One of the main concerns of Inertial Confinement Fusion is the impact of laser parametric instabilities growing during the interaction of the laser pulse with the long-scale plasma corona; the issue is even more serious in the Shock Ignition scheme, where the intensity of the laser spike (~10¹⁶ W/cm²) producing the igniting shock wave is an order of magnitude higher than the intensity needed in the classical direct-drive scheme. Among laser-plasma instabilities, Stimulated Raman Scattering (SRS) and Two Plasmon Decay (TPD) result in the generation of large fluxes of suprathermal hot electrons (HEs), that can be absorbed by the cold fuel, enhancing its entropy and preventing ignition. SRS can also scatter a significant amount of energy both in the backward direction (Back SRS) and at large angles (Side SRS), resulting in larger energy requirements for the laser driver.  The non-linear character of these instabilities makes the extrapolation of analytical models quite inaccurate; a more detailed understanding of these processes therefore calls for experiments dedicated at investigating Laser Plasma Interaction (LPI) in conditions as close as possible to those envisaged in SI. The final aim of this research is identifying the proper ways to tune or mitigate the effects of such instabilities to reach an effective compression and ignition of the fuel.
Here, we will summarize recent experimental results obtained in campaigns at PALS and VULCAN laser facilities, carried out in the framework of the EuroFusion research program. Experiments were aimed at understanding the role of plasma and laser parameters on the growth of Back SRS, Side SRS and TPD as well as identifying the mechanisms originating HEs in conditions relevant for SI.  We will finally show preliminary results of recent experiments aimed at investigating the effects of laser chirped pulses on LPI in experimental conditions relevant for Shock Ignition ICF conditions.
 

laser-plasma interaction,inertial confineme