Scaling laws show paths for improving nuclear fusion yields

In 2022, using deuterium-tritium capsules imploded in an x-ray oven — or hohlraum — the National Ignition Facility produced the first laboratory nuclear fusion reaction that created more energy than the laser input energy. Since then, additional runs have nearly doubled outputs. In light of these achievements, Landen et al. presented semi-analytic expectations for forward-looking strategies that could further improve yields.

“Since a host of design strategies to improve yields beyond ignition have just started up experiments, now was the right time to present semi-analytic extrapolations of expected yield improvements without the bias of ‘calculating’ to the answer,” author Otto Landen said.

The authors combined analytic theory with one-dimensional hydroscaled simulations to extrapolate from the current best 2-4 megajoule outputs. In addition, they clarified the multi-faceted role of hydrogen in improving ablator efficiency, alleviated concerns of increased laser plasma instabilities at larger scale, and highlighted the importance of improving hohlraum efficiency at fixed peak power.

“Now that we have achieved ignition, the most pressing questions are if we can improve outputs by increasing compression, and, if fuel burn-up fraction is limited by ablator-fuel mix, whether that can be mitigated by optimum choice of drive profile, capsule ablator, and dopant profile,” Landen said. “The optimist in me says yes.”

Landen expects that within the decade, ion temperatures will exceed 25 kiloelectron volts, while saturated fuel burn-up fractions and yields could approach 25% and 100 megajoules, respectively. X-ray instrumentation that can map the burn wave will also help scientists study the effects of X-ray bursts associated with ignition that could lead to advances in dense plasma equations of state and opacity.

Source: “What next: Further implosion space exploration on the path to NIF extended yield capability,” by O. L. Landen, R. C. Nora, J. D. Lindl, A. L. Kritcher, S. W. Haan, M. D. Rosen, A. Pak, L. Divol, K. L. Baker, P. A. Amendt, D.D.-M. Ho, J. L. Milovich, J. E. Ralph, D. S. Clark, K. D. Humbird, M. Hohenberger, C. R. Weber, R. Tommasini, D. T. Casey, C. V. Young, D. J. Schlossberg, S. A. Maclaren, E. L. Dewald, P. F. Schmit, T. Chapman, D. E. Hinkel, J. D. Moody, V. A. Smalyuk, O. A. Hurricane, and R. P. J. Town, Physics of Plasmas (2024). The article can be accessed at https://doi.org/10.1063/5.0209027 .

This paper is part of the Papers from the 65th Annual Meeting of the APS Division of Plasma Physics Collection, learn more here .