Scientists at the Lawrence Livermore National Laboratory reported Thursday they have taken a major step toward harnessing the forces that power the sun in an effort to create unlimited energy on Earth.

In experiments at the lab's National Ignition Facility, the scientists successfully fired an array of 192 laser beams at a helium-filled target no larger than a BB shot and instantly heated it to 6 million degrees Fahrenheit. The gas vanished in a tiny explosion.

The scientists said that result marked the most important advance yet in more than 10 years of work at the $3.5 billion facility.

They are seeking two major goals:

-- To create in miniature the explosions of thermonuclear weapons in order to validate the computer codes that test the safety and reliability of America's nuclear stockpile.

-- To show that the immensely powerful lasers can achieve safe fusion reactions that could be scaled up for the eventual production of unlimited and clean energy, a dream nuclear scientists have been pursuing for more than five decades.

Working toward 'ignition'

The successful experiments by a team of 35 physicists, led by ignition facility scientists Siegfried H. Glenzer and L. Jeffrey Atherton, were described Thursday in the online edition of the journal Science. In coming months the team will start a new round of experiments seeking finally to achieve what they call "ignition" - a true thermonuclear reaction inside the laboratory's tiny targets.

"We're confident of our ability to start seeking ignition this summer," Atherton said in an interview. "And we're optimistic that at some point soon we'll achieve it."

To achieve that thermonuclear reaction, the scientists will attempt to use the lasers' immensely powerful beams to reach temperatures of more than 200 million degrees Fahrenheit and pressures millions of times greater than Earth's atmosphere - conditions found only in the interior of the sun and stars.

The beryllium target will be filled with deuterium and tritium - the isotopes of hydrogen - frozen into a crystal at 424 degrees below zero Fahrenheit and blasted by the lasers in a billionth of a second. The target will be held inside a tiny gold cylinder called a hohlraum, about the size of a pencil eraser.

If those experiments succeed, the hydrogen isotopes would be crushed instantly and explode inward until they fuse and yield vastly more energy than the laser beams had pumped into them.

The National Ignition Facility is a 10-story building that was dedicated in May on the heavily guarded and highly classified Livermore site. But for many decades, Livermore scientists foresaw the need for increasingly powerful lasers to reach ignition. Lasers called Janus, Cyclops, Argus and the 20-beam laser named Shiva were used to conduct crucial experiments that led to the 10-year development of the laser array.

Thermonuclear reactions

The new laser array will be used to trigger thermonuclear reactions mimicking in miniature the deadly energy of thermonuclear weapons, and those efforts are the principal aim of the project. It is largely funded by the National Nuclear Security Agency, which oversees America's arsenal of nuclear weapons and seeks to maintain their safety and reliability as the weapons age.

But many scientists foresee that experiments like the ones at the ignition facility could lead the way to the eventual construction of large-scale fusion reactor power plants capable of generating countless megawatts of electricity using the hydrogen isotopes from ocean water as endless fuel.

B. Grant Logan, director of a separate and unclassified attempt to achieve ignition based at the Lawrence Berkeley National Laboratory, said the new report is highly encouraging.

The report, he said in an e-mail, shows "remarkable progress toward the scientific demonstration of fusion ignition and energy gain in the laboratory for the first time in the world. At the rate they are going," he said, "it does appear to me that fusion ignition will be demonstrated soon."