A particle accelerator increases the kinetic energy of charged particles through the work of an electric field. A single electric potential difference gives an energy gain of magnitude to a particle of electric charge crossing in the accelerating direction. Reusing a smaller electric potential difference many times can give a much larger final kinetic energy without requiring the whole apparatus to withstand the equivalent single voltage. A magnetic field can return the particles to the accelerating region: magnetic forces do no work, but they make repeated energy gains possible. The cyclotron turns this separation between bending and acceleration into a particularly elegant machine.
