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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 ?
Designed and constructed by hi-spec technology and fabrication specialist LTi, the lead manufacturer of the cryogenic pressure vessels used in Siemens MRI scanners has used its fabrication expertise to support Tokamak Energy to create the world's first high-field spherical Tokamak ST40 reactor.
This breakthrough is what led to a couple of scientists at Culham, along with Dr Kingham, to form Tokamak Energy.
Bridges have collapsed and airplanes have crashed, with much more disastrous consequences than a tokamak shutting down unexpectedly would have, but improvements in technology have now made these events acceptably unlikely.
Corrientes alrededor de varios mega amperios son utilizadas en los Tokamak, como ejemplo los 7 MA que se han alcanzado en el Tokamak JET (Joint European Torus).
New techniques for enhancing energy confinement need to be tried as part of current experiments at facilities such as the Tokamak Fusion Test Reactor (TFTR) at Princeton University, the Dill-D Tokamak at General Atomics, the Joint European Torus (JET) in the United Kingdom, and the JT-60 in Japan.
Painting and coating for the tokamak complex buildings (tokamak, Tritium and diagnostic) including execution design, Surface preparation, Concrete reparation or surface treatment and related services.
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 is pursuing the long-awaited holy grail of the energy field--nuclear fusion.
As this analysis will show, tokamak fusion power will almost certainly be a commercial failure, which is a tragedy in light of the time, funds, and effort so far expended.
A group of scientists and engineers at the MIT Plasma Science and Fusion Center (PSFC) is about to publish a conceptual design paper of a small fusion pilot plant, using high temperature superconducting magnets, that would produce 270 Megawatts of electricity in a tokamak with a major radius about half the size of ITER, the fusion engineering test reactor currently under construction in France.
MAST, the Mega Amp Spherical Tokamak, (Tokamak is a donut shaped magnetic plasma confinement system) is the UK's own fusion machine, whereas JET, the Joint European Torus, is the world's largest fusion machine.