Experimental Reproducibility in the Alpha-Heating Regime

As inertial confinement fusion experiments begin to self-heat, the question of experimental reproducibility becomes more acute: alpha-particle bootstrapping can amplify small design deviations to produce large changes in observed nuclear yield. Quantifying the expected level of yield variation from known sources of uncertainty is important for assessing the degree to which design choices are intentionally self-heating. Such analysis could also help inform whether experimental results that differ from design calculations are surprising or to be expected. To that end, we use radiation hydrodynamic simulations to explore the sensitivity of various National Ignition Facility indirect drive experiments to known levels of target, laser, and physics uncertainties. First, we confirm the intuition that designs experience greater variability (and hence lower reproducibility) as they approach the self-heating regime. However, we also find that the expected level of alpha heating variation depends not only on the design but also on the path by which that design approaches ignition. In other words, modifications to the same baseline design with identical expectation values of alpha heating can have different variances. Since different design variants show different levels of reproducibility, it may be possible to intentionally seek out self-heating designs that are explicitly more reproducible.

 

Prepared by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-824172.