Inside a vast, hangar-like building in Devens, a trio of employees are working to test and assemble the pieces of what is likely one of the most advanced machines being built on Earth.
One part of a vacuum chamber — weighing 48 tons — has been flown over from a factory in Italy. It’s intended to be able to insulate the machine from a reaction that takes place at more than 180 million degrees Fahrenheit, far hotter than the core of the sun.
This is the fusion reactor being built by Commonwealth Fusion Systems, and if it works as advertised, it will provide a new source of clean power to the electrical grid.
Importantly, it’s a kind of clean power that the Trump administration supports; Secretary of Energy Chris Wright visited CFS earlier this fall, and his agency recently provided $8 million in grant funding based on the company’s technical progress.
But that $8 million is just a drop in the bucket compared to the private funding that CFS has collected since it was founded in 2018: nearly $3 billion from a group of investors, including Google, the Italian energy company Eni, the family that owns Fidelity Investments and the Bill Gates-affiliated investment firm Breakthrough Energy Ventures.
That likely makes CFS the best-funded startup company that Massachusetts has ever seen.
Fusion’s big advantages would be that it’s a virtually limitless source of electricity that doesn’t pump carbon into the atmosphere, and has fewer safety risks compared to traditional nuclear reactors.
CFS spun out from an MIT lab after the Department of Energy cut funding back in 2013 for fusion research at the university. An MIT-affiliated venture capital fund, Engine Ventures, provided early capital and office space for CFS. For a time, it worked out of a former Radio Shack store in Cambridge’s Central Square. Employees dubbed it the “Magnet Shack,” since they were designing high-powered magnets that would coerce hydrogen atoms to smash into each other.
The company moved into a 45-acre, two-building campus in Devens in 2022.
On a tour of the company’s current digs, Ben Byboth, CFS’ director of business development, uses the metaphor of a Nascar race to explain what’s happening inside the reactor to generate power.
“In order to have fusion happen, you need three things: temperature, which is the speed [of the atoms in the reactor.] You need enough density, and you need enough confinement time. It’s basically if you were to go watch a Nascar race … if you make the cars go fast enough, and you put enough of them on the track, and you squeeze the track in, eventually you’ll have a collision.”
Ordinarily, atoms with positively charged nuclei don’t want to merge; fusion reactors get that to happen, producing heat that can turn water into steam, and run a turbine that produces electricity.
Powerful magnets — which CFS is building in its own factory on-site — are a key part of the system.
CFS is building a type of reactor called a tokamak, which has a doughnut-shaped chamber inside it that serves as the race track. This kind of reactor design has been in use since the 1950s for fusion experiments.
But all these experiments so far have required more power as an input than they have delivered as an output — not very helpful if you’re trying to sell electricity to the grid.
CFS, a British startup called Tokamak Energy, and a multi-national scientific project in France, called ITER, are all hoping they will be the first to show that this kind of reactor can produce a net energy gain. (In 2022, an experiment at the Lawrence Livermore National Ignition Facility in California, using a different kind of reactor design, showed net energy production for the first time, generating about 1.5 times the power put into it.)
Byboth said the company is aiming to hit that milestone of net energy gain in 2027. This year and next are “all about assembly of the tokamak, and commissioning our systems that support it. … We’re very much in execution mode now as a company, heads-down, trying to drive everything across the finish line.”
Interestingly, CFS doesn’t use the terms “reactor” or “nuclear” in talking about the device it is building — even though a nuclear reaction is happening inside it. They prefer to call it a fusion “machine” or “device.”
Byboth said that CFS won’t be regulated by the Nuclear Regulatory Commission, which oversees fission-based reactors, but by state agencies such as the Massachusetts Division of Radiation Control, which oversees things like mammography machines, lasers used for tattoo removal and rifle sights that contain tritium — one of the fuels that CFS will use.
So while CFS will use a radioactive fuel, and while the power production process will make metals inside the company’s reactor radioactive, Byboth said it will not produce any spent fuel or high level radioactive waste, as a traditional nuclear fission plant such as New Hampshire’s Seabrook Station does.
The company’s reactor, he said, is “a very different risk profile,” adding, “we don’t have that type of melt-down risk.” He said that CFS has invited residents of nearby homes in Devens for tours and educational sessions at its headquarters.
CFS has more than 1,000 employees, and 600 are on-site at Devens on any given day, Byboth said. (The company continues to hire for a range of roles.)
The company is planning to build its first commercial reactor in Virginia, in collaboration with the utility Dominion Energy. It calls that machine ARC, and the demonstration device it is building in Devens SPARC. The plan is for ARC to be delivering power to the grid in the early part of the 2030s.
While it remains privately held, other fusion power companies have recently been maneuvering to go public. On that possibility, Mumgaard said, “We always keep track of options, but we’re very long-term focused on actually getting SPARC to work and then ARC to work, and make power and then build more power plants. The public markets might be a way to get there at some point.”
But for now, he said, the company has been able to successfully raise money without having to report to Wall Street analysts or a vast number of shareholders, which helps the company stick to its long-term vision.
Anne White, an MIT engineering professor who studies fusion energy, said that heat generated by a fusion reactor could be useful not only for generating electricity, but also as part of other industrial processes that require heat, such as making fertilizer. And White said she doesn’t think it’s unrealistic to expect a first fusion power plant to provide power to the electrical grid within the next decade.
Mumgaard now faces the challenge of hustling to deliver something useful within that timeframe, while also making the completion of the company’s demonstration system, SPARC, seem like a straightforward engineering task. He likes to say CFS already has the script written, and now all that remains is to shoot the movie.
Occasionally, however, he acknowledges that CFS is trying to do something significant — bring online a type of power production that “no one has ever done,” outside of a research lab in California. Getting there, he said, will be a “big breakthrough” for humanity.
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