The renaissance of the stellarator – what it means for fusion energy

An image of fusion energy processes of a tokamak: Stellarators to return as key fusion energy research concept after tokamak focus.

Stellarators to return as key fusion energy research concept after tokamak focus. Image: Unsplash/Google DeepMind

Martin Kupp
Associate Professor/Co-Founder, ESCP Business School/Renaissance Fusion
Alf Köhn-Seemann
Senior Researcher (Plasma, Physics‬ and Fusion‬), University of Stuttgart
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  • Fusion research started with the stellarator but seemingly unsurmountable difficulties meant research turned to a different concept: the tokamak.
  • The stellarator could see a comeback as the concept of quasi-symmetry, advances in performance computing and manufacturing technologies have allowed it to reach a milestone while the tokamak has suffered a setback.
  • Investment in fusion is heating up and 93% of companies believe that fusion electricity will be on the grid in the 2030s or before.

The resurgence of the electric vehicle could prove similar to another source of innovation, this time in fusion science.

Recalling how electric vehicles developed around the same time – as well as faster and better – as internal combustion engine vehicles due to several inherent advantages, such as being quiet and easy to drive, their trajectory changed with the Ford Model T. The new combustion vehicle was available at low cost and in large quantities and for a long time, electric cars disappeared.

It took almost 90 years until Toyota brought the Prius hybrid car to market in 1997 and another 11 before Tesla produced its Roadster. And since then, a frenzy of research and a wide range of new electric models have hit the market. Now, the electric vehicle is the favourite consumer choice, once again.

The same resurgence can be seen with the origins of fusion research in the stellarator, replaced with the tokamak due to seemingly insurmountable difficulties at the time.

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A short history of the stellarator

American scientist Lyman Spitzer developed the idea of the stellarator in 1951. The Princeton Plasma Physics Laboratory (PPPL) was created based on his ideas.

Researchers tried to counter the biggest problem in fusion research at the time – the “drift” (when plasma is isolated from an electric conductor) – by a specific arrangement of the magnetic tube resulting in a twisted magnetic field, forcing the particles in the plasma to alternate between the inside and outside of the tube. The arrangement would allow the plasma to confine long enough to make fusion happen.

The stellarator concept was an elegant solution to a fundamental problem in fusion research but it was challenging to build such a device to the precision needed. In 1968, scientists in the Soviet Union released the results of their tokamak machines, which were simpler to make, as part of the magnetic field cage is created by a strong current flowing in the plasma.

After confirming these initial results, the PPPL decided in 1969 to move from the stellarator to a tokamak design – an important decision followed by other scientists working on fusion projects worldwide.

The long-due rebirth of the stellarator

While the research on tokamaks surged globally, a handful of projects kept exploring the stellarator design. The key problem to solve was the confinement issue that the early stellarator concepts showed.

In 1983, Allen Boozer from PPPL introduced quasi-symmetry – a type of continuous symmetry in the magnetic field strength of a stellarator. This insight helped him design a more symmetrical stellarator, improving its confinement. Jürgen Nührenberg from the Max Planck Institute for Plasma Physics (IPP) in Germany could then show that this quasi-symmetry existed and could potentially be built.

The first major project based on these new findings was the Wendelstein 7-AS at the IPP. Other notable projects are the Helically Symmetric Experiment (HSX) in the United States and the Large Helical Device in Japan.

These projects raised new interest in the stellarator concept, culminating in the Wendelstein 7-X. In December 2017, it set a new stellarator world record for fusion products. In February 2023, it reached a milestone by achieving an energy turnover of 1.3 gigajoules, with the discharge lasting a record eight minutes. Meanwhile, the Lawrence Livermore National Laboratory, which made a long-awaited breakthrough in fusion late last year, suffered a setback as five similar shots have since failed.

Why is now the time for stellarators?

First, the concept of quasi-symmetry described above was a real game-changer and its importance cannot be underestimated. Two additional developments were crucial for the comeback of the stellarator design: advances in performance computing and manufacturing technologies.

The difficulties in designing current-carrying coils to produce the magnetic fields required for confining plasmas to create fusion energy have been critical since the beginning of research into magnetically-confined plasmas in the 1950s. This challenge was especially true for stellarators with more complicated coil configurations than tokamaks. But with advances in computing, this design problem is significantly reduced. And while the design of stellarator coils is still more complicated, thanks to advanced computing, this does not put the stellarator at a disadvantage.

After the computational design, the coil then needs to be built. And for a long time, building stellarator coils to the required precision posed a major issue, putting the stellarator at another disadvantage. But recent advancements in manufacturing technologies, particularly additive manufacturing, address this problem very well.

Where do we go from here?

Researchers are turning their attention back to the stellarator design. In January 2021, David Gates gave a talk on the comeback of the stellarator at one of the PPPL’s Science on Saturday lectures.

Also, commercial startups that bring fusion energy out of the lab and onto the grid have emerged, two of them with stellarators: Renaissance Fusion in Europe and Type One Energy in the United States. And as argued previously, only startups can move deep tech out of the lab because research institutions and big companies aren’t incentivized to invest in deep tech. Despite past financing issues, improvements have led to more investment, with the Deep Tech Investment Paradox report estimating deep tech investments could exceed $200 billion by 2025.

Tech billionaires Bill Gates, Jeff Bezos, Peter Thiel, Marc Benioff and Vinod Khosla were convinced quickly and McKinsey analysis shows private investment in fusion energy has surged over the past 20 years, with the value of investments nearly tripling in 2021.

According to The Global Fusion Industry in 2022 report, 93% of companies believe that fusion electricity will be on the grid in the 2030s or before (up from 83% in 2021).

Private investment in fusion energy has surged over the past 20 years.
Private investment in fusion energy has surged over the past 20 years. Image: Will fusion energy help decarbonize the power system? McKinsey, 2022

As the electric vehicle’s story shows, a technological resurgence can take time and may need to demonstrate breakthroughs in adjacent fields – e.g. the electric car brought advances in high-capacity batteries and low-losses electrical engines. And the stellarator's re-emergence will bring advanced computing and additive manufacturing.

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