Nuclear Fusion Breakthrough Achieved By Scientists At US Lab, With Blast Of 192 Lasers

Unlike fission in which energy is produced by splitting of uranium in current nuclear power plants, fusion produces energy by combining lighter atomic nuclei into a heavier nucleus. The former process releases an enormous amount of energy compared to the negligible amount of energy needed to initiate it. The latter however, has until now, produced only a negative energy gain factor -- less energy output than input.

This changed Tuesday, after scientists at Lawrence Livermore National Laboratory in California, announced that an inertial confinement laser-driven fusion machine at the US National Ignition Facility NIF, produced its first fusion reaction in a laboratory setting with a positive energy gain factor -- more energy than it took to initiate the reaction.

Fusion processes require fuel and a confined environment with sufficient temperature, pressure, and confinement time to create a plasma in which fusion can occur. The combination of these figures that results in a power-producing system is known as the Lawson criterion.

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 according to New York Times, 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.

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.”

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.

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.”

In experimental reactors and laser labs on Earth, fusion lives up to its reputation as a very clean energy source, and devoid of the dangerous long-lived radioactive waste created by current nuclear power plants, which use the fusion process.