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18 results for: All records
Author ORCID ID is 0000000247525141
Full Text and Citations
  1. The LANL Shear Campaign uses millimeter-scale initially solid shock tubes on the National Ignition Facility to conduct high-energy-density hydrodynamic plasma experiments, capable of reaching energy densities exceeding 100 kJ/cm 3. These shock-tube experiments have for the first time reproduced spontaneously emergent coherent structures due to shear-based fluid instabilities [i.e., Kelvin-Helmholtz (KH)], demonstrating hydrodynamic scaling over 8 orders of magnitude in time and velocity. The KH vortices, referred to as “rollers,” and the secondary instabilities, referred to as “ribs,” are used to understand the turbulent kinetic energy contained in the system. Their evolution is used to understand the transition to turbulencemore » and that transition's dependence on initial conditions. Experimental results from these studies are well modeled by the RAGE (Radiation Adaptive Grid Eulerian) hydro-code using the Besnard-Harlow-Rauenzahn turbulent mix model. Information inferred from both the experimental data and the mix model allows us to demonstrate that the specific Turbulent Kinetic Energy (sTKE) in the layer, as calculated from the plan-view structure data, is consistent with the mixing width growth and the RAGE simulations of sTKE.« less
  2. Here, energy-transport effects can alter the structure that develops as a supernova evolves into a supernova remnant. The Rayleigh–Taylor instability is thought to produce structure at the interface between the stellar ejecta and the circumstellar matter, based on simple models and hydrodynamic simulations. Here we report experimental results from the National Ignition Facility to explore how large energy fluxes, which are present in supernovae, affect this structure. We observed a reduction in Rayleigh–Taylor growth. In analyzing the comparison with supernova SN1993J, a Type II supernova, we found that the energy fluxes produced by heat conduction appear to be larger thanmore » the radiative energy fluxes, and large enough to have dramatic consequences. No reported astrophysical simulations have included radiation and heat conduction self-consistently in modeling supernova remnants and these dynamics should be noted in the understanding of young supernova remnants.« less
  3. Direct drive implosions of plastic capsules have been performed at the National Ignition Facility to provide a broad-spectrum (500–2000 eV) X-ray continuum source for X-ray transmission spectroscopy. The source was developed for the high-temperature plasma opacity experimental platform. Initial experiments using 2.0 mm diameter polyalpha-methyl styrene capsules with ~20 μm thickness have been performed. X-ray yields of up to ~1 kJ/sr have been measured using the Dante multichannel diode array. The backlighter source size was measured to be ~100 μm FWHM, with ~350 ps pulse duration during the peak emission stage. Lastly, these results are used to simulate transmission spectramore » for a hypothetical iron opacity sample at 150 eV, enabling the derivation of photometrics requirements for future opacity experiments.« less
  4. On laser-driven platforms the assumption of experiment repeatability is particularly important due to a typically low data acquisition rate that doesn’t often allow for data redundancy. If the platform is repeatable, then measurements of the repeatable dynamics from multiple experiments can be treated as measurements of the same system. In high-energy-density hydrodynamic instability experiments the interface growth is assumed to be one of the repeatable aspects of the system. In this paper we demonstrate the repeatability of the instability growth in the counter-propagating shear experiment at the OMEGA laser facility, where the instability growth is characterized by the tracer layermore » thickness or mix-width evolution. Furthermore, in our previous experiment campaigns we have assumed the instability growth was repeatable enough to identify trends, but in this work we explicitly show that the mix-width measurements for nominally identical experiments are repeatable within the measurement error bars.« less
  5. Here, we report an experimental and computational study investigating the effects of laser preheat on the hydrodynamic behavior of a material layer. In particular, we find that perturbation of the surface of the layer results in a complex interaction, in which the bulk of the layer develops density, pressure, and temperature structure and in which the surface experiences instability-like behavior, including mode coupling. A uniform one-temperature preheat model is used to reproduce the experimentally observed behavior, and we find that this model can be used to capture the evolution of the layer, while also providing evidence of complexities in themore » preheat behavior. Lastly, this result has important consequences for inertially confined fusion plasmas, which can be difficult to diagnose in detail, as well as for laser hydrodynamics experiments, which generally depend on assumptions about initial conditions in order to interpret their results.« less

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