Skip to content
ContentLora

    Tip: press / anywhere to search.

    product

    Wendelstein 7-X

    Also known as W7-X, Wendelstein 7X

    Wendelstein 7-X, the world's largest stellarator, is run by the Max Planck Institute for Plasma Physics (IPP) in Greifswald, Germany.[1] It confines plasma with 50 non-planar superconducting coils and has operated since its first plasma in December 2015.[2][3] In May 2025 it held a record triple product for 43 seconds, surpassing tokamaks over long plasma durations.[4]

    Editor reviewedUpdated Fusion energyPhysicsEnergy and climate
    Key facts

    The machine

    Wendelstein 7-X, described by IPP as the world’s largest and most powerful experiment of its kind, is the flagship stellarator of the Max Planck Institute for Plasma Physics in Greifswald, Germany.[1] A system of 50 non-planar superconducting magnet coils produces its confining field, and it is designed for plasma discharges lasting up to 30 minutes.[2] It produced its first plasma on 10 December 2015.[3] Investment costs from 1995 until it reached its final configuration in December 2021 came to 460 million euros, and total site costs to 1.44 billion euros.[5]

    Its purpose is to investigate whether the optimised stellarator is suitable for a power plant.[6] IPP expected its plasma equilibrium and confinement to be comparable to those of a tokamak of the same size.[7] As a stellarator, it needs no plasma current. That allows steady-state operation and makes it less prone to plasma instabilities.[8]

    2025 records

    The 2025 experimental campaign ended on 22 May with a world record. W7-X sustained a new peak triple product for long plasma discharges for 43 seconds, surpassing the best tokamak results over comparable durations.[4] During that run the plasma exceeded 20 million degrees Celsius and peaked at 30 million degrees.[9] In the same campaign, energy turnover rose to 1.8 gigajoules over a 360-second plasma.[10]

    Long, steady pulses test the property that distinguishes stellarators from tokamaks: the ability to run in steady state.[8] IPP noted that JET, which holds the 69-megajoule fusion-energy record, had three times the plasma volume of W7-X.[11][12]

    The campaign that produced the record, OP 2.3, ended on 22 May 2025, and IPP reported further best values for plasma durations between 30 and 40 seconds in the same run.[13] Two details are worth keeping in view. The record depended on new hardware from abroad: a pellet injector supplied by Oak Ridge National Laboratory, which fires frozen hydrogen pellets into the plasma to refuel it continuously.[14] And IPP later updated its comparison graphic to include previously unpublished JET record values, shown in green.[15]

    The energy-turnover figure has a baseline too: the previous record, set in February 2023, was 1.3 gigajoules, and IPP calculates energy turnover as injected heating power multiplied by plasma duration.[16]

    Plasma pressure, the power-plant parameter

    Besides duration, OP 2.3 tested how much plasma pressure the magnetic field can hold. The ratio of plasma pressure to magnetic pressure reached 3 percent across the full plasma volume for the first time, in experiments where the magnetic field was deliberately lowered to about 70 percent; IPP says a power plant will need 4 to 5 percent across the volume.[17] The same series produced a peak ion temperature of around 40 million degrees Celsius.[18] The distance between 3 percent and the 4 to 5 percent a plant would need is one of the clearest measures of what the optimised stellarator still has to prove.

    How the record compares

    The triple product combines plasma density, temperature and energy confinement time, and it is the standard measure of how close a plasma is to the Lawson criterion.[19][20] According to IPP, earlier devices had sustained such high triple products only for a very few seconds, while W7-X held one for 43 seconds.[4]

    Role in the stellarator push

    W7-X’s operator is also a partner in a planned stellarator power-plant project. In February 2026 IPP joined Proxima Fusion, the Bavarian government and RWE in a framework agreement to build a demonstration stellarator, Alpha, in Garching. IPP will lead the plasma physics and define Alpha’s scientific mission.[21][22] Alpha is budgeted at two billion euros.[23]

    Federal money followed. On 7 October 2026 Germany’s SPRIND launched a milestone-based fusion programme for the research ministry, with 500 million euros by 2029 and total public funding intended to reach as much as 2.5 billion euros; companies that miss a milestone leave the programme, and the final milestone is a Technical Design Report for a demonstration plant.[24][25] Japan is developing the same configuration under the name helical, where Helical Fusion plans preliminary power-on tests of its Helix HARUKA device in 2027.[26][27] See stellarator for the wider picture.

    Questions readers ask

    What is Wendelstein 7-X for?

    It tests whether the optimised stellarator design is suitable for a fusion power plant. It is designed for plasma discharges of up to 30 minutes.[6][2]

    What record did it set in 2025?

    On 22 May 2025 it sustained a record triple product for long plasma discharges for 43 seconds, surpassing tokamaks for comparable durations.[4]

    How much did it cost?

    IPP puts investment costs from 1995 to its final configuration in December 2021 at 460 million euros, and total site costs at 1.44 billion euros.[5]

    How close is it to power-plant conditions?

    In the OP 2.3 campaign the ratio of plasma pressure to magnetic pressure reached 3 percent across the full plasma volume for the first time. IPP says a power plant will need 4 to 5 percent.[17]

    What made the 2025 record possible?

    IPP credits a new pellet injector from Oak Ridge National Laboratory, which fires frozen hydrogen pellets into the plasma so it can be refuelled continuously during long discharges.[14]

    Sources

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

    1. [1]

      Wendelstein 7-X in Greifswald is, according to IPP, the world's largest and most powerful stellarator experiment. confirmedas of 2026-10-10

    2. [2]

      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)
    3. [3]

      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)
    4. [4]

      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

    5. [5]

      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)
    6. [6]

      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)
    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]

      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

    9. [9]

      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

    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]

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

    12. [12]

      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

    13. [13]

      Wendelstein 7-X's OP 2.3 experimental campaign ended on 22 May 2025, and IPP reported further best values for plasma durations between 30 and 40 seconds in the same campaign. confirmedas of 2026-10-10

    14. [14]

      Wendelstein 7-X's 2025 long-pulse triple-product record was enabled by a new pellet injector supplied by Oak Ridge National Laboratory, which fires frozen hydrogen pellets into the plasma to refuel it continuously. confirmedas of 2026-10-10

    15. [15]

      IPP later updated its triple-product comparison graphic to include previously unpublished JET record values, which it marks in green. confirmedas of 2026-10-10

    16. [16]

      Wendelstein 7-X's previous energy-turnover record, set in February 2023, was 1.3 gigajoules, and IPP calculates energy turnover as injected heating power multiplied by plasma duration. confirmedas of 2026-10-10

    17. [17]

      In the OP 2.3 campaign Wendelstein 7-X reached a plasma-pressure-to-magnetic-pressure ratio of 3 percent across the full plasma volume for the first time, in experiments where the magnetic field was reduced to about 70 percent; IPP says a power plant will need 4 to 5 percent. confirmedas of 2026-10-10

    18. [18]

      IPP reported a peak ion temperature of around 40 million degrees Celsius in Wendelstein 7-X's 2025 campaign. confirmedas of 2026-10-10

    19. [19]

      The triple product is the product of plasma density, energy confinement time and temperature, and is the standard figure of merit for fusion performance. confirmedas of 2026-10-10

    20. [20]

      In 1955 the British physicist John D. Lawson estimated the parameters needed for fusion to give more energy out than is put in, setting a minimum for the product of plasma density, confinement time and temperature. confirmedas of 2026-10-10

    21. [21]

      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

    22. [22]

      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

    23. [23]

      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

    24. [24]

      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

    25. [25]

      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

    26. [26]

      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

    27. [27]

      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

    Revision history (2)
    1. Page created.
    2. Refresh: added the OP 2.3 end date, the Oak Ridge pellet injector, the 3 percent plasma-pressure ratio against the 4 to 5 percent a power plant needs, the 1.3 GJ 2023 baseline, IPP's updated graphic including unpublished JET values, and Germany's new milestone funding programme.

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

    Cite this page

    "Wendelstein 7-X." ContentLora, updated Oct 10, 2026. https://contentlora.com/wiki/wendelstein-7-x

    Spotted an error? Suggest a correction or emailcorrections@contentlora.com.

    Keep exploring

    Connections
    Stellarator Machine typeTokamak Compared with
    ☰ Contents