X-ray fluorescence imaging of laser-driven hydrodynamic instability systems with a Ross Pair Imager

Abstract

An experiment has been conducted at the Shenguang-Ⅲ prototype laser facility, demonstrating the application of x-ray fluorescence imaging (XRFI) in diagnosing laser-driven hydrodynamic instability systems in planar geometry. An aluminum (Al)-foam target was used, including a modulated Al disk followed by a low density poly-4-methyl-1-pentene foam cylinder which was doped with titanium (Ti) dioxide nanoparticles to serve as the tracer layer. A blast wave was driven through the rippled interface, triggering the development of hydrodynamic instabilities and the growth of the perturbation. Vanadium plasma radiation dominated by He-α x-rays, was generated with a delay in time, inducing the emission of Ti K-shell fluorescent photons from the tracer layer. A Ross Pair Imager with matched scandium and Ti filters was employed to provide two-dimensional quasi-monochromatic fluorescent images, and the temporal evolution of the perturbation structures in the tracer layer was successfully observed. Furthermore, one-dimensional fluorescent intensity profiles across the perturbation structures were extracted and compared with the simulation results via a combination of the MULTI code, a buoyancy-drag model, a self-similar analysis and an imaging code. The boundaries of the measured profiles were shown to be connected together due to the small initial length of the tracer layer and the large boundary width caused by the curved interfaces and blurring effects, which made the absolute positions of the perturbation structures inaccessible. This research suggests that XRFI works well in qualitatively diagnosing the instability evolution and the experimental design has to be modified to further improve its performance in achieving quantitative information.