HOW DOES IT WORK?
 
Particle accelerators, in general, are composed of three main parts: a source of particles(usually some kind of cathode), a partial vaccuum in a copper tube(where the particles move), and a device to speed up the particles. Copper tubing is used because of its conductivity.
 
In a linac(high energy linear particle accelerator), particles are moved as an electromagnetic wave and accelerated by a series of electromagnetic plates. AC voltage is applied to each one so that when the particles approach the plate, an opposite polarity charge attracts them. As they pass through the plates, the plate polarity is switched so that after it is attracted, it is repelled towards the next plate. In some accelerators, cavities are used instead of plates.
 
These radio-frequency(RF) cavities resonate amplified radio waves - the walls of the cavities reflect the waves, and a wave that is resonant with the cavity will bounce around in it so that as more waves enter the cavity, all of them bounce around together and combine together, resulting in an amplified standing wave. Often a device called a klystron is used to generate and resonate radio or microwaves.
 
As the particles travel through a cavity, they are accelerated by the energy of the wave. Magnets are also used to concentrate the particles into a beam.
 
Lower energy linear accelerators, like a cathode ray tube, just use one pair of electrodes and DC voltage to accelerate electrons.
 

Cavities in the SLAC.
 
The difference in a circular synchrotron accelerator from a linear accelerator is that dipole magnets are used to bend the particle track into a circle. The current of particles is perpendicular to the magnetic field and the consequential perpendicular force causes the particles to move in a circular path in a vacuum. By applying energy, the particles spiral outwards and speeds up. High speeds are achieved by repeatedly sending the particles through the same RF cavities over and over again in a loop.
 
Particles in a cyclotron travel in a circular path between two D-shaped magnets until reaching a gap, where a magnetic field is pointing downwards(is perpendicular). This accelerates the particles. The AC voltage frequency is set up so that by the time the particles come back to the gap again, field has reversed to continue accelerating them in a circle. The maximum acceleration a cyclotron could produce was dependent on the size of the magnets, and cyclotrons fell out of use after synchrotrons were developed.
 

A diagram of a cyclotron, with D-magnets, from the SLAC.
 
Finally, atom smashers have detectors to gather information about the particles - detectors for particle tracks(vertex detector), radiation(Cerenkov detector), energy(liquid argon calorimeter stops most of the particles to measure them),