How a laser fusion experiment sparked an energy explosion of optimism

Scientists have come very close to replicating the power of the sun, but only in a grain of hydrogen for a fraction of a second. Resear...


Scientists have come very close to replicating the power of the sun, but only in a grain of hydrogen for a fraction of a second.

Researchers at Lawrence Livermore National Laboratory reported Tuesday that using 192 gigantic lasers to annihilate a hydrogen pellet, they were able to set off an explosion of more than 10 quadrillion watts of fusion power – the energy released when atoms of hydrogen are fused into helium, the same process that occurs in stars.

Indeed, Mark Herrmann, deputy director of the Livermore Program for Fundamental Weapons Physics, compared the fusion reaction to the 170 quadrillion watts of sunlight bathing the Earth’s surface.

“It’s about 10 percent of that,” Dr. Herrmann said. And all the fusion energy was emanating from a hot spot about as large as a human hair, he said.

But the explosion – essentially a miniature hydrogen bomb – only lasted 100 trillion seconds.

Still, it sparked renewed optimism for fusion scientists who have long hoped that fusion could one day provide a clean and unlimited source of energy for humanity.

“I’m very excited about this,” said Siegfried Glenzer, a scientist at the National SLAC Accelerator Laboratory in Menlo Park, Calif., And who led the first fusion experiments at the Livermore facility years ago, but is not currently involved in the research. “It’s very promising for us to achieve an energy source on the planet that will not emit CO2.

The success also meant a moment of redemption for Livermore’s football stadium-sized laser device, which is named the National Ignition Facility, or NIF Despite an investment of billions of dollars – construction began in 1997 and operations began in 2009 – the device initially generated virtually no merger. In 2014, scientists from Livermore finally signaled success, but the energy produced at the time was tiny – the equivalent of what a 60-watt bulb consumes in five minutes.

On August 8, the energy explosion was much larger – 70% as much as the energy of the laser light hitting the hydrogen target. It is always a losing proposition as an energy source, consuming more energy than it produces. But scientists are convinced that further leaps in energy production were possible with fine tuning of the experiment.

Dr Herrmann said scientists at Livermore would not normally speak until the publication of a scientific paper describing the results. But these findings “have spread like wildfire,” he said, “and so we thought it would be better to release some facts now.”

Stephen Bodner, a retired plasma physicist who has long criticized the NIF, offered his congratulations. “I’m surprised,” he said. “They have come close enough to their goal of ignition and profitability to call it a success.”

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

Riccardo Betti, chief scientist at the University of Rochester Laser Energy Laboratory, gave an analogy to how an automobile engine works. “You provide energy in a very small fraction of the fuel via 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 by a report from the National Academy of Sciences in 1997, that the fusion energy produced must exceed the amount of energy delivered by the hydrogen lasers. “We are on the threshold,” he said.

Scientists at Livermore said they needed to analyze their results more carefully before making more detailed statements.

Dr Glenzer, however, said he was sure the fusion had spread. The fusion reactions produced a torrent of subatomic particles known as neutrons – more than the instruments could count.

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

The improved fusion results also help the National Ignition Facility fulfill its primary purpose – to verify that nuclear weapons are working. After the United States suspension of underground nuclear tests in 1992, laboratory officials argued that some way was needed to verify the computer models that replaced the tests.

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

The focus of the National Ignition Facility is the Target Chamber, a 33-foot-wide metallic 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 that is split via partially reflecting mirrors into 192 beams, then bounces back and forth through laser amplifiers before converging on a gold cylinder the size and shape of an eraser. pencil.

The laser beams penetrate the top and bottom of the cylinder, vaporizing it. This generates an inward x-ray attack that squeezes a BB-sized fuel pellet of carefully frozen deuterium and tritium, the heavier forms of hydrogen. In a brief instant, the imploding atoms merge.

Since the first promising results of 2014, NIF scientists have been tinkering with the setup of the experiment. The hydrogen-containing capsules are now made of diamond instead of plastic – not because diamond is stronger, but because it absorbs x-rays more easily. Scientists have adjusted the design of the golden cylinder and of the laser pulse to minimize instabilities.

Scientists now also have better diagnostic tools.

After years of modest improvements, the combinations of modifications began to pay off, and calculations indicated that the August 8 firing could triple what NIF produced in the spring. Instead, the payoff was a factor of eight, far more than expected.

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

The TIN itself cannot serve as a model for a future power plant. His lasers are ineffective and he can only fire about once a day. A laser fusion power plant would need 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 levels but fire much faster. He said he hoped fusion, eclipsed in recent years by solar power and other energy technologies, would once again gain prominence in efforts to replace fossil fuels.

Federal funding for fusion research is low, even though the Biden administration has focused on reducing climate change.

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

Although Dr Bodner prefers an alternative approach to that of the current experiment, he said the NIF result points to a way forward.

“It shows skeptics that there is nothing fundamentally wrong with the concept of laser fusion,” he said. “It is time for the United States to move forward with a major laser fusion energy program.”

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

Scientists have also used donut-shaped reactors called tokamaks which use magnetic fields to contain and compress hydrogen fuel. In the late 1990s, the Joint European Torus experiment in England was able to generate 16 million watts of fusion energy for a brief moment, about 70% of the way to produce as much energy as it consumed. . An international project called ITER is currently building a larger tokamak reactor in France, scheduled for commissioning in 2025.

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Newsrust - US Top News: How a laser fusion experiment sparked an energy explosion of optimism
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