Nathan Charles Hearn

TWO-DIMENSIONAL BLAST-WAVE-DRIVEN RAYLEIGH-TAYLOR INSTABILITY: EXPERIMENT AND SIMULATION

This paper shows results from experiments diagnosing the development of the Rayleigh-Taylor instability with two-dimensional initial conditions at an embedded, decelerating interface. Experiments are performed at the Omega Laser and use ~5 kJ of energy to create a planar blast wave in a dense, plastic layer that is followed by a lower density foam layer. The single-mode interface has a wavelength of 50 μm and amplitude of 2.5 μm. Some targets are supplemented with additional modes. The interface is shocked then decelerated by the foam layer. This initially produces the Richtmyer-Meshkov instability followed and then dominated by Rayleigh-Taylor growth that quickly evolves into the nonlinear regime. The experimental conditions are scaled to be hydrodynamically similar to SN1987A in order to study the instabilities that are believed to occur at the He/H interface during the blast-wave-driven explosion phase of the star. Simulations of the experiment were performed using the FLASH hydrodynamics code.

Three-dimensional blast-wave-driven Rayleigh-Taylor instability and the effects of long-wavelength modes

This paper describes experiments exploring the three-dimensional (3D) Rayleigh–Taylor instability at a blast-wave-driven interface. This experiment is well scaled to the He/H interface during the explosion phase of SN1987A. In the experiments,  ∼5 kJ of energy from the Omega laser was used to create a planar blast wave in a plastic disk, which is accelerated into a lower-density foam. These circumstances induce the Richtmyer–Meshkov instability and, after the shock passes the interface, the system quickly becomes dominated by the Rayleigh–Taylor instability. The plastic disk has an intentional pattern machined at the plastic/foam interface. This perturbation is 3D with a basic structure of two orthogonal sine waves with a wavelength of 71 μm and an amplitude of 2.5 μm. Additional long-wavelength modes with a wavelength of either 212 or 424 μm are added onto the single-mode pattern. The addition of the long-wavelength modes was motivated by the results of previous experiments where material penetrated unex...

Spike morphology in blast-wave-driven instability experiments

The laboratory experiments described in the present paper observe the blast-wave-driven Rayleigh–Taylor instability with three-dimensional (3D) initial conditions. About 5 kJ of energy from the Omega laser creates conditions similar to those of the He–H interface during the explosion phase of a supernova. The experimental target is a 150 μm thick plastic disk followed by a low-density foam. The plastic piece has an embedded, 3D perturbation. The basic structure of the pattern is two orthogonal sine waves where each sine wave has an amplitude of 2.5 μm and a wavelength of 71 μm. In some experiments, an additional wavelength is added to explore the interaction of modes. In experiments with 3D initial conditions the spike morphology differs from what has been observed in other Rayleigh–Taylor experiments and simulations. Under certain conditions, experimental radiographs show some mass extending from the interface to the shock front. Current simulations show neither the spike morphology nor the spike penetra...