Physics Today by David Kramer 8/17/2021
Lawrence Livermore National Laboratory (LLNL) announced today that it has produced a fusion reaction in the laboratory that yielded more energy than was absorbed by the fuel to initiate it.
Zapping a BB-size capsule of fusion fuel with UV light from 192 lasers at the lab’s $3.5 billion National Ignition Facility (NIF), scientists say they sparked fusion reactions that released 1.3 megajoules of energy, about five times the 250 kilojoules that were absorbed by the capsule. That energy emission from the tiny blob of plasma—roughly a cube with sides measuring the width of a human hair—occurred within about 100 trillionths of a second to yield more than 1016 watts of power.
The shot, which occurred on 8 August, demolished the facility’s previous record yield of 170 kJ, observed in February, and was 25 times as high as the best results obtained just a year ago. “Everyone has a spring in their step,” says NIF director Mark Herrmann. The results have not yet been peer reviewed.
Although the achievement represents a milestone in fusion research, the laboratory stopped short of declaring ignition, the goal for which NIF was named and which it had planned to achieve by 2012. The fusion yield fell short of the 1.9 MJ that the NIF laser brought to bear on the hollow target, called a hohlraum, in which the fuel capsule was suspended. A 1997 National Academy of Sciences review of NIF’s design defined ignition as fusion yield equal to or more than the laser energy input. In NIF’s approach, known as indirect drive, 85% of the laser’s energy is lost in the conversion of UV to x rays that occurs inside the hohlraum.
Stephen Bodner, a former director of the laser fusion program at the Naval Research Laboratory (NRL) and a persistent critic of NIF and the indirect drive approach, congratulated the lab on the achievement, saying it was close enough to ignition for him. “They made spectacular progress,” he says. “I’m surprised they found a way to minimize the laser–plasma problems,” he says. He added that “it demonstrates to the world that there’s no fundamental reason why laser fusion can’t work.”
More:
https://physicstoday.scitation.org/do/10.1063/PT.6.2.20210817a/full/
