Range Of Electron Densities Research Articles

Photoionization process of the hydrogenlike carbon ion embedded in warm and hot dense plasmas.

Complicated many-body interactions between ions and surrounding particles exist in warm and hot dense plasmas. It will significantly alter the atomic structures and dynamic properties of the embedded ions. Recently, the atomic-state-dependent (ASD) screening model has been proposed and shown to be valid for investigating the screening effect in warm and hot dense plasmas over a wide range of electron densities and temperatures. By employing the ASD model, we investigate the photoionization process for the hydrogenlike carbon ion embedded in warm and hot dense plasmas with corresponding Coulomb coupling parameter ranges of 0.05 ≤ Γ ≤ 1.16, where Γ characterizes the ratio of the average potential to thermal energy. It is found that there are stronger plasma screening effects on the ionization energy and photoionization cross section due to the negative-energy electron distributions considered in the ASD model compared to those considering only free electrons. The present results from the ASD model show reasonable agreement with the classical Debye-Hückel (DH) model in weakly coupled plasmas. However, significant deviations of the ionization energy and cross section between these two models are observed in moderately and strongly coupled plasmas, due to the approximate treatment of the plasma-electron density distribution of the DH model. In the region of low photoelectron energies, the positions of the shape resonance peaks of the cross sections obtained from the ASD model differ significantly from those of the DH model due to the different screening effects.

Hydrogen recombination continua in stellar flares

ABSTRACT An increasing interest in stellar flares stimulated various modelling approaches in order to analyse the observed flare fluxes. A particular interest was focused on photometric data obtained from Kepler and TESS satellites which detected thousands of flares on cool dwarf stars, including extremely energetic superflares. Radiation-hydrodynamical simulations, together with a rather rare broad-band spectroscopy, indicate much larger densities in the superflare chromospheres as compared to solar flares. Formation of hydrogen recombination continua under such different densities ranging from 1013 to 1015 cm−3 or more is governed by physics of optically thin to largely thick plasmas, the continuum optical thickness being within the range of four orders of magnitude. Various authors presented simple approximate methods to analyse the photometric data from Kepler or TESS under such diverse regimes of physical conditions. In this letter, we summarize the general physical approach and compute the hydrogen recombination spectra under the above range of electron densities. We show the theoretical contrast with respect to quiet-star continuum for two characteristic stars of G and dMe type. Based on that we distinguish three regimes of the continuum formation and discuss the applicability of various simple approaches.

Electrochemical performance of La0.8A0.2TiO3-δ (A = Li, Mg) based perovskites for solid oxide fuel cell electrode

ABSTRACT For potential use as an electrode in SOFCs, the effects of lithium and magnesium doping for phase development and conductivity of LaTiO3 have been investigated. Using a 1000°C sintering temperature, dense ceramics are created via the traditional solid oxide reaction method. Phase study shows the presence of perovskite phase with monoclinic crystal assembly. Structural characteristics of doped and undoped perovskites were calculated using the VESTA tool. Through the computed XRD spectral analysis, unit cell dimensions are established. To quantify sub-atomic characteristics and examine lattice components, CrystalMaker software also calculates electron density and lattice range. CrystalMaker program is useful for simulating porosity distributions and analysing impure inclusions in crystallisation.The electrical conductivity of the perovskites was analysed using impedance spectrometry and Li-doped structures display a significant increase in conductivity in the phase borderline of disordered perovskite.

Trivelpiece–Gould modes and low-frequency electron–ion instability of non-neutral plasma

The frequency spectra of the Trivelpiece–Gould modes of a waveguide partially filled with non-neutral plasma are determined numerically by solving the dispersion equation. The modes having azimuthal number $m = 1$ are considered. The results are presented for the entire acceptable range of electron densities, magnetic field strengths, for different values of the charge neutralization coefficient. The Cherenkov resonance condition of an ion with a diocotron mode having a finite value of the longitudinal wave vector was studied. The characteristics of resonant low-frequency electron–ion instability caused by relative azimuth motion of electrons and ions in crossed fields and by the anisotropy of the distribution function of ions are discussed. Ions are created by ionization of residual gas in the plasma volume. Due to the anisotropy, instability occurs not only in the vicinity of the resonance, but also outside it. For typical values of plasma parameters in experiments, estimations of the frequency growth rate are given. A conclusion is drawn that this instability can be the cause of the low-frequency oscillations observed in linear devices with non-neutral plasma produced in an electron beam channel.

Damping effect of longitudinal optical phonon—plasmon coupling on thermal radiation from surface micro-gratings on direct and indirect electronic transition type semiconductors

Thermal radiation properties of surface micro-Au-line and space structures on direct and indirect electronic transition-type semiconductors of n-type (n-) GaAs and GaP, respectively, are studied. The electron densities range from 0.62 to 1.0 × 1018 cm−3. The emission spectra of samples on n-GaAs wafers show peak energies significantly shifted from the longitudinal optical (LO) phonon energy due to the LO-phonon−plasmon coupling (LOPC) at 630 K, while partial decoupling is observed. The thermal emission from the sample on n-GaP is peaked at 395.9 cm−1, shifted only by 1.5 cm−1 from the LO-phonon energy, with a linewidth of 12.5 cm−1 at 630 K. The effect of LOPC on the emission from the sample on n-GaP is mostly suppressed because of the electron localization in the X-valley, suggesting an advantage of indirect transition-type semiconductors in LO-phonon resonant infrared emitters using the phonons generated via the electron energy relaxation.

A seven-channels microwave interferometer measurement system for measuring electron density distribution in hypervelocity transient plasma flow

When a hypersonic vehicle is flying in the near space region, the strong friction between the vehicle and the air can cause the air to ionize. As a result, the plasma sheath around the vehicle and the wake flow field behind it are formed, significantly affecting the electromagnetic (EM) scattering characteristics of the vehicle and resulting in the communication blackout. Therefore, the investigation of electron density distribution of the plasma sheath and wake flow field is of the great significance in the detection, communication, etc. of the hypersonic target. In order to meet the requirements for on-ground electron density distribution measurement of the transient plasma flow fields, the feasibility of measuring electron density profile with seven-channel microwave interferometer measurement system is demonstrated in this work. The wake plasma is modeled as a non-uniform multilayer medium, and the full-wave simulation software FEKO is used to calculate the phase-shift information of EM wave transmitting through non-uniform single-layered dielectric plate, uniform and non-uniform multi-layered dielectric plates. According to the simulation results, the dielectric constant of the substrate is retrieved and compared with the preset result. The retrieved results show that it is feasible that the dielectric constant distribution of non-uniform multi-layered dielectric plate is measured by utilizing the proposed microwave interferometer system with one transmission port and seven receptions. The amplitude-phase dynamic range analysis of the proposed Ka-band microwave measurement system is also carried out. The key technologies including large instantaneous amplitude-phase dynamic range and ray tracking inversion algorithm for two-dimensional (2-D) electron density distribution are also developed. Finally, the complete scheme of Ka-band seven-channel microwave interferometer measurement system is introduced. The system includes one lens antenna to generate the required plane wave and seven open-ended waveguide receiving antennas which are asymmetrically arranged to improve the lateral spatial resolution of the system. The system exhibits the amplitude dynamic range and the phase dynamic range of over 65 dB and 180° under 1 MHz IF bandwidth respectively. The plasma electron density distributions are measured by utilizing the proposed seven-channel microwave interferometer system in the ballistic range and multi-functional shock tube. The response time of the system is smaller than 1μs, satisfying the requirement for the two-dimensional distribution measurement of the transient plasma flow field generated by the ballistic range and multi-functional shock tube. The differences between experimental and numerical results are less than 0.5 order of magnitude, and the variations in transient plasma generated in both ballistic target and shock tube equipments are well detected. The measurement range of plasma electron density is 10<sup>10</sup>－10<sup>13</sup> cm<sup>–3</sup> and the spatial resolution is better than 15mm. In addition, the proposed ray tracing method is also used to invert the two-dimensional (2D) electron density distributions of both square layered model and cylindrical layered model under identical experimental state. The results are in consistent with each other, indicating that the proposed ray tracing method can be used in the inversion of 2D electron density distribution of plasma with different shapes.

Effect of plasmon excitations in relativistic quantum electron gas

In this research, we use the generalized quantum multistream model to describe collective qusiparticle excitations in electron gas with arbitrary degree of degeneracy and relativity. The effective Schrödinger–Poisson and square-root Klein–Gordon–Poisson models are applied to study the energy band structure and statistical parameters of finite temperature quantum and relativistic quantum electron gas in neutralizing background charge. Based on the plasmon energy bandgap appearing above the Fermi level, a new equation of state for quasiparticle (collective) excitations with new plasma parameter definition is suggested for dense plasmas applicable to a wide range of electron temperature and density. The new criterion for quasiparticle excitations reveals some interesting aspects of relativistic quantum matter at extreme condition, such as the plasmon blackout and collective quantum pressure collapse, which are studied in the frameworks of both non-relativistic and relativistic quantum phenomena. Current quasiparticle model predicts density-temperature regimes in warm-dense matter for which collective excitations become ineffective. On the other hand, the energy band structure model predicts the quasiparticle pressure collapse in temperature–density regime close to that of white dwarf stars. The energy band structure is a powerful concept in condensed matter physics and is shown to have applications for collective quantum excitations in electron gas. It can also have direct applications in quasiparticle dielectric response and thermodynamic properties of electron gas in inertial confinement fusion, stellar core, compact stars, and charged relativistic quantum environments. It is interesting that the basic thermodynamic behavior of non-relativistic and relativistic quantum electron gases closely match up to temperature and number density of typical white dwarfs where the gravitational collapse is prone to occur. This evidently confirms the relevance of non-relativistic quantum plasmon model to study the collective excitations in warm dense matter and white dwarfs.

KAPPA: A Package for the Synthesis of Optically Thin Spectra for the Non-Maxwellian κ-Distributions. III. Improvements to Ionization Equilibrium and Extension to κ < 2

The KAPPA package is designed for calculations of optically thin spectra for the non-Maxwellian κ-distributions. This paper presents an extension of the database to allow calculations of the spectra for extreme values of κ < 2, which are important for accurate diagnostics of the κ-distributions in the outer solar atmosphere. In addition, two improvements were made to the ionization equilibrium calculations within the database. First, the ionization equilibrium calculations now include the effects of electron impact multi-ionization (EIMI). Although relatively unimportant for Maxwellian distribution, EIMI becomes important for some elements, such as Fe and low values of κ, where it modifies the ionization equilibrium significantly. Second, the KAPPA database now includes the suppression of dielectronic recombination at high electron densities, evaluated via the suppression factors. We find that at the same temperature, the suppression of dielectronic recombination is almost independent of κ. The ionization equilibrium calculations for the κ-distributions are now provided for a range of electron densities.

Further rotation reversal studies in C-Mod L-mode plasmas

Studies of core toroidal rotation reversal phenomenology in C-Mod deuterium L-mode plasmas have been expanded to include details of the dependences on plasma current and toroidal magnetic field. Rotation reversal occurs at a critical density, and universal scaling indicates that the product of ncritq95R ∼ BT/2, with ncrit in 1020/m3, R in m, and BT in T. Measurements in H and He plasmas exhibit similar behavior, including a connection with the linear Ohmic confinement/saturated Ohmic confinement transition and the cutoff for non-diffusive heat transport. Electron density and ion cyclotron range of frequencies power modulation experiments suggest that the collisionality ν* is a unifying parameter. Strong impurity puffing causes the critical density to increase, indicating that the situation is more complicated than only collisionality, perhaps involving the details of the effects of dilution on ion temperature gradient mode stability.

TRIVELPIECE-GOULD MODES OF WAVEGUIDE PARTIALLY FILLED WITH NON-NEUTRAL PLASMA. PART 2

The frequency spectra of electron eigenmodes with the azimuthal number m =1 of a waveguide partially filled with non-neutral plasma are determined numerically within the entire allowable range of electron densities and magnetic field strengths, for various values of the degree of charge neutralization and finite values of the longitudinal wave vector.

How the Exchange Energy Can Affect the Power Laws Used to Extrapolate the Coupled Cluster Correlation Energy to the Thermodynamic Limit.

Finite size error is commonly removed from coupled cluster theory calculations by N-1 extrapolations over correlation energy calculations of different system sizes (N), where the N-1 scaling comes from the total energy rather than the correlation energy. However, previous studies in the quantum Monte Carlo community suggest an exchange-energy-like power law of N-2/3 should also be present in the correlation energy when using the conventional Coulomb interaction. The rationale for this is that the total energy goes as N-1 and the exchange energy goes as N-2/3; thus, the correlation energy should be a combination of these two power laws. Further, in coupled cluster theory, these power laws are related to the low G scaling of the transition structure factor, S(G), which is a property of the coupled cluster wave function calculated from the amplitudes. We show here that data from coupled cluster doubles calculations on the uniform electron gas fit a function with a low G behavior of S(G) ∼ G. The prefactor for this linear term is derived from the exchange energy to be consistent with an N-2/3 power law at large N. Incorporating the exchange structure factor into the transition structure factor results in a combined structure factor of S(G) ∼ G2, consistent with an N-1 scaling of the exchange-correlation energy. We then look for the presence of an N-2/3 power law in the energy. To do so, we first develop a plane-wave cutoff scheme with less noise than the traditional basis set used for the uniform electron gas. Then, we collect data from a wide range of electron numbers and densities to systematically test five methods using N-1 scaling, N-2/3 scaling, or combinations of both scaling behaviors. We find that power laws that incorporate both N-1 and N-2/3 scaling perform better than either alone, especially when the prefactor for N-2/3 scaling can be found from exchange energy calculations.

Study of electron impact excitation of H-like Si13+ ion in dense plasma environment

The relativistic configuration interaction technique has been employed to study the electron impact excitation collision strengths of H-like Si13+ ion in strongly coupled plasma environment. The analytical plasma screening b-potential has been adopted to determine the physical effects of the screened Coulomb interaction due to the influence of plasma on the atomic structure and dynamics affecting atomic processes. The modified Dirac equations are solved to obtain the bound and continuum state wave functions. We examine the plasma screening effect by considering the plasma conditions at the electron temperatures of 200, 600 and 1000 eV over electron density range of 2.0 × 1023 - 1.0 × 1024 cm−3. The present results highlight that the inclusion of plasma environment induces significant effect on the binding energies, transition energies, radiative transition probabilities, oscillator strengths and collision strengths. It has been observed that the collision strength decreases with increase in plasma electron density for a fixed temperature. Our results will be beneficial for laser produced plasmas, high energy density physics, astrophysical applications and will open the door to modelling and advanced diagnostics of solar and stellar plasmas.

Study on the transmission characteristics and band structure of 2D and 3D plasma photonic crystals.

In this paper, 2D and 3D plasma photonic crystals (PPCs) were constructed using argon-mercury glow discharge tubes. Firstly, the collisional radiative model (CRM) was established for the glow discharge process, the average electron density of plasma in the discharge tube was calculated, and the average electron density was experimentally diagnosed by microwave diagnosis. By comparing the calculated and experimental results, the variation range of the average electron density in the tube was given. Secondly, according to the analysis results of the average electron density, a layered model of the discharge tube was established, and the transmission characteristics of the 2D and 3D PPC were calculated and measured. Finally, to analyze the cause of the photonic bandgap (PBG) in the transmission spectra, the band structures of 2D and 3D PPC were calculated using the plane wave expansion (PWE) method and the symplectic finite difference time domain (SFDTD) method. The results show that: the layered model is a valid discharge tube model; for 2D PPC, the formation of Localized Surface Plasmons (LSPs) under TE polarization is the main cause of PBG generation, and the number of LSP bandgap increases as the electron density rises; The existence of cutoff bandgap under TM polarization is due to the cutoff effect of plasma on electromagnetic waves. For 3D PPC, both cutoff bandgap and LSP bandgap exist in the transmission spectra, and the cutoff bandgap is shifted to lower frequencies due to the presence of Fano mode. The results of the study can be used as a reference for communication, microwave device fabrication, and military target stealth.

TRIVELPISE-GOULD MODES OF WAVEGUIDE PARTIALLY FILLED WITH NEUTRAL OR NON-NEUTRAL PLASMA

The frequency spectra of eigenmodes with azimuthal number m = 1 are determined by numerical methods for a waveguide partially filled with neutral or non-neutral plasma. Calculations are performed within the entire permissible range of electron density or magnetic field strengths, for different values of the degree of charge neutralization and the longitudinal wave vector. Areas of existence of bulk and surface electronic modes of waveguide are also defined. The results are presented in the form of dependences on the parameter q = 2ωpe 2/ωce2.

Analysis of hydrogen isotopes retention in thermonuclear reactors with LIBS supported by machine learning

Retention of hydrogen isotopes in thermonuclear reactors is a safety and maintenance issue, thus requires a contactless measurement method of its level. Although calibration free LIBS proved its usefulness on calibrated samples and even in tokamaks, its performance may be deteriorated in next-step fusion devices because of its sensitivity on the plasma parameters as electron temperature and density which are more challenging to be precisely measured than in laboratory conditions. Moreover, both Beryllium and Tungsten have spectral lines in the vicinity of hydrogen alpha line, which may introduce additional uncertainties. Because of these problems the uncertainty of the temperature estimation at the level of several percent leads to serious uncertainties in estimation of elemental composition, even higher than + − 20 at.%.To deal with problems with machine learning (ML) algorithms are proposed. To obtain satisfactory amount of data for training the models, simulated spectra may be used. The simulation allows obtaining synthetic spectra for different concentration of W, Be and D/T for a range of electron temperature and density. At the present stage of the research the data are used for development of classification and regression ML algorithms as logistic and linear regression, SVM, LDA, ANN, which are supported or not with dimensionality reduction by PCA.The results show differences in performance of various models and outline further works on the development of systems operating on real spectroscopic data.

EDGE2D-EIRENE and ERO2.0 predictions of nitrogen molecular break-up and transport in the divertor of JET low-confinement mode plasmas

• Nitrogen-seeded partially detached JET l -mode plasmas studied using EDGE2D-EIRENE and ERO2.0. • Nitrogen line intensities (N I to N V) in the outer divertor are reproduced to within 50% with EDGE2D-EIRENE. • Nitrogen line intensity peak locations shown to be highly sensitive to the upstream electron density. • ERO2.0 simulations with nitrogen molecular dissociation reactions included suggest a high-degree of molecular recycling. EDGE2D-EIRENE simulations of nitrogen-seeded partially detached JET l -mode plasmas show that the divertor N I to N V radiation distributions are highly sensitive to the upstream electron density, and less sensitive to changes in the assumed cross-field particle diffusivity for nitrogen ions. The EDGE2D-EIRENE simulations reproduce the peak intensities of N I to N V as measured by vertically viewing divertor filterscopes to within 50 % for a narrow range of the upstream electron density within the experimental uncertainties, while the predicted profiles are narrower than the measured ones. Including nitrogen atoms only in the ERO2.0 simulations implies lower N III and N IV peak intensities by one and two thirds, respectively, compared to EDGE2D-EIRENE. If nitrogen is assumed to recycle exclusively as molecules instead of atoms, ERO2.0 predicts that the N III and N IV intensities in the divertor increase by up to a factor of two and that the time-averaged, volume-integrated number of N 5+ to N 7+ ions in the plasma also increases by approximately a factor of 2.

Nanoscale active tuning of the second harmonic generation efficiency in semiconductors from super-low to gigantic values

Second harmonic generation efficiency (SHGE) strongly depends on the length of the interaction material along the beam propagation axis. Since a nanoscale interaction length is considered too short even in the optical wavelength scale, the attained SHGE through nanomaterials is usually too low to be of practical use. In this study, it will be shown that by properly adjusting the conduction-band electron density in a semiconductor nanomaterial under a certain optical pumping rate (active tuning), the SHGE can be effectively tuned from being super-low to being ultra-high. Such sharp tunability is only valid for small-scale materials as their density of conduction-band electrons can be rapidly switched between high and low under moderate optical pumping. Using an experimentally verified computational model, we have observed that at a given frequency, for a certain range of conduction-band electron densities, the SHGE can reach up to 1080% for Ga-As and 230% for silicon nanomaterials under active tuning, with respect to the intensity of the first harmonic of the input signal. Such SHGEs are unprecedented, which is very promising for generating higher harmonics via cascaded second harmonic generation performed via adaptive tuning of the conduction band electron density at each stage.

Band Flattening and Landau Level Merging in Strongly-Correlated Two-Dimensional Electron Systems

We review recent experimental results indicating the band flattening and Landau level merging at the chemical potential in strongly-correlated two-dimensional (2D) electron systems. In ultra-clean, strongly interacting 2D electron system in SiGe/Si/SiGe quantum wells, the effective electron mass at the Fermi level increases monotonically in the entire range of electron densities, while the energy-averaged mass saturates at low densities. The qualitatively different behavior of the two masses reveals a precursor to the interaction-induced single-particle spectrum flattening at the chemical potential in this electron system, in which case the fermion “condensation” at the Fermi level occurs in a range of momenta, unlike the condensation of bosons. In strong magnetic fields, perpendicular to the 2D electron layer, a similar effect of different fillings of quantum levels at the chemical potential—the merging of the spin- and valley-split Landau levels at the chemical potential—is observed in Si inversion layers and bilayer 2D electron system in GaAs. Indication of merging of the quantum levels of composite fermions with different valley indices is also reported in ultra-clean SiGe/Si/SiGe quantum wells.

Classical molecular dynamic simulations and modeling of inverse bremsstrahlung heating in low Z weakly coupled plasmas

Classical molecular-dynamics simulations (CMDS) have been conducted to investigate one of the main mechanisms responsible for absorption of radiation by matter, namely, stimulated inverse bremsstrahlung. CMDS of two components plasmas (electrons and ions) for a large range of electron densities and electron temperatures, for ionization Z = 1, were carried out with 2 × 106 particles using the code LAMMPS. A parameterized model (with six adjustable constants), which encompasses most theoretical models proposed in the past to quantify heating rate by stimulated inverse bremsstrahlung, serves as a reference for comparison to our simulations. CMDS results are precise enough to rule out elements of these past models such as coulomb logarithms depending solely upon laser pulsation ω and not upon intensity. The six constants of the parameterized model have been adjusted, and the resulting model matches all our CMDS results and those of previous CMDS in the literature.

Spectroscopy characteristics and decay properties of plasma-embedded atoms in external electric and magnetic fields

This paper describes a computational approach within the framework of relativity theory for explaining the spectral and decay properties of atoms and ions embedded in a plasma and also in the presence of applied external electric and magnetic fields. It uses the configuration interaction approximation and the analytical potential derived from general ion-sphere theory to represent the atomic interactions within the plasma. In the model, the Dirac–Coulomb–Hamiltonian is reconstructed and the effects of the weak electric and magnetic field are treated as small perturbations. The eigenvalues for the orbitals and (radial) wave functions are obtained through the Dirac equations. A diagonalization is performed to include these plasma, electric, and magnetic terms. As an example, an environment with a hot-dense plasma and weak electric and magnetic fields is considered, where the interaction is much weaker than the Coulomb interaction, yet much stronger than the spin–orbit interaction. The atomic structures and spectra of a selected hydrogen atom are presented for a wide range of electron densities, temperatures, and electric and magnetic fields. The behavior of the energy and radiative transitions with respect to these interactions is analyzed in detail. The results obtained from the proposed approach are critically compared with other available results. The present study not only advances our understanding of the electronic structures and radiation characteristics of atomic systems in external fields but may also be relevant for astrophysics and laboratory experiments, especially on the solar corona, laser-produced plasmas, and so on.