fixed target:
injector to a circular accelerator: 
linear collider: 
The beams from a circular accelerator can be used for colliding-beam experiments or extracted from the ring for fixed-target experiments:
colliding beam:
extracted for fixed target:
Circular accelerators use magnets and accelerating regions efficiently, since the particles go around many times, getting multiple kicks of energy each time. This also provides many chances for collisions at the places where the particle beams are made to cross.
