Measuring the rarefaction wave dynamics from shock release in spherical geometry

In inertial confinement fusion (ICF) implosions, the hot-spot pressure, the convergence ratio, and the areal density at stagnation are inversely proportional to the hot-spot pressure at the beginning of the deceleration phase. The hot-spot pressure at the onset of deceleration is set by the stagnation of material in the rarefaction wave from the shock release when its kinetic energy is converted into internal energy. Accurate modeling of the shock release is therefore crucial to understanding ICF performance. Shock release experiments were carried out in spherical geometry on the OMEGA laser using a cone-in-shell setup. A shock, driven by a short picket pulse, breaks out of the shell and releases material from the shell's inner surface. The converging release material collides with a solid fused-silica hemisphere witness at the center of the target at which time the kinetic energy of the release material is converted into internal energy, launching a shock into the witness. VISAR measurements of the release-driven shock in the witness were obtained for varying laser-drive intensities. The measurements are used to validate modeling of the rarefaction wave dynamics in radiation-hydrodynamic simulations.