Proxima Fusion: the Munich spin-out trying to industrialise stellarators
In March 2025, Proxima Fusion presented Stellaris, the world's first integrated concept for a commercial fusion power plant that can be operated reliably and continuously (image rights: Proxima Fusion)
In Munich, a young deeptech company called Proxima Fusion is attempting one of the most demanding transitions in modern energy technology: turning nuclear fusion from a publicly funded scientific pursuit into an engineered system that could one day operate as part of the energy infrastructure. Proxima was founded in 2023 as a spin-out from the Max Planck Institute for Plasma Physics, and in June 2025 it announced a €130 million Series A financing round, which it described as the largest private fusion investment raised in Europe to date.
The scale of that funding matters less than what it is meant to support. Proxima is not promising a near-term energy breakthrough. Instead, it is building an industrial development programme around a specific and technically demanding fusion reactor design known as the stellarator, a concept that has been researched for decades but never commercialised.
From public research to private engineering
Proxima’s roots lie squarely in Europe’s public research ecosystem. The company describes itself as the first spin-out from the Max Planck Institute for Plasma Physics, one of the world’s leading centres for fusion research. For decades, the institute has been at the forefront of stellarator development, most visibly through Wendelstein 7-X, the world’s largest stellarator experiment, located in Greifswald, Germany.
This lineage is central to Proxima’s approach. Fusion is not a sector where progress can be separated from infrastructure. Experiments are large, complex and expensive, and advances are built on cumulative knowledge rather than rapid iteration. Proxima’s premise is that much of the fundamental science has already been established through public investment. The unresolved challenge is whether that knowledge can be translated into an integrated engineering design suitable for long-term operation, maintenance and, eventually, industrial replication.
In that sense, Proxima is not trying to reinvent fusion physics. It is narrowing its focus to the practical problems that begin once the physics is broadly understood: magnets that can be manufactured reliably, materials that can withstand extreme conditions, systems that can run continuously rather than in short experimental bursts, and designs that can be maintained without dismantling an entire machine.
Fusion, explained without the mystique
At its simplest, nuclear fusion is the process that powers the Sun. Light atomic nuclei combine to form heavier ones, releasing energy in the process. Reproducing this on Earth requires creating a plasma — a superheated, electrically charged gas — and keeping it stable under extreme conditions.
The difficulty is not achieving high temperatures alone, but maintaining the right combination of temperature, density and confinement over time. In fusion research, this balance is captured by a metric known as the triple product, which combines all three factors. High values are essential, but sustained performance is what ultimately determines whether a reactor concept can move beyond the laboratory.
This is why fusion progress often appears slow or abstract to non-specialists. Advances are measured in seconds of stable operation or incremental improvements in confinement, rather than in electricity delivered to the grid. Any company entering the field must therefore translate these scientific benchmarks into engineering decisions that can support reliable operation over months and years, not moments.
Why Proxima is betting on stellarators
Most contemporary fusion projects focus on tokamaks, doughnut-shaped devices that use magnetic fields to confine plasma while also driving a strong electrical current through it. Tokamaks are mechanically simpler than stellarators, but that internal plasma current can introduce instabilities that interrupt operation.
Stellarators take a different path. They rely almost entirely on externally generated magnetic fields, shaped by complex coils, to confine the plasma without the need for a large plasma current. The resulting geometry is far more intricate, but it offers a potential advantage: greater inherent stability and suitability for continuous operation, a critical requirement for any future power plant.
Proxima focuses on a particular class known as quasi-isodynamic stellarators, a configuration developed and refined within European research programmes. To make these machines more practical, the company places strong emphasis on high-temperature superconductors, materials that enable stronger magnetic fields than earlier generations of superconducting technology. Stronger fields allow for more compact reactor designs, which in turn can reduce construction complexity and support faster engineering iteration.
The logic behind this approach is well established in fusion engineering. Whether it can be realised in practice remains the central test of Proxima’s strategy.
Publishing the design before building the machine
Rather than leading with experimental claims, Proxima has prioritised making its engineering assumptions explicit. In February 2025, the company and its partners announced the publication of Stellaris, an integrated design concept for a stellarator-based fusion power plant. Proxima described it as the first such concept explicitly designed for reliable, continuous operation.
Stellaris is not a working reactor, and it does not claim to be one. Its importance lies in integration. Fusion systems tend to fail at the interfaces between disciplines: plasma scenarios that strain magnet design, heat loads that exceed material limits, or maintenance requirements that render a system impractical. The Stellaris concept brings these constraints together in a single framework, making trade-offs visible rather than implicit.
By publishing a comprehensive design concept, Proxima invites scrutiny from the wider fusion and engineering community. In a field where optimism can easily outpace reality, that openness is a necessary step toward credibility.
Capital, ambition and accountability
The €130 million Series A announced in June 2025 brought Proxima’s stated total funding to more than €185 million, combining private investment and public support. The round was co-led by Cherry Ventures and Balderton Capital, placing Proxima among the best-funded fusion startups in Europe.
In announcing the financing, Proxima framed fusion not only as an energy technology but as a question of long-term technological leadership. Chief executive and co-founder Francesco Sciortino described fusion as an opportunity to shift energy dependence from natural resources to advanced engineering. Cherry Ventures’ founding partner Filip Dames highlighted the combination of Europe’s scientific base and commercial ambition.
Such statements set expectations as much as they attract attention. Funding at this scale implies a transition from exploratory research to disciplined execution, where progress is measured against milestones, not narratives.
What “net energy” really means
Fusion discussions are often dominated by the idea of net energy or break-even, but the term is frequently misunderstood. Some definitions refer narrowly to the energy produced by fusion reactions compared with the energy delivered to the plasma. Others include the entire system: magnets, heating, cooling and auxiliary infrastructure.
To date, no fusion system has demonstrated net energy gain at the level of a complete power plant. Proxima’s roadmap includes a planned demonstration device, known as Alpha, intended to test key aspects of its stellarator approach in the early 2030s. Such demonstrations are steps along a development path rather than endpoints in themselves.
Understanding this distinction is essential to interpreting fusion milestones realistically. Progress is cumulative, and each stage addresses a different layer of complexity.
Signals from the underlying research
The research base underpinning Proxima’s work continues to advance. In May 2025, scientists at the Max Planck Institute for Plasma Physics reported that Wendelstein 7-X had achieved a world record for sustained high fusion performance, maintaining a peak value of the triple product for 43 seconds during an experimental campaign.
W7-X is a research device, not a prototype power plant, but such results are relevant because they address the same stability and endurance challenges that any future reactor must solve. Improvements in these parameters help narrow the gap between theoretical viability and engineered systems.
An open industrial experiment
Proxima Fusion occupies a distinctive position in the fusion landscape. It is neither a purely academic project nor a company promising near-term energy production. Instead, it is an attempt to industrialise a specific fusion pathway, grounded in decades of public research and expressed through published engineering concepts rather than proprietary claims alone.
Its significance lies in treating fusion as an engineering discipline first and a breakthrough story second. Whether Proxima succeeds will depend on execution: building magnets that perform as designed, integrating complex subsystems, and demonstrating that a stellarator can move from experimental stability to industrial reliability.
Fusion has never lacked ambition. Its history shows that ambition must be matched by engineering discipline. Proxima is betting that this time, the balance can be struck.
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