"I remember a few people said that the place where Proxima is today was impossible," recalls Francesco Sciortino, co-founder and CEO of Proxima Fusion.
Being accused of chasing the impossible is common for scientists and engineers working on nuclear fusion projects worldwide. They are, after all, trying to replicate on Earth the reaction that powers the Sun.
If successful, fusion could provide abundant, cheap, and emission-free electricity. However, the challenges are immense, and a functioning power station is still far off.
Fusion involves fusing hydrogen nuclei together, releasing vast amounts of energy. On the Sun, immense gravitational forces sustain this reaction. On Earth, achieving fusion requires extremely high temperatures - much hotter than those found on the Sun.
To achieve this, a fuel mixture, usually the hydrogen isotopes tritium and deuterium, is heated until it becomes a superheated plasma. This plasma must then be controlled and manipulated to trigger fusion.
There are several ways to attempt this, and Germany's Proxima Fusion is pursuing one of the most challenging methods in the industry.
The most common approach is the tokamak, a doughnut-shaped device that uses powerful magnets to contain the plasma. However, Munich-based Proxima is developing a stellarator, which also uses magnets but features a more complex, twisted reaction chamber. This design is much harder and more expensive to build.
Sciortino describes a fusion reactor as a "dumb machine." So why choose such a difficult path?
If successful, the stellarator's twists and turns make the plasma easier to control than in a tokamak, according to Sciortino. He compares the two: a tokamak is a "beast," while the stellarator is a "little cat."
"A stellarator is objectively very difficult to design and build. But if you succeed, it becomes a dumb machine - just like a microwave oven," Sciortino explains.
Proxima's "dumb machine" will be a stellarator called Alpha, building on decades of research from Germany's Max Planck Institute for Plasma Physics and its W7-X stellarator.
The goal for Alpha is to generate more energy than it consumes, with the insights gained helping to design an even more advanced fusion power plant, Stellaris.
However, Alpha requires significant investment. Proxima recently secured €400 million from the state of Bavaria and is seeking over a billion dollars from the federal government, with a decision expected next year.
Proxima is competing with 53 other groups developing fusion technology, according to the Fusion Industry Association (FIA).
One such project is the UK-based Step (Spherical Tokamak for Energy Production), which plans to build a prototype power plant at a former coal-fired station in West Burton, Yorkshire, backed by the UK government.
"Tokamaks have the advantage of a deep experimental foundation built over decades. They have demonstrated plasma performance closer to what's required for a fusion power plant, including operation with fusion fuel," says Ryan Ramsey, director of Organisational Performance at Step and former captain of the nuclear submarine HMS Turbulent.
For tokamaks, the powerful magnets are relatively simple to construct. "They benefit from comparatively simpler magnetic geometry, with fewer and more regular coils. That has real implications for manufacturability, maintainability, and cost," Ramsey adds.
Sciortino is acutely aware of the challenges facing Proxima. He admits to "losing sleep" over whether they can build the intricate magnets quickly and affordably enough to make the stellarator viable.
"The first magnet we make will be very complicated and very expensive. But can we make it faster than expected, and can we reduce the cost?" Sciortino asks.
Germany's manufacturing expertise is an advantage. Sciortino points to the large number of CNC machinists - operators of computer-controlled machine tools - in Germany, estimating 550,000 compared to 350,000 in the US.
This is crucial for Proxima, which uses a costly type of steel in its magnets that requires precise machining.
Maintaining precision while accelerating development is essential for Sciortino. The W7-X took over a decade to become operational; he aims to have Alpha running in a third of that time.
A prototype magnetic coil is currently under construction, with plans to test it next year. Its twisted geometry makes it one of the most complex magnets in the world, according to Proxima.
After testing, Proxima will build 40 more magnetic coils for the Alpha machine. To achieve this, a magnet factory is being established.
"In 2028, 2029 we need to be able to make magnets at a crazy, crazy speed," says Sciortino.
The work extends beyond Germany. Sciortino notes that key suppliers across Europe could position the continent at the forefront of the future fusion industry.
"We [Europeans] missed the digital wave, didn't we? But it turns out we still have people trained in manufacturing," he says.
At Step, Ramsey emphasizes that fusion is no longer just a physics experiment. "There's real momentum across fusion right now, and that should be seen as a strength rather than something to divide. This isn't a single-path race, it's a set of approaches exploring different trade-offs. The real question now is not which concept is most interesting, but which can credibly deliver a power plant."
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