The Proton Synchrotron (PS) is a key component in CERN’s accelerator complex, where it usually accelerates either protons delivered by the Proton Synchrotron Booster or heavy ions from the Low Energy Ion Ring (LEIR). In the course of its history it has juggled many different kinds of particles, feeding them directly to experiments or to more powerful accelerators.
The PS first accelerated protons on 24 November 1959, becoming for a brief period the world’s highest energy particle accelerator. The PS was CERN’s first synchrotron. It was initially CERN's flagship accelerator, but when the laboratory built new accelerators in the 1970s, the PS’s principal role became to supply particles to the new machines. Over the years, it has undergone many modifications and the intensity of its proton beam has increased a thousandfold.
With a circumference of 628 metres, the PS has 277 conventional (room-temperature) electromagnets, including 100 dipoles to bend the beams round the ring. The accelerator operates at up to 25 GeV. In addition to protons, it has accelerated alpha particles (helium nuclei), oxygen and sulphur nuclei, electrons, positrons and antiprotons.