Electron Collisions Research Articles

Electron-neutral collision cross sections for H2O: II. Anisotropic scattering and assessment of the validity of the two-term approximation

This work proposes a complete and consistent set of cross sections (CS) for electron collisions with water gas molecules to be published in the IST-Lisbon database on LXCat. The set is validated by the electron swarm analysis technique. The anisotropic angular distribution of electrons in rotational collisions is considered by means of the Born approximation in a two-term Boltzmann solver (LisbOn KInetics two-term Boltzmann solver (LoKI-B)) and a Monte Carlo simulations code (LoKI-MC), both freely available as open-source codes. The inclusion of electron anisotropic scattering in rotational collisions significantly improves the agreement between calculations and measurements of the electron drift velocity, reduced mobility, characteristic energy, reduced Townsend ionisation coefficient, reduced effective Townsend coefficient and reduced attachment coefficient. The MC simulations are deemed more accurate and shown to yield similar results as LoKI-B with the proposed set. The use of LoKI-MC also validates the set of CSs against parameters that cannot be obtained by LoKI-B, such as the longitudinal diffusion coefficient or the bulk transport coefficients.

Weakly convergent stochastic simulation of electron collisions in plasmas

Collisions between charged particles can be described and solved using Monte Carlo methods in the framework of stochastic differential equations (SDEs). In this paper, we start from an SDE including the extended Lorentz collision operator, which can recover the collisions between a sampling electron and background ions and electrons. On this basis, we construct a second order weakly convergent algorithm (WCA2) to simulate collisional effects of electrons in plasmas. Superseding the Weiner process by a three-point distribution, WCA2 possesses high weakly convergent accuracy as well as low computational costs. The definition and properties of weak convergence are discussed in detail. The weakly convergent order of WCA2 is verified both theoretically and numerically. Through two trial moment functions, we carefully analyze the numerical solutions of the SDE using rigorous statistical tests in the sense of weak convergence. The criteria and practical operations of finding the benchmark solution of SDEs are introduced at length. In order to illustrate the power of WCA2, we apply it to simulate the backward runaways in plasmas, which is a dramatic physical phenomenon. By comparison with the Euler-Maruyama method and the Cadjan-Ivanov method, the advantage and efficiency of WCA2 is exhibited. The backward runaway probability and its dependence on initial conditions are accurately studied using WCA2.

Nonlinear ion-stopping calculations for a classical free-electron gas at high projectile energies

In this work, we solved the classical equations of motion and Poisson equation self-consistently, equivalent to the nonlinear Vlasov-Poisson equation, for a projectile moving in a static free-electron gas to calculate the full noncentral self-consistent electron-ion potential, and thus the ion stopping power. We investigated the origin of the Barkas effect, namely, the first nonlinear effect for projectiles at high velocities responsible for the difference between the energy-loss results for positively and negatively charged ions traversing the same target. This effect is strongly enhanced by the multipolar part of the electron-ion potential as first suggested by Lindhard [J. Lindhard, Nucl. Instr. and Meth. 132, 1438 (1976)]. Moreover, this effect is partially related to the nonconservation of the angular momentum in electron-ion collisions. These nonlinear calculations are applied to understanding the stopping of protons and antiprotons in Al at high projectile energies.

Effects of rod radius and voltage on streamer discharge in a short air gap

Streamer discharge is the inaugural stage of gas discharge, and the average electron energy directly determines the electron collision reaction rate, which is a key parameter for studying streamer discharge. Therefore, taking into account the average electron energy, this work establishes a fluid chemical reaction model to simulate and study the course of evolution of a streamer discharge in a 5 mm rod–plate gap, considering 12 particles and 27 chemical reactions. It introduces the electron energy drift diffusion equation into the control equation, and analyzes the temporal and spatial changes of average electron energy, electric field intensity and electron density with change in rod radius and voltage. The effects of voltage and rod radius on the course of streamer discharge can be reflected more comprehensively by combining the average electron energies. Three different values of 0.3 mm, 0.4 mm and 0.5 mm are set for the rod radius, and three different values of 5 kV, 6 kV and 7 kV are set for the voltage. The influence of an excitation reaction on the streamer discharge is studied. The findings indicate that, as voltage raises, the streamer head’s electron density, electric field and average electron energy all rise, and the streamer develops more quickly. When the rod radius increases, the electron density, electric field and average electron energy of the streamer head all decrease, and the streamer’s evolution slows down. When an excitation reaction is added to the model, the average electron energy, the magnitude of the electric field and the density of electrons decrease, and the evolution of the streamer slows down. An increase in average electron energy will lead to an increase in electric field strength and electron density, and the development of the streamer will be faster.

A novel high-current, high-resolution, low-kinetic-energy electron source for inverse photoemission spectroscopy

A high-current electron source for inverse photoemission spectroscopy is described. The source comprises a thermal cathode electron emission system, an electrostatic deflector-monochromator, and a lens system for variable kinetic energy (1.6–20 eV) at the target. When scaled to the energy resolution, the electron current is an order of magnitude higher than that of previously described electron sources developed in the context of electron energy loss spectroscopy. Surprisingly, the experimentally measured energy resolution turned out to be significantly better than calculated by standard programs, which include the electron–electron repulsion in the continuum approximation. The achieved currents are also significantly higher than predicted. We attribute this “inverse Boersch-effect” to a mechanism of velocity selection in the forward direction by binary electron–electron collisions.

On the transient spatial localization model

Significant discrepancies relevant to helioseismology between experimental and theoretical photon absorption by plasmas remain unresolved. Interestingly, a new process called transient spatial localization (TSL), where the plasma perturbs the final states in photon ionization processes, ostensibly enhances cross-sections resolving the extant discrepancies. The TSL model, however, is shown to involve ad hoc formulas not derived from fundamental principles and systematic approximations. In addition, a variant of the TSL model, which claimed to enhance electron collisional ionization, is inconsistent with the Schrodinger equation and fails to reproduce known results.

Angular distribution of photons emitted in collision of low-energy electrons with noble gases

The angular distribution of photons emitted at interaction of low-energy electrons with atoms of noble gases is investigated. The angular asymmetry of the bremsstrahlung cross section is significant and strongly depends on the electron and photon energies. The effect of polarization radiation is considered. It is shown that this effect is noticeable even below the electroluminescence threshold, in contrast to the generally accepted point of view. In the case of argon, the account for the polarization radiation improves the agreement between the predictions and the available experimental data for the yield of bremsstrahlung photons.

Hypersatellite Kα Production in Trapped Ar Ions at KK Trielectronic Recombination Energies

We report measurements of hypersatellite radiation of argon ions in the electron energy region of 5200 eV to 7500 eV. Here, we observed a strong enhancement of this hypersatellite Kαh production. Trielectronic recombination (TR) is discussed as a possible channel for Kαh production leading to this enhancement where main TR resonances are expected to occur. Data analysis was mainly based on the extracted intensity ratio of hypersatellite Kαh to Kα lines (Kαh/Kα). In addition, the collisional excitation and the collisional ionisation of the K-shell ions were modeled as main background processes of the Kα X-ray production. The Kαh/Kα intensity ratio shows a significant rise around 6500 eV electron energy by a factor of about two above the background level. This observation is compared with calculations of the expected electron energies for the resonant Kαh emission due to the KK TR process. The observed rise as a function of the electron collision energy, which occurs in the vicinity of the predicted TR resonances, is significantly stronger and energetically much wider than the results of theoretical calculations for the TR process. However, the experimental evidence of this process is not definitive.

Ionization wave propagation of a surface dielectric barrier discharge with a flexible-structure plasma sheet

Plasma sources based on flexible substrates are receiving attention due to their unique adaptability to irregular surfaces and large range of plasma coverage, which endows them with irreplaceable advantages in the fields of material processing and biomedical treatment. Numerous studies have been carried out focusing on the application effects of these flexible plasma sources, while their surface discharge characteristics and mechanisms still lack revelation. In this work, a flexible plasma sheet with a surface dielectric barrier discharge structure is realized via a printed circuit board, and its multiple surface ionization wave (SIW) propagation on curved gas–solid interfaces is studied via experiments and 2D fluid simulation models. Qualitative agreement is achieved between the experiments and simulations. It is found that a positive and a negative discharge are generated at the rising and falling edges of the excitation pulse, respectively. In the positive discharge, SIWs originate at the grounded mesh edge and then propagate to the center in a petal-like pattern, which is shaped by the space electric field. Controlled by electron collision reactions, the development of the excited states of N2 and O2 molecules is similar to that of electrons. In the negative discharge, electrons dissipate and no SIW is generated. The evolution of heavy particles shows differences in this period, which is attributed to the disparate rate coefficients of their consumption reactions. Further study shows that when the plasma sheet changes from convex to concave, the electron density and electron temperature above its surface increase, but the petal patterns of the SIW propagation have no variation. The electron density, electron temperature, and electron impact ionization source will rise as a result of the increasing pulse amplitude or the decreasing duration of the pulse rising edge.

Reaction mechanism explorations on non-thermal plasma reforming of CO2-CH4 by combining kinetics modeling and emission spectroscopy measurements

Plasma-based dry reforming in an atmospheric dielectric barrier discharge (DBD) reactor has been thoroughly studied by combination of experiments and detailed kinetics simulation. With the assistances of in-situ optical emission spectroscopy (OES) measurements and reaction pathway analysis based on plasma kinetic simulation considering non-constant electric field and thermal effects, this study provided deep insights into the reaction mechanism of plasma-based dry reforming under varied feeding gas composition, gas residence time and operation temperature. A CH4 conversion as high as 44.76 % could be achieved without catalyst at 300 °C, with an SEI of 78 J/cm3 and feeding CH4 ratio of 50 %. Increase of feeding CH4 proportions were found to enhance the generation of C2 and C3 hydrocarbons. Consistently, the OES analysis showed that the relative intensities of spectra bands induced by deexcitation of CH, CO, and C2 also increased monotonically. With the same increment in SEI, increasing gas residence time led to larger promotions in CH4 and CO2 conversion, as being compared to increase of input power. The reason could be explained as that CH4 and CO2 molecules experienced more successive micro-discharges with a longer gas residence time, so more energy would be devoted into CH4/CO2 conversion, whereas more energy was dissipated into heat as rudely increased the discharge power due to the limit of reaction time. CO2 conversion continuously decreased with increasing gas temperature, owing to the recombination of CO and O enhanced at higher gas temperatures. Reaction pathway analysis showed that CH4 conversion was mainly induced by electronic dissociation and ionization at the discharge stage, while CO2 was mainly converted by recombination reaction CO2 + CH2 → CH2O + CO and also electron collision vibrational reaction e + CO2 → e + CO2(vn). The formation of C2 hydrocarbon products was supposed to follow the path of CH4 ↔ CH3/CH → C2H6 ↔ C2H5 ↔ C2H4 → C2H2.

Scattering of Free Electrons with Hydrogen Atoms in Proton Exchange Membrane Fuel Cell System

The objective of this work is to study the Klein-Nishina (KN) cross section during the collision of free electrons and atoms (H-atom and Pt-atom) near the cathode of Proton Exchange Membrane Fuel Cell (PEMFCs). The developed KN cross section was computed using MATLAB shows KN cross section decrease with an increase with the temperature. The maximum KN cross section recorded for single scattering is about -70.2m2 and -66m2 in natural log terms during the collision of free electrons with H-atom and Pt-atom, respectively. The maximum KN cross section recorded for 1ml flow of hydrogen is about -26.6m2 and -22.25m2 in natural log term during the collision of free electrons with H-atom and Pt-atom, respectively.

Turning Noise Into Data: Characterization of the Van Allen Radiation Belt Using SDO Spikes Data

The Solar Dynamics Observatory (SDO) is a solar mission in an inclined geosynchronous orbit. Since commissioning, images acquired by Atmospheric Imaging Assembly (AIA) instrument on-board the SDO have frequently displayed “spikes,” pixel regions yielding extreme number of digital counts. These are theorized to occur from energetic electron collisions with the instrument detector system. These spikes are regularly removed from AIA Level 1.0 images to produce clean and reliable data. A study of historical data has found over 100 trillion spikes in the past decade. This project correlates spike detection frequency with radiation environment parameters in order to generate an augmented data product from SDO. We conduct a correlation study between SDO/AIA data and radiation belt activity within the SDO's orbit. By extracting radiation “spike” data from the SDO/AIA images, we produce a comprehensive data product which is correlated not only with geomagnetic parameters such as Kp, Ap, and Sym-H but also with the electron and proton fluxes measured by the GOES-14 satellite. As a result, we find that AIA spikes are highly correlated with the GOES-14 electrons detected by the magnetospheric electron detector and energetic proton, electron and alpha detectors instruments at the equator (where the two satellites meet) with Spearman's Correlation values of ρ = 0.73 and ρ = 0.53, respectively, while a weaker correlation of ρ = 0.47 is shown with magnetospheric proton detector protons for the 2 year period where both missions returned data uninterruptedly. This correlation proves that the SDO spike data can be proven useful for characterizing the Van Allen radiation belt, especially at areas where other satellites cannot.

Исследование отражения плоской электромагнитной волны от неоднородного плазменного слоя, расположенного на идеально проводящей плоскости

A method for numerical modelling of the reflection of an electromagnetic wave from a planar plasma layer with an inhomogeneous electron density of particles covered of an ideally conducting plane is proposed in the work. The frequency responses of wave reflection coefficients modules are calculated for various incidence angles and electron density profiles of carriers using the differential sweep method. The paper shows that in the region of plasma resonance the plasma layer with a parabolic profile of charge carrier concentration has the lowest reflection level. The effect of the effective frequency of electron collisions in an inhomogeneous plasma layer on the reflection level was studied in this work.

Theoretical study of low-energy electron collision with normal-pentane using R-matrix method

Low-energy electron collisions with normal-pentane (n-C5H12) that initiate the plasma to assist combustion are critical in understanding the underlying physics and chemistries. In the present work, we studied this collisional process using the R-matrix method at the static-exchange plus polarization and close-coupling model levels. The scattering calculation was performed by running the UKRmol+ code using the Quantemol Electron Collision interface to obtain elastic differential, momentum transfer, integral, and electronic excitation cross sections up to 20 eV and ionization cross sections up to 1000 eV. Our computed cross-section data are in better agreement with the available experimental results both regarding the magnitude and shape. We also demonstrated the importance of using a diffuse basis set in describing the scattering due to the Rydberg nature of the lowest unoccupied molecular orbitals of n-C5H12.

AC-driven atmospheric pressure glow discharge co-improves conversion and energy efficiency of CO2 splitting

Gap distance and discharge power have great influence on the morphology and characteristics of glow plasma. Unfortunately, there is few research on the influence law and mechanism of these factors for CO2 splitting by glow plasma. In this study, an AC-driven atmospheric pressure glow discharge (APGD) plasma reactor was developed for CO2 splitting. Through the rational design on the plasma reactor accompanied by numerical simulation and systematic experimentation, the unique influence laws and mechanisms on CO2 splitting behavior are unveiled. Several key parameters, such as gap distance, discharge power and gas flow rate, are found able to play synergistic roles in tailoring plasma reactor to co-improve the conversion and energy efficiency. At an optimized gap distance, sufficient electron collisions along the main channel results in the largest active plasma volume, leading to the optimal CO2 splitting performance. The conversion and energy efficiency could also be co-improved by synchronously increasing the discharge power and gas flow rate at a given specific energy input (SEI) value, which exhibits an opposite feature of dielectric barrier discharge (DBD) plasma, because larger plasma volume increases the probability of collision dissociation reaction and lower gas temperature decreases the rate of recombination reaction. The AC-driven APGD reactor can achieve maximum conversion of 11.96% and maximum energy efficiency of 41.51% which superior to the results of most atmospheric pressure plasmas. This work gains insights into the behaviors of AC-driven APGD plasma in CO2 splitting and potentially opens an avenue to develop plasma technology for sustainable CO2 utilization.

Influence of defects on the femtosecond laser damage resistance of multilayer dielectric gratings.

Multilayer dielectric (MLD) gratings with high diffraction efficiency and a high laser-induced damage (LID) threshold for pulse compressors are key to scaling the peak and average power of chirped pulse amplification lasers. However, surface defects introduced by manufacturing, storage, and handling processes can reduce the LID resistance of MLD gratings and impact the laser output. The underlying mechanisms of such defect-initiated LID remain unclear, especially in the femtosecond regime. In this Letter, we model dynamic processes in interactions of a 20-fs near-infrared (NIR) laser pulse and a MLD grating design in the presence of cylindrically symmetrical nodules and particle contaminants and cracks at the surface. Utilizing a dynamic model based on a 2D finite difference in time domain (FDTD) field solver coupled with photoionization, electron collision, and refractive index modification, we study the simulation results for the damage site distribution initiated by defects of various types and sizes and its impact on the LID threshold of the grating design.

New methods to achieve meson, muon and gamma light sources through asymmetric electron positron collisions

We propose methods to produce gamma light source, muon and energetic meson beams such as charged and neutral Kaons, which are boosted to be collimated and with relatively long lifetime. The first type of method is based on asymmetric electron positron collisions with a center-of-mass energy of, e.g. 1020[Formula: see text]MeV, and Kaons can be produced at a rate of [Formula: see text]. The electron and positron beams are either asymmetric in energy, e.g. 10[Formula: see text]GeV electron beam with 26[Formula: see text]MeV positron beam, or asymmetric in space, e.g. 10[Formula: see text]GeV electron and positron beams collisions with an angle around 0.05 radius. Such proposals should be able to be achieved with a reasonable budget. The other type of method relies on TeV positron on target experiment, where Kaon beams can be achieved at around [Formula: see text] per bunch crossing. Such Kaon beams are clean with small contamination, and can have great physics potential on, e.g. hyperon searches through Kaon nuclei collision, Kaon rare decay measurement, and Kaon proton or Kaon lepton collisions. The same technique can also be extended to other final states such as pions and tau leptons.

Research on the trigger process of surface flashover triggered vacuum switch

The key to promoting the development of triggered vacuum switch is an in-depth research on the physical process of its trigger phase. This paper mainly divides the trigger process into metal electrode melt evaporation, neutral metal vapor layer expansion, electron collision ionization multiplication, and charged particle migration. An approximate analytical formulation of the trigger delay time theory is presented based on a one-dimensional heat conduction model and an electron collision ionization multiplication process. The trigger delay time experimental platform is built with a removable vacuum chamber. The influence factors involved in the mathematical description proposed are studied experimentally. Theoretical analysis and experimental results show that both trigger current rise rate and main electrode operating voltage have an approximate inverse relationship with trigger delay time. The main electrode gap distance is directly proportional to the trigger delay time, but the effect will be weaker as the main electrode gap distance increases. Overall, the consistency of the experimental results and theoretical analysis on influence trends well support the theoretical model.

Absolute dielectronic recombination rate coefficients of highly charged ions at the storage ring CSRm and CSRe

Dielectronic recombination (DR) is one of the dominant electron–ion recombination mechanisms for most highly charged ions (HCIs) in cosmic plasmas, and thus, it determines the charge state distribution and ionization balance therein. To reliably interpret spectra from cosmic sources and model the astrophysical plasmas, precise DR rate coefficients are required to build up an accurate understanding of the ionization balance of the sources. The main cooler storage ring (CSRm) and the experimental cooler storage ring (CSRe) at the Heavy-Ion Research Facility in Lanzhou (HIRFL) are both equipped with electron cooling devices, which provide an excellent experimental platform for electron-ion collision studies for HCIs. Here, the status of the DR experiments at the HIRFL-CSR is outlined, and the DR measurements with Na-like Kr25+ ions at the CSRm and CSRe are taken as examples. In addition, the plasma recombination rate coefficients for Ar12+, 14+, Ca14+, 16+, 17+, Ni19+, and Kr25+ ions obtained at the HIRFL-CSR are provided. All the data presented in this paper are openly available at https://doi.org/10.57760/sciencedb.j00113.00092.

Comprehensive Analysis of Copper Plasma: A Laser-Induced Breakdown Spectroscopic Approach

The emergence of diversified applications of laser-induced breakdown spectroscopy in the biomedical field, electronics, space physics, and material processing necessitates a comprehensive understanding of plasma parameters. The present work delineates the structure and evolution of copper plasma under different ambient pressures (0.01 mbar to 100 mbar) along with other plasma parameters. The study reveals the role of ambient pressure in the increase of plasma temperature (Te), electron density (Ne), number of particles in the Debye sphere, plasma frequency, inverse bremsstrahlung absorption coefficient, electron thermal velocity, electron–ion collision frequency and in the decrease of Debye length (λD) and plasma skin depth (PSD). The experimental techniques and the theoretical explanations for the variation of plasma parameters and their applications are also detailed. As the ambient pressure increases, the motion of plasma species becomes restricted, resulting in the increase of Te, calculated using the Boltzmann plot. From the values of λD, PSD, and Ne, it is understood that the copper plasma under investigation is thermally non-relativistic and satisfies McWhirter’s criterion, thus, revealing the local thermodynamic equilibrium condition of plasma. The effects of Debye shielding and stark broadening on the spectral lines are also investigated. Thus, the study helps bring newfangled dimensions to the application of plasma by exploring the possibility of tailoring plasma parameters.