Scientists have come tantalizingly close to reproducing the sun’s power — albeit only in a fraction of a second in a hydrogen atom.
Researchers at Lawrence Livermore National Laboratory reported Tuesday that by using 192 giant lasers to destroy a hydrogen grain, they were able to ignite a burst of more than 10 quadrillion watts of fusion power — energy released when hydrogen atoms are fused together into helium, the same process that takes place in stars.
Mark Herrmann, Livermore’s deputy program director for fundamental weapons physics, compared the fusion reaction to the 170 quadrillion watts of sunshine bathing the Earth’s surface.
“This is about 10 percent of that,” said Dr. Herrmann. And all the fusion energy emanated from a hot spot about the width of a human hair, he said.
But the eruption — essentially a miniature hydrogen bomb — lasted just 100 trillionths of a second.
Yet that sparked a burst of optimism for fusion scientists who have long hoped that fusion could one day provide a limitless, clean source of energy for humanity.
“I’m very excited about this,” said Siegfried Glenzer, a scientist at the SLAC National Accelerator Laboratory in Menlo Park, Calif., who had led the first fusion experiments at the Livermore facility years ago, but is not currently involved in the process. the Research. “This is very promising for us, to realize an energy source on Earth that does not emit CO2.”
Its success also marked a moment of redemption for Livermore’s football stadium-sized laser device called the National Ignition Facility, or NIF. Despite a multi-billion dollar investment—construction began in 1997 and operations began in 2009—the unit barely produced any fusion at first. In 2014, Livermore scientists finally reported success, but the energy produced at the time was minuscule — the equivalent of what a 60-watt light bulb consumes in five minutes.
On August 8, the burst of energy was much greater — 70 percent as much as the energy of laser light hitting the hydrogen target. That is still a loss-making proposition as an energy source, which consumes more power than it produces. But scientists are confident that further jumps in energy output were possible by refining the experiment.
dr. Herrmann said Livermore scientists would normally only talk after a scientific paper detailing the findings was published. But these findings “spread like wildfire,” he said, “and so we thought it would be better to get some facts out now.”
Stephen Bodner, a retired plasma physicist who has long been a critic of NIF, offered congratulations. “I’m surprised,” he said. “They’ve come close enough to their goal of ignition and breakeven to call it a success.”
Promisingly, for the first time, the fusion reactions appeared to be self-sufficient, meaning that the deluge of particles pouring out from the hot spot in the center heated the pellet to the surrounding hydrogen atoms and caused them to fuse together as well.
Riccardo Betti, chief scientist at the University of Rochester’s laser energy lab, gave an analogy to how a car engine works. “You deliver energy in a very small fraction of the fuel through a spark in the spark plug, and then that energy is amplified by the combustion of the fuel,” he said. “So the same thing happened in the Livermore experiment.”
dr. Herrmann was more cautious, noting that the results fell short of the definition set out in a 1997 report by the National Academy of Sciences that the fusion energy produced should be the amount of energy delivered to the hydrogen by the lasers. exceed. “We are on the threshold,” he said.
The Livermore scientists said they needed to analyze their results more carefully before making more detailed claims.
dr. However, Glenzer said he was confident the merger had spread. The fusion reactions produced a deluge of subatomic particles known as neutrons — more than instruments could count.
“The data is pretty clear,” said Dr. glenzer.
The improved fusion results also help the National Ignition Facility fulfill its primary use – to verify that nuclear weapons are working. After the United States suspended underground nuclear testing in 1992, lab officials argued that a way was needed to verify the computer models that replaced the testing.
dr. Herrmann said that within 24 hours of the last experiment, someone working on the nuclear weapons modernization program contacted the NIF team. “They’re interested in applying this to important questions they have,” he said.
The center of the National Ignition Facility is the target chamber, a 10-foot-wide metal sphere with shiny diagnostic equipment radiating outward.
The laser complex fills a building with a footprint equal to three football fields. Each explosion begins with a small laser pulse split into 192 beams via partially reflecting mirrors, then bounced back and forth by laser amplifiers before converging on a gold cylinder about the size and shape of a pencil eraser.
The laser beams enter at the top and bottom of the cylinder and vaporize it. That generates an internal attack of X-rays that compresses a BB-sized fuel pellet of carefully frozen deuterium and tritium, the heavier forms of hydrogen. In a short moment the imploding atoms melt together.
Since the first promising results in 2014, the NIF scientists have been tinkering with the design of the experiment. The capsules containing the hydrogen are now made of diamond instead of plastic — not because diamond is stronger, but because it absorbs X-rays more easily. The scientists modified the design of the gold cylinder and laser pulse to minimize instabilities.
The scientists now also have better diagnostic tools.
After years of only modest improvements, the combinations of adjustments began to pay off, and the calculations indicated that the August 8 shot could triple what NIF had produced in the spring. Instead, the profit was a factor of eight, much more than had been predicted.
“I think everyone was surprised,” said Dr. Herrmann. Part of the current analysis is figuring out which changes have worked so well.
NIF itself cannot serve as a blueprint for a future power plant. The lasers are inefficient and can only fire once a day. A laser fusion plant would have to vaporize hydrogen pellets at a rate of several per second.
dr. Glenzer said SLAC was working on a laser system that would run at a lower power but fire much faster. He said he hoped fusion, which has been eclipsed by solar and other energy technologies in recent years, would regain importance in efforts to replace fossil fuels.
Federal funding for fusion research is low, even though the Biden administration has placed an emphasis on mitigating climate change.
“Sometimes it happens that you get the best results in the worst year of your funding,” said Dr. glenzer.
Although Dr. Bodner prefers an alternative approach to the one in the current experiment, he said the NIF result pointed to a path forward.
“It shows the skeptic that there is nothing fundamentally wrong with the laser fusion concept,” he said. “It is time for the US to move forward with a large-scale laser fusion energy program.”
Lasers are not the only approach aimed at harnessing fusion for future power plants.
Scientists have also used doughnut-shaped reactors called tokamaks, which use magnetic fields to trap and compress the hydrogen fuel. In the late 1990s, the Joint European Torus experiment in England was able to generate 16 million watts of fusion power for a brief moment, about 70 percent of the way to produce as much power as it consumed. An international project called ITER is now building a larger tokamak reactor in France, which is expected to run by 2025.