My own career in science has been intimately tied up in the transition from the old fixed-target technique to colliding-beam work. I have led a kind of double life as both a machine builder and as an experimenter, taking part in building and using the first of the colliding-beam machines, the Princeton–Stanford Electron–Electron Collider, and building the most recent advance in the technology, the Stanford Linear Collider. The beginning was in 1958 and, in the more than three decades since, there has been a succession of both electron and proton colliders that have increased the available center-of-mass energy for hard collisions by more than a factor of 1000.

The history of that advance for both electron and proton colliders (constituent center-of-mass energy is plotted versus time of the first physics experiment) is shown in Fig. 15.1. The important number for the experimenter, the constituent center-of-mass energy, has increased by about a factor of 10 every 12 years for both kinds of systems. On the electron line, one can see a kind of complete cycle in accelerator technology from the birth of the colliding-beam storage ring, to its culmination in LEP II, and the beginning of the next technique for high-energy electron collisions, the linear collider. On the proton line, one has gone from the first bold initiative, the ISR at CERN, which used conventional magnets, to the superconducting magnets that are used in all proton colliders built today.