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 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

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Featured updates on this topic

1 Sep 2015 – At the 2015 LHCP conference the collaborations presented for the first time combined measurements of many properties of the Higgs boson

14 Jul 2015 – The LHCb experiment has observed for the first time particles made up of five quarks.

25 Jun 2015 – One week of LHC operation is being devoted to scrubbing the beam pipes to eliminate electron clouds, which can destabilise the beam.

11 Jun 2015 – The first planned technical stop of the LHC starts on Monday, with five days of maintenance work scheduled for the accelerator and its experiments.

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


26 Nov 2015 – 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

25 Nov 2015 – The accelerator is colliding leads ions at an energy about twice as high as that of any previous collider experiment

19 Nov 2015 – The Large Hadron Collider today collided protons at lower energies than usual to pave the way for studying lead-ion collisions

4 Nov 2015 – After some 400 trillion proton-proton collisions delivered to both ATLAS and CMS, the accelerator will now switch to its heavy-ion programme

3 Sep 2015 – During this week's planned technical stop, engineers modify the electrical system that protects magnet components from high current

24 Aug 2015 – The LHC Operations team is tackling the challenges of a demanding beam regime with a series of rigorous tests

20 Jul 2015 – In a new blog series, ATLAS-collaboration members from all over the world share their stories

12 Jun 2015 – Physicists are using LHC detector technology to retrieve Native American music from old recordings

3 Jun 2015 – Follow all the action live on our blog "LHC Season 2: New frontiers in physics"

2 Jun 2015 – 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