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.

Background measurement methods for opacity experiments conducted at the Z facility.

Laboratory experiments typically test opacity models by measuring spectrally resolved transmission of a sample using bright backlight radiation. A potential problem is that any unaccounted background signal contaminating the spectrum will artificially reduce the inferred opacity. Methods developed to measure background signals in opacity experiments at the Sandia Z facility are discussed. Preliminary measurements indicate that backgrounds are 9%-11% of the backlight signal at wavelengths less than 10 Å. Background is thus a relatively modest correction for all Z opacity data published to date. Future work will determine how important background is at longer wavelengths.

Systematic Study of L-Shell Opacity at Stellar Interior Temperatures.

The first systematic study of opacity dependence on atomic number at stellar interior temperatures is used to evaluate discrepancies between measured and modeled iron opacity [J. E. Bailey et al., Nature (London) 517, 56 (2015)NATUAS0028-083610.1038/nature14048]. High-temperature (>180 eV) chromium and nickel opacities are measured with ±6%-10% uncertainty, using the same methods employed in the previous iron experiments. The 10%-20% experiment reproducibility demonstrates experiment reliability. The overall model-data disagreements are smaller than for iron. However, the systematic study reveals shortcomings in models for density effects, excited states, and open L-shell configurations. The 30%-45% underestimate in the modeled quasicontinuum opacity at short wavelengths was observed only from iron and only at temperature above 180 eV. Thus, either opacity theories are missing physics that has nonmonotonic dependence on the number of bound electrons or there is an experimental flaw unique to the iron measurement at temperatures above 180 eV.

A compact multi-plane broadband (0.5-17 keV) spectrometer using a single acid phthalate crystal.

Acid phthalate crystals such as KAP crystals are a method of choice to record x-ray spectra in the soft x-ray regime (E ∼ 1 keV) using the large (001) 2d = 26.63 Šspacing. Reflection from many other planes is possible, and knowledge of the 2d spacing, reflectivity, and resolution for these reflections is necessary to evaluate whether they hinder or help the measurements. Burkhalter et al. [J. Appl. Phys., 52, 4379 (1981)] showed that the (013) reflection has efficiency comparable to the 2nd order reflection (002), and it can overlap the main first order reflection when the crystal bending axis ( b -axis) is contained in the dispersion plane, thus contaminating the main (001) measurement in a convex crystal geometry. We present a novel spectrograph concept that makes these asymmetric reflections helpful by setting the crystal b -axis perpendicular to the dispersion plane. In such a case, asymmetric reflections do not overlap with the main (001) reflection and each reflection can be used as an independent spectrograph. Here we demonstrate an achieved spectral range of 0.8-13 keV with a prototype setup. The detector measurements were reproduced with a 3D ray-tracing code.

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.

Measurement and models of bent KAP(001) crystal integrated reflectivity and resolution (invited).

The Advanced Light Source beamline-9.3.1 x-rays are used to calibrate the rocking curve of bent potassium acid phthalate (KAP) crystals in the 2.3-4.5 keV photon-energy range. Crystals are bent on a cylindrically convex substrate with a radius of curvature ranging from 2 to 9 in. and also including the flat case to observe the effect of bending on the KAP spectrometric properties. As the bending radius increases, the crystal reflectivity converges to the mosaic crystal response. The X-ray Oriented Programs (xop) multi-lamellar model of bent crystals is used to model the rocking curve of these crystals and the calibration data confirm that a single model is adequate to reproduce simultaneously all measured integrated reflectivities and rocking-curve FWHM for multiple radii of curvature in both 1st and 2nd order of diffraction.

Pinned, optically aligned diagnostic dock for use on the Z facility.

The pinned optically aligned diagnostic dock (PODD) is a multi-configuration diagnostic platform designed to measure x-ray emission on the Z facility. The PODD houses two plasma emission acquisition (PEA) systems, which are aligned with a set of precision machined pins. The PEA systems are modular, allowing a single diagnostic housing to support several different diagnostics. The PEA configurations fielded to date include both time-resolved and time-integrated, 1D spatially resolving, elliptical crystal spectrometers, and time-integrated, 1D spatially resolving, convex crystal spectrometers. Additional proposed configurations include time-resolved, monochromatic mirrored pinhole imagers and arrays of filtered x-ray diodes, diamond photo-conducting diode detectors, and bolometers. The versatility of the PODD system will allow the diagnostic configuration of the Z facility to be changed without significantly adding to the turn-around time of the machine. Additionally, the PODD has been designed to allow instrument setup to be completed entirely off-line, leaving only a refined alignment process to be performed just prior to a shot, which is a significant improvement over the instrument the PODD replaces. Example data collected with the PODD are presented.

A methodology for calibrating wavelength dependent spectral resolution for crystal spectrometers.

High quality absorption spectroscopy measurements were recently achieved at the Sandia National Laboratories Z facility in the soft x-ray range. Detailed spectral resolution knowledge is a key requirement for their interpretation. We present a methodology for measuring the wavelength dependent crystal spectral resolution, with a particular focus on the 7-17 Å range. We apply this procedure to the case of 1st order resolution of a potassium acid phthalate (KAP) convex crystal spectrometer. One calibration issue is that inferring the crystal resolution requires that the x-ray source emission feature widths and spectral profiles are known. To this aim, we resolve Manson x-ray source Si, Al, and Mg Kα line profiles using a KAP crystal spectrometer in 2nd order to achieve relatively high resolution. This information is exploited to measure 1st order KAP resolving powers λ∕Δλ∼1100-1300 in the 7-10 Å wavelength range.

Radiating shock measurements in the Z-pinch dynamic hohlraum.

The Z-pinch dynamic hohlraum is an x-ray source for high energy-density physics studies that is heated by a radiating shock to radiation temperatures >200 eV. The time-dependent 300-400 eV electron temperature and 15-35 mg/cc density of this shock have been measured for the first time using space-resolved Si tracer spectroscopy. The shock x-ray emission is inferred from these measurements to exceed 50 TW, delivering >180 kJ to the hohlraum.

Computers and medical language.

This review article presents principles and problems of automated processing of medical language data. Work on automated processing of information in medical language is surveyed. References and a bibliography are provided as an introduction to the field.

Automatic indexing of pathology data.

A procedure for automated indexing of pathology diagnostic reports at the National Institutes of Health is described. Diagnostic statements in medical English are encoded by computer into the Systematized Nomenclature of Pathology (SNOP). SNOP is a structured indexing language constructed by pathologists for manual indexing. It is of interest that effective automatic encoding can be based upon an existing vocabulary and code designed for manual methods. Morphosyntactic analysis, a simple syntax analysis, matching of dictionary entries consisting of several words, and synonym substitutions are techniques utilized.