Particle Accelerators

What is a particle accelerator and why do we use them?

Just after the Big Bang, the universe was a rapidly expanding ball of fundamental particles. As the universe expanded, it cooled and the particles decayed, changing into other fundamental particles. These particles then joined together and gradually formed the matter that we see around us today.

In particle accelerators we smash beams of particles together in head-on collisions that are energetic enough to turn the clock back to just after the Big Bang. The more energetic the collisions, the more likely we are to make fundamental particles appear again. Once we've produced fundamental particles we can study their behaviour to find out why the universe is made the way it is.

What does a particle accelerator look like?

The biggest particle accelerator in the world is at CERN, the centre for particle physics research, just outside Geneva in Switzerland.

Above ground, you wouldn’t know anything about it, but if you were to go 100m underground, you’d find yourself in a circular tunnel, about the size of a London underground tube tunnel. This is where the Large Hadron Collider (LHC), the world’s most powerful particle accelerator is being built.

Inside the LHC tunnel
(Credit: CERN)

The LHC tunnel runs for about the same distance as the London Underground Circle Line – 27km in a ring underneath the French/Swiss border. If you were inside the accelerator tunnel you would see a tube which runs continuously in either direction. This tube is the "beam pipe" - so-called because inside here, two beams of particles fly round the tunnel. The beams are accelerated to very high energies by magnets surrounding the beam pipe. These make sure that the two particle beams circulate in opposite directions without crashing into each other. When the beams of particles reach their final top energy, the magnets alter their path and bring them into collision at pre-determined points around the accelerator ring.

By this time the particle beams are travelling so close to the speed of light that they collide forty million times a second. Inside each collision we have a snapshot of the fundamental particles that last existed billionths of a second after the Big Bang. Now all we have to do is build gigantic particle detectors at each collision point to try and work out exactly what went on ....

What is particle physics?

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