SPC community seminar – Ben Reichelt

Abstract: High-Z material mix into the hot spot degrades the performance of capsule implosions and can prevent fusion ignition in inertial confinement fusion experiments. Mix associated with hydrodynamic mechanisms related to convergence have previously been the most studied. In this talk, we present results from a series of separated reactant campaigns at OMEGA, showing that the mix mechanisms change as conditions in the capsule vary from hydrodynamic to strongly kinetic. In these experiments, a suite of nuclear and x-ray diagnostics elucidates different mix mechanisms. In contrast to previous separated reactant experiments studying hydrodynamic mix, fusion bang times have been measured to be ~15-50 ps earlier for the separated reactant experiments relative to the control, indicating that the observed mix is not driven by late time hydrodynamical instability and suggesting a non-hydrodynamic mixing mechanism. This effect occurring in thinner, shock driven shells with low collisionality suggests that for these experiments the observed mix is kinetically driven.  Comparison to 1D and 2D hydro simulations replicates this observation 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 uniformly in the hot spot. Finally, shell trajectory and electron-temperature data show that control and separated-reactant implosions behave in a similar manner, as intended. 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. This work was supported in part by the U.S. DOE, NLUF, and SSGF fellowship.

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