Proxima Fusion Eyes Giant HTS Tape Plant With Fujikura, Citing 40,000 km Per Reactor

Proxima Fusion, a fusion startup based in Munich, Germany, is expanding its cooperation with two Japanese companies. On October 28, 2026, timed to German Chancellor Friedrich Merz's visit to Japan, it signed memoranda of understanding (MoUs) with Kyoto Fusioneering and Fujikura. The cooperation covers next-generation gyrotrons for plasma heating, fuel cycle technology for handling tritium and other fuels, and the manufacture of high-temperature superconducting (HTS) tape, which is used to generate the powerful magnetic fields that confine the plasma.

However, these agreements do not mean a formal decision to build a factory, nor do they mean that any fusion-related equipment has been demonstrated. The MoUs set out a framework for cooperation on technology development and commercialization. They do not guarantee specific product orders or deliveries, or the operation of a power plant. Commercializing the stellarator-type fusion reactor Proxima Fusion is pursuing will require a system that can manufacture equipment meeting design requirements at industrial scale and supply it reliably. Based on the contents of the agreements, this article reviews the progress of the company's commercialization plans and the technical challenges that remain to be verified.

Two MoUs signed to coincide with the German chancellor's visit to Japan

The two MoUs signed in Tokyo on October 28, 2026 deepen cooperation with Japanese companies on key technologies needed for the fusion power plant Proxima Fusion is planning. According to Kyoto Fusioneering's announcement, the two companies will continue and expand joint development of next-generation gyrotrons and fuel cycle technology. They plan to use the plasma heating and tritium-related technologies Kyoto Fusioneering has built up to support the commercialization and industrial rollout of fusion technology in Germany. They are also looking at participating in the national "Fusion Hubs" initiative promoted by Germany's Federal Ministry of Research, Technology and Space (BMFTR).

The MoU with Fujikura, announced by Proxima Fusion, concerns the manufacture of high-temperature superconducting (HTS) tape. The two companies will jointly examine the possibility of establishing an industrial-scale HTS tape manufacturing site in Lower Saxony in northern Germany. They will first evaluate the technical requirements for manufacturing and its commercial and economic feasibility, linking Fujikura's manufacturing technology with the long-term demand Proxima Fusion anticipates.

This manufacturing concept is not being disclosed for the first time. On September 9, 2026, Proxima Fusion announced an MoU with the state of Lower Saxony, setting out a plan to invest roughly €140 million in the first two phases, through the end of 2029. Under the plan, funding would be split between public and private sources, with the state government contributing €21 million of the public share. The agreement with Fujikura can be seen as adding a partner with concrete manufacturing expertise to this existing plan and moving the feasibility study forward.

Still, these are plans at this stage. No final investment decision on building the factory or confirmed annual production capacity has been announced, and no performance data has been presented for gyrotrons delivered under the collaboration with Kyoto Fusioneering or for fuel cycle equipment. Industrial cooperation between Japan and Germany advancing against a backdrop of leader-level diplomacy is meaningful, but building a cooperative relationship and completing hardware that meets required performance need to be evaluated separately.

Three key technologies: magnetic field, heating, and fuel cycle

In the stellarator-type fusion reactor Proxima Fusion is developing, each technology covered by this cooperation plays a different role. Fusion power requires a magnetic field to confine ultra-hot plasma, equipment to heat the plasma to the temperature needed for fusion reactions, and a system to continuously supply and recover fuel. These must not only meet their performance targets individually but also work together as a single power plant.

The first element, high-temperature superconducting (HTS) tape, is the material for the electromagnets that generate the strong magnetic field confining the plasma. Unlike a tokamak, a stellarator does not rely on large currents inside the plasma; instead it forms the confining field with external coils of complex three-dimensional shape. In principle, this structure avoids large-scale instabilities caused by plasma current and allows a device suited to steady-state operation. HTS tape can remain superconducting at relatively high temperatures and carry large currents with low loss under strong magnetic fields, making it a key material for high-field coils.

The second element, the gyrotron, is a type of vacuum tube that generates high-power microwaves. To fuse deuterium and tritium nuclei, the plasma must be heated to extremely high temperatures of more than 100 million degrees and kept there. The millimeter-wave electromagnetic waves a gyrotron produces transfer energy to the plasma by resonating with the motion of electrons spiraling in the magnetic field. This heating method is called electron cyclotron resonance heating (ECRH), and it is an important technology in a stellarator's heating system.

The third element, the fuel cycle, refers to the series of systems that supply deuterium (D) and tritium (T) to the reactor, then recover, purify, and reuse unreacted fuel. Tritium in particular barely exists in nature, so large-scale fusion power requires a mechanism to continuously replace what is consumed in the reactor. The envisioned approach is to produce tritium in a blanket surrounding the reactor core, where neutrons generated by fusion reactions react with lithium. Establishing technology to recover this tritium safely and efficiently and resupply it as fuel is a challenge for future continuous operation.

In the conceptual design of its stellarator power reactor, Proxima Fusion sets the ECRH heating power coupled to the plasma at 50 MW. However, this is a requirement derived from the power plant design, and it does not mean that 50 MW of heating performance has been demonstrated through the collaboration with Kyoto Fusioneering. The industrial cooperation is positioned as an effort to actually manufacture and integrate equipment that meets such design requirements.

An estimated 20,000 km of HTS tape for the demonstration reactor and 40,000 km for a commercial reactor

The scale of HTS tape manufacturing is especially important in the cooperation with Fujikura. Proxima Fusion's estimates are that the demonstration reactor "Alpha," planned for the early 2030s, will need about 20,000 km of HTS tape, and that the first commercial plant, "Stellaris," will need about 40,000 km per unit. These figures estimate the length of material required to build the superconducting coils and serve as a basis for considering future manufacturing capacity.

However, 20,000 km and 40,000 km are demand forecasts calculated from current reactor designs and development plans. They are neither shipment records from existing production lines nor confirmed orders placed with Fujikura. HTS tape is already being manufactured and supplied, but reliably supplying tens of thousands of kilometers of material while maintaining the quality fusion reactors require will demand expanded production capacity and more advanced manufacturing technology.

{
  "type": "bar",
  "title": "計画装置におけるHTSテープの推定必要量",
  "unit": "km",
  "categories": ["実証炉 Alpha（構想）", "商用炉 Stellaris（1基当たり構想）"],
  "series": [
    { "name": "推定必要量", "values": [20000, 40000] }
  ],
  "caption": "Proxima Fusionによる将来構想の推定値。確定発注量や既存の製造能力を示すものではない。",
  "source": "Proxima Fusionプレスリリース（2026年10月28日）"
}

Against the backdrop of this long-term demand, the manufacturing site under consideration in Lower Saxony is envisioned as a way to build an HTS tape supply system in Europe. Because fusion reactors need large quantities of high-performance wire, expanding manufacturing capacity and lowering costs through mass production are important conditions for commercialization. By presenting its outlook for future demand, Proxima Fusion makes it easier for materials manufacturers to consider capital investment and production plans.

Nevertheless, the feasibility and profitability of the manufacturing site have not been confirmed. Although a rough estimate of the initial investment and a funding policy have been presented, the final investment decision and the specifications of the production equipment remain matters for future study. On the technical side, a challenge is whether properties such as critical current can be kept uniform along the entire length of long tape while securing sufficient yield. How far unit-length costs can be reduced by scaling up manufacturing is also a factor that will affect the economics of fusion power.

A 1 GW-class power reactor design shown through numerical simulation

An important source for understanding Proxima Fusion's technical vision is a research paper published in an academic journal in 2025. "Stellaris: A high-field quasi-isodynamic stellarator for a prototypical fusion power plant," by J. Lion et al., was accepted on February 6, 2025, and published in Fusion Engineering and Design, Volume 214 (article number 114868). It summarizes a conceptual design of a stellarator-type fusion power reactor that combines high-temperature superconducting magnets with a magnetic field configuration known as quasi-isodynamic (QI).

A distinctive feature of the study is that it examines not only plasma confinement performance but also multiple engineering conditions required of a power reactor in an integrated way. In addition to three-dimensional optimization of the magnetic field configuration and analysis of plasma stability, it evaluates first-wall cooling, divertor heat loads, a tritium-breeding blanket that uses neutrons, and the support structure for the electromagnets. It also examines countermeasures against "quenches," in which superconductivity is lost, and maintenance methods for remotely replacing in-vessel components.

The design values for the power reactor presented in the paper are a maximum fusion power of about 2,700 MW and a thermal output of about 3,150 MW including energy multiplication in the blanket. Assuming a thermal-to-electric conversion efficiency of about one third, this works out to an electrical output of about 1 GW. However, this is the electrical output in the conceptual design, and it does not mean that net power delivered to the grid, after subtracting electricity consumed by equipment within the plant, has been demonstrated.

It should be noted that the results presented in the paper are based on numerical simulations and computational models. Although the magnetic field structure, plasma behavior, neutron transport, heat loads, and other factors are analyzed in detail, no actual Stellaris power plant has been built to generate about 1 GW of electricity. The assumption of a one-third conversion efficiency is also a computational premise, not a figure measured at a power generation facility.

The study considers a broad range of physical and engineering conditions to assess feasibility, but it has not been verified through experiments integrating the entire plant. In real fusion reactors, problems arise that calculations alone cannot fully confirm, such as material degradation from neutron irradiation, prolonged heat loads, electromagnetic forces acting on superconducting coils, and manufacturing tolerances in equipment. Moreover, even if individual designs hold up on paper, it does not follow that the necessary equipment can be manufactured at industrial scale and operated stably as a single system. The current efforts toward building a supply chain can be seen as a step toward overcoming these technical challenges between design and actual hardware.

The commercialization roadmap and what to watch next

Proxima Fusion aims to achieve net energy gain from fusion in the demonstration stellarator "Alpha" in the early 2030s and, building on that result, to realize its first commercial power plant, "Stellaris," in the late 2030s. However, the energy gain Alpha targets refers to scientific energy gain (Q>1), in which the power produced by fusion reactions exceeds the power put into heating the plasma. This differs from obtaining electrical output that exceeds the power consumption of the entire plant, and many more technical challenges must be solved on the way to commercial power generation.

These development goals are a roadmap the company has presented, and neither the current MoUs nor the academic paper guarantees they will be achieved. To judge technical progress, it is necessary to look not only at target years but also at what equipment has been completed at each stage and which performance figures have been confirmed by measurement. Of particular importance is whether the core performance shown in numerical calculations can be reproduced, and whether the necessary peripheral equipment can be integrated and operated stably.

For HTS tape manufacturing, the final investment decision (FID) on the factory planned in Lower Saxony will be the first important marker. After that, the focus will be on whether funding is finalized and whether production line specifications, annual capacity, and the start of mass production become concrete. On the technical side, it will be necessary to check measurement data such as the critical current density of the manufactured tape, uniformity of quality along its length, and joint performance, as well as a track record of supply for coils in actual machines.

For gyrotron heating and the fuel cycle as well, the specifications and measured data of the developed equipment will be the yardstick for judging progress. For gyrotrons, the millimeter-wave output actually obtained, stability during long-duration operation, and power conversion efficiency matter, along with integration testing with the stellarator's heating system. For the fuel cycle, tritium recovery rate, purification performance, safety during continuous circulation, and compatibility with materials need to be verified. After these performances are confirmed individually, there remains the stage of confirming whether the fusion reactor as a whole meets requirements.

The MoUs contain no newly measured equipment performance figures and no quantitative comparison with conventional technologies. For that reason, it cannot be concluded from the signing of the agreements alone that technology readiness level (TRL) has improved. At the same time, moving the technologies needed for fusion power from individual research and development to industrial-scale manufacturing requires early collaboration with materials and equipment manufacturers. The feasibility of the vision Proxima Fusion has presented will become easier to judge concretely through future investment decisions, the build-out of manufacturing facilities, and verification results from actual machines.