skip to main content

DOE PAGESDOE PAGES

5 results for: All records
Author ORCID ID is 0000000172523343
Full Text and Citations
Filters
  1. This paper discusses the modeling of experiments that measure iron opacity in local thermodynamic equilibrium (LTE) using laser-driven hohlraums at the National Ignition Facility (NIF). A previous set of experiments fielded at Sandia's Z facility [Bailey et al., Nature 517, 56 (2015)] have shown up to factors of two discrepancies between the theory and experiment, casting doubt on the validity of the opacity models. The purpose of the new experiments is to make corroborating measurements at the same densities and temperatures, with the initial measurements made at a temperature of 160 eV and an electron density of 0.7 × 10more » 22 cm -3. The X-ray hot spots of a laser-driven hohlraum are not in LTE, and the iron must be shielded from a direct line-of-sight to obtain the data [Perry et al., Phys. Rev. B 54, 5617 (1996)]. This shielding is provided either with the internal structure (e.g., baffles) or external wall shapes that divide the hohlraum into a laser-heated portion and an LTE portion. In contrast, most inertial confinement fusion hohlraums are simple cylinders lacking complex gold walls, and the design codes are not typically applied to targets like those for the opacity experiments. We will discuss the initial basis for the modeling using LASNEX, and the subsequent modeling of five different hohlraum geometries that have been fielded on the NIF to date. This includes a comparison of calculated and measured radiation temperatures.« less
  2. Targets have been developed to measure supersonic radiation transport in aerogel foams using absorption spectroscopy. The target consists of an aerogel foam uniformly doped with either titanium or scandium inserted into an undoped aerogel foam package. This creates a localized doped foam region to provide spatial resolution for the measurement. Development and characterization of the foams is a key challenge in addition to machining and assembling the two foams so they mate without gaps. The foam package is inserted into a beryllium sleeve and mounted on a gold hohlraum. The target is mounted to a holder created using additive manufacturingmore » and mounted on a stalk. As a result, the manufacturing of the components, along with assembly and metrology of the target are described here.« less
  3. Here, we present synthetic transmission spectra generated with PrismSPECT utilizing both the ATBASE model and the Los Alamos opacity library (OPLIB) to evaluate whether an alternative choice in atomic data will impact modeling of experimental data from radiation transport experiments using Sc-doped aerogel foams (ScSi 6O 12 at 75 mg/cm 3 density). We have determined that in the 50-200 eV T e range there is a significant difference in the 1s-3p spectra, especially below 100 eV, and for T e = 200 eV above 5000 eV in photon energy. Examining synthetic spectra generated using OPLIB with 300 resolving power revealsmore » spectral sensitivity to T e changes of ~3 eV.« less
  4. Here, the goal of this work was to investigate the matrix effect of copper in the presence of sodium or magnesium in a laser-induced plasma. Varying amounts of copper were mixed and pressed with a constant amount of sodium or magnesium and a stearic acid binder. Experimental parameters such as delay time and laser pulse energy were varied to observe trends in the emission intensity of the Na I 588.99 nm, Na I 589.59 nm, Mg I 277.98 nm, and Mg II 279.08 nm lines. Experimental observations are supported by theoretical calculations and modeling that show the Na I andmore » Mg I emission intensities increase in the presence of copper while the Mg II line intensity decreases due to the increase in electron density (Ne) of the plasma when copper is added. Lastly, the increase in electron density changes the population of the atomic species within the plasma through an increase in recombination of ions with electrons, shifting the populations toward more neutral states, providing an explanation for the observed matrix effects found in these, and many previous, studies.« less
  5. Laser induced breakdown spectroscopy (LIBS) is a rapid atomic emission spectroscopy technique that can be configured for a variety of applications including space, forensics, and industry. LIBS can also be configured for stand-off distances or in-situ, under vacuum, high pressure, atmospheric or different gas environments, and with different resolving-power spectrometers. In this paper, the detection of uranium in a complex geological matrix under different measurement schemes is explored. Although many investigations have been completed in an attempt to detect and quantify uranium in different matrices at in-situ and standoff distances, this work detects and quantifies uranium in a complex matrixmore » under Martian and ambient air conditions. Investigation of uranium detection using a low resolving-power LIBS system at stand-off distances (1.6 m) is also reported. The results are compared to an in-situ LIBS system with medium resolving power and under ambient air conditions. Uranium has many thousands of emission lines in the 200–800 nm spectral region. In the presence of other matrix elements and at lower concentrations, the limit of detection of uranium is significantly reduced. The two measurement methods (low and high resolving-power spectrometers) are compared for limit of detection (LOD). Of the twenty-one potential diagnostic uranium emission lines, seven (409, 424, 434, 435, 436, 591, and 682 nm) have been used to determine the LOD for pitchblende in a dunite matrix using the ChemCam test bed LIBS system. The LOD values determined for uranium transitions in air are 409.013 nm (24,700 ppm), 424.167 nm (23,780 ppm), 434.169 nm (24,390 ppm), 435.574 nm (35,880 ppm), 436.205 nm (19,340 ppm), 591.539 nm (47,310 ppm), and 682.692 nm (18,580 ppm). The corresponding LOD values determined for uranium transitions in 7 Torr CO2 are 424.167 nm (25,760 ppm), 434.169 nm (40,800 ppm), 436.205 nm (32,050 ppm), 591.539 nm (15,340 ppm), and 682.692 nm (29,080 ppm). The LOD values determine for uranium emission lines using the medium resolving power (10,000 λ/Δλ) LIBS system for the dunite matrix in air are 409.013 nm (6120 ppm), 424.167 nm (5356 ppm), 434.169 nm (5693 ppm), 435.574 nm (6329 ppm), 436.205 nm (2142 ppm), and 682.692 nm (10,741 ppm). The corresponding LOD values determined for uranium transitions in a SiO2 matrix are 409.013 nm (272 ppm), 424.167 nm (268 ppm), 434.169 nm (402 ppm), 435.574 nm (1067 ppm), 436.205 nm (482 ppm), and 682.692 nm (720 ppm). The impact of spectral resolution, atmospheric conditions, matrix elements, and measurement distances on LOD is discussed. The measurements will assist one in selecting the proper system components based upon the application and the required analytical performance.« less
    Cited by 10Full Text Available

"Cited by" information provided by Web of Science.

DOE PAGES offers free public access to the best available full-text version of DOE-affiliated accepted manuscripts or articles after an administrative interval of 12 months. The portal and search engine employ a hybrid model of both centralized and distributed content, with PAGES maintaining a permanent archive of all full text and metadata.