X-RAY SPECTROSCOPIC DIAGNOSTICS OF MIX IN HIGH GROWTH-FACTOR SPHERICAL IMPLOSIONS

Rayleigh-Taylor (RT) instability of the pusher-fuel interface occurrin g upon acceleration and deceleration of the pusher is of major concern for current and future ICF experiments. One common diagnostic techniq ue for measuring pusher-fuel mix in spherical implosion experiments in volves placing spectroscopic dopants both in the capsule fuel region a nd the innermost region of the capsule wall adjacent to the fuel. As t he degree of pusher-fuel mix is increased the pusher dopant x-ray emis sion increases relative to that of the fuel dopant. Spherical implosio n experiments of this type using Ar and Ti dopants in the fuel and pus her, respectively, are being carried out on Nova. We first show that t he Ti He-alpha/Ar He-beta 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 th ese targets and discuss how these processes affect the calculation of simulated spectra. The importance of radiative transfer as well as hig h-density plasma phenomena such as continuum lowering and Stark broade ning is demonstrated. The simulated spectra are also observed to be se nsitive to assumptions regarding the treatment of electron thermal con duction 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 caref ully before they can be relied upon. Preliminary comparisons of experi mental data with simulation are presented. It is shown that the comput ed spectra is sensitive to the laser energy and pusher temperature. Th ese comparisons to data also imply that the inclusion of convective ef fects in computing the electron temperature profile through the mix re gion is necessary in order to satisfactorily model experimental spectr a.