Two-Plasmon-Decay and Stimulated Raman Scattering in Direct-Drive Inertial Confinement Fusion
Han Wen, Ph.D. Defense
Thursday, May 12, 2016
The two-plasmon-decay (TPD) instability and stimulated Raman scattering (SRS) are important processes in the laser-plasma interaction that are capable of influencing the absorption of laser light and the generation of hot electrons in the inertial confinement fusion (ICF) experiments. The linear stage of the SRS and TPD instability near the quarter-critical density have been modeled by a new fluid-type code GLINTS. The absolute growth of the SRS and the TPD instability have been identified and their growth rates can be comparable. The TPD in the case of oblique laser incidence have been studied. The analytical results for the TPD growth rates and thresholds have been obtained and have been compared with the TPD-only GLINTS simulations. The TPD threshold are found to decrease as the angle of incidence θ increases. Different from the results of the theory considering the SRS alone, the GLINTS simulations including both the TPD and the SRS have shown that the growth rates of the SRS driven by an obliquely incident laser beam may increase when θ increases, which can lead to a lower-than-theoretical-prediction instability threshold. The linear and saturation stage of the TPD and the SRS have been studied in two and three spatial dimensions (2-D and 3-D) using the particle-in-cell (PIC) code OSIRIS. By comparing the spectra of the plasma waves in the 2-D and 3-D PIC simulations, the TPD and the stimulated Raman sidescattering have been found to coexist near and below quarter-critical density in the 3-D simulations. The interaction of the TPD and the SRS requires the 3-D modeling. The PIC simulations have shown that the SRS is less effective in accelerating electrons compared to the TPD. The hot electrons energy flux in the 3-D simulations is found to be smaller than in the 2-D simulations with the same parameters.