M. J. Eckart

Lawrence Livermore National Laboratory, Livermore, California, United States

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Publications (56)74.6 Total impact

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    ABSTRACT: The measurement of the absolute neutron yield produced in inertial confinement fusion target experiments conducted on the National Ignition Facility (NIF) is essential in benchmarking progress towards the goal of achieving ignition on this facility. This paper describes three independent diagnostic techniques that have been developed to make accurate and precise DT neutron yield measurements on the NIF.
    11/2013;
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    ABSTRACT: The National Ignition Facility (NIF) utilizes several different pixelated sensor technologies for various measurement systems that include alignment cameras, laser energy sensors, and high-speed framing cameras. These systems remain in the facility where they are exposed to 14MeV neutrons during a NIF shot. The image quality of the sensors degrades as a function of radiation-induced damage. This article reports on a figure-of-merit technique that aids in the tracking of the performance of pixelated sensors when exposed to neutron radiation from NIF. The sensor dark current growth can be displayed over time in a 2D visual representation for tracking radiation induced damage. Predictions of increased noise as a function of neutron fluence for future NIF shots allow simulation of reduced performance for each of the individual camera applications. This predicted longevity allows for proper management of the camera systems.
    Proc SPIE 09/2013;
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    ABSTRACT: Neutron time-of-flight spectra from inertial confinement fusion experiments with tritium-filled targets have been measured at the National Ignition Facility. These spectra represent a significant improvement in energy resolution and statistics over previous measurements, and afford the first definitive observation of a peak resulting from sequential decay through the ground state of ^{5}He at low reaction energies E_{c.m.}≲100 keV. To describe the spectrum, we have developed an R-matrix model that accounts for interferences from fermion symmetry and intermediate states, and show these effects to be non-negligible. We also find the spectrum can be described by sequential decay through ℓ=1 states in ^{5}He, which differs from previous interpretations.
    Physical Review Letters 08/2013; 111(5):052501. · 7.94 Impact Factor
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    ABSTRACT: The National Ignition Facility (NIF) is a 192 laser beam facility that supports the Inertial Confinement Fusion program. During the ignition experimental campaign, the NIF is expected to perform shots with varying fusion yield producing 14 MeV neutrons up to 20 MJ or 7.1 × 10 neutrons per shot and a maximum annual yield of 1,200 MJ. Several infrastructure support systems will be exposed to varying high yield shots over the facility's 30-y life span. In response to this potential exposure, analysis and testing of several facility safety systems have been conducted. A detailed MCNP (Monte Carlo N-Particle Transport Code) model has been developed for the NIF facility, and it includes most of the major structures inside the Target Bay. The model has been used in the simulation of expected neutron and gamma fluences throughout the Target Bay. Radiation susceptible components were identified and tested to fluences greater than 10 (n cm) for 14 MeV neutrons and γ-ray equivalent. The testing includes component irradiation using a Co gamma source and accelerator-based irradiation using 4- and 14- MeV neutron sources. The subsystem implementation in the facility is based on the fluence estimates after shielding and survivability guidelines derived from the dose maps and component tests results. This paper reports on the evaluation and implementation of mitigations for several infrastructure safety support systems, including video, oxygen monitoring, pressure monitors, water sensing systems, and access control interfaces found at the NIF.
    Health physics 06/2013; 104(6):589-96. · 0.92 Impact Factor
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    ABSTRACT: First results from the analysis of neutron image data collected on implosions of cryogenically layered deuterium-tritium capsules during the 2011-2012 National Ignition Campaign are reported. The data span a variety of experimental designs aimed at increasing the stagnation pressure of the central hotspot and areal density of the surrounding fuel assembly. Images of neutrons produced by deuterium–tritium fusion reactions in the hotspot are presented, as well as images of neutrons that scatter in the surrounding dense fuel assembly. The image data are compared with 1D and 2D model predictions, and consistency checked using other diagnostic data. The results indicate that the size of the fusing hotspot is consistent with the model predictions, as well as other imaging data, while the overall size of the fuel assembly, inferred from the scattered neutron images, is systematically smaller than models’ prediction. Preliminary studies indicate these differences are consistent with a significant fraction (20%–25%) of the initial deuterium-tritium fuel mass outside the compact fuel assembly, due either to low mode mass asymmetry or high mode 3D mix effects at the ablator-ice interface.
    Physics of Plasmas 05/2013; 20:056320. · 2.38 Impact Factor
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    ABSTRACT: The neutron spectrum from a cryogenically layered deuterium–tritium (dt) implosion at the National Ignition Facility (NIF) provides essential information about the implosion performance. From the measured primary-neutron spectrum (13–15 MeV), yield (Yn) and hot-spot ion temperature (Ti) are determined. From the scattered neutron yield (10–12 MeV) relative to Yn, the down-scatter ratio, and the fuel areal density (ρR) are determined. These implosion parameters have been diagnosed to an unprecedented accuracy with a suite of neutron-time-of-flight spectrometers and a magnetic recoil spectrometer implemented in various locations around the NIF target chamber. This provides good implosion coverage and excellent measurement complementarity required for reliable measurements of Yn, Ti and ρR, in addition to ρR asymmetries. The data indicate that the implosion performance, characterized by the experimental ignition threshold factor, has improved almost two orders of magnitude since the first shot taken in September 2010. ρR values greater than 1 g cm−2 are readily achieved. Three-dimensional semi-analytical modelling and numerical simulations of the neutron-spectrometry data, as well as other data for the hot spot and main fuel, indicate that a maximum hot-spot pressure of ~150 Gbar has been obtained, which is almost a factor of two from the conditions required for ignition according to simulations. Observed Yn are also 3–10 times lower than predicted. The conjecture is that the observed pressure and Yn deficits are partly explained by substantial low-mode ρR asymmetries, which may cause inefficient conversion of shell kinetic energy to hot-spot thermal energy at stagnation.
    Nuclear Fusion 03/2013; 53(4):043014. · 2.73 Impact Factor
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    ABSTRACT: We present a new diagnostic for the National Ignition Facility (NIF) [1,2]. The Streaked Polar Instrumentation for Diagnosing Energetic Radiation (SPIDER) is an x-ray streak camera for use on almost-igniting targets, up to ~1017 neutrons per shot. It measures the x-ray burn history for ignition campaigns with the following requirements: X-Ray Energy 8-30keV, Temporal Resolution 10ps, Absolute Timing Resolution 30ps, Neutron Yield: 1014 to 1017. The features of the design are a heavily shielded instrument enclosure outside the target chamber, remote location of the neutron and EMP sensitive components, a precise laser pulse comb fiducial timing system and fast streaking electronics. SPIDER has been characterized for sweep linearity, dynamic range, temporal and spatial resolution. Preliminary DT implosion data shows the functionality of the instrument and provides an illustration of the method of burn history extraction.
    Proc SPIE 10/2012; 850505.
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    ABSTRACT: The south pole bang-time diagnostic views National Ignition Facility (NIF) implosions through the lower Hohlraum laser entrance hole to measure the time of peak x-ray emission (peak compression) in indirect-drive implosions. Five chemical-vapor-deposition diamond photoconductive detectors with different filtrations and sensitivities record the time-varying x rays emitted by the target. Wavelength selecting highly oriented pyrolytic graphite crystal mirror monochromators increase the x-ray signal-to-background ratio by filtering for 11-keV emission. Diagnostic timing and the in situ temporal instrument response function are determined from laser impulse shots on the NIF. After signal deconvolution and background removal, the bang time is determined to 45-ps accuracy. The x-ray "yield" (mJ∕sr∕keV at 11 keV) is determined from the time integral of the corrected peak signal.
    The Review of scientific instruments 10/2012; 83(10):10E119. · 1.52 Impact Factor
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    ABSTRACT: The first several campaigns of laser fusion experiments at the National Ignition Facility (NIF) included a family of high-sensitivity scintillator∕photodetector neutron-time-of-flight (nTOF) detectors for measuring deuterium-deuterium (DD) and DT neutron yields. The detectors provided consistent neutron yield (Y(n)) measurements from below 10(9) (DD) to nearly 10(15) (DT). The detectors initially demonstrated detector-to-detector Y(n) precisions better than 5%, but lacked in situ absolute calibrations. Recent experiments at NIF now have provided in situ DT yield calibration data that establish the absolute sensitivity of the 4.5 m differential tissue harmonic imaging (DTHI) detector with an accuracy of ±10% and precision of ±1%. The 4.5 m nTOF calibration measurements also have helped to establish improved detector impulse response functions and data analysis methods, which have contributed to improving the accuracy of the Y(n) measurements. These advances have also helped to extend the usefulness of nTOF measurements of ion temperature and downscattered neutron ratio (neutron yield 10-12 MeV divided by yield 13-15 MeV) with other nTOF detectors.
    The Review of scientific instruments 10/2012; 83(10):10D312. · 1.52 Impact Factor
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    ABSTRACT: DT neutron yield (Y(n)), ion temperature (T(i)), and down-scatter ratio (dsr) determined from measured neutron spectra are essential metrics for diagnosing the performance of inertial confinement fusion (ICF) implosions at the National Ignition Facility (NIF). A suite of neutron-time-of-flight (nTOF) spectrometers and a magnetic recoil spectrometer (MRS) have been implemented in different locations around the NIF target chamber, providing good implosion coverage and the complementarity required for reliable measurements of Y(n), T(i), and dsr. From the measured dsr value, an areal density (ρR) is determined through the relationship ρR(tot) (g∕cm(2)) = (20.4 ± 0.6) × dsr(10-12 MeV). The proportionality constant is determined considering implosion geometry, neutron attenuation, and energy range used for the dsr measurement. To ensure high accuracy in the measurements, a series of commissioning experiments using exploding pushers have been used for in situ calibration of the as-built spectrometers, which are now performing to the required accuracy. Recent data obtained with the MRS and nTOFs indicate that the implosion performance of cryogenically layered DT implosions, characterized by the experimental ignition threshold factor (ITFx), which is a function of dsr (or fuel ρR) and Y(n), has improved almost two orders of magnitude since the first shot in September, 2010.
    The Review of scientific instruments 10/2012; 83(10):10D308. · 1.52 Impact Factor
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    ABSTRACT: The first several campaigns of laser fusion experiments at the National Ignition Facility (NIF) included a family of high-sensitivity scintillator/photodetector neutron-time-of-flight (nTOF) detectors for measuring DD and DT neutron yields. The detectors provided consistent neutron yield benchmarks from below 1E9 (DD) to nearly 1E15 (DT). The detectors demonstrated DT yield measurement precisions better than 5%, but the absolute accuracy relies on cross calibration with independent measurements of absolute neutron yield. The 4.5-m nTOF data have provided a useful testbed for testing improvements in nTOF data processing, especially with respect to improving the accuracies of the detector impulse response functions. The resulting improvements in data analysis methods have produced more accurate results. In summary, results from the NIF 4.5-m nTOF detectors have provided consistent measurements of DD and DT neutron yields from laser-fusion implosions.
    01/2012;
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    ABSTRACT: The National Ignition Facility has been used to compress deuterium-tritium to an average areal density of ~1.0plusmn0.1 g cm -2, which is 67% of the ignition requirement. These conditions were obtained using 192 laser beams with total energy of 1-1.6 MJ and peak power up to 420 TW to create a hohlraum drive with a shaped power profile, peaking at a soft x-ray radiation temperature of 275-300 eV. This pulse delivered a series of shocks that compressed a capsule containing cryogenic deuterium-tritium to a radius of 25-35 mum. Neutron images of the implosion were used to estimate a fuel density of 500-800 g cm -3.
    Physical Review Letters 01/2012; 108(21):215005 (5 pp.). · 7.94 Impact Factor
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    ABSTRACT: Neutron time-of-fight (nTOF) instruments are used to provide data on the performance of National Ignition Facility fusion experiments. nTOF detectors are used to measure the total neutron emission, temperature of the fuel, time of peak emission (bang time), and areal density of the compressed fuel (ρR). These instruments are precision diagnostics with sufficient dynamic range and high signal-to-noise so that the neutron spectrum from inertial confinement fusion implosions can be measured. This talk will focus on data from the scintillation detectors located at 20 m. Analysis techniques using both time-domain and energy-domain data are discussed. The next-generation detector based on an organic crystal scintillator show that improvements to scintillator decay, recording fidelity, and reduced scattering from the housing improve the precision of the neutron spectral measurement. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302.
    11/2011;
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    ABSTRACT: An instrument has been developed to measure X-ray bang-time for inertial confinement fusion capsules; the time interval between the start of the laser pulse and peak X-ray emission from the fuel core. The instrument comprises chemical vapor deposited polycrystalline diamond photoconductive X-ray detectors with highly ordered pyrolytic graphite X-ray monochromator crystals at the input. Capsule bang-time can be measured in the presence of relatively high thermal and hard X-ray background components due to the selective band pass of the crystals combined with direct and indirect X-ray shielding of the detector elements. A five channel system is being commissioned at the National Ignition Facility at Lawrence Livermore National Laboratory for implosion optimization measurements as part of the National Ignition Campaign. Characteristics of the instrument have been measured demonstrating that X-ray bang-time can be measured with ±30 ps precision, characterizing the soft X-ray drive to +/- 1 eV or 1.5%.
    Journal of Instrumentation 02/2011; 6(02):P02009. · 1.66 Impact Factor
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    ABSTRACT: We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of T(RAD)=300 eV and a symmetric implosion to a 100 μm diameter hot core.
    Physical Review Letters 02/2011; 106(8):085004. · 7.94 Impact Factor
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    ABSTRACT: form only given. Neutron time-of-flight (nToF) instruments are used to provide data on the performance of National Ignition Facility (NIF) fusion experiments. Detectors are located at 4.5 and 20 meters from the center of the target chamber with a 3.9 meter detector to be installed soon. These instruments are used to measure the total neutron emission, temperature of the fuel, time of peak emission (bang time), and areal density of the compressed fuel ρr). This talk will focus on data from the 20 meter detectors which are Xylene based liquid scintillators coupled to micro-channel plate photomultipliers. A figure of merit defined by the ratio of number of neutrons from 10 to 12 MeV divided by the number of neutrons between 13 and 15 MeV, called the down-scatter-ratio (DSR), is used to infer ρr. Analysis techniques using both time domain and energy domain data are discussed showing limitations and error analysis of both methods. Simulated data for an improved detector based on an organic crystal scintillator show that improvements to both scintillator decay and recording fidelity improve the precision of the DSR measurement.
    IEEE International Conference on Plasma Science 01/2011;
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    ABSTRACT: The first inertial confinement fusion implosion experiments with equimolar deuterium-tritium thermonuclear fuel have been performed on the National Ignition Facility. These experiments use 0.17 mg of fuel with the potential for ignition and significant fusion yield conditions. The thermonuclear fuel has been fielded as a cryogenic layer on the inside of a spherical plastic capsule that is mounted in the center of a cylindrical gold hohlraum. Heating the hohlraum with 192 laser beams for a total laser energy of 1.6 MJ produces a soft x-ray field with 300 eV temperature. The ablation pressure produced by the radiation field compresses the initially 2.2-mm diameter capsule by a factor of 30 to a spherical dense fuel shell that surrounds a central hot-spot plasma of 50 lm diameter. While an extensive set of x-ray and neutron diagnostics has been applied to characterize hot spot formation from the x-ray emission and 14.1 MeV deuterium-tritium primary fusion neutrons, thermonuclear fuel assembly is studied by measuring the down-scattered neutrons with energies in the range of 10 to 12 MeV. X-ray and neutron imaging of the compressed core and fuel indicate a fuel thickness of (14 6 3) lm, which combined with magnetic recoil spectrometer measurements of the fuel areal density of (1 6 0.09) g cm –2 result in fuel densities approaching 600 g cm –3 . The fuel surrounds a hot-spot plasma with average ion temperatures of (3.5 6 0.1) keV that is measured with neutron time of flight spectra. The hot-spot plasma produces a total fusion neutron yield of 10 15 that is measured with the magnetic recoil spectrometer and nuclear activation diagnostics that indicate a 14.1 MeV yield of ð7:560:1Þ Â 10 14 which is 70% to 75% of the total fusion yield due to the high areal density. Gamma ray measurements provide the duration of nuclear activity of (170 6 30) ps. These indirect-drive implosions result in the highest areal densities and neutron yields achieved on laser facilities to date. This achievement is the result of the first hohlraum and capsule tuning experiments where the stagnation pressures have been systematically increased by more than a factor of 10 by fielding low-entropy implosions through the control of radiation symmetry, small hot electron production, and proper shock timing. The stagnation pressure is above 100 Gbars resulting in high Lawson-type confinement parameters of Ps ' 10 atm s. Comparisons with radiation-hydrodynamic simulations indicate that the pressure is within a factor of three required for reaching ignition and high yield. This will be the focus of future higher-velocity implosions that will employ additional optimizations of hohlraum, capsule and laser pulse shape conditions. V C 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4719686]
    Physics of Plasmas 01/2011; 56(25). · 2.38 Impact Factor
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    ABSTRACT: Proper assembly of capsule mass, as manifested through evolution of fuel areal density (ρR), is fundamentally important for achieving hot-spot ignition planned at the National Ignition Facility (NIF). Experimental information about ρR and ρR asymmetries, Ti and yield is therefore essential for understanding how this assembly occurs. To obtain this information, a neutron spectrometer, called the Magnetic-Recoil Spectrometer (MRS) has been implemented on the NIF. Its primary objective is to measure the absolute neutron spectrum in the range 5 to 30 MeV, from which ρR, Ti and yield can be directly inferred for both low-yield tritium-hydrogen-deuterium (THD) and high-yield DT implosions. In this talk, the results from the first measurements of the absolute neutron spectrum produced in exploding pusher and THD implosions will be presented. This work was supported in part by the U.S. DOE, LLNL and LLE.
    American Physical Society, 52nd Annual Meeting of the APS Division of Plasma Physics; 11/2010
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    ABSTRACT: Neutron time-of-flight (nTOF) spectrometers are integral diagnostics at the National Ignition Facility (NIF) to extract neutron yield, ion temperature and bang time of the implosion. For measurements of the fuel areal density (rhoR), one of these nTOF diagnostics will be operated with low shielding at a comparably close distance of 3.9 m to the hohlraum target to minimize the scattering contribution of the intense 14 MeV neutron signal to the spectral background. This nTOF spectrometer uses CVD diamond semiconductor detectors with sub-ns decay times and without the long tails that often affect the response of fast scintillators. It will measure the fraction of down-scattered neutrons that arrives only ˜10 ns after the large pulse of 14 MeV DT neutrons and that provides a measure of the areal density rhoR and thus the ignition threshold function. We discuss the instrument design, Monte Carlo simulations of its response function, and measurements of the detector response to X-ray and neutron signals at the Laboratory for Laser Energetics (LLE). Special emphasis will be placed on discussing the contributions to the background for the neutrons down-scattered in the fuel into the spectral range of ˜10 to ˜12 MeV.
    11/2010;
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    ABSTRACT: Installation of the neutron time-of-flight (nTOF) diagnostic at the National Ignition Facility (NIF) was completed in 2010. It consists of 18 data channels from 8 detectors along 6 flight paths. Two detector types are used: (1) scintillators coupled to gated photomultiplier tubes or vacuum photodiodes, and (2) chemical-vapor-deposition diamonds. Target-to-detector distances are nominally 4.5 and 22 m. These detectors were calibrated for yield and ion temperature at LLE's OMEGA Laser Facility prior to installation on the NIF. This presentation describes nTOF diagnostic performance in measuring neutron yield, ion temperature, and bang time in D2 and THD (tritium, hydrogen, and deuterium) NIF implosions in 2010. This work is supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302.
    11/2010;