Speaker: Josh Sauppe, LANL (Los Alamos National Laboratory)
Abstract: The advent of high-power laser facilities such as the National Ignition Facility (NIF) has ushered in a new and exciting era in high-energy-density (HED) physics research, and the flexibility of the NIF allows many distinct targets to be fielded beyond the standard indirect-drive inertial confinement fusion (ICF) configuration. Los Alamos scientists are using directly driven cylindrical implosion experiments at the NIF to study hydrodynamic instability growth in regimes relevant to ICF systems, as cylinders enable direct measurements by viewing down the cylinder axis. These physical systems are often modeled in more tractable two-dimensional (2D) simulations with assumed symmetry, but this simplification risks inadvertently masking crucial features. Here, we show experimental evidence of a 3D asymmetry in directly driven cylindrical implosions which was not predicted with 2D modeling, and we accurately reproduce this feature in 3D simulations. The asymmetry arises from the NIF beam geometry and the dependence of laser absorption on beam incidence angle, and we also find that there is a north/south skew to the drive asymmetry. This skew is obscured in radiographs that image down the cylinder axis, complicating inferences of instability growth. This has significant implications for targets with off-normal beam pointing such as polar direct-drive ICF, and it may also be important for a more complete understanding of indirect-drive systems. In particular, differences between experimental data and synthetic data generated from 2D simulations can be misattributed to deficiencies in physics models rather than 3D effects. A similar but more subtle 3D effect is also identified for smaller-scale cylindrical implosion experiments fielded at the OMEGA laser facility, and this is confirmed in recent experiments.