"Really for the first time anywhere, we've gotten more energy out of this fuel than was put into the fuel," Hurricane told reporters earlier this week. "And that's quite unique. And that's kind of a major turning point, in a lot of our minds."

Researchers have faced daunting scientific and engineering challenges in trying to develop nuclear fusion — the process that powers stars, including our sun —for use by humankind. Nevertheless, Hurricane said "people are jazzed" by the prospects.

The scientists, led by physicist Omar Hurricane, described the achievement as important but said much more work is needed before fusion can become a viable energy source. The researchers also noted that their experiment did not produce self-heating nuclear fusion, known as ignition, which would be needed for any fusion power plant.

Unlike fossil fuels or the fission process in nuclear power plants, fusion offers the prospect of abundant energy without pollution, radioactive waste or greenhouse gases.

For the first time, experiments have produced more energy from fusion reactions than the amount of energy put into the fusion fuel, scientists at the federally funded Lawrence Livermore National Laboratory in California said.

Scientists in the U.S. announced a milestone on Wednesday in the costly, decades-old quest to develop fusion energy, which — if harnessed successfully — promises a nearly inexhaustible, environmentally friendly energy source for future generations.

Still years from practicality

Unlike nuclear fission energy, which is derived from splitting atoms, fusion energy is produced by fusing atoms together. Experts believe it will be many years before fusion can become a practical energy source.

"I wish I could put a date on it," said Hurricane. "But it really is (just) research. And, you know, although we're doing pretty good, we'd be lying to you if we told you a date."

The research, published in the journal Nature, included results from two experiments done at the lab's National Ignition Facility.

During the experiment, 192 laser beams were briefly fired into a half-inch-long gold cylinder. The cylinder held a tiny ball that contained the fuel, which was a mix of two kinds of hydrogen, called deuterium and tritium. The energy from the lasers kicked off a process that compressed the ball with force akin to squeezing a basketball down to the size of a pea, said Debbie Callahan, an author of the paper.

That created the extremely high pressure and temperatures needed to get the hydrogen atoms to fuse. It was all over in the blink of an eye, with the reaction confined to a space smaller than the width of a human hair.

"These experiments show an order-of-magnitude improvement in yield performance over past deuterium-tritium implosion experiments," the scientists wrote.

Nuclear fusion would be worthwhile only if it produces more energy than it uses. The results of the experiments, however, were far from that.

The hydrogen fuel did emit more energy than it absorbed from the lasers, a goal of the experiment. But the fuel took in only about 1 percent of all the energy produced by the lasers, so the apparatus is still far short of producing more energy than it requires to operate.

Another key finding was evidence that energy created by the fusion reaction was going back into the remaining fuel, a "bootstrapping" process that is key to boosting the energy output. Hurricane said that showed “promise” for scientists being able to increase the energy output in the future.

Eager to exploit the potential that fusion energy offers to reduce dependence on oil and other fossil fuels, the United States and other nations have invested millions of dollars into fusion research, often with uneven results.

Al Jazeera and wire services