Several kinds of particle accelerators exist. Primarily one differentiate between linear and circular accelerators, which depends on the geometry (straight or round) of the accelerator.
Then there are two methods to create particle collisions. The first is to let the particles in the accelerator collide with a target, e.g. liquid hydrogen, at rest. This is called fixed target experiments. The second is to let the particles in the accelerator collide with each other. The particles are then moving in opposite directions in partly separated orbits. Such an accelerator is called a collider.
In all accelerators are the particle beams kept in a vacuum tube so that the particles will not collide with air molecules.