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Using Very Small-scale Experiments to Investigate Materials: The 21st Century Direction in Basic Pu Research?

Description: Researchers at Lawrence Livermore National Laboratory have developed several techniques to probe the properties of Plutonium using tiny microgram-to-milligram samples. This commentary describes the advantages of this experimental approach, and contains examples of successful experimental setups. One motivation for such experiments is that they couple well to computational simulations of electronic and atomistic properties and processes, and examples of this coupling are discussed.
Date: October 25, 2004
Creator: Chandler, E A
Partner: UNT Libraries Government Documents Department

Analytic models for beam propagation and far-field patterns in slab and bow-tie x-ray lasers

Description: Simplified analytic models for beam propagation in slab and bow-tie x-ray lasers yield convenient expressions that provide both a framework for guidance in computer modeling and useful approximates for experimenters. In unrefracted bow-tie lasers, the laser shape in conjunction with the nearly-exponential weighting of rays according to their length produces a small effective aperture for the signal. We develop an analytic expression for the aperture and the properties of the far-field signal. Similarly, we develop the view that the far-field pattern of refractive slab lasers is the result of effective apertures that are created by the interplay of refraction and exponential amplification. We present expressions for the size of this aperture as a function of laser parameters as well as for the intensity and position of the far-field lineout. This analysis also yields conditions for the refraction limit in slab lasers and an estimate for the signal loss due to refraction.
Date: June 1, 1994
Creator: Chandler, E. A.
Partner: UNT Libraries Government Documents Department

Computer modeling of organic aerogels: Final report of 93-SR-062

Description: Goal of the work was to develop computer models of organic aerogel structures, and to study transport process within these materials. During the course of the research understanding of the structure of all aerogels including acid and neutral-catalyzed silica aerogel was developed. The modeling of transport focused on fluid flow in aerogels. We successfully modified a novel state-of-the-art lattice Boltzmann code to simulate flow at low Knudsen number, and developed a simple molecular dynamics code for gas flow at extremely high Knudsen number (low density). These flow-modeling techniques can be used to study aerogel applications for technology transfer; in addition, these techniques can be used to study flow through other porous materials.
Date: June 10, 1994
Creator: Chandler, E. A.; Calef, D. & Ladd, A. J. C.
Partner: UNT Libraries Government Documents Department

Dispersion relationship for solid state instability growth and sensitivity to equation of state

Description: We have derived an approximate analytical dispersion relation for solid state instability growth following the method of Mikaelian. I He starts with the general eigenvalue equation for the velocity of a perturbation on a finite-thickness fluid layer with surface tension and viscosity, and derives an exact solution numerically from det(M)=0, where M is an 8x8 matrix. He then derives an approximate solution analytically by substituting the inviscid eigenfunctions into the exact eigenvalue equation. The integrations yield a dispersion relation which is a polynomial in the growth rate.
Date: June 1, 1997
Creator: Colvin, J.D.; Wiley, L.G.; Chandler, E.A.; Remington, B.A. & Kalantar, D.H.
Partner: UNT Libraries Government Documents Department

Nova experiments to investigate hydrodynamic instabilities in the solid state

Description: Experiments were done to shock compress and accelerate copper foils at peak presssures of {approximately}3 Mbar above and below the melt temperature to study the effects of material strength on hydrodynamic instabilities. An x-ray drive generated in a hohlraum target was used to generate the shock wave profiles. The growth of a preimposed perturbation at an embedded interface is diagnosed by x-ray radiography. Results obtained using a high contrastshaped laser pulse show that the growth of the modulation is delayed compared to fluid simulations,which could be due to material strength stabilization. In contrast, when a copper foil is placed above the melt temperature at {gt}3 Mbar with a single shock, it melts upon compression and the modulation growth is consistent with fluid modeling. Experimental results from copper shocked to 3 Mbar both below and above the melt temperature are presented and compared with simulation.
Date: July 8, 1997
Creator: Kalantar, D.H.; Remington, B.A.; Chandler, E.A.; Colvin, J.D.; Griswold, D.L.; Turner, R.E. et al.
Partner: UNT Libraries Government Documents Department

High pressure solid state experiments on the NOVA laser

Description: An x-ray drive has been developed to shock compress metal foils in the solid state in order to study the material strength under high compression. The drive has been characterized and hydrodynamics experiments designed to study growth of the Rayleigh-Taylor (RT) instability in Cu foils at 3 Mbar peak pressures have been started. Pre-imposed modulations with an initial wavelength of 20-50 {micro}m, and amplitudes of 1.0-2.5 {micro}m show growth consistent with simulations. In this parameter regime, the fluid and solid states are expected to behave similarly for Cu. An analytic stability analysis is used to motivate an experimental design with an Al foil where the effects of material strength on the RT growth are significantly enhanced. Improved x-ray drive design will allow the material to stay solid under compression throughout the experiment, and dynamic diffraction techniques are being developed to verify the compressed state.
Date: November 1, 1998
Creator: Chandler, E A; Colvin, J D; Gold, D M; Hauer, A A; Kalantar, D H; Meyers, M A et al.
Partner: UNT Libraries Government Documents Department

Application of the Pegasus II Pulsed-Power Facility to the Study of Inertial Instability and Fracture of Cylindrical Tubes of Solid Aluminum

Description: Understanding the surface stability of metals undergoing dynamic fracture at shock breakout is important to several applications in metals processing. The advantages of using the Pegasus II facility to investigate the phenomena occurring at shock break out are described. As an example of the data collected, we concentrate on brief descriptions of two experiments that compared the tensile failure, i.e. ''spall'', patterns in the presence of sinusoidal perturbations seeded on the free inner surface of cylindrical samples of 3 types of Al. These samples were composed variously of soft Al 1100-O, structural grade Al 6061-T6, and ultra-pure 99.99% Al and were subjected to Taylor waves with shock pressures of 14 GPa. We show that the material behind the exiting surface undergoes a type of failure termed here ''microspall'', resulting in the production of a significant volume of low-density, probably granular, material. The failure mechanism, combined with the forces that cause inertial instability, leads to rapid pattern growth in the failed material and subsequent pattern growth on the surface. Pattern growth was studied as a function of perturbation wavelength and amplitude. The different Al samples vary by an order of magnitude in yield strength, and some increase in pattern instability was observed at lower yield strength. The ultra-pure Al has exceptionally large grain size, in the mm range. No appreciable variation of spall pattern was observed due to grain size.
Date: June 23, 1999
Creator: Chandler, E.A.; Stokes, J.; Fulton, R.D.; Morgan, D.V.; Obst, A.W.; Oro, D.M. et al.
Partner: UNT Libraries Government Documents Department

Developing solid state experiments on the Nova laser

Description: An x-ray drive has been developed to shock compress metal foils in the solid state using an internally shielded hohlraum with a high contrast shaped pulse from the Nova laser. The drive has been characterized and hydrodynamics experiments designed to study growth of the Rayleigh-Taylor (RT) instability in Cu foils at 3 Mbar peak pressures in the plastic flow regime have been started. Pre-imposed modulations with an initial wavelength of 20-50 {micro}m, and amplitudes of 1.0-2.5 {micro}m show growth consistent with simulations. In the Nova experiments, the fluid and solid states are expected to behave similarly for Cu. An analytic stability analysis is used to motivate an experimental design with an Al foil where the effects of material strength on the RT growth are significantly enhanced. The conditions reached in the metal foils at peak compression are similar to those predicted at the core of the earth.
Date: August 6, 1999
Creator: Chandler, E A; Colvin, J D; Failor, B H; Gold, D M; Hauer, A; Kalantar, D H et al.
Partner: UNT Libraries Government Documents Department