Quantitative analysis of backlit shadowgraphy as a diagnostic of hydrogen ice surface quality in ICF capsules

We have developed a numerical raytrace model, SHELL3D, which simulates the backlit imaging of cryogenic inertial-confinement fusion (ICF) ignition cap sules in three dimensions. We have used this model to investigate the limit ations of backlit shadowgraphy as a diagnostic of hydrogen ice surface qual ity inside the capsules. We impose known modal perturbations upon the simul ated inner ice surface, and produce simulated shadowgraphs which are then a nalyzed as if they were real experimental data. We find that power spectra derived from backlit shadowgraphs appear to be reliable indicators of ice s urface power spectra out to Fourier mode numbers as high as 80. We also sug gest that some advantages may be obtained by using a collimated backlight, and possibly by utilizing backlit transmission interferometry. These result s support the conclusion that backlit shadowgraphy is a valid quantitative diagnostic of lower-mode ice surface imperfections inside transparent spher ical ICF shells.