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Intersecting Storage Rings site1971 1986

1971: the world’s first proton–proton collider

The world’s first proton–proton collider, the Intersecting Storage Rings (ISR), came into operation in January 1971.

When high-energy particles from an accelerator slam into a stationary target, most of the valuable projectile energy is taken up by the target recoil, and only a small fraction actually feeds the collision. In the 1950s, physicists realized that if two particle beams could be fired at each other, no recoil energy would be wasted, making for much more efficient use of energy in the collisions.

While other physics laboratories concentrated on building machines to collide beams of electrons, CERN worked with protons. The idea was to use the Proton Synchrotron (PS) to feed two interconnected rings, where two intense proton beams could be built up and then made to collide.

The Intersecting Storage Rings (ISR) were formally approved for construction in 1965. The 300-metre diameter ISR was not a big machine by today’s standards, but there were many challenges to overcome to make it work. New high-vacuum techniques had to be developed and new methods for controlling particle beams mastered. The ISR produced the world’s first proton–proton collisions on 27 January 1971, providing CERN with valuable knowledge and expertise for its subsequent colliding-beam projects.

With the construction of the ISR, CERN became an international organization on the ground, as well as in its organizational structure. The machine was constructed in France on land adjoining the original Meyrin site in Switzerland.