Germany and Japan Bet Fusion Will Be Won in Factories, Not Labs

Fusion developers have spent years talking about physics milestones. The latest set of deals between Germany and Japan shifts the focus to manufacturing. The argument from the German side is that commercial fusion will be decided by who can build the components at scale, and the agreements signed during Chancellor Friedrich Merz's state visit to Japan are aimed squarely at that problem.

A government-level declaration, and five commercial agreements

Merz and Japanese prime minister Sanae Takaichi signed a joint declaration to cooperate on advancing nuclear fusion technology. The declaration covers more than fusion. The two leaders also committed to working together on commercial development in space, clean hydrogen, quantum technology and synchrotron radiation science. Fusion is the headline, but the framing is industrial: two countries with deep manufacturing bases agreeing to build supply relationships rather than simply share research.

The commercial side produced five agreements between developers. Proxima Fusion, a spin-out from the Max Planck Institute, was represented by its CEO and co-founder Francesco Sciortino, who signed memoranda of understanding (MoU) with two Japanese companies. Those MoUs are meant to support Proxima's plan to bring a commercial fusion power plant online at Gundremmingen, Germany, by the end of the next decade.

The HTS tape factory is the real bottleneck

The Fujikura agreement is the one I'd watch most closely. It concerns a planned high-temperature superconducting (HTS) tape factory in Lower Saxony. Proxima's stellarator design uses dozens of non-planar coils made from HTS tape, and the numbers are large. The demonstrator plant will need 20,000 km of the material, and the commercial plant will need double that. Proxima says it will draw on Fujikura's "manufacturing expertise" to set up the factory.

HTS tape is the material that lets magnets run at higher field strengths than conventional superconductors, which in turn can shrink the size of a confinement device. For a fusion plant, though, the magnet is only half the story. The tape has to be produced consistently, in long lengths, at a cost and quality that works for a power plant that needs many coils. Whoever can run that production line reliably holds a position that is hard to replicate quickly, which is why a Japanese cable and optical-fibre maker is a sensible partner for a German developer that is still building its first factory.

Gyrotrons and the fuel cycle

Kyoto Fusioneering's role is different. The company will help Proxima develop next-generation gyrotrons for plasma heating, along with fuel cycle technologies. Gyrotrons are high-power microwave sources used for electron cyclotron heating, and they are one of the less glamorous but more constrained subsystems in a magnetic confinement device. Improving their efficiency and output directly affects how much heating power a machine can deliver, and the fuel cycle work addresses how a plant handles and recycles its fuel once it is running. Neither item is headline material, but both are the kind of engineering that determines whether a reactor can operate continuously.

Why stellarators, and why Germany

Stellarators have gained ground as a reactor concept, particularly in Germany. The Max Planck Institute's Wendelstein 7-X research facility hosts what is described as the world's largest stellarator, and it provides the technical basis for Proxima's design. The contrast with the tokamak is worth keeping in mind. Both designs use magnetic fields to confine hot plasma, but a tokamak drives a large current through the plasma to help hold it in shape, while a stellarator relies on twisted, three-dimensional coils to do that work externally.

Proponents argue this gives stellarators a meaningful advantage: they can reach the same confinement quality with lower electrical currents in the plasma, and in principle they can run in steady state without the pulsed behaviour that a tokamak's current drive tends to impose. The trade-off is complexity. Non-planar coils are harder to design and manufacture than the simpler toroidal field coils of a tokamak, which is exactly why the tape factory and coil manufacturing matter so much to the stellarator case. The design's promise and its manufacturing burden are the same thing.

Sciortino put the thesis plainly: "The global race to fusion will be won in factories and supply chains. Japan has spent decades building world-class fusion engineering capabilities; Germany has the leading stellarator engineering in the world and knows how to industrialise." He framed the cooperation as building "a new industry together," and tied Japanese interest in working with Germany to the strong backing fusion has received from the German government and the EU.

More pairings, and a different confinement approach

The Japanese side of the deal is not limited to Proxima. Kyoto Fusioneering also signed an MoU with Focused Energy, a German developer working on laser-driven inertial fusion energy. Inertial fusion compresses fuel with lasers rather than holding plasma in magnetic fields, so it is a distinct technical route from both tokamaks and stellarators. Germany's Gauss Fusion also signed a "joint statement of intent" with Japan's Helical Fusion to advance modular and helical stellarator technology. Taken together, the agreements show German and Japanese developers spreading their bets across confinement approaches rather than converging on one design.

Context: two countries, similar caution about fission

Both governments have taken comparable paths on nuclear technology since the 2011 Fukushima accident. Both have remained largely opposed to new fission plants, yet both have invested heavily in fusion. That split is a big part of why fusion has become the nuclear option that governments in both countries are willing to fund and promote. Germany's companies have collectively raised more than $1bn, though the US and China are generally regarded as the leaders in the race toward commercial fusion.

Takaichi framed the cooperation in industrial terms, saying that "cooperation between Japan and Germany in the field of industrial technology is of great importance," and that both countries play a key role in Asia and Europe based on a shared manufacturing tradition.

What to watch

An MoU is not a contract for steel and superconductor, and the real test is whether the Lower Saxony tape factory moves from memorandum to construction and then to output. The timeline Proxima has set, a commercial plant at Gundremmingen by the end of the next decade, leaves little room for slippage in the supply chain. My read is that the HTS tape line will tell us more about the credibility of the stellarator plan than any single physics result over the next few years. If that factory gets built and runs to spec, the German-Japanese pairing will look like the template for how fusion gets industrialised. If it stalls, the MoUs will be remembered as a good start.