Scientists have spent over 70 years trying to pull nuclear fusion, the super-hot process that powers the Sun, down to Earth — and now they’re closer than ever.
Teams across the world are betting on different techniques to harness this potentially endless supply of clean energy, which emerges when two light nuclei combine to form a heavier nucleus.
Inside the Sun, hydrogen atoms fuse into helium ones. Scientists researching fusion often use deuterium and tritium for this process, which are isotopes of hydrogen.
To recreate the Sun’s built-in power factory, reactors on Earth must reach and sustain a temperature of over 100 million degrees Fahrenheit — nearly seven times hotter than the Sun’s core.
It’ll be no easy feat, but researchers are currently revamping reactor designs from the 1950s and ‘60s in hopes of launching fusion plants in the coming decades. One oddly shaped set-up, the stellarator, has attracted recent attention from scientists and startups alike — but only time will tell if it can outperform its competitors.
Retro reactor inspiration
Fusion energy has received recent fanfare thanks to a technique called inertial confinement fusion, which works by sealing a hydrogen fuel pellet inside a tiny capsule, blasting that capsule with lasers, and letting the resulting shockwaves rock the pellet into fusion. Work on this method began in the early 1960s.
Today, the world’s biggest inertial confinement experiment is underway at the high-profile National Ignition Facility in Livermore, California. In December, the team made history by achieving the fusion Holy Grail of ignition, or drawing more power from the reactor than they put in — a key step toward powering the grid with fusion instead of fossil fuels.
Labs also use magnetic fields to create fusion energy. The first fusion reactors ran on magnetic confinement, in which scientists sculpt a superheated plasma of hydrogen atoms into just the right shape to achieve fusion.
This process is still used today, and magnetic reactors come in a variety of forms — most commonly the donut-shaped tokamak invented by Soviet scientists in the 1950s.
In the south of France, physicists from around the globe are putting the finishing touches on ITER, the largest tokamak yet. The team hopes that the mighty reactor can reach ignition. But not everyone is shining with excitement: Some scientists doubt that ITER will ever achieve its lofty goals.
Among these massive magnetic reactors, there’s a twistier alternative called a stellarator. This configuration emerged in the early 1950s, a more optimistic time when scientists felt that bountiful fusion awaited just around the corner. But decades later, this vintage method has a few key advantages over the tokamak.
And if conditions are just right, the stellarator may return and even win the race toward bringing fusion energy to the grid. Now, startups and researchers are betting on the reactor’s revival.
“This is, at least, my feeling … the stellarator is back,” Thomas Klinger, a physicist at the Max Planck Institute of Plasma Physics in Germany, tells Inverse.
A star is born, and then it dies
The story of the stellarator began with fraud. In 1951, when Argentinian president Juan Perón startled the world with a triumphant claim: Argentina was on the verge of limitless fusion energy.
In the middle of a lake nestled in the foothills of the Andes, a Nazi-era German scientist named Ronald Richter and his underlings constructed a house-sized cement cylinder with a copper coil. Inside that mysterious device called the thermotron, Perón believed, those scientists had successfully ignited hydrogen.
They had done no such thing — scientists didn’t even achieve fusion until 1958. Still, the affair made world headlines, prompting curiosity within academia. One such scientist was a Princeton astrophysicist named Lyman Spitzer.
Spitzer, like his peers at the time, knew that fusion was possible; all you had to do was heat a plasma, or ionized gas, to about 100 million degrees Fahrenheit. Nothing to it!
The only problem was actually containing the plasma. You can do this with magnets, but magnets alone can’t stop plasma from crashing into the walls and losing the immense heat required to sustain a steady supply of energy — at least, not with 1950s technology.
The only problem was actually containing the plasma.
Spitzer’s solution was to twist the plasma container into a tube resembling a figure-8 or Möbius strip — the world’s first stellarator. In theory, this would allow the plasma particles to undulate back and forth, never crashing off course. Spitzer was so confident in his plan that he proposed it to the United States government, which gave him a secret lab in the wilderness of Central New Jersey.
As the world plunged deeper into the Cold War, Spitzer and his colleagues created ever larger, ever more powerful versions of the stellarator, culminating in what they called Model C in 1962. Spitzer hoped that Model C would achieve fusion — but it just couldn’t retain enough heat to get the job done.
Then in the late 1960s, a bombshell dropped across the Iron Curtain: Soviet scientists announced they had used a tokamak to achieve energies far higher than Model C could ever dream of.
With this breakthrough, the tokamak earned its spot as the mainstay of the fusion world, and the stellarator began to fade into history. But now, a modern revival could spark previous generations’ ambitions.
Reviving the stellarator
Confining plasma is somewhat like juggling. A magnetic confinement machine must essentially balance dozens of finely tuned, superpowered magnets. If physicists get this delicate formation even slightly wrong, the plasma either doesn’t grow hot enough or dissipates.
Model C, then, may have been too far ahead of its time. Due to the stellarator’s twisty geometry, the magnetic field inside isn’t symmetrical, and the calculations that guide its plasma become far too complex for physicists to do by hand. Fortunately, by the 1980s, supercomputers had caught up.
But the out-of-fashion stellarator never faded from the drawing board in Garching, a city in what was once West Germany. There, theoretical physicists steadily plied away at the complex calculations. In 1988, to test their math, they opened the first of a new generation of stellarators: Wendelstein 7-AS.
This new-wave design quickly broke every stellarator record, suggesting these revamped reactors could challenge the stagnant tokamaks.
According to scientists, tokamaks have a major disadvantage compared to stellarators: A tokamak requires a strong electric current to help induce the magnetic field that contains the plasma. The current also renders the plasma more delicate, posing a challenge for scientists designing the machines and crunching the numbers.
If physicists lose this battle and the plasma collapses, the current might collapse with it, unleashing an electromagnetic storm with arcing electrons that can damage the machine. “This is a big, big headache in tokamaks,” Klinger of the Max Planck Institute says.
“The magnetic field is a lot easier to predict.”
Stellarators, meanwhile, need no such current and don’t run the same risk of catastrophic collapse. Best of all, stellarators can more easily sustain plasma for long periods of time, a prerequisite for achieving nuclear fusion.
And fortunately for scientists tinkering with the machine, the stellarator can sustain plasma solely with magnets outside the container. “For that reason, the magnetic field is a lot easier to predict, in practice,” Elizabeth Paul, a physicist at Columbia University and Princeton Plasma Physics Laboratory, tells Inverse.
As experiments on Wendelstein 7-AS churned along, the Cold War ended and Germany reunited. That meant more money for the fusion researchers, who used it to build the largest stellarator yet constructed: Wendelstein 7-X (W7X) in East Germany.
W7X came online in 2015, and its operators have steadily cultivated the machine’s powers since. But similar to the National Ignition Facility, W7X isn’t a fusion machine. Instead, it’s meant to demonstrate that physicists can confine and sustain the plasma, an important prerequisite to fusion. By the end of 2018, it had achieved plasma sustained for 100 seconds: close to the world standard for tokamak runs, says Klinger, who is W7X’s director.
“In the past few years, we’ve seen some of the first experimental proof that you can get this good confinement in a stellarator, in a device as large as W7X,” Kenneth Hammond, a physicist at Princeton Plasma Physics Laboratory and part of the program coordinating group at W7X, tells Inverse.
W7X still has another decade or two of progress ahead, Klinger says. The team aims to sustain plasma for half an hour: an important benchmark toward sustaining it indefinitely and, perhaps, powering our daily needs.
An uncertain future
Unlike the National Ignition Facility’s laser-powered reaction, no magnetic fusion facility has yet reached ignition. So if W7X won’t, then who might?
It’s a tricky question. Despite the progress from W7X, stellarators don’t have the same star power as their donut-shaped counterparts. “Most of the funding [in magnetic confinement research], especially in the U.S., goes to the tokamak,” Paul says.
And W7X is one-of-a-kind. There are smaller stellarator machines out there, such as HSX in Wisconsin and CTH in Auburn, Alabama. But if scientists want to test the tricky physics involved in a full-scale power plant, they need to think bigger. “If you are being serious with fusion, you need to build big machines,” says Klinger.
Where might a larger stellarator come from, then? Several startups want to tackle this physics challenge, including New Jersey-based Princeton Stellarators, founded in 2022, and Wisconsin-based Type One Energy, founded in 2019.
Type One — some of whose founders worked on W-7X and HSX — thinks that stellarator research is ready for the market. Within a decade, the company wants to build a stellarator pilot plant: a proof-of-concept for a stellarator generator intended to link up with the electrical grid. “We don’t need to build another large science machine to validate the science or physics of the stellarator,” Christofer Mowry, Type One’s CEO, tells Inverse.
Klinger and Paul say this timeline is pretty ambitious. Predicting exactly when a fusion power plant might emerge, though, is likely a fool’s errand. Many fusion fans will likely have heard the cliché saying that “fusion is always 20 years away.”
But many physicists are pleased that stellarators are back in the spotlight. Private-sector stellarator developers could offer new strategies to improve reactors and, just as importantly, new money that scientists could (in theory) use to ramp up their work.
“We have some more faith in the physics, but how can we use technology to reduce some of the risks or reduce the cost or complexity of the device?” Paul says. “And I think that’s really quite exciting.”
