A Linear or Circular Accelerator?
All accelerators are either linear or circular, 
the difference being whether the 
particle is shot like a bullet from a gun 
(the linear accelerator) or whether the 
particle is twirled in a very fast circle, 
receiving a bunch of little kicks each 
time around (the circular accelerator). Both types accelerate particles by 
pushing them with an electric-field wave.
- 
Linear accelerators (linacs) are used for fixed-target 
experiments, as injectors to circular accelerators, or as linear colliders.
 - Fixed target: 
- Injector to a circular accelerator: 
- Linear collider: 
   - 
The beams from a circular accelerator 
(synchrotron) can be used for 
colliding-beam experiments or 
extracted from the ring for fixed-target experiments: 
 - Colliding beams: 
- Extracted to hit a fixed target: 
  
The particles in a circular accelerator go around in circles because large 
magnets tweak the particle's path enough to keep it in the accelerator.
How do a 
circular accelerator's 
magnets make particles go in a circle?