The Large Hadron Collider (LHC) is the world’s largest and most powerful particle accelerator. It first started up on 10 September 2008, and remains the latest addition to CERN’s accelerator complex. The LHC consists of a 27-kilometre ring of superconducting magnets with a number of accelerating structures to boost the energy of the particles along the way.
Inside the accelerator, two high-energy particle beams travel at close to the speed of light before they are made to collide. The beams travel in opposite directions in separate beam pipes – two tubes kept at ultrahigh vacuum. They are guided around the accelerator ring by a strong magnetic field maintained by superconducting electromagnets. The electromagnets are built from coils of special electric cable that operates in a superconducting state, efficiently conducting electricity without resistance or loss of energy. This requires chilling the magnets to ‑271.3°C – a temperature colder than outer space. For this reason, much of the accelerator is connected to a distribution system of liquid helium, which cools the magnets, as well as to other supply services.
Thousands of magnets of different varieties and sizes are used to direct the beams around the accelerator. These include 1232 dipole magnets 15 metres in length which bend the beams, and 392 quadrupole magnets, each 5–7 metres long, which focus the beams. Just prior to collision, another type of magnet is used to "squeeze" the particles closer together to increase the chances of collisions. The particles are so tiny that the task of making them collide is akin to firing two needles 10 kilometres apart with such precision that they meet halfway.
All the controls for the accelerator, its services and technical infrastructure are housed under one roof at the CERN Control Centre. From here, the beams inside the LHC are made to collide at four locations around the accelerator ring, corresponding to the positions of four particle detectors – ATLAS, CMS, ALICE and LHCb.
How many kilometres of cables are there on the LHC? How low is the pressure in the beam pipe? Discover facts and figures about the in the handy LHC guide
CERN takes safety very seriously. This report by the LHC Safety Assessment Group (LSAG) confirms that LHC collisions present no danger and that there are no reasons for concern
Take a virtual tour of the Large Hadron Collider
Featured updates on this topic
Two years ago, CERN's accelerators and experiments shut down for maintenance, to prepare the LHC for running at 13 TeV
Recent publications from CMS use data from the LHC's first run to shed light on the properties of the Higgs boson
Watch a timelapse video of the huge LHC detectors ALICE, ATLAS, CMS and LHCb preparing to start up again
With ‘LHC Season 2’ starting soon, running at a new high energy, the LHC key is handed back to the machine operators today
The CERN cryogenics team are filling the LHC with liquid helium, cooling entire sections to below 4K
CERN teams are carrying out all required tests to get proton beams back in the LHC for March 2015
Magnets in one sector of the accelerator are fully prepared for the restart at higher energies
Weekend tests with beams brought protons just short of the LHC
The Open Data Portal makes data from real collision events at the LHC openly available to all
In CERN’s 60th year, the first proof of the existence of the Higgs boson earns a Guinness World Record for CERN, ATLAS and CMS
A team is on call 24 hours a day to monitor technical systems and quickly respond to alerts across CERN's accelerator complex
In preparation for the LHC's next run, physicists are calibrating the ATLAS experiment - with high-energy rays from outer space