German startup Proxima Fusion — whose team includes engineers from MIT, Google, SpaceX, and McLaren — has unveiled a fusion energy reactor design it believes offers the quickest route to commercially viable fusion power.

Dubbed Stellaris, the machine is a quasi-isodynamic (QI) stellarator with high-temperature superconducting (HTS) magnets. This type of reactor uses complex, twisted magnetic fields to confine hot plasma, creating the conditions needed for fusion reactions.

“Stellaris is designed to operate in continuous mode and be intrinsically stable,” Francesco Sciortino, Proxima's co-founder and CEO, told TNW. “No other fusion power plant design has yet been demonstrated to be capable of that.”  

Stellaris' design builds on the Wendelstein 7-X, the world's largest stellarator, located at the Max Planck Institute for Plasma Physics in Germany. While Wendelstein 7-X was developed for research, Stellaris could one day power the grid. 

Proxima aims to bring the design to life with its first demonstrator — Alpha — slated for completion in just six years. Alpha will be the first-ever fusion device demonstrating net energy production in a steady state, said Sciortino. The machine will lay the foundation for Proxima's first 1GW fusion reactor, which the company hopes will power up sometime in the 2030s. 

Stellarators have several advantages over their more popular cousin, the tokamak (the type adopted by ITER mega project under construction in France). They need less power to operate and are more stable. Their biggest drawback is complexity — stellarators are notoriously hard to design and build. This is why they were largely set aside in the 1960s for the tokamak. However, advances in computational power are closing the gap.

An AI-enabled fusion reactor design

Similar to other industries like automotive or aerospace, Proxima uses AI supercomputers to rapidly iterate the best fusion reactor designs based on key parameters like cost, material availability, and efficiency. So instead of having to build multiple prototypes, Proxima can jump straight into building a functioning demonstrator. 

“The understanding of complex geometry and its consequences is everything in stellarators,” said Sciortino. “AI is helping Proxima to uncover patterns that lead to simpler, faster, and cheaper designs.” 

Stellaris is designed to generate more power per unit volume than any previous stellarator. HTS magnets create stronger magnetic fields, allowing for smaller, faster-to-build, and more efficient reactors. This approach also reduces costs in both construction and operation. Stellaris uses only existing materials, making it buildable with today's supply chains, the company said. Full details of the reactor were published today in the journal

Munich-based Proxima made history in 2023 as the first company to spin out from the esteemed Max Planck Institute for Plasma Physics, one of the world's leading fusion research centres. The institute focuses exclusively on fusion and has more plasma physicists than MIT.

Proxima raised €20mn in funding last year as it looks to turn the mind-bending physics of fusion into a viable business.   

“When Proxima started its journey, the founders said, ‘This is possible, we'll prove it to you,' and they did,” said Ian Hogarth, a partner at Plural, one of Proxima Fusion's earliest investors. “Stellaris positions QI-HTS stellarators as the leading technology in the global race to commercial fusion.”