The 6th International Conference on Matter and Radiation at Extremes (ICMRE2023)

88 / 2023-04-13 11:48:01

Preliminary observation of stimulated Raman side-scattering dependence on laser intensity in Direct-Drive experiments

inertial confinement fusion,laser plasma instabilities,Stimulated Raman Scattering,Direct-Drive

Inertial Confinement Fusion Physics > Holraum and laser-plasma interaction-I

Direct-Drive Ignition (DD) is an Inertial Confinement Fusion (ICF) scheme in which a fuel target is compressed and ignited by direct laser irradiation. Despite preliminary results anticipating the predominance of Two-Plasmon Decay, recent experiments have evidenced the dominant role of the Stimulated Raman Scattering (SRS). This three-wave coupling leads to the scattering of the incident energy away from the interaction region and the generation of a hot electron population that can preheat the fuel core. Under such conditions, SRS can develop in multiple geometries, such as the standard back-scattering (SRBS) and the more elusive side-scattering (SRSS). However, the inherent complexity of the side-scattering geometry is strongly limiting experimental characterization, preventing to obtain a SRSS comprehensive understanding.



Recent measurements, obtained during the campaigns of the Double-Cone Ignition (DCI) approach at the Shenguang-II Upgrade laser facility, have implemented a new diagnostic specifically designed to measure SRS over a wide range of angles. Direct comparison with backscattering measurement have evidenced a regime dominated by SRSS during the fuel assembling. Thus, these experiments provide an ideal platform to characterize SRSS instability. Parametric scans have been conducted to observe the dependence of SRSS on the incident laser energy, by modifying whether the incident energy or the focal spot dimensions. Different scaling than the classic SRBS sharp intensity threshold have been observed and will be discussed during this presentation.