Measuring shell-$\rho $R perturbations in NIF capsule implosions near peak velocity

Quantitative measurements of shell-$\rho $R perturbations in capsules near peak implosion velocity (PV) are challenging. An external backlighter samples both sides of the shell, unless a re-entrant cone is used (potentially perturbing implosion). Emission from the hot core, after shock-stagnation and prior to PV, can act as a self-backlighter, providing a means to sample one side of the capsule, if emission levels can be increased over nominal values. Adding high-Z gas ($\sim$1{\%} Ar) to the capsule fill in Symcaps ($^{4}$He or propane), should produce a continuum backlighter with significant ($\sim$30x) increase in emission at h$\upsilon $ $\sim$8 keV over nominal fills. From images of the transmitted self-emission, above and below the K-edge of an internally doped high-Z layer (Cu), we can infer the growth at PV of imposed and inherent surface roughness at mode $\sim$60 with amplitudes $\sim$50-nm.