For decades, nuclear fusion—the reaction that powers the sun—has been the ultimate energy dream. If harnessed on Earth, it could provide endless, carbon-free power. But the challenge is huge. Fusion requires temperatures hotter than the sun’s core and a mastery of plasma—the superheated gas in which atoms that have been stripped of their electrons collide, their nuclei fusing. Containing that plasma long enough to generate usable energy has remained elusive.
Now, two companies—Germany’s Proxima Fusion and Tennessee-based Type One Energy—have taken a major step forward, publishing peer-reviewed blueprints for their competing stellarator designs. Two weeks ago, Type One released six technical papers in a special issue of the Journal of Plasma Physics. Proxima detailed its fully integrated stellarator power plant concept, called Stellaris, in the journal Fusion Engineering and Design. Both firms say the papers demonstrate that their machines can deliver commercial fusion energy.
At the heart of both approaches is the stellarator, a mesmerizingly complex machine that uses twisted magnetic fields to hold the plasma steady. This configuration, first dreamed up in the 1950s, promises a crucial advantage: Unlike its more popular cousin, the tokamak, a stellarator can operate continuously, without the need for a strong internal plasma current. Instead, stellarators use external magnetic coils. This design reduces the risk of sudden disruptions to the plasma field that can send high-energy particles crashing into reactor walls.
The downside? Stellarators, while theoretically simpler to operate, are notoriously difficult to design and build. Recent advances in computational power, high-temperature superconducting (HTS) magnets, and AI-enhanced optimization of magnet geometries are changing the game, helping researchers to uncover patterns that lead to simpler, faster, and cheaper stellarator designs.
Two Visions of Fusion with One Goal
While both firms are racing toward the same destination—practical, commercial fusion power—the Proxima paper’s focus leans more toward the engineering integration of its reactor, while Type One’s papers reveal details of its plasma physics design and key components of its reactor.
Proxima, a spinoff from Germany’s Max Planck Institute for Plasma Physics, aims to build a 1-gigawatt stellarator power plant. The design uses HTS magnets and AI optimization to generate more power per unit volume than earlier stellarators, while also significantly reducing the overall size. Proxima has applied for a patent on an innovative liquid-metal breeding blanket, which will be used to breed tritium fuel for the fusion reaction, via the reaction of neutrons with lithium.
Proxima Fusion’s Stellaris design is significantly smaller than other stellarators of the same power.Proxima Fusion
“This is the first time anyone has put all the elements together in a single, fully integrated concept,” says Proxima cofounder and chief scientist Jorrit Lion. The design builds on the Wendelstein 7-X stellarator, a €1.4 billion (US $1.5 billion) project funded by the German government and the European Union, which set records for electron temperature, plasma density, and energy confinement time.
Type One’s stellarator design incorporates three key innovations: an optimized magnetic field for plasma stability, advanced manufacturing techniques, and cutting-edge HTS magnets. The plant it has dubbed Infinity Two is designed to generate 350 megawatts of electricity.
Like Proxima’s plant, Infinity Two will use deuterium-tritium fuel and build on lessons learned from W7-X, as well as Wisconsin’s HSX project, where many of Type One’s founders worked before forming the company. In partnership with the Tennessee Valley Authority, Type One aims to build Infinity Two at TVA’s Bull Run Fossil Plant by the mid-2030s.
“Why are we the first private fusion company with an agreement to develop a fusion power plant with a utility? Because we have a design based in reality,” says Christofer Mowry, CEO of Type One Energy. “This isn’t about building a science experiment. This is about delivering energy.”
AI Points to an Ideal 3D Magnetic-Field Structure
Both firms have relied heavily on AI and supercomputing to help them place the magnetic coils to more precisely shape their magnetic fields. Type One relied on a range of high-performance computing resources, including the U.S. Department of Energy’s cutting-edge exascale Frontier supercomputer at Oak Ridge National Laboratory, to power its highly detailed simulations.
That research led to one of the more intriguing developments buried in these papers: a possible move toward consensus in the stellarator physics community about the ideal three-dimensional magnetic-field structure.
Proxima’s team has always embraced the quasi-isodynamic (QI) approach, used in W7-X, which prioritizes deep particle trapping for superior plasma confinement. Type One, on the other hand, built its early designs around quasi-symmetry (QS), inspired by the HSX stellarator, which aimed to streamline particle motion. Now, based on its optimization research, Type One is changing course.
“We were champions of quasi-symmetry,” says Type One’s lead theorist Chris Hegna. “But the surprise was that we couldn’t make quasi-symmetry work as well as we thought we could. We will continue doing studies of quasi-symmetry, but primarily it looks like QI is the prominent optimization choice we are going to pursue.”
Type One Energy is working with the Tennessee Valley Authority to build a commercial stellarator by the mid-2030s.Type One Energy
The Road Ahead for Stellarators
According to Hegna, Type One’s partnership with TVA could put a stellarator fusion plant on the grid by the mid-2030s. But before it builds Infinity Two, the company plans to validate key technologies with its Infinity One test platform, set for construction in 2026 and operation by 2029.
Proxima, meanwhile, plans to bring its Stellaris design to life by the 2030s, first with a demo stellarator, dubbed Alpha. The company claims Alpha will be the first stellarator to demonstrate net energy production in a steady state. It’s targeted to debut in 2031, after the 2027 completion of a demonstration set of the complex magnetic coils.
Both companies face a common challenge: funding. Type One has raised $82 million and, according to Axios, is preparing for more than $200 million in Series A financing, which the company declined to confirm. Proxima has secured about $65 million in public and private capital.
If the recent papers succeed in building confidence in stellarators, investors may be more willing to fund these ambitious projects. The coming decade will determine whether both companies’ confidence in their own designs is justified, and whether producing fusion energy from stellarators transitions from scientific ambition to commercial reality.
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