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It's Happening: Europe Is Building an Impossible Fusion Reactor

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For fifty years the tokamak — the classic donut-shaped reactor — has dominated fusion research. Now a Munich startup called Proxima Fusion, spun out of the Max Planck Institute and freshly funded with €411 million including checks from Google and energy giant RWE, is betting everything on the shape the field walked away from half a century ago: the stellarator, a twisted "donut" so absurdly complicated it was long believed impossible to build. This is the story of why fusion is so hard, why the tokamak has a fatal flaw, and how Europe's most ambitious energy bet plans to build the first stellarator power plant in history.

Why the Donut Fails

Fusion means slamming atomic nuclei together at 100–150 million degrees Celsius until they merge — but no material can touch that plasma, so it must be held suspended in a magnetic cage. The simplest cage is a donut-shaped torus, yet it leaks: the field is stronger on the inside of the ring, making ions and electrons drift apart until the plasma pushes itself into the walls. The fix is a helical twist in the field lines — and the stellarator is the shape that provides that twist on its own.

The Design the World Walked Away From

The tokamak gets its twist by running a current through the plasma itself, which made it easy to build — and in 1968 the Soviet T-3 convinced the world to abandon stellarators almost overnight. But a transformer only works while the current is changing: every tokamak runs in pulses. ITER, the largest fusion project on Earth, aims for burns of about 400 seconds before it needs a timeout — fine for science, fatal for a power plant. A small group at the Max Planck Institute kept working on the stellarator anyway, and their Wendelstein 7-X finally proved the physics, holding a 40-million-degree plasma for eight full minutes in 2023. But W7-X can never produce more energy than it consumes.

Proxima's Cheat Code: Stronger Magnets

Proxima's bet is that fusion power scales with the fourth power of the magnetic field: double the field, get 16 times the power. W7-X's niobium-titanium magnets quit past 12 tesla, so Proxima uses REBCO, a high-temperature superconducting tape pioneered by MIT and Commonwealth Fusion Systems, to design a machine running at around 9 tesla on-axis versus W7-X's 2–3 — roughly 81 times the potential output. The roadmap: a full-scale test coil in 2027, a demonstration reactor called Alpha targeting net energy gain in the early 2030s, and 50 power plants by 2050. Along the way it would also deliver industrial heat and the neutrons needed for medical isotopes.

The video goes deep into the physics — and into a winding technique so proprietary the host wasn't allowed to film it. Well worth watching in full.

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