The world's largest stellarator is mastering the art of continuous fusion

Countries & Cities · Published 14 October 2026 · Updated 25 October 2026 Swipe more like this →

In short: Creating a star on Earth requires more than just heat; it requires a magnetic cage so complex it defies simple geometry. The Wendelstein 7-X is currently pushing the limits of this engineering feat, aiming to prove that fusion power can run continuously rather than in short, erratic bursts.

The Wendelstein 7-X (W7-X), located in Greifswald, Germany, is the world's largest stellarator. Unlike tokamaks, which use a current through the plasma to maintain stability, stellarators rely on a sophisticated arrangement of external coils to create a magnetic cage. The W7-X utilizes a five-field-period Helias configuration, featuring 50 non-planar and 20 planar superconducting magnetic coils. These coils are designed to induce a magnetic field that prevents the ultra-hot plasma from colliding with the reactor walls. The engineering scale is immense. The coils are arranged around a 16-meter diameter cryostat, which must be cooled to a superconductivity temperature of 4 K using liquid helium. This 'cold mass' weighs about 425 metric tons. To achieve the necessary conditions for fusion, the device aims for a plasma density of 3×10²⁰ particles per cubic metre and temperatures reaching between 60 and 130 megakelvins. A critical breakthrough occurred in 2021 when X-ray imaging data confirmed that magnetic field optimization had substantially reduced 'neoclassical transport'—the process where collisions cause heated particles to escape the magnetic cage. The ultimate goal is continuous operation, a prerequisite for a viable power plant. While early tests in 2015 produced plasma for only 0.1 seconds, recent experiments have pushed durations to 100 seconds and achieved energy turnovers of 1.8 gigajoules over a six-minute run in 2025. This surpassed the records of China's EAST reactor. The project is a massive international undertaking; while the stellarator itself cost €370 million between 1997 and 2014, the total cost for the Greifswald site—including personnel and materials—reached €1.06 billion, largely due to complex coil issues that delayed the schedule by about three years.

theme-key-value human-achievement reflective 3 fusion-energy stellarator physics-engineering claims The Wendelstein 7-X is the world's largest stellarator device as of 2023.

The cryostat has a diameter of 16 metres and a 'cold mass' of about 425 metric tons.

In 2025, the reactor exceeded the record achieved by China's EAST reactor. The total cost for the IPP site in Greifswald reached €1.06 billion over an 18-year period.

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