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 Large Hadron Collider 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
The LHC is operating for several hours with the nuclei of xenon atoms
The Train Inspection Monorail (TIM) is equipped with a camera and several measurement sensors to monitor the LHC tunnel in real-time
The LHC performance continued to surpass expectations when this week it achieved 2220 proton bunches
As CERN’s winter shutdown draws to a close, watch this video to see what has been going on underground
CERN celebrates 25 years since the beginning of the LHC experimental programme
Before the LHC was shut down for the winter, the operators tested techniques under development for its successor, the High-Luminosity LHC (HL-LHC)
The LHC’s 2017 proton run has ended with record luminosity. The special runs will now take place before the winter shutdown.
With 19 days still to go, the LHC has reached its 2017 production target, delivering more than 45 inverse femtobarns to the experiments
CMS experiment delves into the mystery of neutrino masses
An animation made with TED-ED to explore empty space and why it is important for experiments at CERN
The Large Hadron Collider has established a new record of luminosity, delivering a huge amount of data to its experiments
The LHC has been accelerating more and more protons, and to allow the machine to reach its maximum intensity, it will undergo a thorough scrubbing.
Data-taking has started again at the LHC: the experiments are continuing their exploration of physics at the unprecedented energy of 13 TeV.