French start-up Renaissance Fusion, based in Grenoble and Houston, has raised $16.4m in funding in a seed round led by Lowercarbon Capital. Renaissance Fusion, founded in 2019 by Francesco Volpe and Martin Kupp, is working to develop a stellarator reactor. The company expects to be able to ship a small fusion reactor with a 1 GWe capacity in the 2030s. It does not plan to operate the plants directly but will sell its reactors to plant constructors and operators.

Several European investors also participated in the round, including HCVC, Positron Ventures and Norssken. Unruly Capital led the company’s pre-seed round. Using the new funding, Renaissance Fusion plans to triple the size of its team to 60 people by the end of 2023.

Renaissance Fusion offers a unique set of technologies, which it plans to use in its stellarator type fusion reactor. These include liquid metal, which sticks to the inner walls of the reaction chamber, insulating the walls from extreme heat and radioactivity and lowering maintenance costs. The company is also developing high-temperature superconducting coils. These generate strong magnetic fields, allowing a smaller reactor to achieve the same performance as a larger one.

A new manufacturing process using high temperature superconductive magnets (HTS) allows the reactor to be split into separate modules. “We have a technology that is pretty unique,” Renaissance Fusion told Techcrunch. Instead of designing complicated three-dimensional coils to generate a magnetic field, the company simplifies this process by drawing tracks on a cylinder using a laser.

After calculation based on the magnetic field required, the team can determine the shape of the coils needed. The cylinder rotates around an axis while a device moves left and right to engrave tracks with a laser on the surface of the cylinder. The cylinder blocks are then combined to form a reactor.

To deal with the neutrons emitted by the fusion reaction inside the cylinder, liquid lithium is which lines the walls containing the plasma.

Volpe explained: “We inject a layer of liquid metal. It flows around the inside of the cylinder and then it’s extracted at the bottom. It’s thick enough to absorb the majority of the neutrons.”

The design of the liquid metal walls inside the reactor offers several advantages, according to Project Manager Simon Belka. “Liquid lithium protects the solid walls of the reactor, absorbs neutrons much better, guides the heat produced by fusion to the secondary circuit and the turbine producing electricity and, finally, by reacting with the plasma, it creates the necessary tritium for the operation.”

Volpe said Renaissance Fusion is innovative in its use of liquid metal. “We are the only one in commercial magnetic fusion where the liquid lithium faces the plasma.” Currently, the company can create liquid lithium-based walls that are 1cm thick. It will require significant development before it can be used in nuclear fusion, which would require a thickness of 30-40cm.

The company is already considering commercial applications for its technologies that could be released before the 2030s. Volpe believes that the coil patterning technology could be used for MRI and energy storage – “whenever you need a strong magnetic field, a large volume and high precision,” he said.

By 2024, Renaissance Fusion intends to finalise the engineering of its two technologies. Once these proofs of concept have been completed and the marketing launched, the company will work on the construction of a first experimental reactor in order to demonstrate in particular that it is capable of producing more energy than it requires. Finally, at the beginning of the 2030s, it should inaugurate its first reactor with a power of 1 GWe capable of injecting electricity into the network. “Compared with major international public projects, start-ups offer an interesting alternative: we bring new ideas, take more risks to create disruptions and are less dependent on public funding,” said Belka.

Image: The Renaissnace Fusion executive team, including founder Francesco Volpe (centre) (courtesy of Renaissance Fusion)