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Results for “fast electrons”

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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Effect of an electric field on liquid helium scintillation produced by fast electrons

The dependence on applied electric field (0–40 kV/cm) of the scintillation light produced by fast electrons and α particles stopped in liquid helium in the temperature range of 0.44 K to 3.12 K is reported. For both types of particles, the reduction in the intensity of the scintillation signal due to the applied field exhibits an apparent temperature dependence. Using an approximate solution of the Debye-Smoluchowski equation, we show that the apparent temperature dependence for electrons can be explained by the time required for geminate pairs to recombine relative to the detector signal integration time. This finding indicates that the spatial distribution of secondary electrons with respect to their geminate partners possesses a heavy, non-Gaussian tail at larger separations and has a dependence on the energy of the primary ionization electron. Here, we discuss the potential application of this result to pulse shape analysis for particle detection and discrimination.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Fe-single atom catalysts facilitate fast electron transfer with MoS 2 /SnS 2 cathodes in lithium–sulfur batteries

Lithium–sulfur batteries (LSBs) emerge as promising next-generation energy storage systems offering cost-effectiveness, environmental friendliness, and high theoretical energy density. The practical implementation of LSBs faces significant hindrances due to the shuttle effect and sluggish redox reactions. To address these challenges, single-atom catalyst (SAC) based combination materials from d-block elements can offer increased active catalytic sites, rapid charge transfer, accelerated electron migration, and fast sulfur redox conversion kinetics of lithium polysulfides (LiPSs). In this study, we fabricated three different LSB cathodes: pure S, S@MoS 2 /SnS 2 , and S@Fe–MoS 2 /SnS 2 . These cathodes were then used to explore the cycle life, capacity, rate capability, and redox kinetic reactions of LiPSs while assessing the influence of Fe-SACs on their performance. As a result, LSBs with S@Fe–MoS 2 /SnS 2 cathodes demonstrate an extended cycle life of 1000 cycles at a C-rate of 0.2C, maintaining a capacity close to 500 mA h g −1 , the highest initial discharge capacity of 1622 mA h g −1 and 1066 mA h g −1 at 0.05C and 0.2C, and excellent rate capabilities of 708 mA h g −1 and 558 mA h g −1 at 1C and 2C, respectively. The synergistic effect of the Fe-SAC-based combination cathode (S@Fe–MoS 2 /SnS 2 ) creates plentiful adsorptive and highly active catalytic sites, resulting in substantially enhanced capacity for adsorbing soluble long-chain LiPSs. This facilitates ultra-fast redox kinetics, surpassing the performance of the S@MoS 2 /SnS 2 and pure S cathodes. In the ex situ analysis, results from powder X-ray diffraction (XRD) to observe the new phase, soft X-ray absorption spectroscopy (XAS) to investigate the electronic structure, and hard X-ray photoelectron microscopy (HAXPES) with different energies (900 eV, 2000 eV, and 6000 eV) to track the chemical-state evolution of Fe-SACs in MoS 2 /SnS 2 cathodes displayed notable electrochemical reversibility involving S 8 ⇄ LiPSs ⇄ Li 2 S conversion even after 1000 cycles. Additionally, in situ, operando Raman analysis can unveil a novel catalytic mechanism of Fe-SACs in MoS 2 /SnS 2 “facilitating rapid electron transfer” during the discharge and charge processes of LSBs involving the conversion of S 8 ⇄ long-chain LiPSs ⇄ Li 2 S 2 /Li 2 S. This study elucidates the working mechanism of Fe-SAC cathodes, offering insights into overcoming the shuttle effect and facilitating sulfur redox kinetics to advance commercial LSBs.

36 MATERIALS SCIENCE↗
NASA NTRS1975

Quantitative comparisons of type 3 radio burst intensity and fast electron flux at 1 AU

The flux of fast solar electrons and the intensity of the type 111 radio emission generated by these particles were compared at one AU. Two regimes were found in the generation of type 111 radiation: one where the radio intensity is linearly proportional to the electron flux, and another, which occurs above a threshold electron flux, where the radio intensity is approximately proportional to the 2.4 power of the electron flux. This threshold appears to reflect a transition to a different emission mechanism.

Fitzenreiter, R. J.↗
DOE OSTI2021

Infrared surface phonon nanospectroscopy of an interacting dielectric-particle–dielectric-substrate dimer using fast electrons

Refinements in energy monochromation and aberration correction in state-of-the-art scanning transmission electron microscopes has opened access to the far infrared regime for spectroscopic characterization at the nanoscale. At these low energies, the dielectric environment, such as a dielectric slab adjacent to the target specimen, may no longer play a passive role in the spectrum. Instead, the environment may itself host resonances that mix with those of the target and complicate interpretation of its spectral responses. This article explores a theoretical description of the coupling between the collective vibrational surface modes of a dielectric particle and dielectric slab of varying thickness for the purpose of elucidating the interacting phononic excitations in dielectric materials typical of inelastic electron scattering measurements in the infrared. Dynamical coordinates and a governing Hamiltonian are rigorously defined in the quasistatic limit to account for phonon mode mixing and forcing by an aloof electron probe, which travels along a grazing trajectory, parallel to the dielectric slab. As the spectral window of interrogation by fast electron probes has been extended down to thermal energies with unprecedented meV energy resolution, theoretical models like that presented herein are crucial for accurate interpretation of experimental data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1975

Fast electrons in small solar flares

This review summarizes both the direct spacecraft observations of nonrelativistic solar electrons, and observations of the X-ray and radio emission generated by these particles at the sun and in the interplanetary medium. These observations bear on the basic astrophysical process of particle acceleration in tenuous plasmas. We find that in many small solar flares, the nearly 5-100 keV electrons accelerated during flash phase constitute the bulk of the total flare energy. Thus the basic flare mechanism in these flares essentially converts the available flare energy into fast electrons. These electrons may produce the other flare electromagnetic emissions through their interactions with the solar atmosphere. In large proton flares these electrons may provide the energy to eject material from the sun and to create a shock wave which could accelerate nuclei and electrons to much higher energies.

Lin, R. P.↗
NASA NTRS1976

Quantitative comparisons of type III radio burst intensity and fast electron flux at 1 AU

We compare the flux of fast solar electrons and the intensity of the type III radio emission generated by these particles at 1 AU. We find that there are two regimes in the generation of type III radiation: one where the radio intensity is linearly proportional to the electron flux, and the second regime, which occurs above a threshold electron flux, where the radio intensity is proportional to the approximately 2.4 power of the electron flux. This threshold appears to reflect a transition to a different emission mechanism.

Fitzenreiter, R. J.↗
DOE OSTI2024

Spatiotemporal dynamics of fast electron heating in solid-density matter via XFEL

Abstract High-intensity, short-pulse lasers are crucial for generating energetic electrons that produce high-energy-density (HED) states in matter, offering potential applications in igniting dense fusion fuels for fast ignition laser fusion. High-density targets heated by these electrons exhibit spatially non-uniform and highly transient conditions, which have been challenging to characterize due to limitations in diagnostics that provide simultaneous high spatial and temporal resolution. Here, we employ an X-ray Free Electron Laser (XFEL) to achieve spatiotemporally resolved measurements at sub-micron and femtosecond scales on a solid-density copper foil heated by laser-driven fast electrons. Our X-ray transmission imaging reveals the formation of a solid-density hot plasma localized to the laser spot size, surrounded by Fermi degenerate, warm dense matter within a picosecond, and the energy relaxation occurring within the hot plasma over tens of picoseconds. These results validate 2D particle-in-cell simulations incorporating atomic processes and provide insights into the energy transfer mechanisms beyond current simulation capabilities. This work significantly advances our understanding of rapid fast electron heating and energy relaxation in solid-density matter, serving as a key stepping stone towards efficient high-density plasma heating and furthering the fields of HED science and inertial fusion energy research using intense, short-pulse lasers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Surface plasmon enhanced fast electron emission from metallised fibre optic nanotips

Physical mechanisms of electron emission from fibre optic nanotips, namely, tunnelling, multi-photon, and thermionic emission, either prevent fast switching or require intense laser fields. Time-resolved electron emission from nano-sized sources finds applications ranging from material characterisation to fundamental studies of quantum coherence. We present a nano-sized electron source capable of fast-switching (≤1 ns) that can be driven with low-power femtosecond lasers. The physical mechanism that can explain emission at low laser power is surface plasmon enhanced above-threshold photoemission. An electron emission peak is observed and provides support for resonant plasmonic excitation. The electron source is a metal-coated optical fibre tapered into a nano-sized tip. The fibre is flexible and back illuminated facilitating ease of positioning. The source operates with a few nJ per laser pulse, making this a versatile emitter that enables nanometrology, multisource electron-lithography and scanning probe microscopy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Ultra-Fast Electron Microscopic Imaging of Single Molecules With a Direct Electron Detection Camera and Noise Reduction

Time-resolved imaging of molecules and materials made of light elements is an emerging field of transmission electron microscopy (TEM), and the recent development of direct electron detection cameras, capable of taking as many as 1,600 fps, has potentially broadened the scope of the time-resolved TEM imaging in chemistry and nanotechnology. However, such a high frame rate reduces electron dose per frame, lowers the signal-to-noise ratio (SNR), and renders the molecular images practically invisible. Here, we examined image noise reduction to take the best advantage of fast cameras and concluded that the Chambolle total variation denoising algorithm is the method of choice, as illustrated for imaging of a molecule in the 1D hollow space of a carbon nanotube with ~1 ms time resolution. Through the systematic comparison of the performance of multiple denoising algorithms, we found that the Chambolle algorithm improves the SNR by more than an order of magnitude when applied to TEM images taken at a low electron dose as required for imaging at around 1,000 fps. Open-source code and a standalone application to apply Chambolle denoising to TEM images and video frames are available for download.

47 OTHER INSTRUMENTATION↗
NASA NTRS1983

Fast Electronic Solar Cell Tester

Microcomputer controlled system gather current and voltage data. System consists of light source, microcomputer, programable dc power supply, analog/ digital interface, and data storage display equipment. Applies series of test loads to cell via programable dc power supply to obtain I/V characteristic curve and key cell-peformance parameter. Apparatus and programming technique are applicable to devices such as batteries and sensors.

Lathrop, J. W.↗
NASA NTRS2003

Simplified Formulae System for Resonant Inverse Compton Scattering of a Fast Electron in an Intense Magnetic Field

We present simple analytical formulae for the emission spectrum and total power of a special kind of resonant inverse Compton scattering (RICS) of a relativistic electron in an intense magnetic field. In contrast with the available formulae system, we obtain a markedly simplified one based on the semiclassical quantum theory, which is more understandable for people who are unfamiliar with quantum electrodynamics. We show that the RICS process, under an appropriate 'accommodation condition' derived in this paper, is predominantly much more efficient than the coexistent ordinary inverse Compton scattering, and produces highly beamed high-frequency radiation with moderately good monochromaticity. Our formulae are simple to use - thus offering a lucid physical intuition for the theory - and may find wide applications in hard X-ray and gamma-ray astrophysics.

You, J. H.↗