Scientists are creeping closer to their goal of creating a controlled fusion-energy reaction by mimicking the interior of the sun inside the hardware of a laboratory.

In the latest incremental advance, reported Wednesday online in the journal Nature, scientists in Livermore, Calif., 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.

There’s still a long way to go before anyone has a functioning fusion reactor, something physicists have dreamed of since Albert Einstein was alive. A fusion reactor would run on a common form of hydrogen found in sea water, would produce minimal nuclear waste and couldn’t have the kind of meltdown that can occur in a traditional nuclear-fission reactor.

“You kind of picture yourself climbing halfway up a mountain, but the top of the mountain is hidden in clouds,” said Omar Hurricane, the lead author of the Nature paper, in a teleconference with journalists. “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.”

Hurricane and other scientists at the Lawrence Livermore National Laboratory, home of the multi-billion-dollar National Ignition Facility, took pains to calibrate their claims of success. This was not fusion “ignition,” the ultimate ambition of the NIF. The experiment overall requires much more energy on the front end – all those laser shots – than comes out the back end.

But the experiment worked as hoped.

When briefly compressed by the laser pulses, two hydrogen isotopes fused, generating new particles and heating up the fuel further and generating still more nuclear reactions, particles and heat.

“They’ve got a factor of about 100 to go,” said Mark Herrman, director of the Pulse Power Sciences Center at the Sandia National Laboratory, a sister institution to the Livermore lab. “They made 5 million billion fusions, but we want … 100 times more than what they made.”

To frame the challenge further: Even if ignition is achieved in coming years, the contraption required is so elaborate and capital-intensive – total cost of the NIF operation is in the realm of $5 billion – that it may be of limited practical application for generating electricity to power someone’s toaster.

Still, the new result represents progress in the fusion-energy field and came as a relief for Lawrence Livermore scientists after early efforts produced energy yields lower than what had been predicted from computer models.