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    Tokamak

    Also known as tokamak reactor, toroidal chamber with magnetic coils

    A tokamak is a doughnut-shaped machine that confines a fusion plasma with strong magnetic fields. It was first developed in the Soviet Union in the late 1960s and is now the most widely adopted magnetic fusion design.[1][2] Tokamaks hold the fusion-energy record (69 MJ at JET) and long-pulse records of over 1,000 seconds, and they underpin ITER and Commonwealth Fusion Systems' SPARC.[3][4][5]

    Editor reviewedUpdated Fusion energyPhysicsEnergy and climate
    Key facts

    How a tokamak works

    A tokamak is an experimental machine that creates a fusion plasma and confines it with strong magnetic fields inside a doughnut-shaped vessel.[1] Magnetic coils around the vessel shape the charged plasma and keep it away from the walls. This matters because the plasma must reach about 150 million degrees Celsius for deuterium-tritium fusion.[1][6] Part of the confining field, the poloidal field, comes from an electric current induced in the plasma by transformer action. That current is the main difference from a stellarator.[7]

    The design was first developed by Soviet researchers in the late 1960s. It has since been adopted around the world as the most promising magnetic configuration.[2]

    Records and landmark machines

    • JET (UK). The Joint European Torus first ran on deuterium-tritium fuel in 1997 and ended operations at the end of December 2023.[8] In its final campaign it produced a record 69 megajoules over 5 seconds from 0.2 milligrams of fuel.[3]
    • EAST (China). On 20 January 2025 it became the first machine to hold a high-confinement plasma for more than 1,000 seconds, reaching 1,066 seconds at nearly 70 million degrees Celsius.[4]
    • WEST (France). On 12 February 2025 it set a plasma-duration record of 1,337 seconds.[5]
    • iter (France). ITER’s volume and weight are nearly 10 times those of the largest existing tokamaks, and it is designed to reach Q of at least 10.[9][10] Its ninth and final vacuum vessel sector was delivered on 5 October 2026, completing the set of core components on site.[11]

    Magnets and scale

    Large tokamaks rely on superconducting magnets. iter uses niobium-tin and niobium-titanium coils cooled to about 4 kelvin. Its 18 D-shaped toroidal field coils reach a maximum of 11.8 tesla, and the whole magnet system weighs about 10,000 tonnes and stores 51 gigajoules.[12] ITER also plans a tungsten first wall, the material it considers most relevant for later DEMO and commercial machines.[13]

    Compact high-field tokamaks

    High-temperature superconducting magnets let designers build much smaller tokamaks for the same performance; MIT said its 20-tesla magnet matches a conventional device about 40 times larger in volume.[14] commonwealth-fusion-systems is building SPARC on this principle in Massachusetts, aiming to demonstrate net fusion energy (Q>1), which it publicly targets for 2027.[15][16] China is building BEST in Hefei, a burning-plasma tokamak aimed at net fusion power gain and an electricity demonstration around 2030.[17] See hts-fusion-magnets.

    Compact machines are also being used to test unconventional fuels. On 28 September 2026 China’s ENN Group said its EXL-50U spherical tokamak in Langfang had achieved hydrogen-boron fusion reactions, which it called the first such result by a commercial fusion company on its own device.[18] Hydrogen-boron fusion avoids the 14 MeV neutrons that deuterium-tritium fuel produces and the tritium-breeding problem that comes with them, but it needs far higher plasma temperatures than the roughly 150 million degrees Celsius of D-T fusion.[19][20][6] The ENN result was announced by the company and reported by a single outlet, so it is recorded here as reported.

    Simulation and operations

    Running a tokamak is a control problem as much as a physics problem, and operators increasingly pair the machine with a software model. CFS said on 6 January 2026 that it would build a digital twin of SPARC with nvidia and Siemens, using NVIDIA Omniverse libraries and OpenUSD alongside Siemens engineering software.[21] On 8 October 2026 it said the US Department of Energy had selected it to lead an AI-enabled digital twin project for SPARC operations in the second phase of the Genesis Mission.[22] On the public side, ITER plans to test its disruption mitigation system fully during its first research phase.[23]

    Limits and open problems

    The plasma current that helps confine a tokamak plasma is driven by transformer action.[7] By contrast, EUROfusion notes that stellarators, which have no plasma current, can run in steady state and are less prone to plasma instabilities.[24] ITER plans to test its disruption mitigation system fully during its first research phase.[23] Like every D-T machine, a tokamak power plant must also breed tritium and survive 14 MeV neutron bombardment.[20][19]

    Questions readers ask

    What does "tokamak" mean?

    It is a Russian acronym meaning "toroidal chamber with magnetic coils". The design was first developed by Soviet researchers in the late 1960s.[2]

    How does a tokamak differ from a stellarator?

    A tokamak gets part of its confining magnetic field from a current induced in the plasma by transformer action, while a stellarator uses only external helical coils.[7]

    What is the record for fusion energy from a tokamak?

    The Joint European Torus produced 69 megajoules over 5 seconds from 0.2 milligrams of fuel in its final deuterium-tritium experiments, before closing at the end of 2023.[3][8]

    How long can a tokamak run?

    In 2025 France's WEST held a plasma for 1,337 seconds, and China's EAST held a high-confinement plasma for 1,066 seconds.[5][4]

    Can a tokamak burn fuel other than deuterium and tritium?

    China's ENN Group said on 28 September 2026 that its EXL-50U spherical tokamak had achieved hydrogen-boron fusion reactions, which it called a first for a commercial fusion company on its own device. Hydrogen-boron fuel avoids 14 MeV neutrons but needs much higher temperatures than deuterium-tritium fuel.[18][19]

    Sources

    Each numbered claim is a statement we checked against the sources listed with it. Status shows how well established it is.

    1. [1]

      A tokamak is an experimental machine in which a fusion plasma is created and confined by strong magnetic fields in a doughnut-shaped (toroidal) vessel. confirmedas of 2026-10-10

    2. [2]

      The tokamak was first developed by Soviet researchers in the late 1960s and has been adopted worldwide as the most promising magnetic fusion configuration; its name is a Russian acronym for "toroidal chamber with magnetic coils". confirmedas of 2026-10-10

    3. [3]

      In its final deuterium-tritium experiments, announced on 8 February 2024, the Joint European Torus (JET) in the UK produced a record 69 megajoules of fusion energy over 5 seconds from 0.2 milligrams of fuel. confirmedas of 2026-10-10

    4. [4]

      On 20 January 2025 China's EAST tokamak sustained a high-confinement plasma for 1,066 seconds, the first to pass 1,000 seconds, at nearly 70 million degrees Celsius. confirmedas of 2026-10-10

    5. [5]

      On 12 February 2025 France's WEST tokamak set a plasma-duration record of 1,337 seconds (about 22 minutes). confirmedas of 2026-10-10

    6. [6]

      Deuterium-tritium fusion in the laboratory requires temperatures of about 150 million degrees Celsius. confirmedas of 2026-10-10

    7. [7]

      In a tokamak, part of the confining (poloidal) magnetic field comes from a current driven inside the plasma by transformer action, whereas a stellarator generates it with external helical coils. confirmedas of 2026-10-10

    8. [8]

      JET ended scientific operations at the end of December 2023 after more than four decades; it first used deuterium-tritium fuel in 1997. confirmedas of 2026-10-10

    9. [9]

      The ITER tokamak's volume and weight are nearly 10 times those of the largest existing tokamaks, and its combined toroidal field coils form a magnet with a cold mass over 6,000 tonnes storing 41 gigajoules. confirmedas of 2026-10-10

    10. [10]

      ITER's main performance goal, Q of at least 10, means 500 megawatts of thermal fusion power from 50 megawatts of heating power put into the plasma, in 400-second pulses. confirmedas of 2026-10-10

    11. [11]

      On 5 October 2026 ITER took delivery of vacuum vessel sector confirmedas of 2026-10-05

    12. [12]

      ITER's magnets use niobium-tin or niobium-titanium superconductors cooled to about 4 kelvin, including 18 D-shaped toroidal field coils with a maximum field of 11.8 tesla, and total 10,000 tonnes storing 51 gigajoules. confirmedas of 2026-10-10

      • Magnets · ITER Organization (retrieved 2026-10-10)
    13. [13]

      Under the 2024 baseline ITER switched its first wall from beryllium to tungsten, which it considers more relevant for future DEMO and commercial machines. confirmedas of 2026-10-10

    14. [14]

      MIT said high-temperature superconducting magnets allow the same performance as a device about 40 times larger in volume built with conventional low-temperature superconducting magnets. confirmedas of 2026-10-10

    15. [15]

      Commonwealth Fusion Systems says its SPARC tokamak in Devens, Massachusetts, is intended to be the first commercially relevant machine to demonstrate net fusion energy (Q>1). confirmedas of 2026-08-05

    16. [16]

      As of October 2026 Commonwealth Fusion Systems publicly targets 2027 for SPARC to produce more energy from fusion than is needed to power the process, the Q>1 threshold. reportedas of 2026-10-10· forecast

    17. [17]

      China's Burning Plasma Experimental Superconducting Tokamak (BEST), under construction in Hefei, is designed to burn deuterium-tritium plasma, achieve net fusion power gain and demonstrate fusion electricity generation by around 2030. confirmedas of 2026-01-19· forecast

    18. [18]

      On 28 September 2026 ENN Group, based in Langfang, Hebei, said its EXL-50U spherical tokamak had achieved hydrogen-boron fusion reactions, which the company called the first time a commercial fusion company had done so on its own device. reportedas of 2026-09-28

    19. [19]

      A key materials challenge is building components that can withstand the 14 MeV neutrons from deuterium-tritium fusion, energies that fission-reactor experiments cannot easily mimic. confirmedas of 2026-10-10

    20. [20]

      Tritium for future plants is to be bred when neutrons escaping the plasma react with lithium in a blanket lining the reactor wall. confirmedas of 2026-10-10

      • Fuelling · ITER Organization (retrieved 2026-10-10)
    21. [21]

      CFS is building a digital twin of SPARC with NVIDIA and Siemens, announced on 6 January 2026, using NVIDIA Omniverse libraries and OpenUSD together with Siemens engineering software. reportedas of 2026-01-06

    22. [22]

      On 8 October 2026 CFS said the US Department of Energy had selected it as the only private company leading a project in the second phase of the Genesis Mission, for an AI-enabled digital twin platform to optimise SPARC operations. reportedas of 2026-10-08

    23. [23]

      Under the 2024 baseline, all ITER systems, including the disruption mitigation system, will be fully tested during the Start of Research Operation phase, which uses hydrogen and deuterium plasmas. confirmedas of 2026-10-10

    24. [24]

      Because a stellarator has no plasma current, it can in principle run continuously (steady state) and is less prone to plasma instabilities than a tokamak. confirmedas of 2026-10-10

    25. [25]

      A 2024 analysis of the CFS magnet found REBCO superconductors well suited to tokamaks, enabling devices some 30 to 40 times smaller in volume than earlier designs. confirmedas of 2024-04-04

    Revision history (2)
    1. Page created.
    2. Refresh: added ENN's hydrogen-boron result on EXL-50U, ITER's final vacuum vessel sector delivery, CFS's 2027 Q>1 target and a section on digital twins and operations.

    Created Oct 10, 2026. Last reviewed by an editor on Oct 10, 2026. Next scheduled review: Jan 10, 2027.

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