Function Of Electron Temperature Research Articles

Temperature-dependent electron–phonon coupling changes the damage cascades in neutron-irradiation molecular dynamics simulation in W

We present a first-principles-based electron-temperature model that can be used in atomistic calculations. The electron–phonon coupling coefficient in the model is derived from the density of states as a function of electron temperature, and the thermal conductivity of tungsten from our model shows significant improvement over the baseline atomistic calculations in which only ion-thermal contribution to the thermal conductivity is available. The correction to the thermal conductivity also changes damage cascades as cascades cool down more rapidly within our model. The mobility of defects is consequently reduced, leaving more residual damage than the predictions without an electron-temperature model.

Flexural and acoustic phonon-drag thermopower and electron energy loss rate in silicene

We have performed a comprehensive numerical and analytical examination of two crucial transport aspects in silicene: the phonon-drag thermopower, Sp , and the electron’s energy loss rate, Fe . Specifically, our investigation is centered on their responses to out-of-plane flexural phonons and in-plane acoustic phonons in silicene, a two-dimensional allotrope of silicon as a function of electron temperature, T, and electron concentration, n, upto the room temperature. It is found that the calculated quantities have a non-monotonic dependence for the phonon modes for both parameters (T and n) considered while analytical results predict definite dependencies up to the complete low-temperature Bloch–Gruneisen (BG) regime. To provide a more comprehensive picture, we contrast the complete numerical outcomes with the approximated analytical BG results, revealing a convergence within a specific range of temperature and carrier concentration. In light of this convergence, we put forth suggestions to elucidate the underlying factors responsible for this behavior. A comparison based on the magnitude of the calculated quantities can be made from the figures between the two considered phonon modes, which clearly shows that the out-of-plane flexural phonons are effective throughout the considered temperature range. This observation leads us to posit that the dominating contribution of the out-of-plane flexural phonon modes hinges upon the deformation potential constant and phonon energy associated with the phonon mode. Our study carries significant implications for estimating the electrical and thermal properties of silicene and provides valuable insights for the development of devices based on silicene-based technologies.

Temperature-Dependent Functions of the Electron–Neutral Momentum Transfer Collision Cross Sections of Selected Combustion Plasma Species

The collision cross sections (CCS), momentum transfer cross sections (MTCS), or scattering cross sections (SCS) of an electron–neutral pair are important components for computing the electric conductivity of a plasma gas. Larger collision cross sections for electrons moving freely within neutral particles (molecules or atoms) cause more scattering of these electrons by the neutral particles, which leads to degraded electron mobility, and thus reduced electric conductivity of the plasma gas that consists of electrons, neutral particles, and ions. The present work aimed to identify the level of disagreement between four different methods for describing how electron–neutral collision cross sections vary when they are treated as a function of electron temperature alone. These four methods are based on data or models previously reported in the literature. The analysis covered six selected gaseous species that are relevant to combustion plasma, which are as follows: carbon monoxide (CO), carbon dioxide (CO2), molecular hydrogen (H2), water vapor (H2O), potassium vapor (K), and molecular oxygen (O2). The temperature dependence of the collision cross sections for these species was investigated in the range from 2000 K to 3000 K, which is suitable for both conventional air–fuel combustion and elevated-temperature oxygen–fuel (oxy-fuel) combustion. The findings of the present study suggest that linear functions are enough to describe the variations in the collision cross sections of the considered species in the temperature range of interest for combustion plasma. Also, the values of the coefficient of variation (defined as the sample standard deviation divided by the mean) in the collision cross sections using the four methods were approximately 27% for CO, 42% for CO2, 13% for H2, 39% for H2O, 44% for K, and 19% for O2. The information provided herein can assist in simulating magnetohydrodynamic (MHD) power generators using computational fluid dynamics (CFD) models for combustion plasma flows.

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.

Hot electron scaling for two-plasmon decay in ICF plasmas

We present a parametric scaling of hot electron (HE) generation at quarter critical density from the two-plasmon decay process. The study is conducted with the laser plasma simulation environment code, considering Langmuir decay instabilities (LDI) and laser pump depletion in 2D. The parameter scan is conducted as a function of electron temperature, ion–electron temperature ratio, drive strength, and density scale length. The scaling shows an hot electron (HE) conversion fraction up to 40%, HE fluxes up to 6 × 10 14 W / cm 2, and average temperatures in the range of 30 to 100 keV. The electron angular distributions exhibit two main regions: the plasma “bulk,” characterized by homogeneous emission, up to energies of 30 − 60 keV depending on the individual laser–plasma conditions, and a HE tail after ≃ 50 − 60 keV. The mid-energy electrons are homogeneously emitted toward the end of the plasma bulk and acquire energy through electron plasma wave (EPW) Landau damping from Langmuir wave collapse and LDI cascade. The HE tail has electrons emitted in the forward direction and at low divergence, due to turbulence and EPW Landau damping from multi-staged acceleration. Finally, the laser power transmitted through the quarter critical region reaches values from ∼ 80 % down to ∼ 35 % for increasing HE generation, with absorption due to EPW collisional damping in the range of ∼ 10 % − 35 %.

Effective Collision Strengths and Radiative Parameters for Lines in the Sc ii Spectrum

Abstract This work reports large-scale calculations of electron excitation effective collision strengths and transition rates for a wide range of Sc ii spectral lines for astrophysical analysis and modeling. The present results are important for reliable abundance determinations in various astrophysical objects, including metal-poor stars, H ii regions, and gaseous nebulae. Accurate descriptions of the target wave functions and adequate accounts of the various interactions between the target levels are of primary importance for calculations of collision and radiative parameters. The target wave functions have been determined by a combination of the multiconfiguration Hartree–Fock and B-spline box-based close-coupling methods, together with the nonorthogonal orbitals technique. The calculations of the collision strengths have been performed using the B-spline Breit–Pauli R-matrix method. The close-coupling expansion includes 145 fine-structure levels of Sc ii belonging to the terms of the 3p 63d 2, 3p 63d4l (l = 0–3), 3p 63d5l (l = 0–3), 3p 63d6s, 3p 64s 2, 3p 64s4l (l = 0–3), 3p 64s5l (l = 0–1), and 3p 64p 2 configurations. The effective collision strengths are reported as a function of electron temperature in the range from 103 to 105 K. The collision and radiative rates are reported for all of the possible transitions between the 145 fine-structure levels. Striking discrepancies exist with the previous R-matrix calculations of the effective collision strengths for the majority of the transitions, indicating possible systematic errors in these calculations. Thus, there is a need for accurate calculations to reduce the uncertainties in the atomic data. The likely uncertainties in our effective collision strengths and radiative parameters have been assessed by means of comparisons with other collision calculations and available experimental radiative parameters.

Electron power loss in metal-oxide nanostructures in quantizing magnetic field

Hot-electron power loss via electron interaction with bulk longitudinal polar optical phonon in metal-oxide two dimensional nanostructures in the presence of zero and finite quantizing magnetic fields is investigated using electron temperature model. The dependence of power loss in two-dimensional nanostructures of transparent conducting oxides like ZnO, SnO2, CdO, In2O3, Ga2O3 is presented as a function of electron temperature and carrier density in zero and finite magnetic fields. Numerical calculations establish that external quantizing magnetic field enhances power loss of electrons. Further, electron power loss is proportional to the electron temperature and varies inversely with the carrier density. The electron magneto-power loss qualitatively differs from the oscillating dependence of the electron-phonon scattering on the quantizing magnetic field.

Ionization waves (striations) in a low-current plasma column revisited with kinetic and fluid models

A one-dimensional particle-in-cell Monte Carlo collisions method has been used to model the development and propagation of ionization waves in neon and argon positive columns. Low-current conditions are considered, that is, conditions where stepwise ionization or Coulomb collisions are negligible (linear ionization rate). This self-consistent model describes the development of self-excited moving striations, reproduces many of the well-known experimental characteristics (wavelength, spatial resonances, potential drop over one striation, and electron “bunching” effect) of the ionization waves called p, r, and s waves in the literature, and sheds light on their physical properties and on the mechanisms responsible for their existence. These are the first fully kinetic self-consistent simulations over a large range of conditions reproducing the development of p, r, and s ionization waves. Although the spatial resonances and the detailed properties of the striations in the nonlinear regime are of kinetic nature, the conditions of existence of the instability can be obtained and understood from a linear stability analysis of a three-moment set of quasi-neutral fluid equations where the electron transport coefficients are expressed as a function of electron temperature and are obtained from solutions of a 0D Boltzmann equation. An essential aspect of the instability leading to the development of these striations is the non-Maxwellian nature of the electron energy distribution function in the uniform electric field prior to the instability onset, resulting in an electron diffusion coefficient in space much larger than the energy diffusion coefficient.

RADIATION LOSS DETERMINATION AT COLLISION OF ELECTRONS WITH LECTRONEGATIVE ATOMS AND IONS IN PLASMA CURRENT SWITCH DISCHARGES. PART II

Specific radiation-loss power values have been determined for a variety of electronegative elements (C, O, F, Cl) as functions of electron temperature and impurity particle concentration. The maximum radiation-loss power level has been registered for chlorine (≤770 W/cm3) at an electron/impurity density of 1014 cm-3. The minimum radiation-loss power level for the other three elements lies in the range from 0.4 to 2 W/cm3. Considerable radiation losses due to the presence of electronegative elements in the interelectrode discharge may lead to its destabilization, to the change in the plasma parameters (ne, Te), and eventually, to degradation of the current-voltage characteristic of the plasma current switch.

Vacancy-induced enhancement of electron–phonon coupling in cubic silicon carbide and its relationship to the two-temperature model

The electron–phonon coupling factor was calculated for both pristine and vacancy-rich 3C-SiC. Ab initio calculations were performed within the framework of the density functional perturbation theory. Wannier functions were used to interpolate eigenvalues into denser grids through the electron–phonon using Wannier code. The coupling factor was determined through calculations of the electron self-energy, electron–phonon relaxation time, and electronic specific heat. These parameters were extrapolated to high temperatures using a hybrid model which mixes band calculations for electrons below an energy cutoff with the free electron gas model for electrons above the energy cutoff. The electron relaxation times, specific heats, electron drift mobilities, and electron–phonon coupling factors were calculated as a function of electron temperature. Si and C vacancies were found to have a profound effect on electron–phonon coupling for all temperatures, while electronic specific heat capacity was found to be most affected at cryogenic temperatures. The electron drift mobility was calculated at different temperatures using the scattering time. Calculated mobilities were validated with Hall mobility measurements reported in the literature. The importance of structural defects on the electron–phonon coupling is discussed in the context of the two-temperature model, a model that has been widely used to understand aspects of the interaction of solids with pulsed laser irradiation and swift heavy ion irradiation.

Contamination of argon x-ray spectra by tungsten and other elements commonly found in tokamaks

Emission lines which appear in the spectral ranges of ground state transitions from n = 2 levels in He- and H-like argon ions are discussed. X-ray transitions from elements commonly found in tokamaks (tungsten, molybdenum, iron and sulphur) which radiate in the wavelength range from 3700–4000 mÅ are identified by comparison with atomic structure calculations. Individual lines from tungsten charge states in the vicinity of Zn-like W44+ are documented, along with B-like Mo37+. The behaviour of line ratios as a function of electron temperature is examined, in support of the identifications.

Implicit and coupled fluid plasma solver with adaptive Cartesian mesh and its applications to non-equilibrium gas discharges

We present a new fluid plasma solver with adaptive Cartesian mesh (ACM) based on a full-Newton (nonlinear, implicit) scheme for non-equilibrium gas discharge plasma. The electrons and ions are described using drift–diffusion approximation coupled to Poisson equation for the electric field. The electron-energy transport equation is solved to account for electron thermal conductivity, Joule heating, and energy loss of electrons in collisions with neutral species. The rate of electron-induced ionization is a function of electron temperature and could also depend on electron density (important for plasma stratification). The ion and gas temperature are kept constant. The transport equations are discretized using a non-isothermal Scharfetter–Gummel scheme to resolve possible large temperature gradients in the sheaths. We demonstrate the new solver for simulations of direct current (DC) and radiofrequency (RF) discharges. The implicit treatment of the coupled equations allows using large time steps. The full-Newton method (FNM) enables fast nonlinear convergence at each time step, offering significantly improved simulation efficiency. We discuss the selection of time steps for solving different plasma problems. The new solver enables solving several problems we could not solve before with existing software: two- and three-dimensional structures of the entire DC discharges including cathode and anode regions, electric field reversals and double-layer formation, the normal cathode spot and an anode ring, moving striations in diffuse and constricted DC discharges, and standing striations in RF discharges. The developed FNM-ACM technique offers many benefits for tackling the disparity of gas discharge plasma systems' time scales and nonlinearity.

Effect of dielectronic recombination on charge-state distribution in laser-produced plasma based on steady-state collisional-radiative models

Armed with four different steady-state collisional-radiative (CR) models, we investigated the effect of dielectronic recombination (DR) on the charge-state distribution in laser-produced silicon plasma. To assess this effect, we performed a series of temporally resolved spectra of highly charged Si ions in the extreme ultraviolet region. Ab initio calculations of the DR rate coefficients were done for Si6+–Si4+ ions. We also analyzed the evolution of the collisional ionization, radiative recombination, three-body recombination, photo-ionization, and DR rate coefficients as a function of electron temperature. The electron temperature and electron density for different delay times were obtained by comparing the normalized experimental and simulated spectra. The ion fraction and average charge state from the four different CR models were also obtained. The results indicate that the DR process has a greater influence in the stage of plasma evolution that cannot be neglected in plasma diagnoses.

Energy levels, transition rates and electron impact excitation rates for B-like Kr XXXII

Energy levels and transition rates for electric-dipole, electric-quadrupole, electric-octupole, magnetic-dipole, and magnetic-quadrupole transitions among the levels arising from the n≤ 5 configurations in B-like Kr XXXII are calculated by using two state-of-the-art methods, namely, the multi-configuration Dirac–Hartree–Fock (MCDHF) approach and the second-order many-body perturbation theory (RMBPT). Our results are compared with several available experimental and other theoretical values. Electron-impact excitation (EIE) collision strengths are calculated via the independent process and isolated resonance approximation using distorted-wave (denoted by IPIRDW). Radiation damping effects on the resonance excitation contributions are included. Effective collision strengths are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Spectral line intensities are modelled by using collision radiative model, and several line pairs pointed out might be useful for density diagnostics.

Power loss of hot Dirac fermions in silicene and its near equivalence with graphene

The power loss P of hot Dirac fermions through the coupling to the intrinsic intravalley and intervalley acoustic and optical phonons is analytically investigated in silicene as a function of electron temperature T e and density n s . At very low T e , the power dissipation is found to follow the Bloch–Grüneisen power-law and , as in graphene, and for 20–30 K, the power loss is predominantly due to the intravalley acoustic phonon scattering. On the other hand, dispersionless low energy intervalley acoustic phonons begin to dominate the power transfer at temperatures as low as ∼30 K, and optical phonons dominate at K, unlike the graphene. The total power loss increases with T e with a value of ∼1010 eV s−1 at 300 K, which is the same order of magnitude as in graphene. The power loss due to intravalley acoustic phonons increases with n s at higher T e , whereas due to the intervalley acoustic and optical phonons is found to be independent of n s . Interestingly, the energy relaxation time in silicene is about four times higher than that in graphene. For this reason, silicene may be superior over graphene for its applications in bolometers and calorimeters. Power transfer to the surface optical phonons is also studied as a function of T e and n s for silicene on Al2O3 substrate and it is found to be greater than the intrinsic phonon contribution at higher T e . Substrate engineering is discussed to reduce .

Electron-phonon coupling across the superconductor-insulator transition

We measured current-voltage characteristics on both sides of the magnetic-field-driven superconductor-insulator transition. On both sides, these show strong nonlinearities leading to a conduction branch that is independent of phonon temperature. We show that a picture of electron overheating can quantitatively explain our data over the entire magnetic field range. We find that electron-phonon coupling strength remains roughly constant throughout the insulating state and across the superconductor-insulator transition, dropping dramatically as the magnetic field approaches zero. Our findings shed light on the origin of the highly debated saturation of resistance at low temperature, which has been interpreted by some as evidence for a new anomalous metallic phase and by others as a result of electrons failing to cool down. At the heart of this treatment lies the assumption that resistance is a function of electron temperature and not the phononic one. The applicability of this framework implies that the conduction mechanism, present in the superconductor and throughout the insulating phase, does not rely on a phonon bath.

Electron-phonon cooling power in Anderson insulators

First microscopic theory for electron-phonon energy exchange in Anderson insulators is developed. The major contribution to the cooling power as a function of electron temperature is shown to be directly related to the correlation function of the local density of electron states at small energy difference argument. In Anderson insulators not far from localization transition, this correlation function is strongly enhanced by wave-function's multi-fractality and, additionally, by the presence of Mott's resonant pairs of localized states. The theory we develop explains huge enhancement of the cooling power observed in insulating Indium Oxide films as compared to predictions of the theory previously developed for disordered metals. Our results open the way to predict the conditions appropriate for the observation of Many Body Localization transition those presence in electronic insulators was advocated in the seminal paper by Basko, Aleiner and Altshuler (2006) but have not been convincingly demonstrated yet.

Measurement of the Polytropic Index During Solar Coronal Rain Using a Diagram of the Electron Density Distribution as a Function of Electron Temperature

A differential emission measure (DEM) method is used to evaluate the relationship of the electron density and temperature before and after a coronal rain event during an active sun over the period from 20:10 UT on October 6 to 02:10 on October 7, 2011. Observational data were obtained from SDO/AIA for six different extreme ultraviolet (EUV) spectral lines. 240 different coronal loops were analyzed during this time interval, and the average electron density and temperature were obtained using 171 {\AA} (Fe IX) and 193 {\AA} (Fe XII) filters. The relationship between the density and temperature made it possible to estimate the polytropic index in the solar corona before and after the coronal rain. The polytropic index after the termination of the coronal rain was estimated to be {\gamma} = 1.3{\pm}0.06, Which shows the usual thermodynamic properties of study-state coronal plasma. The polytropic index at the time of onset of the coronal rain was, however, estimated to be {\gamma} = 2.1{\pm}0.11, which indicates an unstable thermodynamic process, i.e., thermal instability. It is suggested that the coronal rain is the result of an unstable process, and the coronal plasma returns its stable state after the rain.

Characterization of hot dense plasma with plasma parameters

Characterization of hot dense plasma (HDP) with its parameters temperature, electron density, skin depth, plasma frequency is demonstrated in this work. The dependence of HDP parameters on temperature and electron density is discussed. The ratio of the intensities of spectral lines within HDP is calculated as a function of electron temperature. The condition of weakly coupled for HDP is verified by calculating coupling constant. Additionally, atomic data such as transition wavelength, excitation energies, line strength, etc. are obtained for Be-like ions on the basis of MCDHF method. In atomic data calculations configuration interaction and relativistic effects QED and Breit corrections are newly included for HDP characterization and this is first result of HDP parameters from extreme ultraviolet (EUV) radiations.

Electron Momentum and Energy Relaxation Times in Wurtzite GaN, InN and AlN: A Monte Carlo Study

Electron relaxation process and transport property of hot electrons in wurtzite GaN, InN and AlN are investigated by an ensemble Monte Carlo (EMC) method using the classic three valleys model. Both momentum and energy relaxation processes are studied here, taking into account the effect of temperature and electric field. It can be found that under different electric fields the relaxation mechanisms are much different for the existence of satellite valley structures in III-nitrides. The momentum and energy relaxation processes of InN are different from that of GaN and AlN for the much smaller effective electron mass in the lowest valley of InN. The polar optical phonon scattering is the main energy relaxation process when the electric field is lower, but inter-valley scattering will dominate the energy relaxation process when the electric field is high. The main momentum relaxation mechanisms are ionized impurity, acoustic phonon, and polar optical phonon scattering at lower electric field, but polar optical phonon and inter-valley scattering are the main momentum relaxation mechanisms when the electric field becomes higher. The momentum relaxation time is much lower than the energy relaxation time, the reason is that nearly all scattering mechanisms relax momentum, but only polar optical phonon and inter-valley scattering relax electron energy. The temperature can affect the momentum and energy relaxation by the role in scattering. Finally, the momentum and energy relaxation times as a function of electron temperature are given, which can be used for relaxation time modeling and device transport research.