Studies of laser-plasma interaction physics with low-density targets for direct-drive inertial confinement fusion on the Shenguang III prototype

The physics of laser-plasma interaction is studied on the Shenguang III prototype laser facility under conditions relevant to inertial confinement fusion designs.A sub-millimeter-size underdense hot plasma is created by ionization of a low-density plastic foam by four high-energy(3.2 kJ)laser beams.An interaction beam is fired with a delay permitting evaluation of the excitation of parametric instabilities at different stages of plasma evolution.Multiple diagnostics are used for plasma characterization,scattered radiation,and accelerated electrons.The experimental results are analyzed with radiation hydrodynamic simulations that take account of foam ionization and homogenization.The measured level of stimulated Raman scattering is almost one order of magnitude larger than that measured in experiments with gasbags and hohlraums on the same installation,possibly because of a greater plasma density.Notable amplification is achieved in high-intensity speckles,indicating the importance of implementing laser temporal smoothing techniques with a large bandwidth for controlling laser propagation and absorption.

Shock dynamics and shock collision in foam layered targets

We present an experimental study of the dynamics of shocks generated by the interaction of a double-spot laser in different kinds of targets:simple aluminum foils and foam-aluminum layered targets.The experiment was performed using the Prague PALS iodine laser working at 0.44μm wavelength and irradiance of a few 10^(15)W/cm^(2).Shock breakouts for pure Al and for foam-Al targets have been recorded using time-resolved self-emission diagnostics.Experimental results have been compared with numerical simulations.The shocks originating from two spots move forward and expand radially in the targets,finally colliding in the intermediate region and producing a very strong increase in pressure.This is particularly clear for the case of foam layered targets,where we also observed a delay of shock breakout and a spatial redistribution of the pressure.The influence of the foam layer doped with high-Z(Au)nanoparticles on the shock dynamics was also studied.