America's multibillion-dollar, laser-blasting fusion machine has gotten more energy out of a smidgen of fuel than was put into it — but the most significant thing is how it was done.
The latest experiments, reported in this week's issue of the journal Nature, marked a first for the National Ignition Facility at Lawrence Livermore National Laboratory in California. They're the first laser shots to produce a net gain in energy under any definition, and they're also the first to show evidence of a mechanism that's essential if controlled fusion is ever to become a reality.
The publication follows up on reports that began leaking out last October.
"These results are still a long way from ignition, but they represent a significant step forward in fusion research," Mark Herrmann, a fusion researcher at Sandia National Laboratories in New Mexico, said in a Nature commentary on the research.
Nuclear fusion is the reaction that causes the sun to shine — and a hydrogen bomb to blow up. Under extreme temperature and pressure, hydrogen nuclei are fused into helium nuclei, also known as alpha particles. In the process, a bit of mass is converted into energy in accordance with Einstein's famous formula, E=mc^2.
Controlled fusion could open the way to cheap, abundant, on-demand electric power. But for decades, scientists have tried in vain to harness the reaction.
Tweaking the dialsThe $3.5 billion National Ignition Facility was built to produce tiny jolts of fusion power, lasting less than a nanosecond at a time, by blasting plastic-sheathed capsules containing just 170 micrograms of deuterium-tritium fuel with beams from 192 powerful lasers. The blast compresses the BB-sized capsule so much that it implodes, turning into a speck of stuff that's hot enough and dense enough to undergo fusion.
The researchers behind the Nature study, led by Livermore Lab's Omar Hurricane, repeatedly tweaked the power levels as well as the shapes of the capsules to improve the efficiency of the facility's 19.2-million-joule blasts.
Eddie Dewald / LLNL
A closeup from the National Ignition Facility shows a cutaway view of a gold cylinder known as a hohlraum, with a spherical fusion fuel capsule gleaming inside. The hohlraum measures about half an inch (1 centimeter) in height, and the capsule is about a tenth of an inch (2mm) in diameter. Beams of light from 192 lasers are directed at the capsule to cause an implosion.
Two of their best shots took place on Sept. 27 and Nov. 19 of last year. The researchers figured that about 10,200 to 12,000 joules of energy were absorbed by the fuel in September, and yielded 14,400 joules in return. The November yield was even better: 8,500 to 9,400 joules went into the fuel, and 17,300 joules' worth of energy came out.
That sounds promising — but it's important to remember that more than 99 percent of the energy from the laser blasts was lost due to inefficiencies before it reached the fuel inside its capsule. "The fuel isn't where all the energy has been put into this process," Hurricane reminded reporters during a teleconference this week. "The fuel is just the final little part."
Fighting Mother NatureThe most encouraging news is that specific tweaks led to dramatic increases in the energy output. The best tweak involved front-loading the laser pulse, using what the researchers called a "high-foot" power profile.
"Mother Nature doesn't like putting a lot of energy in small volumes, so she fights you on it. This is a way of fighting back," Hurricane said.
The result was that the alpha particles created through the fusion process added their energy to the mix and helped raise the temperature. Fusion experts say that's what has to happen in order for the total energy output to exceed the total input, leading to the break-even point known as ignition.
"You picture yourself climbing halfway up a mountain, but the top of the mountain is hidden in clouds ... and then someone calls you on your satellite phone and asks you how long it's going to take you to climb to the top of the mountain."
For 60 years, experts have been saying that commercial fusion power could be 30 or 40 years away. While Hurricane is hopeful, he shies away from giving a timetable for future research.
"You picture yourself climbing halfway up a mountain, but the top of the mountain is hidden in clouds ... and then someone calls you on your satellite phone and asks you how long it's going to take you to climb to the top of the mountain," Hurricane said. "You don't know."
He said the high-foot strategy was like a "base camp" on Mount Everest.
"What you do from these base camps is strike out in different directions and try to find the best way up," he said. "The process repeats over and over again." Researchers will continue to tweak the power profile as well as the shape of the fuel capsule and other components to reduce energy-robbing instabilities and inefficiencies.
Seeing the bigger pictureThe laser-blasting process that's employed at the National Ignition Facility, known as inertial confinement, is only one of several strategies being pursued in nuclear fusion research. The other high-profile strategy is magnetic confinement, which involves heating up plasma inside a magnetic field to create the high temperature and pressure needed for fusion.
The current world record for fusion power is held by a magnetic reactor in Britain, called the Joint European Torus, or JET. In 1997, JET briefly produced 16 megawatts of power from a total input power of 24 megawatts. In other words, it got 65 percent of the way to ignition, compared to 1 percent for the National Ignition Facility.
A 35-nation consortium is spending an estimated $18 billion over the course of a decade to build an even bigger magnetic fusion facility in France, known as ITER. About $200 million has been set aside in the 2014 federal budget for the U.S. contribution to ITER.
KIT / ITER
An artist's conception shows a cutaway view for the ITER experimental fusion reactor being constructed in France, with a human figure added at lower right for scale. The reactor is expected to go into operation no earlier than 2020.
Mark Uhran, a spokesman for the US ITER Project Office, declined to comment on the Nature publication, other than to wish the researchers at Livermore Lab "success in achieving their inertially confined fusion mission." The latest results could well be applied first to the National Ignition Facility's other, less publicized mission: providing real-world data to support the maintenance and design of nuclear weapons.
Charles Seife, the author of "Sun in a Bottle: The Strange History of Fusion and the Science of Wishful Thinking," said the alpha-particle heating was "encouraging." But he questioned whether laser fusion would ever attain ignition. "They're so far away it's hard to say," he told NBC News.
Steven Cowley, director of Britain's Culham Center for Fusion Energy, was more optimistic. "We have waited 60 years to get close to controlled fusion — we are now close in both magnetic and inertial confinement research," he told NBC News in an email. "We must keep at it."
Update for 2:30 p.m. ET Feb. 12: Rocket scientist Ben Brockert reminded me on Facebook that most folks don't have a good handle on how much energy a joule represents, so he provides this tip: "The 8,000 joules they got out of the better shot is equal to about 2 food calories, the amount of energy you'd get from eating an eighth of a teaspoon of sugar."
In addition to Hurricane, the authors of "Fuel Gain Exceeding Unity in an Inertially Confined Fusion Implosion" include Debbie Callahan, Daniel Casey, Peter Celliers, Charlie Cerjan, Eduard Dewald, Thomas Dittrich, Tilo Döppner, Denise Hinkel, Laura Berzak Hopkins, Sebastien Le Pape, Tammy Ma, Andrew MacPhee, Jose Milovich, Arthur Pak, Hye-Sook Park, Prav Patel, Bruce Remington, Jay Salmonson, Paul Springer, Riccardo Tommasini and John Kline.
First published February 12 2014, 10:02 AM