Wendy Koch

USA TODAY

Scientists take step forward toward creating pollution-free fusion energy

They use 192 lasers to launch a process that yields energy via a fusion reaction

The decades-long quest to develop a pollution-free energy source via nuclear fusion — the power source of the sun and other stars — has taken what scientists say is a major step forward.

For the first time, a study Wednesday reports, a laboratory experiment got more energy out of fusion than was put into the fuel that sparked the reaction. It fell short, though, of what's considered the holy grail of fusion: "ignition" — the point at which more energy is produced than was used throughout the process.

"We're closer than anyone's gotten before," says Omar Hurricane, a physicist at the federally funded Lawrence Livermore National Laboratory and lead author of the study that appears in the peer-reviewed journal Nature. "It does show there's promise."

Hurricane says he doesn't know how long it will take to make fusion a viable energy source.. "Picture yourself halfway up a mountain, but the mountain is covered in clouds," he told reporters, adding the climber doesn't know what's behind him and the peak.

"This isn't like building a bridge," he says in an interview. "This is an exceedingly hard problem. You're basically trying to produce a star, on a small scale, here on Earth." Nuclear fusion, a process that heats the sun, produces energy when atomic nuclei fuse and form a heavier atom. It's different from nuclear fission, which derives heat used at today's nuclear power plants by splitting atoms.

Scientists have long pursued fusion energy, because it does not emit greenhouse gases that contribute to global warming or leave behind radioactive waste that needs to be stored. Since the late 1940s, researchers have used magnetic fields to contain super-heated hydrogen fuel, and in the 1970s, they began experimenting with powerful lasers.

Lawrence Livermore's National Ignition Facility, which opened in March 2009, has 192 laser beams housed in a 10-story building the size of three football fields. The beams can focus extreme amounts of energy in billionth-of-a-second pulses on a minuscule target.

Hurricane's team used these 192 lasers to heat and compress a small pellet of fuel, contained in a plastic capsule, to a point that fusion reactions occurred. Some of the energy created went back into the remaining fuel in a "bootstrapping" process that can boost output.

Hurricane says the energy produced was twice the amount that was put into the capsule's fuel but only about 1% of that delivered by the lasers to the target to get the process started.

Co-author Debbie Callahan says the capsule had to be compressed 35 times to trigger a reaction — akin to compressing a basketball to the size of a pea. Other study co-authors include 19 additional Livermore physicists (four of whom are women) and John Kline of Los Alamos National Laboratory.

"These results are still a long way from ignition, but they represent a significant step forward in fusion research," says Mark Herrmann of the Sandia National Laboratories' Pulsed Power Sciences Center in an accompanying Nature article. "Achieving pressures this large, even for vanishingly short times, is no easy task."

Steve Cowley, who's working with magnets as director of the United Kingdom's Culham Center for Fusion Energy, said the paper is "truly excellent" for addressing the core problem of instability. "By pushing (the lasers) in a softer manner ... they get a nearly stable compression," he says.

"We have waited 60 years to get close to controlled fusion," he says, adding scientists are "now close" with both magnets and lasers. "We must keep at it."