F. Weber

Lawrence Livermore National Laboratory, Livermore, California, United States

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Publications (48)89.71 Total impact

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    ABSTRACT: Processes during laser plasma experiments typically have time scales that are less than 100 ps. The measurement of these processes requires x-ray detectors with fast temporal resolution. We have measured the temporal responses and linearity of several different x-ray sensitive photoconductive detectors (PCDs). The active elements of the detectors investigated include both diamond (natural and synthetic) and GaAs crystals. The typical time responses of the GaAs PCDs are approximately 60 ps, respectively. Some characterizations using x-ray radiation from a synchrotron radiation source are presented.
    The Review of scientific instruments 11/2008; 79(10):10E304. DOI:10.1063/1.2955614 · 1.58 Impact Factor
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    ABSTRACT: High temperature (“hot”) hohlraums are being developed to heat samples to high temperatures for opacity or other atomic physics studies. Hot hohlraums have been fielded at the National Ignition Facility [D.E. Hinkel, et al., Phys. Plasmas 12 (2005) 056305] and the OMEGA [M.B. Schneider, et al., Phys. Plasmas 13 (2006) 112701] lasers. They reach high radiation temperatures by coupling a maximum amount of laser energy (10 kJ) into small, i.e., 400–800 μm diameter, gold hohlraums in a 1 ns pulse causing the hohlraums to fill with gold plasma. Radiation temperatures of 370 eV have been measured in the laser entrance hole (LEH) region of these targets [D.E. Hinkel, et al., Phys. Rev. Lett. 96 (2006) 195001]. However, the LEH radiation is not the radiation drive of interest as the sample can neither be shielded from the non-thermal components of this radiation nor protected from the gold plasma. To mitigate these problems the source we are developing uses the radiation from the X-ray burnthrough of thin walls of a pair of hot hohlraums to heat a sample. We report on the measured radiation drive of this source and its use to heat a surrogate sample. We characterize the radiative heating of the sample by measuring its thermal expansion.
    High Energy Density Physics 05/2007; DOI:10.1016/j.hedp.2007.02.023 · 1.52 Impact Factor
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    ABSTRACT: A first set of shock timing, laser-plasma interaction, hohlraum energetics and hydrodynamic experiments have been performed using the first 4beams of the National Ignition Facility (NIF), in support of indirect drive Inertial Confinement Fusion (ICF) and High Energy Density Physics (HEDP). In parallel, a robust set of optical and X-ray spectrometers, interferometer, calorimeters and imagers have been activated. The experiments have been undertaken with laser powers and energies of up to 8TW and 17kJ in flattop and shaped 1–9ns pulses focused with various beam smoothing options. The experiments have demonstrated excellent agreement between measured and predicted laser-target coupling in foils and hohlraums, even when extended to a longer pulse regime unattainable at previous laser facilities, validated the predicted effects of beam smoothing on intense laser beam propagation in long scale-length plasmas and begun to test 3Dcodes by extending the study of laser driven hydrodynamic jets to 3Dgeometries.
    The European Physical Journal D 01/2007; 44(2):273-281. DOI:10.1140/epjd/e2006-00111-6 · 1.40 Impact Factor
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    ABSTRACT: An experimental campaign to maximize radiation drive in small-scale hohlraums has been carried out at the National Ignition Facility (NIF) at the Lawerence Livermore National Laboratory (Livermore, CA, USA) and at the OMEGA laser at the Laboratory for Laser Energetics (Rochester, NY, USA). The small-scale hohlraums, laser energy, laser pulse, and diagnostics were similar at both facilities but the geometries were very different. The NIF experiments used on-axis laser beams whereas the OMEGA experiments used 19 beams in three beam cones. In the cases when the lasers coupled well and produced similar radiation drive, images of x-ray burnthrough and laser deposition indicate the pattern of plasma filling is very different.
    Journal de Physique IV (Proceedings) 11/2006; J. Phys. IV France(133):1205. DOI:10.1051/jp4:2006133247 · 0.35 Impact Factor
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    ABSTRACT: Soft x-ray power diagnostics are essential for evaluating high temperature laser plasma experiments. The Dante soft x-ray spectrometer, a core diagnostic for radiation flux and temperature measurements of Hohlraums, installed on the Omega Laser Facility at the Laboratory for Laser Energetics has recently undergone a series of upgrades. Work performed at Brookhaven National Laboratory for the development of the National Ignition Facility (NIF) Dante spectrometer enables the Omega Dante to offer a total of 18 absolutely calibrated channels in the energy range from 50 eV to 20 keV . This feature provides Dante with the capability to measure higher, NIF relevant, radiation temperatures with increased accuracy including a differentiation of higher energy radiation such as the Au M and L bands. Diagnostic monitoring using experimental data from directly driven Au spherical shots is discussed.
    Review of Scientific Instruments 11/2006; DOI:10.1063/1.2336462 · 1.58 Impact Factor
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    ABSTRACT: Deposition of maximum laser energy into a small, high-Z enclosure in a short laser pulse creates a hot environment. Such targets were recently included in an experimental campaign using the first four of the 192 beams of the National Ignition Facility [J. A. Paisner, E. M. Campbell, and W. J. Hogan, Fusion Technology 26, 755 (1994)], under construction at the University of California Lawrence Livermore National Laboratory. These targets demonstrate good laser coupling, reaching a radiation temperature of 340 eV. In addition, the Raman backscatter spectrum contains features consistent with Brillouin backscatter of Raman forward scatter [A. B. Langdon and D. E. Hinkel, Physical Review Letters 89, 015003 (2002)]. Also, NIF Early Light diagnostics indicate that 20% of the direct backscatter from these reduced-scale targets is in the polarization orthogonal to that of the incident light.
    Journal de Physique IV (Proceedings) 06/2006; 133:237-241. DOI:10.1051/jp4:2006133048 · 0.35 Impact Factor
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    ABSTRACT: A first set of shock propagation, laser-plasma interaction, hohlraum energetics and hydrodynamic experiments have been performed using the first 4 beams of the National Ignition Facility (NIF), in support of indirect drive Inertial Confinement Fusion (ICF) and High Energy Density Physics.
    Journal de Physique IV (Proceedings) 06/2006; 133:43-45. DOI:10.1051/jp4:2006133009 · 0.35 Impact Factor
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    ABSTRACT: Radiation drive diagnostics during the NIF early light campaign was supported by an 18 channel soft x-ray spectrometer (Dante). In order to achieve a measurement accuracy of 2% in radiation temperature absolute calibration of the individual channels was necessary and signal distortion through long transmission lines had to be compensated for as well. For fast signals the signal attenuation due to the long (50m) cables amounted to â 20% @ 100MHz, which was corrected by a cable compensation in the frequency domain. The varying effects of cable distortion for a variety of signals between 1ns and 9ns in length were evaluated and corrections were applied. Results of the thus calculated temperatures of the NEL campaign will be presented compared to LASNEX predictions, showing agreement in peak radiation temperature within less than 2%.
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    ABSTRACT: A platform for analysis of material properties under extreme conditions, where a sample is bathed in radiation with a high temperature, is under development. Depositing maximum laser energy into a small, high-Z enclosure produces this hot environment. Such targets were recently included in an experimental campaign using the first four of the 192 beams of the National Ignition Facility [ J. A. Paisner, E. M. Campbell, and W. J. Hogan, Fusion Technol. 26, 755 (1994) ], under construction at the University of California Lawrence Livermore National Laboratory. These targets demonstrate good laser coupling, reaching a radiation temperature of 340 eV. In addition, there is a unique wavelength dependence of the Raman backscattered light that is consistent with Brillouin backscatter of Raman forward scatter [ A. B. Langdon and D. E. Hinkel, Phys. Rev. Lett. 89, 015003 (2002) ]. Finally, novel diagnostic capabilities indicate that 20% of the direct backscatter from these reduced-scale targets is in the polarization orthogonal to that of the incident light.
    Physics of Plasmas 04/2005; 12(5):056305-056305-8. DOI:10.1063/1.1880012 · 2.25 Impact Factor
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    ABSTRACT: High energy (>10 keV) x-ray self-emission imaging and radiography will be essential components of many NIF high energy density physics experiments. In preparation for such experiments, we have evaluated the pros and cons of various static [x-ray film, bare charge-coupled device (CCD), and scintillator + CCD] and time-resolved (streaked and gated) 10-1000 keV detectors.
    Review of Scientific Instruments 10/2004; 75(10):4037-4039. DOI:10.1063/1.1787904 · 1.58 Impact Factor
  • J McDonald · F Weber · RL Griffith · JP Holder · PM Bell
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    ABSTRACT: Due to the planar construction of present x-ray streak tubes significant off-center defocusing is observed in both static and dynamic images taken with one-dimensional resolution slits. Based on the streak tube geometry curved photocathodes with radii of curvature ranging from 3.5 to 18 inches have been fabricated. We report initial off-center focusing performance data on the evaluation of these "improved" photocathodes in an X-ray streak camera and an update on the theoretical simulations to predict the optimum cathode curvature.
    Conference on Fourth-Generation X-Ray Sources and Ultrafast X-Ray; 01/2004
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    ABSTRACT: One key parameter in the design and optimization of ICF indirect drive experiments is the measurement of the absolute radiation drive flux inside the hohlraum. This has been accomplished on both Nova and Omega with the Dante x-ray spectrometer, DMX, and diamond PCDs. With the ability to measure the absolute soft x-ray flux for photon energies up to 3keV we can determine material albedo, laser to x-ray conversion efficiency and the characteristic blackbody temperature. The Dante x-ray spectrometer is the core diagnostic for absolute flux measurement on Omega and a new version capable of measuring photon energies up to 10 keV to cover the predicted fluxes will serve the same function on NIF. Each channel has a characteristic spectral response depending on the transmission of the filters, the reflectivity of the mirrors and the response of the x-ray diodes. Periodic calibrations on these three elements from 60 eV up to 6 keV have been performed for the last two years at the National Synchrotron Light Source at Brookhaven National Lab and compared to previous measurements. This allows us to update the Dante analysis with the latest measured response functions. The Dante measured peak radiation temperatures for various Nova and Omega hohlraum experiments have been compared using the Marshak scaling method and agree well with each other for the expected laser conversion efficiencies of up to 90% for Au hohlraums. This method will be used starting with the early NIF Dante to bridge the experimental data between facilities.
  • F Weber · P Celliers · S Moon · R Snavely · L Da Silva
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    ABSTRACT: This report summarizes the major accomplishments of this three-year Laboratory Directed Research and Development (LDRD) Lab Wide (LW) project entitled, ''An Inner-Shell Photo-Ionized X-Ray Laser at 45 {angstrom}'', tracking code 99-LW-042. The most significant accomplishments of this project include the design of a suitable x-ray laser target, the invention of a measurement technique for the determination of rise times of x-ray pulses on the order of 50 femtoseconds, and a novel setup for generating a traveling wave with an ultrashort optical laser pulse. The pump probe technique for rise time measurement will allow us to detect ultrashort x-ray pulses, whose generation by means of a variety of 4th generation light sources is currently under planning elsewhere.
  • F. Weber · P. Celliers · P. Bell · C. Diamond
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    ABSTRACT: A variety of plasma physics experiments require the recording of continuous time history of x-ray emission. Many laboratories have developed x-ray streak camera technology in order to time resolve x-ray spectra or images produced by laser-driven plasma experiments. These cameras record x rays by converting photons to electrons, which in turn are focused and swept across an electron sensitive area detector as a function of time. X-ray photons impinging on a transmission type photocathode generate photoelectrons which are accelerated to energies between 10 and 20 keV and focused onto a phosphor screen. The light from the phosphor image may be intensified using a microchannel plate, and is usually optically coupled directly onto film or an optical charge coupled device. We have designed and built an x-ray sensitive streak camera readout where we replaced the microchannel plate based intensifier and film package with a modified charge coupled device area detector to directly absorb accelerated photoelectrons emitted from the cathode. This system has been integrated into the streak tube arrangement. We will present a set of system performance data, which have been obtained from both bench top experiments on a dc source and dynamic measurements at the Nova laser facility. X-ray images at various exposure times show better spatial resolution, improved signal to noise ratio, and higher dynamic range. Other advantages include instantaneous data readout, which enables fast postprocessing, and no increase in overall cost for an engineered system.
    Review of Scientific Instruments 01/2001; 72(1):651-651. DOI:10.1063/1.1323481 · 1.58 Impact Factor
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    ABSTRACT: Quantitative measurements of the sensitivity, dynamic range, and image resolution of a Nova secondary ion mass-based x-ray streak camera have been made. Comparisons were made using film versus a 4k×4k optical charge-coupled device for data readout. These tests were performed with and without an optical image intensifier tube, and with a direct electron-sensitive microchannel plate. We present results from these tests and recommendations for the National Ignition Facility core x-ray streak camera. © 2001 American Institute of Physics.
    Review of Scientific Instruments 12/2000; 72(1):751-754. DOI:10.1063/1.1318263 · 1.58 Impact Factor
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    ABSTRACT: Laser plasma interactions in a relativistic parameter regime have been intensively investigated for studying the possibility of fast ignition in inertial confinement fusion (ICF). Using ultra-intense laser systems and particle-in-cell (PIC) simulation codes, relativistic laser light self-focusing, super hot electrons, ions, and neutron production, are studied. The experiments are performed with ultra-intense laser with 50 J energy, 0.5-1 ps pulse at 1053 nm laser wavelength at a laser intensity of 10(19) W/cm(2). Most of the laser shots are studied under preformed plasma conditions with a 100 mu m plasma scale length condition. In the study of laser pulse behavior in the preformed plasmas, a special mode has been observed which penetrated the preformed plasma all the way very close to the original planar target surface. On these shots, super hot electrons have been observed with its energy peak exceeding 1 MeV. The energy transport of the hot electrons has been studied with making use of K alpha emissions from a seeded metal layer in planar targets. The details of ion acceleration followed by beam fusion reaction have been studied with neutron spectrometers. Laser ponderomotive force self-focusing and hot electron generation have been applied to a compressed core to see the effect of heating by injecting 12 beams of 100 ps, 1 TW pulses. (C) 2000 American Institute of Physics. [S1070-664X(00)95605-2].
    Physics of Plasmas 05/2000; 7(5-5):2014-2022. DOI:10.1063/1.874023 · 2.25 Impact Factor
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    ABSTRACT: We have used a soft X-ray laser interferometer to study the collision and subsequent interaction of counter-streaming high-density plasmas. The measured density profiles show the evolution of the colliding plasmas from interpenetration, when the low-density edge of the plasmas first collide, to stagnation at the symmetry plane with density building at the symmetry plane
    IEEE Transactions on Plasma Science 03/1999; 27(1-27):120 - 121. DOI:10.1109/27.763079 · 0.95 Impact Factor
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    Review of Scientific Instruments 01/1999; 70:525. · 1.58 Impact Factor
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    ABSTRACT: We developed a 19.6 nm laser x-ray laser grid-image refractometer (XRL-GIR) to diagnose laser-hole boring into overdense plasmas. The XRL-GIR was optimized to measure two-dimensional electron density perturbation on a scale of a few tens of μm in underdense plasmas. Electron density profiles of laser-produced plasmas were obtained for 1020–1022 cm−3 with the XRL-GIR and for 1019–1020 cm−3 from an ultraviolet interferometer, the profiles of which were compared with those from hydrodynamic simulation. By using this XRL-GIR, we directly observed laser channeling into overdense plasmas accompanied by a bow shock wave showing a Mach cone ascribed to supersonic propagation of the channel front. © 1999 American Institute of Physics.
    Review of Scientific Instruments 12/1998; 70(1):543-548. DOI:10.1063/1.1149380 · 1.58 Impact Factor
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    ABSTRACT: We have used a soft-x-ray laser interferometer to study the collision and subsequent interaction of counterstreaming high-density plasmas. The measured density profiles show the evolution of the colliding plasmas from interpenetration, when the low-density edge of the plasmas first collide, to stagnation at the symmetry plane with density building at the symmetry plane. We compare the measured profiles with density profiles calculated by the radiation hydrodynamic code LASNEX, which predicts plasma stagnation as soon as the plasmas collide, and a particle-in-cell code, which allows for interpenetration, softening the stagnation.
    Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics 05/1997; 55(5). DOI:10.1103/PhysRevE.55.6293 · 2.33 Impact Factor