Story highlights A fusion test produces more energy than it uses, but there's some fine print

Fusion could produce abundant, clean power, but it's never been harnessed

The results are "modest," but "closer than anyone's gotten before," scientist says

The event was over in a fraction of a scintilla of a blink of an eye and released a burst of energy that's not particularly impressive by most standards.

But it's being hailed as a milestone in a decades-long quest to harness the power of nuclear fusion, the same process that powers the sun. For the first time, scientists at the Lawrence Livermore National Laboratory in California say they produced more energy from a reaction in their fuel source than they put into the fuel, said Omar Hurricane, the physicist who led the experiment.

"You're not going to power a car with it. You're not going to power a house with it," Hurricane told CNN. "It'll be a while before we address all the needed scientific challenges and then the engineering challenges to make it more practical, but we're excited. It's a great step forward scientifically."

There is a bit of fine print. The implosion of a tiny pellet holding two hydrogen isotopes did produce more energy than it took to cause it -- about 17,000 joules, which Hurricane compared to the force of a downhill skier doing about 36 mph. However, the pellet received only about 1% of the total energy expended in the experiments, he said.

But the reaction also produced a heating effect that appeared to boost the energy output -- a process dubbed "bootstrapping" by Hurricane's team at Livermore's laser fusion research center, the National Ignition Facility. And that may point scientists toward their ultimate goal of a controlled, sustainable fusion reaction that would provide abundant, safe power, he said.

"We've assembled that stick of dynamite and we've gotten the fuse to light," he said. "If we can get that fuse to burn all the way to the dynamite, it's going to pack a wallop."

The findings were published Wednesday in the scientific journal Nature. While humans have been producing uncontrolled fusion reactions since the 1950s through hydrogen bombs, harnessing nuclear fusion in a controlled setting has eluded scientists for decades.

In a series of tests conducted at the NIF from September through November, scientists used a battery of 192 high-powered lasers to bombard a tiny pellet inside a gold chamber less than an inch long. Inside the pellet was a hair-thin layer of two hydrogen isotopes, deuterium and tritium, chilled to a temperature more than 400 degrees below zero Fahrenheit.

The gold converts the laser light into a bath of X-rays, which cause the surface of the capsule to explode. That drives the capsule inward onto itself, an implosion that builds up pressure on the hydrogen isotopes. The pressure compresses the deuterium-tritium mix to a density more than double that found in the center of the sun, Hurricane said.

Then the deuterium and tritium fuse into one, releasing neutrons and alpha particles -- helium atoms without the electrons circling them. And in a seventh of a billionth of a second, it's over.

However, the most recent experiments produced more helium nuclei, which increased the reaction rate, which produced more alpha particles, Hurricane said. It's that "bootstrapping" that he said may lead scientists to eventually produce a reaction that yields more energy than it consumes.

"It sounds very modest, and it is," he said. "But this is kind of closer than anyone's gotten before, and it is very unique to finally get as much energy out of the fuel as was put into the fuel."