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Brown, G. V.

Publications and source records attributed to Brown, G. V..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Results from a synthetic model of the ITER XRCS-Core diagnostic based on high-fidelity x-ray ray tracing

A high-fidelity synthetic diagnostic has been developed for the ITER core x-ray crystal spectrometer diagnostic based on x-ray ray tracing. This synthetic diagnostic has been used to model expected performance of the diagnostic, to aid in diagnostic design, and to develop engineering tolerances. The synthetic model is based on x-ray ray tracing using the recently developed xicsrt ray tracing code and includes a fully three-dimensional representation of the diagnostic based on the computer aided design. The modeled components are: plasma geometry and emission profiles, highly oriented pyrolytic graphite pre-reflectors, spherically bent crystals, and pixelated x-ray detectors. Plasma emission profiles have been calculated for Xe 44+ , Xe 47+ , and Xe 51+ , based on an ITER operational scenario available through the Integrated Modelling & Analysis Suite database, and modeled within the ray tracing code as a volumetric x-ray source; the shape of the plasma source is determined by equilibrium geometry and an appropriate wavelength distribution to match the expected ion temperature profile. All individual components of the x-ray optical system have been modeled with high-fidelity producing a synthetic detector image that is expected to closely match what will be seen in the final as-built system. Particular care is taken to maintain preservation of photon statistics throughout the ray tracing allowing for quantitative estimates of diagnostic performance.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Electron collisional excitation cross-section measurements and modeling for select Ni-like to Ge-like gold transitions

We have experimentally determined the electron collisional excitation cross-sections for several 3d→4f and 3d→5f excitations in Ni- to Ge-like Au at energies of ~ 0.4, 1, 2, and 3 keV above threshold energy, E T , for the 3d→4f excitations ( E T ~ 2.5 keV) and ~ 0.2, 1, and 2 keV above threshold energy for the 3d→5f excitations ( E T ~ 3.3 keV). The cross-section measurements are possible by using the GSFC micro-calorimeter to record emission spectra from beam plasmas created in the Livermore EBIT-I electron beam ion trap. The cross-sections are experimentally determined from the ratio of the measured intensities of the collisionally excited lines to the intensities of the radiative recombination lines in monoenergetic electron distribution EBIT-I plasmas. The effects of polarization and Auger processes in the beam plasmas are accounted for in the cross-section determination. Experimentally determined cross-sections are compared with those from HULLAC, DWS, and FAC calculations. Finally, the measurements exhibit significant differences with the calculations of these excitation cross-sections.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Emission Lines of Fe xiv, Fe xv, and Fe xvi in the Extreme Ultraviolet Region 40–100 Å

We report on emission spectra of iron in the extreme ultraviolet recorded at an electron density of ~10 11 cm -3 on the Lawrence Livermore electron beam ion trap facility. We present a summary of the observed emission lines, including wavelengths and emission intensities, and present spectra of pure Fe xiv through Fe xvi emission derived from our measurements in the 40–100 Å wavelength range. We show that spectral models, especially the current version of CHIANTI v10.0, describe the M-shell emission from these three charge states of iron reasonably well, and we are able to verify several transitions in CHIANTI for the first time.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Recent enhancements in the performance of the Orion high-resolution x-ray spectrometers

During the past few years, the Orion high-resolution x-ray spectrometers have been successful tools for measuring x-ray spectra from plasmas generated in the Orion laser facility. Duplicate spectrometers also operate successfully at the Livermore EBIT-I and SuperEBIT electron beam ion traps for measuring x-ray polarization. We have recently implemented very high-quality, optically bonded, spherically bent quartz crystals to remove the structure in the x-ray image that had been observed in earlier measurements. The structure had been caused by focusing defects and limited the accuracy of our measurements. In this work, we present before and after images that show a drastic improvement. We, furthermore, have implemented a spherically bent potassium acid phthalate (KAP) crystal on one of our spectrometers. The KAP crystal was prepared in a similar fashion, and we present measurements of the N Ly-β and Ne Lyβ lines taken in first- and second-order reflections at 600 and 1200 eV, respectively. These measurements confirm that KAP crystals can be produced at a quality suitable for extending the spectral coverage to wavelengths longer than those accessible by different quartz crystals, especially those that cover the astrophysically important lines of iron.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

National Opacity Program: Analysis of Opacity-relevant X-ray Emission Spectra (Milestone Report ID 7121)

We have produced high energy density iron plasmas at temperatures above 1 keV and electron densities exceeding 1023 cm -3 (~ 1 g/cm 3 ) using the Orion laser at the Atomic Weapons Establishment. These plasmas were created by irradiating 50 µm diameter layered targets with frequency doubled (λ = 527 nm), 1 ps laser pulses focused to a 100 µm diameter producing an irradiance of ~ 2 x 10 18 W/cm 2 . The buried layer targets consist of 160 nm iron sulfide (FeS), 60 nm potassium chloride (KCl), and 15 nm carbon. The combined layers are tamped on both sides with 3 µm of parylene-N. The x-ray emission from the plasma was measured using two time-resolved, and four time-integrated Bragg crystal spectrometers, as well as one time-integrated imaging system. One time-resolved x-ray spectrometer measured emission from L-shell transitions in highly charged iron, the other from K-shell transitions in helium-like S 14+ and hydrogen-like S 15+ . The time-integrated spectrometers are intensity-calibrated and measured emission from K-shell transitions in sulfur, potassium, chlorine, and both K-shell and L-shell transitions in iron. The density and temperature of the plasma were determined by modeling the x-ray spectra using different spectral and hydrodynamic modeling packages. A brief overview of the uncertainties associated with the measurements and models are presented. We also give an overview of our 1-D HYDRA-DCA radiation-hydrodynamics model and improvements for future work. Our results aid in assessing experimental uncertainties associated with plasma uniformity and with x-ray emission employed as diagnostics in opacity experiments at temperatures and densities not achievable elsewhere and represent a significant step in creating and diagnosing plasmas near LTE. These results are summarized as part of the completion requirements for milestone 7121

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Absolute throughput calibration of multiple spherical crystals for the Orion High-REsolution X-ray spectrometer (OHREX)

We present absolute throughput analysis of several crystals for the Orion High-REsolution X-ray (OHREX) imaging crystal spectrometer using ray tracing and experimental measurements. The OHREX spectrometer is a high-resolution x-ray spectrometer designed to measure spectral line shapes at the Orion laser facility. The spectrometer is fielded with up to two spherical crystals simultaneously covering two independent spectral ranges. Each crystal has a nominal radius of curvature of R = 67.2 cm and is fielded at a nominal Bragg angle of 51.3°. To cover different bands of interest, several different crystals are available, including Ge (111), KAP, and several cuts of quartz, whose resolving power λ/Δλ exceeds 10 000. The calibrated response of the available crystals has previously been reported from measurements at the EBIT-I electron beam ion trap at Lawrence Livermore National Laboratory. Here, we model the absolute throughput of each crystal using ray tracing and verify the results using experimental data for the quartz $(10\bar{1}1)$ crystal.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

High-Precision Determination of Oxygen $K_{α}$ Transition Energy Excludes Incongruent Motion of Interstellar Oxygen

We demonstrate a widely applicable technique to absolutely calibrate the energy scale of x-ray spectra with experimentally well-known and accurately calculable transitions of highly charged ions, allowing us to measure the K-shell Rydberg spectrum of molecular O 2 with 8 meV uncertainty. Here, we reveal a systematic ~450 meV shift from previous literature values, and settle an extraordinary discrepancy between astrophysical and laboratory measurements of neutral atomic oxygen, the latter being calibrated against the aforementioned O 2 literature values. Because of the widespread use of such, now deprecated, references, our method impacts on many branches of x-ray absorption spectroscopy. Moreover, it potentially reduces absolute uncertainties there to below the meV level.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Measurements of inner-shell excited levels of Na-, Mg-, and Al-like europium on the LLNL EBIT

We report on a measurement of several n = 3 → n = 2 inner-shell transitions in sodiumlike, magnesiumlike, and aluminumlike europium, performed at the EBIT-I electron beam ion trap facility at the Lawrence Livermore National Laboratory using an x-ray calorimeter. Although the inner-shell x-ray lines of such M-shell ions are typically dominated by electric dipole allowed transitions, we have also identified a weak feature that appears to be the result of electric quadrupole decay in sodiumlike Eu 52+ . Here, we compare the measured transitions energies to the calculated values obtained using the flexible atomic code. We find agreement in most cases within 2 eV or better.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Transition energy measurements of the X-ray lines of neon-like europium

Here, we report the measurements of the n = 3 → n = 2 L-shell X-ray transitions of neon-like Eu 53+ . These include all seven allowed electric dipole (E1) transitions, five electric quadrupole (E2) transitions, and one magnetic quadrupole (M2) transition. The measurements were carried out at the EBIT-I electron beam ion trap facility at Livermore using an X-ray calorimeter. The measured values agree with many-body perturbation theory calculations within the experimental uncertainties. This includes the transitions that involve a 2s electron and that are, therefore, strongly affected by quantum electrodynamical effects.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Measurements and calculations of 2 s – 2 p transitions in neonlike germanium: Achieving agreement at the 10 – 4 level

Calculations that achieve spectroscopic accuracy, i.e., at the level of 10 –4 or better, are rare and typically restricted to few-electron systems. Here we present high-resolution grating spectrometer measurements of 11 2s 1/2 – 2p 3/2 transitions in neonlike Ge 22+ that distinguish between two different implementations of the many-body perturbation theory (MBPT) method, including our own. The measurements show that our implementation of the MBPT method consistently achieves spectroscopic accuracy at the 10 –4 level for all of the measured lines. Moreover, our calculations improve the 10 –3 accuracy of prior MBPT calculations by an order of magnitude and allow us to make greatly improved predictions of the location of potential photopumped lines in Ge 22+ . Here, the measurements also improve on previous measurements of 2s 1/2 – 2p 3/2 transitions in fluorinelike Ge 23+ and oxygenlike Ge 24+ . Measurements of n = 2 to n = 3 transitions in Al 7+ , Al 8+ , and Al 9+ are used to support our measurement accuracy at the 10 –5 level.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Polarization measurements of Ne-like Mo 32+ x-ray lines excited by an electron beam

We present polarization measurements of the $2{{\rm{p}}}^{5}3{\rm{d}}$ 1 P 1 → 2p 6 1 S 0 resonance line of Ne-like Mo 32+ , commonly known as 3C, as well as the $2{{\rm{p}}}^{5}3{\rm{d}}$ 3 D 1 → 2p 6 1 S 0 intercombination line, commonly known as 3D, as a function of the electron impact energy ranging from near threshold to 6 times threshold (2.75–15 keV). In addition, the x-ray line polarization of the $2{{\rm{p}}}^{5}3{\rm{p}}$ 3 D 2 → 2p 6 1 S 0 electric quadrupole forbidden line was measured at 3 and 4 keV. Excitation of these lines was achieved with the LLNL EBIT-I electron beam ion trap. The degree of polarization of the emission lines was derived by comparing spectra recorded with a flat Ge (111) crystal spectrometer, which is sensitive to polarization, to the spectra recorded by an x-ray calorimeter, which is insensitive to polarization. Here, the experimental measurements were compared to theoretical predictions produced using the Flexible Atomic Code, and good agreement was found.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Observation of He-like Satellite Lines of the H-like Potassium K xix Emission

We present measurements of the H-like potassium (K xix) X-ray spectrum and its He-like (K xviii) satellite lines, which are situated in the wavelength region between 3.34 and 3.39 Å, which has been of interest for the detection of dark matter. The measurements were taken with a high-resolution X-ray spectrometer from targets irradiated by a long-pulse (2 ns) beam from the Orion laser facility. Here, we obtain experimental wavelength values of dielectronic recombination satellite lines and show that the ratio of the Lyα lines and their dielectronic satellite lines can be used to estimate the electron temperature, which in our case was about 1.5 ± 0.3 keV.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

High-resolution measurements of Cl 15 + line shifts in hot, solid-density plasmas

The shifts of the 1s3p 1 P 1 → 1s 2 1 S 0 He-β transition of Cl 15+ were measured in hot (≥ 600 eV), dense (1–2 g/cm 3 ) plasmas generated by a (66–151)-J short-pulse laser beam at the Orion laser facility. The subpicosecond laser beam irradiated optically thin, KCl microdot targets buried in layers of plastic. The measured red shifts ranged from 4.8 ± 1.1 eV for unshocked to 5.9 ± 1.2 eV for shocked targets. Furthermore, these values are significantly smaller than recent predictions from a self-consistent-field ion-sphere model.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

High-resolution Charge Exchange Spectra with L-shell Nickel Show Striking Differences from Models

This work reports on the first high-resolution laboratory spectra of X-ray emission following L-shell charge exchange between nickel ions and neutral H 2 and He. We employ the commonly used charge exchange models found in xspec and spex, acx and spex-cx, to simulate our experimental results. We show that significant differences between data and models exist in both line energies and strengths. Specifically, we find that configuration mixing may play an important role in generating lines from core-excited states, and may be improperly treated in models. These conclusions imply that if applied to astrophysical data, these models may lead to incorrect assumptions of the physical and chemical parameters of the region of interest.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Measurements of the effective electron density in an electron beam ion trap using extreme ultraviolet spectra and optical imaging

In an electron beam ion trap (EBIT), the ions are not confined to the electron beam, but rather oscillate in and out of the beam. As a result, the ions do not continuously experience the full density of the electron beam. To determine the effective electron density, n e,eff , experienced by the ions, the electron beam size, the nominal electron density n e , and the ion distribution around the beam, i.e., the so-called ion cloud, must be measured. We use imaging techniques in the extreme ultraviolet (EUV) and optical to determine these. The electron beam width is measured using 3 d → 3 p emission from Fe xii and xiii between 185 and 205 Å. These transitions are fast and the EUV emission occurs only within the electron beam. The measured spatial emission profile and variable electron current yield a nominal electron density range of n e ~ 10 11 –10 13 cm –3 . We determine the size of the ion cloud using optical emission from metastable levels of ions with radiative lifetimes longer than the ion orbital periods. Here, the resulting emission maps out the spatial distribution of the ion cloud. We find a typical electron beam radius of ~60 μm and an ion cloud radius of ~300 μ m. These yield a spatially averaged effective electron density, ne,eff, experienced by the ions in EBIT spanning ~ 5 × 10 9 –5 × 10 11 cm –3 .

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

High resolution, high signal-to-noise crystal spectrometer for measurements of line shifts in high-density plasmas

The Orion high-resolution x-ray (OHREX) spectrometer has been a successful tool for measuring the shapes of density-broadened spectral lines produced in short-pulse heated plasmas at the Orion laser facility. We have recently outfitted the instrument with a charge-couple device (CCD) camera, which greatly increased the accuracy with which we can perform line-shift measurements. Because OHREX is located on the outside of the Orion target chamber, no provisions for the shielding of electromagnetic pulses are required. With the CCD, we obtained a higher signal-to-noise ratio than we previously obtained with an image-plate detector. As a result, this allowed us to observe structure in the image produced by the diffraction from the two OHREX crystals, which was highly reproducible from shot to shot. This structure will ultimately limit the accuracy of our spectroscopic measurements

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

The Warm Electron Beam Ion Trap (WEBIT): An instrument for ground calibration of space-borne x-ray spectrometers

The warm electron beam ion trap (WEBIT) at Lawrence Livermore National Laboratory is being developed as a pre-launch, ground calibration source for space-borne, high-throughput, high-resolution x-ray spectrometers, such as the x-ray imaging and spectroscopy mission Resolve quantum calorimeter. Historically, calibration sources for calorimeter spectrometers have relied on characteristic line emission from x-ray tubes, fluorescing metals, and radioactive sources. The WEBIT, by contrast, relies on emission from x-ray transitions in highly charged ions, for example, hydrogen-like and helium-like ions, whose energies are well known and whose line shapes are relatively simple. The WEBIT can create astrophysically relevant ions whose x-ray emission falls in the 0.3-12 keV science bandpass of Resolve and has a portable design advantageous for a calibration source. The WEBIT will be used to help calibrate Resolve’s instrumental line shape and gain scale as a function of various operational parameters during both detector subsystem level testing and instrumental level testing.

47 OTHER INSTRUMENTATION↗