Reports from the Heart of the Machine
Editors: Du Wei, Zenan
Through the world's largest laser, the researchers induced fusion fuels to output more energy than they would input heat for the first time, realizing a phenomenon called plasma burning.
With 192 laser beams and temperatures more than three times higher than the center of the sun, scientists have reached a key milestone on the long road to an almost pollution-free fusion energy source, at least in a fraction of a second.
Today, a study by researchers at the National Ignition Facility at lawrence Livermore National Laboratory in California appeared on the cover of the latest issue of The Nature. The researchers succeeded in triggering a fusion reaction that lasted a short time, a major feat because fusion requires very high temperatures and pressures and can easily be extinguished.
The ultimate goal of this research is to generate electricity in the same way that the sun generates heat, by crushing hydrogen atoms and bringing them closer to each other, and then generating helium to release large amounts of energy. But since the theory was proposed, the distance between people and this goal has been "years away".
A team of more than 100 people published the results of four experiments in the paper "Burning Plasma achieved in inertial fusion" and demonstrated their achievements – burning plasma. With these results, along with preliminary results from the tracking experiment released in August 2021, the researchers say they are on the verge of an even bigger advance — ignition. At that point, the fuel can continue to "burn" on its own and will also produce more energy than is needed to stimulate the initial reaction.
Alex Zylstra, an experimental physicist at Lawrence Livermore National Laboratory, said, "We are very close to achieving our next goal."
Nuclear fusion presses together two kinds of hydrogen (deuterium and tritium, two isotopes or forms of hydrogen) in a water molecule. When they fused, Carolyn Kuranz, an experimental plasma physicist at the University of Michigan who was not involved in the study, said, "Small amounts (milligrams) of fuel produce a lot of energy and are so 'clean' that they do not generate radioactive waste." It's basically unlimited clean energy and can be deployed anywhere."
Research review
Researchers around the world have been working on this research for decades, trying different approaches. Of those, 35 countries in southern France collaborated on a project called the International Thermonuclear Experimental Reactor, which uses huge magnetic materials to control overheated plasma. The project is expected to be operational in 2026.
Steven Cowley, director of the Princeton Plasma Physics Laboratory, who was also not involved in the study, said early experiments in the United States and the United Kingdom successfully fused atoms but did not achieve self-heating.
NIF Target Bay at the National Ignition Unit at Lawrence Livermore National Laboratory. The system uses 192 laser beams to converge in the center of a giant sphere, implosing a tiny hydrogen fuel pellet. Image credit: Lawrence Livermore National Laboratory
But now we cannot expect nuclear fusion to be practical. Omar Hurricane, lead scientist at Rens livermore National Laboratory, said, "Scientifically, we are very excited about these results. But we are still a long way from achieving useful energy. Maybe it will take decades."
U.S. National Ignition Unit (NIF).
Technical overview
Obtaining combustion plasma is a critical step in achieving self-sustaining fusion energy. A combustion plasma is a type of plasma, where the fusion reaction itself is the main source of heating in the plasma, is necessary for maintaining and propagating combustion, and can achieve high energy gains.
After decades of fusion studies, researchers achieved a state of burning plasma in the lab, where a laser device can deliver pulsed energy of up to 1.9 megajoules and peak power of up to 500 terawatts in fuel capsules. They used laser light to generate X-rays in the radiation chamber, which then indirectly drove the fuel capsule through X-ray ablation pressure, allowing the implosion process to compress and heat the fuel through mechanical work.
These experiments showed that fusion self-heating exceeded the mechanical power of injecting implosion, satisfying several indicators of burning plasma. In addition, the researchers describe a subset of experiments that appear to have crossed static self-heating boundaries, in which fusion heating exceeds the energy loss of radiation and conduction. These results provide an opportunity to study plasma and combustion plasma physics, which are dominated by α particles, in the laboratory.
Evaluate simple indicators of burning plasma.
Researchers have spent years in the lab, and many attempts have failed. They made adjustments: the fuel capsule was increased by 10 percent.
The fuel capsule is packed in a tiny gold metal cylinder that the researchers aimed at 192 lasers. The researchers heated it to 100 million degrees, creating pressure inside the fuel capsule that is about 50 percent higher than inside the sun's center. Alex Zylstra said the experiments created a combustion plasma that lasted only one part per trillion, but that was enough to be considered successful.
Schematic diagram of an indirectly driven inertial constraint method for fusion.
Overall, the four experiments in the study (november 2020 and February 2021, respectively) produced 0.17 megajoules of energy, far more than previous attempts, but still less than one-tenth of the energy used to start the process. For comparison, an energy of one megajoule can heat about an gallon (about 3.8 liters) of water to 100 degrees Fahrenheit (about 37.8 degrees Celsius).
The parameter space associated with approaching ignition.
Based on previous information, preliminary results from experiments conducted later in 2021 are still being reviewed by other scientists, when the researchers' energy output reached 1.3 megajoules and lasted for 100 trillionths of a second. But even then, that's below the 1.9 megajoules needed to break even.
Reference Links:
https://phys.org/news/2022-01-hot-lab-milestone-road-fusion.html
https://www.reuters.com/business/energy/researchers-achieve-milestone-path-toward-nuclear-fusion-energy-2022-01-26/