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    High-temperature superconducting fusion magnets

    Also known as HTS magnets, REBCO magnets, high-field superconducting magnets

    High-temperature superconducting (HTS) fusion magnets are wound from rare-earth barium copper oxide (REBCO) tape and run at about 20 kelvin rather than 4 kelvin.[1] In 2021 an MIT and Commonwealth Fusion Systems magnet reached 20 tesla. MIT said that lets a tokamak match the performance of a conventional device about 40 times larger in volume.[2][3]

    Editor reviewedUpdated Fusion energyPhysicsEnergy and climate
    Key facts

    What they are

    Large magnetic fusion machines use superconducting coils. iter‘s magnets use niobium-tin or niobium-titanium superconductors cooled to about 4 kelvin. Its 18 toroidal field coils reach a maximum field of 11.8 tesla.[4] High-temperature superconducting magnets instead use tape coated with rare-earth barium copper oxide (REBCO). They can operate at around 20 kelvin.[1] REBCO can carry very high current densities at temperatures up to 20 kelvin while producing extremely high fields.[5]

    The 2021 breakthrough

    On 5 September 2021, MIT and commonwealth-fusion-systems ramped a large HTS magnet, the SPARC Toroidal Field Model Coil, to 20 tesla.[6] MIT called it the most powerful magnetic field of its kind ever created on Earth.[2] According to MIT, this makes it possible to match the performance of a conventional low-temperature superconducting device about 40 times larger in volume.[3]

    The magnet dropped the insulation normally wound between superconducting tape layers. The team also deliberately induced a quench, a sudden loss of superconductivity, to test its failure modes. The results appeared in six peer-reviewed papers in IEEE Transactions on Applied Superconductivity in March 2024.[7] MIT’s Dennis Whyte said the result changed the cost per watt of a fusion reactor by a factor of almost 40.[8] A 2024 analysis reported in Physics World concluded that REBCO is well suited to tokamak magnets.[5]

    Where they are used

    • SPARC. CFS is building this compact tokamak in Devens, Massachusetts, around REBCO magnets first proven in the 2021 model coil, and aims to show net fusion energy (Q>1) with it.[6][9] CFS said SPARC was almost 80 percent complete in August 2026.[10]
    • ARC. CFS’s planned 400-megawatt power plant in Chesterfield County, Virginia.[11] On 30 September 2026 CFS ordered more than 10,000 kilometres of HTS tape from Fujikura for ARC plants, which the companies called the largest agreement of its kind.[12]
    • Industrial supply. CFS’s technology page describes REBCO as a high-temperature superconductor that recently reached industrial maturity.[13]

    Why the temperature matters

    The difference between 4 kelvin and 20 kelvin is large in engineering terms. ITER’s magnets need supercritical helium cooling at about 4 kelvin, while REBCO magnets run at around 20 kelvin.[4][1] Physics World’s 2024 report noted that REBCO can carry very high current densities at up to 20 kelvin, which is what allows compact devices some 30 to 40 times smaller in volume.[5]

    Open questions

    HTS magnets do not address the fuel and materials problems that every deuterium-tritium plant faces, such as breeding tritium and withstanding 14 MeV neutrons.[14][15] CFS intends SPARC, built with these magnets, to be the first commercially relevant machine to show Q>1, and publicly targets 2027 for that result; it has not published a dated first-plasma milestone.[9][16][17] Until SPARC runs, the magnets’ behaviour in a burning-plasma machine is unproven, and the 2021 20-tesla campaign remains the main independently published evidence.[7]

    Tape supply

    A compact high-field machine is, in industrial terms, a tape order. CFS’s agreement with Fujikura on 30 September 2026 covers more than 10,000 kilometres of HTS tape for ARC plants, and Fujikura is expanding manufacturing capacity to deliver it; the companies called it the largest agreement of its kind.[12] The money behind that scale-up is company-reported: CFS said on 30 July 2026 that it had now raised $4 billion in total, about 30 percent of all fusion capital on its own count.[18] Not every design needs superconductors. Helion’s April 2026 research awards included work on copper-silver alloys for resistive magnets, and helion-energy compresses its plasmas in pulses rather than holding them steadily.[19][20]

    Fusion magnets are one application of a wider materials field: REBCO tape carries very high current densities at up to 20 kelvin, far below room temperature but far above the 4 kelvin of older superconductors.[5][1] For the underlying physics, and how far higher-temperature superconductivity has got, see how superconductivity works and the room-temperature superconductivity debate.

    Questions readers ask

    What makes high-temperature superconductors different?

    REBCO tape lets fusion magnets operate at about 20 kelvin, compared with about 4 kelvin for the niobium-tin and niobium-titanium superconductors used in ITER.[1][4]

    Why do stronger magnets matter for fusion?

    Stronger fields allow smaller machines. MIT said its 20-tesla HTS magnet makes it possible to match the performance of a conventional device about 40 times larger in volume.[3]

    Has the technology been independently checked?

    The 2021 test results, including a deliberately induced quench, were published in six peer-reviewed papers in IEEE Transactions on Applied Superconductivity in March 2024. Performance in a burning-plasma machine will not be tested until SPARC runs.[7][16]

    Is there enough HTS tape to build power plants?

    Supply is being scaled up. CFS ordered more than 10,000 kilometres of tape from Fujikura on 30 September 2026, and Fujikura is expanding its manufacturing capacity to deliver it.[12]

    Sources

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

    1. [1]

      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

    2. [2]

      On 5 September 2021 MIT and Commonwealth Fusion Systems ramped a large high-temperature superconducting magnet to 20 tesla, the strongest fusion magnet of its kind. confirmedas of 2026-10-10

    3. [3]

      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

    4. [4]

      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)
    5. [5]

      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

    6. [6]

      The 20-tesla magnet tested in 2021 was the SPARC Toroidal Field Model Coil, built by MIT's Plasma Science and Fusion Center and CFS between 2018 and 2021 to develop REBCO magnet technology for the SPARC tokamak. confirmedas of 2026-10-10

    7. [7]

      The MIT-CFS magnet removed the insulation normally wound between superconducting tape layers, and the 2021 test results were published in six peer-reviewed papers in IEEE Transactions on Applied Superconductivity in March 2024, including a deliberately induced quench. confirmedas of 2024-03-04

    8. [8]

      MIT's Dennis Whyte said the 2021 magnet result changed the cost per watt of a fusion reactor by a factor of almost 40. reportedas of 2024-03-04· interpretation

    9. [9]

      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

    10. [10]

      As of 5 August 2026 CFS said SPARC was almost 80 percent complete. reportedas of 2026-08-05

    11. [11]

      In December 2024 CFS chose the James River Industrial Center in Chesterfield County, Virginia, for ARC, a planned power plant of about 400 megawatts expected to deliver power to the grid in the early 2030s. confirmedas of 2026-10-10

    12. [12]

      On 30 September 2026 CFS agreed to buy more than 10,000 kilometres of HTS tape from Fujikura for its ARC power plants, starting with the Fall Line Fusion Power Station in Chesterfield County, Virginia; the companies called it the largest agreement of its kind, and Fujikura is expanding capacity to supply it. confirmedas of 2026-10-10

    13. [13]

      Commonwealth Fusion Systems describes REBCO (rare-earth barium copper oxide) as a high-temperature superconductor that has recently reached industrial maturity. confirmedas of 2026-10-10

      • Technology · Commonwealth Fusion Systems (retrieved 2026-10-10)
    14. [14]

      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)
    15. [15]

      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

    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]

      In a company blog post current as of October 2026, CFS said it would start operating SPARC "in coming months" and that SPARC is designed to reach Q>10, so Q>1 is not an extremely difficult milestone; CFS has not published a dated first-plasma target. reportedas of 2026-10-10

    18. [18]

      On 30 July 2026 CFS said it had raised a further $1 billion of equity, bringing its total capital raised to $4 billion, which it described as about 30 percent of all capital raised by the fusion industry to date. reportedas of 2026-07-30

    19. [19]

      On 7 April 2026 Helion awarded $4 million under its HERCULES external research programme to 25 proposals across 20 institutions in the United States and United Kingdom, with more than $17 million committed through 2028. reportedas of 2026-04-07

    20. [20]

      Helion's machines magnetically compress pulsed, high-beta field-reversed configuration (FRC) plasmas and aim to recover energy directly as electricity rather than via heat and a steam turbine. confirmedas of 2026-10-10

    Revision history (2)
    1. Page created.
    2. Refresh: added a tape-supply section (Fujikura order, CFS's $4bn, resistive-magnet research at Helion), CFS's 2027 Q>1 target and links to the superconductivity explainer and debate.

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

    Cite this page

    "High-temperature superconducting fusion magnets." ContentLora, updated Oct 10, 2026. https://contentlora.com/wiki/hts-fusion-magnets

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