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The development and characterization of neutron-damaged GaAs x-ray detectors

Description: Photoconductive x-ray detectors are becoming an important x-ray diagnostic as a result of their small size, fast response time, and high sensitivity. We are developing a discrete array of neutron- damaged GaAs detectors to be used in an imaging x-ray spectrometer, and we describe herein the techniques we use to fabricate and characterize them for an upcoming experiment. Using a 225-ps x-ray pulse from a laser-produced plasma, we measured the sensitivity and time response of the detectors to be 7.1 mA/W and on the order of 150 ps FWHM, respectively. The carrier mobility is 741 cm/sup 2//V/center dot/s at a bias of 2 /times/ 10/sup 4/V/cm. 6 figs.
Date: September 9, 1988
Creator: Springer, P.T.
Partner: UNT Libraries Government Documents Department

2D radiation-magnetohydrodynamic simulations of SATURN imploding Z-pinches

Description: Z-pinch implosions driven by the SATURN device at Sandia National Laboratory are modeled with a 2D radiation magnetohydrodynamic (MHD) code, showing strong growth of magneto-Rayleigh Taylor (MRT) instability. Modeling of the linear and nonlinear development of MRT modes predicts growth of bubble-spike structures that increase the time span of stagnation and the resulting x-ray pulse width. Radiation is important in the pinch dynamics keeping the sheath relatively cool during the run-in and releasing most of the stagnation energy. The calculations give x-ray pulse widths and magnitudes in reasonable agreement with experiments, but predict a radiating region that is too dense and radially localized at stagnation. We also consider peaked initial density profiles with constant imploding sheath velocity that should reduce MRT instability and improve performance. 2D krypton simulations show an output x-ray power > 80 TW for the peaked profile.
Date: November 6, 1995
Creator: Hammer, J.H.; Eddleman, J.L. & Springer, P.T.
Partner: UNT Libraries Government Documents Department

Structural determination of larger proteins using stable isotope labeling and NMR spectroscopy

Description: The project sought to employ stable isotope labeling and NMR spectroscopy to study protein structures and provide insight into important biochemical problems. A methylotrophic bacterial expression system has been developed for uniform deuterium and carbon-13 labeling of proteins for structural studies. These organisms grow using methanol as the sole source of carbon and energy. Because isotopically labeled methanol is relatively inexpensive, the methylotrophs are ideal for expressing proteins labeled uniformly with deuterium and/or carbon-13. This expression system has been employed to prepare deuterated troponin C. NMR spectroscopy measurements have been made on the inhibitory peptide from troponin I (residues 96--115), both as the free peptide and the peptide complexed with deuterated troponin C. Proton-NMR spectroscopy resonance-signal assignments have been made for the free peptide.
Date: April 1, 1996
Creator: Unkefer, C.; Hernandez, G.; Springer, P.; Trewhella, J.; Blumenthal, D. & Lidstrom, M.
Partner: UNT Libraries Government Documents Department

Relationship of cytochrome caa sub 3 from Thermus thermophilus to other heme- and copper-containing terminal oxidases

Description: Cytochrome oxidases are a key component of the energy metabolism of most aerobic organisms from mammals to bacteria. They are the final enzyme of the membrane associated respiratory chain responsible for converting the chemical energy of reduced substrates to a transmembrane electrochemical potential, which issused by the cell for a wide variety of energy-requiring processes. The most widely studied oxidase is the cytochrome c oxidase of the mammalian mitochondrion. This complex, integral membrane protein contains 13 subunits and four canonical metal centers: heme center a and a{sub 3}; copper centers CU{sub A} and CU{sub B}. It is responsible for electron transfer from reduced chytochrome c to dioxygen with the concomitant reduction of dioxygen to water and the coupled vectorial transfer of protons across the mitochondrial membrane. In this communication we will describe preliminary results of DNA sequencing experiments with the cytochrome caa{sub 3} oxidase, initially undertaken to determine the nature of the subunits of this oxidase and shed light on the distribution of the metal centers. We will speculate on oxidase gene and protein structures and evolutionary relationships in the light of these results and recent sequencing results from other groups. 47 refs., 4 figs., 1 tab.
Date: January 1, 1990
Creator: Mather, M.W.; Springer, P. & Fee, J.A.
Partner: UNT Libraries Government Documents Department

Sub-picosecond streak camera measurements at LLNL: From IR to x-rays

Description: An ultra fast, sub-picosecond resolution streak camera has been recently developed at the LLNL. The camera is a versatile instrument with a wide operating wavelength range. The temporal resolution of up to 300 fs can be achieved, with routine operation at 500 fs. The streak camera has been operated in a wide wavelength range from IR to x-rays up to 2 keV. In this paper we briefly review the main design features that result in the unique properties of the streak camera and present its several scientific applications: (1) Streak camera characterization using a Michelson interferometer in visible range, (2) temporally resolved study of a transient x-ray laser at 14.7 nm, which enabled us to vary the x-ray laser pulse duration from {approx}2-6 ps by changing the pump laser parameters, and (3) an example of a time-resolved spectroscopy experiment with the streak camera.
Date: December 21, 2003
Creator: Kuba, J; Shepherd, R; Booth, R; Steward, R; Lee, E W; Cross, R R et al.
Partner: UNT Libraries Government Documents Department

Optical Properties in Non-equilibrium Phase Transitions

Description: An open question about the dynamical behavior of materials is how phase transition occurs in highly non-equilibrium systems. One important class of study is the excitation of a solid by an ultrafast, intense laser. The preferential heating of electrons by the laser field gives rise to initial states dominated by hot electrons in a cold lattice. Using a femtosecond laser pump-probe approach, we have followed the temporal evolution of the optical properties of such a system. The results show interesting correlation to non-thermal melting and lattice disordering processes. They also reveal a liquid-plasma transition when the lattice energy density reaches a critical value.
Date: January 5, 2006
Creator: Ao, T; Ping, Y; Widmann, K; Price, D F; Lee, E; Tam, H et al.
Partner: UNT Libraries Government Documents Department

Filtered fluorescer x-ray detector

Description: Recently, an instrument capable of measuring x-rays between 8 and 90 keV was conceived to help understand conditions pertaining to pulsed power research. This resulted in the development of a versatile device that would incrementally detect x-rays emitted at predetermined energy bands over this range. To accomplish this, an array of well characterized filter-fluorescer combinations were produced which would allow fluoresced x-rays to be observed by time resolved electro-optical devices. As many as sixteen channels could be utilized with each channel having a corresponding background channel. Upon completion of the device, a three week series of experiments was then successfully carried out.
Date: April 1, 1995
Creator: Bruns, H.C.; Emig, J.A.; Thoe, R.S.; Springer, P.T. & Hernandez, J.A.
Partner: UNT Libraries Government Documents Department

Laboratory astrophysics

Description: We propose an experiment to test opacity models for stellar atmospheres. Particularly important is to perform experiments at very low density and temperature where line shape treatments give large differences in Rosseland mean opacities for astrophysical mixtures, and to test the range of validity for the unresolved transition array treatments. Experimental requirements are ultra high spectral resolution combined with large homogenous plasma sources lasting tens of nanoseconds, and with Planckian radiation fields. These requirements dovetail nicely with emerging pulsed power capabilities. We propose a high resolution measurement of the frequency dependent opacity, for ultra low density iron plasmas in radiatively driven equilibrium plasmas.
Date: May 1, 1995
Creator: Springer, P.T.; Goldstein, W.H.; Iglesias, C.A.; Wilson, B.G.; Rogers, F.J. & Stewart, R.E.
Partner: UNT Libraries Government Documents Department

Development of backlighting sources for a Compton radiography diagnostic of Inertial Confinement Fusion targets

Description: We present scaled demonstrations of backlighter sources, emitting Bremsstrahlung x-rays with photon energies above 75 keV, that we will use to record x-ray Compton radiographic snapshots of cold dense DT fuel in inertial confinement fusion implosions at the National Ignition Facility (NIF). In experiments performed at the Titan laser facility at Lawrence Livermore National Laboratory, we measured the source size and the Bremsstrahlung spectrum as a function of laser intensity and pulse length, from solid targets irradiated at 2e17-5e18 W/cm{sup 2} using 2-40 ps pulses. Using Au planar foils we achieved source sizes down to 5.5 {micro}m, and conversion efficiencies of about 1e-3 J/J into x-ray photons with energies in the 75-100 keV spectral range. We can now use these results to design NIF backlighter targets and shielding, and to predict Compton radiography performance as a function of the NIF implosion yield and associated background.
Date: May 7, 2008
Creator: Tommasini, R; MacPhee, A; Hey, D; Ma, T; Chen, C; Izumi, N et al.
Partner: UNT Libraries Government Documents Department

3D Simulations of the NIF Indirect Drive Ignition Target Design

Description: The radiation hydrodynamics code Hydra is used to quantify the sensitivity of different NIF ignition point designs to several 3D effects. Each of the 48 NIF quads is included in the calculations and is allowed to have different power. With this model they studied the effect on imploded core symmetry of discrete laser spots (as opposed to idealized azimuthally-averaged rings) and random variations in laser power.
Date: January 5, 2010
Creator: Jones, O S; Milovich, J L; Callahan, D A; Edwards, M J; Landen, O L; Salmonson, J D et al.
Partner: UNT Libraries Government Documents Department

One- and two-dimensional density and temperature measurements of an argon-neon Z-pinch plasma at stagnation

Description: In order to benchmark and improve current 2D radiation magnetohydrodynamic (MHD) models of Z-pinch plasmas, we have performed experiments which characterize the plasma -conditions at stagnation. In the experiments the SATURN pulsed power facility at Sandia National Laboratory was used to create an imploding -Ar-Ne plasma. An absolutely calibrated, high resolution space- and time- resolving Johann crystal spectrometer was used to infer the electron temperature Te from the slope of the hydrogenlike Ne free-bound continuum, and the ion density ni from the Stark broadening of the Ar heliunlike Rydberg series. 2D electron temperature profiles of the plasma are obtained from a set of imaging crystals also focused on the Ne free-bound continuum. We shot two types of gas nozzles in the experiment, annular and uniform fill which varies the amount of mass in the plasma. 2D local thermodynamic equilibrium (LTE) and non-LTE MM models predict a radiating region denser and cooler than measured.
Date: October 1, 1996
Creator: Wong, K.L.; Springer, P.T.; Hammer, J.H.; Iglesias, C.A.; Osterheld, A.L.; Foord, M.E. et al.
Partner: UNT Libraries Government Documents Department

Using Short Pulse Lasers to Address Frontiers in High Pressure Physics

Description: Having laser intensities of 10{sup 21} W/cm{sup 2} yield electrical field strengths of 10{sup 12} V/cm which is comparable to the field strength at the K-shell of neon. Instant field ionization becomes part of the laser-matter interaction allowing to transfer most of the photons momenta directly onto the ions by driving an electrostatic shock through the target equivalent to pressures of several 100 Gbar. Utilization of these high-pressure conditions in form of equation of state measurements, however, strongly depends on the contrast of the femtosecond laser pulse. Currently, the Livermore USP and JanUSP lasers reach contrast values up to 10{sup 8}. This is sufficient to explore near-isochorically heated materials at moderate intensities (10{sup 13}-10{sup 15} W/cm{sup 2}) attaining pressures around 100 Mbar.
Date: August 10, 1999
Creator: Wildmann, K.; Springer, P.T.; Cauble, R.; Foord, M.E.; Guethlein, G.; Ng, A. et al.
Partner: UNT Libraries Government Documents Department

X-Ray Photoionized Plasmas in the Laboratory

Description: The advanced spectroscopic capabilities of the new X-ray telescopes Chandra and XMM lead to a need for improved benchmarking of models for the photoionized accretion-disk plasmas which represent over half of known astrophysical X-ray sources. They report the first laboratory experimental results using 120 TW, 180 eV Z-pinch plasmas to drive iron samples into the photoionized equilibrium. The pinch spectrum, temperature, power and uniformity have been characterized in order to qualify it as a photoionization driver. Preliminary time-integrated (8 {angstrom} to 18 {angstrom}) and time-resolved (12.5 {angstrom} to 16 {angstrom}) absorption and emission spectra of photoionized L-shell Fe and K-shell Na and F were observed using X-ray crystal spectrometers. Plans for upcoming experiments are also discussed.
Date: April 22, 2000
Creator: Heeter, R.F.; Foord, M.E.; Thoe, R.S.; Emig, J.A.; Springer, P.T.; Bailey, J. et al.
Partner: UNT Libraries Government Documents Department

X-Ray-Spectroscopy of Astrophysically-Relevant Photoionized Iron Plasmas at Z

Description: In order to provide benchmark data for models used to interpret X-ray astronomy data from newly-launched orbital telescopes such as Chandra, they have used 120 TW, 180 eV pinch plasmas on the Sandia Z facility to drive iron foils into X-ray photoionized equilibrium. The experiment was designed to achieve photoionization parameters characteristic of accretion-powered objects such as X-ray binaries (neutron stars) and active galactic nuclei (black holes). These objects comprise roughly half of observed X-ray sources, but the interpretation of their spectra is difficult: state-of-the-art models for photoionized iron plasmas do not yet agree on the expected ionization balance. In the initial experiments the foil samples consisted of 200 {angstrom} of iron codeposited with 300 {angstrom} of sodium fluoride and sandwiched between two 1000 {angstrom} layers of Lexan (CH and O). They characterized the pinch spectrum, temperature, power and uniformity and qualified it as a photoionization driver. They obtained time-integrated absorption spectra for the foil from 8 to 18 {angstrom} and identified spectral lines from O VIII, F IX, Na X and XI, and Fe XVII and XVIII, i.e. neon-line and fluorine-like iron. Time-resolved absorption and emission spectra for the foils were also obtained from 12.5 to 16 {angstrom}, and hydrogen-like F and neon-like and fluorine-like Fe were again observed in the 2 ns time window of interest. In subsequent ride along experiments they have developed a density diagnostic and measured the density via foil-expansion imaging at two locations. They conclude by discussing upcoming experiments at Z in which they plan to obtain a full data set of plasma density, temperature, and absorption and emission spectra for multiple photoionization equilibria.
Date: June 12, 2000
Creator: Heeter, R.F.; Bailey, J.E.; Cuneo, M.E.; Emig, J.; Foord, M.E.; Springer, P.T. et al.
Partner: UNT Libraries Government Documents Department

PLEIADES: High Peak Brightness, Subpicosecond Thomson Hard-X-ray source

Description: The Picosecond Laser-Electron Inter-Action for the Dynamic Evaluation of Structures (PLEIADES) facility, is a unique, novel, tunable (10-200 keV), ultrafast (ps-fs), hard x-ray source that greatly extends the parameter range reached by existing 3rd generation sources, both in terms of x-ray energy range, pulse duration, and peak brightness at high energies. First light was observed at 70 keV early in 2003, and the experimental data agrees with 3D codes developed at LLNL. The x-rays are generated by the interaction of a 50 fs Fourier-transform-limited laser pulse produced by the TW-class FALCON CPA laser and a highly focused, relativistic (20-100 MeV), high brightness (1 nC, 0.3-5 ps, 5 mm.mrad, 0.2% energy spread) photo-electron bunch. The resulting x-ray brightness is expected to exceed 10{sup 20} ph/mm{sup 2}/s/mrad{sup 2}/0.1% BW. The beam is well-collimated (10 mrad divergence over the full spectrum, 1 mrad for a single color), and the source is a unique tool for time-resolved dynamic measurements in matter, including high-Z materials.
Date: December 15, 2003
Creator: Kuba, J; Anderson, S G; Barty, C J; Betts, S M; Booth, R; Brown, W J et al.
Partner: UNT Libraries Government Documents Department

Study of X-ray photoionized Fe plasma and comparisons with astrophysical modeling codes

Description: The charge state distributions of Fe, Na and F are determined in a photoionized laboratory plasma using high resolution x-ray spectroscopy. Independent measurements of the density and radiation flux indicate the ionization parameter {zeta} in the plasma reaches values {zeta} = 20-25 erg cm s{sup -1} under near steady-state conditions. A curve-of-growth analysis, which includes the effects of velocity gradients in a one-dimensional expanding plasma, fits the observed line opacities. Absorption lines are tabulated in the wavelength region 8-17 {angstrom}. Initial comparisons with a number of astrophysical x-ray photoionization models show reasonable agreement.
Date: April 29, 2005
Creator: Foord, M E; Heeter, R F; Chung, H; vanHoof, P M; Bailey, J E; Cuneo, M E et al.
Partner: UNT Libraries Government Documents Department

Towards an Integrated Model of the NIC Layered Implosions

Description: A detailed simulation-based model of the June 2011 National Ignition Campaign (NIC) cryogenic DT experiments is presented. The model is based on integrated hohlraum-capsule simulations that utilize the best available models for the hohlraum wall, ablator, and DT equations of state and opacities. The calculated radiation drive was adjusted by changing the input laser power to match the experimentally measured shock speeds, shock merger times, peak implosion velocity, and bangtime. The crossbeam energy transfer model was tuned to match the measured time-dependent symmetry. Mid-mode mix was included by directly modeling the ablator and ice surface perturbations up to mode 60. Simulated experimental values were extracted from the simulation and compared against the experiment. The model adjustments brought much of the simulated data into closer agreement with the experiment, with the notable exception of the measured yields, which were 15-45% of the calculated yields.
Date: October 31, 2011
Creator: Jones, O. S.; Callahan, D. A.; Cerjan, C. J.; Clark, D. S.; Edwards, M. J.; Glenzer, S. H. et al.
Partner: UNT Libraries Government Documents Department

Performance metrics for Inertial Confinement Fusion implosions: aspects of the technical framework for measuring progress in the National Ignition Campaign

Description: The National Ignition Campaign (NIC) uses non-igniting 'THD' capsules to study and optimize the hydrodynamic assembly of the fuel without burn. These capsules are designed to simultaneously reduce DT neutron yield and to maintain hydrodynamic similarity with the DT ignition capsule. We will discuss nominal THD performance and the associated experimental observables. We will show the results of large ensembles of numerical simulations of THD and DT implosions and their simulated diagnostic outputs. These simulations cover a broad range of both nominal and off nominal implosions. We will focus on the development of an experimental implosion performance metric called the experimental ignition threshold factor (ITFX). We will discuss the relationship between ITFX and other integrated performance metrics, including the ignition threshold factor (ITF), the generalized Lawson criterion (GLC), and the hot spot pressure (HSP). We will then consider the experimental results of the recent NIC THD campaign. We will show that we can observe the key quantities for producing a measured ITFX and for inferring the other performance metrics. We will discuss trends in the experimental data, improvement in ITFX, and briefly the upcoming tuning campaign aimed at taking the next steps in performance improvement on the path to ignition on NIF.
Date: December 16, 2011
Creator: Spears, B K; Glenzer, S; Edwards, M J; Brandon, S; Clark, D; Town, R et al.
Partner: UNT Libraries Government Documents Department

Performance and analysis of absorption experiments on x-ray heated low-Z constrained samples

Description: Results of experiments on the absorption of niobium in a hot, dense plasma are presented. These results represent a major step in the development of absorption techniques necessary for the quantitative characterization of hot, dense matter. A general discussion is presented of the requirements for performing quantitative analysis of absorption spectra. Hydrodynamic simulations are used to illustrate the behavior of tamped X-ray-heated matter and to indicate effects that can arise from the two dimensional aspects of the experiment. The absorption spectrum of a low-Z material, in this case aluminum, provides a temperature diagnostic and indicates the advance of the absorption measurement technique to the level of application. The experimental technique is placed in context with a review of other measurements using absorption spectroscopy to probe hot, dense matter.
Date: May 1, 1996
Creator: Lee, R.W.; Cauble, R.; Perry, T.S.; Springer, P.T.; Fields, D.F.; Bach, D.R. et al.
Partner: UNT Libraries Government Documents Department