Betatron
Encyclopedia
A betatron is a cyclotron
developed by Donald Kerst at the University of Illinois
in 1940 to accelerate electrons, but the concepts ultimately originate from Rolf Widerøe and previous development occurred in Germany through Max Steenbeck
in the 1930s. The betatron is essentially a transformer
with a torus-shaped vacuum tube as its secondary coil. An alternating current in the primary coils accelerates electron
s in the vacuum around a circular path.The betatron was the first important machine for producing high energy electrons. Astrophysicist Michio Kaku
built a betatron in his garage while still in high school.
).
The stable orbit for the electrons satisfies
where 
is the flux with the orbit at 
is the radius 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.
, a fast electron) was chosen during a departmental contest. Other proposals were rheotron, inductron, and even Ausserordentlichhochgeschwindigkeitelektronenentwickelndenschwerarbeitsbeigollitron, supposedly German for "extraordinarily high-speed electron producing hard work by golly-tron.".
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-ray
s or gamma ray
s; these x-rays may be used in industrial and medical applications (historically in radiation oncology). A small version of a Betatron was also used to provide electrons converted into neutrons by a target to provide prompt initiation of some nuclear weapon
s.
The Radiation Center, the first private medical center to treat cancer patients with a betatron, was opened by Dr. O. Arthur Stiennon
in a suburb of Madison, Wisconsin
in the late 1950s.
of accelerators, the synchrotron
s, overcome these limitations.
Cyclotron
In technology, a cyclotron is a type of particle accelerator. In physics, the cyclotron frequency or gyrofrequency is the frequency of a charged particle moving perpendicularly to the direction of a uniform magnetic field, i.e. a magnetic field of constant magnitude and direction...
developed by Donald Kerst at the University of Illinois
University of Illinois at Urbana-Champaign
The University of Illinois at Urbana–Champaign is a large public research-intensive university in the state of Illinois, United States. It is the flagship campus of the University of Illinois system...
in 1940 to accelerate electrons, but the concepts ultimately originate from Rolf Widerøe and previous development occurred in Germany through Max Steenbeck
Max Steenbeck
Max Christian Theodor Steenbeck was a German physicist who worked at the Siemens-Schuckertwerke in his early career, during which time he invented the betatron in 1934. He was taken to the Soviet Union after World War II , and he contributed to the Soviet atomic bomb project...
in the 1930s. The betatron is essentially a transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
with a torus-shaped vacuum tube as its secondary coil. An alternating current in the primary coils accelerates electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s in the vacuum around a circular path.The betatron was the first important machine for producing high energy electrons. Astrophysicist Michio Kaku
Michio Kaku
is an American theoretical physicist, the Henry Semat Professor of Theoretical Physics in the City College of New York of City University of New York, the co-founder of string field theory, and a "communicator" and "popularizer" of science...
built a betatron in his garage while still in high school.
How it works
In a betatron, the changing magnetic field from the primary coil accelerates electrons injected into the vacuum torus, causing them to circle round the torus in the same manner as current is induced in the secondary of a transformer (Faraday's LawFaraday's law
Faraday's law may refer to the following:*Faraday's laws of electrolysis in chemistry*Faraday's law of induction, also known as Faraday-Lenz Law, in electromagnetism physics**The Maxwell–Faraday equation...
).
The stable orbit for the electrons satisfies
where is the flux with the orbit at is the radius 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.Etymology
The name "betatron" (a reference to the beta particleBeta particle
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...
, a fast electron) was chosen during a departmental contest. Other proposals were rheotron, inductron, and even Ausserordentlichhochgeschwindigkeitelektronenentwickelndenschwerarbeitsbeigollitron, supposedly German for "extraordinarily high-speed electron producing hard work by golly-tron.".
Applications
Betatrons were historically employed in particle physicsParticle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
experiments to provide high energy beams of electrons—up to about 300 MeV
MEV
MeV and meV are multiples and submultiples of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:In entertainment:* Musica Elettronica Viva, an Italian musical group...
. If the electron beam is directed at a metal plate, the betatron can be used as a source of energetic x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s or gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s; these x-rays may be used in industrial and medical applications (historically in radiation oncology). A small version of a Betatron was also used to provide electrons converted into neutrons by a target to provide prompt initiation of some nuclear weapon
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
s.
The Radiation Center, the first private medical center to treat cancer patients with a betatron, was opened by Dr. O. Arthur Stiennon
O. Arthur Stiennon
Dr. O. Arthur Stiennon, Jr. was a clinical radiologist, inventor, radiation treatment pioneer, software and real estate developer in Madison, Wisconsin. He attended the University of Wisconsin–Madison, graduating Phi Beta Kappa in 1941. He received his M.D...
in a suburb of Madison, Wisconsin
Madison, Wisconsin
Madison is the capital of the U.S. state of Wisconsin and the county seat of Dane County. It is also home to the University of Wisconsin–Madison....
in the late 1950s.
Limitations
The maximum energy that 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 generationof accelerators, the synchrotron
Synchrotron
A synchrotron is a particular type of cyclic particle accelerator in which the magnetic field and the electric field are carefully synchronised with the travelling particle beam. The proton synchrotron was originally conceived by Sir Marcus Oliphant...
s, overcome these limitations.
In popular culture
- In the Frank BlackFrank BlackBlack Francis is an American singer, songwriter and guitarist. He is best known as the frontman of the influential alternative rock band Pixies, with whom he performs under the stage name Black Francis. Following the band's breakup in 1993, he embarked on a solo career under the name Frank Black...
song "Los Angeles", the betatron is referenced in the line "I met a man; he was a good man, sailing and shoring; he got a betatron, man." - The Rap artist 'Canibus' refers to betatrons in his song "Levitibus".