Large Hadron Collider, CERN
France-Switzerland border, north west of Geneva
Electricité de France (EDF)
Geoconsult ZT GmbH
Brown & Root
Intecsa Ingeniería Industrial SA
1998 - 2008
Scientific Installation |
photo ATLAS, Nov 2005 by Frank Hommes, public domain
The subterranean Large Hadron Collider at CERN is the world’s largest single machine and its most powerful particle accelerator. It occupies a 26.7km ring tunnel and was constructed to explore what happened immediately after the Big Bang that initiated our universe billions of years ago. It is tended by scientists from every continent except Antarctica. In constucting it, one of the aims was to find the elusive Higgs boson particle, which was achieved in 2011/12.
The European Organisation for Nuclear Research is usually known as CERN (established 1954), the acronym being derived from its original name Conseil Européen pour la Recherche Nucléaire. CERN consists of 20 member states and six observer nations. Its laboratory facilities straddle the French-Swiss border between the Jura Mountains and Geneva, and contain the world’s largest particle physics research centre.
Most of its research experiments are conducted deep underground, in purpose-built tunnels. All machines, services and technical infrastructure are operated from the CERN Control Centre (46.254609, 6.057098) at Prévessin-Moëns, France (which is what we have mapped at right).
Until the Large Hadron Collider (LHC) was constructed, the centre’s two largest particle accelerators were the Super Proton Synchroton (commissioned 1977), in a ring of tunnels 6.9km in circumference, and the Large Electron Positron Collider (commissioned 1989), in a ring of 26.7km circumference.
In 1994, CERN initiated the project to replace the Large Electron Positron Collider with the more powerful Large Hadron Collider. The new machine was installed in the existing 3.8m internal diameter concrete-lined tunnel, which slopes at a gradient of 1.4 percent. It is situated at an average depth of 100m (175m below the Jura Mountains and 50m underground near Lake Geneva) with associated access shafts, detector caverns, galleries and junction chambers.
Essentially, the Large Hadron Collider was designed to fire packages of hadrons — charged particles (quarks such as protons) — around tubes inside the tunnel. The packages form beams of particles, which pass through a number of accelerating structures to increase their energy. Two particle beams travel in opposite directions, in separate tubes. Once the beams are moving at almost the speed of light, they are made to collide where the tubes cross over inside four particle detectors.
Scientists believe that the colliding particles will recreate in miniature conditions similar to those at the beginning of the Universe, just after the Big Bang some 13.7 billion years ago. They particularly want to investigate the primordial substance called quark-gluon plasma and the Higgs boson particle. The existence of the Higgs boson, named after theoretical physicist Peter Ware Higgs (b.1929), was predicted by the Standard Model of particle physics in the 1970s.
The Standard Model defines quarks as the fundamental building blocks of matter, with forces of varying strength acting through carrier particles (such as bosons and gluons) exchanged between the particles of matter. While particles cannot move faster than the velocity of light (299,792,458m/s) in a vacuum, there are no limits to the energy they can possess.
The Large Hadron Collider uses either hydrogen protons or lead ions — comparatively large quarks that don’t decay — to produce particle beams seven times more energetic than any previous machine.
Protons are formed by removing the orbiting electrons from hydrogen atoms. At the start of their journey they have an energy level of 50MeV, which is increased to 1.4GeV through a series of boosters. They pass through the 628m diameter Proton Synchrotron, accelerating to 25GeV, and then the Super Proton Synchrotron to reach 450GeV. Lastly, the protons are transferred to the Large Hadron Collider (filling separate rings clockwise and anticlockwise) where they are accelerated for 20 minutes to a maximum of 7TeV. The proton beams usually continue circulating for around 10 hours, colliding with an energy of up to 14TeV.
Lead ions have many protons per particle, giving each ion even greater energy than the hydrogen protons. Typically, the lead ion beams have a collision energy of up to 1,150TeV.
The particles are kept in a beam by an ultra-high vacuum and guided around the ring tubes by a strong magnetic field, induced by an array of superconducting electromagnets.
To conduct electricity without resistance or energy loss, the electromagnets are cooled to minus 271.3 degrees Celsius by liquid helium — a temperature near to absolute zero and colder than outer space. The array includes 1,232 dipole magnets 15m long to bend the beams to their orbits, 392 quadrupole magnets 5-7m long to focus the beams and other electromagnets to compress the beams prior to collision, increasing the likelihood of impacts between the subatomic particles.
The engineering works that had to be designed and constructed to complete the transition from Large Electron Positron Collider to Large Hadron Collider were divided into three parts, let to various international companies in 1996. Package 1 consisted of new underground and surface structures at CERN’s Meyrin site in Switzerland. Package 2 comprised new underground and surface structures at CERN’s Cessy site in France. Package 3 included the 2.5km injection tunnel near Meyrin plus all other new structures for the scheme.
Designs were awarded as follows — Package 1, Electricité de France (EDF) and Knight Piésold; Package 2, Gibb (part of Jacobs Engineering Group from 2001), SGI and Geoconsult; Package 3, Brown & Root, Intecsa and Hidrotécnica Portuguesa.
Construction was carried out by — Package 1, Teerag-Asdag, Baresel and Locher; Package 2, Dragados and SELI; Package 3, Taylor Woodrow, Amec and Spie Batignolles, though the injection tunnel was constructed by a Swiss contractor.
Much of the construction work, which commenced in 1998, was carried out while the Super Proton Synchroton and Large Electron Positron Collider (shut down December 2000) were still in operation. Extensive 2D and 3D modelling was undertaken to ensure that the new work did not impact on the experiments.
Four new underground cavern systems had to be excavated for the particle collision detectors: ATLAS, CMS, ALICE and LHCb. The weak ground conditions, (a molasse of sandstones and marls) and the prevention of water ingress were particular challenges that the engineers had to overcome. All the underground excavations are lined in concrete, with 2mm thick waterproof membranes and geotextile drainage blankets.
ATLAS (46.235774, 6.055265) is A Toroidal Large hadron collider ApparatuS and it occupies the largest volume of any particle detector ever constructed. It is 46m long, 25m high and 25m wide, weighs 7,000 tonnes and has eight 25m long superconducting magnet coils forming a cylinder around the central particle beam tube. Located 100m below ground near the main CERN site, close to the village of Meyrin in Switzerland, it examines a wide sector of physics, covering research for the Higgs boson, dark matter, supersymmetry and extra dimensions.
ATLAS is housed in a cavern 35.1m wide, 56.1m long and 42.3m high, with an equipment cavern 23m wide, 65.2m long and from 18.3m to 31.4m high adjoining at right angles. The barrel vaulted roof of the ATLAS cavern is supported by concrete shear collars, and tensioned Freyssinet anchors installed from purpose-built galleries above. Its floor slab is 5m thick. Two access shafts, 60m deep and of 20.5m and 14.5m diameter, connect the vault with the surface. Other infrastructure includes junction and cryogenic chambers, personnel access tunnels and survey galleries.
CMS (46.309806, 6.077279) is a Compact Muon Solenoid near Cessy in France. Weighing 12,500 tonnes, it is 21m long, 15m high and 15m wide, and has similar uses to ATLAS. Its superconducting solenoid coil generates a magnetic field of 4 Tesla, or about 100,000 times stronger than the Earth's.
The cavern for CMS is 27m wide, 53m long and 34m high, and its service cavern alongside is 19m wide, 85m long and 17m high. A 7m wide reinforced concrete pillar, 54m long and 31m high, runs between the two caverns to support loads from the rock canopy above. Each cavern has a central surface access shaft extending some 70m above its roof, of 12m (service) and 21m (CMS) in diameter. Several smaller caverns, shafts and galleries complete the infrastructure.
ALICE (46.267592, 6.018764) is A Large Ion Collider Experiment, situated below St Genis-Pouilly in France. The 26m long, 16m high and 16m wide muon spectrometer detector weighs 10,000 tonnes. It is used to analyse lead ion collisions and for studying the properties of quark-gluon plasma and the Strong Force that binds particles in an atomic nucleus.
LHCb (46.241665, 6.096982) is the Large Hadron Collider beauty experiment and lies near Ferney-Voltaire in France, on the border with Switzerland. The spectrometer is 21m long, 10m high and 13m wide, weighs 5,600 tonnes, and investigates the slight asymmetry between matter and antimatter by studying the relative decays of the 'beauty quark' (b quark) and 'anti-beauty quark' (anti-b quark) particles.
The caverns for ALICE and LHCb are of similar construction to those of ATLAS and CMS, though smaller. The lining of all the caverns consists of grouted steel rock bolts up to 12m long, topped by two layers of fibre-reinforced sprayed concrete with steel mesh in the final layer. The layers are generally a 200-250mm thick primary and a 500-800mm secondary, though the lining is up to 1.3m thick overall in some places.
The size of the cavern access shafts was based on the size of the particle beam tubes, which were assembled at the surface and lowered down the shafts into the detection caverns in segments weighing up to 2,000 tonnes. Apart from CMS, which was prefabricated in 15 sections, all the detectors were constructed in situ.
Two smaller particle detectors were also constructed. LHCf, or Large Hadron Collider forward experiment, is located 140m from the ATLAS collision point. Its twin detectors are each 300mm long, 100mm high, 100mm wide and weigh 40kg. The apparatus measures particles produced in line with the beams in proton-proton collisions, to verify model estimates of the primary energy of ultra-high-energy cosmic rays.
TOTEM, or TOTal Elastic and diffractive cross section Measurement experiment, is close to the CMS collision point. It uses detectors housed in vacuum chambers, known as 'Roman pots', to measure the effective sizes of the protons in the Large Hadron Collider. Four pairs of Roman pots are connected to the particle beam tubes near their cross over point. TOTEM is 440m long, 5m wide and 5m high, and weighs 20 tonnes.
The Large Hadron Collider's power consumption is around 120MW. CERN as a whole uses 230MW, or about the same power consumption as all households in Geneva Canton. The estimated annual energy consumption (2009) for the Large Hadron Collider is some 800,000MWh, based on 270 working days per year (it does not operate in winter).
At 9.28am on 10th September 2008, a particle beam completed the first circuit of the Large Hadron Collider at CERN. The project had cost approximately £3.74 billion — £3 billion (80 percent) for the collider itself, £728 million for the detectors and £17 million for the computers to analyse the data.
Unfortunately, on 19th September 2008, the machine was shut down after a magnetic failure caused one tonne of liquid helium to be spilled in the 26.7km tunnel ring. It was restarted in November 2009.
In December 2011, scientists working in the ATLAS and CMS detectors reported that their experiments showed promising hints of a lightweight Higgs boson. In July 2012, the two detectors' teams confirmed they had found Higgs bosons. In addition, CERN’s website notes that in 2011 and 2012, the Large Hadron Collider detected 1.2 million Higgs boson particles per year.
Upgrades to the current machine were carried out between February 2013 and April 2015.
During 2011, in an international collaboration of physics laboratories, a design study began into enhancing the Large Hadron Collider’s sensitivity by increasing its luminosity tenfold. Luminosity is proportional to the number of collisions occurring during a certain time frame, so the higher the luminosity, the more data can be gleaned about the processes being observed.
The study's technical report was published on 31st October 2015, marking the start of a new project, known as the High-Luminosity Large Hadron Collider. Due to be completed in phases by 2025, the upgraded machine will be able to detect and record rare events that presently are inaccessible. It is thought that to 15 million Higgs bosons per year will be identified.
The proposed scheme includes constructing two new shafts and two new 300m long service tunnels into the tunnel ring. Vibrations caused by the excavation and tunnelling operations must be minimised because live experiments will be continuing throughout the works.
Contractor: Teerag-Asdag AG, Baresel GmbH and Zschokke Locher AG consortium
Contractor: Dragados SA and SELI SPA joint venture
Contractor: Taylor Woodrow, Amec and Spie Batignolles consortium
"LHC the guide", CERN frequently asked questions brochure, Communication Group, CERN, February 2009
"The CERN LHC Project – Design and Construction of Large Caverns in Tight Spaces" by Ralph J.H. Parkin, Paul M. Varley and Francois Laigle, Geotechnical Aspects of Underground Construction in Soft Ground, eds Kastner, Emeriault, Dias and Guilloux, pp.85-94, Lyon, 2002
"An Example of Cooperation in the Field of High Technology: CERN – Large Hadron Collider – Civil Engineering Consultancy Services" by H.-Chr. Kurzweil, Proceedings of EPAC 2000, pp.172-174, Vienna, 2000
"The Role of CERN in the Large Construction Contracts for LHC Civil Works” by Pedro d’Aça Castel-Branco, Civil Engineering Group, CERN, Geneva, 1998