Density measurements for the National Ignition Facility (NIF) opacity platform.

The Opacity Platform on the National Ignition Facility (NIF) has been developed to measure opacities at varying densities and temperatures relevant to the solar interior and thermal cooling rates in white dwarf stars. The typical temperatures reached at NIF range between 150 and 210 eV, which allow these measurements to be performed experimentally. The captured opacities are crucial to validating radiation-hydrodynamic models that are used in astrophysics. The NIF opacity platform has a unique new capability that allows in situ measurement of the sample expansion. The sample expansion data are used to better understand the plasma conditions in our experiments by inferring the sample density throughout the duration of the laser drive. We present the details of the density measurement technique, data analysis, and recent results for Fe and MgO.

Use of computer vision for analysis of image datasets from high temperature plasma experiments.

Great strides have been made in improving the quality of x-ray radiographs in high energy density plasma experiments, enabled in part by innovations in engineering and manufacturing of integrated circuits and materials. As a consequence, the radiographs of today are filled with a great deal of detail, but few of these features are extracted in a systematic way. Analysis techniques familiar to plasma physicists tend toward brittle 1D lineout or Fourier transform type analyses. The techniques applied to process our data have not kept pace with improvements in the quality of our data. Fortunately, the field of computer vision has a wealth of tools to offer, which have been widely used in industrial imaging and, more recently, adopted in biological imaging. We demonstrate the application of computer vision techniques to the analysis of x-ray radiographs from high energy density plasma experiments, as well as give a brief tutorial on the computer vision techniques themselves. These tools robustly extract 2D contours of shocks, boundaries of inhomogeneities, and secondary flows, thereby allowing for increased automation of analysis, as well as direct and quantitative comparisons with simulations.

DANTE as a primary temperature diagnostic for the NIF iron opacity campaign.

The Opacity Platform on the National Ignition Facility (NIF) has been developed to measure iron opacities at varying densities and temperatures relevant to the solar interior and to verify recent experimental results obtained at the Sandia Z-machine, that diverge from theory. The first set of NIF experiments collected iron opacity data at ∼150 eV to 160 eV and an electron density of ∼7 × 1021 cm-3, with a goal to study temperatures up to ∼210 eV, with electron densities of up to ∼3 × 1022 cm-3. Among several techniques used to infer the temperature of the heated Fe sample, the absolutely calibrated DANTE-2 filtered diode array routinely provides measurements of the hohlraum conditions near the sample. However, the DANTE-2 temperatures are consistently low compared to pre-shot LASNEX simulations for a range of laser drive energies. We have re-evaluated the estimated uncertainty in the reported DANTE-2 temperatures and also the error generated by varying channel participation in the data analysis. An uncertainty of ±5% or better can be achieved with appropriate spectral coverage, channel participation, and metrology of the viewing slot.

Erratum: Measurement of Preheat Due to Nonlocal Electron Transport in Warm Dense Matter [Phys. Rev. Lett. 120, 025002 (2018)].

This corrects the article DOI: 10.1103/PhysRevLett.120.025002.

Implementation of a 1-2 keV point-projection x-ray spectrometer on the National Ignition Facility.

A point-projection soft X-ray Opacity Spectrometer (OpSpec) has been implemented to measure X-ray spectra from ∼1 to 2 keV on the National Ignition Facility (NIF). Measurement of such soft X-rays with open-aperture point-projection detectors is challenging because only very thin filters may be used to shield the detector from the hostile environment. OpSpec diffracts X-rays from 540 to 2100 eV off a potassium (or rubidium) acid phthalate (KAP or RbAP) crystal onto either image plates or, most recently, X-ray films. A "sacrificial front filter" strategy is used to prevent crystal damage, while 2 or 3 rear filters protect the data. Since May 2017, OpSpec has been recording X-ray transmission data for iron-magnesium plasmas on the NIF, at "Anchor 1" plasma conditions (temperature ∼150 eV, density ∼7 × 1021 e -/cm3). Upgrades improved OpSpec's performance on 6 NIF shots in August and December 2017, with reduced backgrounds and 100% data return using filter stacks as thin as 2.9 µm (total). Photometric noise is beginning to meet requirements, and further work will reduce systematic errors.

Measurement of Preheat Due to Nonlocal Electron Transport in Warm Dense Matter.

This Letter presents a novel approach to study electron transport in warm dense matter. It also includes the first x-ray Thomson scattering (XRTS) measurement from low-density CH foams compressed by a strong laser-driven shock at the OMEGA laser facility. The XRTS measurement is combined with velocity interferometry (VISAR) and optical pyrometry (SOP) providing a robust measurement of thermodynamic conditions in the shock. Evidence of significant preheat contributing to elevated temperatures reaching 17.5-35 eV in shocked CH foam is measured by XRTS. These measurements are complemented by abnormally high shock velocities observed by VISAR and early emission seen by SOP. These results are compared to radiation hydrodynamics simulations that include first-principles treatment of nonlocal electron transport in warm dense matter with excellent agreement. Additional simulations confirm that the x-ray contribution to this preheat is negligible.

Atomic physics modeling of transmission spectra of Sc-doped aerogel foams to support OMEGA experiments.

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 (ScSi6O12 at 75 mg/cm3 density). We have determined that in the 50-200 eV Te range there is a significant difference in the 1s-3p spectra, especially below 100 eV, and for Te = 200 eV above 5000 eV in photon energy. Examining synthetic spectra generated using OPLIB with 300 resolving power reveals spectral sensitivity to Te changes of ∼3 eV.

Infant feeding practices in the first 24-48 h of life in healthy term infants.

AIM: To examine in-hospital infant feeding practices, focusing on initiation and prevalence of breastmilk expression and to describe the proportion of women having a breast pump immediately after birth. METHODS: Postpartum women were recruited from three hospitals in Melbourne, Australia, between 2009 and 2011. INCLUSION CRITERIA: having had a healthy singleton term infant, intending to breastfeed and fluency in English. Data were collected using a structured questionnaire. RESULTS: Just over 1000 women were recruited at 24-48 h postpartum; 50% were primiparous. Forty-seven per cent of infants had been fully breastfeeding at the breast from birth, and another 47% had received at least some expressed breastmilk. Forty per cent of first-time mothers reported having had a problem breastfeeding, and 46% already had a breast pump prior to the birth of their infant. CONCLUSIONS: Early breastfeeding problems were common, and less than half the infants had fed only at the breast in the first days of life. Given the normalization of breastmilk expression, more evidence is needed regarding the impact of expressing on duration of breastmilk feeding and maternal health outcomes.