tokamak

enUK

tokamak

to·ka·mak

T0250800 (tô′kə-măk′, tŏk′ə-)n. A doughnut-shaped chamber used in fusion research in which a plasma is heated and confined by magnetic fields.

[Russian, from to(roidal'naya) kam(era s) ak(sial'nym magnitnym polem), toroidal chamber with axial magnetic field.]

tokamak

(ˈtɒkəˌmæk) n (General Physics) physics a toroidal reactor used in thermonuclear experiments, in which a strong helical magnetic field keeps the plasma from contacting the external walls. The magnetic field is produced partly by current-carrying coils and partly by a large inductively driven current through the plasma[C20: from Russian to(roidál'naya) kám(era s) ak(siál'nym magnitnym pólem), toroidal chamber with magnetic field]

to•ka•mak

(ˈtoʊ kəˌmæk, ˈtɒk ə-)

n. a type of experimental nuclear fusion reactor in which a plasma of ions circulates in a toroidal tube and is confined to a narrow beam by an electromagnetic field. [1960–65; < Russian tokamák, for to(roidál'naya) kám(era s) ak(siál'nym magnítnym pólem) toroidal chamber with an axial magnetic field]

Thesaurus

Noun

tokamak - a doughnut-shaped chamber used in fusion research; a plasma is heated and confined in a magnetic bottlechamber - a natural or artificial enclosed spacemagnetic bottle - container consisting of any configuration of magnetic fields used to contain a plasma during controlled thermonuclear reactions

Tokamak

enUK

tokamak

[′täk·ə‚mak] (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.

Tokamak

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 H_ω generated by a current I induced along the plasma column; the much stronger toroidal field H_φ, 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 H_φ 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: H_φa/H_ωR > 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 H_⊥ – H_ωa/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, H_φ = 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.

V. S. MUKHOVATOV

tokamak

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noun a doughnut-shaped chamber used in fusion research

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