Simulating Experiments with Radiation Asymmetries and Fill Tubes on the National Ignition Facility

Recent High Density Carbon (HDC) implosion experiments on the National Ignition Facility have reached over 10¹⁶ neutrons owing to increased control of the shape of the capsule. Perturbation sources such as the fill tube and residual 3D shape defects are thought to be the leading candidates for the current limitation in implosion performance.

We present 3D simulations of HDC capsule implosions with multiple sources of perturbations using our in-house 3D radiation-hydrodynamics code Chimera. We assess the impact that the fill tube and radiation asymmetry has in simulations and then post-process the results with synthetic diagnostics to see how they affect observables such as the flange Neutron Activation Diagnostic (fNAD) sky-map and the neutron Time of Flight (nTOF) diagnostic spectrum, as well as the neutron yield, burn width and bang time. Doing so allows us to look at the diagnostic signatures of each perturbation and directly link them back to the dynamics in simulations to determine different mechanisms of burn truncation. Focusing on the fill tube perturbation and asymmetric drive conditions allows us to explore the hypothesis that they are the current sources of the asymmetry observed in the fNADs.