Scientists produced the first fusion reaction in a laboratory that created more energy than it took to start it .

"Scientists studying fusion energy at Lawrence Livermore National Laboratory in California announced on Tuesday that they had crossed a long-awaited milestone in reproducing the power of the sun in a laboratory.

That sparked public excitement as scientists have for decades talked about how fusion, the nuclear reaction that makes stars shine, could provide a future source of bountiful energy.

The result announced on Tuesday is the first fusion reaction in a laboratory setting that actually produced more energy than it took to start the reaction.

“This is such a wonderful example of a possibility realized, a scientific milestone achieved, and a road ahead to the possibilities for clean energy,” Arati Prabhakar, the White House science adviser, said during a news conference on Tuesday morning at the Department of Energy’s headquarters in Washington, D.C. “And even deeper understanding of the scientific principles that are applied here.”

If fusion can be deployed on a large scale, it would offer an energy source devoid of the pollution and greenhouse gases caused by the burning of fossil fuels and the dangerous long-lived radioactive waste created by current nuclear power plants, which use the splitting of uranium to produce energy.

Within the sun and stars, fusion continually combines hydrogen atoms into helium, producing sunlight and warmth that bathes the planets.

In experimental reactors and laser labs on Earth, fusion lives up to its reputation as a very clean energy source.

There was always a nagging caveat, however. In all of the efforts by scientists to control the unruly power of fusion, their experiments consumed more energy than the fusion reactions generated.

That changed at 1:03 a.m. on Dec. 5 when 192 giant lasers at the laboratory’s National Ignition Facility blasted a small cylinder about the size of a pencil eraser that contained a frozen nubbin of hydrogen encased in diamond.

The laser beams entered at the top and bottom of the cylinder, vaporizing it. That generated an inward onslaught of X-rays that compresses a BB-size fuel pellet of deuterium and tritium, the heavier forms of hydrogen.

In a brief moment lasting less than 100 trillionths of a second, 2.05 megajoules of energy — roughly the equivalent of a pound of TNT — bombarded the hydrogen pellet. Out flowed a flood of neutron particles — the product of fusion — which carried about 3 megajoules of energy, a factor of 1.5 in energy gain.

This crossed the threshold that laser fusion scientists call ignition, the dividing line where the energy generated by fusion equals the energy of the incoming lasers that start the reaction.

“You see one diagnostic and you think maybe that’s not real and then you start to see more and more diagnostics rolling in, pointing to the same thing,” said Annie Kritcher, a physicist at Livermore who described reviewing the data after the experiment. “It’s a great feeling.”

The successful experiment finally delivers the ignition goal that was promised when construction of the National Ignition Facility started in 1997. When operations began in 2009, however, the facility hardly generated any fusion at all, an embarrassing disappointment after a $3.5 billion investment from the federal government.

In 2014, Livermore scientists finally reported some success, but the energy produced was minuscule — the equivalent of what a 60-watt light bulb consumes in five minutes. Progress over the next few years was slight and small.

Then, in August last year, the facility produced a much larger burst of energy — 70 percent as much energy as the laser light energy.

In an interview, Mark Herrmann, program director for weapons physics and design at the Livermore, said the researchers then performed a series of experiments to better understand the surprising August success, and they worked to bump up the energy of lasers by almost 10 percent and improve the design of the hydrogen targets.

The first laser shot at 2.05 megajoules was performed in September, and that first try produced 1.2 megajoules of fusion energy. Moreover, analysis showed that the spherical pellet of hydrogen was not squeezed evenly, and some of the hydrogen essentially squirted out the side and did not reach fusion temperatures.

The scientists made some adjustments that they believed would work better.

“The prediction ahead of the shot was that it could go up a factor of two,” Dr. Herrmann said. “In fact, it went up a little more than that.”

The main purpose of the National Ignition Facility is to conduct experiments to help the United States maintain its nuclear weapons. That makes the immediate implications for producing energy tentative.

Fusion would be essentially an emissions-free source of power, and it would help reduce the need for power plants burning coal and natural gas, which pump billions of tons of planet-warming carbon dioxide into the atmosphere each year.

But it will take quite a while before fusion becomes available on a widespread, practical scale, if ever.

“Probably decades,” Kimberly S. Budil, the director of Lawrence Livermore, said during the Tuesday news conference. “Not six decades, I don’t think. I think not five decades, which is what we used to say. I think it’s moving into the foreground and probably, with concerted effort and investment, a few decades of research on the underlying technologies could put us in a position to build a power plant.”

Most climate scientists and policymakers say that to achieve that goal of limiting warming to 2 degrees Celsius, or the even more ambitious target of 1.5 degrees Celsius of warming, the world must reach net-zero emissions by 2050.

Fusion efforts to date have primarily used doughnut-shaped reactors known as tokamaks. Within the reactors, hydrogen gas is heated to temperatures hot enough that the electrons are stripped away from the hydrogen nuclei, creating what is known as a plasma — clouds of positively charged nuclei and negatively charged electrons. Magnetic fields trap the plasma within the doughnut shape, and the nuclei fuse together, releasing energy in the form of neutrons flying outward.

The work at NIF takes a different approach, but so far, little work has gone into turning the idea of a laser fusion power plant into reality. “There are very significant hurdles, not just in the science, but in technology,” Dr. Budil said.

NIF is the world’s most powerful laser, but it is a slow and inefficient one, relying on decades-old technology.

The apparatus, about the size of a sports stadium, is designed to perform basic science experiments, not serve as a prototype for the generation of electricity.

It averages about 10 shots per week. A commercial facility using the laser fusion approach would need much faster lasers, able to shoot at a machine-gun pace, perhaps 10 times a second.

NIF also still consumes far more energy than is produced by the fusion reactions.

Although the latest experiment produced a net energy gain compared to the energy of the 2.05 megajoules in the incoming laser beams, NIF needed to pull 300 megajoules of energy from the electrical grid in order to generate the brief laser pulse.

Other types of lasers are more efficient, but experts say a viable laser fusion power plant would likely require much higher energy gains than the 1.5 observed in this latest fusion shot.

“You’ll need gains of 30 to 100 in order to get more energy for an energy power plant,” Dr. Herrmann said.

He said Livermore would continue to push NIF fusion experiments to higher fusion output.

“That’s really what we’re going to be looking at honestly over the next few years,” Dr. Herrmann said. “These experiments show that even a little bit more laser energy can make a big difference.”

Researchers elsewhere are looking at variations of the NIF experiment. Other types of lasers at different wavelengths might heat the hydrogen more efficiently.

Some researchers favor a “direct drive” approach to laser fusion, using the laser light to directly heat the hydrogen. That would get more energy into the hydrogen, but could also create instabilities that thwart the fusion reactions.

In March, the White House held a summit to seek to accelerate commercial fusion efforts.

“Developing an economically attractive approach to fusion energy is a grand scientific and engineering challenge,” Tammy Ma, who leads an effort at Livermore to study the possibilities. “Without a doubt, it will be a monumental undertaking.”

Dr. Ma said that a report commissioned by the energy department to provide a framework for laser fusion energy research would come out soon.

“Such a program,” she said, “will inevitably require participation from across the community,” including academia, start-up companies and public utilities in addition to national laboratories like Livermore.

The results announced Tuesday will benefit the scientists working on the nuclear stockpile, the NIF’s primary purpose. By performing these nuclear reactions in a lab at a less destructive scale, scientists aim to replace the data they used to gather from underground nuclear bomb detonations, which the United States stopped in 1992.

The greater fusion output from the facility will produce more data “that allows us to maintain the confidence in our nuclear deterrent without the need for further underground testing,” Dr. Herrmann said. “The output, that 30,000 trillion watts of power, creates very extreme environments in itself” that more closely resemble an exploding nuclear weapon.

Riccardo Betti, chief scientist of the Laboratory for Laser Energetics at the University of Rochester, who was not involved with this particular Livermore experiment, said, “This is the goal, to demonstrate that one can ignite a thermonuclear fuel in the laboratory for the first time.”

“And this was done,” he added. “So this is a great result.”"

 

The energy introduced by the lasers into the reaction chamber is now smaller than the energy produced by the reaction. Practically this has no use since the energy to run the lasers is still much bigger than the energy produced by the reaction.