Betatron

A betatron is a type of circular particle accelerator that accelerates electrons using a continuously changing magnetic field, which induces an electric field that drives the electrons around a circular path while simultaneously increasing the magnetic field guiding them, so that the beam radius stays constant as the particles gain energy. First successfully built and demonstrated in 1940 by the American physicist Donald Kerst, the betatron was among the earliest practical machines capable of accelerating electrons to energies in the tens of millions of electron volts, well beyond what electrostatic accelerators of the time could reach. Although largely superseded in high-energy physics research by synchrotrons and linear accelerators, which can reach far higher energies, betatrons found lasting practical use for decades as sources of high-energy x-rays for industrial radiography and, in some medical settings, for radiation therapy.