Researchers at the federally-funded Lawrence Livermore National Laboratory revealed in a study released Wednesday in the peer-reviewed journal Nature that, for the first time, one of their experiments has yielded more energy out of fusion than was used in the fuel that created the reaction.

In a 10-story building the size of three football fields, the Livermore scientists “used 192 lasers to compress a pellet of fuel and generate a reaction in which more energy came out of the fuel core than went into it,” wrote the Washington Post. “Ignition” would mean more energy was produced than was used in the entire process.

"We're closer than anyone's gotten before," said Omar Hurricane, a physicist at Livermore and lead author of the study. "It does show there's promise."

The process ultimately mimics the processes in the core of a star inside the laboratory’s hardware. Nuclear fusion, which is how the sun is heated, creates energy when atomic nuclei fuse and form a larger atom.

"This isn't like building a bridge," Hurricane told USA Today in an interview. "This is an exceedingly hard problem. You're basically trying to produce a star, on a small scale, here on Earth."

A fusion reactor would operate on a common form of hydrogen found in sea water and create minimal nuclear waste while not being nearly as volatile as a traditional nuclear-fission reactor. Fission, used in nuclear power plants, works by splitting atoms.

Hurricane said he does not know how long it will take to reach that point, where fusion is a viable energy source.

"Picture yourself halfway up a mountain, but the mountain is covered in clouds," he told reporters on a conference call Wednesday. “And then someone calls you on your satellite phone and asks you, ‘How long is it going to take you to climb to the top of the mountain?’ You just don’t know.”

The beams of the 192 lasers Livermore used can pinpoint extreme amounts of energy in billionth-of-a-second pulses on any target. Hurricane said the energy produced by the process was about twice the amount that was in the fuel of the plastic-capsule target. Though the amount of energy yielded equaled only around 1 percent of energy delivered by the lasers to the capsule to ignite the process.

“When briefly compressed by the laser pulses, the isotopes fused, generating new particles and heating up the fuel further and generating still more nuclear reactions, particles and heat,” wrote the Washington Post, adding that the feedback mechanism is known as “alpha heating.”

Debbie Callahan, co-author of the study, said the capsule had to be compressed 35 times to start the reaction, “akin to compressing a basketball to the size of a pea,” according to USA Today.

While applauding the Livermore team’s findings, fusion experts added researchers have “a factor of about 100 to go.”

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

Livermore is the site of the multi-billion-dollar National Ignition Facility, funded by the National Nuclear Security Administration. Fusion experiments aren’t the only function of the lab; for example, it also studies the processes of nuclear weapon explosions.

Long-pursued by scientists dating back to Albert Einstein, fusion energy does not emit greenhouse gases or leave behind radioactive waste. Since the 1940s, researchers have employed magnetic fields to contain high-temperature hydrogen fuel. Laser use began in the 1970s.

"We have waited 60 years to get close to controlled fusion," said, Steve Cowley, of the United Kingdom's Culham Center for Fusion Energy. He added scientists are "now close"with both magnets and lasers. "We must keep at it."

Stewart Prager - director of the Princeton Plasma Physics Laboratory, which studies fusion using magnets - told the Post he was optimistic about fusion energy’s future.

“In 30 years, we’ll have electricity on the grid produced by fusion energy – absolutely,”Prager said. “I think the open questions now are how complicated a system will it be, how expensive it will be, how economically attractive it will be.”