Evidence Of Three-Dimensional Asymmetries Seeded By High-Density Carbon-Ablator Nonuniformity In Experiments At The National Ignition Facility

Inertial confinement fusion implosions must achieve high in-flight shell velocity, sufficient energy coupling between the hot spot and imploding shell, and high areal density (rho R = integral rho dr) at stagnation. Asymmetries in rho R degrade the coupling of shell kinetic energy to the hot spot and reduce the confinement of that energy. We present the first evidence that nonuniformity in the ablator shell thickness (similar to 0.5% of the total thickness) in high-density carbon experiments is a significant cause for observed 3D rho R asymmetries at the National Ignition Facility. These shell-thickness nonuniformities have significantly impacted some recent experiments leading to rho R asymmetries on the order of similar to 25% of the average rho R and hot spot velocities of similar to 100 km/s. This work reveals the origin of a significant implosion performance degradation in ignition experiments and places stringent new requirements on capsule thickness metrology and symmetry.