Search

Lawrence Livermore’s National Ignition Facility (NIF) requires a radiation tolerant video camera to remotely monitor varied activities in and around the NIF target chamber. Our present suite of monitor cameras must be either, removed during high yield shots, requiring substantial resources or left in place which greatly reduces their life expectancy. Our goal was to develop a relatively inexpensive, radiation tolerant monitor camera which could be left in place during high yield laser experiments yet continue to give quality data for up to (5) years of operation or about 250 high yield shots. The camera was built around the CMOSIS CMV 2000 / 4000 sensor. Camera components were chosen based on their radiation tolerant performance at the Cobham radiation test facility in CO Springs. The prototype camera was tested both at Cobham and on the NIF during high yield shots. We will present test results as well as predictions for camera life expectancy.

We apply a cascaded linear model analysis to a micro-channel plate x-ray framing camera. We establish a theoretical expression of the Noise Power Spectrum (NPS) at the detector's output and assess its accuracy by comparing it to the NPS of Monte Carlo simulations of the detector's response to a uniform illumination. We also demonstrate that fitting the NPS of experimental data against a parametric model based on this expression can yield valuable information on the imaging ability of framing cameras, offering an alternative approach to the usual method employed to measure their modulation transfer functions.

The National Ignition Facility’s (NIF) harsh radiation environment can cause electronics to malfunction during high-yield DT shots. Until now there has been little experience fielding electronic-based cameras in the target chamber under these conditions; hence, the performance of electronic components in NIF’s radiation environment was unknown. It is possible to purchase radiation tolerant devices, however, they are usually qualified for radiation environments different to NIF, such as space flight or nuclear reactors. This paper presents the results from a series of online experiments that used two different prototype camera systems built from non-radiation hardened components and one commercially available camera that permanently failed at relatively low total integrated dose. The custom design built in Livermore endured a 5 × 1015 neutron shot without upset, while the other custom design upset at 2 × 1014 neutrons. These results agreed with offline testing done with a flash x-ray source and a 14 MeV neutron source, which suggested a methodology for developing and qualifying electronic systems for NIF. Further work will likely lead to the use of embedded electronic systems in the target chamber during high-yield shots.

This qualitative study highlights the lived experiences of former residents of an adolescent residential treatment facility that utilizes the points and levels system of behavior management. Data from 30 in-depth interviews reveal participants’ overall perceptions of the lack of effectiveness of the points system for behavior change and emotional growth. Specifically, this analysis offers information about how the points system operated in this facility, helpful and hurtful aspects of the system, and ways in which the system itself forms barriers to genuine change. These findings strengthen advocacy for alternative methods in residential treatment that encourage meaningful and lasting behavioral and emotional change.

Compton radiography provides a means to measure the integrity, ρR and symmetry of the DT fuel in an inertial confinement fusion implosion near peak compression. Upcoming experiments at the National Ignition Facility will use the ARC (Advanced Radiography Capability) laser to drive backlighter sources for Compton radiography experiments and will use the newly commissioned AXIS (ARC X-ray Imaging System) instrument as the detector. AXIS uses a dual-MCP (micro-channel plate) to provide gating and high DQE at the 40–200 keV x-ray range required for Compton radiography, but introduces many effects that contribute to the spatial resolution. Experiments were performed at energies relevant to Compton radiography to begin characterization of the spatial resolution of the AXIS diagnostic.

In contemporary studies of blackness, scholars are responding to the need for more nuanced representations of everyday life to illustrate the commonalities and divergence of negotiating whiteness. In this essay, I situate the Gullah/Geechee within ongoing struggles for accurate representation and access to power across the contested landscapes of the “New South.” More specifically, I interrogate three economic strategies of urban development—urban renewal, historic preservation, and heritage tourism—as contemporary manifestations of white racism. I begin by defining the Gullah/Geechee as a cultural group within their own situated predicament. Next, I operationalize “the social field of whiteness” and “white racism as habitus” as tools for the subsequent discussion. Finally, I zoom in for a closer look at Charleston, South Carolina, as a local site of this increasingly global process. Throughout this essay, I demonstrate how these particular strategies of urban development serve as “security checkpoints” in the maintenance of race-based inequality across the broader “social field of whiteness.”

We present new designs for the launch and receiver boards used in a high speed x-ray framing camera at the National Ignition Facility. The new launch board uses a Klopfenstein taper to match the 50 ohm input impedance to the ~10 ohm microchannel plate. The new receiver board incorporates design changes resulting in an output monitor pulse shape that more accurately represents the pulse shape at the input and across the microchannel plate; this is valuable for assessing and monitoring the electrical performance of the assembled framing camera head. The launch and receiver boards maximize power coupling to the microchannel plate, minimize cross talk between channels, and minimize reflections. We discuss some of the design tradeoffs we explored, and present modeling results and measured performance. We also present our methods for dealing with the non-ideal behavior of coupling capacitors and terminating resistors. We compare the performance of these new designs to that of some earlier designs.

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.

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 bumthrough and laser deposition indicate the pattern of plasma filling is very different.

High-resolution, high-energy X-ray backlighters are very active area of research for radiography experiments at the National Ignition Facility (NIF) [Miller et al., Nucl. Fusion 44, S228 (2004)], in particular those aiming at obtaining Compton-scattering produced radiographs from the cold, dense fuel surrounding the hot spot. We report on experiments to generate and characterize point-projection-geometry backlighters using short pulses from the advanced radiographic capability (ARC) [Crane et al., J. Phys. 244, 032003 (2010); Di Nicola et al., Proc. SPIE 2015, 93450I-12], at the NIF, focused on Au micro-wires. We show the first hard X-ray radiographs, at photon energies exceeding 60 keV, of static objects obtained with 30 ps-long ARC laser pulses, and the measurements of strength of the X-ray emission, the pulse duration and the source size of the Au micro-wire backlighters. For the latter, a novel technique has been developed and successfully applied.

Recently developed diagnostic techniques at LLNL require recording backlit images of extremely dense imploded plasmas using hard x-rays, and demand the detector to be sensitive to photons with energies higher than 50 keV [R. Tommasini et al., Phys. Phys. Plasmas 18, 056309 (2011); G. N. Hall et al., “AXIS: An instrument for imaging Compton radiographs using ARC on the NIF,” Rev. Sci. Instrum. (these proceedings)]. To increase the sensitivity in the high energy region, we propose to use a combination of two MCPs. The first MCP is operated in a low gain regime and works as a thick photocathode, and the second MCP works as a high gain electron multiplier. We tested the concept of this dual MCP configuration and succeeded in obtaining a detective quantum efficiency of 4.5% for 59 keV x-rays, 3 times larger than with a single plate of the thickness typically used in NIF framing cameras.

X-ray framing cameras based on proximity-focused micro-channel plates (MCP) have been playing an important role as diagnostics of inertial confinement fusion experiments [1]. Most of the current x-ray framing cameras consist of a single MCP, a phosphor, and a recording device (e.g. CCD or photographic films). This configuration is successful for imaging x-rays with energies below 20 keV, but detective quantum efficiency (DQE) above 20 keV is severely reduced due to the large gain differential between the top and the bottom of the plate for these volumetrically absorbed photons [2]. Recently developed diagnostic techniques at LLNL require recording backlit images of extremely dense imploded plasmas using hard x-rays, and demand the detector to be sensitive to photons with energies higher than 40 keV [3]. To increase the sensitivity in the high-energy region, we propose to use a combination of two MCPs. The first MCP is operated in low gain and works as a thick photocathode, and the second MCP works as a high gain electron multiplier [4,5]. We assembled a proof-of-principle test module by using this dual MCP configuration and demonstrated 4.5% DQE at 60 keV x-rays.

As neutron yields increase at the National Ignition Facility (NIF) the need for neutron ‘hardened’ diagnostics has also increased. Gated Imagers located within the target chamber are exposed to neutrons which degrade image quality and damage electronics. In an effort to maintain the signal to noise ratio (S/N) on our images and mitigate neutron induced damage, we have implemented numerous upgrades to our X-ray framing cameras. The NIF Gated X-ray Detector (GXD), design has evolved into the Hardened Gated X-ray Detector, HGXD. These improvements are presented with image data taken on high yield NIF shots showing enhanced image quality. Additional upgrades were added to remotely locate sensitive electronics and ease operational use.

We present initial characterization data from a new single-line-of-sight (SLOS) x-ray framing camera. The instrument uses an image-dissecting structure inside an electron optic tube to produce up to four simultaneous dc images from a single image incident on the cathode and a microchannel plate-based device to provide the temporal gating of those images. A series of gated images have been obtained using a short-pulse UV laser source, and the spatial resolution of those images is compared to those obtained using a more traditional-microchannel plate based system.

Gated, microchannel-plate-based (MCP) framing cameras have been deployed worldwide for 0.2–9 keV x-ray imaging and spectroscopy of transient plasma phenomena. For a variety of spectroscopic and imaging applications, the angular sensitivity of MCPs must be known for correctly interpreting the data. We present systematic measurements of angular sensitivity at discrete relevant photon energies and arbitrary MCP gain. The results can been accurately predicted by using a simple two-dimensional approximation to the three-dimensional MCP geometry and by averaging over all possible photon ray paths.

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.

Critical interpretations of “Burnt Norton” have varied widely over the nearly 80 years since its first publication. While many early scholars saw it as an abstract meditation on philosophy, the revelation in the 1970s, 1980s, and 1990s of the relationship of Eliot and Emily Hale changed to some extent the way in which it is read, with more of a personal view, at least in its inspiration. Indeed, I suggest that “Burnt Norton” and specifically the rose garden passage presents the two figures in the poem at a moment fraught with the possibility of rekindling their earlier romance. Our knowledge of the subsequent poems and of the failure of the further development of their relationship greatly colors our reading of the poem, preventing us from seeing the tension and suspense of this experience as it balances between the attraction of human love and that of a demanding spiritual commitment.

We present evidence of an artifact in gated x-ray framing cameras that can severely impact image quality. This artifact presents as a spatially-varying, high-intensity background and is correlated with experiments that produce a high flux of x-rays during the time before the framing camera is triggered. Dedicated experiments using a short pulse UV laser that arrives before, during, and after the triggering of the framing camera confirm that these artifacts can be produced by light that arrives in advance of the voltage pulse that triggers the camera. This is consistent with these artifacts being the result of photoelectrons produced uniformly at the active area of the camera by early incident light and then selectively trapped by the electromagnetic (EM) fields of the camera. Simulations confirm that the EM field above the active surface can act to confine electrons produced before the camera is triggered. We further present a method to suppress these artifacts by installing a conducting electrode in front of the active area of the framing camera. This device suppresses artifacts by attracting any electrons liberated by x-rays that arrive before the camera is triggered.

We have developed and commissioned a transmitted beam diagnostic (TBD) for the 2ω high intensity interaction beam at the Omega laser facility. The TBD consists of a bare-surface reflector mounted near the target, which collects and reflects 4% of the transmitted light to a detector assembly outside the vacuum chamber. The detector includes a time integrating near-field camera that measures beam spray, deflection, and the absolute transmitted power. We present a detailed description of the instrument and the calibration method and include first measurements on laser heated gas bag targets to demonstrate the performance of the diagnostic.

Gain can vary across the active area of an x-ray framing camera by a factor of 4 (or more!) due to the voltage loss and dispersion associated with pulse transmission in a microstripline-coated microchannel plate. In order to make quantitative measurements, it is consequently important to measure the gain variation ("flat field"). Moreover, because of electromagnetic cross talk, gain variation depends on specific operational parameters, and ideally a flat field would be obtained at all operating conditions. As part of a collaboration between Lawrence Livermore National Laboratory's National Ignition Facility and the Commissariat à l'Énergie Atomique, we have been able to evaluate the consistency of three different methods of measuring x-ray flat fields. By applying all three methods to a single camera, we are able to isolate performance from method. Here we report the consistency of the methods and discuss systematic issues with the implementation and analysis of each.

We describe an experimental method to measure the gate profile of an x-ray framing camera and to determine several important functional parameters: relative gain (between strips), relative gain droop (within each strip), gate propagation velocity, gate width, and actual inter-strip timing. Several of these parameters cannot be measured accurately by any other technique. This method is then used to document cross talk-induced gain variations and artifacts created by radiation that arrives before the framing camera is actively amplifying x-rays. Electromagnetic cross talk can cause relative gains to vary significantly as inter-strip timing is varied. This imposes a stringent requirement for gain calibration. If radiation arrives before a framing camera is triggered, it can cause an artifact that manifests as a high-intensity, spatially varying background signal. We have developed a device that can be added to the framing camera head to prevent these artifacts.

Gated and streaked x-ray detectors generally require corrections in order to counteract instrumental effects in the data. The method of correcting for gain variations in gated cameras fielded at National Ignition Facility (NIF) is described. Four techniques for characterizing the gated x-ray detectors are described. The current principal method of characterizing x-ray instruments is the production of controlled x-ray emission by laser-generated plasmas as a dedicated shot at the NIF. A recently commissioned pulsed x-ray source has the potential to replace the other characterization systems. This x-ray source features a pulsed power source consisting of a Marx generator, capacitor bank that is charged in series and discharged in parallel, producing up to 300 kV. The pulsed x-ray source initially suffered from a large jitter (∼60 ns), but the recent addition of a pulsed laser to trigger the spark gap has reduced the jitter to ∼5 ns. Initial results show that this tool is a promising alternative to the other flat fielding techniques.

Global Ethnography: Forces. Connections, and Imaginations in. Postmodern World. Michael Burawoy. Joseph A. Blum. Sheba George. Zsuzsa Gille. Teresa Gowan. Lynn Haney. Maren Klawiter. Steve H. Lopez. Sean O Riain. and Millie Thayer. Berkeley, CA. and London, UK: University of California Press, 2000. xv. 393 pp. (Paper US$17.95)

The only children's book written by Eudora Welty, The Shoe Bird (1964) offers teachers in the elementary grades a unique opportunity to introduce their students at an early stage in their schooling to the work of a major American author. Yet, because it has been largely ignored by reviewers and scholars alike and is currently out of print, it is almost unknown today, even to those familiar with children's literature. Following its publication, it received only sparse reviews, most of which were cordial but restrained. Helen Bevington in the New York Times Book Review called it a "delightful book," suggesting that children would love both its words and its birds. Emily Maxwell in The New Yorker, which had published a number of Welty's short stories, was more enthusiastic, describing it as a "seriocomic f an ta sy . . , fused with realism," praising its humor and asserting that, for "anything like it," one would have to look to the literature of the late Middle Ages (p. 221). However, J. B. Hardendorff in Library Journal, after criticizing its "stereotyped characterizations" and "heavy-handed moral," concluded that this "contrived story filled with inconsistencies" was "poor fare from such a talented writer of adult fiction." Most scholars have either ignored it entirely or simply noted its date of publication. In only two articles has it received even limited treatment. Jeanne R. Nostrandt suggests that a pageant of birds which Welty photographed in a Negro church in Jackson in the early 1930s was a source for The Shoe Bird, which she calls "mild satire" (pp. 113-117) , and Albert Griffith analyzes the "aggregation of friends" motif prevalent in folk and fairy tales as a structural principle underlying Welty's story.

Steers (n = 59) produced from the mating of Braford, Simbrah, Senepol, and Simmental bulls to Brahman- and Romana Red-sired cows and Brahman bulls to Angus cows were used in this study. Effects of sire breed and age at feeding on muscle tenderness in the major muscles of the chuck when steers were fed to 1.0 cm 12th rib fat were determined. There were no muscle tenderness effects due to sire breed group, with the exception of the serratus ventralis muscle, which was more tender in Brahman- and Braford-sired steers than in Simmental-sired steers. Additionally, the supraspinatus muscle from the yearlings was lower in shear value than that from the calves. The Brahman-sired steers had serratus ventralis muscles with higher percentages (P less than .05) of intramuscular fat than those of Braford-, Simbrah-, and Simmental-sired steers. Fat deposited within the muscle or between muscles in the chuck was not related to muscle tenderness as measured by Warner-Bratzler shear values. Also, percentages of intramuscular fat of the triceps brachii, serratus ventralis, or supraspinatus muscles were not influenced (P greater than .05) by age at feeding.

A 1-mm-square diamond photoconductive detector (PCD) has been installed on the LLNL Nova laser system, for use as a broadband soft x-ray power diagnostic. The PCD is installed behind an array of pinholes, which cast multiple, overlapping images of the source onto the diamond. This allows reduction of the x-ray intensity, to avoid saturation problems, while avoiding the spectral dependency of thin film filters. The diode current is read out on a 5 GHz bandwidth scope. The system is calibrated by comparison to an absolutely calibrated array of filtered vacuum x-ray photodiodes (“dante”). The time response of the PCD and its bias electronics have been characterized using the 5th harmonic (210 nm) of a short pulse (

A first set of shock timing, 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 (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 8 TW and 17 kJ in flattop and shaped 1–9 ns 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 3D codes by extending the study of laser driven hydrodynamic jets to 3D geometries.

Radiography techniques utilizing large-area x-ray sources (typically ⩽7 keV) and pinhole-imaging gated x-ray diagnostics have long been used at the Nova laser facility. However, for targets requiring higher-energy x-ray backlighters (>9 keV), low conversion efficiencies and pinhole losses combine to make this scheme unworkable. The technique of point projection radiography has been improved upon to make imaging at high x-ray energies feasible. In this scheme a “point” source of x-rays, usually a small diameter (⩽25 μm) fiber, is illuminated with a single, 100-ps pulse from the Nova laser. A gated x-ray imager with a 500-ps electronic gate width is used to record the projected image. [K. S. Budil et al., Rev. Sci. Instrum. 67, 485 (1996).] The experimental challenges this technique presents and experimental results will be discussed.

Summary form only given. An experimental campaign to study radiation drive in small-scale halfraums has been carried out using the first four beams of the National Ignition Facility (NIF) at the Lawerence Livermore National Laboratory (Livermore, CA). The targets fill with plasma so quickly that, late in time, most of the laser energy is deposited at the laser entrance hole. Experiments have shown the effect of laser beam conditioning, laser power, and target size on hohlraum performance. The experimental results on X-radiation drive, laser backscatter, hard X-rays, hard X-ray imaging, and X-ray burnthrough are discussed

Summary form only given. Two-dimensional time-resolved images of thermal X-rays have been extensively used in hohlraum experiments at OMEGA and NOVA to study diagnostic hole closure, thermal X-ray burnthrough, and spatial profiles of laser entrance holes. The soft X-ray imager built for the first experiments at the National Ignition Facility had four soft X-ray channels plus a hard X-ray channel and was mated to a four strip gated imager (the FXI). This produced four soft X-ray images per strip, separated in time by 50 ps. The soft X-ray channels consist of a mirror plus a filter. The diagnostic was used to study soft X-ray burnthrough of hot hohlraum targets

We have performed pulsed neutron and pulsed laser tests of a CVD diamond detector manufactured from DIAFILM, a commercial grade of CVD diamond. The laser tests were performed at the short pulse UV laser at Bechtel Nevada in Livermore, CA. The pulsed neutrons were provided by DT capsule implosions at the OMEGA laser fusion facility in Rochester, NY. From these tests, we have determined the impulse response to be 250 ps fwhm for an applied E-field of 500 V/mm. Additionally, we have determined the sensitivity to be 2.4 mA/W at 500 V/mm and 4.0 mA/W at 1000 V/mm. These values are approximately 2 to 5x times higher than those reported for natural Type IIa diamond at similar E-field and thickness (1mm). These characteristics allow us to conceive of a neutron time-of-flight current mode spectrometer based on CVD diamond. Such an instrument would sit inside the laser fusion target chamber close to target chamber center (TCC), and would record neutron spectra fast enough such that backscattered neutrons and x-rays from the target chamber wall would not be a concern. The acquired neutron spectra could then be used to extract DD fuel areal density from the downscattered secondary to secondary ratio.

The targets used in the hot halfraum campaign at OMEGA create many hot electrons, which result in a large flux of hard x rays. The hard x rays produce a high background in the streak camera. The background was significantly reduced by wrapping the streak camera with a high-Z material; in this case, 1/8 in. of Pb. The large hard x-ray flux also adds noise to images from framing cameras which use charge-coupled devices.

Medicine makes an important distinction by saying it is sometimes proper to allow a patient to die but that one should never actively cause a patient to die. The thin, invisible line which separates these views is being tested and will be debated intensely in the future.

We used focus groups to learn the range of issues threatening food security of low income residents in our community. Five major themes emerged from the discussions: literacy, money, time, mental health and self-esteem, suggesting several approaches that could help ensure food security: 1) education, 2) sharing of resources, 3) coalition building, and 4) advocacy. Education programs have to be practical, allowing for demonstrations and hands-on learning while emphasizing skill building and problem solving. Incorporating a social aspect into learning may compensate for the social isolation and would capitalize on the impressive mutual support we witnessed. Strategies based on self-help and peer assistance may counteract low self-esteem and overcome suspicion of health professionals. A community-wide effort is needed to address the factors contributing to food insecurity. We envision the formation of a coalition of professionals, agencies, and low income people to develop a comprehensive strategy for achieving food security.