CERN Accelerating science

This website is no longer maintained. Its content may be obsolete. Please visit for current CERN information.

Home | Sitemap | Contact us
this site all CERN
The Proton Synchrotron (PS) in its tunnel

PS – the Proton Synchrotron

A versatile juggler of particles

The Proton Synchrotron (PS) is a key component in CERN’s accelerator complex, where it accelerates protons delivered by the PS Booster or heavy ions from the Low Energy Ion Ring. In the course of its history it has juggled with 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. CERN’s first synchrotron, it was initially host to CERN’s particle physics programme. However, when CERN 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 m, the PS has 277 conventional (room temperature) electromagnets, including 100 dipoles to bend the beams round the ring, and it 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.

Related links