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
The LHC and its experiments are back in action, now taking physics data for 2016
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The LHCb experiment has observed for the first time particles made up of five quarks.
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The first planned technical stop of the LHC starts on Monday, with five days of maintenance work scheduled for the accelerator and its experiments.
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The LHC has introduced beam for the first time since the year-end technical stop began in December 2015
An update on the maintenance work that’s been carried out on the LHC, the experiments and the machines during the year-end technical stop
In preparation for civil engineering work for the High-Luminosity Large Hadron Collider, vibration measurements have been carried out near the LHC
Linac 4 now reaching milestone energy of 50MeV to act as replacement for ageing Linac2, before taking over at head of accelerator chain in 2020
The accelerator is colliding leads ions at an energy about twice as high as that of any previous collider experiment
The Large Hadron Collider today collided protons at lower energies than usual to pave the way for studying lead-ion collisions