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

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. A similar to 15 mu m shell asymmetry amplitude of the Y-40 spherical harmonic mode was observed for standard NIF ICF hohlraums at a shell radius of similar to 200 mu m (capsule at similar to 5x radial compression). This asymmetry is mitigated by a similar to 10% increase in the hohlraum length.