Cryogenic Target Performance and Fuel-Ablator Perturbation Growth*

OMEGA cryogenic target implosions show a performance boundary that has been correlated with shell stability during the acceleration phase of the implosion: for sufficiently low adiabats and high in-flight aspect ratios (IFAR’s) the measured neutron-weighted shell areal density and neutron yield relative to the clean simulated yield sharply declines. This is thought to be indicative of disruption of the shell because of the Rayleigh-Taylor instability. Direct evidence of this was previously obtained using a Si Heα backlighter driven by a ~20-ps short pulse generated by OMEGA EP. The shadow cast by the shell shortly prior to stagnation, as diagnosed using backlit radiographs, shows a softening near the limb, which is evidence of an ablator-fuel mix region for low adiabat implosions (α ~ 1.9, IFAR = 14), but not for higher-adiabat implosions (α ~ 2.5, IFAR = 10). We present comparison of synthetic radiographs of 2-D simulations, investigating the effectiveness of imprint and other mechanisms (diffusive mix, interfacial surface perturbations) for generating the inferred fuel-ablator mix.