Radiography Studies of Isolated Feature Growth on Laser-Driven Capsules and Foils

Calculations have motivated consideration of target features as a source of hydrodynamic instability in direct-drive implosions. We report results of radiography of surface features on imploding spheres and planar targets. The initial experiments were done with capsules selected to have (exceptional) domes features intrinsic to their fabrication within the field of view of the radiography. Although the domes were predicted to generate highly visible signatures, the observed contrast was weak and suggested that the growth was reduced. Two primary hypotheses under consideration are (i) sensitivity of the dome growth to 3D deviations from assumption of 2D axi-symmetry in calculation, and (ii) target heating by fast electrons generated by laser-plasma instability. We will also discuss more recent planar experiments in which we are using 3-D printed foils, which provide reproducible and varied features, to test these hypotheses.