Charge Exchange Effects Research Articles

Range Separation of the Interaction Potential in Intermolecular and Intramolecular Symmetry-Adapted Perturbation Theory.

Symmetry-adapted perturbation theory (SAPT) is a popular and versatile tool to compute and decompose noncovalent interaction energies between molecules. The intramolecular SAPT (ISAPT) variant provides a similar energy decomposition between two nonbonded fragments of the same molecule, covalently connected by a third fragment. In this work, we explore an alternative approach where the noncovalent interaction is singled out by a range separation of the Coulomb potential. We investigate two common splittings of the 1/r potential into long-range and short-range parts based on the Gaussian and error functions, and approximate either the entire intermolecular/interfragment interaction or only its attractive terms by the long-range contribution. These range separation schemes are tested for a number of intermolecular and intramolecular complexes. We find that the energy corrections from range-separated SAPT or ISAPT are in reasonable agreement with complete SAPT/ISAPT data. This result should be contrasted with the inability of the long-range multipole expansion to describe crucial short-range charge penetration and exchange effects; it shows that the long-range interaction potential does not just recover the asymptotic interaction energy but also provides a useful account of short-range terms. The best consistency is attained for the error-function separation applied to all interaction terms, both attractive and repulsive. This study is the first step toward a fragmentation-free decomposition of intramolecular nonbonded energy.

Ultralow-Power Single-Sensor-Based E-Nose System Powered by Duty Cycling and Deep Learning for Real-Time Gas Identification.

This study presents a novel, ultralow-power single-sensor-based electronic nose (e-nose) system for real-time gas identification, distinguishing itself from conventional sensor-array-based e-nose systems, whose power consumption and cost increase with the number of sensors. Our system employs a single metal oxide semiconductor (MOS) sensor built on a suspended 1D nanoheater, driven by duty cycling─characterized by repeated pulsed power inputs. The sensor's ultrafast thermal response, enabled by its small size, effectively decouples the effects of temperature and surface charge exchange on the MOS nanomaterial's conductivity. This provides distinct sensing signals that alternate between responses coupled with and decoupled from the thermally enhanced conductivity, all within a single time domain during duty cycling. The magnitude and ratio of these dual responses vary depending on the gas type and concentration, facilitating the early stage gas identification of five gas types within 30 s via a convolutional neural network (classification accuracy = 93.9%, concentration regression error = 19.8%). Additionally, the duty-cycling mode significantly reduces power consumption by up to 90%, lowering it to 160 μW to heat the sensor to 250 °C. Manufactured using only wafer-level batch microfabrication processes, this innovative e-nose system promises the facile implementation of battery-driven, long-term, and cost-effective IoT monitoring systems.

Effects of charge exchange on plasma flow in the heliosheath and astrosheathes

ABSTRACT Shock boundary layers are regions bounded by a shock wave on the one side and tangential discontinuity on the other side. These boundary layers are commonly observed in astrophysics. For example, they exist in the regions of the interaction of the stellar winds with the surrounding interstellar medium. Additionally, the shock layers (SLs) are often penetrated by the flows of interstellar atoms, as, for instance, in the astrospheres of the stars embedded by the partially ionized interstellar clouds. This paper presents a simple toy model of an SL that aims to qualitatively describe the influence of charge exchange with interstellar hydrogen atoms on the plasma flow in astrospheric SLs. To clearly explore this effect, magnetic fields are neglected, and the geometry is kept as simple as possible. The model explains why the cooling of plasma due to charge exchange in the inner heliosheath leads to an increase in plasma density in front of the heliopause. It also demonstrates that the source of momentum causes changes in the pressure profile within the SL. The paper also discusses the decrease in plasma density near the astropause in the outer SL in the case of layer heating, which is particularly relevant in light of the Voyager measurements in the heliospheric SL.

The Effect of Angular Scattering Imposed by Charge Exchange and Elastic Collisions on Interstellar Neutral Hydrogen Atoms

Angular scattering (AS) in charge exchange and elastic collisions between interstellar ions and neutral (ISN) atoms has been assumed to be negligible in previous studies. Here, we investigate the momentum transfer associated with the AS of H atoms using Monte Carlo calculations to simulate their transport through the outer heliosheath. We consider two cases where charge exchange and elastic collisions between ISN H atoms and protons occur with and without AS in the outer heliosheath. We show that considering AS decelerates and heats primary ISN H, reducing the effect of selective charge exchange in the outer heliosheath. Secondary ISN H atoms, on the other hand, are not significantly affected by AS. We then simulate the transport of ISN H atoms inside the heliosphere to simulate count rates observed in the lowest energy bin of IBEX-Lo. We study the effect of radiation pressure on the ISN H measurements for the cases with and without AS and compare them with our previous findings. We find an effective radiation parameter (μ eff, which represents force associated with radiation pressure relative to gravity) for the years 2009–2018 based on the longitudinal shift of the ISN H signal. The two cases with and without AS reproduce the longitudinal shift in accordance with variations in solar activity, in agreement with our previous results, and they result in similar values for the μ eff, which is ∼22%–23% larger than the value found based on solar Lyα profile observations.

Energy-loss straggling of helium in elemental solids: The importance of the charge-exchange and bunching effects

In this study, we extend to Helium (He) ions the analysis of the energy-loss straggling of protons in simple materials as presented in NIMB 497 70 (2021). Our findings show that the excess of energy-loss straggling for both protons and He ions is highly correlated to the inhomogeneous distribution of electrons over the unit cell, referred to here as bunching effects, and that charge-exchange straggling has a minor impact, although it can compete with bunching effects for light targets. The Convolution approximation for swift Particles program was used to demonstrate that the bunching effect is a significant contributor to the straggling for both protons and He ions. In addition, we show that packing effects, a special form of bunching is of minor importance. The Yang-O’Connor-Wang formula for He was refined in this work to account for recent experimental data.

Europa's Perturbed Fields and Induced Dipole Affect Energetic Proton Depletions During Distant Alfvén Wing Flybys

AbstractWe investigate the causes of energetic proton (80–540 keV) depletions measured during the two most distant flybys of Europa by Galileo, E17 and E25A, which encountered the Alfvén wings. First, by simulating the proton flux with a Monte Carlo particle tracing code we investigate the effect of: electromagnetic field perturbations, the induced dipole, atmospheric charge exchange and plumes. Inhomogeneous fields associated with the Alfvén wings and the ionosphere strongly affect the depletions. For homogeneous fields the depletion along the trajectory is focused on a narrow pitch angle range and has no structure, whereas the depletion for perturbed (inhomogeneous) fields represents a wider and complex structure. Furthermore, also the induced dipole alters the depletion structure. The effect of plumes (density 2.5 × 1015 m−3) and charge exchange on the proton depletion is minor. Second, we compare the simulations to the proton measurements. The simulations with inhomogeneous fields describe the data qualitatively better than the homogeneous case, suggesting that indeed field perturbations are responsible for the measured losses. We attribute discrepancies between the simulations and the proton measurements to discrepancies between the simulated and real fields. We argue that simulating the fields along the trajectory is a good first step, but that ideally the energetic ion flux is reconstructed well to gain confidence in the interpretation of the simulated magnetic field. In conclusion, energetic ion observations along distant flybys through the Alfvén wings are suitable for isolating the characteristics of the global configuration of the magnetospheric interaction region of Europa (or other moons).

Modeling of aluminum erosion by neutral particles in dedicated EAST experiments using the 3D-GAPS code

To evaluate the erosion effects of charge exchange (CX) neutrals on first wall materials, aluminum (Al) coated samples installed in a cylindrical sleeve were exposed to EAST plasmas with the Material and Plasma Evaluation System (MAPES). The 3D-GAPS code was firstly used to simulate the dedicated experiments with the neutral energy spectrums measured by the Low Energy Neutral Particle Analyzer located at the MAPES. The modeled Al erosion rates with isotropic angular distributions for incident D neutrals are consistent with the measured erosion thicknesses of Al layer by Rutherford backscattering spectrometry before and after the plasma exposure. The effects of neutral reflection coefficients and the heights of cylindrical sleeve on material erosion are also studied. The measured material erosion rate by CX neutrals in EAST verified by the modeling can help to us understand the effects of neutrals on first wall erosion, which is an important erosion process in future fusion reactors.

Electron Spectroscopy of Charge Exchange Effects in Low Energy Ion Scattering at Surfaces: Case Studies of Heavy Ions at Al Surface

This work discusses studies of electron emissions during the interaction of low energy (in the keV energy range and below) singly charged ions with Aluminum surfaces. Analysis of the spectra provides insight into the electronic excitation processes and the dynamics of the interaction of the projectiles with the surface excitation. The work is primarily focused on the clarification of the role of electron promotion in charge exchange processes that occur during the cascade of atomic collisions. The work highlights the importance of the solid environment and of electron correlation in the understanding of charge exchange and energy deposition in ion-solids interactions.

PIC-DSMC Simulation of a Hall Thruster Plume with Charge Exchange Effects Using pdFOAM

To develop technologies for the stable operation of electric propulsion systems, the effects of charge exchange (CEX) on the exhaust plume of a Hall thruster were studied using the particle-in-cell direct simulation Monte Carlo (PIC-DSMC) method. For the numerical analysis, an OpenFOAM-based code, pdFOAM, with a simple electron fluid model was employed. In an example problem using the D55 Hall thruster exhaust plume, the results showed good agreement with experimental measurements of the plasma potential. In the results, CEX effects enhanced Xe+ particle scattering near the thruster exit. However, due to the increase in the plasma potential with CEX effects, fewer Xe2+ particles were near the thruster exit with CEX effects than without CEX effects.

The soft X-ray background with Suzaku. I. Milky Way halo

Abstract We present measurements of the soft X-ray background emission for 130 Suzaku observations at 75° < l < 285° and |b| > 15° obtained from 2005 to 2015, covering nearly one solar cycle. In addition to the standard soft X-ray background model consisting of the local hot bubble and the Milky Way Halo (MWH), we include a hot collisional-ionization-equilibrium component with a temperature of ∼0.8 keV to reproduce spectra of a significant fraction of the lines of sight. Then, the scatter in the relation between the emission measure vs. temperature of the MWH component is reduced. Here, we exclude time ranges with high count rates to minimize the effect of the solar wind charge exchange (SWCX). However, the spectra of almost the same lines of sight are inconsistent. The heliospheric SWCX emissions likely contaminate and give a bias in measurements of temperature and the emission measure of the MWH. Excluding the data around the solar maximum and using the data taken before the end of 2009, at |b| > 35° and 105° < l < 255°, the temperature (0.22 keV) and emission measure (2 × 10−3 cm−6 pc) of the MWH are fairly uniform. The increase of the emission measure toward the lower Galactic latitude at |b| < 35° indicates the presence of a disk-like morphology component. A composite model which consists of disk-like and spherical-morphology components also reproduces the observed emission measure distribution of MWH. In this case, the hydrostatic mass at a few tens of kiloparsec from the Galactic center agrees with the gravitational mass of the Milky Way. The plasma with the virial temperature likely fills the Milky Way halo in nearly hydrostatic equilibrium. Assuming a gas metallicity of 0.3 solar, the upper limit of the gas mass of the spherical component out to 250 kpc, or the virial radius, is ∼ a few × 1010 M⊙.

Effects of charge exchange on the evaporative wind of HD 209458b

ABSTRACT The role of charge exchange in shaping exoplanet photoevaporation remains a topic of contention. Exchange of electrons between stellar wind protons from the exoplanet’s host star and neutral hydrogen from the planet’s wind has been proposed as a mechanism to create ‘energetic neutral atoms’ (ENAs), which could explain the high absorption line velocities observed in systems where mass-loss is occurring. In this paper, we present results from three-dimensional hydrodynamic simulations of the mass-loss of a planet similar to HD 209458b. We self-consistently launch a planetary wind by calculating the ionization and heating resulting from incident high-energy radiation, inject a stellar wind into the simulation, and allow electron exchange between the stellar and planetary winds. We predict the potential production of ENAs by the wind–wind interaction analytically, and then present the results of our simulations, which confirm the analytic limits. Within the limits of our hydrodynamic simulation, we find that charge exchange with the stellar wind properties examined here is unable to explain the absorption observed at high Doppler velocities.

Multi‐Fluid MHD Simulations of Europa's Plasma Interaction Under Different Magnetospheric Conditions

AbstractEuropa hosts a periodically changing plasma interaction driven by the variations of Jupiter's magnetic field and magnetospheric plasma. We have developed a multi‐fluid magnetohydrodynamic (MHD) model for Europa to characterize the global configuration of the plasma interaction with the moon and its tenuous atmosphere. The model solves the multi‐fluid MHD equations for electrons and three ion fluids (Jupiter's magnetospheric O+, as well as O+ and O2+ originating from Europa's atmosphere) while incorporating sources and losses in the MHD equations due to electron impact and photo‐ionization, charge exchange, recombination and other relevant collisional effects. Using input parameters constrained by the Galileo magnetic field and plasma observations, we first demonstrate the accuracy of our model by simulating the Galileo E4 and E14 flybys, which took place under different upstream conditions and sampled different regions of Europa's interaction. Our model produces 3D magnetic field and plasma bulk parameters that agree with and provide context for the flyby observations. We next present the results of a parameter study of Europa's plasma interaction at three different excursions from Jupiter's central plasma sheet, for three different global magnetospheric states, comprising nine steady‐state simulations. By separately tracking multiple ion fluids, our MHD model allows us to quantify the access of the Jovian magnetospheric plasma to Europa's surface and determine how that access is affected by changing magnetospheric conditions. We find that the thermal magnetospheric O+ precipitation rate ranges from (1.8–26) × 1024 ions/s, and that the precipitation rate increases with the density of the ambient magnetospheric plasma.

Theoretical study of spin observables in $$\varvec{pd}$$ elastic scattering at energies $$\varvec{T_p = 800}$$–$$\varvec{1000}$$ MeV

Various spin observables (analyzing powers and spin-correlation parameters) in $pd$ elastic scattering at $T_p = 800-1000$ MeV are analyzed within the framework of the refined Glauber model. The theoretical model uses as input spin-dependent $NN$ amplitudes obtained from the most recent partial-wave analysis and also takes into account the deuteron $D$ wave and charge-exchange effects. Predictions of the refined Glauber model are compared with the existing experimental data. Reasonable agreement between the theoretical calculations and experimental data at low momentum transfers $|t| \lesssim 0.2$ (GeV/$c)^2$ is found for all observables considered. Moderate discrepancies found in this region are shown to be likely due to uncertainties in the input $NN$ amplitudes. Qualitative agreement at higher momentum transfers is also found for most observables except the tensor ones with mixed $x$ and $z$ polarization components. Possible reasons for observed deviations of the model calculations from the data at $|t| > 0.2$ (GeV/$c)^2$ are discussed.

Van der Waals SnSe2(1−x)S2x Alloys: Composition‐Dependent Bowing Coefficient and Electron–Phonon Interaction

AbstractThe design of advanced functional materials with customized properties often requires the use of an alloy. This approach has been used for decades, but only recently to create van der Waals (vdW) alloys for applications in electronics, optoelectronics, and thermoelectrics. A route to engineering their physical properties is by mixing isoelectronic elements, as done for the SnSe2(1−x)S2x alloy. Here, by experiment and first‐principles modeling, it is shown that the value of x can be adjusted over a wide range, indicating good miscibility of the SnS2 and SnSe2 compounds. The x‐dependence of the indirect bandgap energy from Eind = 1.20 eV for SnSe2 to Eind = 2.14 eV for SnS2, corresponds to a large bowing coefficient b ≈ 1 eV, arising from volume deformation and charge exchange effects due to the different sizes and orbital energies of the S‐ and Se‐atoms. This also causes composition‐dependent phonon energy modes, electron–phonon interaction, and temperature dependence of Eind. The alloys are exfoliable into thin layers with properties that depend on the composition, but only weakly on the layer thickness. This work shows that the electronic and vibrational properties of the SnSe2(1−x)S2x alloy and its thin layers provide a versatile platform for development and exploitation.

Excitons in InP, GaP, and GaxIn1−xP quantum dots: Insights from time-dependent density functional theory

Colloidal quantum dots (QDs) of group III-V are considered as promising candidates for next-generation environmentally friendly light emitting devices, yet there appears to be only limited understanding of the underlying electronic and excitonic properties. Using large-scale density functional theory with the hybrid B3LYP functional solving the single-particle states and time-dependent density functional theory accounting for the many-body excitonic effects, we have identified the structural, electronic and excitonic optical properties of InP, GaP and GaInP QDs containing up to a thousand atoms or more. The calculated optical gap of InP QD appears in excellent agreement with available experiments, and it scales nearly linearly with the inverse diameter. The radiative exciton decay lifetime is found to increase surprisingly linearly with increasing the dot size. For GaP QDs, we predict an unusual electronic state crossover at diameter around 1.5 nm whereby the nature of the lowest unoccupied molecular orbital (LUMO) state switches its symmetry from $\Gamma_{5}$-like at larger diameter to $\Gamma_{1}$-like at smaller diameter. After the crossover, the absorption intensity of the band-edge exciton states is significantly enhanced. Finally, we find that Vegard's law holds very well for GaInP random alloyed quantum dots down to ultra-small sizes with less than a hundred atoms. The obtained energy gap bowing parameter of this common-cation compound in QD regime appears positive, size-dependent and much smaller than its bulk parentage. The volume deformation, dominating over the charge exchange and structure relaxation effects, is mainly responsible for the QD energy gap bowing. The present work provides a road map for a variety of electronic and optical properties of colloidal QDs in group III-V that can guide spectroscopic studies.

A semi-classical model for the charge exchange and energy loss of slow highly charged ions in ultrathin materials

We present a simple and reliable method, based on the over-barrier model and Lindhard’s formula, to calculate the energy loss, charge transfer, and normalized intensity of highly charged ions penetrating through 2D ultrathin materials, including graphene and carbon nanomembranes. According to our results, the interaction between the ions and the 2D material can be simplified as an equivalent two-body collision, and we find that full consideration of the charge exchange effect is key to understanding the mechanism of ion energy deposition in an ultrathin target. Not only can this semiclassical model be used to evaluate the ion irradiation effect to a very good level of accuracy, but it also provides important guidance for tailoring the properties of 2D materials using ion beams.

Hydrodynamical interaction of stellar and planetary winds: effects of charge exchange and radiation pressure on the observed Ly α absorption

ABSTRACT Lyman α observations of the transiting exoplanet HD 209458b enable the study of exoplanet exospheres exposed to stellar extreme ultraviolet (EUV) fluxes, as well as the interacting stellar wind properties. In this study we present 3D hydrodynamical models for the stellar–planetary wind interaction including radiation pressure and charge exchange, together with photoionization, recombination, and collisional ionization processes. Our models explore the contribution of the radiation pressure and charge exchange to the Ly α absorption profile in a hydrodynamical framework, and for a single set of stellar wind parameters appropriate for HD 209458. We find that most of the absorption is produced by the material from the planet, with a secondary contribution of neutralized stellar ions by charge exchange. At the same time, the hydrodynamic shock heats up the planetary material, resulting in a broad thermal profile. Meanwhile, the radiation pressure yields a small velocity shift of the absorbing material. While neither charge exchange nor radiation pressure provides enough neutrals at the velocity needed to explain the observations at −100 km s−1 individually, we find that the two effects combined with the broad thermal profile are able to explain the observations.

Влияние рентгеновского излучения на валентное состояние Eu в люминофоре Y-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- : Eu-=SUP=-3+-=/SUP=-

The effect of X-rays on the valence state of Eu ions in a Y2O3 matrix has been studied by the EPR method. The effect of charge exchange of Eu ions (Eu3 + → Eu2 + → Eu3 +) in the Y2O3 structure has been found. The mechanism of europium reduction to the divalent state under the action of X-ray irradiation has been described.

A small electron beam ion trap/source facility for electron/neutral–ion collisional spectroscopy in astrophysical plasmas

Spectra are fundamental observation data used for astronomical research, but understanding them strongly depends on theoretical models with many fundamental parameters from theoretical calculations. Different models give different insights for understanding a specific object. Hence, laboratory benchmarks for these theoretical models become necessary. An electron beam ion trap is an ideal facility for spectroscopic benchmarks due to its similar conditions of electron density and temperature compared to astrophysical plasmas in stellar coronae, supernova remnants and so on. In this paper, we will describe the performance of a small electron beam ion trap/source facility installed at National Astronomical Observatories, Chinese Academy of Sciences.We present some preliminary experimental results on X-ray emission, ion production, the ionization process of trapped ions as well as the effects of charge exchange on the ionization.

Neutral recycling effects on ITG turbulence

The effects of recycled neutral atoms on tokamak ion temperature gradient (ITG) driven turbulence have been investigated in a steep edge pedestal, magnetic separatrix configuration, with the full-f edge gryokinetic code XGC1. An adiabatic electron model has been used; hence, the impacts of neutral particles and turbulence on the density gradient are not considered, nor are electromagnetic turbulence effects. The neutral atoms enhance the ITG turbulence, first, by increasing the ion temperature gradient in the pedestal via the cooling effects of charge exchange and, second, by a relative reduction in the shearing rate.