A 43-second moment at an experimental fusion reactor in Greifswald, Germany changed what is considered achievable. On May 22, 2025, the Wendelstein 7-X stellarator exceeded for the first time the best known values of competing reactor designs, tokamaks, during sustained plasma discharges. Nine months later, Bavaria's state government, energy company RWE, the Max Planck Institute for Plasma Physics (IPP), and Munich-based fusion company Proxima Fusion signed a memorandum making Europe's first commercial fusion power plant concrete: it will be built at Gundremmingen, at the site of a former nuclear power station.
How fusion differs from fission
Nuclear fusion merges light atomic nuclei, typically deuterium and tritium, into heavier ones, releasing substantial energy. The differences from today's nuclear fission are fundamental: no long-lived, highly radioactive waste is generated; neutron activation of reactor walls creates low to medium-level radioactive structural materials, disposable by conventional means after roughly 100 years. A meltdown scenario is physically impossible because the plasma extinguishes within milliseconds at any disruption. Deuterium can be extracted from seawater and is available in virtually unlimited supply.
In plasma physics, two competing designs have competed for decades. Tokamaks, donut-shaped reactors, use a current induced in the plasma itself as part of the confining magnetic field. This forces them into pulsed operation, impractical for a commercial power plant. Stellarators, whose intricately twisted magnetic coils generate the entire confinement field from outside, can theoretically run continuously. For decades, they lagged tokamaks on the central performance metric, the triple product combining density, temperature, and confinement time. As of May 2025, that no longer holds true for sustained discharges.
The Greifswald record: 43 seconds reshape expectations
On May 22, 2025, Wendelstein 7-X sustained a plasma discharge lasting 43 seconds while maintaining a triple product that exceeded the best known tokamak values at comparable discharge durations. The plasma reached 30 million degrees Celsius, with ten gyrotron generators supplying ten megawatts of heating power. Cumulative energy delivered over 360 seconds of plasma operation was 1.8 gigajoules, surpassing the previous record of 1.3 gigajoules.
The breakthrough was enabled by a pellet injector from Oak Ridge National Laboratory in the United States that shot roughly 70 frozen hydrogen pellets at 300 to 800 meters per second into the plasma, demonstrating a central technical challenge for stellarators: continuous plasma refueling over extended operating periods.
Alpha in Garching, Stellaris in Gundremmingen: The two-stage plan
The memorandum of understanding from February 26, 2026 establishes a concrete two-stage plan. The first stage is Alpha, a demonstration stellarator in Garching near the IPP campus. Construction is planned to begin in 2027, with total costs estimated at roughly two billion euros. Bavaria committed up to 400 million euros as its state contribution. By 2031, Alpha is to demonstrate that a stellarator generates more energy than it consumes.
The second stage is Stellaris, according to Proxima Fusion's plans Europe's first commercial fusion power plant, sited at the former Gundremmingen nuclear power station location. RWE, as the station's former operator, brings expertise in constructing and operating complex power plants. The Max Planck Institute leads the science, Proxima handles engineering and construction. Proxima Fusion has now raised 411 million euros from an international and German investor consortium, a significant funding round in European fusion research.
Global fusion landscape
ITER, the international fusion project in Cadarache in southern France, ranks among the costliest scientific projects in history: more than 22 billion euros total budget, tokamak design, operation expected no earlier than the mid-2030s. ITER will not generate electricity but rather establish the scientific foundation for a follow-on project, DEMO, which would first feed electricity to the grid.
Commonwealth Fusion Systems in Devens, Massachusetts pursues a tokamak approach with high-temperature superconductor magnets and has raised multiple billions of dollars from private investors. The structural difference from the stellarator approach is decisive: tokamaks require pulse interruptions, stellarators could run continuously. For a commercial power plant supplying electricity around the clock, that is a substantial advantage.
The Alpha facility is to be the first stellarator to demonstrate net energy and provide the scientific foundation for Stellaris. Germany now has two complementary fusion approaches in competition: Wendelstein 7-X as a research reactor in Greifswald and the commercial stellarator path with Alpha and Stellaris in Bavaria.
2031 as a milestone: If Alpha succeeds, Stellaris draws closer
Later this year, Wendelstein 7-X resumes operation following maintenance. The stated scientific goal of the new experimental campaign is to raise the ratio of plasma pressure to magnetic pressure to four percent, the threshold above which conditions are considered power-plant-relevant. The May 2025 record achieved three percent, the gap to the required four to five percent has narrowed, but remains unclosed.
Construction of Alpha in Garching is to begin in 2027. If the facility achieves net energy by 2031, the path to Stellaris opens. Bavaria has decided on the site, RWE brings industrial infrastructure, the Max Planck Institute for Plasma Physics provides scientific expertise. What until recently seemed a power source of the distant future now has a concrete timetable, concrete sites, and concrete budgets. Whether this plan holds will become clear by 2031.