For the first time in history, scientists at the Lawrence Livermore National Laboratory’s National Ignition Facility, or NIF, achieved a net energy gain through nuclear fusion, a crucial breakthrough in the continuing search for clean energy.
The team, dubbed HYBRID-E, performed an experiment that ignited and released more fusion energy than the laser energy used to drive the system on Dec. 5, said Annie Kritcher, principal designer of the experiment.
“More than 60 years of research and development in lasers, optics, diagnostics, target fabrication, computer modeling and simulation and experimental design culminated in the Dec 5th experiment,” Kritcher said in an email.
The interdisciplinary team included physics, laser and target fabrication teams who combined decades of learning across several fields, Kritcher noted. She added that to enable these fusion reactions, fusion fuel was heated and compressed to more than 100 million degrees until its pressure exceeded twice that at the center of the sun.
According to Daniel Thomas Casey, an experimental physicist at NIF who worked on the project, the team compressed a capsule filled with deuterium and tritium fuel, isotopes of hydrogen. They then fired lasers at the inside of the diamond casing around the capsule, which caused the capsule to implode, Casey added.
“You can take a hot stove filament, heat it up and then turn it off and it’s going to cool down because it’s losing energy through radiation,” Casey said. “It’s the same case here, so you want to get the fusion reactions going really fast so that you can outrun those losses.”
The team did just that, creating 3.6 megajoules of energy, 1.5 more than they put in. He added that the team had been close to this “threshold” for the last 18 months and made significant improvements to how the capsule is manufactured during that time.
Last year on Aug. 8, similar experiments by the team generated 1.35 megajoules of energy, but repeating this proved difficult because of the need for a very optimal target and the necessary laser conditions, among other challenges, Kritcher noted.
“At the highest level, what we really want to do is try to do this again and try to push to even higher and higher gains,” Casey said.
By observing X-rays emitted from neutrons produced in the fusion reaction, the team found that the implosion was asymmetrical on the top and bottom, Casey added. The new work further optimized the target design to produce a more “round” fusion implosion and achieve higher yields, according to Kritcher.
There were further considerations, including making the experimental equipment more resistant to damage and trying to push the input energy up from 1.9 to 2.1 megajoules over the course of the last year, Casey said.
“It wasn’t as symmetric as we could have made it so we made a correction in the recent shot,” Casey said. “We saw that higher laser energy seemed to make the target experiment more robust to imperfections and it’s better when things are as symmetric as possible.”
Casey added that the capsules require the utmost care, as they are smaller than a BB bullet. Even the slightest bump or hole in its wall could jeopardize the experiment, he noted.
Another set of improved capsules have already been made, according to Casey. Casey added that there is a long way to go until nuclear fusion can be utilized as clean energy, but ignition is still a major scientific milestone on the path to fusion energy.
Kritcher said the experiment will be repeated in spring 2023. It will test improved target quality, develop the experimental design further and generate even more fusion energy.
Future energy-generating fusion power plants would require more efficient lasers, higher gain scaled-up designs and extensive technological developments, according to Kritcher.
However, she noted that this is a significant accomplishment that demonstrates that fusion power generation is possible.
Barbara Jacak, a UC Berkeley physics professor, shared similar thoughts.
“It is the proof of principle that we human beings can actually ignite and control a plasma, like a teeny tiny sun,” Jacak said.
“Ignition has been a goal for a long, long time,” Jacak said. “It’s scientifically extremely exciting because one of the things we’ve learned in the last ten years or so is that all the tiny asymmetries can cause issues in the plasma, so having been able to fix that is very important.”