Experimental investigation of the density-scale-length effects on laser-plasma instabilities toward the shock-ignition scheme in direct-drive inertial-confinement fusion
Year: 2025
Authors: Nakatsuji C., Kawasaki K., Idesaka T., Matsuura S., Tanaka D., Sato T., Nagatomo H., Sentoku Y., Takagi Y., Cristoforetti G., Batani D., Nicolai P., Ozaki N., Yogo A., Fujioka S., Shigemori K.
Autors Affiliation: Univ Osaka, Inst Laser Engn, 2-6 Yamadaoka, Suita, Osaka 5650871, Japan; Univ Osaka, Grad Sch Sci, 1-1 Machikaneyama, Toyonaka, Osaka 5650043, Japan; INO CNR, Intense Laser Irradiat Lab, I-56124 Pisa, Italy; Univ Bordeaux, CELIA Ctr Lasers Intenses & Applicat, CNRS, CEA,UMR 5107, F-33405 Talence, France; Univ Osaka, Grad Sch Engn, 2-1 Yamadaoka, Suita, Osaka 5650871, Japan; Natl Inst Adv Ind Sci & Technol, Adv Power Elect Res Ctr, Diamond Wafer Team, 1-8-31 Midorigaoka, Ikeda, Osaka 5638577, Japan.
Abstract: In direct-drive inertial-confinement fusion, understanding and controlling laser-plasma instabilities (LPIs) is crucial to optimizing energy coupling and achieving high-gain fusion. Herein, we report the experimental investigation of the effects of density scale-length on LPIs. The experiment was performed at the GEKKO-XII Laser facility [C. Yamanaka et al., IEEE J. Quantum Electron. 17, 1639 (1981)], specifically to characterize stimulated Raman scattering (SRS) and two-plasmon decay (TPD), and the effects of density scale-lengths on the relationship between these LPIs and hot-electron generation. The experimental results consistently indicate that the reduction in hot-electron generation with increasing density scale-length is strongly correlated with decreases in both SRS and TPD in high-density regions. Rosenbluth gain analysis implies that pump depletion by stimulated Brillouin scattering is not responsible for the observed reduction in SRS and TPD. Instead, spatial and temporal incoherence of propagating laser beams, driven by filamentation, could have suppressed SRS and TPD, as evaluated by filamentation figure of merit (FFOM). On the other hand, the thermally corrected FFOM suggests that hot spots by random phase plates are the origin of the early growth of SRS in low-density regions. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International (CC BY-NC-ND) license (https://creativecommons.org/licenses/by-nc-nd/4.0/).
Journal/Review: PHYSICS OF PLASMAS
Volume: 32 (5) Pages from: 52710-1 to: 52710-10
More Information: The authors are grateful to the technical-support staff at the Institute of Laser Engineering, The University of Osaka, for assisting with the laser operation, target fabrication, plasma diagnostics, and computer simulation. This study was supported by the Joint Usage/Research Center program of the Institute of Laser Engineering, The University of Osaka; the Collaboration Research Program between the National Institute for Fusion Science and ILE (No. 2023NIFS21KUGK136); and a Grant-in-Aid for Scientific Research, Power Laser DX Platform as research equipment shared in MEXT Project for promoting the public utilization of advanced research infrastructure (Program for advanced research-equipment platforms; Grant No. JPMXS0450300021), JSPS International Leading Research (Grant No. JP23K20038), and JSPS Core-to-Core Program (Grant No. JPJSCCA20230003). This work has also been carried out within the framework of the EURO-fusion Enabling research Project No. AWP24-ENR-IFE-02-CEA-02. This work was partly achieved through the use of SQUID at D3 Center, The University of Osaka. Y.T. was supported by JST SPRING (Grant No. JPMJSP2138). K.K., D.T., and Y.T. (after April 2023) were partially supported by the Grant-in-Aid for JSPS Fellows (Grant Nos. 22KJ2224, 23KJ1526, and 23KJ1444).KeyWords: Stimulated Raman-scattering; Hot-electron Generation; Brillouin Backscattering; Parametric-instabilities; Electromagnetic-waves; Intensities Relevant; 2-plasmon Decay; Filamentation; Reduction; RegimeDOI: 10.1063/5.0252485
