Tokamak

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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 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.

V. S. MUKHOVATOV

References in periodicals archive ?
145) Where ITER uses a tokomak, another approach to a controlled fusion reaction injects electrical energy or uses high-energy lasers pointed at a small pellet of fuel that heat or implode it to a point where fusion occurs.
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In a monitoring solution deployed at the University of Wisconsin, photomultiplier tubes positioned around the school's Tokomak torus detect photons, and the tube outputs are digitized by up to 160 channels of Agilent's high-speed Model U 1063-002 Digitizers.
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He also designed a controlled nuclear fusion reactor called Tokomak, and he explored theoretical physics with insights about matter and antimatter.
In addition, the Administration remains committed to construction of the Superconducting Supercollider (SSC), the space station Freedom, and--on a slower schedule--the National Aerospace Plane and the Compact Ignition Tokomak fusion reactor.
From the advances in laser-confinement geeks over at places like the Central Laser Facility (CFL) in the UK or the National Ignition Facility (NIF) in the USA to Tokomaks like the ITER project in France to the new efforts like the joint project between MIT and Columbia University, we seem to be getting ever-closer to the holy grail of commercial nuclear fusion.