The Speed of Things

[WeAreBongo]

What proportion of the speed of light has mankind managed to accelerate something to, be it a particle or a pea?

[WaldoMcFroog]

I did it - speed of light - just a few minutes ago.

I lit a match. ;-)

[jake-the-peg]

Particle accelerators live Cern or Fermilab accelerate particles like protons or electrons to speeds so close to the speed of light that talking about it in terms of speed becomes difficult and not really very useful.

For example at FermiLab in the US they have the ability to get a proton up to 99.99996% the speed of light. Imagine trying to say that in conversation - how many 9's?

So they refer to it in terms of the energy that they can put into a particle.

If you accelerate an electron through 1 volt that's an electron volt of energy.

Inside a television tube the electrons are accelerated by about 20,000eV or 20KeV

FermiLab manages 1Tev which is 1,000,000,000,000 eV or about 50 million times more than a TV.

But that's nothing next year the big collider at Cern will start up and will manage 14 times more energy than FermiLab

It's quite a beast

[WeAreBongo]

Thanks Jake, how do these accelerators accelerate particles? When they collide particles at high speed, how do they ensure they hit each other? - they're tiny!!

[jake-the-peg]

The acceleration is quite easy, there's a big ring with a tube and lots of magnets to keep the particles in the tube.

Then every so often there's an accelerating cavity with an electric field that gives them a push.

When they reach the maximum energy that the ring can achieve (that's determined by how strong the magnets keeping them in are) they're released at the target.

There are two basic types of acceletator - those who hit a fixed target and those who have two rings and collide the beams into each other. the latter type are, unoriginally called colliders.

In a standard machine hitting the target's not that hard the beam typically hits a lump of material or just the body of the detectors themselves.

In a collider getting the beams to hit each other is much harder and there are fewer events to study but obviously you have twice the energy - two cars hitting head on sort of thing

However there are somethings you can't do in a collider - for example you're limited to stable charged particles like electrons or protons.

If you have a fixed target you can create what are called secondary beams - in those you thump your target and filter out all the debris you don't want to leave you with a beam of say high energy neutrinos which you can then let hit your real target