Studying the Transition of Mix Mechanisms Into the Kinetic Regime Using Shock-Driven Separated Reactant Experiments at OMEGA
Benjamin Reichelt, Massachusetts Institute of Technology
High-Z material mix into the hot spot degrades capsule implosions and can prevent fusion ignition in inertial confinement fusion experiments. Hydrodynamic mechanisms related to convergence have previously been the most studied cause of mix. In this talk, we present results from a series of separated reactant campaigns at OMEGA, showing the transition of mix mechanisms from hydrodynamic to diffusive and non-locally kinetic. In these experiments, a suite of nuclear and xray diagnostics have revealed novel phenomena associated with mix through different mechanisms. In contrast to previous separated reactant experiments studying hydrodynamic mix, we have measured fusion bang times shifting earlier by ~15-50 ps for the separated reactant experiments relative to the control, indicating the observed mix is not driven by late time hydrodynamical instability and suggesting a non-hydrodynamic mixing mechanism. These effects occurring in thinner, shock driven shells with low collisionality suggests that for these experiments the observed mix is in the kinetic regime. Comparison to 1D and 2D hydro simulations replicates these trends when hydrodynamical mixing and diffusion models are considered. Measurements of ion temperature in the thicker capsules show lower temperatures for the separated reactant variants relative to control, suggesting the mix is occurring in a region closer to the colder shell rather than uniform mixture in the hot spot. Finally, shell trajectory and electron temperature data show that control and separated reactant capsules behave in a comparable manner. With these novel experiments and comprehensive simulations, mix driven by non-hydrodynamic mechanisms is systematically studied to advance our understanding of controlling mix in inertial fusion implosions.