A particle-accelerator for electrons. The electrons are accelerated by the induced electric field around an altering magnetic field in a transformer core. The accelerator consists of a EI-shaped transformer core with a primary winding and the electron path, which forms the secondary winding.
When the magnetic field is ramped up by current flowing in the primary winding the electrons are accelerated in the induced electric field.
As the energy increases, so do the losses due to synchrotron radiation and this, and the maximum field strength in the core, limits the maximum energy attainable. The largest betatron ever built had a maximum energy of 300 MeV (1950).
The betatron produces a beam with a small spread in energy, but the output is pulsed and the average intensity is low. A better alternative could be the linear accelerator.