26 research outputs found
Equation of state of argon : experiments on Z, density functional theory (DFT) simulations, and wide-range model.
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ALEGRA-MHD : version 4.6
ALEGRA is an arbitrary Lagrangian-Eulerian finite element code that emphasizes large distortion and shock propagation in inviscid fluids and solids. This document describes user options for modeling resistive magnetohydrodynamic, thermal conduction, and radiation emission effects
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ALEGRA-HEDP : version 4.6.
ALEGRA is an arbitrary Lagrangian-Eulerian finite element code that emphasizes large distortion and shock propagation in inviscid fluids and solids. This document describes user options for modeling resistive magnetohydrodynamics, thermal conduction, and radiation transport effects, and two material temperature physics
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Recyclable transmission line concept for z-pinch driven inertial fusion energy.
Recyclable transmission lines (RTL)s are being studied as a means to repetitively drive z pinches to generate fusion energy. We have shown previously that the RTL mass can be quite modest. Minimizing the RTL mass reduces recycling costs and the impulse delivered to the first wall of a fusion chamber. Despite this reduction in mass, a few seconds will be needed to reload an RTL after each subsequent shot. This is in comparison to other inertial fusion approaches that expect to fire up to ten capsules per second. Thus a larger fusion yield is needed to compensate for the slower repetition rate in a z-pinch driven fusion reactor. We present preliminary designs of z-pinch driven fusion capsules that provide an adequate yield of 1-4 GJ. We also present numerical simulations of the effect of these fairly large fusion yields on the RTL and the first wall of the reactor chamber. These simulations were performed with and without a neutron absorbing blanket surrounding the fusion explosion. We find that the RTL will be fully vaporized out to a radius of about 3 meters assuming normal incidence. However, at large enough radius the RTL will remain in either the liquid or solid state and this portion of the RTL could fragment and become shrapnel. We show that a dynamic fragmentation theory can be used to estimate the size of these fragmented particles. We discuss how proper design of the RTL can allow this shrapnel to be directed away from the sensitive mechanical parts of the reactor chamber
Habitat Fragmentation, Variable Edge Effects, and the Landscape-Divergence Hypothesis
Edge effects are major drivers of change in many fragmented landscapes, but are often highly variable in space and time. Here we assess variability in edge effects altering Amazon forest dynamics, plant community composition, invading species, and carbon storage, in the world's largest and longest-running experimental study of habitat fragmentation. Despite detailed knowledge of local landscape conditions, spatial variability in edge effects was only partially foreseeable: relatively predictable effects were caused by the differing proximity of plots to forest edge and varying matrix vegetation, but windstorms generated much random variability. Temporal variability in edge phenomena was also only partially predictable: forest dynamics varied somewhat with fragment age, but also fluctuated markedly over time, evidently because of sporadic droughts and windstorms. Given the acute sensitivity of habitat fragments to local landscape and weather dynamics, we predict that fragments within the same landscape will tend to converge in species composition, whereas those in different landscapes will diverge in composition. This ‘landscape-divergence hypothesis’, if generally valid, will have key implications for biodiversity-conservation strategies and for understanding the dynamics of fragmented ecosystems
Equation of state of CO2 : experiments on Z, density functional theory (DFT) simulations, and tabular models.
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Wavelength dependent measurements of optical fiber transit time, material dispersion, and attenuation
A new method for measuring the wavelength dependence of the transit time, material dispersion, and attenuation of an optical fiber is described. The authors inject light from a 4-ns risetime pulsed broad-band flashlamp into various length fibers and record the transmitted signals with a time-resolved spectrograph. Segments of data spanning an approximately 3,000 {angstrom} range are recorded from a single flashlamp pulse. Comparison of data acquired with short and long fibers enables the determination of the transit time and the material dispersion as functions of wavelength dependence for the entire recorded spectrum simultaneously. The wavelength dependent attenuation is also determined from the signal intensities. The method is demonstrated with experiments using a step index 200-{micro}m-diameter SiO{sub 2} fiber. The results agree with the transit time determined from the bulk glass refractive index to within {+-} 0.035% for the visible (4,000--7,200 {angstrom}) spectrum and 0.12% for the ultraviolet (2,650--4,000 {angstrom}) spectrum, and with the attenuation specified by the fiber manufacturer to within {+-} 10%
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Equation of state of CO2 : experiments on Z, density functional theory (DFT) simulations, and tabular models.
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Aluminum equation of state validation and verification for the ALEGRA HEDP simulation code.
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Nanosecond electrical explosion of thin aluminum wire in vacuum : experimental and computational investigations.
The experimental and computational investigations of nanosecond electrical explosion of thin Al wire in vacuum are presented. We have demonstrated that increasing the current rate leads to increased energy deposited before voltage collapse. Laser shadowgrams of the overheated Al core exhibit axial stratification with a {approx}100 {micro}m period. The experimental evidence for synchronization of the wire expansion and light emission with voltage collapse is presented. Two-wavelength interferometry shows an expanding Al core in a low-ionized gas condition with increasing ionization toward the periphery. Hydrocarbons are indicated in optical spectra and their influence on breakdown physics is discussed. The radial velocity of low-density plasma reaches a value of {approx}100 km/s. The possibility of an overcritical phase transition due to high pressure is discussed. 1D MHD simulation shows good agreement with experimental data. MHD simulation demonstrates separation of the exploding wire into a high-density cold core and a low-density hot corona as well as fast rejection of the current from the wire core to the corona during voltage collapse. Important features of the dynamics for wire core and corona follow from the MHD simulation and are discussed