The original concept behind the construction of particle accelerators was to build machines that could accelerate protons, electrons, and other small particles to very high energies. These particles would then be allowed to collide with stationary targets outside the machine. These collisions would provide information about the fundamental structure of matter.

The earliest linear accelerators and cyclotrons were all built on this design, and they were very successful in producing new data on the composition of matter. But they all possessed one major handicap.

When high energy particles collide with a stationary target, only a relatively small fraction of their energy is available to take part in the reaction. By far the greatest fraction of their energy is used simply to move pieces of the target around. When a proton moving with one TeV (teraelectron, or trillion-electron, volts) of energy strikes a stationary proton, for example...