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 are the most exciting these days.

In a colliding-beam experiment two beams of high-energy particles are made to cross each other.

The advantage of this arrangement is that both beams have significant kinetic energy (energy of speed), so a collision between them is more likely to produce a higher mass particle than would a fixed-target collision at the same energy. Since we are dealing with particles with a lot of momentum, these particles have short wavelengths and make excellent probes.