Betatron

[2] Through the 1920s and 30s a number of theoretical problems related to the device were considered by scientists including Rolf Wideroe,[3][4] Ernest Walton, and Max Steenbeck.

[6][7][8] After the discovery in the 1800s of Faraday's law of induction, which showed that an electromotive force could be generated by a changing magnetic field, several scientists speculated that this effect could be used to accelerate charged particles to high energies.

This device took a step towards the betatron concept by shaping the magnetic field to keep the particles focused in the plane of acceleration.

[2] The first team unequivocally acknowledged to have built a working betatron was led by Donald Kerst at the University of Illinois.

"[15] 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, which may be used in industrial and medical applications (historically in radiation oncology).

A small version of a betatron was also used to provide a source of hard X-rays (by deceleration of the electron beam in a target) for prompt initiation of some experimental nuclear weapons by means of photon-induced fission and photofission in the bomb core.