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

Scientists at the world’s largest nuclear fusion facility have accomplished the phenomenon known as ignition; this created a nuclear reaction that produced more energy than it consumed. The results of the breakthrough at the US National Ignition Facility (NIF), carried out by the administration of US President Joe Biden on December 5 and announced today, excited the global fusion research community. This research aims to take advantage of nuclear fusion, the phenomenon that powers the Sun, to provide a nearly unlimited source of clean energy on Earth.

“This is an incredible achievement,” says Mark Herrmann, assistant director of basic weapons physics at Lawrence Livermore National Laboratory in California, which houses the fusion lab. Herrmann says the landmark experiment follows years of work by multiple teams on everything from lasers and optics to targets and computer models. “Of course that’s what we celebrate.”

NIF, the flagship experimental facility of the U.S. Department of Energy’s nuclear weapons program designed to study the reactions produced by such weapons, was originally aimed to fire by 2012 and has come under criticism for delays and cost overruns. In August 2021, NIF scientists announced that they had used high-power laser devices to achieve a record-breaking reaction that crossed a critical threshold in the ignition path, but efforts to repeat that experiment or shot in the following months fell short. Ultimately, the scientists shelved efforts to repeat that shot and rethink the experimental design—an effort that paid off last week.

“There were a lot of people who thought it wasn’t possible, but I and others who held their faith were somewhat right,” says Michael Campbell, former director of the fusion lab at the University of Rochester in New York and an early researcher. Proponent of NIF while in the Lawrence Livermore lab. “I’m living a cosmos to celebrate.”

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

What has NIF accomplished?

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

“Fusion research has been going on since the early 50s, and it is the first time in the lab that fusion appears to produce more energy than it consumes,” says Campbell.

The experiment safely qualifies as ignition, a benchmark for fusion reactions that focuses on how much energy goes to the target compared to how much energy is released. However, although the fusion reactions produced more than 3 megajoules of energy (more than delivered to the target), NIF’s 192 lasers consumed 322 megajoules of energy in the process.

“This is 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 agrees, saying there are many steps on the road to laser fusion energy. “NIF was not designed to be efficient,” he says. “It is designed to be the largest laser we can build to give us the data we need. [nuclear] stock research program.”

NIF scientists made numerous changes prior to the latest laser shot, based in part on analysis of experiments and computer modeling last year, to achieve ignition. In addition to increasing the laser power by about 8%, the scientists created a new target with fewer defects and adjusted how the laser energy was delivered to the target to create a more spherical internal explosion. Scientists knew they were working at the peak of fusion ignition, and in this regimen, “small changes can make a big difference,” says Herrmann.

Why are these results important?

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

It took more than a decade, “but they can be admired for achieving their goals,” says Stephen Bodner, a physicist who previously chaired the laser fusion program at the U.S. Naval Research Laboratory in Washington, DC. The big question now, Bodner says, is what the Department of Energy will do next: double down on weapons research at the NIF or turn to a laser program specifically geared towards fusion energy research.

What does this mean for fusion energy?

The latest results have already rekindled rumors about a future powered by clean fusion energy, but experts warn they have a long way to go.

NIF scientists readily admit that the facility was not designed with commercial fusion energy in mind, and many researchers doubt that laser-driven fusion will ultimately be the approach that delivers fusion energy. But Campbell believes his latest success could boost confidence in the promise of laser fusion power and eventually open the door to a new program focused on energy applications. “This is absolutely necessary to have the credibility of selling an energy program,” he says.

Lawrence Livermore laboratory director Kim Budil described the success as a proof-of-concept. “I don’t want to give you the impression that we’re going to connect NIF to the grid: it definitely doesn’t work that way,” he said at a press conference in Washington, DC. “But this is the basic building block of the inertial confinement fusion power plan.”

There are many other fusion experiments around the world trying to achieve fusion for energy applications using different approaches. But engineering challenges remain, including the design and construction of facilities that can extract the heat produced by fusion and use it to generate significant amounts of energy that can be converted into usable electricity.

“While this is good news, this result is still far from the actual energy gain required for electricity generation,” Tony Roulstone, a nuclear energy researcher at the University of Cambridge in England, told the Science Media Center. .

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

What are the next major milestones in fusion?

To demonstrate that the type of fusion studied at NIF could be a viable way to generate energy, the efficiency of the yield (the energy released compared to the energy that goes into producing the laser pulses) would need to be at least doubled. .

Time Luce, head of science and operations at the international nuclear fusion project ITER, says researchers will also need to significantly increase the speed at which lasers generate pulses and how quickly they can clear the target chamber to prepare for another burn. Under construction in St-Paul-lez-Durance, France.

“Events that produce enough fusion energy in repeated performance will be a major milestone,” says White.

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; Technique from NIF’s ‘inertial confinement fusion’ approach. ITER will hold a deuterium and tritium plasma in a toroidal vacuum chamber, or tokamak, and heat it until the nuclei coalesce. It will aim to reach the ‘combustion’ stage when it starts doing so in 2035, Luce explains, “where the self-heating power is the dominant source of heating”. This type of self-sustaining fusion is key to producing more energy than put into it.

What does it mean for other fusion experiments?

NIF and ITER are two fusion technology concepts among the many followed by governments around the world. Approaches include magnetic confinement of plasma used by tokamaks and stargazers, and inertial confinement used by NIF, and a hybrid of the two, among others.

The technology required to generate electricity from fusion is largely concept-independent, says White, and the latest breakthrough may not lead researchers to abandon or combine the concepts.

The engineering challenges faced by NIF are different from those at ITER and other facilities. But symbolic success can have widespread effects. “A result like this will increase interest in the advancement of all types of fusion, so it will have a positive impact on fusion research in general,” says Luce.

This article is reproduced with permission and was originally published on December 13, 2022.

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