only one proton. These protons leave the source with a potential of 60 kilovolts and are then subjected to a further voltage of 810 kilovolts in an accelerator tube. Both voltages are supplied by a Cockcroft-Walton accelerator. With a total of 870 kilovolts, the protons are accelerated to a speed of 46 million km/h or 4 percent of the speed of light. The protons are then fed into the Injector-2. Injektor-1 With Injector-1, operating currents of 170 µA and peak currents of 200 µA could be reached. It was also used for low energy experiments, for OPTIS eye therapy and for the LiSoR experiment in the MEGAPIE project. Since December 1, 2010, this ring accelerator has been out of operation. Injektor-2 The Injector-2, which was commissioned in 1984 and developed by what was then SIN, replaced the Injector-1 as the injection machine for the 590 MeV ring cyclotron. Initially, it was possible to operate Injector-1 and Injector-2 alternately, but now only Injector-2 is used to feed the proton beam into the ring. The new cyclotron has enabled an increase in the beam current from 1 to 2 mA, which was the absolute record value for the 1980s. Today, the injector-2 delivers a beam current of ≈ 2.2 mA in routine operation and 2.4 mA in high current operation at 72 MeV, which is about 38 percent of the speed of light. Originally, two resonators were operated at 150 MHz in flat-top mode to enable a clear separation of the proton orbits, but these are now also used for acceleration. Part of the extracted 72 MeV proton beam can be split off for isotope production, while the main part is fed into the Ring Cyclotron for further acceleration. Ring 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. In addition to the