Average Electron Energy Research Articles

Специфика кинетики импульсной катодолюминесценции иона неодима в иттрий-алюминиевом гранате и оксиде иттрия

The kinetics of pulsed cathodoluminescence of Nd3+ ions in single crystals, ceramics, and nanopowders of Nd3+:Y3Al5O12 (Nd3+:YAG) and Nd3+:Y2O3 under excitation by a 2 ns electron beam with average electron energies of 130, 150, and 170 keV was studied. In this case, the luminescence of these substances occurs after the termination of the electron beam. In Nd3+:YAG, there are optical transitions from the 2F25/2 level of the neodymium ion in the ultraviolet and visible regions of the spectrum, as well as from the 4F3/2 level in the near infrared region. In Nd3+:Y2O3, there are not transitions from the 2F25/2 level of the neodymium ion, but infrared luminescence occurs from the 4F5/2 and 4F3/2 levels. The luminescence kinetics is characterized by rise and decay and it is described by the difference of two exponential functions. It is found that the characteristic luminescence decay times are the lifetimes of the 2F25/2, 4F5/2 and 4F3/2 emissive levels, and the rise time is determined by their pumping in recombination and relaxation processes. The rise mechanisms of pulsed cathodoluminescence are substantially different from the mechanisms of "phosphor ignition", which occur during ionization and excitation of the phosphor by an external source.

Влияние вида функции распределения электронов в плазме и дисперсии по энергии электронного пучка на устойчивость низковольтного пучкового разряда

Within the framework of the kinetic approach, the conditions for the loss of stability of a low-voltage beam discharge in inert gases (LVBD) are studied depending on the temperature of the electron beam, the dispersion of the electron beam velocity in the direction of the discharge axis, and the form of the electron energy distribution function (EEDF). Regimes are considered when the interelectrode distance is on the order of the electron mean free path relative to elastic collisions with inert gas atoms. It is shown that the beam temperature Tb, determined in the LVBD by the cathode temperature not exceeding 1500 K, and the dispersion of the beam electron energy, which in the LVBD can be significantly higher than kTb and reaches 1 - 2 eV, have little effect on the conditions for the loss of stability of the LVBD and the magnitude of the growth rate of disturbance amplification at frequencies up to plasma It was found that the form of the EEDF monotonically decreasing with increasing electron energy also does not affect the parameters of the perturbations propagating in the LVBD at the beam energy much higher than the average electron energy in the plasma. The results obtained are applicable not only to LVBD, but also to other types of self-sustained beam discharges.

Monte Carlo simulation of electron drift characteristics in an inert gas with mercury vapor

The Monte Carlo method calculated the kinetic characteristics of electron drift in three inert gases (He, Ar, Xe) in the presence of small impurities (up to 1%) of mercury vapor at an electric field strength E/N = 1-2000 Td taking into account inelastic collisions and analyzed the effect of the concentration of metal vapor on the drift velocity, average electron energy, diffusion and mobility coefficients. In addition, the Townsend ionization coefficient and electron runaway, the electron energy distribution function, and their comparison with the Maxwell and Druvestein distributions are calculated. It has been shown that even insignificant additions of mercury atoms to an inert gas, starting with a fraction of a percent, strongly affect the discharge, in particular, the characteristics of inelastic processes and the charge composition.

Application of energy-balance model from gas discharge to single-surface multipactor

A unified theory of multipactor discharge on a dielectric is proposed by utilizing the similarity of the energy balance between multipactor and collisional gas discharge. In this theory, the electron energy gain in multipactor is predicted using the classical formulas for the electric field powers in gas discharge, and the electron energy loss is caused by electron bombardment to the dielectric surface. As with kinetic effects in collisional gas discharge, the electron energy distribution function is important in saturated multipactor. Due to the complex energy distribution functions in saturated multipactor, the average bombardment electron energies are varied and much larger than the traditional predicted value indicated by the first crossover of unity in the secondary electron yield. Using the proposed energy-balance model, multipactor in envelope microwaves and multipactor under an extra magnetic field are both theoretically predicted. The theoretical results for the surface-normal accumulative electric field and the deposited power in saturated multipactor are consistent with the results from electromagnetic particle-in-cell (PIC) simulations.

Simulation of electron transfer processes in a semiconductor structure using graphene and boron nitride

This paper presents the results of simulating the electron transfer processes in a three-dimensional semiconductor structure containing graphene and layers of boron hexagonal nitride using the Monte – Carlo method. Graphene is currently considered one of the most promising materials for the creation of new semiconductor devices with good performance for high frequency ranges. The use of graphene, which has high mobility of charge carriers, high thermal conductivity and a number of other positive properties, allows the development of new semiconductor devices with good output characteristics. The simulation allowed us to obtain the main characteristics of electron transfer, namely, dependence of speed, average energy, mobility on the strength of the electric field in a semiconductor structure containing a layer of graphene and boron nitride region. Electron transfer processes were simulated considering temperature variations of graphene and boron nitride layers, which is observed with increasing strength of the electric field in the structure. The analysis of the obtained dependencies showed that at small values of electric field strength, which does not exceed approximately 2.5 kV/cm, there is a nonlinear change in electron energy and temperature. At more significant values of electric field strength a quasi-linear change in temperature is observed. The similar course of dependence is observed also for the dependences of the average energy of electrons on the intensity of the electric field for the graphene layer.. The resulting dependencies of electron transfer characteristics can serve the basis for determining output characteristics in multi-layer semiconductor devices containing layers of graphene, boron hexagonal nitride and other materials.

Swarm of Electron Simulation in Carbon Dioxide Parameters for Intermediate E/N Values

The rotational excitation and transfer of low-energy electrons cross-sections in carbon dioxide have been obtained to compare in the theoretical & experimental values of the kinetic and diffusion coefficient. the transport coefficients theoretical values of were gained by calculating the delicate electron energy distribution functions using a putative elastic and inelastic cross-sections combination. The values for movement, drift speed, average electron energy, and power noticeable with experimental data were compared. Alteration were made to the default cross sections until obtaining good agreement. Transport coefficients were calculated for values between (6 × 10−17 - 6×10−15 )V cm2 with energy zoning 0.035 eV at 300k° temperature.

A Comparative Investigation on the Behaviors of Electrons in the Plasma Bullets in Atmospheric-Pressure Argon and Helium Plasma Jets

This article presents a comparative investigation on behaviors of electrons in the Ar and He plasma jets by means of the numerical simulation based on a typical needle-plate discharge configuration with positive applied pulsed voltage and a 1-D particle-in-cell Monte-Carlo collision (PIC-MCC) method. Emphasis is placed on the electrons in the bullet in the jets. In Ar, the bullet velocity is low and the electron density in the bullet is high, compared to He. In He, the energy spectrum of electrons (ESEs) in the bullet is of a low peak and a wide distribution, and the corresponding average electron energy is evidently high, contrary to Ar. The reason for this evident difference is mainly due to their different excitation energies and ionization energies as well as their different cross sections. In Ar and He, two electron densities N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> and Next in the bullet have been calculated. The former is the electron density in the bullet and the latter refers to a density of electrons in the bullet with energy above the lowest excitation threshold inducing the dissociative electron attachment (DEA) to water molecules. Consequently, not only N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> but also N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ext</sub> in Ar is higher than in He, meaning more generation of reactive species in aqueous solution via DEA mechanism. The ESEs in the bullet in Ar are more sensitive to the applied voltage amplitude than in He, thus in Ar, the increase in the applied voltage amplitude induces more evident increase in the average electron energy in the bullet than in He.

The dynamics of a nanosecond gas discharge development with an extended slot cathode in argon

The article presents the results of an experimental study and numerical modelling for the formation and development dynamics of a high-voltage transverse nanosecond discharge generated by a slot cathode in an argon medium at a pressure range of 1–10 Torr. Numerical modelling was carried out under similar experimental conditions for the processes of formation and propagation of ionisation waves, electron density distribution, excited atom and average electron energy in the discharge gap, including the cavity inside the cathode. At a pressure of p = 1 Torr, a classical version of a high-voltage discharge is demonstrated to take place with no penetration of the plasma into the cathode cavity and no observed hollow cathode effect. An increase in gas pressure to 5 Torr leads to a penetration of plasma into the cathode cavity with the formation of a cathodic potential drop (CPD) region. Electrons emitted from the side surfaces of the cavity pass through the CPD region without collisions, oscillate inside the cathode cavity; the hollow cathode effect is fully manifested. At р = 10 Torr, the modelling results qualitatively coincide with the results at р = 5 Torr; in this case, however, hardly any accelerated electrons are observed in the gap between the electrodes, due to their energetic relaxation both inside the cathode cavity and when exiting from it. In both cases, the plasma structure formed at the exit of the cathode cavity involves a concentration of charged particles an order of magnitude higher than that in the rest of the gap, leading to a self-limiting discharge current effect. The results of the numerical modelling are in good agreement with experimental data.

First Ionization Energy as the Asymptotic Limit of the Average Local Electron Energy.

The first vertical ionization energy of an atom or molecule is encoded in the rate of exponential decay of the exact natural orbitals. For natural orbitals represented in terms of Gaussian basis functions, this property does not hold even approximately. We show that it is nevertheless possible to deduce the first ionization energy from the long-range behavior of Gaussian-basis-set wave functions by evaluating the asymptotic limit of a quantity called the average local electron energy (ALEE), provided that the most diffuse functions of the basis set have a suitable shape and location. The ALEE method exposes subtle qualitative differences between seemingly analogous Gaussian basis sets and complements the extended Koopmans theorem by being robust in situations where the one-electron reduced density matrix is ill-conditioned.

Formation of large-volume plasmas in a microhollow cathode sustained discharge with a needle-plate second anode

A large-volume glow discharge is produced using a microhollow cathode sustained discharge (MCSD) with a needle-plate second anode in argon. The length and volume of the glow discharge are approximately 3 cm and 7 cm3, respectively, and the electron density is on the order of 1011 cm−3. The MCSD is also simulated using a two-dimensional self-consistent fluid model with a single plate as the second anode. Both the experimental and simulated results show that MCSD generation originates from cooperative formation that involves the microhollow cathode discharge and a discharge that arises from the second anode. The second anode plays an important role in MCSD generation. The electric field and the average electron energy clearly increase in the region near the second anode. The influence of the structure of the second anode on the MCSD characteristics is investigated. When the second anode has a needle-plate structure instead of a single plate structure, the sustaining voltage, breakdown, and annihilation current of the cathode for MCSD decrease substantially, a higher discharge current is obtained, and a more stable, uniform MCSD is produced. The results also show that both needle and plate contribute to glow discharge formation in the region near the second anode.

Monte Carlo simulation for development of electron avalanches in nitrogen at moderate and high reduced electric field

This paper addresses the simulation of electron avalanches in nitrogen by means of the Monte Carlo method. The data have been obtained for the conditions of classical measurements of the impact ionization coefficient in a wide range of reduced electric fields E/p. It is shown that at moderate E/p values, the results are in a good agreement with the generally accepted approaches in the description of the avalanches based on the drift motion of the electrons and on the diffusion. The high E/p is achieved in the vicinity of the minimum of Paschen's curve due to decreasing the gas pressure. Then the process of development of the single electron avalanche changes radically. The reason is that the runaway electrons appear, which leads to essential longitudinal expansion of the electron cloud. It is revealed that the average electron energy at the front of the cloud turns out to be larger than that at the backside of the cloud.

Spectroscopic Monitoring of Blazar S5 0716+714: Brightness-dependent Spectral Behavior

Abstract In this paper, we report new results of spectroscopic observations of γ-ray blazar S5 0716+714 from 2019 September to 2020 March with the 2.4 m optical telescope at Lijiang Observatory of Yunnan Observatories. The median cadence of observations is ∼1 day. During the second observation period (Epoch2), the observational data reveal an extremely bright state and a bluer-when-brighter (BWB) chromatism. The BWB trend of Epoch2 differs significantly from that of the first observation period (Epoch1). A significantly brightness-dependent BWB chromatism emerges in the total data of Epoch1 and Epoch2. The BWB trend becomes weaker toward the brighter states, and likely becomes saturated at the highest state. Based on a log-parabolic function, a power law of synchrotron peak flux and frequency ν p, and a power law of the curvature of synchrotron spectrum and its ν p, simulation well reproduces the brightness-dependent BWB trend of S5 0716+714. The BWB trend is seemingly controlled by the shift of ν p with respect to the observational window, and effectively may be dominated by the variations of electron average energy and magnetic field in the emitting region.

Evaluating the dielectric strength of promising SF6 alternatives by DFT calculations and DC breakdown tests

In this paper, a calculation method is proposed to predict the dielectric strength (DS) of gases and the DS of some promising SF 6 alternative gases and their mixtures is further evaluated by DC breakdown tests. The calculation method is based on the density functional theory (DFT), so that the DS of the gases can be obtained by only calculating their molecular parameters, including the average static electronic polarizability and adiabatic ionization energy. The paper also presents the DC breakdown strength of the C 4 F 7 N, C 5 F 10 O, and HFO-type gases, and it is found that the experimental DS values are in good agreement with the calculated values. In addition, DC breakdown tests for gas mixtures are also conducted and their synergistic effect is discussed in detail. The results show that the DS of C 4 F 7 N mixed gases is equivalent to that of pure SF 6 gas even under high pressures, indicating their potential applications in HV electrical equipment. The DS of C 5 F 10 O mixed gas is slightly lower than that of C 4 F 7 N mixed gas. Compared with CO 2 , mixing with air brings stronger synergistic effect in C 5 F 10 O and C 4 F 7 N in our experiment. The DS of HFO mixture is substantially less than that of SF 6 because of the weak synergistic effect when mixed with CO 2 or N 2 . This paper presents an effective method to evaluate DS of SF 6 alternative gases and the results are useful for their future engineering applications.

Parametric Interaction of High-Power Laser Radiation with Plasma in a Strong Magnetic Field

The article deals with interaction of an extraordinary laser wave of high amplitude with inhomogeneous plasma in a strong magnetic field in the vicinity of twice the upper-hybrid frequency. The analysis is carried out by means of numerical simulation based on the particle-in-cell (PIC) method. It is demonstrated that in this case, parametric resonance leads to a substantial heating of electrons. The results of analysis of spectra of the longitudinal field suggest that this kind of heating occurs due to nonlinear interaction of the upper-hybrid plasmons driven by the laser wave with electrostatic modes similar to the Bernstein ones in the linear approximation. The dependence of average energy of electrons gained in the course of heating on their initial temperature is investigated.

Ionization features in cathode spot region of vacuum arc

A model of ionization processes in a low-temperature plasma within the cathode region of a vacuum arc is presented. This mathematical model is represented by a system of nonlinear differential equations of drift-diffusion for the electron density and the average energy of second-order electrons. The system of equations was solved by the finite element method in two coordinates in numerical form using the COMSOL Multiphysics software program. It was shown that due to nonequilibrium processes, Langmuir waves appeared at the plasma boundary, which leads to multistage ionization of metal vapor. The arc discharge was presented in the form of a cylindrical plasma column with a length of 200 μm and a diameter of 50 μm. At the interface between the cathode and the plasma column, a double electric layer has appeared which holds hot electrons in the central zone of the discharge. High specific power was focused close to the cathode surface, which provided the continuous supply of metal vapor. The numerical results of the model have appeared to be in good agreement with the experimental data.

Effect of gas concentration on the electron transport and the plasma parameters of the CO2 gas mixture

Electron Swarm Parameters in plasma gas mixtures of Co2 have been calculated. Studies focused on four gas mixtures with Co2, He, and N2 in the ratio 5%: 55%: 40%, 2.5%: 45%: 52.5%, 10%: 50%: 40% and 40%: 40%: 20% respectively. Calculations of the electron energy distribution function f (ε), drift velocity Vd, mobility μ, electron diffusion D, D/μ, electron average energy <ε> and electric field E in the range of electric field to gas number density ratio E/N from 1×10−19 to 5×10−15 at 300 0K were reported in this work. The theoretical calculations shown helium has a good effect on the electrons transition parameters of Co2 laser. Furthermore, at low energy, the total collision rate is increasing slowly for higher electron energy.

Ionization cross-sections for C2H2 and C2H5OH by electron- impact

Secondary electron energy dependent ionization cross-sections for the C2H2 and C2H5OH molecules by electron-collision have been calculated at a set of impinging electron energies 100 and 200 eV. The revisited Jain-Khare semiempirical approach based on the Born approximation has been employed to calculate these cross-sections. The averaged secondary electron energy and the integral total ionization cross-sections are evaluated from the energy dependent ionization cross-sections in energy range ionization threshold to 2000 eV. The calculated total ionization cross-sections are extended up to 6000 eV using Born-Bethe analysis. A comparison of the presently evaluated total ionization cross-sections with the available various theoretical and the experimental results revealed a satisfactory agreement.

A Numerical Investigation on the Reactive Species Generation and Its Correlation With Electron Energy in Atmospheric-Pressure Helium/Humid Air Plasma Jets

In this work, the reactive species generation and its correlation with electron energy in atmospheric-pressure helium/humid air plasma jets have been numerically investigated based on a needle-plane electrode geometry by using a 2-D fluid model. With the increase in the voltage amplitude, the averaged electron energy increases, the respective averaged densities of OH, O(1D), and O− increase, while the averaged H2O2 density decreases. Therefore, between the species generation and electron energy, there is a negative correlation for H2O2 and a positive correlation for OH, O(1D), and O−. In addition, as the humid air concentration increases, the averaged electron energy decreases, but the respective averaged densities of OH, O(1D), O−, and H2O2 increase. Consequently, there is a negative correlation between these species generations and electron energy. Finally, this work shows that a proper high humid air concentration in the plasma jets applied for biomedicine may allow expected electron energy and also generate abundant reactive species.

Tracking the ultrafast nonequilibrium energy flow between electronic and lattice degrees of freedom in crystalline nickel

Femtosecond laser excitation of solid-state systems creates non-equilibrium hot electrons that cool down by transferring their energy to other degrees of freedom and ultimately to lattice vibrations of the solid. By combining ab initio calculations with ultrafast diffuse electron scattering we gain a detailed understanding of the complex non-equilibrium energy transfer between electrons and phonons in laser-excited Ni metal. Our experimental results show that the wavevector resolved population dynamics of phonon modes is distinctly different throughout the Brillouin zone and are in remarkable agreement with our theoretical results. We find that zone-boundary phonon modes become occupied first. As soon as the energy in these modes becomes larger than the average electron energy a backflow of energy from lattice to electronic degrees of freedom occurs. Subsequent excitation of lower-energy phonon modes drives the thermalization of the whole system on the picosecond timescale. We determine the evolving non-equilibrium phonon occupations which we find to deviate markedly from thermal occupations.

Accelerated Electrons Observed Down to

We report the detection of emission from a nonthermal electron distribution in a small solar microflare (GOES class A5.7) observed by the Nuclear Spectroscopic Telescope Array, with supporting observation by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The flaring plasma is well accounted for by a thick-target model of accelerated electrons collisionally thermalizing within the loop, akin to the "coronal thick-target" behavior occasionally observed in larger flares. This is the first positive detection of nonthermal hard X-rays from the Sun using a direct imager (as opposed to indirectly imaging instruments). The accelerated electron distribution has a spectral index of 6.3 ± 0.7, extends down to at least 6.5 keV, and deposits energy at a rate of ~2 × 1027 erg s-1, heating the flare loop to at least 10 MK. The existence of dominant nonthermal emission in X-rays down to <5 keV means that RHESSI emission is almost entirely nonthermal, contrary to what is usually assumed in RHESSI spectroscopy. The ratio of nonthermal to thermal energies is similar to that of large flares, in contrast to what has been found in previous studies of small RHESSI flares. We suggest that a coronal thick target may be a common property of many small microflares based on the average electron energy and collisional mean free path. Future observations of this kind will enable understanding of how flare particle acceleration changes across energy scales, and will aid the push toward the observational regime of nanoflares, which are a possible source of significant coronal heating.