The Nuclear Fusion Lab Achieves “Ignition,” What Does That Mean?

Scientists at the world’s largest nuclear fusion facility have investigated for the first time the phenomenon known as flare-up – creating a nuclear reaction that generates more energy than it consumes. The results of the breakthrough at the US National Ignition Facility (NIF), conducted on December 5 and announced today by US President Joe Biden’s administration, have excited the global fusion research community. This research aims to harness nuclear fusion – a solar-powered phenomenon – to provide a clean, near-infinite energy source on Earth. The researchers caution that despite recent success, there is still a long way to go to achieve this goal.

“It’s an amazing achievement,” says Mark Hermann, deputy director of fundamental weapons physics at Lawrence Livermore National Laboratory in California, which houses the fusion lab. The landmark trial comes after 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 celebrate.”

A flagship experimental facility for the U.S. Department of Energy’s nuclear weapons program designed to study thermonuclear explosions, 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-energy laser device to achieve a record reaction that crossed a critical threshold on the ignition path, but efforts to replicate that experiment, or shot, in the following months were unsuccessful. Ultimately, the scientists scrapped efforts to replicate that shot and rethought the experimental design—an effort that paid off last week.

said Michael Campbell, former director of the fusion lab at the University of Rochester in New York and an early proponent of NIF while in Lawrence Livermore’s lab. “I have Cosmo to celebrate.”

nature It takes a look at the latest NIF experience and what it means for fusion science.

What did NIF achieve?

The facility used its array of 192 lasers to deliver 2.05 megajoules of energy to a pea-sized golden cylinder containing frozen grains of the hydrogen isotopes deuterium and tritium. The energy pulse causes the capsule to collapse, creating temperatures only seen in stars and thermonuclear weapons, and hydrogen isotopes fused into helium, releasing additional energy and creating a chain reaction of fusion. Lab analysis indicates that the reaction released about 3.15 megajoules of energy — nearly 54% more energy than went into the reaction, and more than double the previous record of 1.3 megajoules.

“Fusion research has been going on since the early 1950s, and this is the first time in a laboratory that fusion has produced more energy than it consumed,” says Campbell.

However, while the fusion reactions may have produced more than 3 megajoules of energy—more than was delivered to the target—the 192-megajoule NIF laser consumed 322 megajoules of energy in the process. However, the experiment qualifies as an ignition, which is a standard measure of fusion reactions that focuses on how much energy was pumped into the target compared to how much energy was released.

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

Herrmann acknowledges this, saying there are many more steps on the way to laser fusion power. “NIF was not designed to be effective,” he says. “It’s designed to be the largest laser we can build to give us the data we need to [nuclear] Inventory Research Program”.

To achieve the ignition, the NIF scientists made multiple changes before the latest laser shot, based in part on analysis and computer modeling of experiments conducted last year. In addition to increasing the laser power by about 8%, the scientists created a target with fewer defects and modified how the laser power was delivered to create a more spherical implosion. The scientists knew they were working on the cusp of fusion ignition, and in that system, Herrmann says, “small changes can make a big difference.”

Why are these results important?

On one level, it’s about proving what’s possible, and on that front many scientists have hailed the result as a milestone in fusion science. But the findings hold special significance at NIF: The facility is designed to help nuclear weapons scientists study the extreme heat and pressures in explosions, and that’s only possible if the facility produces high-throughput fusion reactions.

It took more than a decade, “but they can be applauded for reaching their goal,” says Stephen Bodner, a physicist who previously headed the laser fusion program at the US Naval Research Laboratory in Washington, D.C. The big question now, Bodner says, is what the Energy Department will do next: Double down on weapons research at NIF or focus on a laser program geared toward fusion energy research.

What does this mean for fusion energy?

Recent findings have already renewed buzz about a future powered by clean fusion energy, but experts warn there is a long way to go.

NIF was not designed with commercial fusion energy in mind — and many researchers suspect that laser-driven fusion will be the approach that ultimately yields fusion energy. But Campbell believes his latest success could boost confidence in the promise of laser fusion power and open the door to a program focused on energy applications. “This is absolutely necessary to gain credibility to sell an energy program,” he says.

Kim Podell, director of the Lawrence Livermore Laboratory, called the achievement a proof of concept. “I don’t want to give you a feeling that we’re going to plug NIF into the network: That’s definitely not how this works,” she said during a press conference in Washington, D.C. “But this is the basic building block of the inertial fusion energy scheme.”

There are many other fusion experiments around the world that are trying to achieve fusion for energy applications using different approaches. But engineering challenges remain, including designing and building plants that can extract the heat from fusion and use it to generate large amounts of energy that can be converted into usable electricity.

“Despite the positive news, this result is still a long way from realizing the actual energy gains needed to produce electricity,” Tony Rolston, a nuclear energy researcher at the University of Cambridge, UK, said in a statement to the Science Media Centre. .

However, says Ann White, a plasma physicist at the Massachusetts Institute of Technology in Cambridge, “NIF experiments that focus on fusion energy are certainly valuable on the path to commercial fusion energy.”

What are the next major stages in a merger?

To prove that the type of fusion studied at NIF can be a viable method for energy production, the yield efficiency — the energy released compared to the energy that goes into producing the laser pulses — needs to grow by at least two-fold. .

Researchers will also need to dramatically increase the rate at which the laser produces pulses and how quickly they can clean the target chamber to prepare it for another burn, says Tim Loos, chief of science and operations for the International Nuclear Fusion Project ITER, which is under construction in Saint-Paul-les-Durance, France. .

“Sufficient events to produce fusion energy in repeated performance will be an important milestone,” White says.

The US$22 billion ITER project — a collaboration between China, the European Union, India, Japan, Korea, Russia and the United States — aims to achieve self-sustaining fusion, meaning the energy from fusion produces more fusion, through a different method. A technique from the NIF “inertial confinement” approach. ITER would keep the deuterium-tritium plasma confined in an annular vacuum chamber, or tokamak, and heat it until the nuclei fused. When it begins to do so in 2035, it aims to reach a “burn-out” stage, Luce explains, “where self-heating energy is the dominant source of heating.” This self-fusion is the key to producing more energy than is put in.

What does that mean for other fusion experiments?

NIF and ITER are two fusion technology concepts among the many that are being pursued around the world. Methods include magnetic confinement of plasma – used by tokamak and stars – inertial confinement, used by NIF, and hybrid.

The technology required to generate electricity from fusion is largely independent of the concept, White says, and the latest breakthrough wouldn’t necessarily lead researchers to abandon or standardize the concepts.

The engineering challenges NIF faces are different from those of ITER and other facilities. But a symbolic achievement could have far-reaching implications. “A result like this will bring increased interest in advancing all types of fusion, so it should have a positive impact on fusion research in general,” says Luce.

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