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    Stellarator

    Also known as stellarator fusion device, optimised stellarator

    A stellarator is a doughnut-shaped magnetic fusion device whose confining field comes entirely from external helical coils, with no current driven in the plasma.[1] That allows steady-state operation and fewer instabilities. Germany's Wendelstein 7-X set a long-pulse triple-product record in 2025, and Proxima Fusion plans a demonstration stellarator called Alpha.[2][3][4]

    Editor reviewedUpdated Fusion energyPhysicsEnergy and climate
    Key facts

    How a stellarator works

    Like a tokamak, a stellarator confines plasma in a ring-shaped (toroidal) magnetic field.[1] The difference is where the twist in that field comes from. A tokamak induces a current in the plasma to produce its poloidal field, while a stellarator produces it with external helical coils.[5] Because no plasma current is needed, a stellarator has intrinsic advantages. It can operate in steady state, and it is less prone to plasma instabilities.[2]

    wendelstein-7-x, the leading machine, uses a system of 50 non-planar superconducting coils to generate its optimised field.[6] Its designers expected confinement comparable to a tokamak of the same size.[7]

    Results so far

    Wendelstein 7-X in Greifswald, Germany, produced its first plasma on 10 December 2015.[8] Its purpose is to test whether the optimised stellarator is suitable for a power plant.[9] On 22 May 2025 it held a record triple product for 43 seconds. That surpassed the best tokamak results for long plasma durations.[3] In the same campaign it raised its energy turnover to 1.8 gigajoules over a 360-second plasma.[10]

    These are long-pulse records. Peak fusion energy records still belong to tokamaks, such as JET’s 69 megajoules with deuterium-tritium fuel.[11]

    The machine is designed for plasma discharges of up to 30 minutes.[6] Its investment cost from 1995 to its final configuration in December 2021 was 460 million euros.[12] During the 2025 record run, the plasma exceeded 20 million degrees Celsius and peaked at 30 million degrees. IPP noted that JET, the tokamak it was compared with, had three times W7-X’s plasma volume.[13][14]

    From experiment to power plant

    Stellarators have attracted private investment. On 26 February 2026, Proxima Fusion, the Bavarian state government, the utility RWE and the Max Planck Institute for Plasma Physics (IPP) signed a framework agreement to design, build and operate a demonstration stellarator called Alpha in Garching. A follow-on commercial plant, Stellaris, is planned at the former Gundremmingen nuclear power plant site.[4] Alpha is budgeted at two billion euros, and Bavaria has promised up to 400 million euros in co-financing.[15] Proxima raised $518 million in July 2026, one of the year’s largest fusion rounds.[16]

    Germany added a federal funding route on 7 October 2026, when the breakthrough-innovation agency SPRIND launched a milestone-based fusion programme for the research ministry: 500 million euros by 2029, with total public funding intended to reach as much as 2.5 billion euros.[17] It is competitive by design. Independent experts assess each company’s technical and financial milestones, a company that misses one leaves the programme, and the final milestone is a Technical Design Report for a demonstration plant.[18] The programme sits under a Fusion Action Plan adopted on 1 October 2025.[19]

    The helical line in Japan

    Japan is pursuing the same configuration under the name “helical”. Helical Fusion is building Helix HARUKA, which it calls the country’s first integrated pilot reactor using the helical approach, on the campus of the National Institute for Fusion Science in Toki, Gifu Prefecture, with more than 30 Japanese industrial partners.[20] On 29 September 2026 the company said preliminary power-on tests would begin in 2027, with power-on tests of the completed integrated facility around 2030.[21] Its funding is small by comparison with the leading tokamak companies: a 3.23-billion-yen Series B second close announced on 8 October 2026 took cumulative funding, including grants and loans, to about 13.15 billion yen, roughly $84 million.[22] Japan’s METI runs a milestone programme covering stellarator, tokamak and laser approaches with about 60 billion yen of government support over the three years to 2028, and named Helical Fusion a final candidate on 31 August 2026.[23]

    Open questions

    Stellarator power plants face the same fuel and materials problems as any deuterium-tritium machine: tritium breeding and resistance to 14 MeV neutrons.[24][25] Under the 2026 agreement, IPP leads the plasma physics and defines Alpha’s scientific mission, while Proxima Fusion handles engineering and construction.[26]

    Questions readers ask

    How is a stellarator different from a tokamak?

    A tokamak induces a current in the plasma to create part of its magnetic field. A stellarator generates the field entirely with external helical coils, so no plasma current is needed.[5][1]

    Why build a stellarator?

    Without a plasma current, a stellarator can in principle run continuously and is less prone to plasma instabilities.[2]

    Has a stellarator matched tokamak performance?

    In May 2025 Wendelstein 7-X held a record triple product for long plasma discharges for 43 seconds, surpassing tokamaks for comparable durations.[3]

    Is anyone building a stellarator power plant?

    Proxima Fusion, the state of Bavaria, RWE and the Max Planck Institute for Plasma Physics agreed in February 2026 to build a demonstration stellarator, Alpha, in Garching. A commercial plant, Stellaris, is planned at the former Gundremmingen nuclear plant site.[4]

    Is anyone outside Europe building one?

    Yes. In Japan, Helical Fusion is building Helix HARUKA, which it describes as the country's first integrated pilot reactor using the helical approach, on the campus of the National Institute for Fusion Science in Toki.[20]

    What public money is available for stellarators?

    Germany launched a milestone-based fusion programme on 7 October 2026 with 500 million euros by 2029 and up to 2.5 billion euros in total. Japan's METI programme covers stellarators alongside tokamaks and laser fusion, with about 60 billion yen over the three years to 2028.[17][23]

    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 stellarator is a toroidal magnetic confinement device whose poloidal field is generated by external helical coils rather than by a current in the plasma. confirmedas of 2026-10-10

    2. [2]

      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

    3. [3]

      On 22 May 2025 Wendelstein 7-X sustained a record triple product for long plasma discharges for 43 seconds, surpassing tokamak results for comparable durations. confirmedas of 2026-10-10

    4. [4]

      On 26 February 2026 Proxima Fusion, the Bavarian state government, RWE and IPP signed a framework agreement to design, build and operate a demonstration stellarator, Alpha, in Garching, with a commercial plant, Stellaris, planned at the former Gundremmingen nuclear plant site. confirmedas of 2026-10-10

    5. [5]

      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

    6. [6]

      Wendelstein 7-X in Greifswald, Germany, confines its plasma with a system of 50 non-planar superconducting magnet coils and is designed for plasma discharges of up to 30 minutes. confirmedas of 2026-10-10

      • Wendelstein 7-X · Max Planck Institute for Plasma Physics (retrieved 2026-10-10)
    7. [7]

      IPP expected Wendelstein 7-X's plasma equilibrium and confinement to be comparable to those of a tokamak of the same size. confirmedas of 2026-10-10

      • Wendelstein 7-X · Max Planck Institute for Plasma Physics (retrieved 2026-10-10)
    8. [8]

      Wendelstein 7-X produced its first plasma on 10 December 2015. confirmedas of 2026-10-10

      • Wendelstein 7-X · Max Planck Institute for Plasma Physics (retrieved 2026-10-10)
    9. [9]

      Wendelstein 7-X is meant to investigate whether the optimised stellarator design is suitable for a power plant. confirmedas of 2026-10-10

      • Wendelstein 7-X · Max Planck Institute for Plasma Physics (retrieved 2026-10-10)
    10. [10]

      In its 2025 campaign Wendelstein 7-X raised its energy turnover to 1.8 gigajoules over a 360-second plasma. confirmedas of 2026-10-10

    11. [11]

      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

    12. [12]

      Investment costs for Wendelstein 7-X from 1995 to its final configuration in December 2021 were 460 million euros, with total site costs of 1.44 billion euros. confirmedas of 2026-10-10

      • Wendelstein 7-X · Max Planck Institute for Plasma Physics (retrieved 2026-10-10)
    13. [13]

      During the 2025 record run, W7-X's plasma exceeded 20 million degrees Celsius and peaked at 30 million degrees. confirmedas of 2026-10-10

    14. [14]

      IPP noted that JET had three times the plasma volume of Wendelstein 7-X. confirmedas of 2026-10-10

    15. [15]

      The Alpha project is budgeted at two billion euros, with the Bavarian government promising up to 400 million euros in co-financing. confirmedas of 2026-10-10

    16. [16]

      Large recent rounds include CFS's $863 million Series B2 (August 2025), Proxima Fusion's $518 million (July 2026), Helion's $465 million (June 2026) and Inertia Enterprises' $450 million Series A (February 2026). confirmedas of 2026-07-13

    17. [17]

      On 7 October 2026 Germany's Federal Agency for Breakthrough Innovation (SPRIND) launched a milestone-based fusion programme for the research ministry, providing 500 million euros by 2029 with total public funding intended to rise to as much as 2.5 billion euros. confirmedas of 2026-10-07

    18. [18]

      Under the German programme, independent external experts assess each company's technical and financial milestones, a participant that misses a milestone leaves the programme and loses funding, and the final milestone is a Technical Design Report for a fusion demonstration plant. confirmedas of 2026-10-07

    19. [19]

      The German milestone programme is part of a Fusion Action Plan adopted on 1 October 2025 under the country's High-Tech Agenda, and complements existing research funding programmes. confirmedas of 2026-10-07

    20. [20]

      Helix HARUKA is described as Japan's first integrated pilot reactor using the helical (stellarator) approach, built on the campus of the National Institute for Fusion Science in Toki, Gifu Prefecture, with more than 30 Japanese industrial partners. reportedas of 2026-09-29

    21. [21]

      On 29 September 2026 the Japanese company Helical Fusion said it expected to begin preliminary power-on tests at its Helix HARUKA demonstration device in 2027, with power-on tests of the completed integrated facility around 2030. reportedas of 2026-09-29

    22. [22]

      On 8 October 2026 Helical Fusion said Fuji Electric had joined a 3.23-billion-yen (about $20.6 million) Series B second close, bringing the company's cumulative funding, including grants and loans, to about 13.15 billion yen (about $83.8 million). reportedas of 2026-10-08

    23. [23]

      Japan's Ministry of Economy, Trade and Industry runs a milestone-based programme supporting private fusion demonstration across tokamak, stellarator and laser approaches, with about 60 billion yen of government support anticipated over the three years to 2028; Helical Fusion was named a final candidate on 31 August 2026. reportedas of 2026-08-31

    24. [24]

      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)
    25. [25]

      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

    26. [26]

      Under the February 2026 Alpha agreement, IPP leads the plasma physics and defines Alpha's scientific mission, while Proxima Fusion is responsible for engineering and construction. confirmedas of 2026-10-10

    Revision history (2)
    1. Page created.
    2. Refresh: added Japan's Helical Fusion, its Helix HARUKA schedule and funding, and the German and Japanese milestone funding programmes.

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

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