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.

nuclear fusion

Emulating the energy source of the sun and other stars to create energy on earth. What makes nuclear fusion unusual, is that it generates more energy than the energy it takes to operate it. The largest fusion project is the International Thermonuclear Experimental Reactor (ITER) in France, a collaboration of 35 countries that is building a nuclear reactor using the Tokamak design. The Tokamak is a doughnut-shaped vacuum chamber that creates the environment for nuclear fusion.

Comprising millions of parts and costing more than $20 billion, the Tokamak weighs more than 20 thousand tons and requires millions of amps of electricity to drive deuterium and tritium isotopes into each other at 270 million degrees Fahrenheit. Designed to generate 500 megawatts of electricity, the first test is scheduled for 2025, and the reactor is expected to be operational by 2035.

Implosion Rather Than Explosion
Nuclear fusion works the opposite of nuclear fission, which is the nuclear power plant technology in use today. Nuclear fission splits atoms apart, whereas fusion "fuses" atoms together and generates more energy than fission and a million times more than coal, oil or gas.

Considered the Only Hope for the Future
Many scientists consider fusion the only real hope for solving energy production in the future. Countries around the world are always striving for greater productivity. Proponents predict that nuclear fusion is the only way to generate the energy required to support the increased consumption resulting from making more things for an ever-increasing population. Eventually, fossil fuels will run out, and in the meantime, they pollute the atmosphere. Although many people have great hopes in renewable energy, solar and wind cannot meet future energy requirements according to Michael Moore in his 2020 documentary "Planet of the Humans" on YouTube.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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

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References in periodicals archive

Hirsch mentions, for example, superconducting magnets failing in accelerators, causing long downtimes for repair, and plasma-disruptive shutdown in tokamaks. This argument ignores the learning curve of technology improvement.

Keeping fusion flexible

Prieur, Safety Factor Profile Control in a Tokamak, Springer, New York, NY, USA, 2014.

Optimal tracking for a divergent-type parabolic PDE system in current profile control

where [D.sub.max] and [D.sub.min], respectively, denote the diffusion coefficients of H-mode and L-mode, the parameters [v.sub.A], c, [B.sub.p], B, [alpha], [beta], and [g.sub.0] are constants, and [v.sub.A], c, [B.sub.p], and B are the Alfven velocity, the light velocity, the magnetic field which is parallel to the poloidal direction in Tokamak, and the characteristic magnetic field, respectively.

The dynamic mutation characteristics of thermonuclear reaction in Tokamak

Along with NSTX--a complementary experiment at Princeton University--MAST is one of the world's two leading spherical tokamaks (STs).

Three University of Texas physicists awarded patent for nuclear waste invention

Experiments using this technology to heat a high-density plasma in a Tokamak supplied by M.I.T.

Assessing the future of fusion

At Tokamak Energy, we're creating a way to do it quicker by being a private, agile firm.

Powering up: Jonathan Carling, the new chief executive of Tokamak Energy, on moving from luxury cars and engines to 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.

Fusion research time to set a new path: the inherent limitations of the tokamak design for fusion power will prevent it from becoming commercially viable, but the lessons from this effort can inform future research

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.

High Temperature Superconductors Coming of Age for Fusion

MAST on the other hand, pioneered a more spherical shaped Tokamak, which is more compact and requires much less magnetic field to maintain the stability of the plasma than the previous experiments.

Hot stuff: on 12 June a group of IED Members and guests visited Culham Centre for Fusion Energy (CCFE) as part of one of their monthly open evenings Eleanor Fosberry MEng IEng MIED reports

High temperature superconductors have remarkable properties: they conduct electricity with zero resistance, even with simple cooling by liquid nitrogen; they can withstand high magnetic fields and huge current densities - and they continue to be superconducting throughout the plasma pulse in a tokamak.

Super magnets take role in fusion research