CERN Accelerator

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Lore & Background

The LHC was built by CERN between 1998 and 2008 in collaboration with over 10,000 scientists and hundreds of universities and laboratories across more than 100 countries. It occupies a tunnel 27 kilometres in circumference, originally constructed between 1983 and 1988 for the Large Electron–Positron Collider. The tunnel crosses the border between Switzerland and France at four points, with most of it in France. The collider has four crossing points where accelerated particles collide, with nine detectors positioned around them. The LHC primarily collides proton beams, but can also accelerate beams of heavy ions such as lead–lead and proton–lead collisions. The first collisions in 2010 at 3.5 TeV per beam set a new world record. The Higgs boson discovery was announced in 2012, completing the Standard Model. Between 2013 and 2015, the LHC was shut down and upgraded, after which it reached 6.5 TeV per beam. At the end of 2018, it was shut down for maintenance and further upgrades, reopening in April 2022.

In Their Own Story

The LHC's goal is to allow physicists to test predictions of different theories of particle physics, including measuring the properties of the Higgs boson, searching for particles predicted by supersymmetric theories, and studying unresolved questions. Many physicists hope it will help answer fundamental open questions about the basic laws governing interactions among elementary particles and the deep structure of space and time. The LHC collisions have explored whether all known particles have supersymmetric partners, whether there are extra dimensions predicted by string theory, and the nature of dark matter. Other questions include whether the electroweak force and strong nuclear force are manifestations of a single unified force, why gravity is so much weaker than the other forces, and the nature of quark–gluon plasma. The LHC draws roughly 200 MW of electrical power from the French grid, with the accelerator and detectors drawing about 120 MW. Each day of operation generates 140 terabytes of data. When running at 6.5 TeV per proton, the protons have a Lorentz factor of about 6,930 and move at about 0.999999990 c, about 3.1 m/s slower than the speed of light.

Reader's Guide

The LHC is contained in a circular tunnel with a circumference of 26.7 kilometres at a depth ranging from 50 to 175 metres underground. The tunnel contains two adjacent parallel beamlines with beams traveling in opposite directions. Some 1,232 dipole magnets keep the beams on their circular path, while 392 quadrupole magnets keep them focused. About 10,000 superconducting magnets are installed, with each dipole magnet having a mass of 35 tonnes. About 96 tonnes of superfluid helium-4 keeps the magnets at 1.9 K. The LHC uses 470 tonnes of Nb–Ti superconductor. Protons are bunched into up to 2,808 bunches with 115 billion protons each, colliding at intervals of 25 nanoseconds. The design luminosity of 10^34 cm−2s−1 was first reached in June 2016, and by 2017 twice this value was achieved. Before injection, particles are prepared by Linac4 generating 160 MeV negative hydrogen ions, then the Proton Synchrotron Booster, Proton Synchrotron (26 GeV), and Super Proton Synchrotron (450 GeV) before injection into the main ring. The LHC physics programme is mainly based on proton–proton collisions, with shorter periods for heavy-ion collisions, typically one month per year.

Did You Know?

• The LHC tunnel is 27 kilometres in circumference and as deep as 175 metres beneath the France–Switzerland border.
• The first collisions in 2010 achieved an energy of 3.5 TeV per beam, about four times the previous world record.
• The LHC uses about 96 tonnes of superfluid helium-4 to keep its superconducting magnets at 1.9 K (−271.25 °C).
• Each day of LHC operation generates 140 terabytes of data.
• Protons in the LHC travel at about 0.999999990 c, only about 3.1 m/s slower than the speed of light.