Three Papers Highlight the Results Of Record 1.3 Megajoule Yield Experiment
On the first anniversary of this historical achievement, the scientific results of this record experiment have been published in three peer-reviewed papers: 1 in Physical Review Letters and two in Physical Review E. More than 1,000 writers are included in one of the Physical Review Letters paper to recognize and acknowledge the many people who have functioned over many years to allow this significant improvement.
“The record shot was a major scientific development in fusion research, which establishes that fusion ignition in the laboratory is possible at National Ignition Facility (NIF),” stated Omar Hurricane, chief scientist for Lawrence Livermore National Research lab’s (LLNL’s) inertial confinement fusion program. “Achieving the conditions required for ignition has been a long-standing aim for all inertial confinement fusion study and opens up access to a brand-new experimental regime where alpha-particle self-heating outstrips all the cooling mechanisms in the fusion plasma.”
The papers describe, in detail, the outcomes from Aug. 8, 2021, and also the associated design, improvements, and also experimental measurements. LLNL physicist Alex Zylstra, lead experimentalist and the 1st author of the experimental Physical Review E paper, noticed that in 2020 and early 2021, the Laboratory conducted experiments in the “burning plasma” regime for the first time, that set the stage for the record shot.
“From that design, we made several improvements to get to the Aug. 8, 2021, shot,” he said. “Improvements to the physics design and target quality all assisted lead to the success of the August shot, which is argued in the Physical Review E papers.”
This experiment incorporated a few modifications, including an improved target design. “Reducing the coasting-time with more effective hohlraums contrasted to previous experiments was key in moving between the burning plasma and ignition regimes,” said LLNL physicist Annie Kritcher, lead developer and 1st author of the other Physical Review E paper. “The other main changes were developed capsule quality and also a smaller fuel fill tube.”
Since the experiment last August, the group has been executing a series of experiments to try to repeat the performance and also to understand the experimental sensitivities in this brand-new regime.
“Many variables could impact each experiment,” Kritcher stated. “The 192 laser beams don´t perform exactly the same from shot to shot, the quality of targets differs, and the ice layer grows at differing roughness on each target. These experiments offered a chance to test and understand the inherent variability in this brand-new, sensitive experimental regime.”
While the repeat attempts get not reached the same degree of fusion yield as the August 2021 experiment, all of them showed capsule gain greater than unity with yields in the 430– 700 kJ range, significantly higher than the before highest yield of 170 kJ from February 2021.
The information gained from these and other experiments provides crucial clues as to what went right and what changes are needed to repeat that experiment and exceed its performance in the future. The team is also utilizing the experimental data to further understand the fundamental processes of fusion ignition and burn and to enhance simulation devices in support of stockpile stewardship.
Looking ahead, the team is functioning to leverage the accumulated experimental data and simulations to move toward a more robust regime– further beyond the ignition cliff– where general trends found in this brand-new experimental regime could be better divided from variability in targets and laser performance.
Efforts to enlarge fusion performance and robustness are underway through advancements to the laser, improvements to the targets, and changes to the design that further improve power delivery to the hotspot while keeping or even increasing the hot-spot pressure. This includes developing the compression of the fusion fuel and increasing the amount of gas and other avenues.
“It is extremely exciting to get an ‘existence proof’ of ignition in the lab,” Hurricane said. “We are operating in a regime that no researchers have accessed since the end of nuclear testing, and it is an incredible opportunity to expand our knowledge as we continue to make progress.”
More information:
H. Abu-Shawareb et al, Lawson Criterion for Ignition Exceeded in an Inertial Fusion Experiment, Physical Review Letters (2022). DOI: 10.1103/PhysRevLett.129.075001
A. B. Zylstra et al, Experimental achievement and signatures of ignition at the National Ignition Facility, Physical Review E (2022). DOI: 10.1103/PhysRevE.106.025202
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