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Indirectly-driven implosions for which the predicted Rayleigh-Taylor (RT) instability growth rates of pre-imposed capsule surface perturbations are substantially increased by mid-Z-doping of the ablators have been fielded on the Nova laser. The multiple effects on implosion performance of the additional x-ray opacity provided by the ablator dopant is discussed. For best surface finish capsules, the addition of increasing ablator dopant levels is shown to improve the neutron yield. However, as capsule surface roughness is increased, so that RT instability growth increases, this trend is reversed, leading to decreasing yields with increased dopant content. The RT-induced mixing between shell and fuel is further investigated by diagnosing the x-ray emission levels and time histories from Ti and Ar dopants in capsules with predetermined surface roughness. The x-ray line ratios show the expected decrease in fuel temperature with increasing surface roughness. The spectral content, intensity and duration of the Ti spectra, however, suggest 2- or 3-D rather than just 1-D effects are important so that higher than 1-D models of the mix region may be needed.

Rayleigh-Taylor (RT) instability of the pusher-fuel interface occurring upon acceleration and deceleration of the pusher is of major concern for current and future ICF experiments. One common diagnostic technique for measuring pusher-fuel mix in spherical implosion experiments involves placing spectroscopic dopants both in the capsule fuel region and the innermost region of the capsule wall adjacent to the fuel. As the degree of pusher-fuel mix is increased the pusher dopant x-ray emission increases relative to that of the fuel dopant. Spherical implosion experiments of this type using Ar and Ti dopants in the fuel and pusher, respectively, are being carried out on Nova. We first show that the Ti He-α Ar He-β line ratio shows promise as a mix diagnostic for high growth factor targets. We then discuss some of the important physical processes underlying Ar and Ti spectral line formation in these targets and discuss how these processes affect the calculation of simulated spectra. The importance of radiative transfer as well as high-density plasma phenomena such as continuum lowering and Stark broadening is demonstrated. The simulated spectra are also observed to be sensitive to assumptions regarding the treatment of electron thermal conduction in the mix region. Spectral postprocessing of 2-D hydrodynamic simulations using detailed line transfer methods has been carried out and implies that simple escape factor treatments must be tested carefully before they can be relied upon. Preliminary comparisons of experimental data with simulation are presented. It is shown that the computed spectra is sensitive to the laser energy and pusher temperature. These comparisons to data also imply that the inclusion of convective effects in computing the electron temperature profile through the mix region is necessary in order to satisfactorily model experimental spectra.