September 25, 2022

Scientists have come temptingly close to reproducing the power of the sun – if only in a hydrogen speck for a split second.

Researchers at Lawrence Livermore National Laboratory reported Tuesday that by using 192 gigantic lasers to destroy a hydrogen pellet, they were able to ignite an explosion of more than 10 trillion watts of fusion power – energy released when hydrogen atoms are fused into helium – the same process, that expires within stars.

In fact, Mark Herrmann, Livermore’s assistant program director for basic weapon physics, compared the fusion reaction to the 170 quadrillion watts of sunshine bathing the earth’s surface.

“That’s about 10 percent of that,” said Dr. Herrmann. And all of the fusion energy came from a hotspot about the width of a human hair, he said.

But the eruption – essentially a miniature hydrogen bomb – lasted only 100 trillionths of a second.

Still, it sparked a burst of optimism among 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 it,” said Siegfried Glenzer, a scientist at the SLAC National Accelerator Laboratory in Menlo Park, California, who led the first fusion experiments at the Livermore facility years ago but is not currently doing research. “This is very promising for us to achieve an energy source on the planet that does not emit CO2.”

The success also meant a moment of redemption for Livermore’s football stadium-sized laser device known as the National Ignition Facility, or NIF, hardly a merger. In 2014, Livermore scientists finally reported a success, but the energy produced at the time was tiny – the equivalent of what a 60-watt lightbulb uses in five minutes.

On August 8, the burst of energy was much larger – 70 percent as much as the energy of the laser light hitting the hydrogen target. This is still a losing business as an energy source that uses more electricity than it produces. However, the scientists are confident that further jumps in energy output were possible with the fine-tuning of the experiment.

Dr. Herrmann said that Livermore scientists would not normally speak until a scientific paper was published describing the results. But those results “have spread like wildfire,” he said, “so we thought it would be better to get some facts out now.”

Stephen Bodner, a retired plasma physicist and longstanding NIF critic, congratulated. “I’m surprised,” he said. “They got close enough to their ignition and breakeven point goal to be called a success.”

More promising for the first time, the fusion reactions appeared to be self-sustaining, meaning that the stream of particles streaming out from the hot spot in the center of the pellet heated the surrounding hydrogen atoms and caused them to fuse as well.

Riccardo Betti, senior scientist at the University of Rochester’s Laser Energy Laboratory, gave an analogy to how a car engine works. “They provide energy in a very small fraction of the fuel through a spark in the spark plug, and that energy is then amplified as the fuel burns,” he said. “So the same thing happened with the Livermore experiment.”

Dr. Herrmann was more prudent, finding that the results fell short of the definition of a 1997 report by the National Academy of Sciences that the fusion energy produced must exceed the amount of energy given off by the lasers to the hydrogen. “We’re on the threshold,” he said.

The Livermore scientists said they needed to analyze their results more carefully before they could make more detailed claims.

Dr. However, Glenzer said he was certain the merger had spread. The fusion reactions created a deluge of subatomic particles known as neutrons – more than instruments can count.

“The data is pretty obvious,” said Dr. Glenzer.

The improved fusion results are also helping the National Ignition Facility fulfill its primary purpose – to verify that nuclear weapons are working. After the United States suspended underground nuclear tests in 1992, laboratory officials argued that a method was needed to validate the computer models that the tests were replacing.

Dr. Herrmann said that within 24 hours of the latest experiment, someone working on the nuclear weapons modernization program contacted the NIF team. “They are interested in applying this to important questions that they have,” he said.

The center of the National Ignition Facility is the target chamber, a 10 meter wide metal ball with outwardly radiating diagnostic equipment.

The laser complex fills a building the size of three soccer fields. Each explosion begins with a small laser pulse, which is split into 192 beams by partially reflecting mirrors and then reflected back and forth by laser amplifiers before converging on a gold cylinder about the size and shape of an eraser.

The laser beams enter the cylinder at the top and bottom and vaporize it. This creates an inward rush of x-rays that compress a BB-sized fuel pellet made from carefully frozen deuterium and tritium, the heavier forms of hydrogen. In a brief moment, the imploding atoms fuse together.

Since the first promising results in 2014, the NIF scientists have tinkered with the structure 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 better. The scientists adapted the design of the gold cylinder and the laser pulse to minimize instabilities.

Scientists now also have better diagnostic tools.

After years of only modest improvements, the combinations of modifications began to pay off, and the calculations suggested the August 8th shot could triple what NIF had produced in the spring. Instead, the profit was a factor of eight, far more than predicted.

“I think everyone was surprised,” said Dr. Herrmann. Part of the current analysis is figuring out which changes worked so well.

NIF itself cannot serve as a blueprint for a future power plant. His lasers are inefficient and he can only fire about once a day. A laser fusion power 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 operate at lower power but fire much faster. He hoped the merger, overshadowed 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 if the Biden government has placed emphasis on reducing climate change.

“Sometimes it happens that you get the best results in the worst year of your funding,” said Dr. Glenzer.

Although Dr. Bodner preferred an alternative approach to that in the current experiment, he said that the NIF result shows a way forward.

“It shows the skeptic that there is basically nothing wrong with the concept of laser fusion,” he said. “It is time the US moved forward with a major laser fusion energy program.”

Lasers are not the only approach to making fusion usable for future power plants.

Scientists have also used donut-shaped reactors called tokamaks, which use magnetic fields to trap and compress the hydrogen fuel. At the end of the 1990s, the Joint European Torus Experiment in England was able to briefly generate 16 million watts of fusion energy and thus generate around 70 percent of the energy required. An international project called ITER is currently building a larger tokamak reactor in France, which is scheduled to go into operation in 2025.