sics went mad.
Types of Accelerators
The linear accelerator is the simplest type of accelerator. Fundamentally it is a long line of coils (or drift tubes) which charged particles are accelerated through. However, there are two types of linear accelerator. One type of accelerator is the standing-wave linear accelerator; particles travel along a cylindrical vacuum tank through a series of drift tubes, separated by gaps. As the particles cross the gaps, electromagnetic waves, called standing waves, accelerate them. (Or, more simply put, as the particle passes through the drift tube, the current through it is swapped. If the current was kept it would pull the particle back towards the tube when it leaves. Changing the current repels the particle from the end of the tube.) The waves provide an electric field that speeds up the particles by acting on their electric charges.
This type of accelerator can only manage to accelerate particles to 200 MeV. (Ah, if you don't know what this is you should try and find out.) Physicists mainly use them as a primary accelerator that feeds into a synchrotron. In industry and medicine they are used as powerful X-ray machines.
The other type of linear accelerator is the travelling-wave linear accelerator. This speeds particles through a single long pipe by an electromagnetic wave that travels with the particle. This high-frequency wave is called a travelling wave. As long as the wave speed matches the particles' speed, the particles will continue to gain energy.
This type of accelerator can accelerate particles to 30 GeV, this is the Stanford Linear Collider, the longest accelerator in the world at 3.2km. The SLC is used to smash electrons and positrons into each other at 50 GeV to create uncharged weak bosons (the particle for the nuclear weak force).
The more advanced type of particle accelerator is the cyclotron. The idea behind these accelerators relies on the understanding of the effects of fields on charged particles. A cyclotron is made of two magnets and two D-shaped electrodes, which physicists like to call 'Dees'.
The particles are forced into a circular path by the magnetic field; the electrodes are supplied with an alternating current that attracts and repels the particle, thus accelerating the particle. This type of accelerator is much easier to make than a few miles of linear accelerator. However, it is not perfect. As the electrodes accelerate the particles they increase the radius of their path. This means that as the need to produce a faster moving particle the larger the radius of the cyclotron has to be. This is not really a problem for the electrodes but it is a huge problem for the magnets!
With most complicated problems it is often the simplest solution that works best. The linear accelerator is very simple, and does not require a huge magnet. The problem is it has to be very long. How could there be a simple way of making it shorter and more useful? Well, make it circular. The problem with this is that you have to force the electrons into a circular path using magnets. Unlike having a single magnet providing the force to push the particle into a circular path this system requires a series of magnets positioned so as to deflect its path into a circle.
This type of accelerator again suffers the same problem as the cyclotron, yet it's problems are more easily overcome. As the particle travels faster the mass increases, and so the force needed to pull it around in a circle increases. In the synchrotron this is done by increasing the strength of electromagnets used to turn the particle. As soon as the particle is accelerated it needs the force applied to it to increase. In this case the energy required to keep the particle in a circular path instantly becomes too much for any conventional system. This is the main reason that CERN is 27 kilometres long.
Rather worryingly the largest particle accelerator in the world is not the most powerful. CERN can produce particles of 50GeV, which is fairly impressive but not as impressive as the Fermi National Accelerator Laboratory (Ferm