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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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



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.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Major component replacement in a tokamak fusion reactor will be very time-consuming, because of its complex geometry and the attendant long reactor downtimes, which will increase power costs.
Of particular concern will be an aircraft collision with a tokamak fusion power plant.
However, it would definitely hinder a tokamak fusion reactor, where long-term operation is essential.
Hawryluk, the Board noted his scientific leadership previously of the Princeton Large Toms (PLT), Princeton Divertor Experiment (PDX) and Tokamak Fusion Test Reactor (TFTR) projects and, more recently, the National Spherical Torus (NSTX) and National Compact Stellarator (NCSX) projects.
Tokamak Fusion Test Reactor (TFTR) operations Terminated 10 Years ago-The construction of TFTR was started in March 1976 as part of a major US Energy R&D effort in response to the Gulf oil embargo of the mid-1970s.
* First observation of the "bootstrap current" in a tokamak, a self generated current that is the key feature of steady-state tokamak fusion power plants (1986)
China has constructed "an advanced new device," the EAST superconducting tokamak fusion experiment.
The article is a rehash of debates over the commercial potential of the tokamak fusion concept that have occurred periodically over the past three decades and is filled with outdated "facts." Nature quotes British fusion power plant designer Ian Cook as saying, "It's complete rubbish from beginning to end.
These wave-induced currents can enable tokamak fusion reactors to operate continuously, which is necessary for an economical and practical fusion reactor, the Department said.
The Board notes that the world fusion effort is especially in his debt for his early and continuing recognition of the importance of high magnetic field in the design and operation of tokamak fusion devices and for his tireless efforts to urge the construction of a fusion ignition experiment.
A focused technology effort was initiated in March 1986 through the development and implementation of the Project of Fusion and Fission Hybrid Reactor R&D, resulting in accomplishments in the areas of tritium handling, heating and current drive and the design of advanced tokamak fusion reactors.
The conferees note that the fiscal year 2002 funding level included $19,604,000 for the completion of decontamination and decommissioning of the Tokamak Fusion Test Reactor (TFTR), leaving $228,891,000 available for fusion research and facility operations in fiscal year 2002.