Blast-Wave-Driven, Multidimensional Rayleigh-Taylor Instability Experiments.

Abstract

This thesis discusses experiments well-scaled to the blast-wave-driven instabilities that are believed to occur during the explosion phase of SN1987A. Blast waves occur following a sudden, nite release of energy, and consist of a shock front followed by a rarefaction wave. When a blast wave crosses an interface with a decrease in density, hydrodynamic instabilities will develop. These experiments include target materials scaled in density to the He-H layer in SN1987A. About 5 kJ of laser energy from the Omega Laser facility irradiates a 150 µm plastic disk that is followed by a low-density foam cylinder. A blast wave structure similar to those in supernovae is created in the plastic layer. Several types of initial conditions that seed the hydrodynamic instabilities are presented in this thesis. These include 2D, 3D, single-mode and multimode sinusoidal patterns. These conditions produce unstable growth dominated by the Rayleigh-Taylor instability in the nonlinear regime. We have detected the interface structure under these conditions, using dual, orthogonal radiography. Thegrowth of the unstable layer is compared to incompressible mixing models. Recent advances in our x-ray backlighting techniques have greatly improved the resolution of our x-ray radiographic images. Under certain conditions, the improved images show some mass extending beyond the Rayleigh-Taylor spike and penetrating further than previously observed or predicted by current simulations. 3D, hydrodynamic simulations do not show this eect. I will also discuss the amount of mass in these spike extensions, the associated uncertainties, and hypotheses regarding their origin.