Synchrotrons are a class of particle accelerators. The highest energy accelerators in use today, such as the Tevatron at Fermilab and the large electron positron collider (LEP) at the European Organization for Nuclear Research (CERN). The synchrotron incorporates improvements over the simpler cyclotron, which allows it to be used with highly relativistic particles. Instead of one large magnet with a constant magnetic field as found in a cyclotron, the synchrotron has many smaller magnets placed around a ring. As the particles are accelerated, they become heavier according to special relativity. The path of the particles depends on their mass and the magnetic field acting on them; as the particles become more massive, the magnetic field must be turned up in order to keep them traveling around in a circle. Since there are many smaller magnets instead of one large magnet, they can be controlled individually to keep the particles traveling through the accelerator.

A special application is the radiation synchrotron. Unlike synchrotrons built to study high-energy physics, which are designed to minimize the amount of radiation produced, radiation synchrotrons are built specifically to produce high-energy x rays and gamma rays. They have the advantage of producing very narrow and very bright beams of radiation, which makes them ideal for studying condensed matter and biological systems.