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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Optical and mass-spectral characterization of mixed-gas flowing atmospheric-pressure afterglow sources

Plasma-based ambient desorption/ionization (ADI) sources for mass spectrometry (MS) often use helium as the primary discharge gas due to the large reaction cross section of excited helium species with atmospheric gases, which ultimately leads to efficient reagent-ion formation. However, some studies have shown that mixed-gas plasmas provide unique advantages. For instance, our group showed that a helium-oxygen flowing atmospheric-pressure afterglow (He:O 2 -FAPA) source yielded enhanced ion signals for small polar analytes, but compounds with aromatic rings underwent chemical modification to produce pyrylium species. Here, it is shown that the addition of H 2 to the helium FAPA gas significantly decreased the reagent-ion signals, but analyte-ion signal was not affected to the same degree. In addition, mass spectra obtained with He:H 2 -FAPA were chemically cleaner with fewer ions stemming from analyte species and produced less oxidation of analytes. Addition of nitrogen increased the abundance of negative reagent ions (e.g., NO 2 - and NO 3 - ) which led to enhanced ion signal for RDX. To better understand these unique advantages of a mixed-gas FAPA, the impact of molecular-gas (O 2 , N 2 , or H 2 ) addition on the optical-emission spectra from the discharge was also measured. Spatially resolved emission was obtained from the anode- and negative-glow regions. In general, addition of small fractions (~0.1%) of molecular gases decreased helium and OH emission intensities. Atomic oxygen and hydrogen emission increased with the addition of O 2 and H 2 , respectively. Furthermore, emission characteristics of N 2 , N 2 + , and NO with respect to molecular gas composition on He-FAPA were measured. Finally, fundamental plasma parameters, such as OH rotational temperature (T rot ), were also calculated for these mixed-gas systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Understanding interfacial chemistry of positive bias high-voltage degradation in photovoltaic modules

Photovoltaic module degradation from a high system voltage is a prevalent degradation mode in the field, where the enabling degradation mechanisms are inherently dependent on the voltage bias polarity of the installed system. In this study, the effects of positive bias on module performance are confirmed and the underlying chemical degradation processes are more thoroughly investigated to reveal different degradation pathways from those previously reported in negative bias studies. When cells are under +1000 V stress, crystalline silicon mini-modules with poly(ethylene-co-vinyl acetate) (EVA) encapsulant demonstrated a significant photocurrent loss due to EVA discoloration and delamination from increased chemical reactivity at the front-side EVA/cell metallization interface. Brown discoloration of the EVA encapsulant near the cell gridlines is linked to an electrochemical reaction at the Ag gridlines under hot and humid conditions (85 °C, 85% relative humidity). Chemical compositional analysis using X-ray photoelectron spectroscopy (XPS) confirmed that the discoloration is attributed to the formation of silver sulfide (Ag 2 S) and/or silver oxide (Ag 2 O) species at the EVA/Ag gridline interface. The subsequent migration of Ag ions from the cell gridlines into the bulk of the EVA was evident from XPS depth profiling and optical microscopy. However, the Ag signal was not detected at the EVA/glass interface, inferring limited ionic transport through the nominally 0.45 mm thick encapsulant. For the samples studied herein, the sulfur is believed by the process of elimination to come from the ambient air, diffusing into the module through the permeable polymer backsheet.

14 SOLAR ENERGY↗
DOE OSTI2025

New generation bunch shape monitor for ion accelerators

Measuring longitudinal beam parameters is important for operation and development of high intensity linear accelerators, but it is notoriously difficult for proton and ion beams at non-relativistic energies. The Bunch Shape Monitor (BSM) is a device used for measuring the longitudinal bunch distribution in ion linacs. The existing BSM models have poor electron collection efficiency from the wire and are limited to one-dimensional measurements of the phase coordinate. In response to this problem, we have developed a new generation BSM with improved performance. The proposed design incorporates three major innovations: First, the collection efficiency was improved by adding a focusing field between the wire and the entrance slit, which will also allow measurements over a much wider dynamic range. Second, an improvement in the measurement speed was achieved by sampling longitudinal profiles of multiple energy slices simultaneously, where the BSM wire is placed at the exit of an ion spectrometer so that ions with different energies hit the wire at different horizontal coordinates along the wire. Finally, the design incorporates a motion system that can shift the wire and deflecting cavity together, enabling transverse profile measurements like a wire scanner. Here, in this paper, we will provide the design of the new BSM and report on its beam test results at the Spallation Neutron Source facility in Oak Ridge National Laboratory.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Compensation of residual amplitude modulation fluctuations in an optoelectronic system for laser radiation frequency stabilisation

Fluctuations of residual amplitude modulation in a scheme of laser frequency stabilisation by a Fabry – Perot cavity reduce the frequency stability of the laser systems intended for interrogating clock transitions of atoms and ions. The dependences of the residual amplitude modulation on a temperature of the waveguide-based electro-optical modulator used for modulating the radiation phase and on polarisation of the radiation are measured. The parameters are found, at which the influence of the residual amplitude modulation on the frequency stability is minimal. A system for active compensation is created, which reduces the contribution of fluctuations of residual amplitude modulation to the instability down to 2.1 × 10{sup −16}, which makes it possible to reach the thermal noise limit of a silicon cryogenic cavity. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Towards C P -violation studies on superheavy molecules: Theoretical and experimental perspectives

Molecules containing superheavy atoms can be artificially created to serve as sensitive probes to study symmetry-violating phenomena. Here, we provide detailed theoretical studies of quantities relevant to the electron electric dipole moment (eEDM) and nucleus-electron scalar-pseudoscalar interactions in diatomic molecules containing superheavy lawrencium nuclei. The sensitivity to parity and time (or, equivalently, CP) reversal violating properties is studied for different neutral and ionic molecules. The effective electric fields in these systems are found to be about 3–4 times larger than other known molecules on which eEDM experiments are being performed. Similarly, these superheavy molecules exhibit an enhancement of more than 3 times for CP-violating scalar-pseudoscalar nucleus-electron interactions. Our preliminary analysis using the Woods-Saxon nuclear model also demonstrates that these results are sensitive to the diffuse surface interactions inside the Lr nucleus. We also briefly comment on some experimental aspects by discussing the production of these systems.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2025

Stability, electronic quantum states, and magnetic interactions of Er 3+ ions in Ga 2 ⁢O 3

Here, we report an ab initio study of phase stability, defect formation, electronic structure, and multiple magnetic, Dzyaloshinskii-Moriya, optical, hyperfine, and crystal field interactions in erbium (Er)-doped wide band gap 𝛼- and 𝛽-gallium oxides (Ga 2 ⁢O 3 ), critically important to make a foundation for both optoelectronic and quantum information applications. The chemical, structural, mechanical, and dynamical stabilities of the pristine phases are confirmed from respective negative formation energies, negative cohesive energies, favorable elastic constants, and positive phonon frequencies. The phonon dispersions indicate that the Ga-O bonds are uniform in the 𝛼-phase, while they vary in the 𝛽-phase due to the anisotropic polyhedral movement. The defect formation energy analysis confirms that both Er-doped 𝛼- and 𝛽−Ga 2 ⁢O 3 prefer Er 3+ (neutral) state. The underestimated band gaps of the pristine phases from standard density functional theory (DFT) calculations as compared to experimental values are corrected by employing the hybrid functional calculations, resulting in the indirect band gaps of 5.21 eV in 𝛼−Ga 2 ⁢O 3 and 4.94 eV in 𝛽−Ga 2 ⁢O 3 . The site preference energy analysis indicates partial occupation of Er in the octahedral site of Ga. The anisotropic nature of hyperfine tensor coefficients of Er is similar in both phases, which may be due to the occupation of Er in the same octahedral Ga site. On the other hand, the calculated magnetic exchange interaction between two Er dopants is negative for 𝛼 and positive for 𝛽, indicating an antiferromagnetic (AFM) ground state in the former and a ferromagnetic (FM) ground state in the latter. Large values of Dzyaloshinskii-Moriya interactions (DMIs) are obtained along the 𝑥 direction in the 𝛼 and along the 𝑦 direction in the 𝛽. The large DMI may support exotic magnetic textures, a promising direction for spintronic applications. The analysis of dielectric constants and refractive indices of both pristine and Er-doped phases shows a good agreement with available experimental values. The calculated optical anisotropy is slightly higher in 𝛽 than those in 𝛼, which is due to the involvement of lower symmetry in 𝛽. The crystal field coefficients (CFCs) calculated from DFT are used to analyze 4⁢𝑓 multiplets and 4⁢𝑓 −4⁢𝑓 transitions. Thus calculated lowest energy level of the first excited state to the lowest energy level of the ground state is about 1.53 µ⁢m, which is in a good agreement with available experiments, and it falls within the quantum telecommunication wavelength range.

3-dimensional systems↗
DOE OSTI2020

Improved control of electron computer-generated holographic grating groove profiles using ion beam gas-assisted etching

In a transmission electron microscope, electrons are described by matter-waves with wavelengths five orders of magnitude smaller than optical electromagnetic waves. Analogous to optical holography, electron wavefronts can be shaped using nanoscale holographic gratings. Here we demonstrate a novel, scalable nanofabrication method for creating off-axis holographic gratings that demonstrate near ideal diffraction efficiencies for binary, sinusoidal, and blazed grating groove profiles. We show that this method can produce up to 50 µm diameter area gratings that diffract up to 68% of the transmitted electron wave into a desired diffraction order with less than 7% into any other order. Additionally, we find that the amount of inelastically scattered electrons from the material gratings remaining in the coherent diffraction orders from the gratings is negligible in the far field.

Johnson, Cameron W.↗
DOE OSTI2025

Impact of high-temperature annealing on hafnia-silica composite coatings deposited via ion beam sputtering for high-peak power 1064 nm lasers

The maximum power handling fluence of high-peak and average power laser systems is often limited by the laser damage of the coatings on optical components. Furthermore, these multilayer dielectric coatings are limited in their maximum power handling due to laser-damage-prone defects in the lower optical bandgap, higher optical index material. Some of these defects can be mitigated by thermal annealing to high temperatures, which can greatly reduce the linear absorbative precursors. Typically, hafnia and silica are the materials of choice for high-peak and average power laser systems in the ultraviolet through infrared spectral range; however, hafnia crystalizes readily when annealed at high temperatures. In this study, we prepare composite HfO 2 -SiO 2 coatings by co-sputtering hafnia and silica in an ion beam sputtering system and compare them to pure hafnia-based coatings. We demonstrate that crystallinity in hafnia can be completely suppressed when it is mixed with silica, such as the composite coatings in this study. High reflectors were fabricated and annealed, demonstrating that the multilayer dielectric stacks can survive high-temperature annealing and exhibit an excellent linear absorption of 0.2 +/- 1 ppm at 1064 nm. Short- and long-pulse laser damage was explored, demonstrating the complex relationship between linear absorption and the non-linear absorption which drives pulsed laser damage. These results provide an excellent route to the creation of very low linear absorption optical coatings, which also utilize low scattering materials that are best suited for high-peak and average power applications.

Harthcock, Colin [Lawrence Livermore National Labo↗
DOE OSTI2026

Flying focus with arbitrary directionality for spatiotemporal control of laser intensity

Flying focus techniques produce laser pulses whose focal points travel at arbitrary, controllable velocities. While this flexibility can enhance a broad range of laser-based applications, existing techniques constrain the motion of the focal point to the propagation direction of the pulse. Here, we introduce a flying focus configuration that decouples the motion of the focus from the propagation direction. Here, a chirped laser pulse focused and diffracted by a diffractive lens and grating creates a focal point that can move both along and transverse to the propagation direction. The focal length of the lens, grating period, and chirp can be tuned to control the direction and velocity of the focus. Simulations demonstrate this control for a holographic configuration suited to high-power pulses, in which two off-axis pump beams with different focal lengths encode the equivalent phase of a chromatic lens and grating in a gas or plasma. For low-power pulses, conventional solid-state or adaptive optics can be used instead. Multi-dimensional control over the focal trajectory enables new configurations for applications, including laser wakefield acceleration of ions, nonlinear Thomson scattering, and surface-plasmon emission of THz radiation.

Classical optics↗
DOE OSTI2021

Open quantum systems for quarkonia

I review recent applications of the open quantum system framework in the understanding of quarkonium suppression in heavy-ion collisions, which has been used as a probe of the quark–gluon plasma for decades. The derivation of the Lindblad equations for quarkonium in both the quantum Brownian motion and the quantum optical limits and their semiclassical counterparts is explained. The hierarchy of time scales assumed in the derivation is justified from the separation of energy scales in nonrelativistic effective field theories of QCD. Physical implications of the open quantum system approach are also discussed. Finally, I list some open questions for future studies.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Dynamics of plasma atomic layer etching: Molecular dynamics simulations and optical emission spectroscopy

Atomic layer etching is intrinsically dynamic as it involves sequential and repeated exposures of a surface to be etched with different species at different energies. The composition and structure of the near surface region change in both time and depth. Full understanding of this process requires resolving both temporal and spatial variations. In this work, we consider silicon (Si) atomic layer etching (ALE) by alternating exposure to chlorine gas (Cl 2 ) and argon ions (Ar + ). Molecular dynamics (MD) simulations are compared to experimental measurements with the aim of better understanding the dynamics of ALE and to test the simulation procedure. The simulations help to more fully interpret the experimental measurements. Further, optical emission measured just above the surface being etched can be related to etch products and can, therefore, be directly compared to simulation predictions. The simulations capture the measured initial product distribution leaving the surface and match the measured etch per cycle reasonably well. While simulations demonstrate the importance of ion-induced surface damage and mixing into a layer below the surface, the depth of which depends mainly on ion energy, the experiments suggest there is more Cl mixed into the layer than the MD procedure predicts.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2025

Epitaxial strain tuning of Er 3+ in ferroelectric thin films

Er 3+ color centers are promising candidates for quantum science and technology due to their long electron and nuclear spin coherence times, as well as their desirable emission wavelength. By selecting host materials with suitable, controllable properties, we introduce new parameters that can be used to tailor the Er 3+ emission spectrum. PbTiO 3 is a well-studied ferroelectric material with known methods of engineering different domain configurations through epitaxial strain. By distorting the structure of Er 3+ -doped PbTiO 3 thin films, we can manipulate the crystal fields around the Er 3+ dopant. This is resolved through changes in the Er 3+ resonant fluorescence spectra, tying the optical properties of the defect directly to the domain configurations of the ferroelectic matrix. Additionally, we are able to resolve a second set of peaks for films with in-plane ferroelectric polarization. We hypothesize these results to be due to either the Er 3+ substituting different sites of the PbTiO 3 crystal, differences in charges between the Er 3+ dopant and the original substituent ion, or selection rules. Systematically studying the relationship between the Er 3+ emission and the epitaxial strain of the ferroelectric matrix lays the pathway for future optical studies of spin manipulation by altering ferroelectric order parameters.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Implementation of a portable diagnostic system for Thomson scattering measurements on an electrothermal arc source

To fulfill the increasing needs of diagnostic support for researchers in plasma technology, a portable diagnostic package (PDP) equipped for both laser Thomson scattering (TS) and optical emission spectroscopy has been designed and constructed at Oak Ridge National Laboratory (ORNL), aiming to measure the temperature and number density of electrons and temperatures of ions in plasma devices. The PDP has been initially implemented on a high density and low temperature electrothermal arc source (ET-arc) at ORNL to test its TS capability. TS from the plasmas in the ET-arc has been obtained using the PDP. The electron temperature and number density were determined from TS spectra. These results were then compared to measurements from previous studies on the ET-arc. The TS diagnostic measured 0.8 ± 0.1, 1.3 ± 0.2, and 0.7 ± 0.1 eV and (4.4 ± 0.5) × 1021, (5.9 ± 0.7) × 1021, and (4.3 ± 0.5) x 1021 m-3, respectively, from three lines of sight that transect the plasma column.

He, Z. (ORCID:0000000183159882)↗
DOE OSTI2026

Promise of Graph Sparsification and Decomposition for Noise Reduction in QAOA: Analysis for Trapped-Ion Compilations

We develop new approximate compilation schemes that significantly reduce the expense of compiling the Quantum Approximate Optimization Algorithm (QAOA) for solving the Max-Cut problem. Our main focus is on compilation with trapped-ion simulators using Pauli-X operations and all-to-all Ising Hamiltonian HIsing evolution generated by Molmer-Sorensen or optical dipole force interactions, though some of our results also apply to standard gate-based compilations. Our results are based on principles of graph sparsification and decomposition; the former reduces the number of edges in a graph while maintaining its cut structure, while the latter breaks a weighted graph into a small number of unweighted graphs. Though these techniques have been used as heuristics in various hybrid quantum algorithms, there have been no guarantees on their performance, to the best of our knowledge. This work provides the first provable guarantees using sparsification and decomposition to improve quantum noise resilience and reduce quantum circuit complexity. For quantum hardware that uses edge-by-edge QAOA compilations, sparsification leads to a direct reduction in circuit complexity. For trapped-ion quantum simulators implementing all-to-all HIsing pulses, we show that for a (1−ϵ) factor loss in the Max-Cut approximation (ϵ>0), our compilations improve the (worst-case) number of HIsing pulses from O(n2) to O(nlog(n/ϵ)) and the (worst-case) number of Pauli-X bit flips from O(n2) to O(nlog(n/ϵ)ϵ2) for n-node graphs. This is an asymptotic improvement for any constant ϵ>0. We demonstrate that significant improvements to the approximation ratio are obtained using decomposition in simulated trapped-ion experiments with dephasing noise. We further present a generic argument showing that sparsification results in an exponentially improved circuit fidelity lower bound in digital computing schemes based on one- and two-qubit gates, which are relevant to a wide variety of hardwares such as superconducting qubits and certain neutral atom or trapped ion setups, and more sophisticated noise models. We anticipate these approximate compilation techniques will be useful tools in a variety of future quantum computing experiments.

Moondra, Jai [Georgia Institute of Technology]↗
DOE OSTI2026

A Review of Advanced Characterization Methods and Techniques for Amorphous and Poorly Crystalline Materials Applicable to Cementitious Waste Forms

This review covers advanced characterization methods of cementitious materials. The particular focus is to understand cementitious compositions with amorphous content because conventional techniques such as X-ray diffraction are more applicable to materials with long range order. Also of interest is advanced characterization that provides deeper insights into properties such as porosity. There are five groups of characterization methods discussed in this review which are: electron beam/microscopy, X-ray, neutron diffraction and scattering, nuclear magnetic resonance, and optical techniques. The techniques can be further grouped by the categories of nanoscale structural understanding (transmission electron microscopy and pair distribution function), microscale structural understanding (focused ion beam and x-ray tomography), microscopic elemental distributions (energy dispersive spectroscopy and X-ray fluorescence), and chemical binding information (electron energy loss spectroscopy, x-ray absorption spectroscopy, nuclear magnetic resonance, Raman spectroscopy, and infrared spectroscopy), with advantages and disadvantages of each method discussed. The recommendation for further research is to begin with techniques that are easier to prepare samples for, measure, and analyze, such as the optical techniques of Raman and infrared spectroscopy. If more information is needed, pursue collaborations, other techniques, or proposals for beam time at the synchrotron sources.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Erratum to: Soft- and reactive landing of ions onto surfaces: concepts and applications

Soft- and reactive landing of mass-selected ions is gaining attention as a promising approach for the precisely-controlled preparation of materials on surfaces that are not amenable to deposition using conventional methods. A broad range of ionization sources and mass filters are available that make ion soft-landing a versatile tool for surface modification using beams of hyperthermal (<100?eV) ions. The ability to select the mass-to-charge ratio of the ion, its kinetic energy and charge state, along with precise control of the size, shape, and position of the ion beam on the deposition target distinguishes ion soft landing from other surface modification techniques. Soft- and reactive landing have been used to prepare interfaces for practical applications as well as precisely-defined model surfaces for fundamental investigations in chemistry, physics, and materials science. For instance, soft- and reactive landing have been applied to study the surface chemistry of ions isolated in the gas-phase, prepare arrays of proteins for high-throughput biological screening, produce novel carbon-based and polymer materials, enrich the secondary structure of peptides and the chirality of organic molecules, immobilize electrochemically-active proteins and organometallics on electrodes, create thin films of complex molecules, and immobilize catalytically active organometallics as well as ligated metal clusters. In addition, soft landing has enabled investigation of the size-dependent behavior of bare metal clusters in the critical subnanometer size regime where chemical and physical properties do not scale predictably with size. The morphology, aggregation, and immobilization of larger bare metal nanoparticles, which are directly relevant to the design of catalysts as well as improved memory and electronic devices, have also been studied using ion soft landing. This review article begins in section 1 with a brief introduction to the existing applications of ion soft- and reactive landing. Section 2 provides an overview of the ionization sources and mass filters that have been used to date for soft landing of mass-selected ions. A discussion of the competing processes that occur during ion deposition as well as the types of ions and surfaces that have been investigated follows in section 3. Section 4 discusses the physical phenomena that occur during and after ion soft landing, including retention and reduction of ionic charge along with factors that impact the efficiency of ion deposition. The influence of soft landing on the secondary structure and biological activity of complex ions is addressed in section 5. Lastly, an overview of the structure and mobility as well as the catalytic, optical, magnetic, and redox properties of bare ionic clusters and nanoparticles deposited onto surfaces is presented in section 6. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 35:439–479, 2016.

Johnson, Grant E.↗
DOE OSTI2022

A poloidal high- k scattering system for NSTX-U

A previous 5-channel tangential high-k scattering system is being replaced by an 8-channel, poloidal high-k scattering system on the National Spherical Torus eXperiment Upgrade (NSTX-U) device located in Princeton, NJ, USA. The 693 GHz poloidal scattering system replaces a 280 GHz tangential scattering system to study high-k electron density fluctuations on NSTX-U, thereby considerably enhancing planned turbulence physics studies by providing a measurement of the k θ -spectrum of both electron temperature gradient (ETG) and ion temperature gradient (ITG) modes. Two approaches to generating the 693 GHz probe beam are under development: an optically-pumped far-infrared (FIR) laser that generates ~50 mW, and a compact gyrotron that can potentially generate in excess of 5 W. Large aperture optics collect radiation scattered from density fluctuations in the plasma core at 8 simultaneous scattering angles ranging from 2 to 15° corresponding to poloidal wavenumbers that extend to >40 cm -1 . Finally, steerable launch optics coupled with receiver optics mounted on a 5-axis receiver carriage allow the scattering volume to be placed radially from r/a = 0.3 out to the pedestal region (r/a ~ 0.99) and translated horizontally as needed to satisfy wavenumber matching.

47 OTHER INSTRUMENTATION↗