Scientists at the world’s largest nuclear fusion facility, the US National Ignition Facility (NIF), have succeeded in producing a nuclear fusion reaction that generates more energy than it consumes. “This was absolutely necessary for the credibility of a fusion power program.”
Image: The laser preamplifiers at the National Ignition Facility.
The so-called thermonuclear detonation took place on December 5, and on December 13 the US government officially announced the result. The breakthrough has excited the global fusion research community. Nuclear fusion is the phenomenon that powers the sun, and their research aims to use fusion as a source of virtually unlimited clean energy on Earth.
“It’s an incredible achievement,” said Mark Herrmann, deputy director of fundamental weapons physics at Lawrence Livermore National Laboratory in California, where the fusion lab is located. The groundbreaking experiment follows years of work by several teams, with developments ranging from lasers and optics to computer models, Herrmann said. “Of course we celebrate.”
NIF is the flagship of the US Department of Energy’s nuclear weapons program. It was established to study reactions with such weapons. The inflamed response was originally planned to take place as early as 2012, but the center faced criticism for delays and cost overruns. In August 2021, NIF researchers announced that they had used their powerful laser to create a record-breaking response. It passed a critical threshold on its way to ignition, but attempts to repeat that experiment over the following months failed. Eventually, the researchers abandoned efforts to replicate this reaction and changed the design of the experiment — an effort that paid off last week.
“There were many who believed that it was not possible. But we kept our faith that it would work, and we were right,” said Michael Campbell, former director of the fusion lab at the University of Rochester in New York and an early proponent of NIF when he worked at the Lawrence Livermore lab. “I’ll have a drink with that.”
What has NIF achieved?
The facility used its 192 lasers to deliver 2.05 megajoules of energy to a pea-sized gold cylinder containing a frozen flake of the hydrogen isotopes deuterium and tritium. The energy pulse collapsed the capsule, creating temperatures only found in stars and thermonuclear weapons. The hydrogen isotopes fused into helium, releasing additional energy and creating a cascade of fusion reactions. The lab’s analysis shows that about 3.15 megajoules of energy were released – 54% more energy than was put 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 that fusion has produced more energy than it consumes in the laboratory,” Campbell said.
So the experiment falls under the definition of thermonuclear ignition, a measure of fusion reactions that weighs the amount of energy that went into the target against the amount of energy that was released. But while the fusion reactions produced more energy than the input, NIF’s 192 lasers used 322 megajoules of energy in the process.
“It’s a big milestone, but NIF is not a fusion power plant,” said Dave Hammer, a nuclear engineer at Cornell University in Ithaca, New York.
Herrmann also acknowledges this and says there are many steps on the road to laser fusion energy. “NIF is not designed to be efficient,” he says. “It is designed to be the largest possible laser for research for [nucleaire] research program.’
To arrive at the thermonuclear detonation, NIF researchers made several changes to the final laser shot, based in part on analysis and computer modeling of the experiments conducted last year. They increased the laser power by about eight percent and created a new target with fewer imperfections. In addition, they changed the way the laser energy was delivered to the target to create a more spherical implosion. The scientists knew they were on the verge of fusion ignition, and under these circumstances, Herrmann says, “small changes can make a big difference.”
Why are these results important?
On the one hand, it is about proving what is possible. On that front, many scientists have hailed the result as a milestone in fusion science. But the results are particularly important to NIF: the facility is for nuclear weapons researchers to study the intense heat and pressure that occurs in thermonuclear explosions, and this is only possible if the facility produces high-output fusion reactions.
It took more than a decade, “but they achieved their goal,” says Stephen Bodner, a physicist who previously headed the laser fusion program at the US Naval Research Laboratory in Washington DC. According to Bodner, the big question now is what the Ministry of Energy will do: continue weapons research at NIF or switch to a laser program specifically focused on fusion energy research.
What does this mean for fusion energy?
The results have sparked interest in a clean fusion energy future, but experts warn there is still a long way to go.
NIF scientists readily admit that the facility was not designed for commercial fusion power, and many scientists doubt that laser-driven fusion will be the approach that will ultimately deliver fusion power. But Campbell believes the success could increase confidence in laser fusion energy and ultimately open the door to a new program focused on energy applications. “This was absolutely necessary for the credibility of a fusion power program,” he says.
Kim Budil, director of the Lawrence Livermore laboratory, described the achievement as a proof of concept. “I don’t want you to feel that we’re going to connect the NIF to the grid: that’s absolutely not how it works,” she said at a news conference in Washington DC. “But this is the basic building block of an inertial fusion power system.”
There are many other fusion experiments around the world trying to achieve fusion for energy applications using different approaches. But there are still technical challenges. Designing and building plants that convert the heat from fusion into a significant amount of energy, which can in turn be converted into usable electricity, is one of them.
“While this is positive news, this result is still far from the actual energy gains needed to produce electricity,” Tony Roulstone, a nuclear energy researcher at the University of Cambridge, UK, said in a statement to the Science Media Centre.
Still, “the NIF experiments aimed at fusion energy are absolutely valuable on the path to commercial fusion energy,” said Anne White, a plasma physicist at the Massachusetts Institute of Technology in Cambridge.
What are the next big milestones in fusion?
To demonstrate that the type of fusion being investigated at NIF is a viable way to produce energy, the efficiency of the yield – the energy released compared to the energy used to produce the laser pulses – must be increased by at least two orders of magnitude of magnitude.
The speed at which the lasers can produce the pulses needs to be increased, as does the speed at which the target chamber can be evacuated and prepared for another burn, says Time Luce, head of science and operations for the international nuclear fusion project ITER, based in St-Paullez- Durance, France, is under construction.
“Sufficient events that repeatedly produce enough fusion energy will be an important milestone,” Luce says.
The ITER project is a collaboration between China, the EU, India, Japan, Korea, Russia and the USA and costs more than 20 billion euros. It targets self-sustaining fusion: the fusion energy produces fusion again, a different technique than NIF’s inertial fusion approach. ITER traps a plasma of deuterium and tritium in a torus-shaped chamber of magnetic coils, or tokamak, and heats it until the nuclei fuse. When it begins to do so in 2035, the goal is to reach the ‘fire stage’, Luce explains, ‘where the self-heating force is the dominant source of heating’. Such self-sustaining fusion is essential for higher energy output than input.
What does this mean for other fusion experiments?
NIF and ITER are two of many fusion technologies that governments around the world are pursuing. The approaches include magnetic confinement of plasma – in tokamaks and stellarators – and inertial fusion, used by NIF, and a hybrid of the two.
The technology needed to generate electricity from fusion is largely separate from the concept, and, White says, this milestone won’t necessarily prompt researchers to abandon or continue with concepts.
The technical challenges for NIF differ from those for ITER and other facilities. But the symbolic achievement can have major consequences. “A result like this creates more interest in the development of all types of fusion, so it should have a positive effect on fusion research in general,” says Luce.
This article originally appeared in Nature News.