ULTRASONIC CHARACTERIZATION OF INERTIAL CONFINEMENT FUSION-TARGETS

Inertial confinement fusion (ICF) targets designed to achieve ignition must meet strict surface smoothness and sphericity requirements. One potentially valuable method for evaluating the quality of these target s is resonant ultrasound spectroscopy (RUS). When applied to simple ge ometries, such as layered spheres ol rectangular parallelepipeds, RUS may yield significant information about alloy homogeneity, elastic con stants, cavity geometry, the presence of gross defects such as crackin g or hemishell bonding problems, and properties of interior fluids. Th e strengths of RUS techniques for ICF target characterization include applicability at all temperatures of interest with a single apparatus, high sensitivity in frequency spectral measurements, and the inherent acoustic indifference to optically opaque samples. Possible applicati ons and the limitations of RUS methods for examining layer geometry an d material properties are addressed. Preliminary room temperature expe riments with a deuterium-filled aluminum shell ape used to evaluate th e utility of many of the described applications. The frequency spectru m compares favorably with theory and displays measurable mode splittin g, acoustic-mode resonance widths indicative of cavity boundary dissip ative mechanisms, and Low-e elastic modes. The acoustic cavity resonan ce structure confirms the internal gas density and is used to calculat e the two lowest even-order cavity boundary perturbation amplitudes.