Harmonic Generation and Inverse Cascade in the z-Pinch Driven, Preseeded Multimode, Magneto-Rayleigh-Taylor Instability.

The magneto-Rayleigh-Taylor instability (MRTI) plays an essential role in astrophysical systems and in magneto-inertial fusion, where it is known to be an important degradation mechanism of confinement and target performance. In this Letter, we show for the first time experimental evidence of mode mixing and the onset of an inverse-cascade process resulting from the nonlinear coupling of two discrete preseeded axial modes (400- and 550-µm wavelengths) on an Al liner that is magnetically imploded using the 20-MA, 100-ns rise-time Z Machine at Sandia National Laboratories. Four radiographs captured the temporal evolution of the MRTI. We introduce a novel unfold technique to analyze the experimental radiographs and compare the results to simulations and to a weakly nonlinear model. We find good quantitative agreement with simulations using the radiation magnetohydrodynamics code hydra. Spectral analysis of the MRTI time evolution obtained from the simulations shows evidence of harmonic generation, mode coupling, and the onset of an inverse-cascade process. The experiments provide a benchmark for future work on the MRTI and motivate the development of new analytical theories to better understand this instability.

Investigating Effects of Mentoring for Youth with Assault Injuries: Results of a Randomized-Controlled Trial.

Mentoring is considered an evidence-based practice for violence prevention. This study presents a partial replication of the Take Charge! program implemented in partnership with Big Brothers Big Sisters of America (BBBS). One hundred and eighty-eight early adolescents (M age = 12.87; 61.17% male) who were treated for peer-related assault injury in two urban mid-Atlantic emergency departments were randomly assigned to receive a mentor from two BBBS affiliates. Mentors and organization staff were trained in the Take Charge! violence prevention curriculum, which had previously shown evidence of efficacy. Intent-to-treat analyses showed statistically significant improvements in conflict avoidance self-efficacy for the intervention group at 9 months and reductions in fighting at 21 months, but an increase in parental report of aggression at 9 months. Complier average causal effect models revealed evidence of an additional effect for reduced problem behavior at 21 months for intervention adolescents who received a mentor. No effects were found for youth-reported aggression, retaliatory attitudes, deviance acceptance, or commitment to learning. Sensitivity analyses suggested increased aggressive behavior for adolescents in the intervention group who did not receive a mentor (i.e., non-compliers). These findings extend the evidence-base for Take Charge! as a violence prevention curriculum for youth already engaged in violence to "real-world" implementation settings. However, they also suggest that challenges associated with providing youth with mentors can be consequential and that additional supports may be needed for these youth/parents. Clinical trials number: clinicaltrials.gov NCT01770873.

Performance Scaling in Magnetized Liner Inertial Fusion Experiments.

We present experimental results from the first systematic study of performance scaling with drive parameters for a magnetoinertial fusion concept. In magnetized liner inertial fusion experiments, the burn-averaged ion temperature doubles to 3.1 keV and the primary deuterium-deuterium neutron yield increases by more than an order of magnitude to 1.1×10^{13} (2 kJ deuterium-tritium equivalent) through a simultaneous increase in the applied magnetic field (from 10.4 to 15.9 T), laser preheat energy (from 0.46 to 1.2 kJ), and current coupling (from 16 to 20 MA). Individual parametric scans of the initial magnetic field and laser preheat energy show the expected trends, demonstrating the importance of magnetic insulation and the impact of the Nernst effect for this concept. A drive-current scan shows that present experiments operate close to the point where implosion stability is a limiting factor in performance, demonstrating the need to raise fuel pressure as drive current is increased. Simulations that capture these experimental trends indicate that another order of magnitude increase in yield on the Z facility is possible with additional increases of input parameters.

Magnetized Disruption of Inertially Confined Plasma Flows.

The creation and disruption of inertially collimated plasma flows are investigated through experiment, simulation, and analytical modeling. Supersonic plasma jets are generated by laser-irradiated plastic cones and characterized by optical interferometry measurements. Targets are magnetized with a tunable B field with strengths of up to 5 T directed along the axis of jet propagation. These experiments demonstrate a hitherto unobserved phenomenon in the laboratory, the magnetic disruption of inertially confined plasma jets. This occurs due to flux compression on axis during jet formation and can be described using a Lagrangian-cylinder model of plasma evolution implementing finite resistivity. The basic physical mechanisms driving the dynamics of these systems are described by this model and then compared with two-dimensional radiation-magnetohydrodynamic simulations. Experimental, computational, and analytical results discussed herein suggest that contemporary models underestimate the electrical conductivity necessary to drive the amount of flux compression needed to explain observations of jet disruption.

A generalized approach to x-ray data modeling for high-energy-density plasma experiments.

Accurate understanding of x-ray diagnostics is crucial for both interpreting high-energy-density experiments and testing simulations through quantitative comparisons. X-ray diagnostic models are complex. Past treatments of individual x-ray diagnostics on a case-by-case basis have hindered universal diagnostic understanding. Here, we derive a general formula for modeling the absolute response of non-focusing x-ray diagnostics, such as x-ray imagers, one-dimensional space-resolved spectrometers, and x-ray power diagnostics. The present model is useful for both data modeling and data processing. It naturally accounts for the x-ray crystal broadening. The new model verifies that standard approaches for a crystal response can be good approximations, but they can underestimate the total reflectivity and overestimate spectral resolving power by more than a factor of 2 in some cases near reflectivity edge features. We also find that a frequently used, simplified-crystal-response approximation for processing spectral data can introduce an absolute error of more than an order of magnitude and the relative spectral radiance error of a factor of 3. The present model is derived with straightforward geometric arguments. It is more general and is recommended for developing a unified picture and providing consistent treatment over multiple x-ray diagnostics. Such consistency is crucial for reliable multi-objective data analyses.

X-ray self-emission imaging with spherically bent Bragg crystals on the Z-machine.

An x-ray imaging scheme using spherically bent crystals was implemented on the Z-machine to image x rays emitted by the hot, dense plasma generated by a Magnetized Liner Inertial Fusion (MagLIF) target. This diagnostic relies on a spherically bent crystal to capture x-ray emission over a narrow spectral range (<15 eV), which is established by a limiting aperture placed on the Rowland circle. The spherical crystal optic provides the necessary high-throughput and large field-of-view required to produce a bright image over the entire, one-cm length of the emitting column of a plasma. The average spatial resolution was measured and determined to be 18 µm for the highest resolution configuration. With this resolution, the radial size of the stagnation column can be accurately determined and radial structures, such as bifurcations in the column, are clearly resolved. The success of the spherical-crystal imager has motivated the implementation of a new, two-crystal configuration for identifying sources of spectral line emission using a differential imaging technique.

Demonstration of improved laser preheat with a cryogenically cooled magnetized liner inertial fusion platform.

We report on progress implementing and testing cryogenically cooled platforms for Magnetized Liner Inertial Fusion (MagLIF) experiments. Two cryogenically cooled experimental platforms were developed: an integrated platform fielded on the Z pulsed power generator that combines magnetization, laser preheat, and pulsed-power-driven fuel compression and a laser-only platform in a separate chamber that enables measurements of the laser preheat energy using shadowgraphy measurements. The laser-only experiments suggest that ∼89% ± 10% of the incident energy is coupled to the fuel in cooled targets across the energy range tested, significantly higher than previous warm experiments that achieved at most 67% coupling and in line with simulation predictions. The laser preheat configuration was applied to a cryogenically cooled integrated experiment that used a novel cryostat configuration that cooled the MagLIF liner from both ends. The integrated experiment, z3576, coupled 2.32 ± 0.25 kJ preheat energy to the fuel, the highest to-date, demonstrated excellent temperature control and nominal current delivery, and produced one of the highest pressure stagnations as determined by a Bayesian analysis of the data.

Implementation of a Talbot-Lau x-ray deflectometer diagnostic platform for the OMEGA EP laser.

A Talbot-Lau X-ray Deflectometer (TXD) was implemented in the OMEGA EP laser facility to characterize the evolution of an irradiated foil ablation front by mapping electron densities >1022 cm-3 by means of Moiré deflectometry. The experiment used a short-pulse laser (30-100 J, 10 ps) and a foil copper target as an x-ray backlighter source. In the first experimental tests performed to benchmark the diagnostic platform, grating survival was demonstrated and x-ray backlighter laser parameters that deliver Moiré images were described. The necessary modifications to accurately probe the ablation front through TXD using the EP-TXD diagnostic platform are discussed.

Properties of laser-produced GaAs plasmas measured from highly resolved X-ray line shapes and ratios.

The properties of hot, dense plasmas generated by the irradiation of GaAs targets by the Titan laser at Lawrence Livermore National Laboratory were determined by the analysis of high resolution K shell spectra in the 9 keV to 11 keV range. The laser parameters, such as relatively long pulse duration and large focal spot, were chosen to produce a steady-state plasma with minimal edge gradients, and the time-integrated spectra were compared to non-LTE steady state spectrum simulations using the FLYCHK and NOMAD codes. The bulk plasma streaming velocity was measured from the energy shifts of the Ga He-like transitions and Li-like dielectronic satellites. The electron density and the electron energy distribution, both the thermal and the hot non-thermal components, were determined from the spectral line ratios. After accounting for the spectral line broadening contributions, the plasma turbulent motion was measured from the residual line widths. The ionization balance was determined from the ratios of the He-like through F-like spectral features. The detailed comparison of the experimental Ga spectrum and the spectrum simulated by the FLYCHK code indicates two significant discrepancies, the transition energy of a Li-like dielectronic satellite (designated t) and the calculated intensity of a He-like line (x), that should lead to improvements in the kinetics codes used to simulate the X-ray spectra from highly-charged ions.

Characterization and calibration of a multilayer coated Wolter optic for an imager on the Z-machine at Sandia National Laboratories.

The need for a time-resolved monochromatic x-ray imaging diagnostic at photon energies >15 keV has motivated the development of a Wolter optic to study x-ray sources on the Z-machine at Sandia National Laboratories. The work is performed in both the LLNL's x-ray calibration facility and SNL's micro-focus x-ray lab. Characterizations and calibrations include alignment, measurement of throughput within the field of view (FOV), the point-spread function within the FOV both in and out of focus, and bandpass in the FOV. These results are compared with ray tracing models, showing reasonable agreement.

An x-ray optic calibration facility for high energy density diagnostics.

A facility to calibrate x-ray imaging optics was built at Lawrence Livermore National Laboratory to support high energy density (HED) and inertial confinement fusion (ICF) diagnostics such as those at the National Ignition Facility and the Sandia Z-Machine. Calibration of the spectral reflectivity and resolution of these x-ray diagnostics enable absolute determination of the x-ray flux and wavelengths generated in the HED and ICF experiments. Measurement of the optic point spread function is used to determine spatial resolution of the optic. This facility was constructed to measure (1) the x-ray reflectivity to ±5% over a spectral range from 5 to 60 keV; (2) point spread functions with a resolution of 50 µm (currently) and 13 µm (future) in the image plane; and (3) optic distance relative to the x-ray source and detector to within ±100 µm in each dimension. This article describes the capabilities of the calibration facility, concept of operations, and initial data from selected x-ray optics.

Design and raytrace simulations of a multilayer-coated Wolter x-ray optic for the Z machine at Sandia National Laboratories.

Recent breakthroughs in the fabrication of small-radii Wolter optics for astrophysics allow high energy density facilities to consider such optics as novel x-ray diagnostics at photon energies of 15-50 keV. Recently, the Lawrence Livermore National Laboratory, Sandia National Laboratories (SNL), the Smithsonian Astrophysical Observatory, and the NASA Marshall Space Flight Center jointly developed and fabricated the first custom Wolter microscope for implementation in SNL's Z machine with optimized sensitivity at 17.5 keV. To achieve spatial resolution of order 100-200 microns over a field of view of 5 × 5 × 5 mm3 with high throughput and narrow energy bandpass, the geometry of the optic and its multilayer required careful design and optimization. While the geometry mainly influences resolution and the field of view of the diagnostic, the mirror coating determines the spectral response and throughput. Here we outline the details of the design and fabrication process for the first multilayer-coated Wolter I optic for SNL's Z machine (Z Wolter), including its W/Si multilayer, and present results of raytrace simulations completed to predict and verify the performance of the optic.

A Wolter imager on the Z machine to diagnose warm x-ray sources.

A new Wolter x-ray imager has been developed for the Z machine to study the emission of warm (>15 keV) x-ray sources. A Wolter optic has been adapted from observational astronomy and medical imaging, which uses curved x-ray mirrors to form a 2D image of a source with 5 × 5 × 5 mm3 field-of-view and measured 60-300-µm resolution on-axis. The mirrors consist of a multilayer that create a narrow bandpass around the Mo Kα lines at 17.5 keV. We provide an overview of the instrument design and measured imaging performance. In addition, we present the first data from the instrument of a Mo wire array z-pinch on the Z machine, demonstrating improvements in spatial resolution and a 350-4100× increase in the signal over previous pinhole imaging techniques.

Mitigation of hard x-ray background in backlit pinhole imagers.

Experiments were performed to mitigate the hard x-ray background commonly observed in backlit pinhole imagers. The material of the scaffold holding the primary backlighter foil was varied to reduce the laser-plasma instabilities responsible for hot electrons and resulting hard x-ray background. Radiographic measurements with image plates showed a factor of >25 decrease in x-rays between 30 and 67 keV when going from a plastic to Al or V scaffold. A potential design using V scaffold offers a signal-to-background ratio of 6:1, a factor of 2 greater than using the bare plastic scaffold.

Detailed characterization of the LLNL imaging proton spectrometer.

Ultra-intense short pulse lasers incident on solid targets (e.g., thin Au foils) produce well collimated, broad-spectrum proton beams. These proton beams can be used to characterize magnetic fields, electric fields, and density gradients in high energy-density systems. The LLNL-Imaging Proton Spectrometer (L-IPS) was designed and built [H. Chen et al., Rev. Sci. Instrum. 81, 10D314 (2010)] for use with such laser produced proton beams. The L-IPS has an energy range of 50 keV-40 MeV with a resolving power (E/dE) of about 275 at 1 MeV and 21 at 20 MeV, as well as a single spatial imaging axis. In order to better characterize the dispersion and imaging capability of this diagnostic, a 3D finite element analysis solver is used to calculate the magnetic field of the L-IPS. Particle trajectories are then obtained via numerical integration to determine the dispersion relation of the L-IPS in both energy and angular space.

The impact of ionic strength on the adsorption of protons, Pb, Cd, and Sr onto the surfaces of Gram negative bacteria: testing non-electrostatic, diffuse, and triple-layer models.

Bacterial surface adsorption reactions are influenced by electric field effects caused by changes in ionic strength; however, existing datasets are too sparse to definitively constrain these differences or to determine the best way to account for them using thermodynamic models. In this study, we examine the ionic strength dependence of proton and metal adsorption onto the surfaces of Pseudomonas mendocina and Pseudomonas putida by conducting proton, Cd(II), Pb(II), and Sr(II) adsorption experiments over the ionic strength range of 0.001 to 0.6 M. Chosen experimental results are thermodynamically modeled using a non-electrostatic approach, a diffuse layer model (DLM), and a triple-layer model (TLM). The results demonstrate that bacterial surface electric field effects are negligible for proton, Cd, and Pb adsorption onto P. putida and P. mendocina, and that the discrete site non-electrostatic model developed in this study is adequate for describing these reactions. The extent of Sr adsorption is influenced by changes in the bacterial surface electric field; however, the non-electrostatic model better describes Sr adsorption behavior than the DLM or TLM. The DLM and TLM greatly overpredict the effect of the electric field for all adsorption reactions at all ionic strengths tested.

ORL-1 and mu opioid receptor antisera label different fibers in areas involved in pain processing.

Mu opioid receptors (MOR) mediate the analgesic effects of opioid drugs such as morphine. The opioid receptor-like (ORL-1) receptor is structurally related to opioid receptors and the ORL-1 receptor agonist, orphanin FQ/nociceptin, induces analgesia at the spinal level, but appears to recruit different circuitry than that used by mu opioids. When administered intracerebroventricularly, orphanin FQ/nociceptin produces hyperalgesia and/or reverses opioid analgesia. The functionally distinct actions elicited by MOR and ORL-1 receptors, which activate similar intracellular signaling systems and show similar regional distributions, could be explained by their differential cellular localization. By using double label immunohistochemistry and confocal microscopy, the present study investigates the distribution of MOR and ORL-1 receptors in regions of the rat nervous system that are involved with nociceptive processing. In general co-localization of MOR and ORL-1 receptor immunoreactivity was not observed in either perikarya or neuropil in the dorsal root ganglia, nor in the Lissauer's tract and superficial laminae of the spinal cord. Likewise, there was no evidence for co-localization of these receptors within the periaqueductal gray, the nucleus raphe magnus, the gigantocellular reticular nucleus, and the nucleus of the solitary tract. These observations indicate that MOR and ORL-1 receptors are expressed predominantly on different fiber systems in these regions. This differential distribution is consistent with the distinct pharmacology of ORL-1 and MOR receptor agonists and suggests that the antisera to MOR and ORL-1 receptors may provide useful markers for further investigations of analgesic and counteranalgesic pathways modulating pain perception.

Immunohistochemical localization of ORL-1 in the central nervous system of the rat.

A novel member of the opioid receptor family (ORL-1) has been cloned from a variety of vertebrates. ORL-1 does not bind any of the classical opioids, although a high affinity endogenous agonist with close homology to dynorphin has recently been identified. We have generated a monoclonal antibody to the N-terminus of ORL-1 to map areas of receptor expression in rat central nervous system (CNS). Intense and specific immunolabeling was observed in multiple areas in the diencephalon, mesencephalon, pons/medulla, and spinal cord. In the telencephalon, intense labeling was observed in the neuropil throughout layers II-V in the neocortex, the anterior olfactory nuclear complex, the pyriform cortex, the CA1-CA4 fields and dentate gyrus of the hippocampus, and in many of the septal and basal forebrain areas. In contrast to other members of the opioid receptor family, light labeling for ORL-1 was observed in telencephalic areas such as caudate-putamen. In the cerebellum, ORL-1 immunoreactivity was only observed in the deep nuclei. Throughout the CNS the majority of labelling was localized to fiber processes and fine puncta, although labeled scattered perikarya were observed in a few brain areas such as the hilus dentate in the hippocampus and some nuclei in the brainstem and spinal cord. The present mapping study is consistent with the reported distribution of ORL-1 mRNA and provides the first immunohistochemical report on anatomical and cellular distribution of ORL-1 receptor in the rat CNS.

Adenocarcinomas of the esophagus and gastric cardia: medical conditions, tobacco, alcohol, and socioeconomic factors.

Adenocarcinomas of the esophagus and gastric cardia have increased in incidence over the past 10-15 years in Western countries. The cause for this increase in incidence is still unknown. Our study was designed to investigate potential risk factors for adenocarcinomas of the esophagus and gastric cardia and to compare the risk profiles of a group of patients with this cancer with those having distal stomach cancer. We studied 95 incident cases with the pathological diagnosis of adenocarcinomas of the esophagus and gastric cardia, 67 patients with adenocarcinomas of the distal stomach, and 132 cancerfree controls. Patients were seen at Memorial Sloan-Kettering Cancer Center from November 1, 1992 to November 1, 1994. Epidemiological data were collected by a modified National Cancer Institute Health Habits History Questionnaire. Risk factors were analyzed using Mantel-Haenszel methods and a logistic regression model. Hypertension was associated with a 2-fold increased risk of adenocarcinomas of esophagus and gastric cardia after controlling for age, sex, race, education, pack-years of smoking, alcohol use, body mass index, and total dietary intake of calories. Increased risk of adenocarcinomas of esophagus and gastric cardia was associated with age, male gender, and Caucasian race. Tobacco smoking was related to a modest risk of adenocarcinomas of esophagus and gastric cardia. In contrast, the risk of distal stomach cancer was associated with stomach ulcers and pack-years of cigarette smoking. Iron deficiency was significantly associated with increased risk of both adenocarcinomas of the esophagus and gastric cardia and adenocarcinomas of the distal stomach. No obvious associations were identified for occupational exposures, family history of cancer, and physical activities. This study suggests that medical conditions such as hypertension and iron deficiency may be related to the risk of adenocarcinomas of esophagus and gastric cardia and confirms the moderate risk associated with tobacco smoking. Our results indicated an etiological heterogeneity with respect to risk factors identified between adenocarcinomas of esophagus and gastric cardia and those of the distal stomach.

Violence prevention in the primary care setting: a program for pediatric residents.

OBJECTIVE: To measure the effect of a violence prevention program on pediatric residents' violence prevention guidance during well-child visits. DESIGN: Prospective study of an educational intervention. SETTING: Inner-city tertiary care hospital and satellite site. PARTICIPANTS: Pediatric residents. INTERVENTIONS: A 2(1/2)-hour violence prevention program, consisting of an introductory talk, role playing, a printed resident guide, and supplemental reading materials. MAIN OUTCOME MEASURES: Parent or guardian report of violence prevention guidance offered during the well-child visit, using a postvisit survey. RESULTS: Three hundred eight patient encounters were included in the survey: 93 prior to the program, 106 just afterward, and 109 after 6 months. Before the program, guns or violence was discussed at 9.7% of visits; this increased to 19.1% of visits after the program (odds ratio, 2.20; 95% confidence interval, 1.02-4.74). The improvement was sustained 6 months after the program. More than 80% of residents felt the program increased their fund of knowledge and taught them skills, and 93% stated that they would use these skills in the future. CONCLUSION: This one-time educational intervention significantly increased the amount of violence prevention guidance provided by pediatric residents to their patients and families. The effect was sustained after 6 months. Residents regarded the program as a successful method of providing the skills and knowledge needed to address the issue of interpersonal violence in their primary care encounters.