A linear accelerator, also known as a linac, is a type of particle accelerator in which charged particles travel in straight lines through a vacuum chamber. Early linear accelerators were electrostatic accelerators. In more modern types, a high-frequency, alternating electric field is used to accelerate the particles.
Final energies depend on the length of the chamber, and can reach several GeV (billion electron volts). The linear accelerator at Stanford University is 3.2 kilometers (2 miles) long and produces electrons and positrons with energies up to 50 GeV.