NEW YORK — After years of disappointing results and missed deadlines, a $5 billion laser complex has achieved a step reviving optimism that thermonuclear fusion, the process that powers the sun, can one day be harnessed for almost limitless energy.
At the Lawrence Livermore National Laboratory in California, 192 enormous lasers in a structure the size of a football stadium fire at a small gold cylinder, vaporizing it. That generates an onslaught of X-rays rushing inward toward a fuel pellet smaller than a peppercorn, crushing the hydrogen inside into helium and releasing a burst of energy — effectively, a mini hydrogen bomb.
But for four years since the facility began operations in 2009, the last step — the fusion of hydrogen atoms into helium — did not happen, not in significant quantity.
In September, it did.
Writing in Thursday’s issue of the journal Nature, scientists working on the project report on the September shot as well as one in November. In both, the hydrogen fusion generated more energy than had been deposited into the hydrogen.
However, laser-driven fusion remains far from practical, because only about 1 percent of the initial laser energy reached the hydrogen.
“A lot of people are jazzed,” Omar A. Hurricane, the Livermore scientist leading the project, said during a telephone conference on Monday. “We’re certainly in a lot better position than we were. This has been a kind of turning point, I think, here at the lab.”
Hurricane said his team had made further advances. “This sounds very modest,” Hurricane said. “And it is. But this is closer than anyone has gotten before, and it is unique to finally get as much energy out of the fuel as was put in.”
A longstanding hope is that fusion can become a bountiful, cleaner energy source than fossil fuels or nuclear fission, which produces long-lived radioactive waste.
Specialists say the results should help give the giant laser more time to prove its worth and keep taxpayer support.