Measurement of inflight shell areal density perturbations in NIF capsule implosions near peak velocity

Quantitative measurements of shell-RhoR perturbations in capsules near peak implosion velocity (PV) are challenging. An external backlighter samples both sides of the shell, unless a re-entrant cone is used (potentially perturbing implosion). Emission from the hot core, after shock-stagnation and prior to PV, has been used as a self-backlighter, providing a means to sample one side of the capsule. Adding high-Z gas ($\sim$ 1{\%} Ar) to the capsule fill in Symcaps ($^{4}$He), has produced a continuum backlighter with significant increase in emission at photon energies $\sim$ 8 keV over nominal fills. From images of the transmitted self-emission, above and below the K-edge of an internally doped Cu layer, we infer the growth at PV of imposed perturbations (100 nm amplitude, mode 40).