98 Matching Results

Search Results

Advanced search parameters have been applied.

RAPID UNDERCOOLING AND REFREEZE IN LASER-SHOCK-MELTED BI(ZN)

Description: We completed experiments in which we used a high-power laser to shock-melt a Bi(Zn) alloy and refreeze it in the shock release wave. We recovered the samples post shot for microscopic analysis and compared our results with the results from similar prior experiments with pure Bi. The targets in both sets of experiments were four-layer targets composed of BK7 glass, Al, the elemental Bi or Bi(Zn) alloy, and a transparent diagnostic window. There is conductive heating of the Bi through the Al layer from the hot plasma at the Al/BK7 boundary that depends on the Al thickness. Since the Bi(Zn) targets had a much thicker Al layer than did the Bi targets, the two sets of targets had somewhat different thermal histories even though they were driven to the same pressure. In this presentation we compare the resolidified Bi(Zn) microstructure to that of the Bi, accounting for the different thermal histories.
Date: November 1, 2005
Creator: Jankowski, A; Colvin, J; Reed, B & Kumar, M
Partner: UNT Libraries Government Documents Department

Insights on the local density approximation plasma polarization shift as provided by the optimum potential method

Description: The plasma polarization shift computed with a Local Density Functional model of an ion-sphere model is compared with results calculated using an optimum central field effective exchange potential. Indications are that the bulk of the shift is an artifact of the approximate exchange functional describing the interaction between bound and continuum orbitals in the LDA.
Date: January 18, 1995
Creator: Wilson, B. & Liberman, D.A.
Partner: UNT Libraries Government Documents Department

Electrodeless lighting RF power source development. Final report

Description: An efficient, solid state RF power source has been developed on this NICE project for exciting low power electrodeless lamp bulbs. This project takes full advantage of concurrent advances in electrodeless lamp technology. Electrodeless lamp lighting systems utilizing the sulfur based bulb type developed by Fusion Lighting, Inc., is an emerging technology which is based on generating light in a confined plasma created and sustained by RF excitation. The bulb for such a lamp is filled with a particular element and inert gas at low pressure when cold. RF power from the RF source creates a plasma within the bulb which reaches temperatures approaching those of high pressure discharge lamp plasmas. At these temperatures the plasma radiates substantial visible light with a spectrum similar to sunlight.
Date: August 30, 1996
Partner: UNT Libraries Government Documents Department

JINA Workshop Nuclear Physics in Hot Dense Dynamic Plasmas

Description: Measuring NEET and NEEC is relevant for probing stellar cross-sections and testing atomic models in hot plasmas. Using NEEC and NEET we can excite nuclear levels in laboratory plasmas: (1) NIF: Measure effect of excited nuclear levels on (n,{gamma}) cross-sections, 60% and never been measured; (2) Omega, Test cross-sections for creating these excited levels via NEEC and NEET. Will allow us to test models that estimate resonance overlap of atomic states with the nucleus: (1) Average Atom model (AA) (CEA&LLNL), single average wave-function potential; (2) Super Transition Array (STA) model (LLNL), More realistic individual configuration potentials NEET experimental data is scarce and not in a plasma environment, NEEC has not yet been observed.
Date: March 7, 2011
Creator: Kritcher, A L; Cerjan, C; Landen, O; Libby, S; Chen, M; Wilson, B et al.
Partner: UNT Libraries Government Documents Department

Collected abstracts on particle beam diagnostic systems

Description: This report contains a compilation of abstracts on work related to particle beam diagnostics for high temperature plasmas. The abstracts were gathered in early 1978 and represent the status of the various programs as of that date. It is not suggested that this is a comprehensive list of all the work that is going on in the development of particle beam diagnostics, but it does provide a representative view of the work in this field. For example, no abstracts were received from the U.S.S.R. even though they have considerable activity in particle beam diagnostics.
Date: January 1, 1979
Creator: Hickok, R. L.
Partner: UNT Libraries Government Documents Department

Quantum plasma dynamics: Distorted atomic reaction rates for high temperature plasmas. Final report, September 15, 1991--September 14, 1994

Description: The effect of plasma perturbers on ionic systems inside a plasma is complex, time-dependent, and stochastic. It affects not only the population of the various excited and charge states of the ions, but also the life time of these states. The broadening and population of the states inside plasmas must be treated simultaneously in a coherent way. The purpose of this project was to develop a systematic theoretical procedure to treat the effects of plasma perturbers on the atomic reaction rates, in a way consistent with the rate equation approach to plasma modeling. As explained in the following, we have completed the program set out originally. Further works needed are also pointed out. We first formulated a theoretical procedure to treat this problem in a simple form such that the theory may be applied to realistic cases. The crucial features of the conventional approaches for plasma modeling and diagnostics, the pressure broadening theory (PBT) and the rate equations approach (REQ), are adopted in treating the level distortions and population determination. The PBT is effective in treating the distortion, while the REQ approach is suitable in treating multiple cascade effects on the level population. In order to combine both these theories, however, careful examination of the assumptions which have gone into the PBT and REQ formulations had to be carried out, in terms of the distorted state dressing and coarse grain averaging. The various relaxation times involved in the perturber collisions, ionic decay, and averaging time intervals were compared. The resulting theory separates the plasma perturbations into two parts, slow and fast relative to the typical atomic relaxation time involved for a particular state of the target ion. The slow part is to be included in an effective plasma potential, and is to be used in distorting the ionic states.
Date: September 25, 1996
Creator: Hahn, Yukap
Partner: UNT Libraries Government Documents Department

USE OF A UNIQUE BIOBARRIER TO REMEDIATE NITRATE AND PERCHLORATE IN GROUNDWATER

Description: The Los Alamos National Laboratory Colt facility has been used to create target plasma for Magnetized Target Fusion (MTF). The primary results regarding magnetic field, plasma density, plasma temperature, and hot plasma lifetime are summarized and the suitability of these plasma targets for MTF is assessed.
Date: April 1, 2001
Creator: STRIETELMEIER, B. A.; ESPINOSA, M. L. & AL, ET
Partner: UNT Libraries Government Documents Department

ANALYSIS OF DATA FROM Z-PINCH MTF TARGET PLASMA EXPERIMENTS

Description: The Los Alamos National Laboratory Colt facility has been used to create target plasma for Magnetized Target Fusion (MTF). The primary results regarding magnetic field, plasma density, plasma temperature, and hot plasma lifetime are summarized and the suitability of these plasma targets for MTF is assessed.
Date: April 1, 1999
Creator: WYSOCKI, F.; TACCETTI, J. & AL, ET
Partner: UNT Libraries Government Documents Department

950809 Charged particle transport updated multi-group diffusion

Description: In 1974, a charged particle transport scheme was introduced which utilized a multi-group diffusion method for the spatial transport and slowing down of energetic ions in a hot plasma. In this treatment a diffusion coefficient was used which was flux-limited to provide, hopefully, some degree of accuracy when the slowing down of an energetic charged particle is dominated by Coulomb collisions with thermal ions and electrons in a plasma medium. An advantage of this method was a very fast, memory-contained program for calculating the behavior of energetic charged particles which resulted in smoothly varying particle number densities and energy depositions. The main limitation of the original multi-group charged particle diffusion scheme is its constraint to a basic ten group structure; the same ten group structure for each of the five energetic ions tracked. This is regarded as a severe limitation, inasmuch as more groups would be desired to simulate more accurately the corresponding Monte Carlo results of energies deposited over spatial zones from a charged particle source. More generally, it seems preferable to have a different group structure for each particle type since they are created at inherently different energies. In this paper, the basic theory and multi-group description will be given. This is followed by the specific techniques that were used to solve the resultant equations. Finally, the modifications that were made to the cross section data as well as the methods used for energy and momentum deposition are described.
Date: September 1, 1995
Creator: Corman, E.G.; Perkins, S.T. & Dairiki, N.T.
Partner: UNT Libraries Government Documents Department

Collision cross sections for few electron systems. Final report, August 1, 2992--July 31, 1995

Description: The purpose of this project was to produce accurate cross sections for collisionally induced reactions from the ground stated and excited states of species of ions and at present in a hot fusion plasma. The collisional constituents may be divided into two categories for the purpose of calculations: Those in which a bare projectile excites a one electron or two electron ion or atom from its ground state, or excited states to higher excited states or ionized states. Those in which the projectile has one or more electrons attached to it and excites a one electron or two electron ion or atom from its ground state, or excited states to higher excited states or ionized states. During the collision the projectile itself may change its state being simultaneously excited or ionized. Cross sections are needed typically over the whole energy range from low velocities where molecular, orbitals begin to form to high velocities where first Born or more sophisticated asymptotic theories can be used. These high energy cross sections are very useful for experimentalists to check the absolute normalization of their cross sections. The theoretical tools used were therefore both analytical and numerical in character. Numerical calculations were restricted to expansions of the wavefunctions in a set of finite hilbert basis states (FHBS). The many body aspects of the problem, i.e. the important presence of the interelectron force, or correlation mandate a careful systematic approach. But this section was tempered in our strategy by the fact that many of the cross sections needed, especially from excited states, have never been calculated or measured at all. Thus any information we can provide is useful even if later work may modify our results.
Date: December 31, 1995
Creator: Reading, J. F. & Ford, A. L.
Partner: UNT Libraries Government Documents Department

X-Ray Imaging Crystal Spectrometer for Extended X-Ray Sources

Description: Spherically or toroidally curved, double focusing crystals are used in a spectrometer for X-ray diagnostics of an extended X-ray source such as a hot plasma produced in a tokamak fusion experiment to provide spatially and temporally resolved data on plasma parameters such as ion temperature, toroidal and poloidal rotation, electron temperature, impurity ion charge-state distributions, and impurity transport. The imaging properties of these spherically or toroidally curved crystals provide both spectrally and spatially resolved X-ray data from the plasma using only one small spherically or toroidally curved crystal, thus eliminating the requirement for a large array of crystal spectrometers and the need to cross-calibrate the various crystals.
Date: May 1, 1999
Creator: Bitter, Manfred L.; Fraekel, Benjamin; Gorman, James L.; Hill, Kenneth W.; Roquemore, Lane A.; Stodiek, Wolfgang et al.
Partner: UNT Libraries Government Documents Department

Spectroscopic Characterization of Post-Cluster Argon Plasmas During the Blast Wave Expansion

Description: In this work we present temperature diagnostics of an expanding laser-produced argon plasma. A short-pulse (35fs) laser with an intensity of I = 10{sup 17}W/cm{sup 2} deposits {approx} 100 mJ of energy into argon clusters. This generates a hot plasma filament that develops into a cylindrically expanding shock. We develop spectral diagnostics for the temperatures of the argon plasma in the shock region and the preionized region ahead of the shock. A collisional-radiative model is applied to explore line intensity ratios derived from Ar II - Ar IV spectra that are sensitive to temperatures in a few eV range. The results of hydrodynamic simulations are employed to derive a time dependent radiative transport calculation that generates the theoretical emission spectra from the expanding plasma.
Date: May 30, 2002
Creator: Ching, H,-K.; Fournier, K.B.; Edwards, M.J.; Scott, H.A.; Cattolica, R.; Ditmire, T. et al.
Partner: UNT Libraries Government Documents Department

Self-consistent microwave plasma heating rates

Description: Under conditions within a hot overdense plasma corona where the field frequency is much less than the electron plasma frequency and the field period is much less than the hydrodynamic expansion time it is shown that electron field reversal heating can exceed the combined classical heating rates due to inverse bremsstrahlung (skin effect) and field pressure (PdV) by a factor approximately v/ sub e//2v/sub i/ (half the ratio of electron and ion thermal velocities). In particular this rate can exceed the inertial expansion cooling rate at a collisionless corona density of approximately 1 percent solid core density and could be realized experimentally at core temperatures approximately 3--5 keV and microwave field intensities approximately 1 MG. (auth)
Date: October 1, 1975
Creator: Ensley, D.L. & White, R.H.
Partner: UNT Libraries Government Documents Department

Laser-Plasma Interactions in High-Energy-Density Plasmas

Description: High temperature hohlraums (HTH) are designed to reach high radiation temperatures by coupling a maximum amount of laser energy into a small target in a short time. These 400-800 {micro}m diameter gold cylinders rapidly fill with hot plasma during irradiation with multiple beams in 1ns laser pulses. The high-Z plasmas are dense, (electron density, n{sub e}/n{sub c} {approx} 0.1-0.4), hot (electron temperature, T{sub e} {approx} 10keV) and are bathed in a high-temperature radiation field (radiation temperature, T{sub rad} {approx} 300eV). Here n{sub c}, the critical density, equals 9 x 10{sup 21}/cm{sup 3}. The laser beams heating this plasma are intense ({approx} 10{sup 15} - 10{sup 17} W/cm{sup 2}). The coupling of the laser to the plasma is a rich regime for Laser-Plasma Interaction (LPI) physics. The LPI mechanisms in this study include beam deflection and forward scattering. In order to understand the LPI mechanisms, the plasma parameters must be known. An L-band spectrometer is used to measure the and electron temperature. A ride-along experiment is to develop the x-radiation emitted by the thin back wall of the half-hohlraum into a thermal radiation source.
Date: October 17, 2006
Creator: Baldis, H
Partner: UNT Libraries Government Documents Department

Analytical and numerical ray tracing of x-ray lasers

Description: Soft x-ray lasers in 10-30nm range are now routinely produced in hot plasmas generated either by a laser from a solid target or by an electrical discharge in a capillary. Such an x-ray laser is a convenient tool for future applications, such as probing dense plasmas of interest for fusion experiments. Their short wavelength enables plasma diagnosis beyond the capabilities of optical lasers, because the high critical plasma density ({approx}{lambda}{sup 2}) limits the optical beam propagation. In our paper, we present analytical and numerical ray tracing of an x-ray laser in dense amplifying plasmas. A general analytical formula for a beam propagation has been developed for a gradient plasma. The simplified analytical formulaes enable better understanding of processes involved. They also simplify optimization of the beam propagation and ''mapping'' the parameter space for further studies by numerical codes. We discuss implications for a transient x-ray laser that is produced from a slab target by a (sub-)picosecond laser pulse.
Date: December 22, 2003
Creator: Kuba, J; Shlyaptsev, V N; Benredjem, D & Moller, C
Partner: UNT Libraries Government Documents Department

Full-wave Simulations of LH Wave Propagation in Toroidal Plasma with non-Maxwellian Electron Distributions

Description: Abstract: The generation of energetic tails in the electron distribution function is intrinsic to lower-hybrid (LH) heating and current drive in weakly collisional magnetically confined plasma. The effects of these deformations on the RF deposition profile have previously been examined within the ray approximation. Recently, the calculation of full-wave propagation of LH waves in a thermal plasma has been accomplished using an adaptation of the TORIC code. Here, initial results are presented from TORIC simulations of LH propagation in a toroidal plasma with non-thermal electrons. The required efficient computation of the hot plasma dielectric tensor is accomplished using a technique previously demonstrated in full-wave simulations of ICRF propagation in plasma with non-thermal ions.
Date: July 2, 2007
Creator: E.J. Valeo, C.K. Phillips, P.T. Bonoli, J.C. Wright, M. Brambilla, and the RF SciDAC Team
Partner: UNT Libraries Government Documents Department

Full-wave Simulations of ICRF Heating in Toroidal Plasma with Non-Maxwellian Distribution Functions in the FLR Limit

Description: At the power levels required for signicant heating and current drive in magnetically-con ned toroidal plasma, modi cation of the particle distribution function from a Maxwellian shape is likely [T.H. Stix, Nucl. Fusion, 15:737 1975], with consequent changes in wave propagation and in the location and amount of absorption. In order to study these e ects computationally, the nite-Larmor-radius, full-wave, hot-plasma toroidal simulation code, TORIC [M. Brambilla. Plasma Phys. Controlled Fusion, 41:1, 1999], has been extended to allow the prescription of arbitrary velocity distributions of the form ƒ (ν||, ν⊥, Ψ, θ). For H minority heating of a D-H plasma with anisotropic Maxwellian H distributions, the fractional H absorption varies signi cantly with changes in parallel temperature but is essentially independent of perpendicular temperature.
Date: July 18, 2007
Creator: E.J. Valeo, C.K. Phillips, H. Okuda, J.C. Wright, P.T. Bonoli, L.A. Berry, and the RF SciDAC Team
Partner: UNT Libraries Government Documents Department

New Insights to the Sawtooth Oscillation (m/n=1/1 mode) in Hot Plasmas based on High Resolution 2-D Images of Te Fluctuations

Description: Two dimensional (2-D) images of electron temperature fluctuations with high temporal and spatial resolution have been employed to study the sawtooth oscillation (m/n=1/1 mode) in Toroidal EXperiment for Technology Oriented Research (TEXTOR) tokamak plasmas. 2-D imaging data revealed new physics which were not available in previous studies based on the 1-D electron temperature measurement and X-ray tomography. Review of the physics of the sawtooth oscillation is given by comparative studies with prominent theoretical models suggest that a new physics paradigm is needed to describe the reconnection physics of the sawtooth oscillation. The new insights are: A pressure driven instability (not a ballooning mode) leads to the X-point reconnection process. The reconnection process is identified as a random 3-D local reconnection process with a helical structure. The reconnection time scale is similar for different types of sawtooth oscillation ("kink" and tearing type) and is significantly faster than the resistive time scale. Heat flow from the core to the outside of the inversion radius during the reconnection process is highly collective rather than stochastic.
Date: November 26, 2007
Creator: H.K. Park, N.C. Luhmann, Jr, A.J.H. Donné, C.W. Domier, T. Munsat, M.J. Van de Pol, and the TEXTOR Team
Partner: UNT Libraries Government Documents Department

Paradigm Changes in High Temperature Plasma Physics Research and Implications for ITER

Description: Significant high temperature plasma research in both the magnetic and inertial confinement regimes led to the official launching of the International Thermonuclear Experimental Reactor (ITER) project which is aimed at challenging controlled fusion power for human kind. In particular, such an endeavor originated from the fruitful research outcomes from the world wide magnetic confinement devices (primarily based on the Tokamak approach) mainly in advanced countries (US, EU, and Japan). In recent years, all new steady state capable Tokamak devices are operated and/or constructed in Asian countries and incidentally, the majority of the ITER consortium consists of Asian countries. This provides an opportunity to revisit the unresolved essential physics issues and/or extend the understanding of the transient physics to the required steady state operation so that ITER can benefit from these efforts. The core physics of a magnetically confined hot plasma has two essential components; plasma stability and cross-field energy transport physics. Complete understanding of these two areas is critical for the successful operation of ITER and perhaps, Demo reactor construction. In order to have stable high beta plasmas with a sufficiently long confinement time, the physics of an abrupt disruption and sudden deterioration of the energy transport must be understood and conquered. Physics issues associated with transient harmful MHD behavior and turbulence based energy transport are extremely complicated and theoretical understanding needs a clear validation and verification with a new research approach such as a multi-dimensional visualization.
Date: February 22, 2008
Creator: Park, Hyeon K.
Partner: UNT Libraries Government Documents Department