Can Nuclear Fusion Put the Brakes on Climate Change?

The doubters weren’t simply killjoys—they were imaginative thinkers who had devoted decades of their lives to fusion research. It wouldn’t be easy to make H.T.S. into a magnet of sufficient size. And the powerful magnetic field created by H.T.S. was sure to have consequences, which hadn’t been fully studied. There was every reason in the history of experimental science to expect surprises. And funding for fusion projects was already tight; another idea might draw money away from projects that many scientists considered more promising. It was entirely reasonable to ask whether the members of the M.I.T. team were the Wright brothers or Samuel Pierpont Langley—the head of the Smithsonian who in 1903 crashed his very expensive Aerodrome into the Potomac, and then a couple of years later did it again.

After Whyte’s keynote, the M.I.T. crowd went out for lunch at Stubb’s Bar-B-Q. “It’s the kind of place with red-checked tablecloths and food that comes with a lot of napkins,” Whyte said. Everyone around the table knew that the primary funding for their work would end within a year. As Mumgaard recalls, “Basically, we all had pink slips, and yet we were still there. And the question was, Why? We had to learn to listen to ourselves. Did we really believe the field was where we were saying we thought it was?” Was H.T.S. really the shiny new lever that would move fusion dramatically forward? Whyte and his colleagues started to write on a napkin details of how they could make SPARC and then ARC a reality. They wrote down estimates of how much money it would cost to develop it. “It was like this collective dawning, that this thing was really possible,” he told me. Over ribs, they decided that they would fund their work with lottery tickets or with venture capital or with philanthropy—one way or another, they would make their good-enough fusion power plant real.

On September 30, 2016, M.I.T.’s old experimental fusion device, which had been running for twenty-five years, was obliged to shut down by midnight. “This device graduated more than a hundred and fifty Ph.D.s,” Whyte said wistfully. “It set records, even though it’s a hundred times smaller than ITER.” Although M.I.T. was never told why the device was shut down—the Department of Energy continued to fund two other tokamak projects in the U.S.—there was speculation that the reason was that it was the smallest. “Which is ironic, because smaller is where we’re trying to go,” Whyte said. The researchers ran experiments on the machine until the last permitted minute. At 10:30 P.M., they set a world record for temperature and pressure. At midnight, they shared champagne.

“I went home a little after midnight, but I couldn’t sleep,” Whyte said. In his home office, with his wife’s paintings of trees and flowers on the wall, he started going over the data from the final experiments: “I was just sort of plugging in what our results would mean in a machine with a higher magnetic field,” as would be produced with H.T.S. magnets. “It meant spARC could provide a hundred million watts.” This was even more than the team had speculated in Austin. Whyte was seeing fusion’s holy grail.

The M.I.T. team continued to dedicate its time to ARC/SPARC, quilting together fellowships and grants. At one point, to make payroll, technicians went into the basement and loaded trucks with scrap copper to sell. SPARC Underground was set up—a group of interested scientists who met regularly, to discuss plans and work through difficulties. They needed to buy as much H.T.S. as they could, in order to learn more about the material’s characteristics—hammer it, heat it, freeze it, send current through it. “I remember so well the first shipment of H.T.S.,” Mumgaard said. “We waited for months to get this reel of material. It was only five hundred metres. Now, if we’re not talking ten kilometres, we’re not talking anything. These days, you can order this stuff on But then—it was such a moment.”

The team had to solve engineering problems—it also had to solve business problems, including convincing suppliers that there was a market for the material, so that more would be made. “We met with them and asked them if they had considered fusion as a market,” Mumgaard told me. “They were, like, ‘No way, that’s not a real thing.’ ” After two years of extensive lab work and dreamy conversations over five-dollar pitchers of Miller High Life at the Muddy Charles Pub, SPARC Underground became Commonwealth Fusion Systems, a seven-person private fusion-energy company with an ongoing relationship with M.I.T. (C.F.S. funds research at M.I.T., which shares its intellectual resources and some lab space with C.F.S.; patents are filed jointly.) Some of C.F.S.’s funders are European energy companies, and some are philanthropists. By 2021, the company employed about three hundred people, many of them veterans of SpaceX and Tesla.

“Energy is a market,” Mumgaard said. “If you knew there was a ten-trillion-dollar market out there—that is a pull. You couldn’t even have said there was a market that big for computers, or for social media. But you can say that about energy.”

The Plasma Science and Fusion Center, at the northwest corner of the M.I.T. campus, is only a few minutes’ walk from the Cambridge campuses of Pfizer and Moderna. In March, Whyte and Mumgaard met me at the front steps. Mumgaard is now the C.E.O. of C.F.S.; Whyte, a co-founder, remains at M.I.T. They wore T-shirts and had pandemic-untrimmed wavy hair, giving them the look of ambitious surfers. I was there to meet them, but also to meet their magnet, which was still under construction. Maybe it would work, or maybe it would send the team back to the planning stages for years. It was a warm and sunny day. If Kool-Aid had been on offer, I would have drunk not one glass but two.

Aristotle described magnetism as the workings of the soul inside a stone. Magnets have been used to navigate ships, to levitate high-speed trains, to image the inside of a human body, and to move iron filings to make a silly beard on a plastic-bubble-encased drawing of a face. In 1951, the physicist Lyman Spitzer suggested that a magnetic field could serve as a bottle in which to contain a plasma that re-created the pressure and the temperature inside a star. Magnets have been a centerpiece of fusion research ever since.

Mumgaard and Whyte gave me a tour of their lab spaces. The first stop was at what looked like a lectern, in a cubicled room. The room’s distant wall was the control board for M.I.T.’s first experimental fusion device, from the nineteen-seventies. The lectern featured pictures of common plasmas: the sun, lightning, the northern lights, magnetic fusion, and a neon sign reading “OPEN.” Mounted on the lectern was a hollow glass tube with copper wire coiled around it in two places. The wire was set up so that a current could be run through it, and the glass tube was suspended over a metal plate. You may remember a demonstration, from your high-school science class, of an electric current being run through coiled wires, generating an electromagnetic field—this was basically a fancier version of that. “You can turn it on,” Mumgaard said.

I pushed a black button. A purring noise began. “That’s the sound of the vacuum draining the air from the glass tube,” Mumgaard said. He turned a valve, releasing a tiny bit of hydrogen gas into the tube. A hot-pink glowing light appeared, nested within the glass tube like a matryoshka doll. The magnetic field that contained the pink plasma was visible in the form of empty space between the glass and the glow. “That pink is the superheated plasma,” Mumgaard said. “It’s at least a thousand degrees. But touch the glass.” The glass was cool. “Now touch the copper wires.” They were warm, but not hot. The warmth of the copper wires was not on account of their proximity to the superheated plasma but, rather, because copper is not a perfect conductor; some of the energy running through it is lost in the form of heat. Superconductors lose almost no heat—which is energy.

It seemed impossible that the pink plasma inside the tube, which was as hot as lightning, wasn’t in some way dangerous. Couldn’t some of it leak out of the magnetic bottle, with catastrophic consequences? As an answer, Mumgaard twisted a valve to let a tiny bit of air into the glass tube; the plasma vanished. “People think of fusion like they think of fission, as this overwhelming reaction, but, really, it’s such a delicate process,” Whyte said. “It’s like a candle in the wind. Anything can blow it out. Even a single human breath.”

Much of what Mumgaard and Whyte showed me at P.S.F.C. was the standard part of fusion science. A magnetic bottle is an old idea, and plasma is the most common state of matter; it’s the state that 99.9 per cent of the universe is in. Scientists have been studying plasmas, and magnetic bottles, for decades. Much of what seems difficult about fusion to a plasma physicist—How will tritium be produced and recycled? How can edge-localized modes be anticipated and countered? Will quantum computing enable the study of electromagnetic waves in a plasma?—is so much Greek to a layperson. In contrast, much of what seems difficult about fusion to a layperson—super-hot plasmas, magnetic bottles, toroidal coils—is bread and butter for a fusion scientist.

“As energy, fusion is in some sense very prosaic,” Whyte said. “It’s an intense source of heat.”

“And we’ve been turning heat into electricity since James Watt,” Mumgaard added, referring to the eighteenth-century Englishman whose development of the steam engine enabled the Industrial Revolution. Mumgaard often stresses that C.F.S. is building a “standard, even boring” machine, using “boring, non-innovative” technology, “but for very non-boring reasons.”

The one exception is the H.T.S. magnet—the most exciting element of the research, and the one that raises the most doubt within the scientific community. “I just wonder about the material stresses of such a powerful magnetic field,” one scientist said to me. “H.T.S. magnets will definitely be used in future tokamaks, no doubt, but I suspect they’ll be used with a weaker magnetic field.”

“Would you like to sing the national anthem before dinner?”
Cartoon by Justin Sheen

“Most of the criticism we hear is not about the science but about the timeline,” Mumgaard said. The magnets inside ITER took thirty years to develop. “It took us three years.” He could barely repress a grin; it was the one moment of boyish bullishness and ego that I saw in him.

SPARC will have eighteen H.T.S. magnets; each will be composed of sixteen “pancakes”—eight-foot-tall stackable D-shaped slices. I met a pancake in the West Cell, an enormous open laboratory space at M.I.T. which resembles an airplane hangar. What with all the pancakes and doughnuts being tested there, the West Cell has come to be called the West Cell Diner. The pancakes were given names in alphabetical order. The first production pancake was named Egg. When I was there, I saw Strawberry. “We originally planned to have a pancake breakfast for the team when we finished,” Whyte said. “COVID is making that look less likely.”

Strawberry was, incidentally, beautiful. It comprised coils of steel, copper, H.T.S., and helium coolant, because even a high-temperature superconductor has to be kept very cold. (In its internal structure, the magnet was more croissant than pancake.) “I remember when the first pancake was done, and we were moving it so delicately,” Whyte said. “Our hearts were in our mouths—it was, like, Holy cow. Then, the other week, it was the fifteenth pancake. We rolled it over, connected it, like we’d done it a thousand times.”

C.F.S. is not the only enterprise trying to be the Wright brothers. In 2001, Michel Laberge left his job as a physicist and engineer at a printing company and began work on a fusion project that evolved into General Fusion, a Canada-based company developing a technology called magnetized target fusion. General Fusion has the backing of Jeff Bezos, though some plasma physicists note that they haven’t seen enough published work to know how the fusion device is progressing. The U.K. Energy Agency has commissioned General Fusion to build a demonstration plant in Culham, Oxfordshire, where major fusion records were set in the nineteen-nineties. General Fusion has announced its intention to open the plant in 2025, the year that C.F.S. plans to turn on its switch at a SPARC demonstration plant being built in Devens, Massachusetts. There are at least twenty fusion startups now, all benefitting from technological advances in 3-D printing and artificial intelligence. The companies have different risks. TAE, in Orange County, California, uses a fuel, boron, that requires higher temperatures but generates no radioactive by-products. Physicists describe boron fusion as “elegant” and even “perfect,” if also, in certain ways, more difficult. Michl Binderbauer, the head of TAE, told me, “I don’t call these other companies my competitors, I call them my compatriots. We have the same goals, and it will be wonderful for any of us to get there.”

C .F.S.’s seventh hire was Joy Dunn, an aerospace engineer recruited from SpaceX and made head of manufacturing. Dunn, who is thirty-five, has a youthful face and short, rockabilly hair; she loves scuba diving, which made leaving California difficult. She had attended M.I.T. as an undergraduate, and at one of the early C.F.S. meetings she found herself seated next to her fluid-dynamics professor. “I was thinking, I hope he doesn’t remember what grade I got in his class,” she said.

One of Dunn’s main tasks has been producing the magnets, including the pancakes I saw in the West Cell Diner. When I met her, a test of the magnets was imminent, but Dunn told me that she wasn’t really worried about failure. “When they were hiring me, they stressed that it wasn’t a physics problem but an engineering problem,” she said. “That appealed to me. You can’t change the laws of physics, but an engineering problem—that can be solved.”

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