The National Ignition Facility’s 192 laser beams focus onto a tiny target.
Researchers at a laboratory in California say they’ve had a breakthrough in producing fusion reactions with a giant laser. The success comes after years of struggling to get the laser to work and is another step in the decades-long quest for fusion energy.
Omar Hurricane, a researcher at , says that for the first time, they’ve produced significant amounts of fusion by zapping a target with their laser. “We’ve gotten more energy out of the fusion fuel than we put into the fusion fuel,” he says.
Strictly speaking, while more energy came from fusion than went into the hydrogen fuel, only about 1 percent of the laser’s energy ever reached the fuel. Useful levels of fusion are still a long way off. “They didn’t get more fusion power out than they put in with the laser,” says , the head of a huge fusion experiment in the U.K. called the , or JET.
The laser is known as the , or NIF. Constructed at a cost of more than $3 billion, it consists of 192 beams that take up the length of three football fields. For a brief moment, the beams can focus 500 trillion watts of power — more power than is being used in that same time across the entire United States — onto a target about the width of a No. 2 pencil.
The goal is fusion: a process where hydrogen atoms are squeezed together to make helium atoms. When that happens, a lot of energy comes out. It could mean the answer to the world’s energy problems, but fusion is really, really hard to do. Hurricane says that each time they try, it feels like they’re taking a test.
Inside a capsule the width of a No. 2 pencil sits a tiny ball of hydrogen fuel. The lasers squeeze the fuel until it fuses, releasing energy.
“Of course you want to score real well, you think you’ve learned the material, but you just have to see how you do,” he says.
Over the past few years, For all its power, it just couldn’t get the hydrogen to fuse, and researchers didn’t know why. The failures have led NIF’s critics to label the facility an enormous waste of taxpayer dollars. In 2012, the government shifted NIF away from its fusion goals to focus on its other mission: .
But the fusion experiments continued, and Hurricane says researchers now understand why their original strategy wasn’t working. In the journal Nature, that they’ve finally figured out how to squeeze the fuel with the lasers. By doing a lot of squeezing right at the start, they were able to keep the fuel from churning and squirting out. The lasers squeezed evenly and the hydrogen turned into helium.
The new technique can’t reach “ignition,” which is the point at which the hydrogen fusion feeds on itself to make more. Even so, JET’s Cowley says, this is still a big moment for NIF.
“I think it’s still a very important step forward, they reached fusion conditions, they made some fusion happen, and that’s not been done before [with a laser],” he says.
Hurricane says no one knows for sure whether NIF can really reach the point of ignition. “It’s not up to me; it’s up to Mother Nature,” he says. “But we’re certainly going to try.”
When physicists first split the atom in 1938, in the process known as nuclear fission, the feat led very quickly to the bombs that destroyed Hiroshima and Nagasaki and ended World War II. A mere decade or so later this destructive force had been tamed to power the first commercial nuclear power plants. In the late 1940’s, meanwhile, physicists forced atoms to combine against their will to create hydrogen bombs in what’s called nuclear fusion, and they thought they could follow up in the civilian sector. Fusion power planets, scientists predicted in the 1950’s, might be right around the corner.
That was just a tad optimistic. Controlled fusion—which amounts to taming the same awesome force that powers the Sun—has turned out to be much more difficult and more expensive than anyone guessed, and more than a half-century on nobody’s achieved it. Yet as a new paper just published in Nature makes clear, they haven’t given up. By focusing 192 powerful lasers on a tiny sphere encasing 170 millionths of a gram of hydrogen, scientists at Lawrence Livermore National Laboratory forced atomic nuclei to combine, releasing a whopping 17 kilojoules of energy. “It is not surprising,” writes physicist Mark Herrmann of Sandia National Laboratories in an accompanying Nature commentary, “that fusion scientists throughout the world are cheering.”
This might sound a bit over the top when you consider how little hydrogen was involved, and how little power it actually released: 17 kilojoules represents the amount of solar energy that falls on a sq. yard (0.83 sq. m) of Earth (more or less) in full daylight over 17 seconds—and this fusion reaction lasted more like .0000000001 second.
“It sounds very modest,” admitted lead scientist Omar Hurricane at a press briefing. “And it is. But it’s closer than anyone’s ever gotten to ignition”—that is, the self-sustaining process where the fusion reaction can keep going on its own.
The reaction itself is simple: atomic nuclei carry a positive charge, so they try to repel each other. If you can overcome that repulsion and let them crash together and fuse, they release a burst of energy. And the way you do that, says Hurricane, is “you get them running toward each other at high velocity.”
Inside the Sun, that’s no problem. That high velocity comes from the 27-million-degree temperatures at the Sun’s core, which keep nuclei moving with enormous energy. Under other circumstances, most of the nuclei would just escape without colliding. But the enormous pressures created by the Sun’s gravity keep them confined indefinitely. Sooner or later, they crash.
It’s no problem in an H-bomb either: hydrogen fuel is heated and compressed by an old-fashioned atomic bomb. The compression doesn’t last long, but the energy released in a fraction of a second is hundreds of times more powerful than an A-bomb. For a self-sustaining fusion reaction, you somehow need to get hydrogen very hot and keep it from escaping. That’s the tough part. One technique traps a gas of hydrogen atoms in a magnetic “bottle,” then heats the gas to millions of degrees with high-energy radio waves.
But the Livermore scientists have long focused on another method, known as inertial fusion. They bombard a spherical capsule of hydrogen with lasers from all directions, vaporizing the container itself and driving the hydrogen inward. “We need to compress the capsule by a factor of 35,” says Livermore physicist and co-author Debbie Callahan. The capsule itself is a fraction of an inch across, but the compression, she says, “is equivalent to compressing a basketball to the size of a pea.”
When that happens, the temperature shoots sky-high, the pressure reaches 150 billion times atmospheric pressure on Earth, and the hydrogen—more precisely, it’s a mixture of deuterium and tritium, which are heavier varieties of hydrogen—begins to fuse. “It’s quite ferocious,” says Hurricane.
It will have to get a lot more ferocious to deliver usable power, which would presumably come from blasting one capsule after another in unbroken succession. How long it will take to make a commercial reactor, says Hurricane, “is anybody’s guess. We’re working like mad, but this is research—it’s not a power plant, not a reactor.”
The same can be said for the magnetic confinement technique, whose most advanced experiment, the Joint European Torus (JET), briefly produced 16 megawatts of fusion energy back in 1997. That reaction wasn’t self-sustaining either, and the technical barriers to making this kind of fusion work are no less daunting than those the Livermore scientists face.
But don’t tell the scientists that. “We’ve waited 60 years to get close to controlled fusion, and we are now close in both magnetic and inertial,” says Steven Cowley, director of the Culham Center for Nuclear Energy, in England, where JET is located. “We must keep at it.”
Though an important milestone, the result does not mean that your Delorean is soon going to sport a Mr. Fusion reactor. NIF would need to sustain temperatures and pressures much greater than they are currently capable of before they can harness fusion energy.
Nuclear fusion is the energy source of the stars. Deep in our sun’s belly, hydrogen atoms slam into one another at high speed, getting mashed together to form helium atoms and releasing copious amounts of energy. Creating viable fusion energy here on Earth has been a dream since the dawn of the Atomic Age. With true fusion power, the amount of water you use in a single shower could provide all your energy needs for a year. But for six decades, fusion has remained a far-off dream.
To create fusion reactions at NIF, scientists shoot 192 lasers simultaneously with a peak power of 500 trillion Watts, roughly the energy the U.S. consumes every six minutes. This heats up a 1 centimeter gold cylinder to millions of degrees, producing X-rays that get focused at a plastic shell the size of a BB pellet. The X-rays blast the shell, creating an implosion that shrinks the gas inside pellet to 1/35th of its size, compressing isotopes of hydrogen known as deuterium and tritium to incredible densities. At the center of this hydrogen plasma, in an area smaller than the width of a human hair, the atoms fuse. This gives off energy, which should in theory set off a chain reaction that ignites the rest of the hydrogen and creates a self-sustaining ball of fusion.
Amplifiers to increase the laser power at NIF. Image: Damien Jemison/LLNL
Because of this convoluted process, only 1/200th of the energy that the lasers generate is imparted to the hydrogen fuel, compressing it enough to produce a small amount of fusion. Until now, the energy given off by the fusing hydrogen hasn’t been enough to set off a chain reaction. The hydrogen fuel also always consumed more energy than it put out. But during experiments late last year, NIF researchers were finally able to get the hydrogen to give off as much as 1.7 times more energy than it had taken in, a result that appears today in Nature. In subsequent experiments last month, the team was able to produce as much as 2.6 times more energy than was put into the hydrogen fuel.
“The physics is a breakthrough,” said physicist Riccardo Betti of the University of Rochester, who was not involved in the work. “If fusion will ever become a viable source of energy, we may look back and say that in 2013, for the first time, a plasma produced more energy out than it took in.”
But the dream of fusion energy isn’t yet a reality. “In terms of making energy to power the grid, it’s still light-years away,” Betti said.
NIF is a $3.5-billion facility that was built to study the dynamics of nuclear explosions for the National Nuclear Security Administration and to test the integrity of the country’s nuclear stockpile without exploding any bombs. After the 1963 Partial Test Ban Treaty, the U.S., Russia, and many other countries agreed to only test atomic bombs underground, and since 1992 the U.S. has placed a moratorium on any nuclear testing. But not being able to physically test the bombs “is like having a car that you’re studying but not allowed to start,” said Livermore Lab physicist Paul Springer, a co-author of the recent fusion results. NIF was the answer to this problem.
When NIF was first being built, researchers were confident that it would produce fusion reactions fairly quickly. The point when fusion becomes self-sustaining is known as ignition. The fusing hydrogen atoms at the fuel center send out helium nuclei, which knock into other hydrogen atoms, setting off a cascading chain-reaction of expansion fusion that should produce more energy than the entire experiment consumes. While ignition requires extremely high temperatures and pressures, computer simulations in 2009 predicted that NIF would achieve the energies to generate it by 2012. Of course, reality doesn’t work as well as a digital model, and the deadline passed without achieving ignition.
A view inside the gold cylinder where hydrogen is compressed to incredible densities. Image: Lawrence Livermore National Security
Troubles came when scientists found it was extremely difficult to get their hydrogen fuel to compress in the right way. In order to generate the intense pressure and temperatures inside the hydrogen gas needed for fusion, the tiny pellet had to collapse perfectly symmetrically. But small instabilities appearing in the pellet meant that the plasma imploded unevenly, sending fingers of cold gas into the center that doused the fusion reactions.
Over the years, NIF scientists learned from their experiments. They studied the way that the pellet collapsed, and tweaked their designs. They also learned how to time their laser pulses to give the hydrogen the perfect kick. With this knowledge, researchers have been able to go back and improve their simulations, which are now in better agreement with what is physically seen in experiments.
But the latest achievements are still a long way from creating self-sustaining fusion reactions, which would require the hydrogen to reach temperatures of hundreds of millions of degrees and pressures a thousand times more than what is currently possible. The implosion continues to be more of an amorphous blob than a perfect spherical cave-in. To go forward, researchers will have to “make the collapse rounder and more stable against things that cause distortions,” said Springer.
Still, a future with fusion power is starting to look more possible. A European team is also attempting to generate fusion energy at the $20 billion International Thermonuclear Experimental Reactor (ITER) currently under construction in France. That facility will trap superheated hydrogen plasma in a donut-shaped magnetic chamber, an entirely different technique than what has been achieved at NIF, meaning that the lessons from the Livermore Lab won’t be entirely applicable. Rather than set unrealistic deadlines, ITER is moving forward at a very slow and steady pace.
In the meantime, the NIF team is happy with their achievements and cautiously optimistic of their future prospects. “We’ve all been extremely excited about the results that we’ve been getting,” said physicist Denise Hinkel of Livermore Lab, another co-author. “Many people have been waiting for something like this to happen.”