Exploring the late time asymptotic evolution of Rayleigh-Taylor instability via NIF discovery science experiments*

The late time asymptotic evolution of Rayleigh-Taylor instability (RTI) is self-similar and the amplitudes of the spikes and bubbles are described by the equation h_S/B = α_S/B gt², which is commonly used in various physical and engineering systems. There are significant discrepancies between theoretical, computational, and experimental calculations of α_B. Experiments of uncontrolled broadband initial conditions and theoretical models of immiscible fluids yield α_B~0.05, while simulations of narrowband initial conditions and miscible fluids yield α_B~0.025. We present recent experiments at the National Ignition Facility, which measured the late time growth of RTI for miscible fluids (plasma state) from a well-characterized short wavelength initial perturbation. The fronts of the bubbles, the spikes and the blast wave, which initiated the instability, were each extracted from the experimental data at different times. The values of α_B and α_s where calculated using simulation of the 1D dynamics of the system and a Buoyancy-Drag (BD) model for the instability.