What is the Large Hadron Collider?

THE Large Hadron Collider - a "Big Bang" atom-smasher in Geneva - is set to fire up again today after three YEARS of closure.

The vast scientific accelerator is being launched for its third run to research the extremes of particle physics which make up the universe.

What is the Large Hadron Collider?

The headquarters of CERN, the European Council for Nuclear Research, are based in Geneva on the Franco-Swiss border.

One hundred meters underground, lies the LHC - a vast ring of superconducting magnets for landmark scientific research.

Accelerators were invented in 1930s to investigate the structure of atoms, but the LHC is the most monumental of its kind.

Experiments conducted inside the massive machine help scientists reach ground-breaking discoveries about how the universe works - including the confirmation of a "God particle" 10 years ago.

What does the Large Hadron Collider do?

The enormous structure fires two high energy particles beams directly at each other to make them collide.

They travel at close to the speed of light with such precision that scientists compared their experiments to firing two needles at each other from over six miles apart so that they meet halfway.

The beams are fired in opposite directions in two tubes kept at ultrahigh vacuum and get guided around the accelerator ring by the super strong magnetic field.

These electromangnets are kept at -456.34 Fahrenheit - colder than outer space - to run without resistance or energy loss.

Once up and running again, the LHC will run around the clock for close to four years at a record energy, providing greater precision and discovery potential than ever before.

Scientists will be looking at the Higgs boson, or "God particle", 10 years after its discovery with unprecedented precision and in new channels.

They will also study the properties of matter under extreme temperature and density, searching for dark matter and other new phenomena.

How big is the Large Hadron Collider?

The accelerator is an eye-watering 17 mile ring of superconducting magnets, made up of a chain of several structures.

Thousands of magnets propel the beams around the LHC, all of different varieties and sizes.

Among these magnets are 1232 15-meter long dipole magnets to bend the beams, and 392 5-7-meter long quadrupole magnets to focus the beams.

A third type of magnet "squeezes" the particles closer together just before they hit each other, to increase their chances of collision.

Can you visit the Large Hadron Collider?

Visitors cannot actually access the tunnel of the Large Hadron Collider, but you can head to the CERN headquarters in Geneva to learn a lot about particle physics.

Guided tours of the wider Laboratory are completely free, although reservation is required and places are limited.

Groups of 12 or more people must be booked online up to 9 months in advance, whereas individuals can register on site upon availability.

Underground tours of detectors are very limited but there is plenty to see elsewhere.

As it lies on the border, CERN has two main sites - one in France and the other in Switzerland.

The visitor reception can be found at the Meyrin site in Switzerland.