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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Layout and performance of HPK prototype LGAD sensors for the High-Granularity Timing Detector

The High-Granularity Timing Detector is a detector proposed for the ATLAS Phase II upgrade. The detector, based on the Low-Gain Avalanche Detector (LGAD) technology, will cover the pseudo-rapidity region of 2.4 < |n| < 4.0 with two end caps on each side and a total area of 6.4 m 2 . The timing performance can be improved by implanting an internal gain layer that can produce signals with a fast rising edge. It significantly improves the signal-to-noise ratio. The required average timing resolution per track for a minimum ionizing particle is 30 ps at the start and 50 ps at the end of the HL-LHC operation. This is achieved with several layers of LGAD. The innermost region of the detector would accumulate a 1MeV neutron-equivalent fluence up to 2.5 10 15 n eq /cm 2 including a safety factor of 1.5 before being replaced during the scheduled shutdowns. The addition of this new detector is expected to play an important role in the mitigation of high pile-ups at the HL-LHC. The layout and performance of the various versions of LGAD prototypes produced by Hamamatsu (HPK) have been studied by the ATLAS Collaboration. The breakdown voltages, depletion voltages, inter-pad gaps, collected charge as well as the time resolution have been measured and the production yield of large size sensors has been evaluated.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Guanidinium-Based Ionic Covalent-Organic Nanosheets for Sequestration of Cr(VI) and As(V) Oxoanions in Water

Chromium- and arsenic-based oxoanions are among the major highly toxic and carcinogenic inorganic pollutants present in groundwater, demanding fast and selective sequestration. Efficient capturing and removal of these highly mobile oxometallates at neutral pH presents a great challenge in groundwater cleanup. In this report, a series of guanidinium-based ionic organic covalent nanosheets (iCONs) with varying hydrogen bonding, steric, and electronic properties was studied to examine the structure–activity relationship in the adsorption and removal of chromium- and arsenic-based oxoanions in water. Structural modulations in iCONs were found to alter the guanidinium acidity, thus regulating the oxoanion uptake limits via ion exchange. The hydrogen bonding, steric, and electrostatic interactions at/near the guanidinium-based anion binding site in iCONs exerted heavy influences on the uptake efficiency and selectivity of arsenate but not on those of chromate. Further analyses revealed that the parallel bidentate hydrogen bonding interactions play a key role in the weak binding of arsenate to the protonated/positively charged guanidine motifs, whereas the strong ion–ion interactions between chromate and guanidinium appear to be more tolerant to the geometric and structural perturbation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Pitting Propagation Behavior on Low Alloy AISI 4130 (UNS G41300) Steel Exposed to Various Alkali and Alkaline Earth Metal Chlorides

Pit propagation studies were conducted to elucidate whether alkali and alkali earth metal cations such as Na+ and Rb+ present in the form of metal chloride salts such as RbCl affect pitting behavior in distinctly different manner than NaCl. Pit propagation studies were conducted on a low alloy steel using one-dimensional (1-D) pit method over pit depths from 300-1000 µm. LSV and EIS of planar electrodes of 4130 in a range of Cl- solutions were conducted and revealed no detected differences in impedance, open circuit, corrosion potential (Ecorr), passive current density (ipass), and pitting potential (Epit) as a function of salt type. In the case of one-dimensional pits during fast downward scan rates, the saturation potential (Esat) varied as a function of cation identity when pit depths were shallow. Mass transported limited current density also differed with cations in shallow pits when various alkali metal and alkaline metal cations were present. The limiting current density was increased for RbCl relative to NaCl The pit surface potential (Esurf) of activated pit surfaces reached Ecorr prior to establishing a condition where the pit electrolyte surface concentration (Csurf) was less than the critical concentration for active acidified pitting (i.e. Csurf<Ccrit) in this marginally passivating steel. For various Esurf and pit current density (ipit) combinations at constant Csurf where Ccrit< Csurf < Csat, E-log(i) plots were constructed using the method of Tianshu to create IR ohmic voltage corrected Tafel plots for various fixed pit solution concentrations. Under these conditions, the influence of cation identity on charge transfer controlled kinetics indicated slight differences in Tafel behavior where RbCl was slightly more aggressive than NaCl for low alloy steel oxidation. Differences in metal cation identity exert no effect on passive or breakdown on planar electrodes and only effect pit propagation stage in shallow pits.

Demarest, Chalres↗
DOE OSTI2020

Bright trion emission from semiconductor nanoplatelets

The trion, a quasiparticle comprising one exciton and an additional charge carrier, offers unique opportunities for generating spin-photon interfaces that can be used in developing quantum networks. Trions are also actively sought after for integrated optoelectronic devices including photovoltaics, photodetectors, and spintronics. However, formation of trions in strongly confined low-dimensional materials is often deemed detrimental. This is because trion emission in such materials is typically prohibited due to the predominant nonradiative Auger recombination processes. Semiconductor nanoplatelets with their strong confinement in the thickness direction and extended lateral geometries exhibit large exciton coherence sizes and reduced carrier-carrier interactions that may enable unprecedented trion properties. In this paper, we perform optical spectroscopic studies of individual CdSe nanoplatelets at cryogenic temperatures and observe bright trion emission with intensities comparable to that of neutral exciton emission. We perform carrier dynamics studies of the nanoplatelets and find that due to their extended lateral geometry, the fast radiative decay rate of the nanoplatelets at cryogenic temperatures is comparable to the inhibited Auger recombination rate, leading to the bright trion emission. Our tight-binding theory further reveals distinct size-tunable trion emission in the nanoplatelets that is advantageous for efficient trion emission. These properties make semiconductor nanoplatelets potential candidates as photon sources for optoelectronic and quantum logic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Towards the construction of the Mu2e electromagnetic calorimeter at Fermilab

Mu2e will search for the Charge Lepton Flavor Violating (CLFV) conversion of a muon into an electron in the field of a nucleus. A clean discovery signature is provided by the mono-energetic conversion electron (E e = 104.96 MeV). If no events are observed, Mu2e will set a limit on the ratio between the conversion and the nuclear capture rate below 3 × 10$^{-17}$ (at 90% C.L.). In order to confirm that the observed candidate is an electron, the calorimeter resolution requirements are to provide E res < 10%, T res < 500 ps for 100 MeV electrons while working in vacuum and in a high radiation environment and high magnetic field. The calorimeter is made of two annular aluminum disks, each one filled with 674 pure CsI crystals read out by SiPMs. A sophisticated mechanics and cooling system has been developed to support the crystals and cool the sensors. Radiation hard analog and fast digital electronics have been developed. In this paper the QC tests performed on the produced components and the construction status are reported, as well as the results obtained on the large size prototype with test beam data and at a cosmic ray test stand.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Development of High Performance Medium Velocity Superconducting Elliptical Cavities for Hadron Linacs

There is a solid scientific need for continuous wave (CW) proton or heavy ion linear accelerators (linacs) in the energy range up to about 1 GeV per nucleon (GeV/u). Only superconducting (SC) cavities can provide cost-efficient acceleration in CW mode. While low velocity, bc < 0.5 (b is the relative velocity of a charged particle and c is the speed of light), and high velocity, bc > 0.9, SC accelerating structures are established, there is a need in high-performance medium velocity SC accelerating structures. Currently, no superconducting (SC) CW proton or ion accelerators operate in the medium velocity range. We have developed a robust technology for producing high-performance medium-velocity elliptical cavities operating in the frequency range between 600 and 700 MHz. The project was performed in collaboration with Fermi and Argonne National Laboratories. The 5-cell, βopt = 0.65, 644 MHz elliptical cavities built at MSU have been used for this research. An advanced surface treatment method based on nitrogen doping to achieve a high-quality factor and a high accelerating gradient has been demonstrated. The surface treatment has been performed at ANL, and nitrogen doping at FNAL. A stable resonance control with the slow and fast tuner system has also been verified. FNAL developed a dedicated resonance control system for the stable operation of the combined tuner.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Monofluorinated acetal electrolyte for high-performance lithium metal batteries

High degree of fluorination for ether electrolytes has resulted in improved cycling stability of lithium metal batteries due to stable solid electrolyte interphase (SEI) formation and good oxidative stability. However, the sluggish ion transport and environmental concerns of high fluorination degree drive the need to develop less fluorinated structures. Here, we depart from the traditional ether backbone and introduce bis(2-fluoroethoxy)methane (F2DEM), featuring monofluorination of the acetal backbone. High coulombic efficiency and stable long-term cycling in Li||Cu half cells can be achieved with F2DEM even under fast Li metal plating conditions. The performance of F2DEM is further compared with diethoxymethane (DEM) and 2-[2-(2,2-difluoroethoxy)ethoxy]-1,1,1-trifluoroethane (F5DEE). A significantly lower overpotential is observed with F2DEM, which improves energy efficiency and enables its application in high-rate conditions. Comparative studies of F2DEM with DEM and F5DEE in anode-free lithium iron phosphate (LiFePO4) LFP pouch cells and high-loading LFP coin cells further show improved capacity retention of F2DEM electrolyte, demonstrating its practical applicability. More importantly, we also extensively investigate the underlying mechanism for the superior performance of F2DEM through various techniques, including X-ray photoelectron spectroscopy, scanning electron microscopy, cryogenic electron microscopy, focused ion beam, electrochemical impedance spectroscopy, and titration gas chromatography. Overall, F2DEM facilitates improved Li deposition morphology with reduced amount of dead Li. This enables F2DEM to show superior performance, especially under higher charging and slower discharging rate conditions.

25 ENERGY STORAGE↗
DOE OSTI2023

Calibration of a compact ASIC-based data acquisition system for neutron/$γ$ discrimination and spectroscopy with organic scintillators

Segmented neutron detectors that use silicon photomultipliers (SiPMs) are receiving significant attention in nuclear security applications. Some of these detectors employ hundreds of channels and would therefore benefit from the use of high-channel-density and low-cost-per-channel data acquisition (DAQ) systems. Candidate DAQ systems that meet these requirements exist, but few perform full waveform digitization, which permits neutron and gamma-ray interaction discrimination via pulse shape. In this work, we study the performance of the TOFPET2 (PETsys Electronics), an ASIC-based DAQ designed for positron emission tomography, which has been adapted to provide sensitivity to pulse shape by the use of variable-period charge integration. We use a light-emitting diode to calibrate a combination of an ON Semiconductor (SensL) 60035-64P J-Series SiPM and TOPFET2 DAQ and evaluate the linearity of their response and dynamic range. Here, the calibration curve was obtained by comparing the DAQ response to that measured with a photodiode interfaced with a traditional waveform digitizer. This calibration process was used for rudimentary spectroscopy of various neutron and sources.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Moderate active Fe 3+ doping enables improved cationic and anionic redox reactions for wide-voltage-range sodium storage

Layered metal oxides are promising cathode materials for sodium-ion batteries (SIBs) due to their high theoretical specific capacity and wide Na + diffusion channels. However, the irreversible phase transitions and cationic/anionic redoxes cause fast capacity decay. Herein, P2-type Na 0.67 Mg 0.1 Mn 0.8 Fe 0.1 O 2 (NMMF-1) cathode material with moderate active Fe 3+ doping has been designed for sodium storage. Uneven Mn 3+ /Mn 4+ distribution is observed in NMMF-1 and the introduction of Fe 3+ is beneficial for reducing the Mn 3+ contents both at the surface and in the bulk to alleviate the Jahn–Teller effect. The moderate Fe 3+ /Fe 4+ redox can realize the best tradeoff between capacity and cyclability. Therefore, the NMMF-1 demonstrates a high capacity (174.7 mAh g -1 at 20 mA g -1 ) and improved cyclability (78.5% over 100 cycles) in a wide-voltage range of 1.5–4.5 V (vs. Na + /Na). In-situ X-ray diffraction reveals a complete solid-solution reaction with a small volume change of 1.7% during charge/discharge processes and the charge compensation is disclosed in detail. This study will provide new insights into designing high-capacity and stable layered oxide cathode materials for SIBs.

25 ENERGY STORAGE↗
DOE OSTI2022

Methods to Calculate Electronic Excited-State Dynamics for Molecules on Large Metal Clusters with Many States: Ensuring Fast Overlap Calculations and a Robust Choice of Phase

Here, we present an efficient set of methods for propagating excited-state dynamics involving a large number of configuration interaction singles (CIS) or Tamm-Dancoff approximation (TDA) single-reference excited states. Specifically, (i) following Head-Gordon et al., we implement an exact evaluation of the overlap of singly-excited CIS/TDA electronic states at different nuclear geometries using a biorthogonal basis and (ii) we employ a unified protocol for choosing the correct phase for each adiabat at each geometry. For many-electron systems, the combination of these techniques significantly reduces the computational cost of integrating the electronic Schrodinger equation and imposes minimal overhead on top of the underlying electronic structure calculation. As a demonstration, we calculate the electronic excited-state dynamics for a hydrogen molecule scattering off a silver metal cluster, focusing on high-lying excited states, where many electrons can be excited collectively and crossings are plentiful. Interestingly, we find that the high-lying, plasmon-like collective excitation spectrum changes with nuclear dynamics, highlighting the need to simulate non-adiabatic nuclear dynamics and plasmonic excitations simultaneously. In the future, the combination of methods presented here should help theorists build a mechanistic understanding of plasmon-assisted charge transfer and excitation energy relaxation processes near a nanoparticle or metal surface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Electronic Spin Relaxation and Clustering in High-Pressure High-Temperature Synthesized Microcrystalline Diamond Particles with Reduced Nitrogen Content

The negatively charged nitrogen-vacancy (NV – ) color center in diamonds is widely studied because of numerous applications of this unique quantum system in sensing and quantum information sciences. While substitutional nitrogen is required to form the NV – centers in diamond, it also yields other paramagnetic defects─primarily the neutrally charged substitutional nitrogen centers (P1)─that decrease NV – spin coherence, which in turn degrades performance in applications. Herein, we investigate high-pressure high-temperature synthesized diamond microparticles (ca. 140–185 μm) having lower─ranging from 3 to 38 ppm─than the typical nitrogen content of type 1b diamond ( ca. 100 ppm and higher) typically used for the production of fluorescent diamond particles with NV – centers. A suite of electron paramagnetic resonance, optically detected magnetic resonance, and nuclear magnetic resonance methods are used to characterize spin properties of P1 and NV – centers in the particles. Upon decreasing the nitrogen content from 29 to 3 ppm, the ensemble NV – T 2 relaxation time increased by about 3-fold as measured directly in the Hahn Echo experiment at magnetic field of 1.2 T. Analysis of electronic relaxation of P1 centers revealed the existence of at least two distinct populations of P1 centers, consisting of fast and slower relaxing spins and allowed for an estimation of local concentrations. Even with <10 ppm nitrogen contents, the analysis indicated a highly heterogeneous distribution of P1 centers, suggesting the possibility of P1 spin clustering even at low nitrogen concentrations. The combined data demonstrate that the particles prepared from HPHT diamond with a low nitrogen content offer improved spin properties that are beneficial for NV – sensing applications.

Carbon↗
DOE OSTI2024

Optically multiplexed neutron time-of-flight technique for inertial confinement fusion

Neutron time-of-flight (nTOF) detectors are crucial in diagnosing the performance of inertial confinement fusion (ICF) experiments, which implode targets of deuterium–tritium fuel to achieve thermonuclear conditions. These detectors utilize the fusion neutron energy spectrum to extract key measurements, including the hotspot ion temperature and fuel areal density. Previous work [Danly et al., Rev. Sci. Instrum. 94, 043502 (2023)] has demonstrated adding 1D spatial resolution to an nTOF-like detector using a neutron aperture and streak camera to measure the ion temperature profile of an ICF implosion. By contrast, the study presented herein explores modifying the 1D detector to use a fast photomultiplier tube (PMT) to validate the design of a 2D spatially resolved instrument based on reconstruction from 1D profiles. The modification would collect time-of-flight traces from separate scintillators in an imaging array with one PMT using optical fibers of varying lengths to time-multiplex the signals. This technique has been demonstrated in ride-along experiments on the OMEGA laser with 20 fiber-coupled scintillator channels connected to a Photek PMT210. Results provide constraints on the fiber lengths and PMT gating requirements to promote pulse fidelity throughout all channels. Calibration of the detector to fixed nTOFs can provide a preliminary estimate of the instrument response function (IRF), although measurement of the IRF is currently under way. These results suggest that nTOF signals can potentially be time-multiplexed with fibers so long as the design is strategic to mitigate signal-to-noise reduction, modal dispersion, and charge build-up in the PMT, which has implications beyond ion temperature imaging.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

An Atom-Precise Approach to Damp First-Order Phase Transitions and Its Implications for Neuromorphic Signal Processing

Neuromorphic computing inspired by mammalian intelligence aims to emulate the nonlinear dynamics of biological neurons and synapses to achieve fast, low-energy, and highly efficient information processing. Brain-inspired computing relies on the design and discovery of materials exhibiting nonlinear current–voltage profiles, frequently underpinned by electronic state transitions, to achieve spiking neurons and dynamically tunable synapses. A signature challenge in the design of artificial neurons is controlling the steepness of first-order transitions in active elements, as abrupt transitions are at risk of driving unstable voltage and temperature oscillations, which result in catastrophic device failure. A critical knowledge gap is the lack of structure–function correlations mapping the composition and atomistic structure of crystalline solids to nonlinear dynamical response characteristics. Here, we address the key question of how modification of atomistic structure correlates with alteration of neuron-like functionality. Constructing oscillator circuits from millimeter-scale single crystals enables high-resolution atomic structure solutions, which we use to demonstrate that the selective positioning of Pb cations modifies charge ordering along a one-dimensional CuxV2O5 framework even at low insertion stoichiometries, thereby providing an atom-precise design parameter for damping first-order transitions. We use temperature-variant X-ray diffraction and X-ray spectroscopy to elucidate the suppression of Cu-ion shuttling based on the precise positioning of Pb ions in seven-coordinated tunnel interstitial sites as the mechanistic basis for transition broadening, thus bridging a critical gap between statistical mechanics and quantum chemical descriptions of phase transitions. Such mechanistic understanding thus paves the way to site-selective modification strategies for modulating the sharpness of first-order transitions, with an exemplary demonstration here in tuning neuronal signal processing.

Crystal structure↗
DOE OSTI2023

A hybrid 3D/2D field response calculation for liquid argon detectors with PCB based anode plane

Liquid Argon Time Projection Chamber (LArTPC) technology is commonly utilized in neutrino detector designs. It enables detailed reconstruction of neutrino events with high spatial precision and low energy threshold. Its field response (FR) model describes the time-dependent electric currents induced in the anode-plane electrodes when ionization electrons drift nearby. An accurate and precise FR is a crucial input to LArTPC detector simulations and charge reconstruction. Established LArTPC designs have been based on parallel wire planes. It allows accurate and computationally economic two-dimensional (2D) FR models utilizing the translational symmetry along the direction of the wires. Recently, novel LArTPC designs utilize electrodes formed on printed circuit board (PCB) in the shape of strips with through holes. The translational symmetry is no longer a good approximation near the electrodes and a new FR calculation that employs regions with three dimensions (3D) has been developed. Extending the 2D models to 3D would be computationally expensive. Fortuitously, the nature of strips with through holes allows for a computationally economic approach based on the finite-difference method (FDM). In this paper, we present a new software package pochoir that calculates LArTPC field response for these new strip-based anode designs. This package combines 3D calculations in the volume near the electrodes with 2D far-field solutions to achieve fast and precise field response computation. We apply the resulting FR to simulate and reconstruct samples of cosmic-ray muons and 39 Ar decays from a Vertical Drift (VD) detector prototype operated at CERN. We find the difference between real and simulated data within 5%. Current state-of-the-art LArTPC software requires a 2D FR which we provide by averaging over one dimension and estimate that variations lost in this average are smaller than 7%.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Revisiting matrix-based inversion of scanning mobility particle sizer (SMPS) and humidified tandem differential mobility analyzer (HTDMA) data

Abstract. Tikhonov regularization is a tool for reducing noise amplification during data inversion. This work introduces RegularizationTools.jl, a general-purpose software package for applying Tikhonov regularization to data. The package implements well-established numerical algorithms and is suitable for systems of up to ∼ 1000 equations. Included is an abstraction to systematically categorize specific inversion configurations and their associated hyperparameters. A generic interface translates arbitrary linear forward models defined by a computer function into the corresponding design matrix. This obviates the need to explicitly write out and discretize the Fredholm integral equation, thus facilitating fast prototyping of new regularization schemes associated with measurement techniques. Example applications include the inversion involving data from scanning mobility particle sizers (SMPSs) and humidified tandem differential mobility analyzers (HTDMAs). Inversion of SMPS size distributions reported in this work builds upon the freely available software DifferentialMobilityAnalyzers.jl. The speed of inversion is improved by a factor of ∼ 200, now requiring between 2 and 5 ms per SMPS scan when using 120 size bins. Previously reported occasional failure to converge to a valid solution is reduced by switching from the L-curve method to generalized cross-validation as the metric to search for the optimal regularization parameter. Higher-order inversions resulting in smooth, denoised reconstructions of size distributions are now included in DifferentialMobilityAnalyzers.jl. This work also demonstrates that an SMPS-style matrix-based inversion can be applied to find the growth factor frequency distribution from raw HTDMA data while also accounting for multiply charged particles. The outcome of the aerosol-related inversion methods is showcased by inverting multi-week SMPS and HTDMA datasets from ground-based observations, including SMPS data obtained at Bodega Marine Laboratory during the CalWater 2/ACAPEX campaign and co-located SMPS and HTDMA data collected at the US Department of Energy observatory located at the Southern Great Plains site in Oklahoma, USA. Results show that the proposed approaches are suitable for unsupervised, nonparametric inversion of large-scale datasets as well as inversion in real time during data acquisition on low-cost reduced-instruction-set architectures used in single-board computers. The included software implementation of Tikhonov regularization is freely available, general, and domain-independent and thus can be applied to many other inverse problems arising in atmospheric measurement techniques and beyond.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Online and Offline Data Quality Monitoring for the Mu2e Calorimeter

This thesis presents the design, implementation, and validation of a calorimeter Data Quality Monitoring (DQM) toolchain for the Mu2e experiment at Fermilab. Mu2e searches for charged lepton flavor violation via coherent muon-to-electron conversion in the field of an aluminum nucleus, $\mu^- Al \rightarrow e^-Al$, a process whose observation would constitute clear evidence of physics beyond the Standard Model. Achieving target sensitivity requires stringent control of detector performance and data integrity during acquisition, as subtle issues in readout configuration, data formatting, or electronics behavior can compromise reconstruction and bias downstream analyzes. To address these challenges, this work develops a multi-layer DQM approach spanning both raw data validation and reconstructed digi-level diagnostics. At the low level, a fragment analysis component performs word- and bit-field decoding of calorimeter readout blocks, enabling sanity checks of the expected structure and producing detailed error and integrity statistics useful for commissioning and troubleshooting. At the digi level, the CaloDigiDQM analyzer is implemented within the art framework and transforms each CaloDigiCollection into a structured hierarchy of ROOT histograms designed for fast drill-down diagnostics. The module generates coherent monitoring views at global, disk, board, and channel granularity, including occupancy, waveform-derived features (baseline, RMS, peak amplitude and position), and left-right sensor consistency metrics. Detector-aware channel-to-electronics mapping is performed through the conditions system (CaloDAQMap), ensuring that diagnostics remain aligned with hardware identifiers used in operations. For end-to-end testing without reliance on live DAQ data, a synthetic CaloDigi producer is developed to generate realistic waveforms with controlled noise and pulse shapes. The resulting system supports both offline ROOT-file production and online operation, including optional histogram streaming through otsdaq via ots::HistoSender. This toolchain provides a practical and scalable foundation for calorimeter commissioning and stable data collection, enabling early detection of anomalies and reducing operational risk for Mu2e.

Vakulenko, Mark [Drew U.] (ORCID:0009000276197818)↗
DOE OSTI2022

Evolution of the Heliotail Lobes over a Solar Cycle as Measured by IBEX

Energetic neutral atom (ENA) measurements by IBEX reveal that the heliotail comprises an energy-dependent multilobe structure. We examine the heliotail evolution over 11 yr of IBEX observations covering a full solar cycle (SC). We find the following: (1) The heliotail structure persists over the entire SC, comprising three ENA-enhanced and two ENA-suppressed lobes. (2) Lobe sizes and locations are generally stable but exhibit variations in ENA fluxes driven by the SC. (3) Lobe centers follow a cyclic behavior over multiple SC phases, indicating direct signatures of slow and fast solar wind (SW) interactions in the inner heliosheath (IHS). (4) The tilted plane passing through the port–starboard lobes' centers oscillates in latitude but maintains its tilt from the ecliptic plane, likely a consequence of the interstellar magnetic field draping around the heliosphere. (5) The transition of the central heliotail from a single lobe at ~1.1 keV to two lobes above ~2 keV is SC-dependent and directly reflects the IHS plasma properties, i.e., when ENA fluxes from fast SW from the polar coronal holes change over time. (6) The central lobe exhibits a substructure that is enhanced and offset from the downwind direction, possibly indicating an asymmetric ENA emission or an asymmetry in the parent plasma distribution. These results reveal the general stability of the heliotail structure over time and distinct variations in individual lobes' properties in relation to the SC phases. Furthermore, results show the effects of multiple SC phases in the tail, reflecting different ENA travel times and source histories.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Constructing Ultrathin W-Doped NiFe Nanosheets via Facile Electrosynthesis as Bifunctional Electrocatalysts for Efficient Water Splitting

Exploring cost-effective and efficient bifunctional electrocatalysts via simple fabrication strategies is strongly desired for practical water splitting. Herein, an easy and fast one-step electrodeposition process is developed to fabricate W-doped NiFe (NiFeW)-layered double hydroxides with ultrathin nanosheet features at room temperature and ambient pressure as bifunctional catalysts for water splitting. Notably, the NiFeW nanosheets require overpotentials of only 239 and 115 mV for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, to reach a current density of 10 mA/cm 2 in alkaline media. Their exceptional performance is further demonstrated in a full electrolyzer configuration with the NiFeW as both anode and cathode catalysts, which achieves a low cell voltage of 1.59 V at 10 mA/cm 2 , 110 mV lower than that of the commercial IrO 2 (anode) and Pt (cathode) catalysts. Moreover, the NiFeW nanosheets are superior to various recently reported bifunctional electrocatalysts. Such remarkable performances mainly ascribe to W doping, which not only effectively modulates the electrocatalyst morphology but also engineers the electronic structure of NiFe hydroxides to boost charge-transfer kinetics for both the OER and HER. Hence, the ultrathin NiFeW nanosheets with an efficient fabrication strategy are promising as bifunctional electrodes for alkaline water electrolyzers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗