Experimental Hydrodynamic Instability at High Energy Density.

Abstract

This dissertation presents a series of experiments on various aspects of shock-driven hydrodynamic instability at high energy density (HED). This is an aspect of physics with ramifications in many important applications, for example in the confinement of fusion fuel and in many astrophysical phenomena. The common theme in this research lies in the experimental technique. These experiments, and others like them, are typically performed using a system of initially-solid plastic and carbon foam, where the surface of the plastic in contact with the foam can be easily machined with a seed perturbation, allowing for precise control of the unstable interface growth under well-characterized initial conditions. A high-powered, pulsed laser is then used to irradiate the system, driving a shock wave into it. This shock ionizes and accelerates the system, converting it into an HED plasma. The acceleration and/or the subsequent motion of the shocked plasma provides the impetus that drives the instability, where the particular mechanisms at work are controlled by the direction of incidence of the shock upon the material interface, as well as by appropriate choice of an initial interface perturbation.

The first three experiments explore various details of three important interface processes: Rayleigh-Taylor and Kelvin-Helmholtz instability, as well as Richtmyer-Meshkov physics. The final experiment studies the generation of fast electrons by the interaction of a laser with a material. These electrons are produced in virtually any HED system involving a laser, and can affect the system's dynamics significantly. They are of particular interest for the fast-ignition concept in inertial-confinement fusion, and also can have an effect on imaging-based diagnostics, such as the X-ray radiography techniques that are the primary method for diagnosing the instability experiments that are the focus of this dissertation.