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Tokamak
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A tokamak (/ˈtoʊkəmæk/; Russian: токамáк) is a device which uses a powerful magnetic field generated by external magnets to confine plasma in the shape of an axially symmetrical torus.[1] The tokamak is one of several types of magnetic confinement devices being developed to produce controlled thermonuclear fusion power. The tokamak concept is currently one of the leading candidates for a practical fusion reactor.[2]
The proposal to use controlled thermonuclear fusion for industrial purposes and a specific scheme using thermal insulation of high-temperature plasma by an electric field was first formulated by the Soviet physicist Oleg Lavrentiev in a mid-1950 paper.[3] In 1951, Andrei Sakharov and Igor Tamm modified the scheme by proposing a theoretical basis for a thermonuclear reactor, where the plasma would have the shape of a torus and be held by a magnetic field.[4]
The first tokamak was built in 1954,[5]. In 1968 the electronic plasma temperature of 1 keV was reached on the tokamak T-3, built at the I. V. Kurchatov Institute of Atomic Energy under the leadership of academician L. A. Artsimovich.[6][7][8]
By the mid-1960s, the tokamak designs began to show greatly improved performance. The initial results were released in 1965, but were ignored; Lyman Spitzer dismissed them out of hand after noting potential problems in their system for measuring temperatures. A second set of results was published in 1968, this time claiming performance far in advance of any other machine. When these were also met skeptically, the Soviets invited British scientists from the laboratory in Culham Centre for Fusion Energy (Nicol Peacock et al.) to the USSR with their equipment.[9] Measurements on the T-3 confirmed the results,[10][11] spurring a worldwide stampede of tokamak construction. It had been demonstrated that a stable plasma equilibrium requires magnetic field lines that wind around the torus in a helix. Devices like the z-pinch and stellarator had attempted this, but demonstrated serious instabilities. It was the development of the concept now known as the safety factor (labelled q in mathematical notation) that guided tokamak development; by arranging the reactor so this critical factor q was always greater than 1, the tokamaks strongly suppressed the instabilities which plagued earlier designs.
By the mid-1970s, dozens of tokamaks were in use around the world. By the late 1970s, these machines had reached all of the conditions needed for practical fusion, although not at the same time nor in a single reactor. With the goal of breakeven (a fusion energy gain factor equal to 1) now in sight, a new series of machines were designed that would run on a fusion fuel of deuterium and tritium. These machines, notably the Joint European Torus (JET) and Tokamak Fusion Test Reactor (TFTR), had the explicit goal of reaching breakeven.
Instead, these machines demonstrated new problems that limited their performance. Solving these would require a much larger and more expensive machine, beyond the abilities of any one country. After an initial agreement between Ronald Reagan and Mikhail Gorbachev in November 1985, the International Thermonuclear Experimental Reactor (ITER) effort emerged and remains the primary international effort to develop practical fusion power. Many smaller designs, and offshoots like the spherical tokamak, continue to be used to investigate performance parameters and other issues. As of 2024[update], JET remains the record holder for fusion output, with 69 MJ of energy output over a 5-second period.[12]
- ^ "DOE Explains...Tokamaks". Energy.gov. Retrieved 15 December 2023.
- ^ Greenwald, John (24 August 2016). "Major next steps for fusion energy based on the spherical tokamak design". Princeton Plasma Physics Laboratory. United States Department of Energy. Archived from the original on 19 September 2021. Retrieved 16 May 2018.
- ^ B.D.Bondarenko The role of O. A. Lavrentiev in raising the issue and initiating research on controlled thermonuclear fusion in the USSR Archived 12 September 2017 at the Wayback Machine // UFN 171, 886 (2001).
- ^ "The Soviet Magnetic Confinement Fusion Program: An International future (SW 90-" (PDF). Archived from the original on 5 November 2010. Retrieved 27 June 2019.
- ^ V.Reshetov "An ocean of energy" Archived 13 November 2013 at the Wayback Machine // Around the world
- ^ Garry McCracken, Peter Stott (2015). Fusion: The Energy of the Universe. Elsevier Academic Press. p. 167. ISBN 978-0-12-481851-4.
- ^ L.A.Artsimovich; et al. (1969). Experimental studies on Tokamak installations (CN-24/B-1). Proceedings of the Third International Conference on Plasma Physics and Controlled Nuclear Fusion Research Held by the International Atomic Energy Agency at Novosibirsk, 1–7 August 1968. Vol. 1 (Plasma Physics and Controlled Nuclear Fusion Research. ed.). Vienna: IAEA. pp. 157–173.
- ^ Juho Miettunen (2015). Modelling of global impurity transport in tokamaks in the presence of non-axisymmetric effects (PhD thesis). Helsinki: Unigrafia Oy. p. 19. ISBN 978-952-60-6189-4.
- ^ Robert Arnoux (9 October 2009). "Off to Russia with a thermometer". ITER Newsline 102. Archived from the original on 8 July 2019. Retrieved 8 July 2019.
- ^ Peacock N. J.; et al. (1969). "Measurement of the Electron Temperature by Thomson Scattering in Tokamak T3". Nature. 224 (5218): 488–490. Bibcode:1969Natur.224..488P. doi:10.1038/224488a0. S2CID 4290094.
- ^ Evgeny Velikhov (2004). "I didn't let my soul be lazy. To the 95th anniversary of the birth of Academician L. A. Artsimovich". Herald of the Russian Academy of Sciences. 74 (10): 940. Archived from the original on 22 October 2020.
- ^ "Nuclear fusion: new record brings dream of clean energy closer". www.bbc.co.uk. 8 February 2024. Retrieved 8 February 2024.
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