2D X-Ray Radiography of Imploding Capsules at the National Ignition Facility

Abstract

First measurements of the in-flight shape of imploding inertial confinement fusion (ICF) capsules at the National Ignition Facility (NIF) were obtained by using two-dimensional x-ray radiography. The sequence of area-backlit, time-gated pinhole images is analyzed for implosion velocity, low-mode shape and density asymmetries, and the absolute offset and center-of-mass velocity of the capsule shell. The in-flight shell is often observed to be asymmetric even when the concomitant core self-emission is round. $\mathrm{A}\ensuremath{\sim}15\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ shell asymmetry amplitude of the ${Y}_{40}$ spherical harmonic mode was observed for standard NIF ICF hohlraums at a shell radius of $\ensuremath{\sim}200\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ (capsule at $\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}$ radial compression). This asymmetry is mitigated by a $\ensuremath{\sim}10%$ increase in the hohlraum length.