HOME

TheInfoList




A cyclotron is a type of
particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel electric charge, charged particles to very high speeds and energies, and to contain them in well-defined particle beam, beams. Large accelerators are used for funda ...
invented by Ernest O. Lawrence in 1929–1930 at the
University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public In public relations Public relations (PR) is the practice of managing and disseminating information from an individual or an organization ...

University of California, Berkeley
, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: January 26, 1932, granted: February 20, 1934 A cyclotron accelerates
charged particle In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. " ...
s outwards from the center of a flat cylindrical vacuum chamber along a spiral path. The particles are held to a spiral trajectory by a static magnetic field and accelerated by a rapidly varying (
radio frequency Radio frequency (RF) is the oscillation Oscillation is the repetitive variation, typically in time Time is the indefinite continued sequence, progress of existence and event (philosophy), events that occur in an apparently irreversible p ...
) electric field. Lawrence was awarded the 1939
Nobel Prize in Physics The Nobel Prize in Physics is a yearly award given by the Royal Swedish Academy of Sciences for those who have made the most outstanding contributions for mankind in the field of physics. It is one of the five Nobel Prizes established by the will ...
for this invention. Cyclotrons were the most powerful particle accelerator technology until the 1950s when they were superseded by the
synchrotron A synchrotron is a particular type of cyclic particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2011, until 2007 it was the most po ...

synchrotron
, and are still used to produce particle beams in physics and
nuclear medicine Nuclear medicine is a medical specialty A medical specialty is a branch of medical practice that is focused on a defined group of patients, diseases, skills, or philosophy. Examples include children (paediatrics Pediatrics (American and Bri ...
. The largest single-magnet cyclotron was the
synchrocyclotron A synchrocyclotron is a special type of cyclotron A cyclotron is a type of particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2 ...
built between 1940 and 1946 by Lawrence at the
University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public In public relations Public relations (PR) is the practice of managing and disseminating information from an individual or an organization ...

University of California, Berkeley
, which could accelerate protons to 730 mega electron volts (
MeV In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "P ...
). The largest cyclotron of its kind is the multimagnet
TRIUMF TRIUMF is Canada Canada is a country in the northern part of North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean, Atlantic to the Pacific Ocean, Pacific and northwa ...
accelerator at the
University of British Columbia The University of British Columbia (UBC) is a public university, public research university with campuses near Vancouver and in Kelowna, British Columbia. Established in 1908, UBC is British Columbia's oldest university. The university ranks a ...

University of British Columbia
in
Vancouver, British Columbia Vancouver ( ) is a major city in western Canada, located in the Lower Mainland region of British Columbia. As the List of cities in British Columbia, most populous city in the province, the 2016 Canadian census, 2016 census recorded 631,486 pe ...
, which can produce 520 MeV protons. Close to 1500 cyclotrons are used in nuclear medicine worldwide for the production of
radionuclide A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide A nuclide (or nucleide, from atomic nucleus, nucleus, also known as nuclear species) is a class of atoms characterized by their number of protons, ''Z'', their ...
s.


History

In 1928 Hungarian physicist Leo Szilárd invented and patented the linear accelerator. In January 1929, Szilárd became the first person to discuss the resonance condition (what is now called the cyclotron frequency) for a circular accelerating apparatus, in a patent application in Germany. He also invented and patented the first cyclotron and
betatron A betatron is a type of cyclic particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2011, until 2007 it was the most powerful particle ...
too. A couple months later, in the early summer of 1929, Ernest Lawrence came up with the cyclotron idea when he read a paper by
Rolf Widerøe Rolf Widerøe (11 July 1902 – 11 October 1996) was a Norway, Norwegian accelerator physics, accelerator physicist who was the originator of many particle accelerator, particle acceleration concepts, including the ''resonance accelerator'' and th ...
describing a drift tube
linac A linear particle accelerator (often shortened to linac) is a type of particle accelerator that accelerates charged subatomic particles or ions to a high speed by subjecting them to a series of Oscillation, oscillating electric potentials along ...

linac
. He published a paper in Science in 1930, and patented the device in 1932. He used large electromagnets recycled from obsolete
Poulsen arc The arc converter, sometimes called the arc transmitter, or Poulsen arc after Danish engineer Valdemar Poulsen Valdemar Poulsen (23 November 1869 – 23 July 1942) was a Danish engineer Engineers, as practitioners of engineering, are Profess ...
radio transmitters provided by the
Federal Telegraph Company The Federal Telegraph Company was a United States manufacturing and communications company that played a pivotal role in the 20th century in the development of radio communications. Founded in Palo Alto, California in 1909 by Cyril Frank Elwell, th ...
. A graduate student, , did much of the work of translating the idea into working hardware. At the
Radiation Laboratory The Radiation Laboratory, commonly called the Rad Lab, was a microwave Microwave is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituen ...
of the
University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public In public relations Public relations (PR) is the practice of managing and disseminating information from an individual or an organization ...

University of California, Berkeley
, Lawrence and his collaborators constructed a series of cyclotrons which were the most powerful accelerators in the world at the time; a 4.8 MeV machine (1932), a 8 MeV machine (1937), and a 16 MeV machine (1939). He also developed a , 730 MeV
synchrocyclotron A synchrocyclotron is a special type of cyclotron A cyclotron is a type of particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2 ...
(1945). Lawrence received the 1939
Nobel Prize in Physics The Nobel Prize in Physics is a yearly award given by the Royal Swedish Academy of Sciences for those who have made the most outstanding contributions for mankind in the field of physics. It is one of the five Nobel Prizes established by the will ...
for the invention and development of the cyclotron and for results obtained with it. The first European cyclotron was constructed in
Leningrad Saint Petersburg ( rus, links=no, Санкт-Петербург, a=Ru-Sankt Peterburg Leningrad Petrograd Piter.ogg, r=Sankt-Peterburg, p=ˈsankt pʲɪtʲɪrˈburk), formerly known as Petrograd (1914–1924) and later Leningrad (1924–1991), ...
(then
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a that spanned during its existence from 1922 to 1991. It was nominally a of multiple national ; in practice and were highly until its final years. The ...
) in the physics department of the Radium Institute, headed by . This Leningrad instrument was first proposed in 1932 by
George Gamow George Gamow (March 4, 1904 – August 19, 1968), born Georgiy Antonovich Gamov (russian: Георгий Антонович Гамов), was a Ukrainian-Russian born American American(s) may refer to: * American, something of, from, or related ...
and and was installed and became operative by 1937. In
Nazi Germany Nazi Germany, (lit. "National Socialist State"), ' (lit. "Nazi State") for short; also ' (lit. "National Socialist Germany") officially known as the German Reich from 1933 until 1943, and the Greater German Reich from 1943 to 1945, was ...

Nazi Germany
a cyclotron was built in 1937, in
Otto Hahn Otto Hahn (; 8 March 1879 – 28 July 1968) was a German chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin Medieval Latin was the form of Latin Latin (, or , ) is a classical language ...

Otto Hahn
laboratory in Berlin-Dahlem (Kaiser Wilhelm Institure), also used by
Rudolf Fleischmann Rudolf Fleischmann (1 May 1903 – 3 February 2002) was a German experimental nuclear physicist from Erlangen, Bavaria. He worked for Walther Bothe at the Physics Institute of the University of Heidelberg and then at the Institute for Physics ...
. It was the first cyclotron with a Greinacher multiplier to rise the voltage to 2.8 MV and 3 mA current. A second cyclotron ws built in
Heidelberg Heidelberg () is a university town in the German state The Federal Republic of Germany, as a federal state, consists of sixteen partly sovereign federated states (german: Land (state), plural (states); commonly informally / federated s ...

Heidelberg
under supervision of
Walther Bothe Walther Wilhelm Georg Bothe (; 8 January 1891 – 8 February 1957) was a German nuclear physicist, who shared the Nobel Prize in Physics in 1954 with Max Born Max Born (; 11 December 1882 – 5 January 1970) was a German physicist A phy ...
and
Wolfgang Gentner Wolfgang Gentner (23 July 1906 in Frankfurt am Main – 4 September 1980 in Heidelberg) was a German experimental nuclear physics, nuclear physicist. Gentner received his doctorate in 1930 from the University of Frankfurt. From 1932 to 1935 he had ...
, with support from the
Heereswaffenamt ''Waffenamt'' (WaA) was the German Army Weapons Agency. It was the centre for research and development of the Weimar Republic The Weimar Republic (german: Weimarer Republik ) was the German state from 1918 to 1933 when it functioned as ...
, and became operative in 1943.


Principle of operation

A cyclotron accelerates a
charged particle beam A charged particle beam is a spatially localized group of electrically charged particle In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized physical body, object to ...
using a
high frequency High frequency (HF) is the ITU 260px, ITU Monument, Bern The International Telecommunication Union is a specialized agency of the United Nations responsible for all matters related to information and communication technologies Infor ...
alternating
voltage Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is the ...

voltage
which is applied between two hollow "D"-shaped sheet metal electrodes called "dees" inside a vacuum chamber. The dees are placed face to face with a narrow gap between them, creating a cylindrical space within them for the particles to move. The particles are injected into the center of this space. The dees are located between the poles of a large
electromagnet An electromagnet is a type of magnet A magnet is a material or object that produces a magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each poin ...

electromagnet
which applies a static
magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each point in a subset of space. For instance, a vector field in the plane can be visualised as a collection of arrows with ...

magnetic field
''B'' perpendicular to the electrode plane. The magnetic field causes the particles' path to bend in a circle due to the
Lorentz force In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. " ...

Lorentz force
perpendicular to their direction of motion. If the particles' speeds were constant, they would travel in a circular path within the dees under the influence of the magnetic field. However a
radio frequency Radio frequency (RF) is the oscillation Oscillation is the repetitive variation, typically in time Time is the indefinite continued sequence, progress of existence and event (philosophy), events that occur in an apparently irreversible p ...
(RF) alternating voltage of several thousand
volt The volt is the derived unit for electric potential The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as the amount of work (physics), work energy needed to move a ...

volt
s is applied between the dees. The voltage creates an oscillating electric field in the gap between the dees that accelerates the particles. The frequency is set so that the particles make one circuit during a single cycle of the voltage. To achieve this, the frequency must match the particle's
cyclotron resonance Cyclotron resonance describes the interaction of external forces with charged particles experiencing a magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each p ...
frequency :f = \frac, where ''B'' is the
magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each point in a subset of space. For instance, a vector field in the plane can be visualised as a collection of arrows with ...

magnetic field
strength, ''q'' is the
electric charge Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative'' (commonly carried by protons and electrons respectively). Like c ...
of the particle and ''m'' is the
relativistic mass The word ''mass'' has two meanings in special relativity: ''invariant mass'' (also called rest mass) is an invariant quantity which is the same for all observers in all reference frames, while the ''relativistic mass'' is dependent on the velocity ...
of the charged particle. Each time after the particles pass to the other dee electrode the polarity of the RF voltage reverses. Therefore, each time the particles cross the gap from one dee electrode to the other, the
electric field An electric field (sometimes E-field) is the physical field that surrounds electrically-charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' ' ...

electric field
is in the correct direction to accelerate them. The particles' increasing speed due to these pushes causes them to move in a larger radius circle with each rotation, so the particles move in a
spiral In mathematics, a spiral is a curve which emanates from a point, moving farther away as it revolves around the point. Helices Two major definitions of "spiral" in the American Heritage Dictionary are:
path outward from the center to the rim of the dees. When they reach the rim a small voltage on a metal plate deflects the beam so it exits the dees through a small gap between them, and hits a target located at the exit point at the rim of the chamber, or leaves the cyclotron through an evacuated beam tube to hit a remote target. Various materials may be used for the target, and the
nuclear reactions In nuclear physics and nuclear chemistry, a nuclear reaction is semantically considered to be the process in which two atomic nucleus, nuclei, or a nucleus and an external subatomic particle, collide to produce one or more new nuclides. Thus, a ...
due to the collisions will create secondary particles which may be guided outside of the cyclotron and into instruments for analysis. The cyclotron was the first "cyclical" accelerator. The advantage of the cyclotron design over the existing electrostatic accelerators of the time such as the Cockcroft-Walton accelerator and
Van de Graaff generator A Van de Graaff generator is an electrostatic generator 12" Quadruple Sector-less Wimshurst Machine (Bonetti Machine) An electrostatic generator, or electrostatic machine, is an electric generator, electromechanical generator that produces ''st ...

Van de Graaff generator
, was that in these machines the particles were only accelerated once by the voltage, so the particles' energy was equal to the accelerating voltage on the machine, which was limited by air breakdown to a few million volts. In the cyclotron, in contrast, the particles encounter the accelerating voltage many times during their spiral path, and so are accelerated many times, so the output energy can be many times the accelerating voltage.


Particle energy

Since the particles in a cyclotron are accelerated by the voltage many times, the final energy of the particles is not dependent on the accelerating voltage but on the strength of the magnetic field and the diameter of the accelerating chamber, the dees. The classic cyclotron can only accelerate particles to speeds much slower than the
speed of light The speed of light in vacuum A vacuum is a space Space is the boundless three-dimensional Three-dimensional space (also: 3-space or, rarely, tri-dimensional space) is a geometric setting in which three values (called paramet ...
,
nonrelativistic The theory of relativity usually encompasses two interrelated theories by Albert Einstein Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest ...
speeds. For nonrelativistic particles, the centripetal force F_\; required to keep them in their curved path is :F_ = \; where m\; is the particle's mass, v\; its velocity, and r\, is the radius of the path. This force is provided by the
Lorentz force In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. " ...

Lorentz force
F(B)\, of the magnetic field B\, :F(B) = qvB\; where q\, is the particle's charge. The particles reach their maximum energy at the periphery of the dees, where the radius of their path is r\;=\;R the radius of the dees. Equating these two forces : = qvB\; :v = \, So the output energy of the particles is Therefore, the limit to the cyclotron's output energy for a given type of particle is the strength of the magnetic field B, which is limited to about 2 T for
ferromagnetic Ferromagnetism is the basic mechanism by which certain materials (such as iron Iron () is a with Fe (from la, ) and 26. It is a that belongs to the and of the . It is, on , right in front of (32.1% and 30.1%, respectively), formi ...
electromagnets, and the radius of the dees R, which is determined by the diameter of the magnet's pole pieces. So very large magnets were constructed for cyclotrons, culminating in Lawrence's 1946 synchrocyclotron, which had pole pieces (15.3 feet) in diameter.


Types

The cyclotron has evolved in a number of different forms *''Classic cyclotron'' - The first type of cyclotron, described in previous sections, which had uniform magnetic field and constant frequency, is mostly obsolete. It was limited to completely
nonrelativistic The theory of relativity usually encompasses two interrelated theories by Albert Einstein Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest ...
energies (the output energy small compared to the particle's
rest energy The invariant mass, rest mass, intrinsic mass, proper mass, or in the case of bound systems simply mass, is the portion of the total mass of an object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** ...
), and had focusing problems. *''
Synchrocyclotron A synchrocyclotron is a special type of cyclotron A cyclotron is a type of particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2 ...
'' - an obsolete machine which extended energies into the relativistic regime by decreasing the radio frequency of the oscillator as the orbit of the particle got larger to keep it in synchronism with the particle. This was the most powerful accelerator during the 1950s, before the
synchrotron A synchrotron is a particular type of cyclic particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2011, until 2007 it was the most po ...

synchrotron
. It operated in pulses, instead of continuously, so its luminosity (beam current) was very low. *''Isochronous cyclotron (isocyclotron)'' - a category which includes most current machines, extends output energy into the relativistic regime by using shaped pole pieces extending outwards from a center to create a nonuniform magnetic field stronger in peripheral regions to increase centripetal force on the particle as it gains relativistic mass, with alternating-gradient focusing to keep the beam focused. :*''"Sector focused", "spiral-ridged", "azimuthally-varying-field"'' - these describe machines in which the pole surfaces have hills and valleys azimuthally, making the field increase and decrease as the particles move in the ring, which keeps the beam collimated by alternating-gradient focusing. :*''Separated sector cyclotron'' - a machine in which the magnet is in separate sections, separated by gaps without field *''H cyclotron'' - a cyclotron that accelerates negative hydrogen ions, which make it easy to deflect the beam out of the machine. At the beam exit point at the periphery of the dees, a metal foil strips the electrons from the hydrogen ions, transforming them into positively charged H+ ions. These are bent in the opposite direction by the magnet, so the beam leaves the machine.


Relativistic considerations

In the non-relativistic approximation, the cyclotron frequency does not depend upon the particle's speed or the radius of the particle's orbit. As the beam spirals outward, the rotation frequency stays constant, and the beam continues to accelerate as it travels a greater distance in the same time period. In contrast to this approximation, as particles approach the
speed of light The speed of light in vacuum A vacuum is a space Space is the boundless three-dimensional Three-dimensional space (also: 3-space or, rarely, tri-dimensional space) is a geometric setting in which three values (called paramet ...
, the cyclotron frequency decreases proportionally to the particle's
Lorentz factor The Lorentz factor or Lorentz term is a quantity Quantity is a property that can exist as a multitude or magnitude, which illustrate discontinuity and continuity. Quantities can be compared in terms of "more", "less", or "equal", or by assi ...

Lorentz factor
. A rigorous proof of this fact (starting from Newton's second law) is given here: . Acceleration of relativistic particles therefore requires either modification to the frequency during the acceleration, leading to the ''synchrocyclotron'', or modification to the magnetic field during the acceleration, which leads to the ''isochronous cyclotron''. The relativistic mass can be rewritten as :m = \frac = \frac = \gamma , where :m_0 is the particle
rest mass The invariant mass, rest mass, intrinsic mass, proper mass, or in the case of bound systems simply mass, is the portion of the total mass of an object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** ...
, :\beta = \frac is the relative velocity, and :\gamma=\frac=\frac is the
Lorentz factor The Lorentz factor or Lorentz term is a quantity Quantity is a property that can exist as a multitude or magnitude, which illustrate discontinuity and continuity. Quantities can be compared in terms of "more", "less", or "equal", or by assi ...

Lorentz factor
. The relativistic cyclotron frequency and angular frequency can be rewritten as :f = \frac = \frac = = , and :\omega = = \frac = \frac = = , where :f_0 would be the cyclotron frequency in classical approximation, :\omega_0 would be the cyclotron angular frequency in classical approximation. The
gyroradius The gyroradius (also known as radius of gyration, Larmor radius or cyclotron radius) is the radius In classical geometry Geometry (from the grc, γεωμετρία; ' "earth", ' "measurement") is, with , one of the oldest branches of . ...
for a particle moving in a static magnetic field is then given by :r = \frac = \frac = \frac, because :\omega r = v = \beta c where v would be the (linear) velocity.


Synchrocyclotron

A synchrocyclotron is a cyclotron in which the frequency of the driving RF electric field is varied to compensate for relativistic effects as the particles' velocity begins to approach the speed of light. This is in contrast to the classical cyclotron, where the frequency was held constant, thus leading to the synchrocyclotron operation frequency being : f = \frac = , where f_0 is the classical cyclotron frequency and \beta = \frac again is the relative velocity of the particle beam. The rest mass of an electron is 511 keV/c2, so the frequency correction is 1% for a magnetic vacuum tube with a 5.11 kV direct current accelerating voltage. The proton mass is nearly two thousand times the electron mass, so the 1% correction energy is about 9 MeV, which is sufficient to induce
nuclear reaction In nuclear physics and nuclear chemistry, a nuclear reaction is a process in which two atomic nucleus, nuclei, or a nucleus and an external subatomic particle, collide to produce one or more new nuclides. Thus, a nuclear reaction must cause a t ...
s.


Isochronous cyclotron

An alternative to the synchrocyclotron is the ''isochronous cyclotron'', which has a magnetic field that increases with radius, rather than with time. Isochronous cyclotrons are capable of producing much greater beam current than synchrocyclotrons, but require azimuthal variations in the field strength to provide a
strong focusing In accelerator physics Accelerator physics is a branch of applied physics Applied physics is the application of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýs ...
effect and keep the particles captured in their spiral trajectory. For this reason, an isochronous cyclotron is also called an "AVF (azimuthal varying field) cyclotron". This solution for focusing the particle beam was proposed by L. H. Thomas in 1938. Recalling the relativistic
gyroradius The gyroradius (also known as radius of gyration, Larmor radius or cyclotron radius) is the radius In classical geometry Geometry (from the grc, γεωμετρία; ' "earth", ' "measurement") is, with , one of the oldest branches of . ...
r = \frac and the relativistic cyclotron frequency f = \frac, one can choose B to be proportional to the Lorentz factor, B = \gamma B_0. This results in the relation r = \frac which again only depends on the velocity v, like in the non-relativistic case. Also, the cyclotron frequency is constant in this case. The transverse de-focusing effect of this radial field gradient is compensated by ridges on the magnet faces which vary the field azimuthally as well. This allows particles to be accelerated continuously, on every period of the
radio frequency Radio frequency (RF) is the oscillation Oscillation is the repetitive variation, typically in time Time is the indefinite continued sequence, progress of existence and event (philosophy), events that occur in an apparently irreversible p ...
(RF), rather than in bursts as in most other accelerator types. This principle that alternating field gradients have a net focusing effect is called
strong focusing In accelerator physics Accelerator physics is a branch of applied physics Applied physics is the application of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýs ...
. It was obscurely known theoretically long before it was put into practice. Examples of isochronous cyclotrons abound; in fact almost all modern cyclotrons use azimuthally-varying fields. The
TRIUMF TRIUMF is Canada Canada is a country in the northern part of North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean, Atlantic to the Pacific Ocean, Pacific and northwa ...
cyclotron mentioned below is the largest of its kind with an outer orbit radius of 7.9 metres, extracting protons at up to 510 MeV, which is 3/4 of the speed of light. The PSI cyclotron reaches higher energy and higher intensity but is smaller because of using a higher magnetic field.


Usage

For several decades, cyclotrons were the best source of high-energy beams for
nuclear physics Nuclear physics is the field of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in ot ...
experiments; several cyclotrons are still in use for this type of research. The results enable the calculation of various properties, such as the mean spacing between atoms and the creation of various collision products. Subsequent chemical and particle analysis of the target material may give insight into
nuclear transmutation Nuclear transmutation is the conversion of one chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike che ...
of the elements used in the target. Cyclotrons can be used in
particle therapy Particle therapy is a form of external beam radiotherapy External beam radiotherapy (EBRT) is the most common form of radiotherapy (radiation therapy). The patient sits or lies on a couch and an external source of ionizing radiation is poin ...
to treat
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumor A benign tumor is a mass of cells Cell most often refers to: * Cell (biolo ...

cancer
. Ion beams from cyclotrons can be used, as in
proton therapy In the field of medical treatment, proton therapy, or proton radiotherapy, is a type of particle therapy that uses a beam of protons to irradiation, irradiate diseased Tissue (biology), tissue, most often to treat cancer. The chief advantage of ...
, to penetrate the body and kill tumors by
radiation damage Radiation damage is the effect of ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of s or s that have sufficient to s or s by detaching s from them. The particles generally travel at a speed ...
, while minimizing damage to healthy tissue along their path. Cyclotron beams can be used to bombard other atoms to produce short-lived
positron The positron or antielectron is the antiparticle s (left) and antiparticles (right). From top to bottom; electron The electron is a subatomic particle In physical sciences, subatomic particles are smaller than atom An atom is ...

positron
-emitting isotopes suitable for
PET imaging Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in Metabolism, metabolic processes, and in other physiological activities including blo ...
. More recently some cyclotrons currently installed at hospitals for radio isotopes production have been retrofitted to enable them to produce
technetium-99m Technetium-99m (99mTc) is a metastable In chemistry and physics, metastability denotes an intermediate energetic state within a dynamical system other than the system's ground state, state of least energy. A ball resting in a hollow on a slop ...
. Technetium-99m is a diagnostic isotope in short supply due to difficulties at Canada's
Chalk River Chalk River (2016 population: 1029) is a small rural village, part of the Laurentian Hills municipality in Renfrew County Renfrew County is a county A county is a geographical region of a country used for administrative or other purpos ...

Chalk River
facility.


Advantages and limitations

The cyclotron was an improvement over the
linear accelerator A linear particle accelerator (often shortened to linac) is a type of particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel electric charge, charged particles to very high speeds and energies, a ...
s (''linac''s) that were available when it was invented, being more cost- and space-effective due to the iterated interaction of the particles with the accelerating field. In the 1920s, it was not possible to generate the high power, high-frequency radio waves which are used in modern linacs (generated by
klystron A klystron is a specialized linear-beam vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current An electric current is a stream of charged particles, such as e ...

klystron
s). As such, impractically long linac structures were required for higher-energy particles. The compactness of the cyclotron reduces other costs as well, such as foundations, radiation shielding, and the enclosing building. Cyclotrons have a single electrical driver, which saves both money and power. Furthermore, cyclotrons are able to produce a continuous stream of particles at the target, so the average power passed from a particle beam into a target is relatively high. The
spiral In mathematics, a spiral is a curve which emanates from a point, moving farther away as it revolves around the point. Helices Two major definitions of "spiral" in the American Heritage Dictionary are:
path of the cyclotron beam can only "sync up" with klystron-type (constant frequency) voltage sources if the accelerated particles are approximately obeying
Newton's laws of motion Newton's laws of motion are three law Law is a system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its ...
. If the particles become fast enough that relativistic effects become important, the beam becomes out of phase with the oscillating electric field, and cannot receive any additional acceleration. The classical cyclotron is therefore only capable of accelerating particles up to a few percent of the speed of light. To accommodate increased mass the magnetic field may be modified by appropriately shaping the pole pieces as in the
isochronous cyclotron A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Jan ...
s, operating in a pulsed mode and changing the frequency applied to the dees as in the
synchrocyclotron A synchrocyclotron is a special type of cyclotron A cyclotron is a type of particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2 ...
s, either of which is limited by the diminishing cost effectiveness of making larger machines. Cost limitations have been overcome by employing the more complex
synchrotron A synchrotron is a particular type of cyclic particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2011, until 2007 it was the most po ...

synchrotron
or modern,
klystron A klystron is a specialized linear-beam vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current An electric current is a stream of charged particles, such as e ...

klystron
-driven
linear accelerator A linear particle accelerator (often shortened to linac) is a type of particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel electric charge, charged particles to very high speeds and energies, a ...
s, both of which have the advantage of scalability, offering more power within an improved cost structure as the machines are made larger.


Notable examples

One of the world's largest cyclotrons is at the
RIKEN is a large scientific research institute A research institute, research centre, or research center is an establishment founded for doing research. Research institutes may specialize in basic research or may be oriented to applied research. Alt ...

RIKEN
laboratory in Japan. Called the SRC or Superconducting Ring Cyclotron, it has six separated superconducting sectors, and is 19 m in diameter and 8 m high. Built to accelerate heavy ions, its maximum magnetic field is 3.8  T, yielding a bending ability of 8 T·m. The total weight of the cyclotron is 8,300 t. The Riken magnetic field covers from 3.5 m radius to 5.5 m with the maximum beam radius of about . It has accelerated uranium ions to 345 MeV per atomic mass unit.
TRIUMF TRIUMF is Canada Canada is a country in the northern part of North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean, Atlantic to the Pacific Ocean, Pacific and northwa ...
, Canada's national laboratory for nuclear and particle physics, houses the world's largest cyclotron of its kind. The 18 m diameter, 4,000 t main magnet produces a field of 0.46 T while a 23 MHz 94  electric field is used to accelerate the 300 μA beam. The TRIUMF field goes from radius with the maximum beam radius of . Its large size is partly a result of using negative hydrogen ions rather than protons; this requires a lower magnetic field to reduce EM stripping of the loosely bound electrons. The advantage is that extraction is simpler; multi-energy, multi-beams can be extracted by inserting thin carbon stripping foils at appropriate radii. TRIUMF is a non-profit incorporation with charitable status located at the University of British Columbia.


Related technologies

The spiraling of electrons in a cylindrical vacuum chamber within a transverse magnetic field is also employed in the
magnetron Image:Magnetron2.jpg, Magnetron with section removed to exhibit the cavities. The cathode in the center is not visible. The antenna emitting microwaves is at the left. The magnets producing a field parallel to the long axis of the device are not ...

magnetron
, a device for producing high frequency radio waves (
microwaves Microwave is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space a ...
). The
synchrotron A synchrotron is a particular type of cyclic particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2011, until 2007 it was the most po ...

synchrotron
moves the particles through a path of constant radius, allowing it to be made as a pipe and so of much larger radius than is practical with the cyclotron and
synchrocyclotron A synchrocyclotron is a special type of cyclotron A cyclotron is a type of particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2 ...
. The larger radius allows the use of numerous magnets, each of which imparts angular momentum and so allows particles of higher velocity (mass) to be kept within the bounds of the evacuated pipe. The magnetic field strength of each of the bending magnets is increased as the particles gain energy in order to keep the bending angle constant.


In fiction

The
United States Department of War The United States Department of War, also called the War Department (and occasionally War Office in the early years), was the United States Cabinet department originally responsible for the operation and maintenance of the United States Army, al ...
famously asked for dailies of the Superman comic strip to be pulled in April 1945 for having Superman bombarded with the radiation from a cyclotron. In 1950, however, in '' Atom Man vs. Superman'',
Lex Luthor Alexander Joseph "Lex" Luthor ( or ) is a fictional character appearing in American comic books published by DC Comics. The character was created by Jerry Siegel and Joe Shuster. Lex Luthor originally appeared in ''Action Comics'' #23 (cover da ...
uses a cyclotron to start an earthquake. In
Ghostbusters ''Ghostbusters'' is a 1984 American supernatural The supernatural encompasses supposed phenomena or entities that are not subject to the . This term is attributed to , such as s, s, , and . It also includes claimed abilities embodied in ...
a miniature cyclotron forms part of the proton pack used for catching ghosts.


See also

*
Beamline In accelerator physics Accelerator physics is a branch of applied physics Applied physics is the application of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''ph ...
*
Bremsstrahlung ''Bremsstrahlung'' (), from "to brake" and "radiation"; i.e., "braking radiation" or "deceleration radiation", is electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fund ...

Bremsstrahlung
(radiation) *
Cyclotron radiation Cyclotron radiation is electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and tim ...
*
Cyclotron resonance Cyclotron resonance describes the interaction of external forces with charged particles experiencing a magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each p ...
*
Fast neutron therapy Fast neutron therapy utilizes high energy neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the ...
*
Gyrotron High-power 140 GHz gyrotron for plasma heating in the Wendelstein 7-X fusion experiment, Germany. A gyrotron is a class of high-power linear-beam vacuum tubes which generates millimeter wave, millimeter-wave electromagnetic waves by the cyclotron ...

Gyrotron
*
Particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel electric charge, charged particles to very high speeds and energies, and to contain them in well-defined particle beam, beams. Large accelerators are used for funda ...
* Radiation reaction force * Sándor Gaál *
Synchrotron A synchrotron is a particular type of cyclic particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2011, until 2007 it was the most po ...

Synchrotron


References

ef. 1414. Lawrence, EO and Edlefsen, NE. On the production of high speed protons. Science 1930, v.72 (1867) pps. 376-7 (abst)


Further reading

* * * *


External links


General

*


Facilities


The 88-Inch Cyclotron
at Lawrence Berkeley National Laboratory
The first Cyclotron in Amsterdam, Netherlands (1964)
at the site of the Free University
National Superconducting Cyclotron Laboratory
of the Michigan State University—Home of coupled K500 and K1200 cyclotrons; the K500, the first superconducting cyclotron, and the K1200, formerly the most powerful in the world.
Rutgers Cyclotron
Students at Rutgers University built a 1 MeV cyclotron as an undergraduate project, which is now used for a senior-level undergraduate and a graduate lab course.
RIKEN Nishina Center for Accelerator-based Science
Home of the most powerful cyclotron in the world {{Authority control 1932 introductions Accelerator physics American inventions Nuclear medicine Particle accelerators