Nell’anniversario di un anno dal raggiungimento di una resa di oltre 1,3 megajoule presso la National Ignition Facility di LLNL, i risultati scientifici di questo esperimento standard sono stati pubblicati in tre articoli sottoposti a revisione paritaria: uno in Physical Review Letters e due in Physical Review E. Questo l’immagine stilizzata mostra un bersaglio criogenico utilizzato negli esperimenti di fusione inerziale per individuare i record. Credito: James Wickboldt/LLNL
Dopo decenni di ricerca sulla fusione a confinamento inerziale, la resa di oltre 1,3 megajoule (MJ) È stato raggiunto per la prima volta l’8 agosto 2021. Gli scienziati del Lawrence Livermore National Laboratory (LLNL) hanno messo la National Ignition Facility (NIF) sulla soglia dell’acquisizione della fusione e dell’accensione scientifica.
In occasione del primo anniversario di questo traguardo storico, i risultati scientifici di questo esperimento standard sono stati pubblicati in tre documenti sottoposti a revisione paritaria. Un documento è stato pubblicato in messaggi di revisione fisica e due dentro revisione fisica. Nel messaggi di revisione fisica Ricerca, oltre 1.000 autori sono inclusi per identificare e apprezzare le molte persone che hanno lavorato per molti decenni per consentire questo importante progresso.
“Il colpo record è stato un importante progresso scientifico nella ricerca sulla fusione, che dimostra che l’accensione della fusione in vitro è possibile nel NIF”, ha affermato Omar Hurrican, scienziato capo del programma di fusione di autoconfinamento di LLNL. “Il raggiungimento delle condizioni per l’accensione è stato un obiettivo di lunga data di tutta la ricerca sulla fusione con autoconfinamento e consente l’accesso a un nuovo regime sperimentale in cui l’autoriscaldamento delle particelle alfa supera tutti i meccanismi di raffreddamento della fusione.[{” attribute=””>plasma.”
The results from August 8, 2021, are described in detail in the papers. They also include the associated design, improvements, and experimental measurements. LLNL physicist Alex Zylstra, lead experimentalist and first author of the experimental Physical Review E paper, noted that in 2020 and early 2021 the Lab conducted experiments in the “burning plasma” regime for the first time. These set the stage for the record shot.
“From that design, we made several improvements to get to the August 8, 2021, shot,” he said. “Improvements to the physics design and quality of target all helped lead to the success of the August shot, which is discussed in the Physical Review E papers.”
This experiment incorporated a few important changes, including an improved target design. “Reducing the coasting-time with more efficient hohlraums compared to prior experiments was key in moving between the burning plasma and ignition regimes,” said LLNL physicist Annie Kritcher, lead designer and first author of the design Physical Review E paper. “The other main changes were improved capsule quality and a smaller fuel fill tube.”
Since the experiment last August, the researchers have been executing a series of experiments to attempt to repeat the performance and to understand the experimental sensitivities in this new regime.
“Many variables can impact each experiment,” Kritcher said. “The 192 laser beams do not perform exactly the same from shot to shot, the quality of targets varies and the ice layer grows at differing roughness on each target. These experiments provided an opportunity to test and understand the inherent variability in this new, sensitive experimental regime.”
Although the repeat attempts have not reached the same level of fusion yield as the August 2021 experiment, all of them demonstrated capsule gain greater than unity. They have had yields in the 430-700 kJ range, which are significantly higher than the previous highest yield of 170 kJ from February 2021. The data gained from these and other experiments are providing crucial clues as to what went right and what changes are needed in order to not only repeat that experiment but also exceed its performance in the future. The scientists are also utilizing the experimental data to increase understanding of the fundamental processes of fusion ignition and burn. They’re also working to enhance simulation tools in support of stockpile stewardship.
Looking ahead, the research team is working 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 new experimental regime can be better separated from variability in targets and laser performance.
Efforts to increase fusion performance and robustness are underway via improvements to the laser and improvements to the targets. Additionally, they’re working on modifications to the design that further improve energy delivery to the hotspot while maintaining or even increasing the hot-spot pressure. This includes improving the compression of the fusion fuel, increasing the amount of fuel, and other avenues.
“It is extremely exciting to have an ‘existence proof’ of ignition in the lab,” Hurricane said. “We’re operating in a regime that no researchers have accessed since the end of nuclear testing, and it’s an incredible opportunity to expand our knowledge as we continue to make progress.”
References:
“Lawson Criterion for Ignition Exceeded in an Inertial Fusion Experiment” by H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), 8 August 2022, Physical Review Letters.
DOI: 10.1103/PhysRevLett.129.075001
“Experimental achievement and signatures of ignition at the National Ignition Facility” by A. B. Zylstra et al., 8 August 2022, Physical Review E.
DOI: 10.1103/PhysRevE.106.025202
“Design of an inertial fusion experiment exceeding the Lawson criterion for ignition” by A. L. Kritcher et al., 8 August 2022, Physical Review E.
DOI: 10.1103/PhysRevE.106.025201
