Scientists Behind Nuclear Fusion Milestone Near Repeat of Feat in Recent Test

(Bloomberg) -- The scientists behind last year’s nuclear fusion breakthrough, which raised the possibility of an abundant and clean future energy source, have not yet been able to duplicate their historic achievement. But they’re close.

Last month, the team at Lawrence Livermore National Laboratory in California triggered a nuclear fusion reaction that produced as much energy as it took to create, as the world’s most powerful laser blasted a tiny diamond capsule filled with hydrogen. That one-for-one balance fell just shy of achieving “ignition” — the long-sought point at which a controlled fusion reaction generates more energy than went into it. 

Nuclear fusion powers the stars, and ignition has been a holy grail for entire generations of scientists. The Livermore lab near San Francisco finally achieved it for the first time on Dec. 5, pouring in 2.05 megajoules of energy through the lab’s laser and getting 3.15 megajoules back. 

Since then, the lab has tried eight similar experiments without reaching ignition, said Richard Town, associate program director for the effort. But the June 5 experiment hit what he called breakeven, with 1.87 megajoules of laser energy going in and an equal amount of fusion energy coming out. It was the second-largest amount of energy one of the lab’s experiments — or “shots” — has produced so far, Town said in an interview. 

The team tweaks its approach each time. For this particular shot, the researchers used a slightly longer pulse from the laser to help compress the hydrogen fuel and trigger fusion, and that seemed to boost the output, Town said. The team aims to achieve ignition again this year.

“We’re making progress,” Town said. “We haven’t got a headline 3 megajoules again, or higher. But I think with every experiment, we have to ask ourselves, ‘What are we learning?’”

Nuclear power plants today use fission — splitting atoms apart — whereas fusion smashes atoms together. It can in theory supply energy without producing nuclear waste like the spent fuel rods from today’s fission reactors. 

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