Technology

Stellarators are the most efficient, steady and stable fusion machines.

Several approaches are close to demonstrating net fusion electricity. Laser fusion compresses a capsule to very high pressures by means of powerful lasers. Tokamaks and stellarators are doughnut shaped devices that magnetically levitate hot ionized gases (plasmas) and heat them to temperatures hotter than the Sun.

Stellarators have a competitive advantage over Laser Fusion

Stellarator heating has higher off-the-plug efficiency: delivering 1kWh to the plasma costs 2-3 kWh of electricity in a stellarator, compared to over 100 kWh in laser fusion.
Another advantage is that stellarators can stay “on” all the time, whereas high power lasers are pulsed and have low repetition rates.

…and over Tokamaks…

Stellarators confine plasmas as well as tokamaks of the same size and magnetic field*, but are simpler to operate and energetically more efficient because they do not need a current in the plasma. As a result, stellarators get rid of the current-related instabilities that plague tokamaks, and are naturally steady rather than pulsed. They also get rid of the power-hungry current drive systems that tokamaks require to “stretch” their pulses, meaning that most stellarator electricity output goes to the grid rather than being recirculated to the power plant.
* Source: Magnetic configuration effects on the Wendelstein 7-X stellarator by Nature Physics

…there are challenges

Instead of relying on plasma currents like tokamaks, stellarators confine the plasma by specially shaped 3D magnetic fields. Historically this translated in complicated coils of expensive and time-consuming design, modelling and manufacturing.

But not anymore, thanks to our unique technologies! Our simplifications have clear competitive advantages in the race to the first power-plant.

Renaissance Fusion’s simplified stellarators

Simple coil surfaces

We are proving that simple, elegant coils can generate complex magnetic fields. In other words, we decouple engineering from physics: we build 1D or 2D coils (typically on cylindrical surfaces, not necessarily of circular cross-section) to generate the 3D magnetic fields needed in stellarators and several spin-offs.

Simple HTS Manufacturing

Only High Temperature Superconductors (HTS) can generate the high magnetic fields needed to make fusion smaller and cheaper. The benefits are impressive: a 4x increase in magnetic field reduces the plasma volume by 256x.

The problem is that these man-made materials are scarce and expensive, but at Renaissance Fusion we are skipping some intermediate steps (tapes, cables) and directly depositing and patterning HTS on large surfaces. It’s like changing paradigm from individual transistors to photolithography. We think it will be a big revolution.

Thick, flowing liquid walls

Our liquid Lithium-based walls stop 99.99% of the neutron energy before they can reach solid materials and make them radioactive. Brute force would require a 1.5 meter thick liquid wall. With clever materials, we do it in 40 cm.

The liquid metal is also the “working fluid” extracting heat from the stellarator and transferring it to turbine-propelling steam. Plus, it copes with the high temperatures and heat-fluxes of compact fusion.

Thirdly, it breeds one of the fuels: Tritium. Our liquid materials allow Li tritide extraction by simple precipitation.

Most fusion reactions produce neutrons, making the fusion devices - not just stellarators - radioactive and difficult to maintain. Moreover, some components deteriorate quickly, increasing replacement costs.
We are the only magnetic fusion entity, public or private, that surrounds the plasma with a liquid wall thick enough to stop most neutrons. Surrounding the plasma is necessary because neutrons are emitted in all directions.
We obtain this by circulating a small electric current (dashed line) in the liquid metal (blue), via electrodes (+,-). The current interacts with the strong magnetic field B that confines the plasma. As a result, the liquid metal injected from the top of a cylinder does not fall vertically, but along its solid walls, and shields them.
Lithium is a good neutron absorber, but thickness is reduced by adding good attenuators like Lithium hydrides. As a bonus, hydrides facilitate the precipitation of Lithium tritide, from which Tritium is extracted.

From: Complex “Coil Winding Surface”

Typical stellarator design involves (1) a metric, for instance fusion gain Q, (2) a plasma shape optimizing that, (3) a surface just outside the plasma and finally (4) numerically identifying, on said surface, coil shapes and currents that accurately generate the plasma shape. There has been a tendency to adopt complex surfaces and then simplify the coils on those surfaces.
To: Simplified “Coil Winding Surface”

We do the reverse: we adopt simple surfaces, at the cost of more complex current patterns on those surfaces. This cost is negligible for us: just a different programming of the laser engraving. The net result is leaner, faster, cheaper manufacturing, easier maintenance and transportability.
From: Traditional tape based HTS coils

Typically, tapes are coated with thin films in several machines.Then they are stuck together and combined into a cable. Cables are then wrapped around a 3D reference shape for multiple turns to create the stellarator coils. Finally, the coils are carefully positioned around the complicated stellarator vacuum vessel and surrounded by a cryostat.
To: Direct deposition and patterning of HTS coils

We skip tapes and cables altogether and directly deposit the relevant films on large surfaces, then engrave them with a laser. The laser can draw complicated circuits, generating complex magnetic fields. Simple multi-layer deposition replaces tape stacking and multi-turns.
From: Large Reactors

Traditional designs envision fields of about 5 T generated by Low Temperature Superconductors (LTS) and plasma volumes large enough to produce net energy. Fusion heat is spread over large surfaces, for solid walls to cope with it. The resulting plasma doughnut has a radius of about 20 m, and the reactor is obviously even larger.
To: Small Reactors, same Power

HTS generate higher fields (10 T or higher), more efficient at confining plasmas. As a result, the same fusion power is produced in smaller volumes and, thanks to liquid metal walls, it can be collected on smaller surfaces. That is, the “aspect ratio”of the doughnut can be low, making the plasma even more compact (about 4 m in radius).

HTS Milestones

May-June 2024

Demonstrated manual polishing process: developed liquid suspension used in polishing process, ensured it meets process specifications, etc.
July 2024

Reception of the MOCVD vacuum chamber: first installations and tests.
November 2024

Reception of the first PVD’s vacuum chamber.
January 2025

Defined the HTS characterization workflow (in-house processes and external collaborations). Set up of an internal characterization lab (AFM, microscopy, profilometry, etc.).
June 2025

Acquired small Physical Vapor Deposition (PVD) machine to test new processes in reduced scale before transposition to large, in-house machines.
July 2025

Analyzed the MOCVD exhaust gases (in small scale, in collaboration with U. Lorraine) and identified the equipment to safely handle it at large scale.
October 2025

Commissioned the MOCVD roll-to-roll system on a 20-m long, 24-cm wide Hastelloy tape.
Commissioned our oxygen furnace.
November 2025

Commissioned the vacuum system of our first PVD machine, as well as its roll-to-roll system (on a 10 m long, 24 cm wide Hastelloy tape). Installed the fluid distribution lines and deposition systems.
December 2025

First PVD deposition.
Full installation (reactor, test of the roll-to-roll system) and vacuum sealing of the MOCVD.
First HTS oxygenation tests.

Liquid Metal Milestones

July 2022

First in-house batch of GaInSn: we “cooked” the alloy in house as in “Breaking Bad”. This is the same material found in your mercury-free thermometer, in ml quantities, but we cooked tens of liters, in a brewery pot.
October 2022

Our first table-top liquid metal loop, built with parts from “Leroy Merlin” (a European “Home Depot”).
February 2023

Our first liquid metal pump built in-house, by arraying permanent magnets on a rotor, with a whooping 110 kW maximum power.
March 2023

Largest GaInSn loop in the world: 7m long, 1 m/s flow (“Skyfall 0”).
July 2023

First levitation of a liquid metal flow (1-2 cm thick) in a meter-sized cylinder by electromagnetic forces (“Skyfall 1a”).
December 2023

Completed our in-house 3D free-surface Liquid Metal (LM) Magnetohydrodynamics (MHD) code and successfully benchmarked it against experimental results. Now regularly used to predict and interpret LMMHD experiments.
February 2024

First levitation and control of a very thick liquid metal flow in a cylinder. The cylinder diameter (1 m) approaches reactor scales, and the flow thickness (10 cm of GaInSn, equivalent in mass to 120 cm of Li-LiH) exceed by 3.5x our reactor needs. Compared to Skyfall 1a, we also greatly reduced the fall of droplets that could radiatively collapse the plasma (“Skyfall 1b”).
March 2025

Identified two “finalist” solid materials that will withstand dynamic corrosion by hot liquid metals in our stellarator reactor (only few microns per day).
May 2025

Completed our first large Annular Linear Induction Pump (ALIP) for hot Sn, Li and other metals – the first company and one of only 2-3 organizations worldwide to ever build and ALIP of that scale and the first one, ever, capable of operating at up to 850 C.
June 2025

First successful test of a proprietary “freeze valve” to stop the liquid metal flow by rapid solidification.

Magnet and Cryogenics Milestones

May 2023

In-house design of an HTS-based high performance undulator. Peak field of 1.5T showcasing the benefits of laser-engraved wide multi-layered HTS.
June 2023

Proof-of-Concept validation of our magnet grooving technology using aluminium plates – to produce a gyrotron field profile with a peak flux density of 20mT in the bore.
February 2024

1st laser-engraved copper MRI magnet cooled to liquid nitrogen temperature. Produced a field with a uniformity of 50ppm over an 8cm diameter spherical volume, measured with an NMR probe.
March 2024

Nicola20 HTS magnet. A 20cm bore magnet using 200m of HTS tape producing 0.23T on axis and 0.9T peak on the windings, operating at liquid nitrogen temperature.
September 2024

Development and demonstration of a novel thermal management system to handle thermal gradients up to 79oC/mm.
February 2025

Commissioned and tested our in-house electron beam scanning system that will allow us to map a stellarator field.
June 2025

Development of our parallel HTS tape winding machine for high-field magnet manufacturing, featuring automated web-tension control and tape alignment.
September 2025

Nicola100 HTS magnets cooled down successfully to 18 K using our in-house designed and built cryogenic cooling system.
October 2025

Successful integration and combined test of the Nicola100 HTS magnets together with a 700oC flowing liquid metal loop.
November 2025

1st successful demonstration of a stellarator magnetic field using a laser-engraved copper magnet operating at liquid nitrogen temperature.