A storage ring is a type of circular particle accelerator where the particle beam may be kept in circulation for extended periods of time, possibly hours. They are an evolution of the synchrotron design.
They were invented by American physicist Gerard K. O'Neill in 1956 as a method of constructing a collider, although the first important storage ring, the Italian ADA, was constructed in 1961. Its revolution was being the first matter-antimatter collider in history, being an electron-positron collider reaching around 100 MeV in center-of-mass energy.
The Large Hadron Collider (LHC) of CERN, as of 2025 the most powerful collider in the world, is primarily a proton storage ring, though it's also used for heavy ion collisions like proton-lead and lead-lead.