Inertial confinement fusion (ICF) requires high compression of fusion fuel, to densities approaching 1000 times liquid density of deuterium-tritium (DT), at central temperatures in excess of 5 keV. ...The direct-drive approach to ICF is more energy efficient than indirect drive if the stringent drive symmetry and hydrodynamic stability requirements can be met by a suitable laser irradiation and target design. Experiments using cryogenic fuel capsules in conjunction with distributed phase plates (DPPs) on the frequency-tripled OMEGA laser system have achieved compressed DT fuel densities in the 100-200 times liquid density regime, but the experiments exhibited deviations from one-dimensional performance.
As a simple two-dimensional model of convection in the liquid phase during crystal growth using the Bridgman technique, we consider the fluid flow in a shallow rectangular cavity heated from one ...side. For an aspect ratio of 4 (aspect
ratio =
length
height
), previous numerical studies have shown the existence of two types of oscillatory solution. The first of these has been well-studied for a range of Prandtl numbers from 0 to 0.015. However, the form of the second has been observed only in a time-dependent study for a Prandtl of zero. We locate the new Hopf bifurcation which gives rise to this latter solution and study its dependence on Prandtl number. Before the onset of oscillations, various steady corotating multi-cell solutions are found depending on the aspect ratio of the cavity. We compute how the transition between three corotating cells and two corotating cells takes place for changing aspect ratio. Understanding can be facilitated by comparison with analogous problems. We consider tilting the cavity to the Bénard configuration, where the fluid is heated from below rather than from the side. In this case a no-flow solution exists where heat is transferred by conduction alone. This solution becomes unstable to counter-rotating cells at a symmetry-breaking bifurcation. We study how this symmetry-breaking bifurcation disconnects as the cell is tilted and the solutions evolve into the side-wall cavity solutions. In addition we trace the saddle-node and Hopf bifurcations found in the side-wall heated problem for changing tilt and reveal that they also exist in the Bénard convection limit; disconnected solutions in the Bénard problem have not been studied previously.
The behaviour of iron during anodizing of sputter-deposited Ta/Fe alloys in ammonium pentaborate electrolyte has been examined by transmission electron microscopy, Rutherford backscattering ...spectroscopy, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy. Anodic films on Ta/1.5 at.% Fe, Ta/3 at.% Fe and Ta/7 at.% Fe alloys are amorphous and featureless and develop at high current efficiency with respective formation ratios of 1.67, 1.60 and 1.55 nm
V
−1. Anodic oxidation of the alloys proceeds without significant enrichment of iron in the alloy in the vicinity of the alloy/film interface and without oxygen generation during film growth, unlike the behaviour of Al/Fe alloys containing similar concentrations of iron. The higher migration rate of iron species relative to that of tantalum ions leads to the formation of an outer iron-rich layer at the film surface.
Non-thickness-limited (NTL) growth of anodic films on tantalum is a remarkable recently reported phenomenon whereby anodic films can be formed on tantalum to high thickness due to a change in the ...film growth mechanism from the usual high-field type of process. The present work employs transmission electron microscopy to reveal the structure, composition, and morphology of an NTL-type film formed by anodizing tantalum at 1 A m exp -2 in 10 wt% dibasic potassium phosphate/glycerol electrolyte at 453 K. A relatively compact, amorphous layer of NTL-type film material, composed of essentially tantala, was formed above an inner layer of usual high-field-type tantala under the selected conditions of anodizing and drying of the electrolyte. The field for growth of NTL-type film material is < =10 MV m exp -1 , compared with approx =400 MV m exp -1 for high-field growth. Thus, the thickness of the inner layer is approximately equal to the product of the formation ratio for usual anodic tantala and the final anodizing voltage.
Qualitatively incorrect bifurcation diagrams are computed unless the symmetries both of the solutions and of the underlying differential equation are properly accounted for. In the context of the ...computation of solutions to partial differential equations using the finite element method, this requires careful thought when designing a suitable computational domain and corresponding grid. Here we consider the problem of computing the interaction of hexagon and roll solutions bifurcating from a spatially uniform equilibrium solution of an E(2) equivariant partial differential equation. As an example of where such an interaction occurs we consider a partial differential equation describing the directional solidification of a dilute binary alloy. We show that if the symmetry is not taken into account then spurious disconnections can occur. We describe how to overcome this problem by constructing novel grids which have hexagonal symmetry and enough translational symmetry to enable the computation of the correct bifurcation structure.
The National Ignition Facility (NIF) is a 192-beam, 1.8-MJ (ultraviolet) laser facility that is currently planned to start operating in 2002. The NIF mission is to provide data critical to this ...Nation's science-based stockpile stewardship (SBSS) program and to advance the understanding of inertial confinement fusion and assess its potential as an energy source. The NIF project involves a collaboration among the Lawrence Livermore National Laboratory (LLNL), Los Alamos National Laboratory (LANL), Sandia National Laboratory (SNL), and the University of Rochester's Laboratory for Laser Energetics (UR/LLE). In this paper, the role of the University of Rochester in the research, development, and planning required to assure the success of the NIF will be presented. The principal roles of the UR/LLE in the NIF are (1) validation of the direct-drive approach to NIF using the OMEGA 60-beam, 40-kJ UV laser facility; (2) support of indirect-drive physics experiments using OMEGA in collaboration with LLNL and LANL; (3) development of plasma diagnostics for NIF; (4) development of beam-smoothing techniques; and (5) development of thin-film coatings for NIF and cryogenic-fuel-layer targets for eventual application to NIF.
Photoluminescence (PL) and electroluminescence (EL) from porous anodic alumina (PAA) with incorporated sol-gel derived films, doped with erbium, europium and terbium, for possible optoelectronic ...applications, are described. For example, visible (green) and IR PL from erbium doped titania and indium-tin oxide specimens is displayed. A strong dependence of red PL from the europium doped yttrium-aluminium garnet/PAA structure on the excitation wavelength is revealed. An EL cell, based on a europium or terbium doped xerogel/PAA/indium-tin oxide electrode, has been developed and characterised by the current-voltage response.
The effects of current density and temperature on the anodic films formed on tantalum in dilute H sub(3)PO sub(4) (0.06%wt) solution have been studied by transmission electron microscopy, using ...ultramicrotomed sections, and Rutherford backscattering spectroscopy. Two-layered films have been identified, comprising an inner relatively pure Ta sub(2)O sub(5) layer, adjacent to the metal/film interface, and an outer layer containing incorporated PO super(3) sub(4) super(-) sub( )anions. The total amount and depth of incorporated phosphorus species increase with increasing current density and decreasing temperature, in correspondence with the enhancement of the electric field. The formation conditions for the films include those relevant to the commercial anodising of tantalum for capacitors for which the extent of phosphorus incorporation is shown to be comparatively low. copyright 2002 Elsevier Science Ltd. All rights reserved.
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