This nuclear fusion plant is simultaneously the hottest and coldest place in the solar system

CNN

06-05-2025

In an unassuming industrial park 30 miles outside Boston, engineers are building a futuristic machine to replicate the energy of the stars. If all goes to plan, it could be the key to producing virtually unlimited, clean electricity in the United States in about a decade.
The donut-shaped machine Commonwealth Fusion Systems is assembling to generate this energy is simultaneously the hottest and coldest place in the entire solar system, according to the scientists who are building it.
It is inside that extreme environment in the so-called tokamak that they smash atoms together in 100-million-degree plasma. The nuclear fusion reaction is surrounded by a magnetic field more than 400,000 times more powerful than the Earth's and chilled with cryogenic gases close to absolute zero.
The fusion reaction — forcing two atoms to merge — is what creates the energy of the sun. It is the exact opposite of what the world knows now as 'nuclear power' — a fission reaction that splits atoms.
Nuclear fusion has far greater energy potential, with none of the safety concerns around radioactive waste.
SPARC is the tokamak Commonwealth says could forever change how the world gets its energy, generating 10 million times more than coal or natural gas while producing no planet-warming pollution. Fuel for fusion is abundant, derived from deuterium, found in seawater, and tritium extracted from lithium. And unlike nuclear fission, there is no atomic waste involved.
The biggest hurdle is building a machine powerful and precise enough to harness the molten, hard-to-tame plasma, while also overcoming the net-energy issue – getting more energy out than you put into it.
'Basically, what everybody expects is when we build the next machine, we expect it to be a net-energy machine,' said Andrew Holland, president of the Fusion Industries Association, a trade group representing fusion companies in the US and Europe. 'The question is, how fast can you build that machine?'
Commonwealth's timeline is two years. With over $2 billion raised in private capital, it has an audacious goal: to produce more energy than it consumes by 2026, then build the world's first fusion-fueled power plant by the early 2030s in Virginia.
'It's like a race with the planet,' said Brandon Sorbom, Commonwealth's chief science officer. Commonwealth is racing to find a solution for global warming, Sorbom said, but it's also trying to keep up with new power-hungry technologies like artificial intelligence. 'This factory here is a 24/7 factory,' he said. 'We're acutely aware of it every minute of every hour of every day.'
Perhaps most urgently, Commonwealth and other western companies are also racing to beat Chinese scientists at achieving net energy amid a rapid fusion buildout in China, where one enormous facility has emerged in satellite images.
Virginia Gov. Glenn Youngkin nodded to that while speaking alongside Commonwealth's CEO, Bob Mumgaard, at a March energy conference.
'China is building fusion plants, and therefore we've got to get moving,' Youngkin said. 'There's a race to lead the world in power generation.'
Fusion science is mostly settled. The hard part is maintaining a reaction long enough to generate electricity out of it.
For tokamaks, like the one being built at Commonwealth, the name of the game is building powerful magnets strong enough to contain plasma – a superheated cloud of charged gas in which fusion reactions happen. Plasma is very hot and very light; it's a million times less dense than the air we breathe.
'I won't call the plasma clever, there's no intelligence there, but the plasma has many, many ways in which it can thwart your abilities to confine it,' Jerry Navratil, a professor of fusion energy and plasma physics at Columbia University, told CNN.
That is where the freezing wall of giant magnets come in, acting to both cool and restrain the unruly plasma. Only when the plasma gets colder can it even become visible.
The lightweight, delicate nature of plasma is why fusion is so safe: It can be turned off, so to speak, as easily as blowing a candle.
'If you were to blow a breath of air onto the plasma, you would kill it,' Sorbom said. '(If) a meteor hits the plant and ruptures the vacuum vessel, everything just shuts down. It's not like you have something like Fukushima or Chernobyl where there's this runaway chain reaction.'
Even though it will tower 30 feet, about three stories, when built, the SPARC tokamak is much smaller than conventional power plants running on coal, gas or nuclear energy, a key advantage that will allow it to fit into power plants in the future. It is petite compared to ITER, the monster French research tokamak that is as tall as a 22-story building.
'ITER is so big that it requires things like the world's largest cranes just to move some of the pieces around,' Sorbom said. 'This is now small enough that we have standard equipment to move things around – something that you'd find in any auto manufacturing facility. You don't have to invent a totally new industrial supply chain for everything.'
Thus far, the scientific conventional wisdom has been the bigger the tokamak, the more powerful its performance. Sorbom and his team have disrupted that idea with new magnet technology. The magnets are big, but their secret weapon is an unassuming piece of thin, highly-conductive metal tape layered into each one – maximizing its power in a relatively small space. This tape can carry 200 amps of electrical current – as much as a house's electrical breaker.
Navratil said SPARC is using the most tested form of technology with their magnetic tokamak. However, a lot of questions remain on how well it will work.
'They're pushing the technology to places we've never been before, which obviously entails risk,' Navratil said. 'Once the thing is going then the question is, can the surrounding structures withstand any kind of energy bombardment that comes from the plasma?'
For instance, Navratil noted if the electrical current running through the magnet does something unexpected, it could sustain damage. But, he said, if the first runs of SPARC prove the magnet technology works, it would be a major advancement for the field.
'If those magnets function as expected properly, that'll be a major step forward,' Navratil said. 'If that's all they do, they will have actually contributed quite a bit to the development of fusion energy.'
Beyond technology breakthroughs, the US also needs to think about the kind of supply chains needed to breed more tritium fuel for fusion, which require access to lithium reserves, Jean Paul Allain, who leads the US Energy Department's Office of Fusion Energy Sciences, told CNN in an interview last year. The Chinese have been particularly adept at securing those supply chains, Allain noted.
'Access to lithium deposits around the world are in high demand,' Allain said. 'The Chinese have been establishing themselves in Latin America for a long time, precisely because they're looking at some of these raw materials.'
Inside a sprawling Houston ballroom in March, Mumgaard, Commonwealth's CEO, spoke to hundreds of fossil fuel CEOs and lobbyists about the future of an energy that could eventually replace oil and gas.
At that CERAWeek conference, Virginia's Youngkin also noted he is keenly interested in getting energy wherever he can find it to support the state's growing data center industry, advanced manufacturing and population growth.
'We need a lot more power,' Youngkin said. 'Whoever wins this power race is going to unleash the economic opportunity that comes quickly.'
Oil and gas companies are among the investors in Commonwealth Fusion and other fusion startups, Holland, the president of the Fusion Industry Association, said.
'I think that other energy companies, companies that want to be not oil companies, or not renewable companies, are looking at fusion,' Holland said. 'Physically, fusion is decoupling energy from resources, from something that you have to pull out of the ground or rely on weather. It makes energy something that you can manufacture.'
Sorbom said that although he thinks fusion could eventually 'replace' a 'whole bunch of things,' he also sees it as a way to provide 'way more energy for everybody.'
'One of the things that's always excited me about fusion is that if you look at quality of life metrics, they all get better when you add energy to the system,' he said.
Holland emphasized fusion will be 'the next part of the energy industry.'
'And ultimately, it will be the thing that powers humanity into kind of the next age of civilization.'