For a long time, fusion power startups have faced a persistent question: Can the technology actually work?

However, with the achievement of net-positive fusion power no longer being the realm of science fiction, a new wave of startups has emerged, focusing on more practical concerns: Can reactors be built at a lower cost? How can maintenance be simplified? The answers to these questions could be the deciding factor between success and failure.

Francesco Volpe, the founder and CTO of Renaissance Fusion, is hopeful that his company will be able to provide the answers. With decades of experience studying fusion, Volpe has drawn inspiration from various projects, culminating in a unique approach to fusion reactor design that has caught the attention of investors.

Renaissance has secured a €32 million Series A1 funding round, led by Crédit Mutuel Impact’s Révolution Environnementale et Solidaire fund, with participation from Lowercarbon Capital. The company plans to utilize this funding to build a demonstrator that will test the fundamental components of its innovative design.

Fusion with a twist

Fusion power promises to generate substantial amounts of clean electricity from an abundant fuel source. Most fusion startups are pursuing one of two approaches: inertial confinement or magnetic confinement. Stellarators, which Volpe is designing, fall into the latter category, characterized by their complex twists and bulges that stabilize the plasma.

A major experiment in Germany has validated the stellarator concept, but the intricate magnets were challenging to manufacture. Renaissance, based in Grenoble, aims to simplify the stellarator design, and its approach combines existing ideas rather than reinventing them.

The startup’s reactor design features a polygon of segmented tubes, each adorned with etchings resembling topographic map lines. These lines, however, are not merely decorative; they mark the high-temperature superconducting (HTS) magnets that define the plasma’s contours.

Volpe explained, “I wanted to simplify these to the bare minimum.” The first simplification, the segmented tubes, was inspired by his graduate research on the Wendelstein 7-AS experimental stellarator.

Volpe observed, “When you look at it from the top, you recognize a pentagonal form. So, I thought, why not take it to the limit? Let’s make actual cylinders, not approximate ones.” Other reactor designs use cylinders, but they typically shape the plasma into a doughnut shape, not the radical curves of 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 flexible cables into a stellarator shape. Although the cables were simpler to make than most stellarators’ complex magnets, the 3D printing aspect wasn’t commercially viable.

Volpe further simplified the idea by flattening the magnets. The tubes in Renaissance’s design will be coated with wide sheets of HTS magnets, with a laser etching thin, meandering lines that encircle the tube, separating one magnet from the next.

The magnetic field strength will vary depending on the width of the superconducting stripes. Where the material is thicker, the magnetic field will be stronger, pushing back against the plasma. Thinner areas will have a weaker magnetic field, allowing the plasma to bulge. Advanced computer simulations will determine the plasma’s exact shape.

To protect the tubes from neutrons emitted during the fusion reaction, Renaissance will fill the inside with liquid lithium. An electric current will be applied to the liquid metal, creating a magnetic field that draws it to the powerful magnets on the outside of the tubes. Suspended within the liquid, small spheres containing molten lead will absorb some of the neutron bombardment. The liquid blanket will also breed more fuel and transfer heat to power steam turbines.

Magnetic carpets

Volpe stated that Renaissance is on track to produce wide HTS “carpets” in the coming months. A demonstrator, integrating tubular HTS magnets and liquid lithium walls, is expected to be ready by the end of 2026. Volpe hopes to build a complete stellarator by the early 2030s, a timeline 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 showed promise on its own but, together, could pave the way for a more affordable fusion reactor. “You connect the dots,” Volpe said. “It’s the essence of inspiration.”