Experimental Study On The Growth Of Planar Hydrodynamic Instability Under Radiation-driven Conditions

The study of hydrodynamic instabilities is an important topic in high energy density physics. The research on the hydrodynamic instabilities has been motivated by the inertial confinement fusion and astrophysics. In comparison with hydrodynamic instability experiments in convergent geometry, the planar hydrodynamic instability experiments facilitate to study the influence of a single factor, and can deepen the understanding of hydrodynamic instability growth mechanism. Therefore,we have conducted a serial of planar hydrodynamic instability experiments. Data processing technique, ablative Rayleigh-Taylor instability, classic Rayleigh-Taylor instability and classic Richtmyer-Meshkov instability have been studied in this dissertation. They are given as follows:1. A improved method for approximating backlighter on-nodes to process face-on perturbation data has been developed. In this paper, we have summarized the processes of imaging and the perturbation data analysis, it is found that the obtained results used usual method will have a large error in the case of large optical depth. Therefore, we have developed a improved method. Numerical simulations show the relative error acquired by the improved method is always kept fixed at a low value when optical depth increases. This paper analyzed the change of modulation transfer function when x-ray wavelength, size of pinhole aperture, magnification have changed. Fresnel diffraction can stimulate the optimal pinhole aperture, x-ray wavelength and magnification with optimal spatial resolutions and an excellent signal-to-noise ratio.2. We study the influence of dopant ratio, radiation, laser pulse shape and coupling of mode coupling effect for ablative Rayleigh-Taylor instability. First, experimental results show that density gradient effect can suppress the generation of the second harmonic, the more the Br is doped, the smaller the density gradient scale length can be achieved. The density gradient effects also suppress the feedback of third-order harmonic to the fundamental mode, which induces the nonlinear saturation amplitude to exceed 0.1X, as the classical prediction shows. Secondly, the growth rate of Shenguang III prototype facility experiments is smaller than the growth rate of Shenguang II facility experiments. It is because the Au M band x-rays and radiation temperature increase the ablation velocity and density gradient scale length. More Au M band x-ray becomes, and more obvious the preheat effect is. The preheat effect changes density distribution in the neighborhood of ablation front, which can improve the density gradient stabilization and ablation stabilization. At same time, the increased radiation temperature also can enhance stabilization effect. Thirdly, in the two-mode experiments, the generation of k1-k2 mode is the result from the interaction of the original mode k1 and k2. When the two original modes arrive at their saturation amplitudes, perturbation of k1-k2 mode will grow slowly. It is manifested that they will cease to affect the growth of the generated k1-k2 mode when the two high modes saturate. Modes of similar wavelengths of k1+k2 mode can constructively interfere to creat local structures with an amplitude much larger than the individual modes' amplitudes. Thus it is caused that saturation at individual mode amplitudes significantly lower than 0.1 ?. The growth of original modes should be related with the inverse cascade in k space. Lastly, the ablative Rayleigh-Taylor instability experiments which used shaped laser pulse shapes show that the high-foot drive is more stable than the low-foot drive. The simulations show that the density gradient scale length and ablation velocity with high-foot drive are higher than those with the low-foot drive. Prepulse can change the density distribution of ablation front, so the density gradient scale length can be increased by optimizing the intensity and duration time of prepulse. At the same time, the prepulse drive can reduce the peak density of ablation front and increase the ablation velocity. Therefore, the ablative Rayleigh-Taylor instability can be stabilized by optimizing the prepulse shape.3. We have established a measurement method for the growth of Al sample hydrodynamic instabilities. We evaluate the influence of Au M band on the growth of Richtmyer-Meshkov instability. The simulations show that Au M band preheats the front interface of Al sample and increases the density of Al sample, but it doesn't affect the Richtmyer-Meshkov instability growth of rear interface of Al sample. We measure the linear growth of Rayleigh-Taylor instability and Richtmyer-Meshkov instability, and obtain the linear growth rates of the two experiments by combination of simulation and empirical formula. The obtained linear growth rate agree quite well with the measurable results. The comparisons show that we can estimate the perturbation gowth of hydrodynamic instabilities by combination of simulation and empirical formula.