Spectroscopic determination of core gradients in inertial confinement fusion implosions

摘要

We report on a collaborative effort that has led to the development of a spectroscopic method for the determination of the gradient structure in ICF implosion cores based on the self-consistent analysis of simultaneous X-ray monochromatic images and X-ray line spectra. This technique is applied to a series of stable and spherically symmetric implosion experiments where Ar-doped D{sub}2-filled plastic shells were driven with the GEKKO and OMEGA laser systems. Argon K-shell X-ray line spectra were measured with streak crystal spectrometers, while X-ray monochromatic imagers recorded core images based on the Ar Heβ line. The analysis self-consistently determines the temperature and density gradients that yield the best fits to both the spatial distribution of monochromatic emissivity and spectral line shapes. A multi-objective genetic algorithm is used to efficiently perform the analysis. This measurement is critical for understanding the spectra formation and plasma dynamics associated with the implosion process. In addition, since the results are independent of hydrodynamic simulations they are important for the verification and benchmarking of detailed fluid dynamic models of high energy density plasmas.