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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 ?
In this development, LTi Metaltech (or LTi) of Oxfordshire is expert in high integrity welded structures and has supported neighbouring high-tech company Tokamak Energy with its aim to create the ST40 fusion reactor, a crucial prototype step towards a device to produce electricity for the first time in 2025.
We've actually built one of these small tokamaks with high-temperature superconducting magnets.
Compact, high-field tokamaks provide another exciting opportunity for accelerating fusion energy development, so that it's available soon enough to make a difference to problems like climate change and the future of clean energy -- goals I think we all share," says Dennis Whyte, the Hitachi America Professor of Engineering, director of the Plasma Science and Fusion Center, and head of the Department of Nuclear Science and Engineering at MIT.
The findings have confirmed the hypothesis that the operation of plasmathe fuel in which all particles are ionized and can react to a magnetic fieldin a tokamak is compatible with metallic walls.
Alcator C-Mod is a tokamak - a doughnut-shaped device that can contain high-energy, plasma produced using relatively low and inexpensive magnetic fields.
Tokamak Energy, which is working on nuclear fusion, is one of the first five companies to receive support from the institution's Stephenson Fund.
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.
Indudablemente, los dispositivos precursores de los complejos Tokamaks y Stellarators fueron las maquinas lineales de plasmas frios.
The patented tokamak is surrounded by an area that would house a nuclear waste fuel source and waste byproducts of the nuclear fuel cycle.
The NSTAB code has been developed to model 3D equilibrium and stability in tokamaks with a poloidal field provided by net plasma current or in stellarators with external coils for the poloidal field.
For decades, researchers have seen hints that impurities in fuel appear to boost performance of tokamaks.