High-energy Electron Flux Research Articles

Solar Flare Ribbon Fronts. II. Evolution of Heating Rates in Individual Flare Footpoints

Solar flare ribbon fronts appear ahead of the bright structures that normally characterize solar flares, and can persist for an extended period of time in spatially localized patches before transitioning to “regular” bright ribbons. They likely represent the initial onset of flare energy deposition into the chromosphere. Chromospheric spectra (e.g., He i 10830 Å and the Mg ii near-UV lines) from ribbon fronts exhibit properties rather different to typical flare behavior. In prior numerical modeling efforts we were unable to reproduce the long lifetime of ribbon fronts. Here we present a series of numerical experiments that are rather simple but which have important implications. We inject a very low flux of nonthermal electrons (F = 5 × 108 erg s−1 cm−2) into the chromosphere for 100 s before ramping up to standard flare energy fluxes (F = 1010−11 erg s−1 cm−2). Synthetic spectra not only sustained their ribbon-front-like properties for significantly longer: in the case of harder nonthermal electron spectra, the ribbon front behavior persisted for the entirety of this weak-heating phase. Lengthening or shortening the duration of the weak-heating phase commensurately lengthened or shortened the ribbon front lifetimes. Ribbon fronts transitioned to regular bright ribbons when the upper chromosphere became sufficiently hot and dense, which happened faster for softer nonthermal electron spectra. Thus, the lifetime of flare ribbon fronts are a direct measure of the duration over which a relatively low flux of high-energy electrons precipitates to the chromosphere prior to the bombardment of a much larger energy flux.

Prediction of High-Energy Electron Flux at Geosynchronous Orbit using a Neural Network Technique

Prediction of High-Energy Electron Flux at Geosynchronous Orbit using a Neural Network Technique

Enormous impulsive enhancement of particle fluxes observed on Aragats on May 23, 2023

An unprecedented thunderstorm ground enhancement (TGE) event was recorded on May 23, 2023, at Aragats Mountain, the highest peak in Armenia. This event showcased a maximum flux intensity surpassing 3 million particles per minute per square meter for energies above 0.4 MeV. Distinctly, the fluence of the event was measured at approximately ≈700 particles/cm2. The comprehensive instrumentation at the Aragats research station, including a suite of spectrometers and detectors, enabled precise cross-correlation of measurements. The electron flux at energies exceeding 10 MeV was observed at roughly ≈55,000 particles per minute per square meter. Additional measurements, including cloud base heights and corona discharge detections, validated the intensity of the electric field, reaching approximately 2.1 kV/cm at elevations 50–100 m above ground level. Our observations confirm that TGE is a universal and significant atmospheric event, contributing a substantial flux of high-energy electrons to the global electrical circuit. Integrating such TGE phenomena into Earth's numerical models is imperative, considering their impact on aviation and aerospace operation safety.

Radiation Synthesis of High-Temperature Wide-Bandgap Ceramics.

This paper presents the results of ceramic synthesis in the field of a powerful flux of high-energy electrons on powder mixtures. The synthesis is carried out via the direct exposure of the radiation flux to a mixture with high speed (up to 10 g/s) and efficiency without the use of any methods or means for stimulation. These synthesis qualities provide the opportunity to optimize compositions and conditions in a short time while maintaining the purity of the ceramics. The possibility of synthesizing ceramics from powders of metal oxides and fluorides (MgF2, BaF2, WO3, Ga2O3, Al2O3, Y2O3, ZrO2, MgO) and complex compounds from their stoichiometric mixtures (Y3Al3O12, Y3AlxGa(5-x) O12, MgAl2O4, ZnAl2O4, MgWO4, ZnWO4, BaxMg(2-x) F4), including activators, is demonstrated. The ceramics synthesized in the field of high-energy electron flux have a structure and luminescence properties similar to those obtained by other methods, such as thermal methods. The results of studying the processes of energy transfer of the electron beam mixture, quantitative assessments of the distribution of absorbed energy, and the dissipation of this energy are presented. The optimal conditions for beam treatment of the mixture during synthesis are determined. It is shown that the efficiency of radiation synthesis of ceramics depends on the particle dispersion of the initial powders. Powders with particle sizes of 1-10 µm, uniform for the synthesis of ceramics of complex compositions, are optimal. A hypothesis is put forward that ionization processes, resulting in the radiolysis of particles and the exchange of elements in the ion-electron plasma, dominate in the formation of new structural phases during radiation synthesis.

γ-photons and high-energy electrons produced by neutron irradiation in nuclear materials

Neutrons interacting with atomic nuclei in most of the materials included in the current fusion reactor designs—notably tungsten, ferritic and stainless steels, copper alloys—generate a γ-photon flux that is comparable in magnitude and energy with that of the neutrons, and which in turn generates an intense flux of high-energy electrons in the materials themselves. The occurrence of these γ- and electron fluxes has implications, among others, for the mobility of crystal defects in the materials, for the stability of the plasma, and for the internal heating of reactor components. While a highly spatially resolved numerical calculation of neutron, photon, and electron fluxes on the reactor scale is computationally unfeasible, it is possible to provide estimates based on solutions of Boltzmann's transport equation in a stationary and homogeneous material. Within their limits of validity, these estimates are robust and straightforward and they enable studying photon and electron generation in various materials, under different fission and fusion irradiation conditions and at various locations inside a reactor. We show that the irradiation environment provided by the IFMIF irradiation facility is similar to the expected fusion power plant conditions both in terms of the energy and intensity of photons and electrons generated by the neutrons in tungsten and steels.

High heat flux reduction to materials using current filaments

Reducing high electron and ion heat fluxes is one of the critical issues for shielding satellites and spacecraft. One of the ideas for shielding high particle and heat fluxes is to apply an external magnetic field generated by injecting current filaments. In this work, we model a flow of plasma, which includes electrons and ions in a small region, by using two spatial dimensions and three coordinates for velocities (2D3V) Particle-In-Cell (PIC) code to study the effects of the injected current filaments on particle and heat fluxes to the wall. The plasma enters the simulation domain from the source region at the left boundary and is fully absorbed in the conductor wall at the right boundary. Current filaments are injected to change the magnetic field structure of the system. We compare particle density, particle flux, and heat flux with and without injecting the current filaments into the domain in two dimensions. Based on the simulation results, we found that injecting current filaments can reduce the peak fluxes to the wall and transfer some of those fluxes along the wall. Therefore, injecting the current filaments is a good candidate for shielding satellites and spacecraft from high-energy ion and electron fluxes.

The Optimization of Radiation Synthesis Modes for YAG:Ce Ceramics.

Synthesis in the radiation field is a promising direction for the development of materials transformation processes, especially those differing in melting temperature. It has been established that the synthesis of yttrium-aluminum ceramics from yttrium oxides and aluminum metals in the region of a powerful high-energy electron flux is realized in 1 s, without any manifestations that facilitate synthesis, with high productivity. It is assumed that the high rate and efficiency of synthesis are due to processes that are realized with the formation of radicals, short-lived defects formed during the decay of electronic excitations. This article presents descriptions of the energy-transferring processes of an electron stream with energies of 1.4, 2.0, and 2.5 MeV to the initial radiation (mixture) for the production of YAG:Ce ceramics. YAG:Ce (Y3Al5O12:Ce) ceramics samples in the field of electron flux of different energies and power densities were synthesized. The results of a study of the dependence of the morphology, crystal structure, and luminescence properties of the resulting ceramics on the synthesis modes, electron energy, and electron flux power are presented.

Cross-satellite calibration of high-energy electron fluxes measured by FengYun-4A based on Arase observations

Cross-satellite calibration of high-energy electron fluxes measured by FengYun-4A based on Arase observations

Short-term forecast of high-energy electron flux based on GPR

Short-term forecast of high-energy electron flux based on GPR

Average characteristics of high-energy magnetospheric electron flux enhancements and the parameters of near-Earth and interplanetary medium in 1987–2021

ABSTRACT Based on the data of 35-yr (1987–2021) measurements of magnetospheric electron fluxes with energy >2 MeV in geostationary orbits, solar wind speed, and geomagnetic activity, a catalogue of electron flux enhancements was compiled in which the electron fluence exceeds 108 cm–2 sr–1 d–1. The epoch superposition method performed using the GOES-13 spacecraft data shows that large electron flux enhancements are preceded by a significant increase in the solar wind velocity and the Ap index of geomagnetic activity, and immediately before the increase the relativistic electron flux decreases. For the events of the catalogue, the average characteristics of electron flux enhancements and parameters of the interplanetary and near-Earth medium were calculated: the mean values of the diurnal and total fluences during an event and the average duration of electron enhancements. The average duration of the electron flux enhancement is 5 d, and the maximum duration is 24 d. Based on the calculated mean values of the electron fluences, solar wind velocity, and Ap-index of geomagnetic activity on the day of electron enhancement and on previous days, a typical behaviour of these parameters during and before an electron flux enhancement was obtained. The average characteristics of electron flux enhancements and the parameters of interplanetary and near-Earth medium are calculated before large electron flux enhancements, when the fluence exceeds 3 × 108, 5 × 108, and 109 particles cm–2 sr–1 d–1, respectively. It is shown that the greater the increase in solar wind velocity and geomagnetic activity the larger the subsequent electron flux enhancement.

Consideration of the Intricacies Inherent in Molecular Beam Epitaxy of the NaCl/GaAs System.

The high cost of substrates for III–V growth can be cost limiting for technologies that require large semiconductor areas. Thus, being able to separate device layers and reuse the original substrate is highly desirable, but existing techniques to lift a film from a substrate have substantial drawbacks. This work discusses some of the complexities with the growth of a water-soluble, alkali halide salt thin film between a III–V substrate and overlayer. Much of the difficulty stems from the growth of GaAs on an actively decomposing NaCl surface at elevated temperatures. Interestingly, the presence of an in situ electron beam incident on the NaCl surface, prior to and during GaAs deposition, affects the crystallinity and morphology of the III–V overlayer. Here, we investigate a wide range of growth temperatures and the timing of the impinging flux of both elemental sources and high energy electrons at different points during the growth. We show that an assortment of morphologies (discrete islands, porous material, and fully dense layers with sharp interfaces) and crystallinity (amorphous, crystalline, and highly textured) occur depending on the specific growth conditions, driven largely by changes in GaAs nucleation which is greatly affected by the presence of the reflection high energy electron diffraction beam.

Particle loading as a design parameter for composite radiation shielding

An evaluation of the radiation shielding performance of high-Z-particle-loaded polylactic acid (PLA) composite materials was pursued. Specimens were produced via fused deposition modeling (FDM) using copper-PLA, steel-PLA, and BaSO4-PLA composite filaments containing 82.7, 75.2, and 44.6 wt% particulate phase contents, respectively, and were tested under broad-band flash x-ray conditions at the Sandia National Laboratories HERMES III facility. The experimental results for the mass attenuation coefficients of the composites were found to be in good agreement with GEANT4 simulations carried out using the same exposure conditions and an atomistic mixture as a model for the composite materials. Further simulation studies, focusing on the Cu-PLA composite system, were used to explore a shield design parameter space (in this case, defined by Cu-particle loading and shield areal density) to assess performance under both high-energy photon and electron fluxes over an incident energy range of 0.5–15 MeV. Based on these results, a method is proposed that can assist in the visualization and isolation of shield parameter coordinate sets that optimize performance under targeted radiation characteristics (type, energy). For electron flux shielding, an empirical relationship was found between areal density (AD), electron energy (E), composition and performance. In cases where EAD≥2 MeV∙cm∙g−1, a shield composed of >85 wt% Cu results in optimal performance. In contrast, a shield composed of <10 wt% Cu is anticipated to perform best against electron irradiation when EAD<2 MeV∙cm∙g−1.

Electron Surfing Acceleration at Rippled Reconnection Fronts

The reconnection front (RF), one of the most efficient accelerators of particles in the terrestrial magnetosphere, is a sharp plasma boundary resulting from transient magnetic reconnection. It has been both theoretically predicted and observationally confirmed that electron-scale substructures can develop at the RFs. How such electron-scale structures modulate the electron energization and transport has not been fully explored. Based on high-resolution data from MMS spacecraft and particle tracing simulations, we investigate and compare the electron acceleration across two typical RFs with or without rippled electron-scale structures. Both observations and simulations reveal that high-energy electron flux behind the RF increases more dramatically if the electrons encounter a rippled RF surface, as compared to a smooth RF surface. The main acceleration mechanism is electron surfing acceleration, in which electrons are trapped by the ripples, due to the large local magnetic field gradient, and therefore undergo surfing motion along the motional electric field.

Constraining time dependent dark matter signals from the Sun

Dark matter (DM) particles captured by the Sun can produce high-energy electrons outside the Sun through annihilating into meta-stable mediators. The corresponding cosmic-ray electron signals observed by the space-based experiments will be time dependent due to the orbital motion of the space-based detectors. The shape of this time dependence is predictable given the orbital information of the detectors. Since the high-energy CR electron (with energy E > 100 GeV) fluxes are expected to be constant in time, non-observation of such time variation can be used to place upper limits on the DM annihilation cross section. We analyze the time dependence of dark matter cosmic-ray signals in three space-based experiments: AMS-02, DAMPE and CALET. Under the assumption that no time dependent signal is observed, we derive the 95% C.L. exclusion limits on the signal strength from the current data. We map our limits onto the parameter space of the dark photon model and find that the constraints are comparable with that derived from the supernova SN1987A.

Investigation of Interaction Mechanisms of High Energy Electrons and Gamma Quantum with Aqueous Solution of Methyl Orange Dye

The level of development of modern nuclear technologies forms a request for the development of new branches of science. At the same time, chemical dosimetry methods are also being improved [1, 2]. The essence of such methods consists in the quantitative determination of the radiation-chemical damages to the molecules of a substance when it is exposed to ionizing radiation [3, 4]. Liquid and solid solutions of organic dyes have intense bands optical absorption and fluorescence in the visible region of the spectrum, which makes it possible to use them in dosimetry systems [5, 6]. The use of organic dyes makes it possible to determine the absorbed dose in the range from 10-6 to 104 M Rad [7, 8]. In this work, we studied the processes of interaction of gamma-ray and high-energy electron fluxes with an aqueous solution of the organic dye methyl orange (C14H14N3О3SNa) [9, 10]. The calculations and experiment were carried out on a resonant electron accelerator with energies up to 30 MeV. The electron beam energy was 15 MeV. A tungsten converter was used to generate gamma quanta. The thickness of the converter varied from 0 to 6 mm. We have developed a computer program in C++ to simulate the irradiation process. This program uses the Geant4 class library based on the Monte Carlo method and runs in multi-threaded mode. For calculations, the model “PhysicsList emstandard_opt3” was chosen as the most suitable one. The value of radiation damage per one incident electron and produced gamma-quantum is determined in the work. The simulation results are compared with experimental data. Based on the results obtained, conclusions were drawn about the main mechanisms leading to the decomposition of organic dye molecules, and methods for optimizing the experiment for further research were proposed.

Constraints on the spatially dependent cosmic-ray propagation model from Bayesian analysis

The energy spectra of primary and secondary cosmic rays (CRs) generally harden at several hundreds of GeV, a finding which can be naturally interpreted by means of propagation effects. We adopt a spatially dependent CR propagation model to fit the spectral hardening, where a slow-diffusion disk (SDD) is assumed near the galactic plane. We aim to constrain the propagation parameters with a Bayesian parameter estimation based on a Markov chain Monte Carlo sampling algorithm. The latest precise measurements of carbon spectrum and B/C ratio are adopted in the Bayesian analysis. The $^{10}\mathrm{Be}/^{9}\mathrm{Be}$ and Be/B ratios are also included to break parameter degeneracies. The fitting result shows that all the parameters are well constrained. Especially, the thickness of the SDD is limited to 0.4--0.5 kpc above and below the galactic plane, which could be the best constraint for the slow-diffusion region among similar works. The $\overline{p}/p$ ratio and the amplitude of CR anisotropy predicted by the SDD model are consistent with the observations, while the predicted high-energy electron and positron fluxes are slightly and significantly lower than the observations, respectively, indicating the necessity of extra sources.

A Dynamical Model of Equatorial Magnetosonic Waves in the Inner Magnetosphere: A Machine Learning Approach

AbstractEquatorial magnetosonic waves (EMS), together with chorus and plasmaspheric hiss, play key roles in the dynamics of energetic electron fluxes in the magnetosphere. Numerical models, developed following a first principles approach, that are used to study the evolution of high energy electron fluxes are mainly based on quasilinear diffusion. The application of such numerical codes requires statistical models for the distribution of key magnetospheric wave modes to estimate the appropriate diffusion coefficients. These waves are generally statistically modeled as a function of spatial location and geomagnetic indices (e.g., AE, Kp, or Dst). This study presents a novel dynamic spatiotemporal model for EMS wave amplitude, developed using the Nonlinear AutoRegressive Moving Average eXogenous machine learning approach. The EMS wave amplitude, measured by the Van Allen Probes, are modeled using the time lags of the solar wind and geomagnetic indices as inputs as well as the location at which the measurement is made. The resulting model performance is assessed on a separate Van Allen Probes data set, where the prediction efficiency was found to be 34.0% and the correlation coefficient was 56.9%. With more training and validation data the performance metrics could potentially be improved, however, it is also possible that the EMS wave distribution is affected by stochastic factors and the performance metrics obtained for this model are close to the potential maximum.

Creation of Negatively Charged Boron Vacancies in Hexagonal Boron Nitride Crystal by Electron Irradiation and Mechanism of Inhomogeneous Broadening of Boron Vacancy-Related Spin Resonance Lines.

Optically addressable high-spin states (S ≥ 1) of defects in semiconductors are the basis for the development of solid-state quantum technologies. Recently, one such defect has been found in hexagonal boron nitride (hBN) and identified as a negatively charged boron vacancy (). To explore and utilize the properties of this defect, one needs to design a robust way for its creation in an hBN crystal. We investigate the possibility of creating centers in an hBN single crystal by means of irradiation with a high-energy (E = 2 MeV) electron flux. Optical excitation of the irradiated sample induces fluorescence in the near-infrared range together with the electron spin resonance (ESR) spectrum of the triplet centers with a zero-field splitting value of D = 3.6 GHz, manifesting an optically induced population inversion of the ground state spin sublevels. These observations are the signatures of the centers and demonstrate that electron irradiation can be reliably used to create these centers in hBN. Exploration of the spin resonance line shape allowed us to establish the source of the line broadening, which occurs due to the slight deviation in orientation of the two-dimensional B-N atomic plains being exactly parallel relative to each other. The results of the analysis of the broadening mechanism can be used for the crystalline quality control of the 2D materials, using the spin embedded in the hBN as a probe.

Controlling radiolysis chemistry on the nanoscale in liquid cell scanning transmission electron microscopy.

When high-energy electrons from a scanning transmission electron microscope (STEM) are incident on a liquid, the vast majority of the chemical reactions that are observed are induced by the radiolysis breakdown of the liquid molecules. In the study of liquids, the radiolysis products of pure water are well known, and their rate of formation for a given flux of high-energy electrons has been studied intensively over the last few years for uniform TEM illumination. In this paper, we demonstrate that the temporal and spatial distribution of the electron illumination can significantly affect the final density of radiolysis products in water and even change the type of reaction taking place. We simulate the complex array of possible spatial/temporal distributions of electrons that are accessible experimentally by controlling the size, the scan rate and the hopping distance of the electron probe in STEM mode and then compare the results to the uniformly illuminated TEM mode of imaging. By distributing the electron dose both spatially and temporally in the STEM through a randomised "spot-scan" mode of imaging, the diffusion overlap of the radiolysis products can be reduced, and the resulting reactions can be more readily controlled. This control allows the resolution of the images to be separated from the speed of the induced reaction (which is based on beam current alone) and this facet of the experiment will allow a wide range of chemical reactions to be uniquely tailored and observed in all liquid cell STEM experiments.

Влияние компактирования исходной шихты на радиационный синтез YAG:Се-керамики

It has been shown that the morphology of YAG: Ce ceramic samples, synthesized in the field of high-energy electron flux, depends on the degree of compaction of the initial charge of Y, Al, Ce oxides. The fraction of the YAG phase is higher in the samples of ceramics obtained from the compacted charge. The spectral characteristics of the luminescence of samples, synthesized from a mixture of the same composition, does not depend on the degree of compaction.