High-Energy-Density Physics Experiments Relevant to Astrophysical Systems.

Abstract

This thesis details a trio of distinct high-energy-density experiments, each related to a specific astrophysical phenomenon. The greatest attention is paid to the application of novel diagnostic techniques to a radiative shock system in xenon gas. The radiative shock was created using the OMEGA Laser to launch a beryllium pusher into a xenon-filled shock tube. Significant radiative cooling of the xenon leads to a layer of dense gas that facilitates x-ray radiography and, in a novel application of the technique, x-ray Thomson scattering. Previously limited to low-Z, solid density materials, the investigation of the fast, high-Z, weakly coupled Xe shock with scattered x-rays required concurrent developments in experimental design, theory, and diagnostic capabilities. Similar structures abound in astrophysics; examples include the interaction of shocks with molecular clouds, blast waves generated by gamma-ray bursts, and the evolution of late-stage supernova remnants.

Other aspects of gamma-ray bursts and supernovae physics were explored with an experiment on the ultrafast HERCULES Laser, and simulations of an experiment designed for the National Ignition Facility, respectively. At the HERCULES Laser, a relativistic electron beam was imaged after propagation through increasing lengths of background plasma. The beam was observed to evolve and break apart as a result of filamentation instabilities, the same forces that act on the charged particle fluxes from gamma-ray bursts.

Finally, the radiative shock was revisited by performing 1D simulations of a 200 MBar, x-ray driven pressure pulse that is only achievable at the National Ignition Facility. The HYDRA code was used to model shock propagation though a Rayleigh-Taylor unstable interface in a low-density foam target. Using models of radiative Rayleigh-Taylor growth from literature, the plasma conditions were extracted from the simulations and used to predict the instability growth in the upcoming experiment. Although they study vastly different regimes, each of the these experiments relates the physics of astrophysical objects to laboratory-based laser plasma science, and in doing so advances understanding of both fields.