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(plasma physics)
A device for confining a plasma within a toroidal chamber, which produces plasma temperatures, densities, and confinement times greater than that of any other such device; confinement is effected by a very strong externally applied toroidal field, plus a weaker poloidal field produced by a toroidally directed plasma current, and this current causes ohmic heating of the plasma.



a closed magnetic trap, or magnetic bottle, of toroidal shape that is used for the generation and confinement of a high-temperature plasma. The name “Tokamak” is an acronym formed from the Russian words for “toroidal chamber with an axial magnetic field.” Such a device was first proposed in 1950 by I. E. Tamm and A. D. Sakharov as a means of achieving controlled thermonuclear fusion. Fundamental contributions to the development and study of Tokamak-type systems have been made by a group of Soviet scientists headed by L. A. Artsimovich, which in 1956 instituted a series of experimental investigations of such systems at the I. V. Kurchatov Institute of Atomic Energy.

The magnetic field that confines and stabilizes the plasma in a Tokamak is the sum of three fields: the field Hω generated by a current I induced along the plasma column; the much stronger toroidal field Hφ, which is parallel to the current; and the relatively weak transverse field H, which is directed parallel to the major axis of the torus. The field Hφ is produced by coils wound on the torus, and the field H is generated by conductors located along the torus. The lines of force of the overall magnetic field have the form of helices, which in running numerous times around the torus form a system of nested closed magnetic surfaces.

The plasma in a Tokamak is magnetohydrodynamically stable if the Kruskal-Shafranov condition is satisfied: Hφa/HωR > 1, where R is the major radius of the torus and a is the radius of the cross section of the plasma column. The transverse field HHωa/R is required to keep the plasma in equilibrium. The plasma is heated by the current that flows through it. Alternating magnetic fields and the injection of energetic neutral atoms are used to provide additional heating of the plasma.

The first quasi–steady-state thermonuclear reaction was obtained in 1968 with the T-4 Tokamak, which was built at the Institute of Atomic Energy. The parameters of the T-4 were as follows: a = 17 cm, R = 90 cm, Hφ = 3.5 × 104ergs, I = 1.5 × 105 amperes. The maximum attained plasma parameters were the following: temperature of deuterium ions, ~8 × 106°K; density of the ions, ~ 1014 cm–3; and time of plasma confinement, ~0.02 sec. During the early 1970’s the Tokamak systems took the world lead in research on controlled thermonulear fusion. A number of Tokamaks much larger than the T-4 had been constructed by 1976; examples are the T-10 in the USSR, the PLT and Alcator in the USA, and the TFR in France. A number of designs for thermonuclear reactors are based on Tokamak systems; the designs are scheduled for implementation at the end of the 20th century.


References in periodicals archive ?
Over the past decade, several privately funded startup companies have sprung up in the United States and elsewhere in pursuit of practical fusion power based on radically different approaches from the tokamak.
Residual radiation is present in the Tokamaks however staff are protected from this by a system involving 900 tonne, 3ft thick concrete doors, meaning that the exposure to radiation in the control room is actually lower than outside in the natural environment as the shielding blocks out all the background radiation that would otherwise be present.
The Kolmogoroff-Arnold-Moser theory displays small denominators at rational surfaces of 3D solutions, and analysis of the continuous spectrum shows that the stability of tokamaks is marginal (9).
s method is confirmed at higher densities, it may lead to a compact, environmentally acceptable fusion power plant capable of burning Helium-3, a non-radioactive fuel which, unlike the government TOKAMAK program, produces negligible amounts of neutron radiation, minimal heat pollution and will not breed nuclear weapons.
fusion program currently operates two tokamaks that are producing state-of-the-art scientific results: DIII-D, at General Atomics in San Diego, was designed and built during the 1970s.
The Associated Laboratory has been created to develop cooperation on CEA's long-pulse tokamak WEST and ASIPP's EAST, particularly in the fields of actively cooled, metallic plasma-facing components; long-duration plasma operation in an actively cooled, metallic environment; long-pulse heating and current drive; and ITER technology support.
The good news about this stampede to tokamaks was that it led to an explosion of understanding of tokamak plasmas and dramatic increases in their performance.
In 1977, as negotiations for siting the JET device stalled, Sheffield came back to the USA to head up a new tokamak project at the Oak Ridge National Laboratory (ORNL) in Tennessee.
The particles escape from these chambers, known as a tokamaks, more than 100 times faster than present theory predicts they should, stealing critical energy away from the reactor.
Plasma rotation in magnetic fields was another topic that he worked on throughout his life, first on rotation in theta pinches and later in tokamaks.