Diagnosis of pusher-fuel mix in indirectly driven Nova implosions.

A key issue for inertial confinement fusion (ICF) is the hydrodynamic stability of the imploding capsule. Imperfections on the capsule surface can grow into large perturbations that degrade capsule performance. Understanding this process is crucial if the authors are to successfully predict requirements for future high-gain ICF capsules. Experiments on the Nova laser at Lawrence Livermore National Laboratory have directly measured perturbation growth on planar foils, and three experimental groups have investigated backlit perturbation growth using imploding spheres. In addition to these efforts, which concentrate on indirectly driven implosions, is work investigating the hydrodynamic stability of directly driven ICF capsules. In these direct-drive experiments the laser light shines directly on the capsules, causing the implosion and providing the seed for perturbation growth. This article reports measurement, via emission from spectroscopic tracers, of the full process of perturbation growth leading to pusher-fuel mix in spherical implosions, and shows perturbation growth dependence on initial perturbation amplitude and wavelength. In contrast to the cited direct-drive work, the authors have in this experiment separated the drive from the perturbation seed.