Effects of spatial beam coherence and plasma scale length on stimulated Raman scattering and two-plasmon decay

Year: 2026

Authors: Nakatsuji C., Takagi Y., Cristoforetti G., Matsuura S., Honda T., Tanaka D., Batani D., Sato T., Horimoto S., Nagatomo H., Sentoku Y., Nicolaï P.D., Taketoshi K., Yamagata N., Ozaki N., Arikawa Y., Yogo A., Fujioka S., Shigemori K.

Autors Affiliation: Univ Osaka, Inst Laser Engn, Suita, Osaka 5650871, Japan; CNR, INO, Intense Laser Irradiat Lab, I-56124 Pisa, Italy; Univ Bordeaux, Ctr Lasers Intenses & Applicat, CNRS, CEA,UMR 5107, F-33405 Talence, France; Univ Osaka, Grad Sch Engn, Suita, Osaka 5650871, Japan.

Abstract: We present an experimental investigation demonstrating that the suppression of parametric instabilities in laser-plasma interactions under conditions relevant to direct-drive inertial confinement fusion, specifically backward stimulated Raman scattering (SRS) and two-plasmon decay (TPD), shows the effects of spatial beam coherence and plasma-density scale length. Experiments were performed with the GEKKO-XII kilojoule laser, both with and without random phase plates. Results indicate that SRS suppression is enhanced under conditions of initial spatial incoherence, whereas TPD is influenced primarily by the plasma scale length. A comparison of the relationship between the SRS and TPD signals and hot-electron measurements suggests that TPD is the primary source of hot electrons across all experimental conditions. These findings underscore the importance of beam coherence in determining instability dominance and carry implications for mitigating hot-electron preheat in ignition-scale inertial-confinement implosions as well as for developing hot-electron-driven schemes such as shock ignition.

Journal/Review: PHYSICAL REVIEW E

Volume: 114 (1)      Pages from: 15202-1  to: 15202-9

More Information: The authors would like to acknowledge the technical-support staff at the Institute of Laser Engineering (ILE), The University of Osaka (UOsaka), for assistance with the laser operation, target fabrication, plasma diagnostics, and computer simulation. This study was supported by the Collaboration Research Program between the National Institute for Fusion Science and ILE, UOsaka, Grant No. 2024NIFS21KUGK136; JST SPRING, Grant No. JP-MJSP2138; Power Laser DX Platform as research equipment shared in The MEXT Project for promoting the public utilization of advanced research infrastructure (Program for advanced research-equipment platforms), Grant No. JPMXS0450300124; and the Japan Society for the Promotion of Science (JSPS) International Leading Research, Grant No. JP23K20038. This work was carried out within the EUROfusion Enabling Research Projects No. AWP24-ENR-IFE-02-CEA-02 and No. CfP-FSD-AWP26-ENR-01, funded by the Euratom Research and Training Programme (Grants No. 633053 and No. 101052200). This work was partly achieved through the use of SQUID at D3 Center, UOsaka. D.T. and Y.T. were partially supported by the Grant-in-Aid for JSPS Fellows, Grants No. 23KJ1526 and No. 23KJ1444.
KeyWords: Inertial-confinement Fusion; Laser-beam; Brillouin; Reduction; Filamentation
DOI: 10.1103/ppxh-562y