Like the Injector-2, the Ring Cyclotron, which has a circumference of about 48 m, went into operation in 1974. It was specially developed at SIN and is at the heart of the PSI proton accelerator facilities. The protons are accelerated to 80 percent of the speed of light on the approximately 4 km long track, which the protons cover inside the ring in 186 laps. This corresponds to a kinetic energy of 590 MeV. Only three such rings exist worldwide, namely: TRIUMF in Vancouver, Canada; LAMPF in Los Alamos, USA; and the one at PSI. TRIUMF has only reached beam currents of 500 µA and LAMPF 1 mA.