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    ITER

    Also known as International Thermonuclear Experimental Reactor, ITER Organization

    ITER is a tokamak being built in Saint-Paul-lez-Durance, France, by seven members: Europe, China, India, Japan, South Korea, Russia and the United States. It aims to produce 500 MW of fusion power from 50 MW of heating (Q of at least 10).[1][2] Its 2024 baseline moved research operations to 2034 and deuterium-tritium operation to 2039. Six of nine vacuum-vessel modules were installed by July 2026, and the ninth and final vessel sector reached the site on 5 October 2026.[3][4][5]

    Editor reviewedUpdated Fusion energyEnergy and climatePhysics
    Key facts

    What ITER is for

    ITER is designed to demonstrate the scientific and technological feasibility of fusion power, and it will be the world’s largest experimental fusion facility.[6] It has three mission goals. The first is to demonstrate the integration of systems needed for industrial-scale fusion. The second is to reach Q of at least 10, meaning 500 megawatts of thermal fusion power for 50 megawatts of heating, in 400-second pulses. The third is eventually to reach Q of at least 5 in steady state.[6][2] It is a tokamak whose volume and weight are nearly 10 times those of the largest existing tokamaks.[7]

    Members and cost sharing

    ITER is under construction in Saint-Paul-lez-Durance in southern France. Europe, as host, contributes almost half of construction costs, and the other six members (China, India, Japan, South Korea, Russia and the United States) contribute equally to the rest.[1]

    The machine

    ITER’s magnet system weighs about 10,000 tonnes and stores 51 gigajoules. It uses niobium-tin and niobium-titanium superconductors cooled to about 4 kelvin, including 18 D-shaped toroidal field coils with a maximum field of 11.8 tesla.[8] The combined toroidal field coils have a cold mass of more than 6,000 tonnes and store 41 gigajoules.[7] Compact private tokamaks instead use hts-fusion-magnets that run at about 20 kelvin.[9] Under the 2024 baseline, ITER switched its first wall from beryllium to tungsten, judging tungsten more relevant to future DEMO and commercial machines.[10]

    The 2024 rebaseline

    The previous baseline, set in 2016, aimed for a brief, low-energy “First Plasma” in 2025. ITER said publicly from October 2020 that this date was no longer achievable.[11] It blamed Covid-19 disruption, first-of-a-kind components that proved more difficult than expected, quality problems that required repairs, and over-optimistic planning.[11] The new baseline, presented in July 2024, sets these dates:[3]

    • Start of Research Operation, with a more complete machine: 2034
    • Deuterium-deuterium operation: 2035
    • Full magnetic energy: 2036
    • Start of deuterium-tritium operation: 2039, about four years later than the 2016 plan

    All systems, including the disruption mitigation system, are to be fully tested during the first research phase.[12]

    Progress in 2026

    On 28 July 2026 ITER lowered the sixth of nine vacuum-vessel sector modules into the tokamak pit. The installation came almost six months ahead of schedule and put two-thirds of the torus-shaped core in place. ITER says it is on track to place the final module in 2027.[4]

    Manufacturing then finished as well. On 5 October 2026 vacuum vessel sector #2, the ninth and last, was delivered, and ITER said that with it all the components needed to complete the core machine were on site; in-vessel components, plant systems and other equipment are still to come.[5][13] The nine sectors were divided between two members, Europe making five and Korea four, and six years passed between the first delivery and the last.[14]

    Assembly continues in the pit. Each sector module combines a vacuum vessel sector, two toroidal field coils and a set of thermal shield panels.[15] In September 2026 ITER said module 9, which it called the critical path, should finish sub-assembly by the end of November 2026 and move to the pit at the beginning of December, freeing the sub-assembly tool for the last sector.[16]

    Tritium breeding on ITER

    ITER will also test the technology a power plant needs to make its own fuel. Test blanket systems are to be hosted near the plasma in two equatorial ports, each independently integrated and operated with its own coolant, tritium extraction, purification and control systems; ITER describes the programme as an essential step toward the capabilities required for DEMO and future power plants.[17] Breeding matters because a deuterium-tritium plant must produce more tritium than it burns, and the world’s civilian stock is only tens of kilograms.[18][19] Private developers are pursuing the same problem: in July 2026 commonwealth-fusion-systems became the first international partner in UKAEA’s LIBRTI programme.[20]

    Why it still matters

    ITER’s target of Q of at least 10 is well above the Q>1 goal that Commonwealth Fusion Systems has set for its private SPARC machine.[2][21] It is also a large future user of the world’s tritium supply, which ITER puts at around 20 kilograms.[22] Long-pulse records at EAST and WEST in 2025 were described by ITER’s science division as evidence that control of high-temperature plasmas is maturing.[23]

    Questions readers ask

    When will ITER start operating?

    Under the 2024 baseline, the Start of Research Operation is in 2034, deuterium-deuterium operation in 2035, full magnetic energy in 2036 and deuterium-tritium operation in 2039.[3]

    Why was ITER delayed?

    ITER cited Covid-19 disruption, first-of-a-kind components that proved harder than expected, quality problems that required repairs, and over-optimistic planning.[11]

    Who pays for ITER?

    Europe, as host, pays almost half of construction costs. China, India, Japan, South Korea, Russia and the United States share the rest equally.[1]

    Will ITER produce electricity?

    Generating electricity is not among ITER's stated goals. Its mission is to demonstrate the integration of systems for industrial-scale fusion and to reach Q of at least 10, measured in thermal fusion power.[2][6]

    Are all of ITER's components built?

    The core ones are. On 5 October 2026 the ninth and final vacuum vessel sector was delivered, which ITER said meant every component needed to complete the core machine was on site. In-vessel components, plant systems and other equipment are still to come.[5][13]

    Sources

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

    1. [1]

      ITER is being built in Saint-Paul-lez-Durance in southern France; Europe, as host, pays almost half of construction costs and China, India, Japan, South Korea, Russia and the United States share the rest equally. confirmedas of 2026-10-10

    2. [2]

      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

    3. [3]

      ITER's 2024 baseline schedules the Start of Research Operation in 2034, deuterium-deuterium operation in 2035, full magnetic energy in 2036 and the start of deuterium-tritium operation in 2039, about four years later than the 2016 plan. confirmedas of 2026-10-10

    4. [4]

      On 28 July 2026 ITER installed the sixth of nine vacuum-vessel sector modules in the tokamak pit, putting two-thirds of the tokamak core in place almost six months ahead of schedule, and says it is on track to place the last module in 2027. confirmedas of 2026-07-29

    5. [5]

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

    6. [6]

      ITER is designed to demonstrate the scientific and technological feasibility of fusion power and will be the world's largest experimental fusion facility; its mission goals are to demonstrate integration of systems for industrial-scale fusion, reach Q of at least 10, and eventually reach Q of at least 5 in steady state. confirmedas of 2026-10-10

    7. [7]

      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

    8. [8]

      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)
    9. [9]

      Fusion magnets wound with REBCO (rare-earth barium copper oxide) tape operate at about 20 kelvin, warmer than the roughly 4 kelvin needed by earlier superconducting fusion magnets. confirmedas of 2026-10-10

    10. [10]

      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

    11. [11]

      ITER attributed the abandonment of its 2025 first-plasma date to Covid-19 disruption, first-of-a-kind components that proved harder than expected, quality problems requiring repairs, and over-optimistic planning. confirmedas of 2026-10-10

    12. [12]

      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

    13. [13]

      ITER's project leadership said that with sector confirmedas of 2026-10-05

    14. [14]

      ITER's nine vacuum vessel sectors were split between two members, five made in Europe and four in Korea, and six years passed between delivery of the first and the ninth sector. confirmedas of 2026-09-21

    15. [15]

      Each of the nine ITER tokamak sector modules has three main elements, a vacuum vessel sector, two toroidal field coils and a set of vacuum vessel thermal shield panels. confirmedas of 2026-09-07

    16. [16]

      As of September 2026 ITER was completing sub-assembly of sector module confirmedas of 2026-09-07

    17. [17]

      ITER will host test blanket systems in two equatorial ports, each with its own coolant, tritium extraction, purification and control systems, which ITER describes as an essential step toward the capabilities required for DEMO and future fusion power plants. confirmedas of 2026-09-14

    18. [18]

      To be self-sufficient in fuel, deuterium-tritium power plants need a tritium breeding ratio greater than one, and lithium-6, the isotope most important for breeding, is only about 7.6% of natural lithium. confirmedas of 2024-05-20

    19. [19]

      Today's civilian tritium comes mainly from heavy-water fission reactors such as Canada's CANDU units, with an estimated 20 to 30 kilograms available. confirmedas of 2024-05-20

    20. [20]

      On 1 July 2026 the UK Atomic Energy Authority named CFS the first international company to join LIBRTI, a 220-million-pound programme aiming to demonstrate net tritium production, with CFS building the first test articles. confirmedas of 2026-07-01

    21. [21]

      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

    22. [22]

      ITER puts the global tritium inventory at around 20 kilograms, which it will draw on during operation. confirmedas of 2026-10-10

      • Fuelling · ITER Organization (retrieved 2026-10-10)
    23. [23]

      ITER's head of science said long-pulse tokamak operation in the range foreseen for ITER, as shown at EAST and WEST, demonstrates that knowledge of how to control high-temperature plasmas is mature. confirmedas of 2026-10-10· interpretation

    Revision history (2)
    1. Page created.
    2. Refresh: added the 5 October 2026 delivery of the ninth and final vacuum vessel sector, the sector module 9 schedule, the Europe and Korea procurement split and the test blanket module programme.

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

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