The term linac is a shortened version of "linear accelerator." A linac is a particle accelerator that accelerates charged particles in a straight line. Charged particles enter the accelerator at one end and are accelerated as they pass through a series of voltages placed along the beam path. Because the path the particles follow is shorter and they pass through fewer accelerating voltages, linacs cannot accelerate particles as much as circular accelerators can. However, linacs are easier to build and run, and they are often used to create beams of particles to be injected into a synchrotron. SLAC is a linac, as were J.J. Thomson's cathode ray tubes.