims to upgrade the CERN super-accelerator to increase its luminosity (one of the main indicators of a particle accelerator’s performance), and that is the number of collisions per unit area in a given time. This will increase the probability of possible discoveries. While the LHC is capable of producing up to 1 billion proton-proton collisions per second, the HiLumi LHC will be able to further increase this number. It is assumed to increase the peak brightness, that is the number of events produced per second, by a factor of 5 and the integrated brightness, that is the total amount of data collected by the experiments, by a factor of 10. Work will be done to increase the power of the accelerator, but also of the detectors. In total, more than 1.2 km of the current machine are being replaced with new high-tech components, such as magnets, collimators and radio-frequency cavities. Around 150 new magnets and 16 crab cavities will be installed. Their function is to tilt the proton packets so that they move sideways, just like a crab. There will also be major civil engineering work, with the construction of new buildings, shafts, caverns and underground tunnels, mainly at two locations, in Switzerland at the CMS (Compact Muon Solenoid) detector and in France at the Atlas (A Toroidal LHC ApparatuS) detector.
The super-accelerator is expected to return to investigate the secrets of the universe around 2026-2027.
Wells and tunnels
This is where the Pini Group’s experience in underground infrastructures comes into play. We talk about it with engineer Marco Ruggiero.
Engineer, what part of the project are you carrying out at CERN?
“Our construction site is in Cessy on French territory, about 10 km from Geneva. The accelerator is located in a 27 km long circular tunnel, one third of which is on Swiss territory and two thirds on French territory. We work in an area of countryside, where there are industrial adjacencies to CERN. In addition to the main office, every 3 km or so along the perimeter of the tunnel there are access shafts surrounded by industrial buildings.”
What do you need to achieve?
“This is a project to extend the accelerator at point 5. It involves the construction of an 80-metre high access shaft with a diameter of more than 10 metres, a service cavern, a transformation corridor more than 300 metres long, various connecting tunnels, emergency exits and the infrastructure access facilities. CERN’s equipment will then be located inside.”
What stage are you at?
“The concrete part has been completed, now we have to install prefabricated modules and do metalwork. We expect to finish the underground work in January 2022. The construction site started in 2018 and during the peak phases it employed a total of a hundred people.”
What are the difficulties in carrying out such a project?
“Basically, we have to work in the vicinity of an existing technologically advanced structure, so we have to be very careful that the vibrations produced by the excavations do not damage the LHC equipment.”
Is a client of international standing and the highest level of research particularly demanding?
“The client required the project to be managed using BIM (Building Information Modelling). Our BIM manager worked constantly with the developers of Autodesk Revit to optimise specific tools for underground construction. Let’s say that there was a continuous dialogue, with a high demand for precision.”
It is curious that in order to analyse the infinitesimally small, it is necessary to build cyclopean structures?
“The destination of our work is certainly fascinating. But personally, I’m mainly interested in large-scale projects, in managing large construction sites. That’s one of the reasons why I switched from hydroelectric construction to underground infrastructure. Because nowadays it is the latter that see the greatest challenges, the most important projects from an engineering point of view. With Pini, for example, we are working on the Brenner tunnel and the Turin-Lyon high-speed train. Large connection works and complex underground projects.”
Beyond the Boson
CERN’s LHC accelerator has become famous in mass culture as it led to the first detection of the Higgs Boson (improperly called the ‘God particle’) in 2012. The Higgs Boson was theorised in 1964 and plays a key role in the Standard Model of physics, as it gives mass to elementary particles. Following the demonstration of the Higgs boson’s existence, physicists all over the world are now aiming to use the LHC (in the HiLumi version) to get answers to various questions they consider fundamental. According to Wikipedia, the questions they would like answered are
- What is the origin of the mass of baryons? Will generating quark and gluon plasmas result in the non-perturbative origin of a large fraction of the mass of the universe?
- Why do elementary particles have different masses? In other words, do particles interact with the Higgs field?
- According to some evidence, 95% of the mass-energy of the universe has a nature different from the known one. What is this? In other words, what are dark matter and dark energy?
- Do supersymmetric particles exist?
- Are there dimensions other than the three spatial and temporal dimensions, as predicted by various string theory models?
- What are the characteristics that can explain the asymmetry between matter and antimatter, i.e. the virtual absence of antimatter in the universe?
- What can be known, in more detail, about already known objects, such as the top quark?