Electron Collisions Research Articles

Tellurium emission line in kilonova AT 2017gfo

ABSTRACT The late-time spectra of the kilonova AT 2017gfo associated with GW170817 exhibit a strong emission line feature at $2.1\, {\rm \mu m}$. The line structure develops with time and there is no blueshifted absorption feature in the spectra, suggesting that this emission line feature is produced by electron collision excitation. We attribute the emission line to a fine structure line of Tellurium (Te) III, which is one of the most abundant elements in the second r-process peak. By using a synthetic spectral modelling including fine structure emission lines with the solar r-process abundance pattern beyond the first r-process peak, i.e. atomic mass numbers A ≳ 88, we demonstrate that [Te iii] $2.10\, \rm \mu m$ is indeed expected to be the strongest emission line in the near infrared region. We estimate that the required mass of Te iii is ∼10−3 M⊙, corresponding to the merger ejecta of 0.05 M⊙, which is in agreement with the mass estimated from the kilonova light curve.

Nonlinear microtearing modes in MAST and their stochastic layer formation

First nonlinear gyrokinetic simulations of microtearing modes in the core of a MAST case are performed on two surfaces of the high-collisionality discharge used in Valovič et al (2011 Nucl. Fusion 51 073045) to obtain the favorable energy confinement scaling with collisionality, . On the considered surfaces microtearing modes dominate linearly at binormal length scales of the order of the ion Larmor radius. While the effect of electron collision frequency is moderate in linear simulations, a strong dependence on this parameter is found in nonlinear simulations at , where r and a are the surface and tokamak minor radius, respectively. The dynamics of magnetic islands generated by microtearing modes is analysed, showing that the radial extent of the stochastic region caused by islands overlapping plays an important role in determining the saturation level of the microtearing mode driven heat flux. Local nonlinear gyrokinetic simulations show that the microtearing mode driven heat flux, , is largely dominated by magnetic flutter and depends strongly on the magnetic shear, . Comparing two surfaces, and , reveals that is negligible at (), with the electron temperature gradient (ETG) driven heat flux, , comparable to the experimental electron heat flux, , while is significantly larger and comparable to and at (). Microtearing modes cause more experimentally significant transport in higher regions and may influence (together with ETG modes) the observed scaling of energy confinement time with collisionality (Valovič et al 2011 Nucl. Fusion 51 073045).

State estimation of the dynamic behavior of plasma properties in a Hall effect thruster discharge

The dynamic behaviors of the plasma properties in a Hall effect thruster discharge channel are estimated using a physics-constrained extended Kalman filter (PC-EKF) with a zero-dimensional global plasma model. The state estimates obtained using the global plasma EKF model are augmented by experimental data, in this case a discharge current signal. The use of state estimation allows for the determination of time-resolved plasma behaviors that may be difficult to measure experimentally, such as electron temperature and bulk velocity. The model is applied to investigate the plasma behavior at various thruster operating conditions, i.e. at varying discharge voltages and discharge currents. The estimated plasma properties are used to determine the classical electron collision frequency and the anomalous electron scattering frequency, which are shown to vary in time.

Predicting the exclusive diffractive electron-ion cross section at small x with machine learning in Sartre

The event generator Sartre has been used extensively for simulations of electron-ion collisions in preparation for the Electron-Ion Collider (EIC). Sartre simulates exclusive diffraction in eA collisions, in principle for any nuclear species and exclusive final state, usually a vector meson. The coherent and incoherent cross sections for each process are calculated in the colour dipole model for small x from the first and second moments of the respective amplitude, averaged over initial state spatial configurations. Taking these averages is a very CPU demanding task. In order to function as an efficient event generator, these amplitude moments are saved into lookup tables which are used as input for the event generation, making the latter a very fast process. However, there are many recent and ongoing developments of the dipole models underlying the calculations, both in terms of fits of the model parameters to new data as well as new parametrisations of the dipole or proton geometries. Therefore, it is desirable to have a more flexible method for producing the lookup tables. Here, we propose a method using neural networks which can reduce the table production time by 90% while retaining the same precision in the resulting cross sections.

Low-Energy Electron and Positron Scattering by para-Difluorobenzene.

The Schwinger multichannel method is employed in calculations of the elastic integral and differential cross sections for collisions of low-energy electrons and positrons with para-difluorobenzene (1,4-C6H4F2). The present calculations involving electron scattering have been performed using both static-exchange and static-exchange plus polarization levels of approximation. Our results indicate the presence of three resonances of π*-character in the low-energy region and a fourth resonance, of σ*-character, at higher energy levels. With respect to the positron scattering, the calculations were conducted using the static plus polarization approximation at three different polarization levels. The present calculated electron and positron cross sections show a reasonable agreement with the total cross sections measured by Makochekanwa et al. (J. Phys. B, 2004, 37, 1841). It is also important to highlight that our computed integral cross section for electron scattering indicates the presence of a Ramsauer-Townsend minimum, while the integral cross section for positron scattering indicates the presence of a virtual state.

Changing pattern of N2 dissociation in N2–Ar RF plasma during E–H mode transition

The behaviour of nitrogen plasma mixed with varying proportions of argon (10%–80%) is investigated under different RF discharge conditions. It is observed that at a relatively low RF power of 200 W (E-mode) the dissociation fraction (DF) of nitrogen increases with the growing concentration of argon, whereas the opposite happens for a higher RF power of 1000 W (H-mode), when the DF rapidly falls from a high value as the argon percentage starts to increase. This rising trend of DF closely follows the argon metastable fraction (MF) in the E-mode, and for the H-mode it is not followed until the argon percentage crosses the 20% mark. The electron density, temperature and electron energy probability function (EEPF) are obtained using a RF compensated Langmuir probe and to evaluate the vibrational and rotational temperatures, DF, MF etc, a separate optical emission spectroscopy technique is incorporated. At 5 × 10−3 mbar of working pressure and 10% argon content the EEPF profile reveals that the plasma changes from non-Maxwellian to Maxwellian as the RF power jumps from 200 W to 1000 W, and for a fixed RF power the high energy tail tends to move upwards with the gradual increment of argon. These observations are reverified theoretically by considering electron–electron collision frequency and electron bounce frequency as a function of electron temperature. Overall, all the major experimental phenomena in this study are explained in terms of EEPF profile, electron–electron collision effect, electron and gas temperature, electron density and argon metastable population.

Increased intracellular crowding during hyperosmotic stress

Hyperosmotic stress activates in live cells numerous processes and also promotes intracellular protein/RNA aggregation and phase separation. However, the time course and the extent of these changes remain largely uncharacterized. To investigate dynamic changes in intracellular macromolecular crowding (MMC) induced by hyperosmotic stress in live cells, we used fluorescence lifetime imaging microscopy and fluorescence correlation spectroscopy (FCS) to quantify changes in the local environment by measuring the fluorescence lifetime and the diffusion of the monomeric enhanced green fluorescent protein (eGFP), respectively. Real-time monitoring of eGFP fluorescence lifetime showed that a faster response to environmental changes due to MMC is observed than when measuring the acceptor/donor emission ratio using the MMC-sensitive Förster resonance energy transfer sensor (GimRET). This suggests that eGFP molecular electronic states and/or collision frequency are affected by changes in the immediate surroundings due to MMC without requiring conformational changes as is the case for the GimRET sensor. Furthermore, eGFP diffusion assessed by FCS indicated higher intracellular viscosity due to increased MMC during hyperosmotic stress. Our findings reveal that changes in eGFP fluorescence lifetime and diffusion are early indicators of elevated intracellular MMC. Our approach can therefore be used to reveal in live cells short-lived transient states through which MMC builds over time, which could not be observed when measuring changes in other physical properties that occur at slower time scales.

Calculated cross sections for electron collisions with the BeN molecule

We report a low energy electron collision calculation with the BeN molecule in its X ground state using the molecular R-matrix method at a single geometry, namely, the equilibrium a 0 of the molecule. Using a suitable target model, we have calculated the elastic cross section and cross sections for electron impact excitation in several low-lying excited states of BeN. Cross sections for electron impact dissociation is derived from the electronic excitation cross sections. In addition, molecular data on bound sates of BeN and e-BeN negative ion resonances and widths at the target equilibrium Re that may be relevant for other studies are also provided.

Contribution of electron density to plasma decomposition rate of methane

Hydrogen extraction from methane will be a common and useful technique in hydrogen production systems and fuel cycle systems of deuterium-tritium fusion reactors. Since tritium is a precious fuel, it needs to be extracted from impurity gases such as tritiated methane contained in the exhaust gas from the plasma vessel of a fusion reactor. An experimental work was conducted in this study to investigate the electron collision of methane decomposition reaction in helium plasma. A special attention was placed on the electron density distribution in a plasma chamber, and the dependence of the decomposition rate on the methane/helium ratio. The experimental results showed that methane decomposition rate and electron density tended to increase linearly with increasing RF power. This suggests that a strong dependence of electron collision on methane decomposition. Eventually, the dependence of methane decomposition rate on electron density, total pressure, and inlet methane concentration in a gas flow-type helium plasma reactor was successfully formulated. This study provides new sight for demonstrating the contribution of electron density in RF plasma assisted methane decomposition, and the summarized equation offers potential for reactor design on promising energy utilization.

Exclusive ηc production by γ⁎γ interactions in electron-ion collisions

One of the main goals of future electron-ion colliders is to improve our understanding of the structure of hadrons. In this letter, we study the exclusive ηc production by γ⁎γ interactions in eA collisions and demonstrate that future experimental analysis of this process can be used to improve the description of the ηc transition form factor. The rapidity, transverse momentum and photon virtuality distributions are estimated considering the energy and target configurations expected to be present at the EIC, EicC and LHeC and assuming different predictions for the light-front wave function of the ηc meson. Our results indicate that the electron-ion colliders can be considered an alternative to providing supplementary data to those obtained in e−e+ colliders.

Влияние высыпающихся релятивистских электронов на характеристики сигналов системы РСДН-20 во время события 28 марта 2017

Based on the experimental data of the EISCAT radar and numerical modeling methods, the influence of the fluxes of subrelativistic (relativistic) electrons of the Earth's outer radiation belt on the operation of the RSDN-20 long-range navigation system operating at frequencies of 11.905 kHz, 12.649 kHz and 14.881 kHz has been studied. As a result of computational experiments, a slight decrease in attenuation under perturbed conditions was obtained at a frequency of 14.881 kHz with a slight, less than an order of magnitude increase in the electron concentration in the D- and E-layers of the ionosphere. At lower frequencies and in the case of an increase in concentration in the reflection region, an increase in signal attenuation is observed. It is shown that the violation of monotonicity in the frequency dependence of signal attenuation is associated with the position of the boundary between regions with different types of signal attenuation and the height of the signal reflection from the ionosphere. In the case when the intersection point of the high-altitude profile of the electron collision frequency υe with the profile of the doubled plasma frequency 2ωe is inside the signal reflection region, a nonlinear type of attenuation dependence on frequency is observed. The phases of RSDN-20 signals are weakly affected by the precipitation of relativistic energy electrons into the atmosphere. A comparison of the amplitudes of the signals obtained in computational experiments and the signals recorded at the observatories of the Polar Geophysical Institute Lovozero and Barentsburg showed partial agreement in most of the changes recorded during the precipitation of subrelativistic electrons in the polar ionosphere. The presented estimates can be used on short radio paths of 100–200 km in the high latitude region to monitor the state of the ionosphere.

Propagation Characteristics of Terahertz Waves in Magnetized Dusty Plasma

The propagation characteristics, including reflectivity, transmissivity, and absorptivity, of terahertz (THz) waves in magnetized dusty plasmas sheath are investigated theoretically by the analytic method. Both the right-and left-hand circularly polarized (RCP and LCP) waves are considered. The calculation results illustrate that external magnetic field, plasma slab thickness, electron collision frequency, dust particles, and electron relaxation rate can affect the propagation characteristics of THz waves in plasmas. When dust particles are absent, a strong external magnetic field will cause the transmissivity of RCP waves to produce a transmissivity valley at the lower frequency band. Due to the action of external magnetic field and dust particles, a transmissivity peak appears at the lower frequency band for RCP waves. Increasing the density or radius of dust particles can cause an increase in transmissivity peak. For LCP waves, the transmissivity increases monotonously as the frequency of THz wave increases, whether the dust particles exist or not. These simulation results may provide a significant theoretical basis for solving the problem of “blackout.”

X-ray Thomson scattering spectra from density functional theory molecular dynamics simulations based on a modified Chihara formula.

We study ab initio approaches for calculating x-ray Thomson scattering spectra from density functional theory molecular dynamics simulations based on a modified Chihara formula that expresses the inelastic contribution in terms of the dielectric function. We study the electronic dynamic structure factor computed from the Mermin dielectric function using an ab initio electron-ion collision frequency in comparison to computations using a linear-response time-dependent density functional theory (LR-TDDFT) framework for hydrogen and beryllium and investigate the dispersion of free-free and bound-free contributions to the scattering signal. A separate treatment of these contributions, where only the free-free part follows the Mermin dispersion, shows good agreement with LR-TDDFT results for ambient-density beryllium, but breaks down for highly compressed matter where the bound states become pressure ionized. LR-TDDFT is used to reanalyze x-ray Thomson scattering experiments on beryllium demonstrating strong deviations from the plasma conditions inferred with traditional analytic models at small scattering angles.

Study of Electron Collisions with Isoprene, 1,2-Butadiene, and Their Isomers.

Isoprene, 1,2-butadiene, and their isomers play an important role in aerosols in the atmosphere, interstellar media, and extraterrestrial life. Since electrons are everywhere, studying how electrons interact with these molecules is an important part of studying such environments. To date, however, little investigation has been conducted in this area. Bearing this in mind, we conducted a thorough investigation to report the various electron scattering cross sections of isoprene, 1,2-butadiene, and their isomers. The methods used for this purpose are reliable within the limits of adopted model potentials. The optical potential method was used to get the total elastic and inelastic cross sections, while the complex scattering potential ionization contribution method was used to get the total ionization cross section from the inelastic contribution. The results from these approximations are pretty close to the results from earlier experiments and theories. Furthermore, most of these isomers are being explored for the first time. Besides, their isomeric effect is also discussed. A correlation between the cross sections of molecules is demonstrated, which can be used to predict cross sections of those molecules where previous data are not available.

Particle pump-out induced by trapped electron mode turbulence in electron cyclotron heated plasmas on XuanLong-50 spherical torus

Particle pump-out effects induced by low-frequency (<200 kHz) density fluctuations were observed in solely electron cyclotron wave (ECW)-heated plasmas on the spherical torus XuanLong-50 (EXL-50) without a central solenoid. The intensity of the relative density fluctuations increases with increasing ECW power and decays when the ECW is turned off while sustaining the plasma current. The electron densities are maintained relatively high and steady when the density fluctuations are completely absent, indicating that the outward transport of electrons is dominated by the particle pump-out effect of the ECW. The density fluctuations are modulated by a supersonic molecular beam injection pulse and the modulation amplitude decreases with increasing electron density at the same ECW injection power and decreasing ECW power at the same electron density, respectively. Analysis revealed that a critical value of electron temperature gradient (ETG) triggers the density fluctuations, and the intensity of the relative density fluctuations is positively correlated with the ETG and approximately inversely proportional to the effective collision frequency. With plasma parameters similar to those of EXL-50 experiments, the HD7 code simulations demonstrate that trapped electron mode (TEM) turbulence can be excited by ETG higher than the critical value observed in the experiment. In addition, the dependence of the mode growth rate (supposed to be proportional to the saturation level of fluctuations in quasi-linear theory) and the measured intensity of the density fluctuations is comparable. The simulated outward particle flux integrated over the poloidal wave number spectrum is significant and proportional to ETG. These observations demonstrate that the density fluctuation is TEM turbulence, which is driven by ETG and induces particle pump-out when the electron density/effective electron collision frequency is low. The potential relevance of this work with the controls of plasma profiles, impurities, helium ash, and heat transport in future reactors of similar low effective collision frequency is also discussed.

Low-temperature chemistry in plasma-driven ammonia oxidative pyrolysis

Ammonia is gaining increasing attention as a green alternative fuel for achieving large-scale carbon emission reduction. Despite its potential technical prospects, the harsh ignition conditions and slow flame propagation speed of ammonia pose significant challenges to its application in engines. Non-equilibrium plasma has been identified as a promising method, but current research on plasma-enhanced ammonia combustion is limited and primarily focuses on ignition characteristics revealed by kinetic models. In this study, low-temperature and low-pressure chemistry in plasma-assisted ammonia oxidative pyrolysis is investigated by integrated studies of steady-state GC measurements and mathematical simulation. The detailed kinetic mechanism of NH3 decomposition in plasma-driven Ar/NH3 and Ar/NH3/O2 mixtures has been developed. The numerical model has good agreements with the experimental measurements in NH3/O2 consumption and N2/H2 generation, which demonstrates the rationality of modelling. Based on the modelling results, species density profiles, path flux and sensitivity analysis for the key plasma-produced species such as NH2, NH, H2, OH, H, O, O(1D), O2(a1Δg), O2(b1Σg+), Ar∗, H−, Ar+, NH3+, O2− in the discharge and afterglow are analyzed in detail to illustrate the effectiveness of the active species on NH3 excitation and decomposition at low temperature and relatively higher E/N values. The results revealed that NH2, NH, H as well as H2 are primarily generated through the electron collision reactions e + NH3 → e + NH2 + H, e + NH3 → e + NH + H2 and the excited-argon collision reaction Ar∗ + NH3 + H → Ar + NH2 + 2H, which will then react with highly reactive oxidative species such as O2∗, O∗, O, OH, and O2 to produce stable products of NOx and H2O. NH3 → NH is found a specific pathway for NH3 consumption with plasma assistance, which further highlights the enhanced kinetic effects.

Cross Sections for Electron Collisions with N2, N2*, and N2+

Electron collision cross section data are complied from the literature for electron collisions with the nitrogen molecules, N2, N2+, and N2*. Cross sections are collected and reviewed for total scattering, elastic scattering, momentum transfer, rotational excitation, vibrational excitation, electronic excitation, dissociative processes, and ionization. The literature has been surveyed up to the end of 2021. For each of these processes, the recommended values of the cross sections are presented.

Improving dynamic collision frequencies: Impacts on dynamic structure factors and stopping powers in warm dense matter

Simulations and diagnostics of high-energy-density plasmas and warm dense matter rely on models of material response properties, both static and dynamic (frequency-dependent). Here, we systematically investigate variations in dynamic electron–ion collision frequencies ν(ω) in warm dense matter using data from a self-consistent-field average-atom model. We show that including the full quantum density of states, strong collisions, and inelastic collisions lead to significant changes in ν(ω). These changes result in red shifts and broadening of the plasmon peak in the dynamic structure factor, an effect observable in x-ray Thomson scattering spectra, and modify stopping powers around the Bragg peak. These changes improve the agreement of computationally efficient average-atom models with first-principles time-dependent density functional theory in warm dense aluminum, carbon, and deuterium.

Influence of plasma fluctuation on the electronic structures and electron collisional excitation and ionization processes

Studies demonstrated significant discrepancies between the experimental observations of Stillman et al. [Phys. Rev. E 95, 063,204 (2017)] and almost all recent state-of-the art theoretical predictions for the He-α (1s2p→1s2) line shift of Al11+ ions placed in a hot dense plasma environment. Here, we suggest a new distorted wave method to determine the electronic structure and collision dynamics of highly stripped ions placed in plasmas. The method incorporating the plasma fluctuation, which yields modification term to the calculation of the central-field potential, is applied to the above problem. By adjusting the parameter q, which characterizes the intensity of the plasma fluctuation, we reproduce the experimental line shifts well over the whole range (of temperature and density) measured. In addition, we perform a calculation by incorporating the screened potential of Stanton and Murillo [Phys. Rev. E 91, 033,104 (2015)] and the current results (from ab-initio calculations) are in much better agreement with the experimental data than most previous theoretical results. Finally, we perform the calculation of electron collisional excitation and ionisation dynamic processes, where the continuous electron wave function is obtained by numerically solving the modified coupled Dirac equation. A careful investigation of the effect of plasma fluctuation on the integrated cross sections is made. The present work not only leads to further stimulation of the development of shielding models in extreme conditions, but also has important applications in laboratory and space plasmas.

Collision off-axis position dependence of relativistic nonlinear Thomson inverse scattering of an excited electron in a tightly focused circular polarized laser pulse

This paper presents a novel view of the impact of electron collision off-axis positions on the dynamic properties and relativistic nonlinear Thomson inverse scattering of excited electrons within tightly focused, circularly polarized laser pulses of varying intensities. We examine the effects of the transverse ponderomotive force, specifically how the deviation angle and speed of electron motion are affected by the initial off-axis position of the electron and the peak amplitude of the laser pulse. When the laser pulse intensity is low, an increase in the electron’s initial off-axis distance results in reduced spatial radiation power, improved collimation, super-continuum phenomena generation, red-shifting of the spectrum’s harmonic peak, and significant symmetry in the radiation radial direction. However, in contradiction to conventional understandings, when the laser pulse intensity is relatively high, the properties of the relativistic nonlinear Thomson inverse scattering of the electron deviate from the central axis, changing direction in opposition to the aforementioned effects. After reaching a peak, these properties then shift again, aligning with the previous direction. The complex interplay of these effects suggests a greater nuance and intricacy in the relationship between laser pulse intensity, electron position, and scattering properties than previously thought.