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 ($\rho R=\int \rho dr$) 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 ($\sim 0.5\%$ 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 $\sim 25\%$ of the average $\rho R$ and hot spot velocities of $\sim 100\mathrm{km}/\mathrm{s}$. 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.

• Received 4 August 2020
• Revised 22 October 2020
• Accepted 30 November 2020

DOI:https://doi.org/10.1103/PhysRevLett.126.025002