Nonideality Of Plasma Research Articles

Polarizabilities of the negative ions of hydrogen and positronium in nonideal classical plasmas

We investigate the polarizability of the negative ions of hydrogen and positronium embedded in nonideal classical plasmas using correlated exponential wavefunctions. The interactions among the charged particles in plasmas have been taken care of by a pseudopotential, derived from a solution of Bogolyubov's hierarchy equations. The effects of nonideality of plasma on the ground state energies and the static and dynamic dipole polarizabilities of the negative ions have been studied in detail for wide range of nonideality. The results show interesting features.

Non-ideal classical plasma: laser pulse effects and dynamic dipole polarizabilities

The properties of a hydrogen atom inside a non-ideal classical plasma, in terms of its behavior in the presence of an applied laser pulse, are explored. The strength of the pulse is chosen such that it maintains near sphericity of the system. The pulse parameters have a strong bearing on the final state attained by the system after its interaction with the pulse. Dynamic dipole polarizability is calculated and the poles are observed to be red shifted with an increase in non-ideality as well as an increase in plasma temperature. The polarizabilities for frequencies of the field below the frequency corresponding to the first pole are found to be greater for larger values of field frequency, plasma non-ideality and electron plasma temperature.

Effects of non-ideality of classical plasmas on the 1Se resonance states in H−

The effects of the non-ideality (NI) of the classical plasmas on the 1Se resonance states of the negative ion of hydrogen (H−) have been investigated theoretically by using the stabilization method. The organized effect of the plasma charged particles is represented by a pseudopotential, which depends on the Debye length D and the non-ideality parameter γ. Densities of the resonance states as a function of D and γ are calculated by employing a highly correlated and extensive basis set. Convergence of the resonance parameters (energy and width) is ensured by increasing the number of terms in the basis. Three 1Se resonance states are found to emerge below the H(4S) excitation threshold. Our present results for lowest lying resonance for plasma-free cases as well as in weakly coupled plasmas are in excellent agreement with the established results in the literature. An extensive study is carried out to explore the changes in the resonance parameters of the three states due to the effects of plasma NI. It is found that, for a given Debye length, the resonance energy increases, and the resonance width decreases with increasing plasma non-ideality.

Study of atomic spectroscopy and electron collision process in non-ideal classical plasmas

This manuscript presents an approach to the calculation of atomic properties and the electron collision excitation process in a non-ideal classical plasma, based on the relativistic distorted wave methodology. The method incorporating the pseudopotential obtained from a sequential solution of the Bogolyubov chain equations, that yields modification term to the calculation of the central field potential, is employed to characterize the interactions among the charged particles in plasmas. The bound/continuous state wave functions and the electron collision excitation matrix elements are determined using the aforementioned pseudopotential within a relativistic Dirac–Coulomb atomic structure framework. Systematic investigations on the effects of non-ideality of plasma on the electronic structures, radiative properties, and excitation cross sections within a selected temperature and density range are carried out in the specific cases of H atom and Ca18+ ion as they make it possible to reproduce the reference data well and thus to conclude with the reliability of the (present) method developed. Apart from its fundamental importance, this study is essential for several applications, especially for the analysis of atomic processes in non-ideal plasmas, and offers a new perspective for the calculation of atomic properties under different conditions in various astrophysical and laboratory plasmas.

Photodetachment of H− in non-ideal classical plasmas

The effects of non-ideality of classical plasmas on the cross sections of the photodetachment of the negative ion of hydrogen (H−) have been investigated within the framework of the dipole approximation. An effective potential, deduced from a solution of Bogolyubov's hierarchy equations, has been used to model the interactions among the charged particles in the non-ideal classical plasmas. Wave functions and energies of H−(1S) and H(1s) are calculated accurately by employing extensive basis sets within the framework of Ritz's variational principle. A detailed study is made on the changes of photodetachment cross section due to the varying non-ideality of plasma in a wide range. It is found that the wavelength corresponding to the maximum value of the photodetachment cross section moves forward due to the increasing non-ideality of plasma.

Particle-in-cell Monte Carlo-collision modeling of non-ideal effects in wave-heated dense microplasmas

A computational model for non-ideal plasma effects during the time evolution of a second-stage laser-heated discharge at high pressures is presented. The model extends a classical one-dimensional particle-in-cell Monte Carlo-collision (PIC-MCC) approach coupled with Maxwell's equations for the laser-heating process of a xenon plasma at 300 K temperature and 10–100 bar pressure. Plasma non-ideality resulting from Coulomb coupling at high plasma densities is manifested as a depression in the effective ionization potential of atoms and enhanced collision cross sections. These non-ideal effects are represented using the Ecker–Kröll model in the context of the PIC-MCC approach. We find that full ionization of the plasma is obtained on the picosecond timescale, starting from the skin layer and quickly expanding throughout the domain through an anomalous extension of the skin depth. More critically, we show that the inclusion of the non-ideal plasma effects results in more rapid ionization compared to an ideal plasma, especially at higher pressures. The ionization delay reduction is of the order of a fraction of a picosecond, corresponding to a 16% decrease at 100 bar. As the amplitude of the wave field is lowered, the ionization rate is lowered, making the plasma non-ideality effects more prominent.

Scattering of slow electron from hydrogen atom in non-ideal classical plasmas: Zero-energy resonances

The scattering of slow electrons from the hydrogen atom embedded in non-ideal classical plasma has been investigated by using the effective range theory. A pseudopotential, which has been derived from a solution of Bogolyubov's hierarchy equations, is used to represent the interactions among the charged particles in plasma. A detailed study is made on the effects of non-ideality of plasma on the scattering dynamics for a wide range of the non-ideality parameter. In particular, the zero-energy resonance phenomenon has been studied in detail by evaluating the singlet scattering length. It is found that the scattering length suffers significant changes when the non-ideality parameter approaches its critical value.

Electron transfer in proton‐hydrogen collisions in nonideal classical plasmas

AbstractEffects of nonideality of classical plasma on the reaction: p + H(1s) → H(nlm) + p has been investigated by carrying out fully quantum mechanical calculations within the framework of a first‐order distorted wave method. Scattering amplitude is calculated conveniently by employing a simple, variationally determined wave function of hydrogen atom embedded in nonideal classical plasma. A detailed study is made on the changes in electron transfer cross sections due to the nonideality of plasma varying from 0 to 4 and the incident proton energy lying between 10 and 500 keV. It has been found that nonideality of plasma causes substantial change in capture cross section.

Properties of the Positronium Negative Ion Embedded in Non-ideal Classical Plasmas

Properties of the positronium negative ion embedded in non-ideal classical plasmas have been studied theoretically. A pseudopotential, derived from a solution of Bogolyubov’s hierarchy equations, is used to describe the interaction potentials of the charged particles in the ion. A large basis set is employed in Rayleigh–Ritz variational method to compute accurately various quantities, such as binding energy, cusp values, annihilation rate, associated with the ground state of the ion. A detailed study is made on the effects of non-ideality of plasma on those quantities. In particular, special emphasis is given to determine the ranges of plasma screening parameters within which the ion remains stable.

Stability of the negative ion of hydrogen in nonideal classical plasmas.

The stability of the negative ion of hydrogen (H^{-}) embedded in nonideal classical plasma has been studied by computing the ground state energy of the ion quite accurately. The interactions among the charged particles in plasma have been modelled by a pseudopotential, derived from a solution of Bogolyubov's hierarchy equations. An extensive basis set is employed in Rayleigh-Ritz variational method to compute the ground state energy of H^{-} for various values of plasma parameters. Effects of nonideality of plasma on the stability of the ion have been investigated in detail for a wide range of nonideality. Particular emphasis is made to compute accurately the critical values of the plasma screening parameters.

Scattering in non-ideal classical plasmas: Scattering length and zero-energy resonances

A fully quantum mechanical calculation has been performed to investigate the scattering of charged particles in nonideal classical plasmas (NICPs). Interactions among the charged particles in NICP have been depicted by a pseudopotential, derived from a sequential solution of Bogolyubov's chain equations. The Schwinger variational method (SVM) has been employed in the momentum space to compute the scattering phase shifts accurately for various plasma parameters. A detailed study has been made on the dynamics of electron-electron (e-e) and electron-proton (e-p) scattering in NICP for a wide range of plasma parameters. Special attention is paid to explore the scattering dynamics at low incident energies. In particular, scattering length and zero-energy resonances have been investigated in detail. Furthermore, effects of nonideality of plasma on the total cross section and transport cross section have also been studied.

Stability of hydrogen atom in non-ideal classical plasmas

The stability of a hydrogen atom embedded in classical nonideal plasma has been investigated. The interaction potential between the proton and the electron has been modeled by a pseudopotential, which is obtained from a sequential solution of Bogolyubov chain equations. The critical values of the plasma screening parameters have been determined quite accurately within the framework of the Rayleigh-Ritz variational method by employing an extensive wave function following a definitive prescription. Convergence of the results has been corroborated by increasing the number of terms in the wave function. A detailed study has been carried out on the effects of nonideality of plasma on the bound states for the density and temperature lying in the ranges of 2.7 × [1023–1026] m−3 and [104–105] K, respectively. It is found that the atom remains bound in the aforementioned density and temperature ranges.

Polarized reflectivity properties of shock-compressed plasma with strong interaction of particles

New results of s- and p-polarized reflectivity measurements on non-ideal plasma at the frequency of external electromagnetic field νlas = 2.83×1014 s−1, the plasma density ρ = 1.8 g/cm3 and the parameter of Coulomb non-ideality of plasma Γ = 1.4 are presented. Using a Fermi-like density profile along the shock wave front, the reflectivity coefficients of non-ideal plasma were calculated for newly obtained experimental data. As physically expected, a single profile is sufficient to obtain good agreement with the experimental data at all investigated optical laser frequencies.

Equation of state of a dense plasma: Analytical results on the basis of quantum pair interaction potentials in the random phase approximation

In this work, using recently obtained expansion of the dielectric function in the long wave length limit by Moldabekov et al (2015 Phys. Plasmas 22 102104), we extended previously obtained formulas for the equation of state of the semiclassical dense plasma from Ramazanov et al (2015 Phys. Rev. E 92 023104) to the quantum case. Inner energy and contribution to the pressure due to plasma non-ideality derived for both Coulomb pair interaction and quantum pair interaction potentials. Obtained analytical result for the equation of state reproduces the Montroll-Ward contribution, which corresponds to the quantum ring sum. It was shown that the obtained results are consistent with the Thomas-Fermi approximation with the first order gradient correction. Additionally, the generalization of the quantum Deutsch potential to the case of the degenerate electrons is discussed. Obtained results will be useful for understanding of the physics of dense plasmas as well as for further development of the dense plasma simulation on the basis of the quantum potentials.

Comparison of the detailed plasma composition for different models

A self-consistent model with compensation for strongly coupled plasma is described. The effective algorithm to solve the equations of this model is proposed. The calculation of the ionization tables is performed. This model is compared with the Thomas-Fermi model with quantum and exchange corrections (TFC) and with the self-consistent model of ionization equilibrium without compensation. It is established that the model is in agreement with the TFC model for rarefied and rather dense plasma and differs from it for condensed matter. The effects of plasma non-ideality and electron degeneration are considered.

Self-consistent compensated microfield model for a strongly coupled plasma

A compensated microfield model of plasma nonideality is proposed as an improvement of the traditional microfield models. In this model, a double contribution of a microfield to the truncation of statistical sums removed. The new method of truncation of the statistical sums of atoms or ions is compared with the results of experiments and computations performed by well-known Debye-type and other models. It is shown that only the microfield model correctly describes experiments. Ionization of Li and Hg atoms is calculated. The effect of metallization of plasma—an abrupt increase of ionization from zero to a single ionization at low temperatures and nearly normal densities—is qualitatively described. The results of calculation of Hg vapor ionization qualitatively agree with known experimental results on the measurement of electric conductivity of this vapor.

Collisional recombination in nonideal plasmas

We suggest a model that allows one to consider the kinetics of collisional recombination in a nonideal plasma and to calculate its rate by the molecular dynamics method. We have found that the dependence of the collisional recombination rate on the plasma coupling parameter differs significantly from the extrapolation of the three-body recombination rate to the nonideal region. The recombination rate in a strongly coupled plasma has been found to decrease with increasing coupling parameter. We have established that the effect of plasma nonideality increases with ion charge. The recombination kinetics is shown to depend significantly on how the ions are arranged in the medium. Collisional recombination transforms into three-body one as the coupling parameter of the medium decreases.

Pair fluctuations in nonideal plasma and their restriction at the ionization threshold

A self-consistent fluctuation approach is developed to the consideration of the spectral region intermediate between discrete and continuous levels of energy in nonideal plasma. Pair fluctuations are identified within the classical method of molecular dynamics. The transition of pair fluctuations in the limit of low degrees of nonideality of plasma to excited atoms is considered. The domains of existence of excited atoms and pair fluctuations are estimated. The pattern of restraint of statistical sum of atom in nonideal plasma is clarified.

A numerical study of expected accuracy and precision in Calibration-Free Laser-Induced Breakdown Spectroscopy in the assumption of ideal analytical plasma

Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS) has been proposed several years ago as an approach for quantitative analysis of Laser-Induced Breakdown Spectroscopy spectra. Recently developed refinement of the spectral processing method is described in the present work. Accurate quantitative results have been demonstrated for several metallic alloys. However, the degree of accuracy that can be achieved with Calibration-Free Laser-Induced Breakdown Spectroscopy analysis of generic samples still needs to be thoroughly investigated. The authors have undertaken a systematic study of errors and biasing factors affecting the calculation in the Calibration-Free Laser-Induced Breakdown Spectroscopy spectra processing. These factors may be classified in three main groups: 1) experimental aberrations (intensity fluctuations and inaccuracy in the correction for spectral efficiency of a detection system), 2) inaccuracy in theoretical parameters used for calculations (Stark broadening coefficients and partition functions) and 3) plasma non-ideality (departure from thermal equilibrium, spatial and temporal inhomogeneities, optical thickness, etc.). In this study, the effects of experimental aberrations and accuracy of spectral data were investigated, assuming that the analytical plasma is ideal. Departure of the plasma conditions from ideality will be the object of future work. The current study was based on numerical simulation. Two kinds of metallic alloys, iron-based and aluminum-based, were studied. The relative weight of the error contributions was found to depend on the sample composition. For the here-investigated samples, the experimental aberrations contribute to the overall uncertainty on the quantitative results more than theoretical parameters. The described simulation method can be applied to the Calibration-Free Laser-Induced Breakdown Spectroscopy analysis of any other kind of sample.

Optical emission spectroscopy of electrical discharge machining plasma

Plasma created during electrical discharge machining is systematically investigated using optical emission spectroscopy. Typical spectra show a strong Hα and continuum radiation, with many lines emitted by impurities coming from electrode and workpiece materials. The dielectric molecules are cracked by the discharge. Changing polarity affects the electrode wear and workpiece erosion rates, which can be qualitatively seen on the spectra. Time-resolved spectroscopy shows that the plasma density reaches 2 × 1018 cm−3 at the beginning of the discharge. This extreme density causes the merging of lines, strong Stark broadening and shift of the Hα line. Afterwards, the density decreases rapidly with time. The electron temperature remains roughly constant around 0.7 eV. The low temperature and the high density measured prove that the EDM plasma is non-ideal (Γ ≃ 0.45). Absence of the Hβ line, asymmetric shape of the Hα line and complex structures around Hα are other spectroscopic evidences of the plasma non-ideality.