Nuclear Fusion Lab Achieves ‘Ignition’: What Does It Mean?

Source: Scientific American
By Jeff Tollefson, Elizabeth Gibney, Nature magazine on December 13, 2022

Fusion researchers at the U.S. National Ignition Facility created a reaction that made more energy than they put in

Scientists at the world’s largest nuclear-fusion facility have achieved the phenomenon known as ignition—creating a nuclear reaction that generates more energy than it consumes. Results of the breakthrough at the US National Ignition Facility (NIF), conducted on 5 December and announced today by US President Joe Biden’s administration, has excited the global fusion-research community. That research aims to harness nuclear fusion—the phenomenon that powers the Sun—to provide a source of near-limitless clean energy on Earth.

“It’s an incredible accomplishment,” says Mark Herrmann, the deputy director for fundamental weapons physics at Lawrence Livermore National Laboratory in California, which houses the fusion laboratory. The landmark experiment follows years of work by multiple teams on everything from lasers and optics to targets and computer models, Herrmann says. “That is of course what we are celebrating.”

A flagship experimental facility of the US Department of Energy’s nuclear-weapons programme that was designed to study reactions created by such weapons, NIF originally aimed to achieve ignition by 2012 and has faced criticism for delays and cost overruns. In August 2021, NIF scientists announced that they had used their high-powered laser device to achieve a record reaction that crossed a critical threshold on the path to ignition, but efforts to replicate that experiment, or shot, in the following months fell short. Ultimately, scientists scrapped efforts to replicate that shot and rethink the experimental design—an effort that paid off last week.

“There were a lot of people who didn’t think it was possible, but I and others who kept the faith feel somewhat vindicated,” says Michael Campbell, former director of the fusion laboratory at the University of Rochester in New York and an early proponent of NIF while at Lawrence Livermore lab. “I’m having a cosmo to celebrate.”

Nature looks at NIF’s latest experiment and what it means for fusion science.

WHAT DID NIF ACHIEVE?

The facility used its set of 192 lasers to deliver 2.05 megajoules of energy onto a pea-sized gold cylinder containing a frozen pellet of the hydrogen isotopes deuterium and tritium. The pulse of energy caused the capsule to collapse, creating temperatures only seen in stars and thermonuclear weapons, and the hydrogen isotopes fused into helium, releasing additional energy and creating a cascade of fusion reactions. The laboratory’s analysis suggests that some 3.15 megajoules of energy was released—roughly 54% more than the energy that went into the reaction and more than double the previous record of 1.3 megajoules.

“Fusion research has been going on since the early 50s, and this is the first time in the laboratory that fusion has ever produced more energy than it consumed,” says Campbell.

The experiment safely qualifies as ignition, a benchmark measure for fusion reactions that focuses on how much energy went into the target compared to how much energy was released. However, while the fusion reactions may have produced more than 3 megajoules of energy—more than was delivered to the target—NIF’s 192 lasers consumed 322 megajoules of energy in the process.

“It’s a big milestone, but NIF is not a fusion-energy device,” says Dave Hammer, a nuclear engineer at Cornell University in Ithaca, New York.

Herrmann acknowledges as much, saying that there are many steps on the path to laser fusion energy. “NIF was not designed to be efficient,” he says. “It was designed to be the biggest laser we could possibly build to give us the data we need for the [nuclear] stockpile research programme.”

To achieve ignition, NIF scientists made multiple changes before the latest laser shot, based in part on analysis and computer modelling of the experiments conducted last year. In addition to boosting the laser power by around 8%, scientists created a new target with fewer imperfections and adjusted how the laser energy was delivered onto the target in order to create a more spherical implosion. Scientists knew they were operating at the cusp of fusion ignition, and in that regime, Herrmann says, “little changes can make a big difference.”

Dec 13, 2022
NNSA Deputy Administrator for Defense Programs Dr. Marvin “Marv” Adams, and LLNL Director Dr. Kim Budil explain the fusion energy breakthrough announced in Dec. 2022.

Credit: US Department of Energy

Another point of view focusing on the why now:

A thorough analysis by Nassim Haramein of the Resonance Science Foundation…highly recommended to give it a read!