Physics of matter and Rayleigh–Taylor hydro mixing in high-energy-density plasmas

This work considers the available experimental data on Rayleigh–Taylor mixing in high-energy-density plasmas. The experiments at the SACLA facility use the experimental platform coupling a high-power optical laser, an x-ray free-electron laser, and a lithium fluoride crystal for studying Rayleigh–Taylor unstable plasmas. The experiments report the measurements of fluctuations of the x-ray imagery intensity with high spatial resolution over a large field of view. We analyze the fluctuation spectra of the x-ray imagery intensity vs spatial frequencies. A rigorous statistical method is employed to find parameters of the data model, including their mean values, statistical errors, goodness-of-fit, and statistics of residuals. The effect is examined of the range of spatial frequencies, selecting the interval with tolerable statistical attributes and a large span of scales. We find that the fluctuation spectra are accurately described by compound functions that capture, through a product of a power-law and an exponential, both self-similar and scale-dependent spectral parts. The self-similar dynamics have steep spectra, strong correlations, and weak fluctuations. The attributes of the scale-dependent dynamics directly determine the value of the kinematic viscosity. Our data analysis finds the characteristics of Rayleigh-Taylor mixing and the physics of the matter in high-energy-density plasmas. Our results explain the experimental observations and elucidate their consistency with group theory and other experiments. We report the data-based value of the kinematic viscosity in high-energy-density plasmas.