The Ring cyclotron is a separated sector cyclotron with a fixed beam energy of 590 MeV, built by PSI and commissioned in 1974. The 72 MeV proton beam from the Injector 2 cyclotron enters the Ring from the back and is injected at a radius of 2.1 m. The protons are accelerated in about 180 revolutions and are then extracted at the full energy at a radius of 4.5 m. Before 1984, the protons were pre-accelerated by the now decommissioned Injektor 1 cyclotron built by Philips.
The design of the Ring is based on criteria that allow operation at very high beam intensities: an open structure of four large high-power RF-cavities providing a high acceleration voltage at a frequency of 50 MHz, and a flat-top cavity operating at the third harmonic (150 MHz), which increases the phase acceptance and reduces the energy spread. The resulting large and phase-independent energy gain per revolution gives good turn separation and allows for beam extraction with low losses. This is a mandatory condition for high current operation in a high power cyclotron.
