What is the Large Hadron Collider?

LHC accelerator tunnel
First superconducting magnets installed in the LHC tunnel in April 2005. Image © CERN
The LHC at CERN, the European Organization for Nuclear Research, is the largest, most complex and most powerful particle accelerator ever built. It operates in a circular 27-kilometer tunnel about 100 meters underground, between Switzerland's Lake Geneva and France's Jura mountains. The LHC creates almost a billion proton-proton collisions per second at an energy of 8 trillion electron volts, the highest any accelerator has achieved.

At the heart of the LHC are superconducting magnets made of niobium-titanium. Cooled to nearly absolute zero by superfluid helium, the coils of these magnets conduct electricity without resistance. The LHC's 1,232 dipole magnets guide the opposing beams of speeding protons in their circular orbits. Several thousand additional magnets fine-tune the beams' orbits, and some 400 quadrupole magnets focus the protons into hair-thin beams that collide within the LHC experiments. Cryogenic, electronic and information systems of unprecedented scope and complexity support the LHC's 'round-the-clock operation.

The LHC physics program mainly uses proton-proton collisions, but the LHC can also accelerate lead ions to create collisions with an energy of 1,150 TeV during shorter running periods, typically one month per year.