Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) uses a system of intense radio waves to give the particle beam a little extra 'kick' of energy to accelerate it each time it travels around the ring. This is called the radio frequency, or RF, system. The RF cavity system is shown here. The Relativistic Heavy Ion Collider (RHIC) one of only two operating heavy-ion colliders, and the only spin-polarized proton collider ever built. Located at Brookhaven National Laboratory (BNL) and used by an international team of researchers, it is the only operating particle collider in the US.