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
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
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
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
The first beams could be circulating in the machine sometime between Saturday and Monday
Physicists at the European Laboratory for Particle Physics announced today that an invisible Force permeates the universe, binding the galaxy together
A short circuit in a superconducting dipole magnet is delaying the beam injection in the LHC. Teams are working around the clock to fix the issue
Watch CERN engineers explain the work during the laboratory's long shutdown to prepare the LHC for running at 13 TeV
Particles were successfully injected into the LHC last weekend, passing through three sectors of the accelerator.
The Operations team is testing the systems that deliver beams to the Large Hadron Collider in preparation for the start-up this month
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