Get Betatron essential facts below. View Videos or join the Betatron discussion. Add Betatron to your PopFlock.com topic list for future reference or share this resource on social media.
Early betatron at University of Illinois. Kerst is at right, examining the vacuum chamber between the poles of the 4-ton magnet.
A German 6 MeV betatron (1942)
A 35 MeV betatron used for photonuclear physics at the University of Melbourne.
A betatron is a type of cyclic particle accelerator. It is essentially a transformer with a torus-shaped vacuum tube as its secondary coil. An alternating current in the primary coils accelerates electrons in the vacuum around a circular path. The betatron was the first machine capable of producing electron beams at energies higher than could be achieved with a simple electron gun.
In a betatron, the changing magnetic field from the primary coil accelerates electrons injected into the vacuum torus, causing them to circle around the torus in the same manner as current is induced in the secondary coil of a transformer (Faraday's Law).
The stable orbit for the electrons satisfies
is the flux within the area enclosed by the electron orbit,
is the radius of the electron orbit, and
is the magnetic field at .
In other words, the magnetic field at the orbit must be half the average magnetic field over its circular cross section:
This condition is often called Widerøe's condition.
The name "betatron" (a reference to the beta particle, a fast electron) was chosen during a departmental contest. Other proposals were "rheotron", "induction accelerator", "induction electron accelerator", and even "Außerordentlichehochgeschwindigkeitselektronenentwickelndesschwerarbeitsbeigollitron", a suggestion by a German associate, for "Hard working by golly machine for generating extraordinarily high velocity electrons" or perhaps "Extraordinarily high velocity electron generator, high energy by golly-tron."
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 (via 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.
The maximum energy that a betatron can impart is limited by the strength of the magnetic field due to the saturation of iron and by practical size of the magnet core. The next generation of accelerators, the synchrotrons, overcame these limitations.