F.W. Doss

Wall shocks in high-energy-density shock tube experiments

The radiative precursor of a sufficiently fast shock has been observed to drive the vaporization of shock tube material ahead of the shock. The resulting expansion drives a converging blast wave into the gas volume of the tube. The effects of this wall shock may be observed and correlated with primary shock parameters. We demonstrate this process in experiments performed on the Omega Laser Facility, launching shocks propagating through xenon with speeds above 100 km/s driven by ablation pressures of approximately 50 Mbars. Wall shocks in laser experiments, in which the principal shock waves themselves should not be radiative, are also reported—in which the wall shocks have been launched by some other early energy source.

Oblique radiative shocks, including their interactions with nonradiative polytropic shocks

A theory of shocks dominated by radiation energy flux in optically mixed thin-upstream thick-downstream systems, in which the temperature immediately ahead and some short distance behind the shock front are equilibrated by radiation transport, is presented. This theory is applied to determine properties of the normal and oblique radiative shock, followed by applications to interactions when radiative and polytropic shocks are present in the same system. Comparison with experimental data is presented.

Target Fabrication at the University of Michigan

Abstract At the University of Michigan (U-M), we have successfully fabricated and characterized targets for our experimental campaigns since 2003. Because of the unique production environment, we iterate many models in the course of a single-shot plan and have the flexibility to test and alter target designs as needed throughout the build process. Over the past few years, many advances in target design and fabrication have allowed greater degrees of design complexity while retaining the high level of build precision necessary for microscale experiments on facilities such as the OMEGA laser. Extensive target metrology is carried out during and after the fabrication process to allow for full knowledge of experimental conditions and to ensure that all targets are within required specifications. Analysis of the variability in metrology measurements over the multiple-shot campaigns allows for the quantification of improvements in the target build quality and metrology measurements. We present a summary of the capabilities and recent developments of target fabrication at U-M, as well as progress and analysis of build repeatability.

Increasing shot and data collection rates of the Shock/Shear experiment at the National Ignition Facility

Updates to the Los Alamos laser-driven high-energy-density Shock/Shear mixing- layer experiment are reported, which have collectively increased the platforms shot and data acquisition rates. The strategies employed have included a move from two-strip to four-strip imagers (allowing four times to be recorded per shot instead of two), the implementation of physics-informed rules of engagements allowing for the maximum flexibility in a shots total energy and symmetry performance, and splitting the lasers main drive pulse from a monolithic single pulse equal to all beams into a triply-segmented pulse which minimizes optics damage.

Sensitivity analysis of experimental parameters on 1D HYADES output

The Center for Radiative Shock Hydrodynamics (CRASH) at the University of Michigan is a focused effort to do predictive science in the regime of radiative hydrodynamics. The current plan with CRASH is to use 2D HYADES (or H2D) to model the laser-energy-deposition portion of the experiment, before passing the results to the CRASH code to be used as its initial conditions. HYADES is a Lagrangian Radiation Hydrodynamics code in either 1D or 2D with 3D laser ray-tracing in 2D. It is written and developed by Jon Larsen at Cascade Sciences Inc. Data from radiating shock experiments, carried out on the Omega Laser at LLE, will be used to assess the predictive capability of the CRASH code. We will show results of a series of 1D simulations using HYADES, performed to examine the sensitivity of various physical quantities to the variability of experimental parameters. Code results are analyzed at 1.1 ns and 13 ns to correspond to the time that the data are exchanged between the two codes and the time at which data were collected for the radiative shock experiments. Conducting the initial sensitivity study in 1D will allow for a more directed approach to sensitivity studies in 2D and 3D, and will stimulate further analysis of the experimental data.

Challenges to understanding radiative shocks

Shock waves driven above a threshold velocity near 100 km/s become strongly radiative, converting most of the incoming energy flux into radiation. We produce such shock waves in Xe or Ar by using a laser to shock, ionize, and accelerate a Be plate into a gas-filled shock tube. Structure develops in these systems due to both radiative energy transfer and hydrodynamic instability. We are conducting such experiments, implementing a code to model them, and implementing software to assess the predictive capability of the code in our Center for Radiative Shock Hydrodynamics.

Using high power lasers to create radiative shock waves

The paper discusses experiments, modeling, and uncertainty assessment radiative shocks produced by using high-power lasers to launch a thin Be plate into Xe gas at > 100 km/s.