linear accelerator

In physics, a type of particle accelerator in which the particles move along a straight tube. Particles pass through a linear accelerator only once – unlike those in a cyclotron or synchrotron (ring-shaped accelerators), which make many revolutions, gaining energy each time.

The world's longest linac is the Stanford Linear Collider, in which electrons and positrons are accelerated along a straight track 3.2 km/2 mi long and then steered into a head-on collision with other particles. The first linear accelerator was built in 1928 by the Norwegian engineer Ralph Wideröe to investigate the behaviour of heavy ions (large atoms with one or more electrons removed), but devices capable of accelerating smaller particles such as protons and electrons could not be built until after World War II and the development of high-power radio- and microwave-frequency generators.