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
One week of LHC operation is being devoted to scrubbing the beam pipes to eliminate electron clouds, which can destabilise the beam.
The Large Hadron Collider is colliding particles at unprecedented energy, marking the start of the accelerator's second physics run
After two years of intense maintenance and consolidation the Large Hadron Collider is back in operation
Today the ATLAS and CMS experiments presented for the first time a combination of their results on the mass of the Higgs boson
Physicists are using LHC detector technology to retrieve Native American music from old recordings
Follow all the action live on our blog "LHC Season 2: New frontiers in physics"
On 3 June, experiments at the LHC are set to collect their first physics data in two years, marking the start of the accelerator's second run
The MOEDAL, TOTEM and LHCf experiments are preparing to collect data from collisions in the LHC at 13 teraelectronvolts
Last night, for the first time, protons collided in the Large Hadron Collider (LHC) at the record-breaking energy of 13 TeV. See the first images
These first collisions at 13 TeV in the LHC are to set up systems that protect detectors from stray particles before they are fully switched on
Watch 11 physicists from the LHC experiments ALICE, ATLAS, CMS and LHCb explain what they hope to discover during the accelerator's second run
This morning, for the first time in two years, proton-proton collisions were delivered to the LHC experiments at injection energy: 450 GeV per beam
Last night the LHC operations team successfully circulated a beam at 6.5 TeV - one of many steps before the LHC can deliver collisions to experiments
With proton beams back in the LHC, operations experts have weeks of work to do before they can collide beams in experiments at the energy of 13 TeV