Fusion power startups have long been stalked by one stubborn question: Will the technology work?
But now, with net-positive fusion power no longer the stuff of science fiction, a fresh crop of startups have been founded on more mundane questions: Can reactors be built for less money? How can maintenance be made simpler? The answers could mean the difference between profitability and failure.
Francesco Volpe hopes they will be, at least. The founder and CTO of Renaissance Fusion has been studying fusion for decades. He has drawn inspiration from various projects over the years, which have culminated in a unique take on a fusion reactor design that’s attracting the attention of investors.
Renaissance raised a €32 million Series A1, the company exclusively told TechCrunch. The round was led by Crédit Mutuel Impact’s Révolution Environnementale et Solidaire fund with participation from Lowercarbon Capital. The startup plans to use those funds to build a demonstrator that should prove the basic parts of its novel design.
Fusion with a twist
Fusion power promises to generate large amounts of clean electricity from an abundant source of fuel. Most fusion startups are pursuing one of two approaches: inertial confinement, where lasers compress fuel pellets to ignite fusion pulses, and magnetic confinement, where large magnets corral plasma into long-burning fusion reactions.
Stellarators, the kind which Volpe is designing, belong in the latter camp. They are defined by their seemingly random twists and bulges that are meant to stabilize the plasma by working with its quirks rather than fighting against them. One major experiment in Germany has proven the validity of the concept, but its convoluted magnets were challenging to manufacture.
Grenoble-based Renaissance set out to simplify the stellarator. It isn’t the only company to try to do so — Thea Energy is another — and its approach blends rather than reinvents.
The startup’s reactor design looks like a polygon of segmented tubes, each decorated with etchings that resemble lines on a topographic map. But the lines aren’t frippery; instead, they demarcate the high-temperature super conducting (HTS) magnets that define the quirky contours of the plasma inside.
“I really wanted to simplify these to the bare minimum,” Volpe told TechCrunch.
The first simplification — the segmented tubes — was inspired by his graduate research using Wendelstein 7-AS, an experimental stellarator.
“When you look at that from the top, you kind of recognize a pentagonal form,” he said. “So I thought, why don’t we push this to the limit. Let’s literally make cylinders — not approximate cylinders, but actual cylinders.”
Other reactor designs use cylinders, but they tend to shape plasma into a doughnut shape, not the radical curves that define a stellarator. To give his design the necessary twists, Volpe drew on the work of a Spanish colleague, who 3D printed a scaffold to guide cheap, flexible cables into the form of a stellarator. The cables were far simpler to make than most stellarators’ complex magnets, but the 3D printing part wasn’t quite as commercializable.
Volpe simplified the idea further. Rather than replicate the plasma’s complexity in three-dimensional magnets, he flattened them. The tubes in Renaissance’s design will be coated with wide sheets of HTS magnets. Into that coating, a laser will etch a series of thin, meandering lines that encircle the tube. These lines will separate one magnet from the next.
At points where the superconducting stripes are wider, the magnetic field will be stronger. They’ll push back harder against the plasma in the tube. Where the material is thinner, the magnetic field will be weaker, allowing the plasma to bulge. The exact shape of the plasma will be determined by advanced computer simulations.
To protect the tubes from neutrons flying out of the fusion reaction, Renaissance will bathe the inside with liquid lithium. To make sure the liquid flows against the wall and doesn’t drip onto the plasma, the company applies an electric current to the liquid metal, giving it a magnetic field that will draw it to the powerful magnets on the outside of the tubes. Suspended within the liquid, small spheres containing molten lead will absorb a portion of the neutron bombardment. The liquid blanket will also do triple duty by breeding more fuel for the reactor and transferring heat to power steam turbines.
Magnetic carpets
Volpe said that Renaissance is on track to produce wide HTS “carpets” in the coming months. A demonstrator, which will integrate tubular HTS magnets and liquid lithium walls, should be ready by the end of 2026. Volpe hopes that the startup can build a complete stellarator by the early 2030s, a timeline that’s similar to other fusion startups.
Volpe hopes the demonstrator will prove that the concept is greater than the sum of its parts, each of which were promising on their own but together could pave the way to a cheaper fusion reactor. “You connect the dots. It’s the essence of inspiration,” Volpe said.