High-Energy-Density Physics Experiments of Rayleigh-Taylor Instability Growth at Low-Density Contrast

Abstract: The Rayleigh-Taylor instability (RTI) occurs at the interface between two fluids of different densities when the lighter fluid pushes the heavier fluid. Light-fluid “bubbles” and heavy-fluid “spikes” form and interpenetrate across the interface, creating a mixed-fluid layer which continues to grow in size, thereby lowering the potential energy of the system. This hydrodynamic instability is encountered throughout nature and engineered systems. In the realm of high-energy-density (HED) physics, mixing due to RTI has profound consequences for inertial confinement fusion (ICF) and astrophysical systems, such as supernovae. To develop reliable predictive capabilities, we must understand how the initial conditions, including seed spectrum and density contrast, affect the evolution of RTI. Recent classical fluids experiments and numerical simulations have observed a reacceleration of single-mode RTI growth, beyond the terminal velocity predicted by potential-flow models. In low-density-contrast systems, secondary instabilities may arise, which modify the internal mixing dynamics and macroscopic growth rate. This dissertation discusses the design and results of experiments performed at Omega-60, a 30-kJ laser facility capable of creating HED conditions. In this experimental platform, a blast wave drives RTI growth at an embedded interface inside a shock tube. X-ray radiography captures the evolution of the mixed-fluid region from early to late times. Experimentally measured bubble- and spike-front positions are compared with potential-flow models and radiation-hydrodynamics simulations.