Laser Fusion Experiment Delivers An Energetic Burst of Optimism


Scientists have come encouragingly close to reproducing the power of the sun – albeit with just a speck of hydrogen for just a fraction of a second.

Researchers at Lawrence Livermore National Laboratory reported Tuesday that they were able to ignite bursts of fusion power of more than 10 quadrillion watts by using 192 gigantic lasers to destroy a pellet of hydrogen. the same process that occurs in stars.

Indeed, Livermore’s assistant program director for basic weapons physics, Mark Herrmann, likened the fusion reaction to 170 quadrillion watts of sunlight covering the Earth’s surface.

Dr. “About 10 percent of that,” Herrmann said. And all of the fusion energy emanates from a hot spot as wide as a human hair, he said.

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

Still, this sparked an explosion of optimism for fusion scientists, who had long hoped that fusion could one day provide an unlimited, 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, California, who led the first fusion experiments at the Livermore facility years ago but is not currently involved in this experiment. Research. “This is very promising for us to have a CO2-free energy source on the planet.”

The success also marked a moment of salvation for Livermore’s football stadium-sized laser device called the National Ignition Facility, or NIF. almost no fusion. Livermore scientists in 2014 finally reported success, but then the energy produced was very small – the equivalent of a 60-watt light bulb consuming in five minutes.

On August 8, the burst of energy was much larger – as much as 70 percent of the energy of the laser light hitting the hydrogen target. This is still a lost proposition as an energy source that consumes more power than it produces. But the scientists are confident that further jumps in energy output are possible by fine-tuning the experiment.

Dr. Normally, Livermore scientists wouldn’t speak until a scientific paper is published explaining the findings, Herrmann said. But these findings are “spreading like wildfire,” he said, “so we thought it would be better to get some facts out now.”

Stephen Bodner, a retired plasma physicist who has long been critical of the NIF, offered his congratulations. “I was surprised,” he said. “They got close enough to their firing and head-to-head target to call it a success.”

More promisingly, fusion reactions seemed to be self-sustaining for the first time, meaning that a flood of particles flowing out from the central hot spot heats the hydrogen atoms surrounding the pellet, causing them to fuse as well.

Riccardo Betti, chief scientist at the University of Rochester Laser Energy Laboratory, made an analogy of how a car engine works. “You energize 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 by the following. 1997 National Academy of Sciences reportthat the fusion energy produced must exceed the amount of energy delivered to the hydrogen by the lasers. “We are on the threshold,” he said.

Livermore said the scientists should analyze their results more carefully before making more detailed claims.

However, Dr. Glenzer said he was confident the fusion was spreading. The fusion reactions produced a flood of subatomic particles known as neutrons, more numerous than instruments could count.

“The data are pretty clear,” said Dr. Glenzer.

The improved fusion results also help the National Ignition Facility realize its primary use – to verify the operation of nuclear weapons. after the United States Underground nuclear test suspended in 1992Lab officials argued that a way was needed to validate the computer models that replaced the test.

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 the important questions they have,” he said.

The centerpiece of the National Ignition Facility is the target chamber, a 33-foot-wide metal sphere with gleaming diagnostic equipment radiating outward.

The laser complex fills a building the size of three football fields. Each blast begins with a small laser pulse that is partially split into 192 beams through reflective mirrors, then bounces back and forth through laser amplifiers before merging on a gold cylinder that is about the size and shape of a pencil eraser.

Laser beams enter from the top and bottom of the cylinder and vaporize the cylinder. This creates an inward attack of X-rays that compresses a BB-size fuel pellet of carefully frozen deuterium and tritium, the heavier forms of hydrogen. In a short time, the inwardly exploding atoms fuse together.

Since the first promising 2014 results, NIF scientists have been grappling with setting up 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. The scientists adjusted the design of the gold cylinder and the laser pulse to minimize instabilities.

Scientists now have better diagnostic tools, too.

After years of only modest improvements, the modification combinations began to bear fruit, and calculations showed that the 8 August shot could triple what NIF produced in the spring. Instead, the gain was eight times more than predicted.

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

NIF cannot serve as a blueprint for a future power plant. Their lasers are inefficient and can fire only once a day. A laser fusion plant needs to vaporize hydrogen pellets at a rate of a few seconds per second.

Dr. Glenzer said the SLAC is working on a laser system that will operate at lower power levels but fire much faster. He said he hopes fusion, which has been overshadowed by solar and other energy technologies in recent years, will regain importance in efforts to replace fossil fuels.

Federal funding for fusion research is low, even as the Biden administration has emphasized climate change mitigation.

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

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

“This shows skeptics that there is nothing fundamentally wrong with the laser fusion concept,” he said. “The time has come for the US to move forward with a major laser fusion energy program.”

Lasers are not the only approach aimed at leveraging fusion for future power plants.

Scientists have also used annular reactors called tokamaks, which use magnetic fields to trap and compress hydrogen fuel. In the late 1990s, the Common European Torus experiment in the UK was able to generate 16 million watts of fusion power for a short time and went about 70 percent of the way to producing as much power as it consumed. An international project called ITER it is now building a larger tokamak reactor in France, which is scheduled to start operating in 2025.



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