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.



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

Featured updates on this topic

11 Feb 2014 – A team composed of CERN staff, industrial support and mechanics from Pakistan have given access to the last LHC splice for inspection

19 Dec 2013 – Higgs boson decays, a Nobel prize for Higgs and Englert and a huge Open Days event were among the big stories at CERN this year

25 Nov 2013 – When night falls over CERN, a team of X-ray experts go underground to perform tests on the Large Hadron Collider


4 Mar 2014 – The start of the LAA project in 1986 propelled electronics at CERN into the era of microelectronics

12 Nov 2013 – Collider, a new exhibition about the LHC, opens in London this week. It will stay for 6 months before a planned international tour

26 Sep 2013 – CERN and Google have joined forces to create panoramic virtual tours of the CERN site

25 Jul 2013 – Results presented by LHC experiments give further credence to strength of Standard Model

27 Jun 2013 – Conception of the LHC experiments took many years, this year three of them celebrate their 20th anniversaries

7 Jun 2013 – Watch a quadrupole magnet being lowered into the ALICE cavern for transportation to its required spot on the LHC

8 May 2013 – A new result from the CMS collaboration takes a step toward revealing the origin of the mysterious "ridge effect"

25 Apr 2013 – The Science Museum in London is launching a new exhibition featuring digital detector caverns and magnets from the LHC

9 Apr 2013 – CERN surveyors have taken new measurements of the height of the LHC magnets in the tunnel, to see how geological shifts may be affecting the machine

19 Mar 2013 – Watch Jean-Phillipe Tock of the Technology department explain how CERN technicians are upgrading interconnections on the Large Hadron Collider