Bottling the sun: The world has been trying to master this limitless clean energy source since the 1930s. We’re now closer than ever


ITER’s fusion energy experiments will take place inside the vacuum vessel of a donut-shaped machine called a tokamak.

Saint-Paul-lez-Durance, France — From a small hill in the southern French region of Provence, you can see two suns. One has been blazing for four-and-a-half billion years and is setting. The other is being built by thousands of human minds and hands, and is — far more slowly — rising. The last of the real sun’s evening rays cast a magical glow over the other — an enormous construction site that could solve the biggest existential crisis in human history.

It is here, in the tiny commune of Saint-Paul-lez-Durance, that 35 countries have come together to try and master nuclear fusion, a process that occurs naturally in the sun — and all stars — but is painfully difficult to replicate on Earth.

Fusion promises a virtually limitless form of energy that, unlike fossil fuels, emits zero greenhouse gases and, unlike the nuclear fission power used today, produces no long-life radioactive waste.

Mastering it could literally save humanity from climate change, a crisis of our own making.


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Workers inspecting superconductors at ITER.

If it is mastered, fusion energy will undoubtedly power much of the world. Just 1 gram of fuel as input can create the equivalent of eight tons of oil in fusion power. That’s an astonishing yield of 8 million to 1.

Atomic experts rarely like to estimate when fusion energy may be widely available, often joking that, no matter when you ask, it’s always 30 years away.

But for the first time in history, that may actually be true.

In February, scientists in the English village of Culham, near Oxford, announced a major breakthrough: they generated and sustained a record 59 megajoules of fusion energy for five seconds in a giant donut-shaped machine called a tokamak.

It was only enough to power one house for a day, and more energy went into the process than came out of it. Yet it was a truly historic moment. It proved that nuclear fusion was indeed possible to sustain on Earth.


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A view from the top of the tokamak chamber. The tokamak will ultimately weigh 23,000 tons, the combined weight of three Eiffel Towers.

This was excellent news for the project in France, the International Thermonuclear Experimental Reactor, better known as ITER. Its main objective is to prove fusion can be utilized commercially. If it can, the world will have no use for fossil fuels like coal, oil and gas, the main drivers of the human-made climate crisis.

There has been a huge sense of momentum at ITER since the success in the UK, but the people working on the project are also undergoing a major change. Their director general, Bernard Bigot (pronounced bi-GOH in French), died from illness on May 14 after leading ITER for seven years.

Before his death, Bigot shared his infectious optimism for fusion energy from his sunny office, which overlooked the shell of ITER’s own tokamak, a sci-fi like structure still under construction.

“Energy is life,” Bigot said. “Biologically, socially, economically.”


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Workers carry exhaust pipes away from the assembly hall. These pipes are used to expel exhaust from trucks that deliver the large components to the clean facility.

When the Earth was populated by less than a billion people, there were enough renewable sources to meet demand, Bigot said.

“Not anymore. Not since the Industrial Revolution and the following population explosion. So we embraced fossil fuels and did a lot of harm to our environment. And here we are now, 8 billion strong and in the middle of a drastic climate crisis,” he said.

“There is no alternative but to wean ourselves off our current main power source,” he said. “And the best option seems to be the one the universe has been utilizing for billions of years.”

Mimicking the sun

Fusion energy is created by forcing together two particles that, by nature, repel. After a small amount of fuel is injected into the tokamak, giant magnets are activated to create a plasma, the fourth state of matter, which is a bit like a gas or soup that is electrically charged.

By raising temperatures inside the tokamak to unfathomably high levels, the particles from the fuel are forced to fuse into one. The process creates helium and neutrons — which are lighter in mass than the parts they were originally made of.

The missing mass converts to an enormous amount of energy. The neutrons, which are able to escape the plasma, then hit a “blanket” lining the walls of the tokamak, and their kinetic energy transfers as heat. That heat can be used to warm water, create steam and turn turbines to generate power.

This all requires the tokamak to contain serious heat. The plasma needs to reach at least 150 million degrees Celsius, 10 times hotter than the core of the sun. It begs the question: How can anything on Earth hold such high temperatures?

It’s one of many hurdles that generations of fusion energy seekers have managed to overcome. Scientists and engineers designed giant magnets to create a strong magnetic field to keep the heat bottled up. Anything else would simply melt.

What those working on fusion have been trying to do inside their machines is essentially replicate the sun. The sun is a perpetual fusion factory, made up of a gigantic burning ball of plasma. It fuses several hundred tons of hydrogen into helium each second.

Plasma is the stuff 99.9% of the universe is made of, including the stars, our sun and all interstellar matter. Down here on Earth, for instance, it’s used in televisions and neon lights, and we can see it in lightning and the aurora.

As awesome as that all sounds, generating fusion energy in itself isn’t actually the hard part, several experts at ITER said. Humanity has been pulling off nuclear fusion reaction ever since the invention of the H-bomb, after all. The main challenge is sustaining it. The tokamak in the UK — called the Joint European Torus, or JET — held fusion energy for five seconds, but that’s simply the longest that machine will go for. Its magnets were made of copper and were built in the 1970s. Any more than five seconds under such heat would cause them to melt.

ITER uses newer magnets that can last much longer, and the project aims to produce a 10-fold return on energy, generating 500 megawatts from an input of 50 megawatts.


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Workers assembling some of the four poloidal field coils, which will make up part of the magnetic field cage necessary to contain the plasma. Each measures between 22 and 24 meters in diameter.

But ITER’s goal isn’t to actually use the energy for power but to prove that it can sustain fusion energy for much longer than JET was able to. Success here will mean commercial-scale machines can start generating fusion in the future.

While the sun fuses hydrogen atoms to create helium, the JET project used two hydrogen isotopes called deuterium and tritium, which ITER will also use. These isotopes behave almost identically to hydrogen, in terms of their chemical makeup and reactions.

Both deuterium and tritium are found in nature. Deuterium is abundant in both fresh and saltwater — the deuterium from just 500 milliliters of water, with a little tritium, could power a house for a year. Tritium is rare, but it can be synthetically produced. At the moment, only 20 kilograms of it exist in the world, and demand amounts to no more than 400 grams per year. But at a yield of 8 million to 1, only tiny amounts of both elements are required to generate a lot of fusion energy.

Tritium is an exceptionally pricey substance: a single gram is currently worth around $30,000. Should nuclear fusion take off, demand will go through the roof, presenting the world’s fusion masters with yet another challenge.


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Workers preforming precision welding on superconductors during construction.

A 10 million-part project

From afar, ITER looks like a project ready to go. From up close, it’s clear it’s still a ways off.

The construction — across 39 building sites — is incredibly complex. The main worksite is a markedly sterile environment, where tremendous components are being put into place with the help of 750-ton cranes. Workers have already put together the shell of the tokamak, but they are still awaiting some parts, including a giant magnet from Russia that will sit at the top of the machine.

The dimensions are mind-blowing. The tokamak will ultimately weigh 23,000 tons. That’s the combined weight of three Eiffel towers. It will comprise a million components, further differing into no fewer than 10 million smaller parts.

This powerful behemoth will be surrounded by some of the largest magnets ever created. Their staggering size — some of them have diameters of up to 24 meters — means they are are too large to transport and must be assembled on site in a giant hall.

Given the huge number of parts involved, there’s simply no room for error.

Even the digital design of this enormous machine sits across 3D computer files that take up more than two terabytes of drive space. That’s the same amount of space you could save more than 160 million one-page Word documents on.


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One of nine sectors of the vacuum vessel, which will soon be hoisted onto giant cranes for assembly.

Wartime nuclear fusion

Behind hundreds of workers putting the ITER project together are around 4,500 companies with 15,000 employees from all over the globe.

Thirty-five countries are collaborating on ITER, which is run by seven main members — China, the United States, the European Union, Russia, India, Japan and South Korea. It looks a little like the UN Security Council, though the late Bigot, among others, have tried hard to keep geopolitics out of ITER entirely.

But as Russia seeks to redraw Europe’s map with its war in Ukraine, and even challenge the post-war world order, there are concerns over the country’s continued role in ITER, and just as many over its potential exclusion.

Russia has been cut out of a number of other international scientific projects in the fallout of its war, but the European Commission has explicitly made an exception for ITER in its sanctions.

Part of this is because Russia is inextricably linked with not only the project but fusion energy historically.


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The black platform in the lower part of the frame is the tokamak complex, a 400,000-ton edifice that brings together the tokamak, diagnostics and tritium buildings. The concrete structure behind it is the diagnostic building.

Countries began seeking fusion energy in the 1930s, building all sorts of machines over decades. But it was the tokamak, created in the Soviet Union, that proved most successful. In 1968, Soviet researchers made a huge fusion breakthrough — they were able to achieve the high temperatures required and contain the plasma for a sustained period, which had never been done before.

The tokamak became the machine to replicate. Even the word tokamak — a portmanteau for “toroidal magnetic confinement” — is from the Russian language.

Russia has also provided some of the most critical elements of the ITER project and is one of its main funders. The magnet for the top of the tokamak, for example, was made in St. Petersburg and waits there, ready to be sent to France, said ITER’s head of communications, Laban Coblentz.

So far, Russia’s involvement in the project hasn’t changed in any way, he said.

“ITER is really a child of the Cold War,” Coblentz said. “It’s a deliberate collaboration by countries that are ideologically unaligned who simply share a common goal for a better future.”

He pointed out that the seven main members have been through many tense events since ITER’s conception in 1985.

“Before anything around the latest Russia circumstances, that has to date never affected the collaborative spirit. I think it is not an exaggeration to say that ITER is a project of peace,” he said.


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Inside the tokamak pit, a worker measures the connection between a cylindrical passage known as a feeder stub and the cryostat base, which helps keep the tokamak’s vacuum cool.

But Coblentz conceded that the war in Ukraine was “unprecedented” and that he couldn’t predict what it might mean for Russia’s future in ITER — something that will be a delicate issue for the next director general. Part of Bigot’s job was to coordinate the seven main members and their often-differing views on the handling of various political, ideological and economic issues.

When asked, before Russia’s invasion of Ukraine, whether managing these differences got challenging, Bigot gave a wry smile.

“Now, that is truly no small feat,” he said.

“But our joint commitment remains as strong as ever. I can say that, from the beginning of my involvement with the project, daily politics has had virtually no impact on our endeavors,” he said.

“Each of the partners seems quite aware dropping the ball could easily mean the demise of the entire project. This, of course, is a tremendous responsibility.”


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A winding stair case behind ITER’s heating, ventilation and air conditioning system in its 60-meter high assembly hall.

Geopolitics has always played a role in ITER. Just finding the right location for it took years and involved more than a decade of technical studies, political bargaining and diplomatic fine-tuning. France’s Saint-Paul-lez-Durance was finally made the official site in 2005 at a meeting in Moscow, and the agreement on construction was signed in Paris a year after.

As the diplomacy and technology fell in step, building began. In 2010, the foundations were laid, and in 2014, the first construction machines were switched on.

Time is running out

The scale and ambition of the ITER project may seem enormous, but it is, at the very least, a proportional response to the mess humans have made of the planet. Since 1973, global energy usage has more than doubled. By the end of the century, it might actually triple. Seventy percent of all carbon dioxide emissions into the atmosphere are created through humans’ energy consumption. And 80% of all the energy we consume is derived from fossil fuels.

Now, the Earth is barreling toward levels of warming that translate into more frequent and deadly heat waves, famine-inducing droughts, wildfires, floods and rising sea levels. The impacts of the climate crisis are getting harder and harder to reverse as entire ecosystems reach tipping points and more human lives are put on the line.


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A welder stands behind a protective shield at the lowest level of the ITER cryostat base.

The world is now scrambling to rapidly decarbonize and speed up its transition from planet-baking fossil fuels to renewable energy like solar, wind and hydropower. Some countries are banking on nuclear fission energy, which is low-carbon but comes with a small, but not negligible, risk of disaster, storage problems for radioactive waste and a high cost.

But there are serious questions about whether the world can make this green transition fast enough to avert catastrophic climate change.

That’s where fusion could be an 11th-hour hero — if the world masters it in time.

When the late physicist Stephen Hawking was asked by Time in 2010 which scientific discovery he would like to see in his lifetime, he pointed to exactly this process.

“I would like nuclear fusion to become a practical power source,” he said. “It would provide an inexhaustible supply of energy, without pollution or global warming.”


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Part of the vacuum vessel, a hermetically sealed steel container that will house the fusion reactions and acts as a first safety containment barrier.

A new era

The experts working on nuclear fusion have overcome enormous challenges already, and so many, including Bigot, dedicated their entire careers to it and never saw it come into practical use.

Now commercial businesses are preparing to generate and sell fusion energy, so optimistic they are that this energy of the future could come online by mid-century.

But as ever with nuclear fusion, as one challenge is overcome another seems to crop up. The limited stocks and price of tritium is one, so ITER is trying to produce its own. On that front, the outlook isn’t bad. The blanket within the tokamak will be coated with lithium, and as escaped plasma neutrons reach it, they will react with the lithium to create more tritium fuel.

Time and money are always concerns for big projects, but “big” doesn’t even begin to describe the scale of ITER, which is truly one of the world’s largest and most ambitious international energy collaborations in history.

One day’s delay costs about a million euros, Bigot said.

The European Union is footing 45% of the project’s ever-mounting construction costs. All the other participant countries are contributing a little over 9% each, by rough estimations. Initially, the entire construction was estimated at around 6 billion euros ($6.4 billion). Right now, the total has more than tripled to around 20 billion euros.


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Part of the cryostat for testing the poloidal field coils. The cryostat will help confine the plasma.

The 2001 predictions envisioned the first batch of plasma being produced in 2016, another missed goal. Some observers had considered the project dead in the water, but after Bigot took the helm, the project was streamlined and got back on track. Bigot had a reputation as a micromanager, Coblentz said, but that’s exactly what was needed to get this complicated project in order.

“When you got here, his car was in place at 7 a.m., and often here until 9 or 10 p.m. at night,” Coblentz said. “So you always had the impression that no detail was too large or too small for him to take seriously and be involved in.”

Though under his leadership, expectations and deadlines were also revised to be more realistic. First plasma is now expected in 2025, and the first deuterium-tritium experiments are hoped to take place in 2035, though even those are now under review — delayed, in part, by the pandemic and persistent supply chain issues.

Yet with one of the world’s biggest projects running behind time on his lap, Bigot remained passionate and optimistic about ITER’s potential until his last breath.

“Hydrogen fusion is a million times more efficient than burning up fossil fuels. What we are trying to do here is actually, really very much like creating a small artificial sun on Earth,” he said. “This fusion power plant will be in operation all the time. This sun, so to speak, will never set.”


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Dusk falls over the ITER complex in Saint-Paul-lez-Durance, France.



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