A betatron is a particle accelerator in the cyclotron family. As the name implies, a betatron is used to accelerate beta particles: electrons. An alternating magnetic field between two pairs of semicircular segments (called dees) imparts regular increases in kinetic energy to the electrons as they circle within the cyclotron.

The cyclotron article contains more details about the operation of these instruments.

Betatrons were historically employed in particle physics experiments to provide high energy beams of electrons—up to about 300 MeV. If the electron beam is directed at a metal plate, the betatron can be used as a source of energetic x-rays or gamma rays; these x-rays may be used in industrial and medical applications.

Because the mass of the electron increases at relativisitic speeds, the cyclotron becomes less efficient at higher energies, placing an uppper limit on its beam energy. These relativistic effects are accommodated in the next generation of accelerators, the synchrocyclotrons.