Part 2 of 3 Parts (Please read Part 1 first)
     The NIF was opened at the LLNL in 2009 with the promise of achieving fusion ignition. The U.S National Academy of Sciences (NAS) defines fusion ignition as an experiment that generates more energy than it consumes. This threshold is also referred to as the Lawson Criterion. After the NIF missed the initial deadline of achieving ignition in 2012, LLNL scientists began a decade-long effort to fine-tune the experimental system. Finally, last August, the researchers finished a series of precise adjustments to aspects of the facility including the lasers and the ignition target. The target consisted of a tiny gold capsule containing a frozen pellet of the hydrogen isotopes deuterium and tritium. The final experiment with the adjusted parameters gave them their breakthrough moment.
     In under four billionths of a second, one hundred and ninety-two laser beams delivered one thousand and nine hundred kilojoules to the target capsule. As the target collapsed under the onslaught to the laser beams, hydrogen isotopes at the core of the pellet began to fuse into helium. This released a torrent of energy and created a cascade of reactions that ultimately released more than one thousand three hundred kilojoules of energy. This was around eight times the previous record for fusion energy production. It was also a one-thousand-fold improvement on the earliest experiments at the NIF.
      Although it did not meet the NAS definition of ignition, the shot did result in a high-yield fusion reaction that safely qualified as ignition as defined by the criteria used by scientists at the NIF. Hurricane referred to it as a “Wright brothers’ moment”. Even the harshest critics of the NIF were impressed.
      Last September, the leaders of the inertial-confinement fusion program created a plan for three experiments to determine whether the results of last August’s experiments could be repeated. This set of experiments began last October and yielded only four hundred to seven hundred kilojoules of energy. These results represent a step-change in the operations at the NIF. However, they did not come close to the August breakthrough, and they did not surpass what the NIF scientists describe as the ignition threshold.
       Hurricane said that his team’s analysis of those experiments indicates that inconsistencies in the fabrication of the target and inevitable shifts in the lasers’ performance due to their age produced minute but important differences in the shape of the implosion. He said, “We understand why the repeat shots performed the way they did. But we’re still trying to pin down what exactly about these engineering aspects we need to control better.”
     In light of those experimental results, Hurricane advocated for additional repeat experiments that could be used to better understand the shot-to-shot variation. However, the NIF program leaders decided instead to move on. Hurricane said that the team is now looking at methods of boosting the laser energy by more than ten percent. They are also going to modify the targets to make more efficient use of that energy.
Please read Part 3 next