A nuclear fusion reaction first produces more energy than was put into it

Photo: Laser amplifiers at the National Ignition Facility.

The so-called thermonuclear detonation occurred on December 5, and on December 13 the US government officially announced the result. This breakthrough has excited the global fusion research community. Nuclear fusion is the phenomenon that generates energy for the sun, and their research aims to use fusion as a source of clean, virtually unlimited energy on Earth.

“It’s an amazing achievement,” said Mark Hermann, deputy director of fundamental weapons physics at Lawrence Livermore National Laboratory in California, where the fusion lab is located. Herrmann said the groundbreaking experiment follows years of work by multiple teams, with developments ranging from lasers and optics to computer models. “Of course we celebrate.”

NIF is the lead in the US Department of Energy’s nuclear weapons program. It was created to study the reactions of such weapons. The inflammatory response was originally scheduled for early 2012, but the center has faced criticism for delays and cost overruns. In August 2021, NIF scientists announced that they have used their powerful laser to create a record-breaking response. He crossed a critical threshold on his way to ignition, but attempts to repeat that experience over the following months were unsuccessful. Ultimately, the scientists abandoned efforts to replicate this reaction and changed the design of the experiment—an effort that paid off last week.

“There were a lot of people who thought it wasn’t possible. But we kept believing it would work and we were proven right,” said Michael Campbell, former director of the fusion lab at the University of Rochester in New York and an early supporter of NIF when he was working in Lawrence Livermore’s lab. “I’ll have a drink for that.”

The facility used 192 lasers to deliver 2.05 megajoules of energy to a pea-sized gold cylinder containing frozen flakes of the hydrogen isotopes deuterium and tritium. The energy pulse collapsed the capsule, creating temperatures found only in stars and thermonuclear weapons. Hydrogen isotopes fused into helium, releasing additional energy and creating a chain reaction of fusion. Lab 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 a laboratory,” said Campbell.

So the experiment falls under the definition of thermonuclear ignition, which is 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, the 192-megajoule NIF laser consumed 322 megajoules of energy in the process.

“It’s a huge milestone, but NIF is not a fusion power plant,” said Dave Hammer, a nuclear engineer at Cornell University in Ithaca, New York.

Herrmann acknowledges this, too, saying that there are many steps along the way to laser fusion energy. “NIF is not designed to be effective,” he says. “It was designed to be the largest possible laser for searching devices [nucleaire] research programme.’

To get to the thermonuclear detonation, NIF scientists made several changes to the latest laser shot, based in part on analysis and computer modeling of experiments conducted last year. They increased the laser power by about eight percent, creating a new target with fewer defects. In addition, they modified the way the laser energy was delivered to the target to create a more spherical implosion. Scientists knew they were on the verge of a combustion ignition, and in those conditions, Herrmann says, “small changes can make a big difference.”

On the one hand, it is about proving what is possible. On this front, many scientists have hailed the result as a milestone in fusion science. But the findings are particularly important to NIF: The facility is for nuclear weapons scientists to study the extreme heat and pressure that occur in thermonuclear explosions, and that’s only possible if the facility produces high-output fusion reactions.

It took more than a decade, “but they hit their goal,” says Stephen Bodner, a physicist who previously headed the laser fusion program at the US Naval Research Laboratory in Washington, D.C. According to Bodner, the big question now is what the DOE will do: continue weapons research at NIF or move to a laser program focused specifically on fusion energy research.

The results have reignited interest in the future of clean fusion energy, 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 researchers doubt that laser-driven fusion will be the approach that will ultimately deliver fusion power. But Campbell believes success could boost confidence in laser fusion energy and eventually open the door to a new program focused on energy applications. “This was absolutely essential to the credibility of the fusion energy program,” he says.

Kim Podell, director of the Lawrence Livermore Laboratory, called the achievement a proof of concept. “I don’t want you to feel like we’re going to hook NIF into the network: That’s not the way it works at all,” she said at a press conference in Washington, D.C. “But this is the basic building block of an inertial fusion energy system.”

There are many other fusion experiments around the world that are trying to achieve fusion for energy applications using different approaches. But technical challenges remain. Designing and building plants that convert the heat generated by fusion into a large amount of energy, which in turn can be converted into usable electricity, is one of them.

“While this is positive news, this result is still very far from 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.

“NIF experiments targeting fusion energy are certainly valuable on the path to commercial fusion energy,” said Ann White, a plasma physicist at MIT in Cambridge.

To prove that the type of fusion being studied at NIF is a viable method for energy production, the yield efficiency—the energy released compared to the energy used to produce the laser pulses—must be increased by at least two orders of magnitude.

The speed at which the laser can produce the pulses must be increased, as well as the speed at which the target chamber can be evacuated and prepared for another burn, says Time Luce, chief of science and operations for the International Nuclear Fusion Project ITER, headquartered in Saint-Paul-les-Durance, France, being built. .

“Enough events that repeatedly produce enough fusion energy would be an important milestone,” says Luce.

The ITER project is a collaboration between China, the European Union, India, Japan, Korea, Russia and the United States and costs more than 20 billion euros. It aims for self-sustained fusion: fusion energy produces fusion again, a different technique from NIF’s inertial fusion approach. ITER traps a plasma of deuterium and tritium in a ring-shaped chamber of solenoid coils, or tokamak, and heats them until the nuclei fuse. When you begin to do so in 2035, the goal is to reach a “fire stage,” Luce explains, “where the self-heating power is the dominant source of heating.” This self-sustaining fusion is necessary to produce energy above the input.

NIF and ITER are two of the many fusion technologies pursued by governments around the world. Methods include magnetic confinement of plasma – in tokamak and stars – and inertial fusion, which NIF uses, and a hybrid of the two.

The technology needed to generate electricity from fusion is largely separate from the concept, and White says the breakthrough won’t necessarily cause researchers to abandon or continue with the concepts.

The technical challenges of NIF differ from those facing ITER and other facilities. But a symbolic achievement can have disastrous consequences. “A result like this leads to more interest in advancing all types of fusion, so it should have a positive impact on fusion research in general,” says Luce.

This article previously appeared on Nature News.