Robustness to Hydrodynamic Instabilities in Indirectly-Driven Layered Capsule Implosions

We analyze the performance of 3 layered capsule implosions on the NIF^1,2 via detailed 2D and 3D simulations. These were high adiabat, moderate convergence ratio implosions with a large amount of unablated ablator mass, features that improve hydrodynamic stability. Nevertheless, while two of these implosions exhibit robustness to asymmetries in experiment and produced neutron yields within 20% of 1D simulations, which do not account for the impacts of hydrodynamics instabilities, the third implosion produced only 14% of the yield from a 1D simulation. We perform a detailed analysis of these three implosions, which suggests that the combination of several large asymmetry seeds result in the significantly degraded performance: a large 30μm fill tube, the presence of microstructure in the HDC ablator, and a higher level of drive asymmetry. Thus, while it is possible to stabilize an implosion through various means, the factors that determine stability cannot be considered independently. Furthermore, when these asymmetries are combined in 2D simulations, they can exhibit destructive interference and underpredict the yield degradation compared to experiment.

¹A. Zylstra et al. Phys. Plasmas 25, 056304, 2018.

²S. MacLaren et al. Phys. Plasmas 25, 056311, 2018.