In this Review Article, we discuss a range of soft x-ray power diagnostics at inertial confinement fusion (ICF) and pulsed-power fusion facilities. This Review Article describes current hardware and analysis approaches and covers the following methods: x-ray diode arrays, bolometers, transmission grating spectrometers, and associated crystal spectrometers. These systems are fundamental for the diagnosis of ICF experiments, providing a wide range of critical parameters for the evaluation of fusion performance.

During inertial confinement fusion experiments at the National Ignition Facility (NIF), a capsule filled with deuterium and tritium (DT) gas, surrounded by a DT ice layer and a high-density carbon ablator, is driven to the temperature and densities required to initiate fusion. In the indirect method, 2 MJ of NIF laser light heats the inside of a gold hohlraum to a radiation temperature of 300 eV; thermal x rays from the hohlraum interior couple to the capsule and create a central hotspot at tens of millions degrees Kelvin and a density of 100-200 g/cm3. During the laser interaction with the gold wall, m-band x rays are produced at ∼2.5 keV; these can penetrate into the capsule and preheat the ablator and DT fuel. Preheat can impact instability growth rates in the ablation front and at the fuel-ablator interface. Monitoring the hohlraum x-ray spectrum throughout the implosion is, therefore, critical; for this purpose, a Multilayer Mirror (MLM) with flat response in the 2-4 keV range has been installed in the NIF 37° Dante calorimeter. Precision engineering and x-ray calibration of components mean the channel will report 2-4 keV spectral power with an uncertainty of ±8.7%.

We describe a joint experimental and theoretical investigation on oxygen double photoionization-the emission of two electrons from atomic oxygen following single photon absorption. High-resolution experimental measurements were performed at the Advanced Light Source, revealing sharp resonance structure superimposed on the more familiar Wannier-like, nearly-linear background. These resonance features are attributed to ionization-plus-excitation Feshbach resonances embedded in the double ionization continuum, doubly-excited states that lie above the double-ionization threshold. Such features are absent in the double photoionization cross section of He, or other quasi-two-electron systems, for which the doubly-ionized atomic core remains inert. For a corresponding theoretical analysis, the R-matrix with pseudostates (RMPS) method was invoked by calculating final-state, two-electron resonances-plus-continua wavefunctions and corresponding single-photon absorption cross sections. Overall agreement is found in the direct, background double photoionization cross section. However, the RMPS method, using a small basis due to practical computational limitations, was unable to reproduce quantitatively the smooth background or the sharper resonance features observed in the measurements, showing instead large-scale oscillations about the experimental background, and characteristic pseudoresonance jitter, associated with an insufficient convergence of the pseudostate representation to the true two-electron infinite series of Feshbach resonances embedded in the two-electron continuum. The prominent resonance structure observed highlights the need to consider multiple excitation processes in atoms more complex than He or quasi-two-electron systems.

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. 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.

Verification of physics models and computer simulations are heavily reliant upon the accuracy of experimental measurements. Calibration of instrument responses becomes an important step to achieve this goal. This paper presents systematic studies of bent potassium acid phthalate (KAP) crystals using Lawrence Berkeley National Laboratories, Advanced Light Source, beamline 9.3.1 in the energy range of 2.3 to 7.5 keV. A set of KAP crystals, gradually bent from flat up to a 50.8 mm cylindrical curvature. The measured integrated reflectivity for this set of KAP crystals shows good agreement with the X-ray Oriented Program (XOP) calculations when adjusting the Debye-Waller temperature factor and using the multilamellar model in the calculations. Significant differences in rocking curve profiles were observed between experimental measurements and theory. A forward convolution model and software code were developed to include experimental parameters, allowing the investigation of the difference between measurements and calculations. After considering the experimental parameters, good agreements were obtained for the rocking curve profiles for all bending radii with a unique set of parameters. Our results show that XOP can be a useful and reliable tool to predict performance of cylindrically bent KAP crystals in this energy range.

The Fe/MgO magnetic tunnel junction is a classic spintronic system, with current importance technologically and interest for future innovation. The key magnetic properties are linked directly to the structure of hard-to-access buried interfaces, and the Fe and MgO components near the surface are unstable when exposed to air, making a deeper probing, nondestructive, in-situ measurement ideal for this system. We have thus applied hard x-ray photoemission spectroscopy (HXPS) and standing-wave (SW) HXPS in the few kilo-electron-volt energy range to probe the structure of an epitaxially grown MgO/Fe superlattice. The superlattice consists of 9 repeats of MgO grown on Fe by magnetron sputtering on an MgO(001) substrate, with a protective Al2O3 capping layer. We determine through SW-HXPS that 8 of the 9 repeats are similar and ordered, with a period of 33 ± 4 Å, with the minor presence of FeO at the interfaces and a significantly distorted top bilayer with ca. 3 times the oxidation of the lower layers at the top MgO/Fe interface. There is evidence of asymmetrical oxidation on the top and bottom of the Fe layers. We find agreement with dark-field scanning transmission electron microscope (STEM) and x-ray reflectivity measurements. Through the STEM measurements, we confirm an overall epitaxial stack with dislocations and warping at the interfaces of ca. 5 Å. We also note a distinct difference in the top bilayer, especially MgO, with possible Fe inclusions. We thus demonstrate that SW-HXPS can be used to probe deep buried interfaces of novel magnetic devices with few-angstrom precision.

The fragmentation of the tetrachloromethane molecule following core-shell photoexcitation and photoionization in the neighborhood of the chlorine K-edge has been studied by using time-of-flight mass spectroscopy and monochromatic synchrotron radiation. Branching ratios for ionic dissociation were derived for all the detected ions, which are informative of the decay dynamics and photofragmentation patterns of the core-excited species. In addition, the absorption yield has been measured with a new assignment of the spectral features. The structure that appears above the Cl 1s ionization potential in the photoionization spectrum has been ascribed to the existing connection with electron-CCl4 scattering through experimental data and calculations for low-energy electron-molecule cross sections. In addition, the production of the doubly ionized Cl fragment, Cl2+, as a function of the photon energy has been analysed in the terms of a simple and an appealing physical picture, the half-collision model.

Inner-shell ionization of a 1s electron by either photons or electrons is important for X-ray photoionized objects such as active galactic nuclei and electron-ionized sources such as supernova remnants. Modeling and interpreting observations of such objects requires accurate predictions for the charge state distribution (CSD), which results as the 1s-hole system stabilizes. Due to the complexity of the complete stabilization process, few modern calculations exist and the community currently relies on 40-year-old atomic data. Here, we present a combined experimental and theoretical study for inner-shell photoionization of neutral atomic nitrogen for photon energies of 403-475 eV. Results are reported for the total ion yield cross section, for the branching ratios for formation of N+, N2+, and N3+, and for the average charge state. We find significant differences when comparing to the data currently available to the astrophysics community. For example, while the branching ratio to N2+ is somewhat reduced, that for N+ is greatly increased, and that to N3+, which was predicted to be zero, grows to approximate to 10% at the higher photon energies studied. This work demonstrates some of the shortcomings in the theoretical CSD data base for inner-shell ionization and points the way for the improvements needed to more reliably model the role of inner-shell ionization of cosmic plasmas.

The interfaces between two condensed phases often exhibit emergent physical properties that can lead to new physics and novel device applications and are the subject of intense study in many disciplines. We here apply experimental and theoretical techniques to the characterization of one such interesting interface system: the two-dimensional electron gas (2DEG) formed in multilayers consisting of SrTiO3 (STO) and GdTiO3 (GTO). This system has been the subject of multiple studies recently and shown to exhibit very high carrier charge densities and ferromagnetic effects, among other intriguing properties. We have studied a 2DEG-forming multilayer of the form [6 unit cells (u.c.) STO/3 u.c. of GTO](20) using a unique array of photoemission techniques including soft and hard x-ray excitation, soft x-ray angle-resolved photoemission, core-level spectroscopy, resonant excitation, and standing-wave effects, as well as theoretical calculations of the electronic structure at several levels and of the actual photoemission process. Standing-wave measurements below and above a strong resonance have been exploited as a powerful method for studying the 2DEG depth distribution. We have thus characterized the spatial and momentum properties of this 2DEG in detail, determining via depth-distribution measurements that it is spread throughout the 6 u.c. layer of STO and measuring the momentum dispersion of its states. The experimental results are supported in several ways by theory, leading to a much more complete picture of the nature of this 2DEG and suggesting that oxygen vacancies are not the origin of it. Similar multitechnique photoemission studies of such states at buried interfaces, combined with comparable theory, will be a very fruitful future approach for exploring and modifying the fascinating world of buried-interface physics and chemistry.

X-ray absorption spectroscopy is a unique experimental technique that can provide ground state electronic structure information about transition metal complexes with unoccupied d-manifold. The quantitative treatments of pre-edge and rising-edge features have already been developed for the sulfur- and chlorine-ligand K-edge excitations. The complementarity of using multiple core excitation edges from hard, tender, and soft X-ray energy regions has been defined for the first paper of this series. The given study provides compelling evidence for the transferability of the empirical transition dipole integral from ligand K-edge to metal L-edge and back to ligand K-edge in the tender X-ray energy range. The case study was performed for a series of homoleptic chloropalladium compounds at the chlorine K- and palladium L-edges. We propose the method described here to be generally applicable for other core level excitations, where complementarity of ground state electronic structural information from XANES analysis can provide the complete electronic structure description.

The presence and role of polysulfide radicals in the electrochemical processes of lithium sulfur (Li–S) batteries is currently being debated. Here, first‐principles interpretations of measured X‐ray absorption spectra (XAS) of Li–S cells are leveraged with an ether‐based electrolyte. Unambiguous evidence is found for significant quantities of polysulfide radical species (LiS3, LiS4, and LiS5), including the trisulfur radical anion S3 −, present after initial discharge to the first discharge plateau, as evidenced by a low energy shoulder in the S K‐edge XAS below 2469 eV. This feature is not present in the XAS of cells at increased depth of discharge, which, by our analysis, exhibit increasing concentrations of progressively shorter polysulfide dianions. Through a combination of first‐principles molecular dynamics and associated interpretation of in situ XAS of Li–S cells, atomic level insights into the chemistries are provided that underlie the operation and stability of these batteries.

We present the first-ever measurement of nondipole chiral angular distribution parameters for C 1s photoemission from each enantiomer of camphor in the photon energy range 296-343eV using linearly polarized light. The angular distribution parameters are determined to be enantiomer-specific, suggesting a new form of linear dichroism.

The presence and role of polysulfide radicals in the electrochemical processes of lithium sulfur batteries (Li-S) is currently being debated. In particular, the radical trisulfur anion, S 3 .- , has concurrently been purported as a key species or has been discounted as existing during battery operation. 1,2 While radical species could be formed via a direct electrochemical pathway, the prevailing assumption is formation via the dissociation of Li 2 S 6 to LiS 3 . 3 It is unclear how critical the formation of polysulfide radical anions is to the remaining redox pathways. 4 It is not known if the radicals are an essential intermediate for complete reduction of sulfur (or complete oxidation of Li 2 S). In addition, the concentration of radical anions relative to polysulfide dianion species (Li 2 S x ) formed during redox reactions has not yet been quantified. Recently, X-ray absorption spectroscopy (XAS) has been utilized to probe Li-S reaction mechanisms. 2,4,5 If properly interpreted, sulfur K-edge XAS can provide powerful insights into the molecular species formed during the charge and discharge reactions of the Li-S battery. The challenge of interpreting spectroscopic data of Li-S chemistry has been the lack of spectral standards for isolated polysulfide species. Due to possible spontaneous polysulfide disproportionation and the establishment of equilibrium mixtures in solution, establishing standards for specific molecular species is necessarily complicated, if not impossible. As a result, fingerprinting is frequently performed using solid analogs, which may induce errors in the analysis since the correspondence between the solid and solution phase XAS is by no means guaranteed. A recent advance towards establishing standards, and thus atomistic interpretations of XAS experimental measurements, has been the use of electronic structure methods based on density functional theory (DFT). In a previous work we demonstrated that the XAS of dissolved lithium polysulfide dianion species and various polysulfide radicals can be obtained via first-principles molecular dynamics and DFT spectral simulations. 7,8 In this work, XAS was performed on Li-S cells containing an ether-based electrolyte. Cells were discharged to various depths and probed using XAS at the sulfur K-edge. First principles calculations were performed to obtain XAS of single polysulfide molecules. These theoretical spectra were then used to determine the distribution of polysulfide species present in the battery electrolyte. 6 This analysis revealed the presence of polysulfide radical anions in significant concentrations after early stages of discharge. Whereas previous studies probed the sulfur cathode in an attempt to directly examine the charge and discharge reaction processes, this present study explores a different question, also pertinent to Li-S cells: if cell discharge were stopped at specific points in the discharge process, what intermediate species would be present in the battery electrolyte after ample time has been given for polysulfide dissolution to occur? This question is of some importance, as real-world consumer batteries will be stopped and started as the user chooses so that it would be useful to know what species can be expected in the battery electrolyte if dissolution were to occur. Our results provide further insight into the discharge and disproportionation reactions that take place in the electrolyte during cycling. References 1. C. Barchasz, F. Molton, C. Duboc, J.-C. Leprêtre, S. Patoux, F. Alloin, Analytical Chemistry, 84 (2012) 3973. 2. M. Cuisinier, P. E. Cabelguen, B. D. Adams, A. Garsuch, M. Balasubramanian, L. F. Nazar, Energy & Environmental Science, 7 ( 2014 ) 2697. 3. D.-H. Han, B.-S. Kim, S.-J. Choi, Y. Jung, J. Kwak, S.-M. Park, Journal of The Electrochemical Society, 151 ( 2004 ) E283. 4. M. Cuisinier, C. Hart, M. Balasubramanian, A. Garsuch, L. F. Nazar, Advanced Energy Materials, 1401801 ( 2015 ). 5. T. A. Pascal, K. H. Wujcik, J. Velasco-Velez, C. Wu, A. A. Teran, M. Kapilashrami, J. Cabana, J. Guo, M. Salmeron, N. Balsara, D. Prendergast, The Journal of Physical Chemistry Letters, 5 ( 2014 ) 1547. 6.K. H. Wujcik, T. A. Pascal, D. Devaux, D. Prendergast, N. P. Balsara, Advanced Energy Materials, In revision ( 2015 ). 7. K. H. Wujcik, J. Velasco-Velez, C. H. Wu, T. Pascal, A. A. Teran, M. A. Marcus, J.Cabana, J. Guo, D. Prendergast, M. Salmeron, N. P. Balsara, Journal of The Electrochemical Society, 161 ( 2014 ) A1100. 8. T. A. Pascal, C. D. Pemmaraju, D. Prendergast, Physical Chemistry Chemical Physics, In Revision ( 2015 ).

The photo-fragmentation of the dimethyl sulfoxide (DMSO) molecule was studied using synchrotron radiation and a magnetic mass spectrometer. The total cationic yield spectrum was recorded in the photon energy region around the sulfur K edge. The sulfur composition of the highest occupied molecular orbital's and lowest unoccupied molecular orbital's in the DMSO molecule has been obtained using both ab initio and density functional theory methods. Partial cation and anion-yield measurements were obtained in the same energy range. An intense resonance is observed at 2475.4 eV. Sulfur atomic ions present a richer structure around this resonant feature, as compared to other fragment ions. The yield curves are similar for most of the other ionic species, which we interpret as due to cascade Auger processes leading to multiply charged species which then undergo Coulomb explosion. The anions S(-), C(-), and O(-) are observed for the first time in deep-core-level excitation of DMSO.

8:20am AC+AS+MI+SA+SS-MoM1 Novel Synthetic and Spectroscopic Techniques in Actinide Materials Chemistry, Stefan Minasian, Lawrence Berkeley National Laboratory, E. Batista, Los Alamos National Laboratory, C.H. Booth, Lawrence Berkeley National Laboratory, D. Clark, Los Alamos National Laboratory, J. Keith, Colgate University, W. Lukens, Lawrence Berkeley National Laboratory, S. Kozimor, R.L. Martin, Los Alamos National Laboratory, D. Nordlund, SLAC National Accelerator Laboratory, D. Shuh, T. Tyliszczak, Lawrence Berkeley National Laboratory, D. Sokaras, SLAC National Accelerator Laboratory, X.-D. Weng, Los Alamos National Laboratory, T.-C. Weng, SLAC National Accelerator Laboratory INVITED The development of a detailed, quantitative understanding of electronic structure and bonding for a broad range actinide materials remains a significant scientific challenge. Recent advances have shown that the 1s to np transition intensities measured by Cl and S K-edge X-ray absorption spectroscopy (XAS) directly relate to coefficients of covalent orbital mixing in M–Cl and M–S bonds. The scientific progress associated with these Cl and S XAS studies suggests that using synchrotron-generated radiation to quantify covalency for ligands beyond Cl and S would have a wide impact. The nature of chemical bonds between actinides and light atoms such as oxygen, nitrogen, and carbon is of particular interest because these interactions control the physics and chemistry of many technologically important processes in nuclear science. However, obtaining accurate light atom K-edge XAS spectra on non-conducting compounds is notoriously difficult, because the measurement is highly sensitive to surface contamination, self-absorption, and saturation effects. Fortunately, recent upgrades at synchrotron facilities, advancements in beamline instrumentation, and sample preparation methods suggest that these insights are now within reach. Specifically, comparing XAS spectra measured in transmission with a scanning transmission X-ray microscope (STXM) with those from non-resonant inelastic X-ray scattering (NIXS) and timedependent density functional theory provides a sound basis for validation of bulk-like excitation spectra.

The 2013 ALS User Meeting, held from October 7–9, began with a welcome from Users' Executive Committee chair Corie Ralston and Berkeley Lab director Paul Alivisatos. ALS director Roger Falcone followed with a “state of the ALS” presentation that reminded everyone of the ALS mission: “Supporting users in doing outstanding science in a safe environment.” Falcone gave the 400-plus meeting attendees an update on ALS beamlines, which included good news about increased user numbers thanks to the new RAPIDD access system, enhanced robotics, and remote capabilities. Falcone reflected that ALS metrics continue to represent the highly productive users—the number of journal articles and papers per user based on ALS research has continued to grow in the past year. Looking forward, Falcone touched on how a proposed ALS upgrade to a diffraction-limited light source would increase scientific capabilities. The Lab's government relations representative, Don Medley, followed with a presentation on how to talk about science with elected representatives. Medley spoke about framing discussions in terms of the “value of our country's science ecosystem.”