Take a smidgen of hydrogen, then blast it with lasers to set off a small thermonuclear explosion. Do it right, and maybe you can solve the world’s energy needs.
A small group of start-ups have embarked on this quest, pursuing their own variations on this theme — different lasers, different techniques to set off the fusion reactions, different elements to fuse together.
“There has been rapid growth,” said Andrew Holland, chief executive of the Fusion Industry Association, a trade group lobbying for policies to speed the development of fusion.
Private enterprise promises quick innovation, but it was a breakthrough achieved by a big, costly and ponderous government-run project that spurred this wave of attention to laser fusion.
In December last year, after years of trying, the National Ignition Facility, or NIF, at Lawrence Livermore National Laboratory reported that it had finally lived up to its middle name: ignition. For the first time anywhere, a laser-induced burst of fusion produced more energy than that supplied by the incoming lasers.
“We’re really excited by the NIF results,” said Kramer Akli, who manages the inertial fusion energy sciences program at the United States Department of Energy.
A decade ago, a report by the National Academy of Sciences found much to like in the energy potential of laser fusion but recommended that the United States hold off major investments until ignition was achieved.
That time is now.
The dream of fusion is easy to explain.
The sun generates heat and light by jamming — fusing — hydrogen atoms together into helium. Harnessing that phenomenon on Earth could lead to a bountiful energy source that does not generate planet-warming carbon dioxide or long-lived radioactive waste.
For more than 70 years, fusion research has largely focused on mimicking the inside of the sun in reactors known as tokamaks, which trap superhot hydrogen gas within strong magnetic fields so that atoms will collide and fuse.
NIF offered another possibility. It was designed primarily to help verify computer simulations of nuclear explosions after a treaty banned tests of actual exploding nuclear weapons. But a secondary aim of NIF was to explore the possibility that technology could be adapted to provide a bountiful, clean source of energy.
Until two years ago, NIF sputtered well short of its goals. But in December 2022, a burst finally crossed the threshold of ignition.
“Simply put, this is one of the most impressive scientific feats of the 21st century,” Jennifer M. Granholm, the U.S. secretary of energy, said during a celebratory news conference announcing the success.
In July this year, Livermore repeated the feat, generating even more energy.
The researchers at Livermore are joined by scientists at other institutions, like the Naval Research Laboratory in Washington and the Laboratory for Laser Energetics at the University of Rochester in New York. While the lasers at those institutions are not powerful enough to create fusion, they allow scientists to investigate some of the basic science and tweak their concepts on a smaller scale.
“There’s still a lot of foundational science and technology to be done,” said Dr. Akli of the Energy Department, but he added that he currently did not see any showstopping obstacles.
“We are not predicting the timeline, but I’m really very optimistic,” he said.
Private enterprise is jumping in too, and scientists are following.
Debra Callahan worked on NIF at Livermore for more than 20 years. An experiment she contributed to in August 2021 represented a major advance. Although it still fell short of ignition, the amount of fusion energy released leaped upward, and it was clear that the explosion had generated torrents of particles that heated the surrounding hydrogen, setting off cascades of additional fusion reactions.
To celebrate, Dr. Callahan got a tattoo inked on her left forearm: a drawing of the sun with an infinity sign inside.
She also left Livermore. Today, Dr. Callahan is a senior scientist at Focused Energy Inc., one of the start-up laser fusion companies.
“For me, that’s the next grand challenge — to try to make fusion energy,” she said. “I’d like to see more clean energy for my daughter and her future children.”
Since the beginning of the year, the Energy Department has gathered views across academia and industry about the technological challenges that stand between the basic science result of NIF and commercial laser fusion power plants hooked onto the electrical grid.
The agency has bestowed modest awards to a couple of the start-ups to begin designing what such a power plant would look like, and it is looking to finance consortiums of institutions to tackle pieces of laser fusion research, including high-power lasers that are able to fire at high rates, and fuel targets that can be manufactured in quantity at low cost.
Longview Fusion Energy Systems of Orinda, Calif., has the simplest strategy: Directly replicate NIF’s approach, but use more modern components.
“What we’re really happy with is that the basis of what we’re doing has been proven to be sound,” said Edward Moses, the company’s chief executive. Dr. Moses led the building and early operations of NIF, which began firing its lasers in 2009. During that time, Livermore spent $100 million on developing a design for a commercial power plant based on NIF, Dr. Moses said.
“It was vetted by eight of the major utilities,” Dr. Moses said. “So we have that as an asset.”
The key upgrade in Longview’s design will be the lasers. NIF’s lasers are powerful but woefully inefficient. Of the energy NIF pulls from the electrical grid for each firing, about 1 percent is converted into laser light. The lasers are also only able to fire about 10 times a week.
Longview intends to use lasers powered by diodes from the semiconductor industry, a technology that can be 20 percent efficient and fire several times a second.
Dr. Moses, however, has his critics, who remember his time as the head of NIF and say he overpromised and overhyped the energy potential. Some also doubt that NIF’s method of ignition is the future.
In NIF’s approach, known as indirect drive, the laser beams do not directly hit the hydrogen fuel. Instead, they annihilate a surrounding gold cylinder that is about the size and shape of a pencil eraser. That generates a bath of inward-rushing X-rays that compresses a round pellet that contains a layer of deuterium and tritium, the heavier forms of hydrogen.
The problem is that the extra step of generating X-rays throws away much of the laser energy.
“Indirect drive is not going to be the basis of an inertial fusion energy facility,” said David A. Hammer, a professor of nuclear engineering at Cornell University who has served on a NIF advisory panel.
In its place, some, including some at the Naval Research Laboratory, want to attempt direct drive, where lasers directly implode hydrogen pellets, a more energy-efficient approach that would generate more power and potentially more economically viable.
Stephen Obenschain, who led the Naval Research Laboratory laser fusion program for more than two decades, left last year to start a direct-drive fusion company, LaserFusionX. The naval research laboratory researchers have been pushing to use a type of laser that uses argon and fluoride gases to produce ultraviolet laser light.
Computer simulations, they say, indicate that argon-fluoride lasers of modest power could generate energy gains — the ratio of fusion energy output divided by the energy of the incoming lasers — of 100 or more. (The NIF burst in July produced a gain of 1.8.)
Energy gains that high could enable power plants that are smaller and less expensive than what others envision.
Lasers gain their power by lining up light waves in synchrony. But that also makes it difficult for the lasers to provide uniform illumination, leading to unequal squeezing. “We went the opposite extreme and tried to turn it into partially incoherent light,” Dr. Obenschain said.
The argon-fluoride laser can shine more evenly, and that mitigates the instabilities as the hydrogen implodes, Dr. Obenschain said. A laser system at the naval lab has already demonstrated that it can fire five times a second, and doubling that would be “a minor change,” he said.
Dr. Obenschain said he had started thinking about creating a company a couple of years ago after seeing billions of dollars from venture capitalists pouring into companies using the traditional tokamak fusion approach. “So all of a sudden, there appeared to be opportunity,” he said.
And the Livermore success helps convince investors that laser fusion is more than a fantasy. “Certainly the NIF shot helps in selling,” Dr. Obenschain said. “I think we could get from a standing start to a reactor in about 16 years.”
Another start-up, Xcimer Energy of Redwood City, Calif., is planning to use krypton-fluoride gas lasers, but at much higher energies — eventually, a system that puts out about twice as much energy as NIF’s lasers — and employ a hybrid indirect-direct drive approach. Xcimer proposes using an indirect pulse of X-rays to initially warm the pellet but then hitting it directly with lasers to initiate fusion.
“It leverages what was demonstrated on NIF,” said Conner Galloway, chief executive and co-founder of Xcimer. “Similar compression of fuel, similar convergence of the fuel hot spot ignition.”
Focused Energy — the company where Dr. Callahan now works — also plans to use multiple pulses. But it will, like Longview, use diode-powered solid-state lasers. The first pulse compresses the fuel pellet but not as strongly as in NIF. A second laser pulse creates a beam of protons that slams into the collapsing pellet and ignites the fusion.
The Focused Energy approach is more complex than direct drive, but with a gentler compression of the fuel, instabilities are easier to avoid. “It’s a trade-off,” Dr. Callahan said.
There is also more than one way to smash atoms into a heavy element. HB11 Energy of Sydney, Australia, plans to use the fusion of the element boron and hydrogen.
This hydrogen-boron fusion reaction offers key advantages. Boron is plentiful and easy to obtain. By contrast, tritium, the heavy form of hydrogen needed for most other laser fusion concepts, has a half-life of only 12 years. Thus, those reactors will have to generate the tritium they use. Also, most of the energy from deuterium-tritium fusion comes out as fast-moving neutrons, which slam into the reactor, weakening the structure and turning it mildly radioactive.
The lack of radioactivity for hydrogen-boron fusion means “all the downside that we know about nuclear goes away,” said Warren McKenzie, the managing director of HB11.
The downside is that it is harder to get hydrogen and boron to fuse together.
“The simple way of looking at that is we’ve still got some science to do,” Dr. McKenzie said. “But if we can make the science work, our engineering bar is much, much lower.”
Marvel Fusion of Munich is also using hydrogen and boron but in a different way. It will mix the elements with deuterium and tritium, forming chemical bonds that allow the fuel to be a solid at room temperature. That eliminates the need to freeze the deuterium and tritium at ultralow temperatures.
A room-temperature fuel will allow the embedding of structures in the target that will act as tiny particle accelerators. When the laser hits, the structures explode.
That is a better way to initiate fusion, said Hartmut Ruhl, a physics professor at Ludwig Maximilian University who is Marvel’s chief scientist.
“It is very easy to reach extremely high temperatures in the fuel,” he said. “It’s also very easy to quickly compress the fuel.”
Two companies — First Light Fusion, a spinoff from the University of Oxford in England, and NearStar Fusion of Chantilly, Va. — do not plan to use lasers at all. Instead, they will smash projectiles into fuel pellets, using the force of impact to fuse the hydrogen atoms. NearStar adds a crushingly strong magnetic field to help retain the heat within each implosion.
The Department of Energy will provide multimillion-dollar awards to Focused Energy and Xcimer Energy to come up with concepts for a pilot power plant, and the companies will need to meet various milestones in order to be paid. The approach is similar to how NASA set up its contracts with Elon Musk’s SpaceX for the development of the Falcon 9 rocket and the Dragon capsule.
Marvel Fusion has announced a public-private partnership with Colorado State University that will serve as a test bed for the company’s fusion development.
Marvel will provide two lasers, which will cost $50 million; the university will build surrounding infrastructure for $100 million.
“We’re building exactly those lasers for the Colorado facility — ultrashort pulse, ultrahigh intensity — that can drive this particular concept,” said Moritz von der Linden, the chief executive of Marvel.
The facility, added to the university’s laser center, will be available for other researchers as well.
For now, the competitors are largely rooting for each other.
“I don’t think these fusion approaches are competition,” said Todd Ditmire, a physics professor at the University of Texas at Austin who co-founded Focused Energy. “I hope we all get it to work. There’s enough energy demand to go around.”