Abstract
Irradiating a small capsule containing deuterium and tritium fuel directly with intense laser light causes it to implode, which creates a plasma hot enough to initiate fusion reactions between the fuel nuclei. Here we report on such laser direct-drive experiments and observe that the fusion reactions produce more energy than the amount of energy in the central so-called hot-spot plasma. This condition is identified as having a hot-spot fuel gain greater than unity. A hot-spot fuel gain of around four was previously accomplished at the National Ignition Facility in indirect-drive inertial confinement fusion experiments where the capsule is irradiated by X-rays. In that case, up to 1.9 MJ of laser energy was used, but in contrast, our experiments on the OMEGA laser system require as little as 28 kJ. As the hot-spot fuel gain is predicted to grow with laser energy and target size, our work establishes the direct-drive approach to inertial fusion as a promising path towards burning and ignited plasmas in the laboratory. Additionally, we report a record (direct-drive) fusion yield of 0.9 kJ on OMEGA, which we achieved with thin-ice deuterium–tritium liner targets.
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Data availability
Raw data were generated at the Laboratory for Laser Energetics and are not available to the general public. Derived data supporting the findings of this study are available from the corresponding authors upon request.
Code availability
The simulation codes used in this paper are not available to the general public.
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Acknowledgements
We thank P. Patel for discussions regarding the relationship between neutron and X-ray emission. This report was prepared as an account of work sponsored by an agency of the US Government. Neither the US Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process or service by trade name, trademark, manufacturer or otherwise does not necessarily constitute or imply its endorsement, recommendation or favouring by the US Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the US Government or any agency thereof. This work was performed at the Laboratory for Laser Energetics for the US Department of Energy National Nuclear Security Administration under grant no. DE-NA 0003856, and grants no. DE-SC0021072 and DE-SC0022132 from the Department of Energy Office of Fusion Energy Science. Funding for the targets utilized in this study was provided by General Atomics and funded through NNSA contract 89233119CNA000063.
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C.A.W. and R.B. conceived the study and wrote the paper. V.G., R.B., A.L. and R.E. developed predictive models used to design high-performance experiments. V.G., C.A.W., R.B., J.P.K., A.L., D.C., P.S.F., R.Ejaz., C.A.T., W.T., M.J.R., S.P.R., C.Stoeckl. and V.N.G. designed and executed experiments used in training the predictive models used for this work. V.G., C.A.W., R.B., A.L. D.P., J.P.K. and C.J.F designed and executed the high-performance experiment series. D.C., K.S.A., R.Epstein., J.C.-N., I.V.I., J.A.M., P.B.R., T.J.B.C., S.X.H., W.S. and V.N.G. contributed to the radiation–hydrodynamic simulation development used in this work. V.G., C.J.F., V.Y.G., W.T., D.H.E., S.I., M.J.R., H.M.C., M.G.J., R.D.P., J.A.F., R.C.S. and S.P.R. contributed to the development and analysis of diagnostics used in this work. D.B, C.F., M.K., R.T.J., M.J.B., J.M., B.S., D.G., C.Shuldberg., M.F. and D.R.H. were responsible for fielding the implosion targets used in this work. K.A.B., S.S. and L.J.W. were responsible for managing the OMEGA laser. M.L. and S.F.B.M. were responsible for managing the Omega facility and experimental operations. E.M.C. and C.D. were responsible for project management for the Laboratory for Laser Energetics.
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Extended data
Extended Data Fig. 1 SRTe x-ray Image.
Spatially resolved electron temperature (SRTe) diagnostic experimental x-ray image of shot number 102154. The photon simulated luminescence (PSL) is an analog for brightness. Fourier analysis of the hot-spot modes show that the \(\ell = 2\) mode is typically dominant in OMEGA implosions, and the inferred hot-spot volumes account for ellipticity. The majority of recent high-yield OMEGA implosions are round, with low semi-major to semi-minor axis ratios a/b. For example, shot 102154 has a/b = 1.03 ± 0.02.
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Williams, C.A., Betti, R., Gopalaswamy, V. et al. Demonstration of hot-spot fuel gain exceeding unity in direct-drive inertial confinement fusion implosions. Nat. Phys. (2024). https://doi.org/10.1038/s41567-023-02363-2
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DOI: https://doi.org/10.1038/s41567-023-02363-2
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