Search Results - (Author, Cooperation:R. W. Lee)

2018-02-02

American Physical Society (APS)

0031-9007

1079-7114

Physics

Plasma and Beam Physics

2012-01-27

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

1089-7550

AIP Digital Archive

Physics

Rapid solidification (melt spinning) and powder metallurgy (sintering) methods have been successfully developed to fabricate excellent permanent magnets from RE2Fe14B-based alloys (RE=rare earth). Hot deformation of a chill-cast ingot is a potentially simpler and less costly method. However, development of this method will require better understanding of the coercivity mechanisms in this form of the magnet material. Toward this end, this paper reports results of a study of the dependence of the room-temperature demagnetization of a die-upset chill-cast ingot on composition and postpress heat treatment. Substitution of Pr for Nd and Cu for Fe results in smaller 2:14:1 grain size which leads to improved magnetic alignment and higher coercivity in a die-upset ingot. Postpress heat treatment produces a reversible order of magnitude coercivity change from a low-coercivity state (quench from 1000 °C) to a high-coercivity state (quench from 600 °C). This large effect is discussed in the light of electron probe analyses of the grain boundaries. A contributor to coercivity in these materials appears to be the REFe2 component of the eutectic.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

The morphology of the 33.8 A(ring) emission from laser-irradiated targets was studied using a concave mirror with a W/B4C multilayer coating. The mirror had peak normal-incidence reflectance of 1.8% at a wavelength of 33.8 A(ring). The emissions from a variety of targets were imaged on film with a spatial resolution of 30 μm in the target plane. Radiatively heated, low-density plastic and silica foams, x-ray laser targets, and a gas-filled enclosure were imaged. Several targets were simultaneously imaged at wavelengths of 33.8 and 130 A(ring) using two normal-incidence microscopes.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

X-ray spectroscopy is a valuable tool for diagnosing laser-imploded capsules. Using a compact spectrometer/streak camera, which fits down a 6-in.-diam tube, we routinely perform time-resolved measurements of deuterium-filled capsules, seeded with Ar, on implosions driven by the NOVA laser. Future high performance targets will preclude the use of Ar as a diagnostic; we are pursuing spectral diagnostics at higher proton energy (Ne-like Xe) and have performed a series of direct drive implosions of capsules filled with Xe, and with Kr, to help validate line broadening models for Ne-like ions. We will discuss the details of the instrument and these experiments.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

The broadening of x-ray spectral lines has become an established diagnostic of Ne in high-density plasmas, particularly those of interest in inertial confinement fusion (ICF). Work to date has concentrated mostly on the broadening of K-shell lines in moderate Z (Z∼10–20) ions in plasmas with electron densities up to 1024 cm−3. In this paper we report on calculations of line broadening for Ne-like Xe (Xe44+) appropriate for diagnosis of higher density plasmas with Ne∼1025 cm−3. These calculations have been performed with a recently developed state of the art computer code which treats the ion and electron broadening in the quasi-static and impact approximations, respectively. In this paper, we summarize recent work examining the behavior of the width of the Ne-like Xe 3–2 and 4–2 transitions with electron density. The broadening of the 1s–3p line in H-like Ar and the 1s2–1s3p transition in He-like Ar is also studied in order to benchmark the code used in the calculations.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

In an experimental study of the physics of fast ignition, the characteristics of the hot electron source at laser intensities up to 1020 W cm−2 have been measured and a diagnosis of the heating at depth by hot electrons has been initiated. Generation of hot electrons with more than 30% efficiency has been observed. Preliminary heating data suggest temperatures kT in the range 300–800 eV.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

This article presents the results of experiments in which a high-power laser was used to irradiate low density (4–9 mg/cm3) silica aerogel and agar foam targets. The laser–solid interaction and energy transport through the material were monitored with time-resolved imaging diagnostics, and the data show the production and propagation of an x-ray emission front in the plasma. The emission-front trajectory data are found to be in significant disagreement with detailed simulations, which predict a much more rapid heating of the cold material, and the data suggest that this discrepancy is not explainable by target inhomogeneities. Evidence suggests that energy transport into the cold material may be dominated by thermal conduction; however, no completely satisfactory explanation for the discrepancies is identified, and further experimental and theoretical research is necessary in order to resolve this important problem in laser–plasma interaction physics. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The results of a proof of principle experiment is presented to illustrate the utility of the capillary discharge as a medium for the efficient production of soft x-ray lasing. The duration of the capillary discharge plasma, 8 μs, is long enough to allow multiple pulses from a Q-switched mode-locked Nd glass laser to be used as a heating source to create a hot, relatively dense plasma several times per discharge.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A study was undertaken to find the optimal conditions for generating x rays using a high-power frequency-doubled Nd laser pulse for x-ray backlighting application. More than 30 laser shots on the Lawrence Livermore National Laboratory JANUS Research Laser system have been studied. The following specific questions are addressed: (a) X-ray yield dependence on the laser parameters: (i) temporal pulse width and (ii) focusing conditions. (b) X-ray source size versus target dimensions by using a tungsten wire with various diameters. (c) Influence of background plasma on the x-ray yield from the wire using 25-μm wires surrounded by plastic.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

Pin plasma sources are used as x-ray backlights for an Al plasma produced by focusing 1.06-μm laser light to irradiances of 1012 W/cm−2. Spatially resolved absorption features of the helium- like states of ionization of the plasma allow ground-state densities of the helium and hydrogenlike stages to be measured. Comparison with simulations indicates the need for realistic opacity effects to produce a high enough state of ionization for the plasma temperature. Work performed under the auspices of the U.S. DOE by the Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

We have developed a streaked crystal spectrograph for time-resolving x-ray lines from laser-produced plasmas. The spectrograph combines an ellipsoidally curved crystal and x-ray streak camera to optimize spectral coverage and resolution, even though the instrument is located a meter from the source. The instrument has been used at Novette to measure S lines doped in concentrations of 4% in the center of CH foils. Time histories of the temperature and density of the CH plasma have been derived from relative intensities of the S lines. Details of the experiment and analysis will be presented along with the instrument design.

Electronic Resource

1089-7666

AIP Digital Archive

Physics

Analysis is presented of K- and L-shell spectra obtained from Ar and Xe dopants seeded into the fuel region of plastic capsules indirectly imploded using the Nova laser. Stark broadening measurements of the n=3-1 lines in H- and He-like Ar (Ar Ly-β and He-β, respectively) are used to infer fuel electron density, while spatially averaged fuel electron temperature is deduced from the ratio of the intensities of these lines. Systematic variations in Ar spectral features are observed as a function of drive conditions. A spectral postprocessing code has been developed to simulate experimental spectra by taking into account spatial gradients and line transfer effects, and shows good agreement with experimental data. It is shown that correct modeling of the x-ray emission requires a proper treatment of the coupled radiative transfer and kinetics problem. Continuum lowering effects are shown not to affect diagnostic line ratios, within the confines of a simple model. A recently developed diagnostic based on fitting measured line profiles of Ar He-β and its associated dielectronic satellites to theory is shown to provide a simultaneous measure of electron temperature and electron density. L-shell Xe spectroscopy is under development as an electron temperature and electron-density diagnostic. Density and temperature sensitive ratios of spectral features each consisting of many lines have been identified. Observed Xe spectra from imploded cores show the same qualitative behavior with temperature, as predicted by model calculations of Xe emission spectra. Stark broadening of Ne-like Xe 4-2 lines appears viable as an electron density diagnostic for Ne∼1025 cm−3 and is under continuing investigation. (Based on the invited paper 8I3 at the 1992 APS/DPP annual meeting [Bull. Am. Phys. Soc. 37, 1553 (1992)].)

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Using theoretical calculations to generate Lyman β and δ Stark-broadened line profiles, we have found a simple parameterization of the line intensity full width at half maximum over a broad range of the atomic species [Z∈(6,18)], electron density [NE∈(1019,1025) cm−3], and electron temperature (TE=250,500,1000 eV). The parameters of the fits are presented together with a discussion of the method.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

Time-resolved x-ray spectroscopy is used to study the implosion of indirectly driven inertial confinement fusion capsules on the Nova laser. Through the use of high-Z dopants (Ar and Xe) in the fuel, measurements of the peak temperature, from emission line ratios, and density, from line broadening, are obtained. These measurements indicate peak electron temperatures of ∼1–1.6 keV and electron (and deuteron) densities in the range of 1.0–2.0×1024 cm−3, depending on the type of laser drive used. The higher densities are achieved on targets that are driven with a shaped laser drive that allows a more isentropic compression of the fuel. Emission from high-Z pusher dopants have also been studied. These dopants can provide information on pusher conditions and can be used to study mix at the pusher fuel interface.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A theoretical study of a laser-irradiated capillary discharge is presented. The discharge produces a columnar flow of low-temperature plasma (1 eV) with a density of 1019 atoms/cm3. This ambient low-temperature plasma is then irradiated by a 1.06-μm Nd glass laser with pulse lengths from 100 ps to 1 ns. The resultant plasma is studied, using hydrodynamic simulations coupled to a detailed kinetics model.

Electronic Resource

1750-3841

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Process Engineering, Biotechnology, Nutrition Technology

20 barrows were used to study the effects of hot and cold processing of pork loin chops and roasts precooked by conventional or microwave methods. Cooking time, losses, palatability and histological characteristics were determined. Precooking of hot processed chops appeared unfeasible due to decreased tenderness related to muscle contraction. Precooking of hot processed roasts by conventional roasting appeared feasible because of lower cooking losses and acceptable tenderness as compared to that of cold processed roasts. Microwave precooking of chops and roasts was less desirable than conventional precooking because of increased cooking losses and decreased tenderness. Sarcomere length and fiber diameter were related to muscle tenderness.

Electronic Resource

1432-0649

42.55.Vc ; 32.30.Rj ; 52.70

Springer Online Journal Archives 1860-2000

Physics

Abstract We point out that existing Ne-like X-ray lasers have sufficient brightness to be used as pump sources in resonant pump-fluorescence experiments, and we discuss some of the potential benefits and limitations of such experiments. In preliminary experiments, we have measured the line overlap of the Ne-like yttrium X-ray laser near 155 Å with 4f−3d transitions in H-like Na and He-like Mg. These experiments used a high-resolution grating spectrometer, and calibrated the wavelength of the yttrium laser by comparison against lines of known wavelength. The results indicate that the wavelength of the yttrium laser is 154.985 ± 0.025 Å, a factor of 2–4 improvement in precision over previous calibrations. We find that the yttrium laser is ≈ 100 mÅ to the long-wavelength side of both the He-like Mg line and the H-like Na line, so that neither resonance is perfect; however, Stark broadening could improve the overlap in the latter scheme, and bulk Doppler shifting could improve both resonances. We also find a good resonance between the yttrium laser and an un-identified transition which we tentatively attribute to copper.

Electronic Resource

1432-0800

Springer Online Journal Archives 1860-2000

Energy, Environment Protection, Nuclear Power Engineering

Medicine

Electronic Resource

0925-4994

Law

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