Signatures of Target Performance and Mixing in Titanium-Doped Target Implosions on OMEGA

82 LLE Review, Volume 70 In recently published work we discussed the signatures of mixing1 and of target performance2 provided by incorporating a titanium-doped layer within the shell of imploding targets. We report here on the results of an experiment on OMEGA using such targets. We observe the predicted absorption features formed by the titanium layer: absorption lines due to 1s–2p transitions in titanium ions of incomplete L shell, as well as K-edge absorption in cold titanium. We also observe oscillations due to extended x-ray absorption fine structure (EXAFS) above the Ti K edge. The observed spectra are simulated by a radiative-transport model that uses LILAC profiles and OPLIB opacity values. The observed core temperature and shell areal density are found to fall short of the one-dimensional predicted values. We attribute this shortfall to a lack of irradiation symmetry, which leads to hydrodynamic instability and mixing [distributed phase plates (DPP’s) were not used in this experiment, although the SSD modulator was activated]. The introduction of a sharp density jump at the interfaces of the titanium layer introduces a Rayleigh-Taylor (RT) unstable layer, which makes the target more unstable. Signatures of mixing include the emission of the He-α line of Ti+20 due to titanium migrating to the core, as well as the EXAFS spectrum indicating cold titanium close to peak compression. The spectral signatures due to the titanium layer are shown to provide very useful signatures of target performance.