The Large Hadron Collider

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.

The Large Hadron Collider is the world's largest and most powerful particle accelerator (Image: CERN)

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 detectorsATLAS, CMS, ALICE and LHCb.

Explore the CERN Control Centre with Google Street View (Image: Google Street View)


Technicians get around the tunnel on bicycles

Facts and Figures [PDF]

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

Download the LHC guide [PDF]

CERN firefighters during their daily safety training

Safety of the LHC

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

Read about the safety of the LHC


Virtual tour

Take a virtual tour of the Large Hadron Collider

Voir en français

Featured updates on this topic

25 Nov 2016 – The Train Inspection Monorail (TIM) is equipped with a camera and several measurement sensors to monitor the LHC tunnel in real-time

19 Aug 2016 – The LHC performance continued to surpass expectations when this week it achieved 2220 proton bunches

8 Jul 2016 – The LHC has chalked up a series of new records, providing its experiments with a torrent of new data

3 Jun 2015 – The Large Hadron Collider is colliding particles at unprecedented energy, marking the start of the accelerator's second physics run


6 Jun 2017 – 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.

23 May 2017 – Data-taking has started again at the LHC: the experiments are continuing their exploration of physics at the unprecedented energy of 13 TeV.

15 May 2017 – Adjustments to the thousands of pieces of equipment making up the LHC are ongoing before data taking can start for 2017

29 Apr 2017 – For the first time this year, the LHC is circulating beams of protons, following a 17-week-long extended technical stop

29 Apr 2017 – We meet Rende Steerenberg, who is the group leader for the accelerator and technical teams

14 Mar 2017 – See in images how the “heart” of the CMS detector, its Pixel Tracker, was replaced

5 Aug 2016 – Particle physicists are showcasing a wealth of brand new results from LHC experiments at CERN, at the “ICHEP 2016” conference in Chicago

2 Jun 2016 – Higher intensity beams are circulating in the LHC providing more and more collisions to the experiments

10 May 2016 – A design for a Lego LHC needs about 3000 more signatures for Lego to consider it for a new product

9 May 2016 – The LHC and its experiments are back in action, now taking physics data for 2016