Three-Dimensional Characterization of Cryogenic Target Ice Layers Using Multiple Shadowgraph Views

LLE Review, Volume 104 169 Introduction The 60-beam, 30-kJ OMEGA Laser System1 studies the laserdriven direct-drive ignition approach to inertial confinement fusion (ICF) in which many individual high-power laser beams directly illuminate a spherical target to create a spherically symmetric implosion. Current designs for high-gain ICF targets include a layer of condensed hydrogen fuel that adheres to the inner surface of a thin spherical shell ablator. Laser energy delivered to the target ablates its outer surface and the ablation pressure drives the fuel layer inward, compressing both it and the gaseous fuel at the target’s center. The drive pressure is varied in time such that the fuel density is compressed by a factor of as much as 4000 while remaining relatively cold. However, shock waves resulting from the drive-pressure variations, along with compressive work, heat the gaseous core “hot spot” to the high temperatures needed to initiate burning the fuel.