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Resonantly-enhanced, four-photon ionization of krypton at laser intensities exceeding 10/sup 13/ W/cm/sup 2/

Description: The yield of singly- and multiply- charged ions of krypton and xenon is presented as a function of laser intensity and frequency. The measurements were performed using the second harmonic output of a well-characterized, tunable picosecond dye laser in the range 285 to 310 nm at laser intensities from 1 x 10/sup 12/ to 10/sup 14/ W/cm/sup 2/. Enhancement of the Kr/sup +/ yield by two orders of magnitude by three-photon resonant, four-photon ionization is observed in the vicinity of the 4d'(5/2)/sub 3/ and the 4d(3/2)/sub 1/ intermediate states. A model incorporating line shifts and widths scaling linearly with intensity is in good agreement with the experimental results.
Date: December 1, 1987
Creator: Perry, M.D.; Landen, O.L. & Campbell, E.M.
Partner: UNT Libraries Government Documents Department

LLNL Contribution to LLE FY09 Annual Report: NIC and HED Results

Description: In FY09, LLNL led 238 target shots on the OMEGA Laser System. Approximately half of these LLNL-led shots supported the National Ignition Campaign (NIC). The remainder was dedicated to experiments for the high-energy-density stewardship experiments (HEDSE). Objectives of the LLNL led NIC campaigns at OMEGA included: (1) Laser-plasma interaction studies in physical conditions relevant for the NIF ignition targets; (2) Demonstration of Tr = 100 eV foot symmetry tuning using a reemission sphere; (3) X-ray scattering in support of conductivity measurements of solid density Be plasmas; (4) Experiments to study the physical properties (thermal conductivity) of shocked fusion fuels; (5) High-resolution measurements of velocity nonuniformities created by microscopic perturbations in NIF ablator materials; (6) Development of a novel Compton Radiography diagnostic platform for ICF experiments; and (7) Precision validation of the equation of state for quartz. The LLNL HEDSE campaigns included the following experiments: (1) Quasi-isentropic (ICE) drive used to study material properties such as strength, equation of state, phase, and phase-transition kinetics under high pressure; (2) Development of a high-energy backlighter for radiography in support of material strength experiments using Omega EP and the joint OMEGA-OMEGA-EP configuration; (3) Debris characterization from long-duration, point-apertured, point-projection x-ray backlighters for NIF radiation transport experiments; (4) Demonstration of ultrafast temperature and density measurements with x-ray Thomson scattering from short-pulse laser-heated matter; (5) The development of an experimental platform to study nonlocal thermodynamic equilibrium (NLTE) physics using direct-drive implosions; (6) Opacity studies of high-temperature plasmas under LTE conditions; and (7) Characterization of copper (Cu) foams for HEDSE experiments.
Date: October 1, 2009
Creator: Heeter, R F; Landen, O L; Hsing, W W & Fournier, K B
Partner: UNT Libraries Government Documents Department

Generalized x-ray scattering cross section from non-equilibrium solids and plasmas

Description: We propose a modified x-ray form factor that describes the scattering cross section in warm dense matter valid for both the plasma and the solid (crystalline) state. Our model accounts for the effect of lattice correlations on the electron-electron dynamic structure, as well as provides a smooth transition between the solid and the plasma scattering cross sections. In addition, we generalize the expression of the dynamic structure in the case of a two-temperature system (with different electron and ion temperatures). This work provides a unified description of the x-ray scattering processes in warm and dense matter, as the one encountered in inertial confinement fusion, laboratory astrophysics, material science, and high-energy density physics and it can be used to verify temperature relaxation mechanisms in such environments.
Date: February 7, 2006
Creator: Gregori, G; Glenzer, S H & Landen, O L
Partner: UNT Libraries Government Documents Department

Numerical Modeling of Hohlraum Radiation Conditions: Spatial and Spectral Variations due to Sample Position, Beam Pointing, and Hohlraum Geometry

Description: View-factor simulations are presented of the spatially varying radiation conditions inside double-ended gold hohlraums and single-ended gold hohlraums (''halfraums'') used in inertial confinement fusion (ICF) and high energy density (HED) physics experiments [J. Lindl, Phys. Plasmas 11, 339 (2004); M. D. Rosen, Phys. Plasmas 3, 1803 (1996)]. It is shown that in many circumstances, the common assumption that the hohlraum ''drive'' can be characterized by a single temperature is too simplistic. Specifically, the radiation conditions seen by an experimental package can differ significantly from the wall reemission measured through diagnostic holes or laser entrance holes (LEHs) by absolutely calibrated detectors. Furthermore, even in situations where the radiation temperature is roughly the same for diagnostics and experimental packages, or for packages at different locations, the spectral energy distributions can vary significantly, due to the differing fractions of reemitting wall, laser hot spots, and LEHs seen from different locations. We find that the spatial variation of temperature, and especially the differences between what diagnostics looking in the LEH measure vs. the radiation temperature on wall-mounted experimental packages, is generally greater for double-ended hohlraums than it is for halfraums. View-factor simulations can also be used to explore experimental variables (halfraum length and geometry, sample position, and beam pointing) that can be adjusted in order to, for example, maximize the radiation flux onto a sample, or other package. In this vein, simulations of hohlraums and halfraums with LEH shields are also presented.
Date: January 25, 2005
Creator: Cohen, D H; Landen, O L & MacFarlane, J J
Partner: UNT Libraries Government Documents Department

Three-dimensional simulations of Nova capsule implosion experiments

Description: Capsule implosion experiments carried out on the Nova laser are simulated with the three-dimensional HYDRA radiation hydrodynamics code. Simulations of ordered near single mode perturbations indicate that structures which evolve into round spikes can penetrate farthest into the hot spot. Bubble-shaped perturbations can burn through the capsule shell fastest, however, causing even more damage. Simulations of a capsule with multimode perturbations shows spike amplitudes evolving in good agreement with a saturation model during the deceleration phase. The presence of sizable low mode asymmetry, caused either by drive asymmetry or perturbations in the capsule shell, can dramatically affect the manner in which spikes approach the center of the hot spot. Three-dimensional coupling between the low mode shell perturbations intrinsic to Nova capsules and the drive asymmetry brings the simulated yields into closer agreement with the experimental values.
Date: November 1, 1995
Creator: Marinak, M.M.; Tipton, R.E. & Landen, O.L.
Partner: UNT Libraries Government Documents Department

High-energy x-ray microscopy of laser-fusion plasmas at the National Ignition Facility

Description: Multi-keV x-ray microscopy will be an important laser-produced plasma diagnostic at future megajoule facilities such as the National Ignition Facility (NIF).In preparation for the construction of this facility, we have investigated several instrumentation options in detail, and we conclude that near normal incidence single spherical or toroidal crystals may offer the best general solution for high-energy x-raymicroscopy at NIF and at similar large facilities. Kirkpatrick-Baez microscopes using multi-layer mirrors may also be good secondary options, particularly if apertures are used to increase the band-width limited field of view.
Date: August 26, 1997
Creator: Koch, J.A.; Landen, O.L. & Hammel, B.A.
Partner: UNT Libraries Government Documents Department

Time-resolved probing of electron thermal transport in plasma produced by femtosecond laser pulses. Revision 1

Description: We present the first direct observation of a supersonic ionization front supported by electron thermal transport in a hot solid density plasma produced by 100fsec-laser-pulse irradiation of a transparent fused quartz target.
Date: April 20, 1994
Creator: Vu, B. T. V.; Szoke, A.; Landen, O. L. & Lee, R. W.
Partner: UNT Libraries Government Documents Department

Time-resolved probing of electron thermal conduction in femtosecond-laser-pulse-produced plasmas

Description: We present time-resolved measurements of reflectivity, transmissivity and frequency shifts of probe light interacting with the rear of a disk-like plasma produced by irradiation of a transparent solid target with 0.1ps FWHM laser pulses at peak intensity 5 {times} 10{sup l4}W/CM{sup 2}. Experimental results show a large increase in reflection, revealing rapid formation of a steep gradient and overdense surface plasma layer during the first picosecond after irradiation. Frequency shifts due to a moving ionization created by thermal conduction into the solid target are recorded. Calculations using a nonlinear thermal heat wave model show good agreement with the measured frequency shifts, further confining the strong thermal transport effect.
Date: June 1, 1993
Creator: Vue, B. T. V.; Szoke, A. & Landen, O. L.
Partner: UNT Libraries Government Documents Department

Hard X-ray Imaging for Measuring Laser Absorption Spatial Profiles on the National Ignition Facility

Description: Hard x-ray (''Thin wall'') imaging will be employed on the National Ignition Facility (NIF) to spatially locate laser beam energy deposition regions on the hohlraum walls in indirect drive Inertial Confinement Fusion (ICF) experiments, relevant for ICF symmetry tuning. Based on time resolved imaging of the hard x-ray emission of the laser spots, this method will be used to infer hohlraum wall motion due to x-ray and laser ablation and any beam refraction caused by plasma density gradients. In optimizing this measurement, issues that have to be addressed are hard x-ray visibility during the entire ignition laser pulse with intensities ranging from 10{sup 13} to 10{sup 15} W/cm{sup 2}, as well as simultaneous visibility of the inner and the outer laser drive cones. In this work we will compare the hard x-ray emission calculated by LASNEX and analytical modeling with thin wall imaging data recorded previously on Omega and during the first hohlraum experiments on NIF. Based on these calculations and comparisons the thin wall imaging will be optimized for ICF/NIF experiments.
Date: April 25, 2006
Creator: Dewald, E L; Jones, O S; Landen, O L; Suter, L; Amendt, P; Turner, R E et al.
Partner: UNT Libraries Government Documents Department

Imploded Capsule Fuel Temperature and Density Measurement by Energy-Dependent Neutron Imaging

Description: Neutron imaging systems measure the spatial distribution of neutron emission from burning inertial confinement fusion (ICF) targets. These systems use a traditional pinhole geometry to project an image of the source onto a two-dimensional scintillator array, and a CCD records the resulting scintillation image. The recent history of ICF neutron images has produced images with qualities that have improved as the fusion neutron yields have increased to nearly 10{sup 14} neutrons. Anticipated future neutron yields in excess of 10{sup 16} at the National Ignition Facility and LMJ have raised the prospect of neuron imaging diagnostics which simultaneously probe several different characteristics of burning fusion targets. The new measurements rely on gated-image recording to select images corresponding to specific bands of neutron energies. Gated images of downscattered neutrons with energies from 5 to 8 MeV can emphasize regions of the target which contain DT fuel which is not burning. At the same time, gated images which select different portions of the 14-MeV spectral peak can produce spatial temperature maps of a burning target. Since the neutron production depends on the DT fuel density and temperature, simultaneous images of temperature and neutron emission can be combined to infer the an image of the source density using an Abel inversion method that is analogous to the method that has been used in x-ray imaging. Thus, with higher-yield sources, neutron imaging offers the potential to record simultaneously several critical features that characterize the performance of an ICF target: the neutron emission distribution, the temperature and density distributions, and the distribution of nonburning fuel within the target.
Date: September 28, 2005
Creator: Moran, M J; Koch, J; Landen, O L; Haan, S W; Barrera, C A & Morse, E C
Partner: UNT Libraries Government Documents Department

High order reflectivity of graphite (HOPG) crystals for x ray energies up to 22 keV

Description: We used Kr K{alpha} (12.6 keV) and Ag K{alpha} (22.1 keV) x-rays, produced by petawatt class laser pulses interacting with a Kr gas jet and a silver foil, to measure the integrated crystal reflectivity of flat Highly Oriented Pyrolytic Graphite (HOPG) up to fifth order. The reflectivity in fourth order is lower by a factor of 50 when compared to first order diffraction. In second order the integrated reflectivity decreases from 1.3 mrad at 12.6 keV to 0.5 mrad at 22.1 keV. The current study indicates that HOPG crystals are suitable for measuring scattering signals from high energy x ray sources (E {ge} 20 keV). These energies are required to penetrate through the high density plasma conditions encountered in inertial confinement fusion capsule implosions on the National Ignition Facility.
Date: April 30, 2008
Creator: Doeppner, T; Neumayer, P; Girard, F; Kugland, N L; Landen, O L; Niemann, C et al.
Partner: UNT Libraries Government Documents Department

In-Flight Measurements of Capsule Adiabats in Laser Driven Spherical Implosions

Description: We present the first x-ray Thomson scattering measurements of temperature and density from spherically imploding matter. The shape of the Compton downscattered spectrum provides a first-principles measurement of the electron velocity distribution function, dependent on T{sub e} and the Fermi temperature T{sub F} {approx} n{sub e}{sup 2/3}. In flight compressions of Be and CH targets reach 6-13 times solid density, with T{sub e}/T{sub F} {approx} 0.4-0.7, resulting in minimum adiabats of {approx}1.6-2. These measurements are consistent with low-entropy implosions and predictions by simulations using radiation-hydrodynamic modeling.
Date: March 7, 2011
Creator: Kritcher, A L; Doppner, T; Fortman, C; Ma, T; Landen, O L; Wallace, R et al.
Partner: UNT Libraries Government Documents Department

X-ray Induced Pinhole Closure in Point Projection X-ray Radiography

Description: In pinhole-assisted point-projection x-ray radiography (or ''backlighting''), pinholes are placed between the sample of interest and an x-ray source (or ''backlighter'') to effectively limit the source size and hence improve the spatial resolution of the system. Pinholes are generally placed close to such x-ray backlighters to increase the field-of-view, leading to possible vaporization and pinhole closure due to x-ray driven ablation, thereby potentially limiting the usefulness of this method. An experimental study and modeling of time-dependent closure and resolution is presented. The pinhole closure timescale is studied for various pinhole sizes, pinhole to backlighter separations and filtering conditions. In addition the time-dependent resolution is extracted from one-dimensional wire imaging prior to pinhole closure. Cylindrical hydrodynamic modeling of the pinhole closure shows reasonable agreement with data, giving us a predictive capability for pinhole closure in future experiments.
Date: January 13, 2006
Creator: Bullock, A B; Landen, O L; Blue, B E; Edwards, J & Bradley, D K
Partner: UNT Libraries Government Documents Department

Solid-Density Plasma characterization with X-ray scattering on the 200-J Janus Laser

Description: We present collective x-ray scattering (CXS) measurements using a Chlorine He-{alpha} x-ray source pumped with less than 200 J of laser energy. The experimental scattering spectra show plasmon resonances from shocked samples. These experiments use only 10{sup 12} x-ray photons at the sample of which 10{sup -5} have been scattered and detected with a highly efficient curved crystal spectrometer. Our results demonstrate that x-ray scattering is a viable technique on smaller laser facilities making CXS measurements accessible to a broad scientific community.
Date: April 25, 2006
Creator: Neumayer, P B; Gregori, G; Ravasio, A; Price, D; Bastea, M; Landen, O L et al.
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

X-ray framing cameras for > 5 keV imaging

Description: Recent and proposed improvements in spatial resolution, temporal resolution, contrast, and detection efficiency for x-ray framing cameras are discussed in light of present and future laser-plasma diagnostic needs. In particular, improvements in image contrast above hard x-ray background levels is demonstrated by using high aspect ratio tapered pinholes.
Date: July 20, 1995
Creator: Landen, O.L.; Bell, P.M.; Costa, R.; Kalantar, D.H. & Bradley, D.K.
Partner: UNT Libraries Government Documents Department

Detailed measurements and shaping of gate profiles for microchannel-plate-based X-ray framing cameras

Description: Gated, microchannel-plate-based (MCP) framing cameras are increasingly used worldwide for x-ray imaging of subnanosecond laser-plasma phenomena. Large dynamic range (> 1,000) measurements of gain profiles for gated microchannel plates (MCP) are presented. Temporal profiles are reconstructed for any point on the microstrip transmission line from data acquired over many shots with variable delay. No evidence for significant pulse distortion by voltage reflections at the ends of the microstrip is observed. The measured profiles compare well to predictions by a time-dependent discrete dynode model down to the 1% level. The calculations do overestimate the contrast further into the temporal wings. The role of electron transit time dispersion in limiting the minimum achievable gate duration is then investigated by using variable duration flattop gating pulses. A minimum gate duration of 50 ps is achieved with flattop gating, consistent with a fractional transit time spread of {approx} 15%.
Date: October 3, 1994
Creator: Landen, O.L.; Hammel, B.A.; Bell, P.M.; Abare, A. & Bradley, D.K.
Partner: UNT Libraries Government Documents Department

10 (micro)m and 5 (micro)m Pinhole-Assisted Point-Projection Backlit Imaging for NIF

Description: Pinhole-assisted point-projection backlighting with 10{micro}m and 5 {micro}m pinholes placed a small distance of order 1 mm away from the backlighter produces images with large field of view and high resolution. Pinholes placed closely to high-power backlighter sources can vaporize and close due to x-ray driven ablation, thereby limiting the usefulness of this method. A study of streaked 1-D backlit imaging of 25 {micro}m W wires using the OMEGA laser is presented. The pinhole closure timescale for 10 {micro}m pinholes placed 0.45 mm and 1 mm distant from the backlighter is 1.3 ns and 2.2 ns, respectively. Similar timescales for 5 {micro}m pinholes is also presented. Successful wire imaging prior to pinhole closure is clearly demonstrated.
Date: June 5, 2001
Creator: Bullock, A.B.; Landen, O.L. & Bradley, D.K.
Partner: UNT Libraries Government Documents Department

Neutron detectors for fusion reaction-rate measurements

Description: Fusion reactions in an inertial-confinement fusion (ICF) target filled with deuterium or a deuterium/tritium fuel release nearly monoenergetic neutrons. Because most the neutrons leave the compressed target without collision, they preserve reaction-rate information as they travel radially outward from their point of origin. Three fast, neutron detector techniques, each capable of measuring the fusion reaction-rate of ICF targets, have been demonstrated. The most advanced detector is based on the fast rise-time of a commercial plastic scintillator material (BC-422) which acts as a neutron-to-light converter. Signals, which are recorded with a fast optical streak camera, have a resolution of 25 ps. Good signals can be recorded for targets producing only 5 x 10{sup 7} DT neutrons. Two other detectors use knock-on collisions between neutrons and protons in a thin polyethylene (CH{sub 2}) converter. In one, the converter is placed in front of the photocathode of an x-ray streak camera. Recoil protons pass through the photocathode and knock out electrons which are accelerated and deflected to produce a signal. Resolutions < 25 ps are possible. In the other, the converter is placed in front of a microchannel plate (MCP) with a gated microstrip. Recoil protons eject electrons from the gold layer forming the microstrip. If a gate pulse is present, the signal is amplified. Present gate times are about 80 ps.
Date: February 10, 1994
Creator: Lerche, R. A.; Phillion, D. W.; Landen, O. L.; Murphy, T. J. & Jaanimagi, P. A.
Partner: UNT Libraries Government Documents Department

Time-Space Position of Warm Dense Matter in Laser Plasma Interaction Process

Description: Laser plasma interaction experiments have been perform performed using an fs Titanium Sapphire laser. Plasmas have been generated from planar PMMA targets using single laser pulses with 3.3 mJ pulse energy, 50 fs pulse duration at 800 nm wavelength. Electron density distributions of the plasmas in different delay times have been characterized by means of Nomarski Interferometry. Experimental data were cautiously compared with relevant 1D numerical simulation. Finally these results provide a first experience of searching for the time-space position of the so-called warm dense plasma in an ultra fast laser target interaction process. These experiments aim to prepare near solid-density plasmas for Thomson scattering experiments using the short wavelength free-electron laser FLASH, DESY Hamburg.
Date: September 25, 2006
Creator: Cao, L F; Uschmann, I; Forster, E; Zamponi, F; Kampfer, T; Fuhrmann, A et al.
Partner: UNT Libraries Government Documents Department

Development of Compton Radiography Diagnostics for Inertial Confinement Fusion Implosions

Description: An important diagnostic tool for inertial confinement fusion will be time-resolved radiographic imaging of the dense cold fuel surrounding the hot spot. The measurement technique is based on point-projection radiography at photon energies from 60-200 keV where the Compton effect is the dominant contributor to the opacity of the fuel or pusher. We have successfully applied this novel Compton Radiography technique to the study of the final compression of directly driven plastic capsules at the OMEGA facility. The radiographs have a spatial and temporal resolution of {approx}10 {micro}m and {approx}10ps, respectively. A statistical accuracy of {approx}0.5% in transmission per resolution element is achieved, allowing localized measurements of areal mass densities to 7% accuracy. The experimental results show 3D non-uniformities and lower than 1D expected areal densities attributed to drive asymmetries and hydroinstabilities.
Date: November 16, 2010
Creator: Tommasini, R; Hatchett, S P; Hey, D S; Izumi, N; Koch, J A; Landen, O L et al.
Partner: UNT Libraries Government Documents Department