The CERN Intersecting Storage Rings: The Leap into the Hadron Collider Era.

The history of colliding-beam devices can be traced back to 1956, when a group at the Midwestern Universities Research Association put forward the idea of particle stacking in circular accelerators. Of course, people who worked with particle accelerators had already speculated about the high center-of-mass energies attainable with colliding beams, but such ideas were unrealistic with the particle densities then available in normal accelerator beams. The invention of particle stacking fundamentally changed this situation. It opened up the possibility of making two intense proton beams collide with a sufficiently high interaction rate to enable experimentation in an energy range otherwise unattainable by known techniques. A group at CERN started investigating this possibility in 1957, first by studying a special two-way fixed-field alternating gradient accelerator and then in 1960 by turning to the idea of two intersecting storage rings that could be fed from the CERN 28 GeV Proton Synchrotron (PS). This change in concept for these initial studies was stimulated by the promising performance of the PS at the very start of its operation in 1959. In 1961 the Accelerator Research Division at CERN had gained sufficient confidence to present its first proposal for a 2 x 25 GeV storage ring system. This system was intended essentially for protons, but other particles were mentioned in the proposal. This led to a series of important actions. First, in 1962, France offered a site next to the original CERN site. [ABSTRACT FROM AUTHOR]