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Spectroscopic temperature measurements of non-equilibrium plasmas

Description: The characterization of laser-produced plasmas has required the application of spectroscopic techniques to non-standard conditions where kinetics models have not been extensively tested. The plasmas are produced by the Nova laser for the study of inertial confinement fusion, can be mm in size, and evolve on sub-nanosecond time scales. These targets typically achieve electron temperatures from 2-4 keV and electron densities of 10{sup 20}-10{sup 22} cm{sup {minus}3}. The authors have measured the electron temperature of two types of targets: bags of gas and hohlraums, Au cylinders with laser entrance holes in the flat ends. By comparing data from different targets, they examine the time-dependence of spectroscopic plasma diagnostics.
Date: April 24, 1996
Creator: Back, C.A.; Glenzer, S.H.; Lee, R.W. & MacGowan, B.J.
Partner: UNT Libraries Government Documents Department

Laser scattering in large-scale-length plasmas relevant to National Ignition Facility hohlraums

Description: We have used homogeneous plasmas of high density (up to 1.3 X 10{sup 21} electrons per cm{sup 3}) and temperature ({approximately} 3 keV) with large density scale lengths ({approximately}2 mm) to approximate conditions within National Ignition Facility (NIF) hohlraums. Within these plasmas we have studied the dependence of stimulated Raman (SRS) and Brillouin (SBS) scattering on beam smoothing and plasma conditions at the relevant laser intensity (3{omega}, 2 X 10{sup 15}Wcm{sup 2}). Both SBS and SRS are reduced by the use of smoothing by spectral dispersion (SSD).
Date: October 1, 1996
Creator: MacGowan, B.J.; Berger, R.L. & Afeyan, B.B.
Partner: UNT Libraries Government Documents Department

Observation of multiple mechanisms for stimulating ion waves in ignition scale plasmas

Description: The laser and plasma conditions expected in ignition experiments using indirect drive inertial confinement have been studied experimentally. It has been found that there are at least three ways in which ion waves can be stimulated in these plasmas and have significant effect on the energy balance and distribution in the target. First ion waves can be stimulated by a single laser beam by the process of Stimulated Brillouin Scattering (SBS) in which an ion acoustic and a scattered electromagnetic wave grow from noise. Second, in a plasma where more than one beam intersect, ion waves can be excited at the `beat` frequency and wave number of the intersecting beams, causing the side scatter instability to be seeded, and substantial energy to be transferred between the beams [R. K. Kirkwood et. al. Phys. Re0319v. Lett. 76, 2065 (1996)]. And third, ion waves may be stimulated by the decay of electron plasma waves produced by Stimulated Raman Scattering (SRS), thereby inhibiting the SRS process [R. K. Kirkwood et. al. Phys. Rev. Lett. 77, 2706 (1996)].
Date: November 1, 1996
Creator: Kirkwood, R.K.; MacGowan, B.J. & Montgomery, D.S.
Partner: UNT Libraries Government Documents Department

Observation of multiple mechanisms for stimulating ion waves in ignition scale plasmas. Revision 1

Description: The laser and plasma conditions expected in ignition experiments using indirect drive inertial confinement have been studied experimentally. It has been shown that there are at least three ways in which ion waves can be stimulated in these plasmas and have significant effect on the energy balance and distribution in the target. First ion waves can be stimulated by a single laser beam by the process of Stimulated Brillouin Scattering (SBS) in which an ion acoustic and a scattered electromagnetic wave grow from noise. Second, in a plasma where more than one beam intersect, ion waves can Lie excited at the `beat` frequency and wave number of the intersecting beams,, causing the side scatter instability to be seeded, and substantial energy to be transferred between the beams [R. K. Kirkwood et. al. Phys. Rev. Lett. 76, 2065 (1996)]. And third, ion waves may be stimulated by the decay of electron plasma waves produced by Stimulated Raman Scattering (SRS), thereby inhibiting the SRS process [R. K. Kirkwood et. al. Phys. Rev. Lett. 77, 2706 (1996)].
Date: March 3, 1997
Creator: Kirkwood, R.K.; MacGowan, B.J. & Montgomery, D.S.
Partner: UNT Libraries Government Documents Department

Interaction between stimulated raman scattering and ion acoustic waves in ignition relevant plasmas

Description: We have observed that the scattering of light by stimulated Langmuir waves (SRS) in ignition scale plasmas is dependent on the properties of the ion acoustic wave, indicating that a nonlinear coupling between the two waves limits the scattered energy.
Date: June 1, 1997
Creator: Kirkwood, R.K.; MacGowan, B.J. & Montgomery, D.S.
Partner: UNT Libraries Government Documents Department

Thomson scattering in the corona of laser-produced gold plasmas

Description: Thomson scattering measurements of the electron temperature in laser- produced gold plasmas are presented. We irradiated a flat gold disk target with one laser beam of the Nova laser facility. A second laser beam probed the plasma at a distance of 500{mu}m with temporally resolved Thomson scattering. The electron temperature measurements are compared with hydrodynamic simulations using the code LASNEX for experiments applying smoothed and unsmoothed heater beams. In case of an unsmoothed heater beam the simulations predict temperatures which are about 40% higher than our measured data. Although the agreement is improved for a smoothed heater beam, discrepancies exist in the decay phase of the plasma. We discuss possible explanations for these observations.
Date: May 8, 1996
Creator: Glenzer, S.H.; Back, C.A.; Estabrook, K.G. & MacGowan, B.J.
Partner: UNT Libraries Government Documents Department

The study of parametric instabilities in NIF-scale plasmas on Nova

Description: At the same time we experimentally reproduced the plasma conditions expected within the NIF using plasmas produced by the Nova laser. The plasmas were created by irradiating a thin walled gas balloon or a sealed hohlraum containing of order one atmosphere of a low-Z gas (e.g. C{sub 5}H{sub 12}, C{sub 5}D{sub 12} or CO{sub 2}). When the gas is ionized and heated the resultant plasmas are homogeneous, and of high density ({approximately}10{sup 21} electron/cm{sup 3}) and temperature ({approximately}3 keV) with large scale density scale lengths ({approximately}2 mm). Nine of the Nova beams were used to produce the plasma, the tenth beam was configured as an interaction beam that was sent through the performed plasma after a delay of order 500 psec. The SRS and SBS scattered from the plasma, together with the effects of the plasma on the transmitted beam, were studied as a function of the interaction beam intensity, beam smoothing and plasma constituents. The interaction beam was smoothed by using radon phase plates (RPPs), and 4 different colors within the f/8 beam to mimic the NIF laser architecture. The 4-color set-up divided the f/8 beam in to 4 separate quadrants each of which had its wavelength shifted relative to the other quadrants. The wavelength separation of the colors was approximately 1.4{Angstrom} at 3{omega}. Since each beam quadrant could have its frequency conversion crystals individually tuned for its wavelength, the 4-color scheme approximated ``bandwidth`` on the interaction beam without losing 3{omega} conversion efficiency. We have also studied the use of a laser bandwidth of approximately 0.7{Angstrom} and smoothing by Spectral Dispersion (SSD) with all of the quadrants set at the same color, to further reduce the reflected SBS. These studies were performed with both f/4.3 and f/8 interaction beam focusing.
Date: September 26, 1994
Creator: MacGowan, B.J.; Back, C.A. & Berger, R.L.
Partner: UNT Libraries Government Documents Department

X-ray diagnostics of hohlraum plasma flow

Description: In this study we use spectroscopy and x-ray imaging to investigate the macroscopic plasma flow in mm-sized laser-produced hohlraum plasmas. By using multiple diagnostics to triangulate the emission on a single experiment, we can pinpoint the position of dopants placed inside the hohlraum. X-ray emission from the foil has been used in the past to measure electron temperature. Here we analyze the spatial movement of dopant plasmas for comparison to hydrodynamic calculations.
Date: May 13, 1996
Creator: Back, C.A.; Glenzer, S.H.; Landen, O.L.; MacGowan, B.J. & Shepard, T.D.
Partner: UNT Libraries Government Documents Department

Spatially resolved x-ray laser spectra and demonstration of gain in nickel-like systems

Description: A recent series of experiments have provided spatially resolved near field images of several candidate x-ray lasing transition in neon-like, nickel-like, and hydrogen-like ions from laser-produced plasmas. From these time-gated, spatially, and spectrally resolved measurements the source size for the J = 0 - 1 and the J = 2 - 1 transitions in Ne-like selenium have been determined. Source regions as small as 50 ..mu..m have been observed on transitions with gain-length products >9. In addition, we have obtained the first experimental evidence for the amplification of spontaneous emission in the nickel-like ions of europium and ytterbium. Gains of order 1 cm/sup -1/ and gain-length products of up to 3.8 are observed on the J = 0 - 1, 4d-4p transitions in Eu + 35 at 65.26 and 71.00 A. Analogous transitions in Yb = +42 have been identified and some evidence for ASE has been observed. 7 refs., 11 figs.
Date: September 25, 1987
Creator: Whelan, D.A.; Keane, C.J.; MacGowan, B.J.; Matthews, D.L.; Trebes, J.E. & Eckart, M.J.
Partner: UNT Libraries Government Documents Department

Modeling NIF Experimental Designs with Adaptive Mesh Refinement and Lagrangian Hydrodynamics

Description: Incorporation of adaptive mesh refinement (AMR) into Lagrangian hydrodynamics algorithms allows for the creation of a highly powerful simulation tool effective for complex target designs with three-dimensional structure. We are developing an advanced modeling tool that includes AMR and traditional arbitrary Lagrangian-Eulerian (ALE) techniques. Our goal is the accurate prediction of vaporization, disintegration and fragmentation in National Ignition Facility (NIF) experimental target elements. Although our focus is on minimizing the generation of shrapnel in target designs and protecting the optics, the general techniques are applicable to modern advanced targets that include three-dimensional effects such as those associated with capsule fill tubes. Several essential computations in ordinary radiation hydrodynamics need to be redesigned in order to allow for AMR to work well with ALE, including algorithms associated with radiation transport. Additionally, for our goal of predicting fragmentation, we include elastic/plastic flow into our computations. We discuss the integration of these effects into a new ALE-AMR simulation code. Applications of this newly developed modeling tool as well as traditional ALE simulations in two and three dimensions are applied to NIF early-light target designs.
Date: August 31, 2005
Creator: Koniges, A E; Anderson, R W; Wang, P; Gunney, B N; Becker, R; Eder, D C et al.
Partner: UNT Libraries Government Documents Department

Polarization Smoothing on the National Ignition Facility

Description: We have recently implemented polarization smoothing (PS) on one quad of the NIF laser. Specially cut KDP and DKDP crystals at 420 x 420 mm sizes were used to scramble the incident 351 nm laser polarization over the beam aperture. The intensity contrast deduced from the measured focal spot images for one of the NIF beams is in very good agreement with the expected contrast. KDP and DKDP crystals are known to produce considerable amount of transverse stimulated Raman scattering (SRS) when irradiated with large beams at {approx}1-2 GW/cm2. In order to measure the transverse SRS, we attached optical fibers on the side of one of the PS crystals. The KDP PS crystal showed > 1 J/cm2 side scattered SRS at irradiances of 1.2 GW/cm2. The DKDP (70% deuteration level) PS crystal showed significantly less SRS. Detailed analysis of the SRS scattering in the PS crystal is in progress.
Date: September 2, 2005
Creator: Dixit, S N; Munro, D; Murray, J R; Nostrand, M; Wegner, P J; Froula, D et al.
Partner: UNT Libraries Government Documents Department

On the Accuracy of X-Ray Spectra Modeling of Inertial Confinement Fusion Plasmas

Description: We have performed x-ray spectroscopic experiments in homogeneous gas bag plasmas where we independently measure the temperature with Thomson scattering. We find that collisional radiative (kinetics) modeling of the intensities of the He-{beta} line and its dielectronic capture satellites is generally in agreement with the measured spectra. On the other hand, for the particular case of satellites arising from inner-shell electron collisional excitation, we find discrepancies of up to a factor of two between experiment and kinetics models. We have ruled out possible effects on the line emission due to plasma gradients, radiative transport, and suprathermal electron excitation leaving errors in the atomic physics modeling to be the most likely explanation. The determination that there are problems with the collisionally populated states is important for the interpretation of inertial confinement fusion capsule implosions where electron densities and temperature have been measured using the spectral line shape of the He-{beta} transition of Ar XVII. The analysis of the implosion data has required Stark broadening calculations coupled to a kinetics model to calculate the detailed line intensities and widths. Despite remaining discrepancies, the good agreement between the experimental dielectronic capture satellites and the HULLAC calculations suggests that HULLAC is a more appropriate code for the construction of the kinetics models of the He-{beta} complex from high density plasmas than previously used codes (e.g. MCDF). HULLAC results in higher temperatures for the implosion conditions of Ref.(5,6) in closer agreement with the 2-D radiation hydrodynamic modeling and other spectroscopic techniques. These results indicate that benchmarking kinetics codes with Thomson scattering is an important area in present ICF research.
Date: May 30, 2000
Creator: Glenzer, S.H.; Fournier, K.B.; Hammel, B.A.; Lee, L.W.; MacGowan, B.J. & Back, C.A.
Partner: UNT Libraries Government Documents Department

Characterization of laser-produced fusion plasmas with thomson scattering

Description: Thomson scattering has been developed at the Nova laser facility as a direct and accurate diagnostic to characterize inertial confinement fusion plasmas. Measurements from methane-filled, ignition relevant hohlraums apply the theory for two ion species plasmas, which has been tested in separate open geometry experiments, to obtain electron and ion temperatures. The experimental data provide a benchmark for two-dimensional hydrodynamic simulations using LASNEX, which is presently in use to predict he performance of future megajoule laser- driven hohlraums of the National Ignition Facility (NIF). The data are consistent with modeling using significantly inhibited heat transport at the peak of the drive. Furthermore, we find that stagnating plasma regions on the hohlraum axis are well described by the calculations. The result implies that stagnation in gas-filled hohlraums occurs too late to directly affect the capsule implosion in ignition experiments.
Date: July 9, 1997
Creator: Glenzer, S.H.; Back, C.A.; Suter, L.J.; MacGowan, B.J.; Landen, O.L.; Lindl, J.D. et al.
Partner: UNT Libraries Government Documents Department

Recent advances in indirect drive ICF target physics at LLNL

Description: In preparation for ignition on the National Ignition Facility, the Lawrence Livermore National Laboratory� s Inertial Confinement Fusion Program, working in collaboration with Los Alamos National Laboratory, Commissariat a 1� Energie Atomique (CEA), and Laboratory for Laser Energetics at the University of Rochester, has performed a broad range of experiments on the Nova and Omega lasers to test the fundamentals of the NIF target designs. These studies have refined our understanding of the important target physics, and have led to many of the specifications for the NIF laser and the cryogenic ignition targets. Our recent work has been focused in the areas of hohlraum energetics, symmetry, shock physics, and target design optimization & fabrication.
Date: January 13, 1998
Creator: Bernat, T P; Collins, G W; Haan, S; Hammel, B A; Landen, O L; MacGowan, B J et al.
Partner: UNT Libraries Government Documents Department

Target experimental area and systems of the U.S. National Ignition Facility

Description: One of the major goals of the US National Ignition Facility is the demonstration of laser driven fusion ignition and burn of targets by inertial confinement and provide capability for a wide variety of high energy density physics experiments. The NIF target area houses the optical systems required to focus the 192 beamlets to a target precisely positioned at the center of the 10 meter diameter, 10-cm thick aluminum target chamber. The chamber serves as mounting surface for the 48 final optics assemblies, the target alignment and positioning equipment, and the target diagnostics. The internal surfaces of the chamber are protected by louvered steel beam dumps. The target area also provides the necessary shielding against target emission and environmental protection equipment. Despite its complexity, the design provides the flexibility to accommodate the needs of the various NIF user groups, such as direct and indirect drive irradiation geometries, modular final optics design, capability to handle cryogenic targets, and easily re-configurable diagnostic instruments. Efficient target area operations are ensured by using line-replaceable designs for systems requiring frequent inspection, maintenance and reconfiguration, such as the final optics, debris shields, phase plates and the diagnostic instruments. A precision diagnostic instrument manipulator (DIMS) allows fast removal and precise repositioning of diagnostic instruments. In addition the authors describe several activities to enhance the target chamber availability, such as the target debris mitigation, the use of standard experimental configurations and the development of smart shot operations planning tools.
Date: December 17, 1999
Creator: Tobin, M; Van Wonterghem, B; MacGowan, B J; Hibbard, W; Kalantar, D; Lee, F D et al.
Partner: UNT Libraries Government Documents Department

Gain measurements at 5 nm in nickel-like ytterbium

Description: Soft x-ray gain has been demonstrated at 5.03 nm within a laser produced plasma of Ni-like ytterbium. Experiments will also be described with higher Z Ni-like ions which can produce even shorter wavelength x-ray laser transition. 3 refs.
Date: March 1, 1988
Creator: MacGowan, B.J.; Bourgade, J.L.; Combis, P.; Keane, C.J.; Louis-Jacquet, M.; Matthews, D.L. et al.
Partner: UNT Libraries Government Documents Department

Recombination x-ray laser experiments using exploding ribbon Al targets

Description: We present data obtained from recent recombination x-ray laser experiments carried out at the Nova and Phebus lasers using exploding ribbon Al targets irradiated with 100 ps pulses of 0.53-{mu}m light. Spatially and temporally resolved x-ray and soft x-ray spectra will be shown. These spectra revealed the plasma to be insufficiently ionized so as to produce inversions in H-like Al. Conditions were found to be appropriate for inversion in He- and Li-like Al, however, and evidence for amplification of the AlXI 105.7 {Angstrom} (5f-3d) and AlXII 88.9 (5f-3d) and 130.1 {Angstrom} (4f-3d) lines was seen. These results will be discussed in detail and related to other work regarding the discrepancies between expected and measured electron temperatures in plasmas of this type.
Date: November 1, 1990
Creator: Keane, C.J.; Eder, D.C.; MacGowan, B.J.; Matthews, D.L. & Whelan, D.A.
Partner: UNT Libraries Government Documents Department

Characterizing high energy spectra of NIF ignition hohlraums using a differentially filtered high energy multi-pinhole X-ray imager

Description: Understanding hot electron distributions generated inside hohlraums is important to the ignition campaign for controlling implosion symmetry and sources of preheat. While direct imaging of hot electrons is difficult, their spatial distribution and spectrum can be deduced by detecting high energy x-rays generated as they interact with the target materials. We used an array of 18 pinholes, with four independent filter combinations, to image entire hohlraums with a magnification of 0.87x during the hohlraum energetics campaign on NIF. Comparing our results with hohlraum simulations indicates that the characteristic 30 keV hot electrons are mainly generated from backscattered laser plasma interactions rather than from hohlraum hydrodynamics.
Date: May 11, 2010
Creator: Park, H; Dewald, E D; Glenzer, S; Kalantar, D H; Kilkenny, J D; MacGowan, B J et al.
Partner: UNT Libraries Government Documents Department

Energetics of Multiple-Ion Species Hohlraum Plasmas

Description: A study of the laser-plasma interaction processes in multiple-ion species plasmas has been performed in plasmas that are created to emulate the plasma conditions in indirect drive inertial confinement fusion targets. Gas-filled hohlraums with densities of xe22/cc are heated to Te=3keV and backscattered laser light is measured by a suite of absolutely calibrated backscatter diagnostics. Ion Landau damping is increased by adding hydrogen to the CO2/CF4 gas fill. We find that the backscatter from stimulated Brillouin scattering is reduced is monotonically reduced with increasing damping, demonstrating that Landau damping is the controlling damping mechanism in ICF relevant high-electron temperature plasmas. The reduction in backscatter is accompanied by a comparable increase in both transmission of a probe beam and an increased hohlraum radiation temperature, showing that multiple-ion species plasmas improve the overall hohlraum energetics/performance. Comparison of the experimental data to linear gain calculations as well as detailed full-scale 3D laser-plasma interaction simulations show quantitative agreement. Our findings confirm the importance of Landau damping in controlling backscatter from high-electron temperature hohlraum plasmas and have lead to the inclusion of multi-ion species plasmas in the hohlraum point design for upcoming ignition campaigns at the National Ignition Facility.
Date: November 5, 2007
Creator: Neumayer, P; Berger, R; Callahan, D; Divol, L; Froula, D; London, R et al.
Partner: UNT Libraries Government Documents Department

Optical Alignment Techniques for Line-Imaging Velocity Interferometry and Line-Imaging Self-Emission of Targets at the National Ignition Facility (NIF)

Description: The National Ignition Facility (NIF) requires optical diagnostics for measuring shock velocities in shock physics experiments. The nature of the NIF facility requires the alignment of complex three-dimensional optical systems of very long distances. Access to the alignment mechanisms can be limited, and any alignment system must be operator friendly. The Velocity Interferometer System for Any Reflector measures shock velocities, shock breakout times, and emission of 1- to 5-mm targets at a location remote to the NIF target chamber. Three optical systems using the same vacuum chamber port each have a total track of 21 meters. All optical lenses are on kinematic mounts or sliding rails, enabling pointing accuracy of the optical axis to be checked. Counter-propagating laser beams (orange and red) align these diagnostics to a listing of tolerances. Movable aperture cards, placed before and after lens groups, show the spread of alignment spots created by the orange and red alignment lasers. Optical elements include 1-in. to 15-in. diameter mirrors, lenses with up to 10.5-in. diameters, beamsplitters, etalons, dove prisms, filters, and pellicles. Alignment of more than 75 optical elements must be verified before each target shot. Archived images from eight alignment cameras prove proper alignment before each shot.
Date: July 31, 2007
Creator: Malone, R M; Celeste, J R; Celliers, P M; Frogget, B .; Guyton, R L; Kaufman, M I et al.
Partner: UNT Libraries Government Documents Department

The National Ignition Facility: The World's Largest Laser

Description: The National Ignition Facility (NIF) is a 192-beam laser facility presently under construction at LLNL. When completed, NIF will be a 1.8-MJ, 500-TW ultraviolet laser system. Its missions are to obtain fusion ignition and to perform high energy density experiments in support of the U.S. nuclear weapons stockpile. Four of the NIF beams have been commissioned to demonstrate laser performance including target and beam alignment. During this time, NIF demonstrated on a single-beam basis that it will meet its performance goals and demonstrated its precision and flexibility for pulse shaping, pointing, timing and beam conditioning. It also performed four important experiments for Inertial Confinement Fusion and High Energy Density Science. Presently, the project is installing production hardware to complete the project in 2009 with the goal to begin ignition experiments in 2010. An integrated plan has been developed including the NIF operations, user equipment such as diagnostics and cryogenic target capability, and experiments and calculations to meet this goal.
Date: September 29, 2005
Creator: Moses, E I; Bibeau, C; Bonanno, R E; Haynam, C A; MacGowan, B J; Kauffman, R L et al.
Partner: UNT Libraries Government Documents Department

Lawrence Livermore National Laboratory's activities to achieve ignition by x-ray drive on the National Ignition Facility

Description: The National Ignition Facility (NIF) is a MJ-class glass laser-based facility funded by the Department of Energy which has achieving thermonuclear ignition and moderate gain as one of its main objectives. In the summer of 1998, the project is about 40% complete, and design and construction is on schedule and on cost. The NIF will start firing onto targets in 2001, and will achieve full energy in 2004. The Lawrence Livermore National Laboratory (LLNL), together with the Los Alamos National Laboratory (LANL) have the main responsibility for achieving x-ray driven ignition on the NIF. In the 1990�s, a comprehensive series of experiments on Nova at LLNL, followed by recent experiments on the Omega laser at the University of Rochester, demonstrated confidence in understanding the physics of x-ray drive implosions. The same physics at equivalent scales is used in calculations to predict target performance on the NIF, giving credence to calculations of ignition on the NIF. An integrated program of work in preparing the NIF for x-ray driven ignition in about 2007, and the key issues being addressed on the current ICF facilities [(Nova, Omega, Z at Sandia National Laboratory (SNL), and NIKE at the Naval Research Laboratory (NRL)] are described.
Date: July 20, 1998
Creator: Bernat, T. P.; Hammel, B. A.; Kauffman, R. L.; Kilkenny, J. D.; Landen, O. L.; Lindl, J. D. et al.
Partner: UNT Libraries Government Documents Department