Observation and modelling of stimulated Raman
scattering driven by an optically smoothed laser beam in
experimental conditions relevant for shock ignition

Year: 2021

Authors: Cristoforetti G., Hüller S., Koester P., Antonelli L., Atzeni S., Baffigi F., Batani D., Baird C.,
Booth N., Galimberti M., Glize K., Héron A., Khan M., Loiseau P., Mancelli D., Notley M., Oliveira P., Renner O., Smid M., Schiavi A., Tran G., Woolsey N.C., Gizzi LA.

Autors Affiliation: 1 – Intense Laser Irradiation Laboratory, INO-CNR, Italy
2 – Centre de Physique Théorique CPHT, CNRS, France
3 – York Plasma Institute, Department of Physics, University of York, UK
4 – Dipartimento SBAI, Università di Roma ‘La Sapienza’, Italy
5 – Université de Bordeaux, CNRS, CEA, France
6 – STFC Rutherford Appleton Lab, Central Laser Facility, UK
7 – Key Laboratory for Laser Plasmas (MOE), Shanghai Jiao Tong University, China
8 – CEA, DAM, DIF, France
9 – Université Paris-Saclay, CEA, France
10 – Institute of Physics, ELI Beamlines, Institute of Plasma Physics, Czech Academy of Sciences, Czech Republic
11 – Helmholtz-Zentrum Dresden-Rossendorf, Germany

Abstract: We report results and modelling of an experiment performed at the Target Area West Vulcan laser facility, aimed
at investigating laser–plasma interaction in conditions that are of interest for the shock ignition scheme in inertial
confinement fusion (ICF), that is, laser intensity higher than 1016 W/cm2 impinging on a hot (T > 1 keV),
inhomogeneous and long scalelength pre-formed plasma. Measurements show a significant stimulated Raman scattering
(SRS) backscattering (∼ 4%−20% of laser energy) driven at low plasma densities and no signatures of two-plasmon
decay (TPD)/SRS driven at the quarter critical density region. Results are satisfactorily reproduced by an analytical
model accounting for the convective SRS growth in independent laser speckles, in conditions where the reflectivity is
dominated by the contribution from the most intense speckles, where SRS becomes saturated. Analytical and kinetic
simulations well reproduce the onset of SRS at low plasma densities in a regime strongly affected by non-linear Landau
damping and by filamentation of the most intense laser speckles. The absence of TPD/SRS at higher densities is
explained by pump depletion and plasma smoothing driven by filamentation. The prevalence of laser coupling in the
low-density profile justifies the low temperature measured for hot electrons (7−12 keV), which is well reproduced by
numerical simulations.

Journal/Review: HIGH POWER LASER SCIENCE AND ENGINEERING

Volume: 9      Pages from: e60  to: e60

KeyWords: Laser-Plasma Interaction, Kinetic simulations, Inertial Confinement Fusion
DOI: 10.1017/hpl.2021.48