Simulations of Gas-Ablator Mix in Symcap Implosions at the National Ignition Facility

Two longstanding questions in ICF physics have been the extent to which capsule ablator material mixes into the burning fusion fuel and degrades performance, and the mechanism by which this mixing occurs. Several recent campaigns at the National Ignition Facility have examined this question through the use of separated reactants. A layer of CD plastic is placed on the inner surface of the CH shell and the shell is filled with a gas mixture of H and T. This allows for a direct measurement of neutron yield proportional to the amount of gas-ablator mixing. More recently, Ge dopant has been added to the CD layer, in order to move the mix into the partially ionized regime, as a stepping stone to higher-Z platforms which hope to use radiation trapping to lower the threshold for ignition.

This presentation will examine simulations of ablator-gas mix using two mixing paradigms: a Reynolds-averaged model which assumes fully-developed turbulence, and a Multicomponent Navier-Stokes diffusion-like model. We assess the ability of each model to simultaneously match the Ge doped and undoped capsules, and suggest future improvements to the models.