The ISR - a pioneering machine

31 January 2001

The ISR - a pioneering machine

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The Intersecting Storage Rings (ISR) at CERN, the European centre for research in particle physics near Geneva, was the first machine to provide head-on collisions between proton beams. When it started up in 1971, it dramatically increased the highest energies explored by particle physicists, as much more energy is released when particles collide head-on than when a beam collides with a fixed target. With a diameter of 300-metre the ISR was not a big machine; nor was it an accelerator. Instead it stored protons transferred from CERN's Proton Synchroton, and stacked them in tight bunches in two interlaced pipes - the image shows the pipes crossing at one of their intersections. To store the protons in this way required new techniques to produce the very high vacuum needed to keep the protons circulating. New methods for controlling particle beams were also developed, in particular, Simon van der Meer's invention of 'stochastic cooling'. This ultimately won him the Nobel Prize in 1984, after the discovery of the W and Z particles, carriers of the weak force.

Credit: CERN Photo

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