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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Hyperfine structure and isotope shifts of xenon measured for near-infrared transitions with Doppler-free saturated absorption spectroscopy

Hyperfine structure and isotope shifts of Xe were investigated with Doppler-free saturated absorption spectroscopy for all transitions in the 820-841 nm spectral interval. The Xe samples were commercial gases of natural isotopic abundances. The measurements were performed by employing a widely tunable narrow line Ti:sapphire laser. The hyperfine structures for 129 Xe and 131 Xe were well resolved. For the transitions with the wavelengths in vacuum near 820.860 nm and 841.150 nm also isotope shifts of the even isotopes were clearly observed. The modeling of the shapes of the observed absorption lines qualitatively reproduces experimental spectral profiles. The measured absorption peaks of the hyperfine structure and isotope shifts of Xe isotopes present characteristic spectral fingerprints for their identification. Eventually, quantitative spectral analysis will provide isotopic abundances of natural, as well as radioactive Xe gas samples.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Water Solubility at Saturation for CO 2 –CH 4 Mixtures at 323.2 K and 9.000 MPa

The concentration of H 2 O dissolved in CO 2 –CH 4 supercritical fluids is an important parameter that can control shale permeability, affect CH 4 transmissivity, and ultimately impact the efficiency of CO 2 enhanced gas recovery (EGR) operations. Here, we use in situ high-pressure infrared (IR) spectroscopic titrations to quantify the solubility of H 2 O in six CO 2 –CH 4 mixtures, ranging from pure CO 2 to pure CH 4 , at shallow shale reservoir conditions of 323.2 K and 9.000 MPa. Measured concentrations of H 2 O at saturation increase with increasing mole percent CO 2 , and our results are in agreement with limited data available in the literature. We use these experimental results to benchmark three current thermodynamic multiphase routines: the mixed-solvent electrolyte (MSE), STOMP-COMP, and the Statistical Associating Fluid Theory for variable range Mie potentials (SAFT γ-Mie) equations of state. We find that, of these models, MSE and STOMP-COMP accurately predict maximum H 2 O solubilities of the binary CO 2 –H 2 O and CH 4 –H 2 O systems, and they also reproduce the shape of the water solubility curve as a function of mole percent CO 2 . Hence, these routines should work well to predict H 2 O content in reservoir simulations and help to make informed decisions concerning injection strategies for CO 2 EGR in shale plays at shallow depths.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Operation of Layered LiCoO 2 to Higher Voltages with a Localized Saturated Electrolyte

The commercialization of lithium-ion batteries started with the layered LiCoO 2 (LCO) cathode for portable electronics, but only 50% of its theoretical capacity can be used in practical cells due to detrimental surface and bulk degradations when charged to high voltages. Here we demonstrate here that the stability of electrolyte plays a critical role in the performance of LCO at high voltages by employing a localized saturated electrolyte (LSE). With a cutoff voltage of 4.5 V, LCO achieves an initial 1C discharge capacity of 176 mA h g -1 and a capacity retention of 80% over 230 cycles. Even with a cutoff voltage of 4.6 V, LCO with 2% aluminum doping displays an initial discharge capacity of 189 mA h g -1 at 1C rate with 80% capacity retention over 137 cycles. With extensive analytical characterization, we show that the improved cycling stability stems from a suppression of the O3 to H1-3 phase transition as well as a robust inorganic-rich cathode-electrolyte interphase (CEI) facilitated by the LSE. This work highlights the importance of protecting the surface as well as the bulk with appropriate electrolytes for the high-voltage, higher-energy-density operation of LCO.

25 ENERGY STORAGE↗
DOE OSTI2012

Note: Voltage and intensity dependence of the saturation curves of free-air ionization chambers irradiated with chopped synchrotron radiation beams

Current saturation characteristics of free-air ionization chambers with electrode gaps of 4.2 and 8.4 mm were investigated using pulsed photon beam obtained by periodically interrupting synchrotron radiation beams with a chopper. Pulsed photon beams of 10 and 15 keV with pulse duration of 2.5 {mu}s and a frequency of 230 Hz were produced by chopping the beam. The measured recombination rate was found to be proportional to the intensity and inversely proportional to the applied voltage.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Global current profile effects on the evolution and saturation of magnetic islands

The nonlinear evolution of magnetic islands is investigated by means of numerical simulations. The growth and saturation of the island are shown to depend not only on asymptotic tearing mode stability parameter {Delta}{sup Prime} but also on the initial global current profile. Presence of the external current sheets leads to the formation of different island state for the same value of {Delta}{sup Prime }. It is found that the flow vorticity generated by the interacting current sheets is an important feature of nonlocal interactions and nonlocal effects in magnetic islands dynamics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

The effect of strain induced by Ag underlayer on saturation magnetization of partially ordered Fe{sub 16}N{sub 2} thin films

Partially ordered Fe-N thin films were grown by a facing target sputtering process on the surface of a (001) Ag underlayer on MgO substrates. It was confirmed by x-ray diffraction that the Ag layer enlarged the in-plane lattice of the Fe-N thin films. Domains of the ordered α″-Fe{sub 16}N{sub 2} phase within an epitaxial (001) α′-Fe{sub x}N phase were identified by electron diffraction and high-resolution aberration-corrected scanning transmission electron microscopy (STEM) methods. STEM dark-field and bright-field images showed the fully ordered structure of the α″-Fe{sub 16}N{sub 2} at the atomic column level. High saturation magnetization(Ms) of 1890 emu/cc was obtained for α″-Fe{sub 16}N{sub 2} on the Ag underlayer, while only 1500 emu/cc was measured for Fe-N on the Fe underlayer. The results are likely due to a tensile strain induced in the α″-Fe{sub 16}N{sub 2} phase by the Ag structure at the interface.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Observing and preventing rubidium runaway in a direct-infusion xenon-spin hyperpolarizer optimized for high-resolution hyper-CEST (chemical exchange saturation transfer using hyperpolarized nuclei) NMR

Xenon is well known to undergo host-guest interactions with proteins and synthetic molecules. As xenon can also be hyperpolarized by spin exchange optical pumping, allowing the investigation of highly dilute systems, it makes an ideal nuclear magnetic resonance probe for such host molecules. The utility of xenon as a probe can be further improved using Chemical Exchange Saturation Transfer using hyperpolarized nuclei (Hyper-CEST), but for highly accurate experiments requires a polarizer and xenon infusion system optimized for such measurements. We present the design of a hyperpolarizer and xenon infusion system specifically designed to meet the requirements of Hyper-CEST measurements. One key element of this design is preventing rubidium runaway, a chain reaction induced by laser heating that prevents efficient utilization of high photon densities. Using thermocouples positioned along the pumping cell we identify the sources of heating and conditions for rubidium runaway to occur. We then demonstrate the effectiveness of actively cooling the optical cell to prevent rubidium runaway in a compact setup. This results in a 2–3-fold higher polarization than without cooling, allowing us to achieve a polarization of 25% at continuous flow rates of 9 ml/min of {sup 129}Xe. The simplicity of this design also allows it to be retrofitted to many existing polarizers. Combined with a direction infusion system that reduces shot-to-shot noise down to 0.56% we have captured Hyper-CEST spectra in unprecedented detail, allowing us to completely resolve peaks separated by just 1.62 ppm. Due to its high polarization and excellent stability, our design allows the comparison of underlying theories of host-guest systems with experiment at low concentrations, something extremely difficult with previous polarizers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Influence of the electron spin resonance saturation on the power sensitivity of cryogenic sapphire resonators

Here, we study the paramagnetic ions behavior in presence of a strong microwave electromagnetic field sustained inside a cryogenic sapphire whispering gallery mode resonator. The high frequency measurement resolution that can be now achieved by comparing two Cryogenic Sapphire Oscillators (CSOs) permit to observe clearly the non-linearity of the resonator power sensitivity. These observations that, in turn, allow us to optimize the CSO operation are well explained by the electron spin resonance saturation of the paramagnetic impurities contained in the sapphire crystal.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Quantitative chemical exchange saturation transfer with hyperpolarized nuclei (qHyper-CEST): Sensing xenon-host exchange dynamics and binding affinities by NMR

The reversible binding of xenon to host molecules has found numerous applications in nuclear magnetic resonance studies. Quantitative characterization of the Xe exchange dynamics is important to understand and optimize the physico-chemical behavior of such Xe hosts, but is often challenging to achieve at low host concentrations. We have investigated a sensitive quantification technique based on chemical exchange saturation transfer with hyperpolarized nuclei, qHyper-CEST. Using simulated signals we demonstrated that qHyper-CEST yielded accurate and precise results and was robust in the presence of large amounts of noise (10%). This is of particular importance for samples with completely unknown exchange rates. Using these findings we experimentally determined the following exchange parameters for the Xe host cryptophane-A monoacid in dimethyl sulfoxide in one type of experiment: the ratio of bound and free Xe, the Xe exchange rate, the resonance frequencies of free and bound Xe, the Xe host occupancy, and the Xe binding constant. Taken together, qHyper-CEST facilitates sensitive quantification of the Xe exchange dynamics and binding to hydrophobic cavities and has the potential to analyze many different host systems or binding sites. This makes qHyper-CEST an indispensable tool for the efficient design of highly specific biosensors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Transformer ratio saturation in a beam-driven wakefield accelerator

We show that for beam-driven wakefield acceleration, the linearly ramped, equally spaced train of bunches typically considered to optimise the transformer ratio only works for flat-top bunches. Through theory and simulation, we explain that this behaviour is due to the unique properties of the plasma response to a flat-top density profile. Calculations of the optimal scaling for a train of Gaussian bunches show diminishing returns with increasing bunch number, tending towards saturation. For a periodic bunch train, a transformer ratio of 23 was achieved for 50 bunches, rising to 40 for a fully optimised beam.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Superlinearity, saturation, and the PMT—Tailoring and calibration methodology for prompt radiation detectors

This work illustrates predominant measureable nonlinearities in photomultiplier tubes (PMTs) and introduces a controllable one called “Superlinearity,” signifying both a positive nonlinear response and the ability to extend linear operation by counteracting gain saturation mechanisms — charge depletion, space-charge field limitation, and secondary emission surface effects. Recognizing superlinearity and its effect on the temporal step response leads to a true definition of linearity, free of a small-signal linear assumption. Furthermore, given the prevalent use of glass microchannel-plate (MCP) PMTs in favor of a faster impulse response in spite of a small charge limit, we are motivated to examine their nonlinear amplitude response and deploy tailored gain bias string methods to fully harness the maximum linear gain as is usually done for transmissive metal mesh and reflective metal dynode PMTs. Our characterization methodology applies standard NIST-traceable calibrated laboratory equipment with absolute input-referenced techniques, examining step responses over many orders of magnitude in controlled illumination. By doing so, we quantitatively reveal the superlinearity strength independent of charge depletion, yielding true linear responsivity and effectively doubling the small-signal linear limit; this is very relevant to PMT modeling and charge deconvolution efforts. In conclusion, with further development, the tailoring strategies we introduce could be applied to MCP detectors, extracting all useful capillary charge with a significant improvement in large linear signal quality.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Trap Passivation for Reducing On-Resistance and Saturation Voltage in Wafer-Bonded InGaAs-Channel/GaN-Drain Vertical FETs

High frequency and high power are the driving forces behind semiconductor transistor technology. However, conventional devices have the tradeoff of either being high speed or high breakdown—but not both. Wafer-bonded current aperture vertical electron transistors (BAVETs) help eliminate the tradeoff by combining a high-speed III-As channel to a high-breakdown III-N drift region. The device presented herein comprises of an InAlAs gate-barrier/InGaAs channel, wafer-bonded to an InGaN/GaN drift region, with the InGaAs/InGaN interface referred to as the wafer-bonded interface (WBI). The electronic behavior of WBIs is yet less known but necessary in realizing the potential of a BAVET. Herein, strong trap activity at the WBI is shown to be the cause of abnormally high saturation voltage ( V DS_SAT ) in BAVETs. The traps cause unintentional space charge (SC) region in the drain region of the device. This causes a drain resistance, a higher ON-resistance ( R ON ), and a higher V DS_SAT . Here, the challenge is overcome by hydrogen passivation of traps at WBI by using a p-doping for the InAlAs layer, which reduces the trap-charge concentration at the WBI. Consequently, the width of the SC region is reduced and a reduction in V DS_SAT is demonstrated, wherein it reduces from >12 to 5 V.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Implementation of a Doppler-Free Saturation Spectroscopy (DFSS) Diagnostic for Helicon Wave Electric Field Vector Measurement in Edge Plasma in DIII-D

A laser-based technique known as Doppler-free saturation spectroscopy (DFSS) has been designed, fabricated, and installed on the DIII-D National Fusion Facility to measure the helicon wave electric field vector in the edge plasma. These experimental measurements quantify phenomena resulting in decreased current drive efficiency due to wave/edge plasma interactions. This implementation of DFSS on DIII-D is the first of its kind on a tokamak and thus presents unique engineering challenges, including integration of the system onto an existing multidiagnostic port flange without impacts to system serviceability, as well as maintaining precise laser alignment over a 2-m distance during disruptions and thermal drift of the vessel. Further, these challenges were resolved using innovative design approaches such as a novel decoupled shutter system to facilitate serviceability of the in-vessel mirror assemblies without the need for personnel vessel entry, as well as an ex-vessel piezo-mirror-based optical system for laser beam shaping and real-time steering of the measurement location. The solutions to these engineering challenges were demonstrated during the successful installation and operation of these diagnostic components during the 2022 DIII-D vent and subsequent experimental campaign.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Influence of electron saturation of Tamm levels on the field-emission properties of silicon crystals

It has been shown that the plasma-chemical modification of the morphology and composition of the surface phase influences the emissivity of silicon crystals. It has been found that the saturation of Tamm states with electrons during the preparation of atomically clean silicon surfaces, along with stabilizing passivation of surface atoms in a highly ionized microwave plasma using Halon 14, decreases a threshold electric field at which field emission begins more than twofold and increases the maximal density of the field emission current by more than an order of magnitude compared with wafers covered by native oxide or subjected to ion physical etching in argon. Physicochemical mechanisms responsible for the modification of the silicon surface and the field-emission properties of silicon have been considered.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Saturation Carrying Capacity for Group A Particles in a Circulating Fluidized Bed

Empirical models continue to play a significant role in the design process of multiphase chemical reactors, particularly riser reactors in circulating fluidized bed (CFB) processes. It is imperative that accurate, industrial relevant correlations are developed to aid these design efforts. Using poor correlations could result in startup issues and significant redesign work. In this work, a new correlation is proposed to predict the saturation carrying capacity of Geldart Group A particles. This new correlation improves upon the currently available correlations for these materials and covers a broad range of Geldart Group A particles (particle diameters from 52 to 70 µm, and Archimedes numbers ranging from 5 to 20), superficial gas velocities (1 to 4 m/s), and riser diameters (0.066 to 0.3048 m). The new correlation has an Absolute Average Percent Deviation of only 17.6%, making it the most accurate correlation for Geldart Group A particles in the current literature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

The Evaporation and Survival of Cluster Galaxy Coronae. I. The Effectiveness of Isotropic Thermal Conduction Including Saturation

We simulate the evolution of cluster galaxy hot interstellar medium (ISM) gas that is a result of the effects of ram pressure and thermal conduction in the intracluster medium (ICM). At the density and temperature of the ICM, the mean free paths of ICM electrons are comparable to the sizes of galaxies, therefore electrons can efficiently transport heat that is due to thermal conduction from the hot ICM to the cooler ISM. Galaxies consisting of dark matter halos and hot gas coronae are embedded in an ICM-like “wind tunnel” in our simulations. In this paper, we assume that thermal conduction is isotropic and include the effects of saturation. We find that as heat is transferred from the ICM to the ISM, the cooler denser ISM expands and evaporates. This process is significantly faster than gas loss due to ram pressure stripping; for our standard model galaxy, the evaporation time is 160 Myr, while the ram pressure stripping timescale is 2.5 Gyr. Thermal conduction also suppresses the formation of shear instabilities, and there are no stripped ISM tails since the ISM evaporates before tails can form. Observations of long-lived X-ray emitting coronae and ram pressure stripped X-ray tails in galaxies in group and cluster environments therefore require that thermal conduction is suppressed or offset by some additional physical process. The most likely process is anisotropic thermal conduction that is due to magnetic fields in the ISM and ICM, which we simulate and study in the next paper in this series.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1961

THE DENSITIES OF SATURATED LIQUID HYDROGEN

This laboratory is engaged in a programme for the determination of thermostatic, thermodynamic, and transport properties of para-hydrogen, emphasizing high densities. Reported here are new data for the density of saturated liquid pura-hydrogen from boiling point to critical point. A review of hydrogen properties includes densities of normal hydrogen from triple to critical points and of pura-hydrogen up to the boiling point? More recent determinations of vapour pressures and critical constants have been made for both hydrogen modification.

LIQUID HYDROGEN↗