Shell Mix in the Compressed Core of Spherical Implosions

Abstract

The Rayleigh-Taylor instability in its highly nonlinear, turbulent stage causes atomic-scale mixing of the shell material with the fuel in the compressed core of inertial-confinement fusion targets. The density of shell material mixed into the outer core of direct-drive plastic-shell spherical-target implosions on the 60-beam, OMEGA laser system is estimated to be $3.4(\pm 1.2)\mathrm{g}/\mathrm{c}{\mathrm{m}}^{\mathrm{3}}$ from time-resolved x-ray spectroscopy, charged-particle spectroscopy, and core x-ray images. The estimated fuel density, $3.6(\pm 1)\mathrm{g}/\mathrm{c}{\mathrm{m}}^{\mathrm{3}}$, accounts for only $\sim 50\%$ of the neutron-burn-averaged electron density, $n_e=2.2(\pm 0.4)\times {10}^{24}\mathrm{c}{\mathrm{m}}^{\mathrm{-}\mathrm{3}}$.