Nuclear power is booming again.

With energy prices on the rise, along with demands for energy independence and an urgent need for carbon-free power, plans to walk away from nuclear energy are now being revised in Japan, South Korea, and even Germany. Last month, Europe announced green bonds for nuclear, and the U.S., thanks to the Inflation Reduction Act, will soon spend millions new nuclear designs, incentives for nuclear production and domestic uranium mining, and, after years of paucity in funding, cash for fusion.

The new investment comes as fusion—long considered a pipe dream—has attracted real money from big venture capital and big companies, who are increasingly betting that abundant, cheap, clean nuclear will be a multi-trillion dollar industry. Last year, investors like Bill Gates and Jeff Bezos injected a record $3.4 billion into firms working on the technology, according to Pitchbook. One fusion firm, Seattle-based Helion, raised a record $500 million from Sam Altman and Peter Thiel. That money has certainly supercharged the nuclear sector: The Fusion Industry Association says that at least 33 different companies were now pursuing nuclear fusion, and predicted that fusion would be connected to the energy grid sometime in the 2030s.

You’ve likely heard this one before. The running joke is that economically harnessing fusion power, which is what a star or hydrogen bomb does, is about 30 years away. What’s not a joke is that we have about zero years to stop powering our civilization with earth-warming energy. The challenge with fusion is to achieve net energy gain, where the energy produced by a fusion reaction exceeds the energy used to make it. One milestone came quietly this month, when a team of researchers at the National Ignition Facility at Lawrence Livermore National Lab in California announced that an experiment last year had yielded over 1.3 megajoules (MJ) of energy, setting a new world record for energy yield for a nuclear fusion experiment. The experiment also achieved scientific ignition for the first time in history: after applying enough heat using an arsenal of lasers, the plasma became self-heating. (Researchers have since been trying to replicate the result, so far without success.)

And you’d be forgiven for missing another milestone in July, when the Energy Dept. announced awards of between $50,000 and $500,000, to ten fusion companies working on projects with universities and national labs. Here are a few of the awardees, whose projects offer a sampling of the opportunities—and hard problems—in fusion.

COMMONWEALTH FUSION SYSTEMS

On a growing campus an hour outside of Boston, the MIT spinoff Commonwealth Fusion Systems is building their first machine, SPARC, with a goal of producing power by 2025. “You’ll push a button,” CEO and cofounder Bob Mumgaard told the Khosla Ventures CEO Summit this summer, “and for the first time on earth you will make more power out than in from a fusion plasma. That’s about 200 million degrees—you know, cooling towers will have a bunch of steam go out of them—and you let your finger off the button and it will stop, and you push the button again and it will go.” With an explosion in funding from investors including Khosla, Bill Gates, George Soros, Emerson Collective and Google to name a few—they raised $1.8 billion last year alone—CFS hopes to start operating a prototype in 2025.

Think of a fusion reactor as a boiler, in which the plasma inside the reactor’s tokamak produces 650-degree heat in the form of a moving fluid—in Commonwealth’s case it’s molten salt, but it could be steam or high temperature helium—which enters a heat exchanger, making steam that eventually turns a turbine. Except, in this case, the heat in the boiler isn’t made by the combustion of carbon into CO2, but the fusion of hydrogen into helium.

Like the three-decade-old ITER project in France, set for operation in 2025, Commonwealth and many other companies will try to reach net energy gain using a machine called a tokamak, a bagel-shaped device filled with super-hot plasma, heated to about 150 million degrees, within which hydrogen atoms can fuse and release energy. To control that hot plasma, you need to build a very powerful magnetic field. Commonwealth’s breakthrough was tape—specifically, a high-temperature-superconducting steel tape coated with a compound called yttrium-barium-copper oxide. When a prototype was first made commercially available in 2009, Dennis Whyte, director of MIT’s Plasma Science and Fusion Center, ordered as much as he could. With Mumgaard and a team of students, his lab used coils of the stuff to build a new kind of superconducting magnet, and a prototype reactor named ARC, after Tony Stark’s energy source. Commonwealth was born in 2015.

One morning last December, the company fired up its newest supermagnet—a 10-ton, 8-foot-tall device made of hundreds of tightly-twisted coils—and quietly pushed its magnetic field beyond a whopping 20 tesla, a record for a magnet of its size. (Most MRIs operate at a strength of about 1 tesla.) Eventually, 18 of these magnets will surround the SPARC’s tokamak, which CFS says could produce as much as 11 times more energy than it consumes, and at prices cheaper than fossil fuels. Mumgaard estimates the world will need something to replace the world’s 60,000 carbon-emitting power stations, which account for about half of global energy use. Ten thousand fusion plants would do it.

“The exciting part about this technology is that by shrinking the scale and keeping the power the same, we make more ‘power per stuff,’ which makes it much more likely to be economically competitive,” Mumgaard told Fast Company in 2018. “The types of materials that are in this are materials that are commodities, and if you add up those materials you get a cost of electricity that undercuts existing energy prices.”

TAE TECHNOLOGIES

Southern California-based TAE Technologies has raised a whopping $1.2 billion since it was founded in 1998, and $250 million in its latest round. The round, announced in July, was led by Chevron’s venture arm, Google, and Sumitomo, a Tokyo-based holding company that aims to deploy fusion power in the Asia-Pacific market. TAE’s approach, which involves creating a fusion reaction at incredibly high heat, has a key advantage. Whereas ITER uses the hydrogen isotopes deuterium and tritium, an extremely rare element that must be specially created from lithium—and that produces as a byproduct radioactive-free neutrons—TAE’s linear reactor is completely non-radioactive, because it relies on hydrogen and boron, two abundant, naturally-occurring elements that react to produce only helium.

The problem is, this requires temperatures on the order of one billion degrees Celsius. (By comparison, ITER requires only a temperature of 150 million degrees Celsius. The sun’s core, its hottest part, can be as hot as 15 million degrees Celsius.) TAE says that its current test reactor has managed to keep plasma stable at 75 million degrees Celsius, or 167 million Fahrenheit—more than twice its initial target. With its double-decker-bus-sized machine, which it says currently costs over $250 million to construct, the company is aiming to build an even larger machine, Copernicus, to do the test at double the heat. It says it plans to start delivering power to grids by 2030, followed by “broader commercialization” during the next decade.

GENERAL ATOMICS

General Atomics, of San Diego, California, has the largest tokamak in the U.S. Its powerful magnetic chamber, called the DIII-D National Fusion Facility, or just “D-three-D,” now features a Toroidal Field Reversing Switch, which allows for the redirection of 120,000 amps of the current that power the primary magnetic field. It’s the only tokamak in the world that allows researchers to switch directions of the magnetic fields in minutes rather than hours. Another new upgrade, a traveling-wave antenna, allows physicists to inject high-powered “helicon” radio waves into DIII-D plasmas so fusion reactions occur much more powerfully and efficiently.

“We’ve got new tools for flexibility and new tools to help us figure out how to make that fusion plasma just keep going,” Richard Buttery, director of the project, told the San Diego Union-Tribune in January. The company is also behind eight of the magnet modules at the heart of the ITER facility, including its wild Central Solenoid — the world’s most powerful magnet — in a kind of scaled up version of the California machine.

But like an awful lot in fusion, ITER has been hampered by cost overruns and delays, with “first plasma” not expected to occur in 2025 as previously expected due to global pandemic-related disruptions. Some have complained that the money going to ITER has distracted from other more practical energy projects—the latest price tag is $22 billion—and others doubt if the project can ever produce net energy gain.

GENERAL FUSION

Based in Canada, General Fusion is backed by Jeff Bezos and building on technology originally developed by the U.S. Navy and explored by Russian scientists for potential use in weapons. Inside the machine, molten metal is spun to create a cavity, and pumped with pistons that push the metal inward to form a sphere. Hydrogen, heated to super-hot temperatures and held in place by a magnetic field, fills the sphere to create the reaction. Heat transferred to the metal can be turned into steam to drive a turbine and generate electricity. As CEO Christofer Moery told Fast Company last year, “to re-create a piece of the sun on Earth, as you can imagine, is very, very challenging.” Like many fusion companies, GF depends on modern supercomputers and advanced modeling and computational techniques to understand the science of plasma physics, as well as modern manufacturing technologies and materials.

“That’s really opened the door not just to being able to make fusion work but to make it work in a practical way,” he says. This has been difficult to make work, but with a demonstration center it opened last year near Oxford, GF isn’t aiming to generate electricity but to gather the data needed to later build a commercial pilot plant that could—and to generate more interest in fusion.

“Part of what we want to do with this demonstration plant is make the promise of fusion something that is more in the public’s consciousness, and in the policymakers’ consciousness, so as they plot what the future energy systems look like, they consider how to incorporate fusion in that,” Mowry said. “Because it will be coming here faster than people realize.”

PRINCETON FUSION SYSTEMS

Princeton Fusion Systems of Plainsboro, New Jersey, is a small business focused on developing small, clean fusion reactors for both terrestrial and space applications. A spinoff of Princeton Satellite Systems, which specializes in spacecraft control, the company’s Princeton FRC reactor is built upon 15 years of research at the Princeton Plasma Physics Laboratory, funded primarily by the U.S. DOE and NASA, and is designed to eventually provide between 1 and 10 megawatts of power in off-grid locations and in modular power plants, “from remote industrial applications to emergency power after natural disasters to off-world bases on the moon or Mars.” The concept uses radio-frequency electromagnetic fields to generates and sustain a plasma formation called a Field-Reversed Configuration (FRC) inside a strong magnetic bottle. The experiment at Princeton holds the record for the longest time that such a reaction has been stably held—at 300 ms. Princeton has attracted over $2.5 million in grants from the Dept. of Energy’s ARPA-E advanced technology program.

TOKAMAK ENERGY

Tokamak Energy, a U.K.-based company named after the popular fusion device, announced in July that its ST-40 tokamak reactor had reached the 100 million Celsius threshold for commercially viable nuclear fusion. The achievement was made possible by a proprietary design built on a spherical, rather than donut, shape. This means that the magnets are closer to the plasma stream, allowing for smaller and cheaper magnets to create even stronger magnetic fields. The Princeton Large Torus tokamak first reached this temperature threshold in 1978, but Tokamak’s is the first to do so with a spherical, privately-funded device. The company has raised nearly $100 million from investors including Legal & General, in addition to grants from the Dept. of Energy.

MIFTI

Magneto-Intertial Fusion Technologies, or MIFTI, of Tustin, Calif., founded by researchers from the University of California, Irvine, is developing a reactor that uses what’s known as a Staged Z-Pinch approach. A Z-Pinch design heats, confines, and compresses plasma using an intense, pulsed electrical current to generate a magnetic field that could reduce instabilities in the plasma, allowing fusion to persist for longer periods of time. But only recently have MIFTI’s scientists been able to overcome the instability problems, the company says, thanks to software made available to them at UC-Irvine by the U.S. Air Force. MIFTI is predicting an energy gain from ten to fifty times the energy used to create it. Since its launch in 2008, the company has raised $1.6 million in venture capital and received a $4.5 million award from the Dept. of Energy’s ARPA-E program. Separate research on Z-pinch chambers at Lawrence Livermore National Laboratory spun off another fusion startup, Seattle-based Zap Energy, in 2017.

HELICITY SPACE

Based in Pasadena, California, Helicity Space is developing a propulsion and power technology based on a specialized magneto inertial fusion concept. The system, a spin on what fellow fusion engineer, Seattle-based Helion is doing, appears to use twisted compression coils, like a braided rope, to achieve a known phenomenon called the Magnetic Helicity. (See a description in this presentation.) According to ZoomInfo and Linkedin, Helicity has over $4 million in funding and up to 10 employees, all aimed, the company says, at “enabling humanity’s access to the solar system, with a Helicity Drive-powered flight to Mars expected to take two months, without planetary alignment.”