Tokamak
Encyclopedia
A tokamak is a device using a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

to confine a plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

in the shape of a torus
Torus
In geometry, a torus is a surface of revolution generated by revolving a circle in three dimensional space about an axis coplanar with the circle...

(doughnut). Achieving a stable plasma equilibrium requires magnetic field lines that move around the torus in a helical
Helix
A helix is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for...

shape. Such a helical field can be generated by adding a toroidal
Toroidal and poloidal
The earliest use of these terms cited by the Oxford English Dictionary is by Walter M. Elsasser in the context of the generation of the Earth's magnetic field by currents in the core, with "toroidal" being parallel to lines of latitude and "poloidal" being in the direction of the magnetic field...

field (traveling around the torus in circles) and a poloidal
Toroidal and poloidal
The earliest use of these terms cited by the Oxford English Dictionary is by Walter M. Elsasser in the context of the generation of the Earth's magnetic field by currents in the core, with "toroidal" being parallel to lines of latitude and "poloidal" being in the direction of the magnetic field...

field (traveling in circles orthogonal to the toroidal field). In a tokamak, the toroidal field is produced by electromagnet
Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...

s that surround the torus, and the poloidal field is the result of a toroidal electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...

that flows inside the plasma. This current is induced
Electromagnetic induction
Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field. It underlies the operation of generators, transformers, induction motors, electric motors, synchronous motors, and solenoids....

inside the plasma with a second set of electromagnets.

The tokamak is one of several types of magnetic confinement devices
Magnetic confinement fusion
Magnetic confinement fusion is an approach to generating fusion power that uses magnetic fields to confine the hot fusion fuel in the form of a plasma. Magnetic confinement is one of two major branches of fusion energy research, the other being inertial confinement fusion. The magnetic approach is...

, and is one of the most-researched candidates for producing controlled thermonuclear fusion power
Fusion power
Fusion power is the power generated by nuclear fusion processes. In fusion reactions two light atomic nuclei fuse together to form a heavier nucleus . In doing so they release a comparatively large amount of energy arising from the binding energy due to the strong nuclear force which is manifested...

. Magnetic fields are used for confinement since no solid material could withstand the extremely high temperature of the plasma. An alternative to the tokamak is the stellarator
Stellarator
A stellarator is a device used to confine a hot plasma with magnetic fields in order to sustain a controlled nuclear fusion reaction. It is one of the earliest controlled fusion devices, first invented by Lyman Spitzer in 1950 and built the next year at what later became the Princeton Plasma...

.

Tokamaks were invented in the 1950s by Soviet
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

physicists Igor Tamm and Andrei Sakharov
Andrei Sakharov
Andrei Dmitrievich Sakharov was a Soviet nuclear physicist, dissident and human rights activist. He earned renown as the designer of the Soviet Union's Third Idea, a codename for Soviet development of thermonuclear weapons. Sakharov was an advocate of civil liberties and civil reforms in the...

, inspired by an original idea of Oleg Lavrentyev.

The word tokamak is a transliteration
Transliteration
Transliteration is a subset of the science of hermeneutics. It is a form of translation, and is the practice of converting a text from one script into another...

of the Russian
Russian language
Russian is a Slavic language used primarily in Russia, Belarus, Uzbekistan, Kazakhstan, Tajikistan and Kyrgyzstan. It is an unofficial but widely spoken language in Ukraine, Moldova, Latvia, Turkmenistan and Estonia and, to a lesser extent, the other countries that were once constituent republics...

word токамак, an acronym of either "тороидальная камера с магнитными катушками" (toroidal'naya kamera s magnitnymi katushkami)—toroidal chamber with magnetic coils, or "тороидальная камера с аксиальным магнитным полем" (toroidal'naya kamera s aksial'nym magnitnym polem)—toroidal chamber with axial magnetic field.

History

Although nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...

research began soon after World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

, the programs in various countries were each initially classified
Classified information
Classified information is sensitive information to which access is restricted by law or regulation to particular groups of persons. A formal security clearance is required to handle classified documents or access classified data. The clearance process requires a satisfactory background investigation...

as secret. It was not until after the 1955 United Nations
United Nations
The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...

International Conference on the Peaceful Uses of Atomic Energy in Geneva that programs were declassified and international scientific collaboration could take place.

Experimental research of tokamak systems started in 1956 in Kurchatov Institute
Kurchatov Institute
The Kurchatov Institute is Russia's leading research and development institution in the field of nuclear energy. In the Soviet Union it was known as I. V. Kurchatov Institute of Atomic Energy , abbreviated KIAE . It is named after Igor Kurchatov....

, Moscow
Moscow
Moscow is the capital, the most populous city, and the most populous federal subject of Russia. The city is a major political, economic, cultural, scientific, religious, financial, educational, and transportation centre of Russia and the continent...

by a group of Soviet scientists led by Lev Artsimovich
Lev Artsimovich
Lev Andreevich Artsimovich was a Soviet physicist, academician of the Soviet Academy of Sciences , member of the Presidium of the Soviet Academy of Sciences , and Hero of Socialist Labor .- Academic research :Artsimovich worked on the...

. The group constructed the first tokamaks, the most successful being T-3 and its larger version T-4. T-4 was tested in 1968 in Novosibirsk
Novosibirsk
Novosibirsk is the third-largest city in Russia, after Moscow and Saint Petersburg, and the largest city of Siberia, with a population of 1,473,737 . It is the administrative center of Novosibirsk Oblast as well as of the Siberian Federal District...

, conducting the first ever quasistationary thermonuclear fusion reaction.

In 1968, at the third IAEA
International Atomic Energy Agency
The International Atomic Energy Agency is an international organization that seeks to promote the peaceful use of nuclear energy, and to inhibit its use for any military purpose, including nuclear weapons. The IAEA was established as an autonomous organization on 29 July 1957...

International Conference on Plasma Physics and Controlled Nuclear Fusion Research at Novosibirsk
Novosibirsk
Novosibirsk is the third-largest city in Russia, after Moscow and Saint Petersburg, and the largest city of Siberia, with a population of 1,473,737 . It is the administrative center of Novosibirsk Oblast as well as of the Siberian Federal District...

, Soviet scientists announced that they had achieved electron temperature
Electron temperature
If the velocities of a group of electrons, e.g., in a plasma, follow a Maxwell-Boltzmann distribution, then the electron temperature is well-defined as the temperature of that distribution...

s of over 1000 eV
Electronvolt
In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...

in a tokamak device. British and American scientists met this news with skepticism, since they were far from reaching that benchmark; they remained suspicious until laser scattering tests confirmed the findings a few years later.

Toroidal design

Positively and negatively charged ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s and negatively charged 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 a fusion plasma are at very high temperatures, and have correspondingly large velocities. In order to maintain the fusion process, particles from the hot plasma must be confined in the central region, or the plasma will rapidly cool. Magnetic confinement fusion devices exploit the fact that charged particles in a magnetic field feel a Lorentz force
Lorentz force
In physics, the Lorentz force is the force on a point charge due to electromagnetic fields. It is given by the following equation in terms of the electric and magnetic fields:...

and follow helical paths along the field lines.

Early fusion research devices were variants on the Z-pinch
Z-pinch
In fusion power research, the Z-pinch, also known as zeta pinch or Bennett pinch , is a type of plasma confinement system that uses an electrical current in the plasma to generate a magnetic field that compresses it...

and used electrical current to generate a poloidal magnetic field to contain the plasma along a linear axis between two points. Researchers discovered that a simple toroidal field, in which the magnetic field lines run in circles around an axis of symmetry, confines a plasma hardly better than no field at all. This can be understood by looking at the orbits of individual particles. The particles not only spiral around the field lines, they also drift across the field
Guiding center
In many cases of practical interest, the motion in a magnetic field of an electrically charged particle can be treated as the superposition of a relatively fast circular motion around a point called the guiding center and a relatively slow drift of this point...

. Since a toroidal field is curved and decreases in strength moving away from the axis of rotation, the ions and the electrons move parallel to the axis, but in opposite directions. The charge separation leads to an electric field and an additional drift, in this case outward (away from the axis of rotation) for both ions and electrons. Alternatively, the plasma can be viewed as a torus of fluid with a magnetic field frozen in. The plasma pressure results in a force that tends to expand the torus. The magnetic field outside the plasma cannot prevent this expansion. The plasma simply slips between the field lines.

For a toroidal plasma to be effectively confined by a magnetic field, there must be a twist to the field lines. There are then no longer flux tubes that simply encircle the axis, but, if there is sufficient symmetry in the twist, flux surfaces. Some of the plasma in a flux surface will be on the outside (larger major radius, or "low-field side") of the torus and will drift to other flux surfaces farther from the circular axis of the torus. Other portions of the plasma in the flux surface will be on the inside (smaller major radius, or "high-field side"). Since some of the outward drift is compensated by an inward drift on the same flux surface, there is a macroscopic equilibrium with much improved confinement. Another way to look at the effect of twisting the field lines is that the electric field between the top and the bottom of the torus, which tends to cause the outward drift, is shorted out because there are now field lines connecting the top to the bottom.

When the problem is considered even more closely, the need for a vertical (parallel to the axis of rotation) component of the magnetic field arises. The Lorentz force of the toroidal plasma current in the vertical field provides the inward force that holds the plasma torus in equilibrium.

Plasma heating

In an operating fusion reactor, part of the energy generated will serve to maintain the plasma temperature as fresh deuterium
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

and tritium
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

are introduced. However, in the startup of a reactor, either initially or after a temporary shutdown, the plasma will have to be heated to its operating temperature
Operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...

of greater than 10 keV (over 100 million degrees Celsius). In current tokamak (and other) magnetic fusion experiments, insufficient fusion energy is produced to maintain the plasma temperature.

Ohmic heating

Since the plasma is an electrical conductor, it is possible to heat the plasma by inducing a current through it; in fact, the induced current that heats the plasma usually provides most of the poloidal field. The current is induced by slowly increasing the current through an electromagnetic winding linked with the plasma torus: the plasma can be viewed as the secondary winding of a transformer. This is inherently a pulsed process because there is a limit to the current through the primary (there are also other limitations on long pulses). Tokamaks must therefore either operate for short periods or rely on other means of heating and current drive. The heating caused by the induced current is called ohmic (or resistive) heating; it is the same kind of heating that occurs in an electric light bulb or in an electric heater. The heat generated depends on the resistance of the plasma and the current. But as the temperature of heated plasma rises, the resistance decreases and ohmic heating becomes less effective. It appears that the maximum plasma temperature attainable by ohmic heating in a tokamak is 20-30 million degrees Celsius. To obtain still higher temperatures, additional heating methods must be used.

Neutral-beam injection

Neutral-beam injection involves the introduction of high-energy (rapidly moving) atoms into the ohmically heated, magnetically confined plasma. The atoms are ionized as they pass through the plasma and are trapped by the magnetic field. The high-energy ions then transfer part of their energy to the plasma particles in repeated collisions, increasing the plasma temperature.

Magnetic compression

A gas can be heated by sudden compression. In the same way, the temperature of a plasma is increased if it is compressed rapidly by increasing the confining magnetic field. In a tokamak system this compression is achieved simply by moving the plasma into a region of higher magnetic field (i.e., radially inward). Since plasma compression brings the ions closer together, the process has the additional benefit of facilitating attainment of the required density for a fusion reactor.

High-frequency electromagnetic waves are generated by oscillators (often by gyrotron
Gyrotron
Gyrotrons are high powered vacuum tubes which emit millimeter-wave beams by bunching electrons with cyclotron motion in a strong magnetic field. Output frequencies range from about 20 to 250 GHz, covering wavelengths from microwave to the edge of the terahertz gap. Typical output powers range from...

s or klystron
Klystron
A klystron is a specialized linear-beam vacuum tube . Klystrons are used as amplifiers at microwave and radio frequencies to produce both low-power reference signals for superheterodyne radar receivers and to produce high-power carrier waves for communications and the driving force for modern...

s) outside the torus. If the waves have the correct frequency (or wavelength) and polarization, their energy can be transferred to the charged particles in the plasma, which in turn collide with other plasma particles, thus increasing the temperature of the bulk plasma. Various techniques exist including electron cyclotron resonance
Electron cyclotron resonance
Electron cyclotron resonance is a phenomenon observed both in plasma physics and condensed matter physics. An electron in a static and uniform magnetic field will move in a circle due to the Lorentz force...

heating (ECRH) and ion cyclotron resonance
Ion cyclotron resonance
Ion cyclotron resonance is a phenomenon related to the movement of ions in a magnetic field. It is used for accelerating ions in a cyclotron, and for measuring the masses of an ionized analyte in mass spectrometry, particularly with Fourier transform ion cyclotron resonance mass spectrometers...

heating. This energy is usually transferred by microwaves.

Tokamak cooling

The fusion reactions in the plasma spiraling around a tokamak reactor produce large amounts of high energy neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

s. These neutrons, being electrically neutral, are no longer held in the stream of plasma by the toroidal magnets and continue until stopped by the inside wall of the tokamak. This is a large advantage of tokamak reactors since these freed neutrons provide a simple way to extract heat from the plasma stream; this is how the fusion reactor generates usable energy. The inside wall of the tokamak must be cooled because these neutrons yield enough energy to melt the walls of the reactor. A cryogenic system is used to prevent heat loss from the superconducting magnet
Superconducting magnet
A superconducting magnet is an electromagnet made from coils of superconducting wire. They must be cooled to cryogenic temperatures during operation. In its superconducting state the wire can conduct much larger electric currents than ordinary wire, creating intense magnetic fields...

s. Mostly liquid helium
Liquid helium
Helium exists in liquid form only at extremely low temperatures. The boiling point and critical point depend on the isotope of the helium; see the table below for values. The density of liquid helium-4 at its boiling point and 1 atmosphere is approximately 0.125 g/mL Helium-4 was first liquefied...

and liquid nitrogen
Liquid nitrogen
Liquid nitrogen is nitrogen in a liquid state at a very low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colourless clear liquid with density of 0.807 g/mL at its boiling point and a dielectric constant of 1.4...

are used as refrigerant
Refrigerant
A refrigerant is a substance used in a heat cycle usually including, for enhanced efficiency, a reversible phase change from a liquid to a gas. Traditionally, fluorocarbons, especially chlorofluorocarbons, were used as refrigerants, but they are being phased out because of their ozone depletion...

s. Ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...

plates specifically designed to withstand high temperatures are also placed on the inside reactor wall to protect the magnets and reactor.

Currently in operation

(in chronological order of start of operations)
• TM1-MH (since 1977 Castor, since 2007 Golem) in Prague
Prague
Prague is the capital and largest city of the Czech Republic. Situated in the north-west of the country on the Vltava river, the city is home to about 1.3 million people, while its metropolitan area is estimated to have a population of over 2.3 million...

, Czech Republic
Czech Republic
The Czech Republic is a landlocked country in Central Europe. The country is bordered by Poland to the northeast, Slovakia to the east, Austria to the south, and Germany to the west and northwest....

; in operation in Kurchatov Institute
Kurchatov Institute
The Kurchatov Institute is Russia's leading research and development institution in the field of nuclear energy. In the Soviet Union it was known as I. V. Kurchatov Institute of Atomic Energy , abbreviated KIAE . It is named after Igor Kurchatov....

since early 1960s; 1977 renamed to Castor and moved to IPP CAS, Prague; 2007 moved to FNSPE, Czech Technical University in Prague
Czech Technical University in Prague
Czech Technical University in Prague is one of the largest universities in the Czech Republic, and the oldest institute of technology in Central Europe....

, and renamed to Golem
• T-10, in Kurchatov Institute
Kurchatov Institute
The Kurchatov Institute is Russia's leading research and development institution in the field of nuclear energy. In the Soviet Union it was known as I. V. Kurchatov Institute of Atomic Energy , abbreviated KIAE . It is named after Igor Kurchatov....

, Moscow
Moscow
Moscow is the capital, the most populous city, and the most populous federal subject of Russia. The city is a major political, economic, cultural, scientific, religious, financial, educational, and transportation centre of Russia and the continent...

, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

(formerly Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

); 2 MW; in operation since 1975
• TEXTOR, in Jülich
Jülich
Jülich is a town in the district of Düren, in the federal state of North Rhine-Westphalia, Germany. Jülich is well known as location of a world-famous research centre, the Forschungszentrum Jülich and as shortwave transmission site of Deutsche Welle...

, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

; in operation since 1978
• Joint European Torus
Joint European Torus
JET, the Joint European Torus, is the largest magnetic confinement plasma physics experiment worldwide currently in operation. Its main purpose is to open the way to future nuclear fusion experimental tokamak reactors such as ITER and :DEMO....

(JET), in Culham
Culham
Culham is a village and civil parish on the north bank of the River Thames, just over south of Abingdon in Oxfordshire.-Manor:The toponym comes from the Old English Cula's hamm, referring to the village's position in a bend of the Thames...

, United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

; 16 MW; in operation since 1983
• Novillo Tokamak, at the Instituto Nacional de Investigaciones Nucleares,in Mexico City
Mexico City
Mexico City is the Federal District , capital of Mexico and seat of the federal powers of the Mexican Union. It is a federal entity within Mexico which is not part of any one of the 31 Mexican states but belongs to the federation as a whole...

, Mexico; in operation since 1983
• JT-60
JT-60
JT-60 is the flagship of Japan's magnetic fusion program, previously run by the Japan Atomic Energy Research Institute and currently run by the Japan Atomic Energy Agency's Naka Fusion Institute in Ibaraki Prefecture, Japan...

, in Naka
Naka, Ibaraki
is a city located in Ibaraki, Japan. Naka was formerly a town in Naka District and became a city after merging with the neighboring town of Urizura on January 21, 2005....

, Ibaraki Prefecture
Ibaraki Prefecture
is a prefecture of Japan, located in the Kantō region on the main island of Honshu. The capital is Mito.-History:Ibaraki Prefecture was previously known as Hitachi Province...

, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

; in operation since 1985
• STOR-M
The Plasma Physics Laboratory at the University of Saskatchewan was established in 1959 by H. M. Skarsgard. Early work centered on research with a Betatron.-STOR-1M:STOR-1M is Canada's first tokamak built in 1983...

The University of Saskatchewan is a Canadian public research university, founded in 1907, and located on the east side of the South Saskatchewan River in Saskatoon, Saskatchewan, Canada. An "Act to establish and incorporate a University for the Province of Saskatchewan" was passed by the...

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

in operation since 1987; first demonstration of alternating current in a tokamak.
• Tore Supra
Tore Supra
Tore Supra is a French tokamak that began operating after the discontinuation of TFR and of Petula...

, at the CEA
Commissariat à l'Énergie Atomique
The Commissariat à l'énergie atomique et aux énergies alternatives or CEA, is a French “public establishment related to industrial and commercial activities” whose mission is to develop all applications of nuclear power, both civilian and military...

The CEA Cadarache facility is a French scientific research centre which specialises in nuclear energy research. It is located in the commune of Saint-Paul-lès-Durance, Bouches-du-Rhône, in the southern region of Provence-Alpes-Côte-d'Azur...

, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

; in operation since 1988
ADITYA is a medium size tokamak installed at the Institute for Plasma Research in India. It has a major radius of 0.75 metres and a minor radius of the plasma is 0.25 metres. The maximum field strength is 1.2 tesla produced by the help of 20 toroidal field coils spaced symmetrically in the toroidal...

, at Institute for Plasma Research
Institute for Plasma Research
Institute for Plasma Research is an autonomous physics research institute located in India. The institute is involved in research in aspects of plasma science including basic plasma physics, research on magnetically confined hot plasmas and plasma technologies for industrial applications. It is a...

(IPR) in Gujarat, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

; in operation since 1989
• DIII-D, in San Diego, USA
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

; operated by General Atomics
General Atomics
General Atomics is a nuclear physics and defense contractor headquartered in San Diego, California. General Atomics’ research into fission and fusion matured into competencies in related technologies, allowing the company to expand into other fields of research...

since the late 1980s
• COMPASS, in Prague
Prague
Prague is the capital and largest city of the Czech Republic. Situated in the north-west of the country on the Vltava river, the city is home to about 1.3 million people, while its metropolitan area is estimated to have a population of over 2.3 million...

, Czech Republic
Czech Republic
The Czech Republic is a landlocked country in Central Europe. The country is bordered by Poland to the northeast, Slovakia to the east, Austria to the south, and Germany to the west and northwest....

; in operation since 2008, previously operated from 1989 to 1999 in Culham, United Kingdom
• FTU
The Frascati Tokamak Upgrade is a tokamak operating at Frascati, Italy. Building on the Frascati Tokamak experiment, FTU is a compact, high-magnetic-field tokamak...

, in Frascati
Frascati
Frascati is a town and comune in the province of Rome in the Lazio region of central Italy. It is located south-east of Rome, on the Alban Hills close to the ancient city of Tusculum. Frascati is closely associated with science, being the location of several international scientific...

, Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

; in operation since 1990
• Tokamak ISTTOK, at the Instituto de Plasmas e Fusão Nuclear
Instituto de Plasmas e Fusão Nuclear
Instituto de Plasmas e Fusão Nuclear is a research unit of Instituto Superior Técnico , Lisbon, and a leading Portuguese institution in physics research...

, Lisbon
Lisbon
Lisbon is the capital city and largest city of Portugal with a population of 545,245 within its administrative limits on a land area of . The urban area of Lisbon extends beyond the administrative city limits with a population of 3 million on an area of , making it the 9th most populous urban...

, Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...

; in operation since 1991
ASDEX Upgrade is a divertor tokamak, that went into operation at the Max-Planck-Institut für Plasmaphysik, Garching in 1991...

, in Garching
Garching bei München
Garching bei München or Garching is a city in Bavaria, Germany near Munich. It is the home of several research institutes and university departments. It became a city on 14 September 1990.-Location:...

, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

; in operation since 1991
• Alcator C-Mod
Alcator C-Mod
Alcator C-Mod is a tokamak, a magnetically confined nuclear fusion device, at the MIT Plasma Science and Fusion Center. It is the tokamak with the highest magnetic field and highest plasma pressure in the world...

, MIT
Massachusetts Institute of Technology
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...

, Cambridge
Cambridge, Massachusetts
Cambridge is a city in Middlesex County, Massachusetts, United States, in the Greater Boston area. It was named in honor of the University of Cambridge in England, an important center of the Puritan theology embraced by the town's founders. Cambridge is home to two of the world's most prominent...

, USA; in operation since 1992
• Tokamak à configuration variable
Tokamak à configuration variable
The Tokamak à configuration variable is a research fusion reactor of the École polytechnique fédérale de Lausanne. Its particularity is that its torus section is three times higher than wide...

(TCV), at the EPFL, Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....

; in operation since 1992
• TCABR, at the University of São Paulo
University of São Paulo
Universidade de São Paulo is a public university in the Brazilian state of São Paulo. It is the largest Brazilian university and one of the country's most prestigious...

, São Paulo
São Paulo
São Paulo is the largest city in Brazil, the largest city in the southern hemisphere and South America, and the world's seventh largest city by population. The metropolis is anchor to the São Paulo metropolitan area, ranked as the second-most populous metropolitan area in the Americas and among...

, Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

; this tokamak was transferred from Centre des Recherches en Physique des Plasmas in Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....

; in operation since 1994.
• HT-7
HT-7
HT-7, or Hefei Tokamak-7, is an experimental superconducting tokamak nuclear fusion reactor built in Hefei, China, to investigate the process of developing fusion power. The HT-7 was developed with the assistance of Russia, and was based on the earlier T-7 tokamak reactor...

, in Hefei
Hefei
Hefei is the capital and largest city of Anhui Province in Eastern China. A prefecture-level city, it is the political, economic, and cultural centre of Anhui...

, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

; in operation since 1995
• HL-2A, in Chengdu
Chengdu
Chengdu , formerly transliterated Chengtu, is the capital of Sichuan province in Southwest China. It holds sub-provincial administrative status...

, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

; in operation since 2002
• MAST
Mega Ampere Spherical Tokamak
The Mega Ampere Spherical Tokamak, or MAST experiment is a nuclear fusion experiment in operation at Culham, Oxfordshire, England since December 1999. It follows the highly successful START experiment...

, in Culham
Culham
Culham is a village and civil parish on the north bank of the River Thames, just over south of Abingdon in Oxfordshire.-Manor:The toponym comes from the Old English Cula's hamm, referring to the village's position in a bend of the Thames...

, United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

; in operation since 1999
• NSTX
National Spherical Torus Experiment
The National Spherical Torus Experiment is an innovative magnetic fusion device based on the spherical tokamak concept that was constructed by the Princeton Plasma Physics Laboratory in collaboration with the Oak Ridge National Laboratory, Columbia University, and the University of Washington at...

in Princeton, New Jersey
Princeton, New Jersey
Princeton is a community located in Mercer County, New Jersey, United States. It is best known as the location of Princeton University, which has been sited in the community since 1756...

; in operation since 1999
• EAST (HT-7U), in Hefei
Hefei
Hefei is the capital and largest city of Anhui Province in Eastern China. A prefecture-level city, it is the political, economic, and cultural centre of Anhui...

, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

; in operation since 2006
• KSTAR
KSTAR
The KSTAR, or Korea Superconducting Tokamak Advanced Research is a magnetic fusion device being built at the National Fusion Research Institute in Daejon, South Korea. It is intended to study aspects of magnetic fusion energy which will be pertinent to the ITER fusion project as part of that...

, in Daejon, South Korea
South Korea
The Republic of Korea , , is a sovereign state in East Asia, located on the southern portion of the Korean Peninsula. It is neighbored by the People's Republic of China to the west, Japan to the east, North Korea to the north, and the East China Sea and Republic of China to the south...

; in operation since 2008

Previously operated

• LT-1, Australia National University's plasma physics group built the first tokamak outside of Soviet Union circa 1963
• T-3, in Kurchatov Institute
Kurchatov Institute
The Kurchatov Institute is Russia's leading research and development institution in the field of nuclear energy. In the Soviet Union it was known as I. V. Kurchatov Institute of Atomic Energy , abbreviated KIAE . It is named after Igor Kurchatov....

, Moscow, Russia (formerly Soviet Union);
• T-4, in Kurchatov Institute
Kurchatov Institute
The Kurchatov Institute is Russia's leading research and development institution in the field of nuclear energy. In the Soviet Union it was known as I. V. Kurchatov Institute of Atomic Energy , abbreviated KIAE . It is named after Igor Kurchatov....

, Moscow, Russia (formerly Soviet Union); in operation in 1968
• Texas Turbulent Tokamak, University of Texas, USA; in operation from 1971 to 1980.
• Tokamak de Fontenay aux Roses
Tokamak de Fontenay aux Roses
The Tokamak de Fontenay-aux-Roses was the first French tokamak, built in a research centre of the French Atomic Energy Commission in Fontenay-aux-Roses, a commune in the southwestern suburbs of Paris, France....

(TFR), near Paris, France
• Alcator A and Alcator C, MIT, USA; in operation from 1975 until 1982 and from 1982 until 1988, respectively.
• TFTR, Princeton University
Princeton University
Princeton University is a private research university located in Princeton, New Jersey, United States. The school is one of the eight universities of the Ivy League, and is one of the nine Colonial Colleges founded before the American Revolution....

, USA; in operation from 1982 until 1997
• T-15, in Kurchatov Institute
Kurchatov Institute
The Kurchatov Institute is Russia's leading research and development institution in the field of nuclear energy. In the Soviet Union it was known as I. V. Kurchatov Institute of Atomic Energy , abbreviated KIAE . It is named after Igor Kurchatov....

, Moscow, Russia (formerly Soviet Union); 10 MW; in operation from 1988 until 2005
• UCLA Electric Tokamak
Electric Tokamak
The UCLA Electric Tokamak is a low field magnetic fusion tokamak device with a large aspect ratio.The machine has a major radius of 5 metres, a minor radius of 1 metre, plasma current of 45 kiloamperes and can produce a core electron plasma temperature of 300 electronvolts. First plasma was...

, in Los Angeles
Los Ángeles
Los Ángeles is the capital of the province of Biobío, in the commune of the same name, in Region VIII , in the center-south of Chile. It is located between the Laja and Biobío rivers. The population is 123,445 inhabitants...

, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

; in operation from 1999 to 2005
• Tokamak de Varennes; Varennes
Varennes, Quebec
Varennes is an off-island suburb of Montreal, in southwestern Quebec, Canada on the Saint Lawrence River in the Regional County Municipality of Lajemmerais. The city is approximately 15 miles from Downtown Montreal. The population as of the Canada 2006 Census was 20,950...

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

; in operation from 1987 until 1999; operated by Hydro-Québec
Hydro-Québec
Hydro-Québec is a government-owned public utility established in 1944 by the Government of Quebec. Based in Montreal, the company is in charge of the generation, transmission and distribution of electricity across Quebec....

and used by researchers from Institut de recherche en électricité du Québec
IREQ
L'Institut de recherche d'Hydro-Québec , known by its acronym IREQ is a research institute established in 1967 by government-owned utility Hydro-Québec. IREQ operates from Varennes, a town on the south shore of Montreal, Quebec, Canada...

(IREQ) and the Institut national de la recherche scientifique (INRS)
• START
Small Tight Aspect Ratio Tokamak
The Small Tight Aspect Ratio Tokamak, or START was a nuclear fusion experiment that used magnetic confinement to hold plasma. The experiment began at the Culham Science Centre in the United Kingdom in 1991 and was retired in 1998. It was built as a low cost design, largely using parts already...

in Culham, United Kingdom; in operation from 1991 until 1998
• COMPASS in Culham; in operation until 2001
• HL-1M Tokamak,Chengdu,China; in operation from 1994 to 2001

Planned

• ITER
ITER
ITER is an international nuclear fusion research and engineering project, which is currently building the world's largest and most advanced experimental tokamak nuclear fusion reactor at Cadarache in the south of France...

The CEA Cadarache facility is a French scientific research centre which specialises in nuclear energy research. It is located in the commune of Saint-Paul-lès-Durance, Bouches-du-Rhône, in the southern region of Provence-Alpes-Côte-d'Azur...

, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

; 500 MW; construction began in 2008, first plasma expected in 2018
• SST-1
SST-1 (tokamak)
SST-1 is a plasma confinement experimental device under construction in the Institute for Plasma Research in India. It is designed as a medium-sized tokamak with superconducting magnets....

, in Institute for Plasma Research
Institute for Plasma Research
Institute for Plasma Research is an autonomous physics research institute located in India. The institute is involved in research in aspects of plasma science including basic plasma physics, research on magnetically confined hot plasmas and plasma technologies for industrial applications. It is a...

Gandhinagar, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

; 1000 seconds operation; currently being assembled
• DEMO
DEMO
DEMO is a proposed nuclear fusion power plant that is intended to build upon the expected success of the ITER experimental nuclear fusion reactor. Whereas ITER's goal is to produce 500 megawatts of fusion power for at least 500 seconds, the goal of DEMO will be to produce at least four times that...

; 2000 MW, continuous operation, connected to power grid. Planned successor to ITER; construction to begin in 2024 according to preliminary timetable.

• The section on Dimensionless parameters in tokamaks in the article on Plasma scaling
Plasma scaling
The parameters of plasmas, including their spatial and temporal extent, vary by many orders of magnitude. Nevertheless, there are significant similarities in the behaviors of apparently disparate plasmas. Understanding the scaling of plasma behavior is of more than theoretical value...

• Edge-Localized Mode
• Stellarator
Stellarator
A stellarator is a device used to confine a hot plasma with magnetic fields in order to sustain a controlled nuclear fusion reaction. It is one of the earliest controlled fusion devices, first invented by Lyman Spitzer in 1950 and built the next year at what later became the Princeton Plasma...

• Reversed-field pinch

• CCFE - site from the UK fusion research centre CCFE
Culham Centre for Fusion Energy
The Culham Centre for Fusion Energy , located at the Culham Science Centre, near Culham, Oxfordshire, is the site of the Joint European Torus , Mega Ampere Spherical Tokamak and the now closed Small Tight Aspect Ratio Tokamak .Since September 2008 the director has been Professor Steven Cowley, and...

.
• Plasma Science - site on tokamaks from the French CEA
Commissariat à l'Énergie Atomique
The Commissariat à l'énergie atomique et aux énergies alternatives or CEA, is a French “public establishment related to industrial and commercial activities” whose mission is to develop all applications of nuclear power, both civilian and military...

.
• Fusion Programs at General Atomics
General Atomics
General Atomics is a nuclear physics and defense contractor headquartered in San Diego, California. General Atomics’ research into fission and fusion matured into competencies in related technologies, allowing the company to expand into other fields of research...

, including the DIII-D National Fusion Facility, an experimental tokamak.
• Fusion and Plasma Physics Seminar at MIT OCW
• Unofficial ITER fan club, Club for fans of the biggest tokamak planned to be built in near future.
• www.tokamak.info Extensive list of current and historic tokamaks from around the world.
• SSTC-1 Overview video of a small scale tokamak concept.
• SSTC-2 Section View Video of a small scale tokamak concept.
• SSTC-3 Fly Through Video of a small scale tokamak concept.
• http://www.plasma.inpe.br/LAP_Portal/LAP_Site/Text/Tokamak_Development.htm Information on conditions necessary for nuclear reaction in a tokamak reactor