Renaissance Fusion Targets Cost-Competitive Fusion

Oil and natural gas supplies have become less certain over the last few weeks, and this has increased interest in alternative sources of energy, such as fusion. As you might recall, fusion machines maintain a hot plasma within a donut-shaped structure. Nuclear fusion differs from nuclear fission, which generates electricity with uranium fuel. Fission isn’t popular due to meltdown risk, nuclear waste, proliferation risk, and cost. Fusion doesn’t face these issues but is still in development.

For fusion to be useful, it must produce electricity at a cost below that of fossil fuels. This is theoretically referred to as “economic fusion,” and it would entail low-cost continuous operation. Renaissance Fusion, a company based in Grenoble, France, is leading the way to produce such a machine.

Founded by Francesco Volpe in 2020, Renaissance Fusion employs over 100 people and has raised over $70 million. More importantly, it’s the only company to have published papers describing a machine that achieves economic fusion by design. The approach relies on new technologies that still need to be verified with experiments. Volpe and his team are working to demonstrate them, and this article reviews their recent accomplishments.

Moving heat outward

The plasma inside a fusion machine radiates heat outward, causing the internal surface of the chamber to heat up. This heat must be moved outward to generate steam, press on the fan turbine blades, and create electrical power. The easiest way to do this is to pump molten metal toward the hot plasma and then outward. There are two ways to do this: One involves having liquid metal flow in front of the internal surface plate, and the other involves flowing liquid behind the plate.

Liquid metal wall

Flowing liquid in front is referred to as “liquid metal wall.” This is illustrated here, with the liquid metal shown in red.

To get this to work, magnets would need to push the molten metal outward, toward the metal plate, while it flows and removes heat. The alternative cooling method is to expose an approximately 2-mm-thick metal plate to plasma radiation and cool it by flowing molten metal along its back surface within channels.

However, radiation from the plasma will eventually damage the metal plate, requiring replacement. This involves machine disassembly, which is expensive. Therefore, it’s more cost-effective to protect the metal plate with flowing molten metal and rarely disassemble, if at all. In other words, a liquid metal wall is probably required to achieve economic fusion. This is new technology, which means it needs to be verified with experiments.

Volpe’s liquid metal status

Volpe and his team have developed a physical experiment that circulates liquid metal through a cylindrical chamber. Superconducting magnets and currents push the liquid outward so that it coats the internal surface of the chamber wall as it falls from the top to the bottom. They are currently circulating liquid tin at °C and hope to soon circulate liquid lithium at 850°C, which is needed by their design.

Next-generation magnets

Renaissance Fusion’s machine uses irregular-shaped magnets to compress the plasma. In theory, these could be manufactured using 3D printing on a rotating tube via ion deposition. Within a vacuum environment, alternating layers of superconductor and “insulator” could potentially be printed. The illustration below shows how approximately five irregularly-shaped magnets could be printed per tube, within a 12-tube system, producing a total of 60 magnets.

Volpe’s team has created a machine, pictured below, that prints superconductors on a 24-cm-wide tape. This is 20× wider than that typically done in today’s superconducting magnets. This is an intermediate step to printing directly onto a tube.

Renaissance Fusion is the only company developing a fusion machine that produces competitively priced electricity by design, and this makes it one of the most important players in the fusion industry.

---

See also: