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

Abstract

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.

Investigation of the Langdon effect on the nonlinear evolution of SRS from the early-stage inflation to the late-stage development of secondary instabilities

“…The reduction of Landau damping due to the Langdon effect and nonlinear kinetic trapping, as well as the resultant change from convective to absolute SRS growth, can serve as possible reasons for the underestimated SRS reflectivity obtained by the convective gain model in numerical analysis of the experiments under the assumption of Maxwellian EEDFs [8,9,11], which is helpful for further improvement to the physical modeling and simulation of SRS. However, for SRS in the complicated realistic plasma of ICF experiments [9,32,48,49], it should be noted that nonuniform plasma condition [10] and the high dimensional effects such as wavefront bowing, self-focusing, sideloss, etc [50][51][52], which are not present in the current model, also play important roles in the evolution of SRS. So, further work with multi-dimensional effects considered should be done under more realistic laser and plasma conditions to assess the importance of the Langdon effect to SRS in ICF experiments.…”

Modeling the x-ray enhancement in foams for laser-driven soft x-ray sources

“…In the simulation, only the inverse bremsstrahlung is considered in laser energy deposition. In reality, laser-plasma interactions (LPIs) are extremely complex, including several different parametric processes [17]. In the case where parametric processes have a considerable effect on laser energy deposition, the absorbed laser energy may be considerably different between the two targets, and the corona expansion work may be different between the two targets.…”

Suppression of stimulated Brillouin and Raman scatterings using an alternating frequency laser and transverse magnetic fields

“…Laser plasma instabilities (LPIs), such as stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS), are critical issues in the realization of laser-driven inertial confinement fusion (ICF). [1][2][3][4] SBS in plasmas is the decay of an incident light wave into a scattered light wave and an ionacoustic wave (IAW). SRS is the process of incident light wave decay into a scattered light wave and an electron plasma wave (EPW).…”