Plasma Screening Effects Research Articles

Influence of the dynamic plasma screening on the Ramsauer phenomena for the polarization collision in thermal plasmas

The dynamic plasma screening effects on the Ramsauer phenomena for the electron-atom polarization collision are investigated in dense plasmas. The phase theory and the effective Buckingham potential with the dynamic Debye length are employed to obtain the phase shift and total collision cross section as functions of the collision energy, and Debye length, polarizability, scattering length, and thermal energy. The result shows that the energy for the Ramsauer minimum increases with an increase of the thermal energy. It is also found that the dynamic plasma screening effect suppresses the total polarization cross section below the Ramsauer energy. However, it is found that the dynamic plasma screening effect enhances the total polarization cross section above the Ramsauer energy. The screening effect on the Ramsauer energy is also discussed.

Influence of the renormalization plasma screening on the electron-atom collision in partially ionized plasmas

The renormalization plasma screening effects on the elastic electron-atom collision are investigated in partially ionized dense hydrogen plasmas using the eikonal method. It is found that the renormalization plasma screening suppresses the eikonal phase shift and cross section for the elastic electron-atom collision in partially ionized plasmas. It is also found that the renormalization plasma screening effect on the elastic electron-atom collision process increases with an increasing impact parameter. In addition, it is found that the maximum position of the differential cross section is receded from the center of the atom with an increase of the Debye length.

Screening Effects on the Ion–Ion Collisions in Nonideal Dense Metal Plasmas

The plasma screening and quantum effects on ion–ion collisions are investigated in a nonideal Al and Cu dense metal plasma. Eikonal analysis and the effective pseudopotential model of the quantum–mechanical and plasma screening effects are used to obtain the eikonal phase shift and eikonal cross section for the ion–ion collision as functions of the impact parameter, collision energy, de Broglie wavelength, and Debye length in nonideal metal plasmas. The result shows that the plasma screening effect is more important than the quantum–mechanical effect in ion collisions in nonideal metal plasmas. The result shows that the eikonal phase shift decreases with an increase in the quantum–mechanical effect. Note that the Al–Cu ion collision cross section is found to be greater than the Al–Al and Cu–Cu ion collision cross sections in a dense metal plasma.

Cooper-type minima in quadrupole photoionization of plasma-embedded hydrogen atoms

The quadrupole photoionization of hydrogen atoms under the perturbation of plasma screening effects is investigated by the complex-coordinate rotation method. The Debye–Hückel (DH) and modified-DH potentials are adopted for describing the different features of plasmas. Comparisons of the quadrupole photoionization cross sections for these two screened potentials are made. The variation of cross sections with various Debye screening lengths is presented for illustrating the appearance of Cooper-type minima and shape resonances induced by plasma screening. The relations between the Cooper-type minima and the instability of the initial bound states are discussed.

A consistent approach for mixed detailed and statistical calculation of opacities in hot plasmas

Absorption and emission spectra of plasmas with multicharged-ions contain transition arrays with a huge number of coalescent electric-dipole (E1) lines, which are well suited for treatment by the unresolved transition array and derivative methods. But, some transition arrays show detailed features whose description requires diagonalization of the Hamiltonian matrix. We developed a hybrid opacity code, called SCORCG, which combines statistical approaches with fine-structure calculations consistently. Data required for the computation of detailed transition arrays (atomic configurations and atomic radial integrals) are calculated by the superconfiguration code SCO ( Super-Configuration Opacity), which provides an accurate description of the plasma screening effects on the wave-functions. Level energies as well as position and strength of spectral lines are computed by an adapted RCG routine of R. D. Cowan. The resulting code provides opacities for hot plasmas and can handle mid- Z elements. The code is also a powerful tool for the interpretation of recent laser and Z-pinch experimental spectra, as well as for validation of statistical methods.

Formula omitted] embedded in a Debye plasma: Electronic and vibrational properties

The effect of plasma screening on the electronic and vibrational properties of the H 2 + molecular ion was analyzed within the Born–Oppenheimer approximation. When a molecule is embedded in a plasma, the plasma screens the electrostatic interactions. This screening is accounted in the Schrödinger equation by replacing the Coulomb potentials with Yukawa potentials that incorporate the Debye length as a screening parameter. Variational expansions in confocal elliptical coordinates were used to calculate energies of the 1 s σ g and 2 p σ u states over a range of Debye lengths and bond distances. When the Debye length is comparable to the equilibrium bond distance, the dissociation energy is reduced while the equilibrium internuclear separation is increased. Expectation values, static dipole polarizabilities and spectroscopic constants were calculated for the 1 s σ g state.

Plasma screening effects on the atomic structure and radiative opacity of dense carbon plasmas based on the DLA model

A study of plasma screening effects using a Debye-Hückel model is presented. The effects on the energy levels, oscillator strengths, ionization potential and photoionization cross sections of different ionization stages of carbon and on the radiative opacity of hot dense carbon plasmas are presented. The treatment of the atomic structure and radiative opacity is based on the detailed fine-structure level accounting formalism. For the basic atomic data, we compare our calculated energy levels and oscillator strengths with other theoretical results available in the literature and good agreement is found. The calculated ionization potential depressions of helium-like carbon, C V, are compared with the experimental and other theoretical results for a variety of plasma condition. Since the Saha–Boltzmann equation, which determines the ion stage populations, is dependent on the energy levels and ionization potentials of all ionization stages of carbon, the plasma screening effects on these quantities were included to obtain the population distribution. The screening effects play an important role on the spectrally resolved opacity by affecting the position and intensity of the absorption peaks and the K-shell ionization thresholds. With the decrease of Debye screening length, the number and intensity of the absorption peaks are reduced. In particular, the continuum opacity near the K-edge will be so sufficiently affected by the screening effects as to be experimentally observed. Finally, the plasma screening effects on the Rosseland and Planck mean opacities are investigated.

Kinetic linear model of the interaction of helical magnetic perturbations with cylindrical plasmas

The linear kinetic model of the interaction of helical rotating magnetic perturbations (resonant and nonresonant) with a tokamak plasma developed in [M. F. Heyn et al., Nucl. Fusion 46, S159 (2006)] is extended by a Galilean invariant collision operator and a different finite Larmor radius expansion scheme of particle current density. The model is applied to study the plasma screening effect on resonant magnetic perturbations and the resulting torques acting on the plasma at various orders of Larmor radius expansion.

Convergent-close-coupling calculations for excitation and ionization processes of electron-hydrogen collisions in Debye plasmas

Electron-hydrogen scattering in weakly coupled hot-dense plasmas has been investigated using the convergent-close-coupling method. The Yukawa-type Debye-H\"uckel potential has been used to describe the plasma screening effects. The target structure, excitation dynamics, and ionization process change dramatically as the screening is increased. Excitation cross sections for the $1s\ensuremath{\rightarrow}2s,2p,3s,3p,3d$ and $2s\ensuremath{\rightarrow}2p,3s,3p,3d$ transitions and total and total ionization cross sections for the scattering from the $1s$ and $2s$ states are presented. Calculations cover the energy range from thresholds to high energies ($250$ eV) for various Debye lengths. We find that as the screening increases, the excitation and total cross sections decrease, while the total ionization cross sections increase.

The photoionization of excited hydrogen atom in plasmas

The photoionization processes of excited hydrogen atoms in plasma environments are investigated using the method of complex coordinate rotation. The standard Debye–Hückel model and modified Debye–Hückel model are adopted to describe the plasma screening effects. The photoionization cross sections of plasma-embedded excited hydrogen atoms varied with different screening lengths are displayed to illustrate the influence of plasma screening. The results of the Debye–Hückel model compared with the modified Debye–Hückel are presented. The shape resonances and Cooper minima due to the plasma screening are observed and discussed.

Electron-impact excitation of Ti21+ in Debye plasmas

The plasma screening effect on electron-impact excitation is studied by using the relativistic distorted-wave description and exemplified by the excitation of Ti21+ ion. The total and differential cross sections for the 1s–2s and 1s–2p excitations are calculated in the energy range from threshold to 5 times threshold energy, and the magnetic sublevel cross sections are also given. Comparison of present calculations with other results, when available, is made.

Atomic Structures and Radiative Properties of He-like Ions in Debye Plasmas

A detailed investigation of plasma screening effects on atomic structure and transition properties are presented for He-like ions embedded in dense plasma environment. Multi-configuration Dirac-Fock calculations were carried out for these ions by considering a Debye-Hückel potential. A large-scale relativistic configuration-interaction method is adopted to calculate transition energies and transition probabilities and to allow for a systematic improvement of the calculations. Comparison of the presently calculated results with others, when available, is made.

Scattering of slow electrons by hydrogen atoms in weakly coupled Debye plasmas

An effective range theory is used to study the elastic scattering of electrons by the ground state of hydrogen atoms in weakly coupled plasma environments for low electron energies. The plasma screening effect is represented by screened Coulomb potentials (SCPs) of Debye type. Highly correlated and variationally determined wavefunctions for H− in plasmas are used to determine the effective range of the ion states. The results for S-wave singlet phase shifts for the incident electron momentum in the range [0, 0.75] au are reported, to the best of our knowledge, for the first time in the literature. For the unscreened case, our reported results are in good agreement with some of the most accurate results available in the literature.

Plasma screening effects on the Ramsauer minima for the polarization electron–atom scattering in weakly coupled plasmas

The plasma screening effects on the Ramsauer phenomena for the polarization electron–atom scattering in weakly coupled plasmas are investigated by using the phase theory. The Fermi pseudopotential and Buckingham potential are employed to obtain the scattering phase shift and scattering cross section as functions of the scattering length, polarizability, collision energy, and Debye radius. It is shown that the Ramsauer energy for the Ramsauer minimum is found to be increased with decreasing Debye radius. It is also found that the plasma screening effect enhances the Ramsauer minimum of the electron–atom scattering cross section below the Ramsauer energy. However, the plasma screening effect suppresses the Ramsauer minimum above the Ramsauer energy.

Photodetachment ofH−in dense quantum plasmas

We have made an investigation to study the plasma screening effect of dense quantum plasmas on the photodetachment cross section of hydrogen negative ion within the framework of dipole approximation. Plasma screening effect has been taken care of by the exponential cosine-screened Coulomb potential (ECSCP). The asymptotic forms of highly correlated wave functions for the initial bound states of H(-) and the plane wave form for the final e(-)-H states are used to evaluate the transition matrix elements. Results for photodetachment cross section in dense quantum plasmas are reported for the plasma screening parameter in the range [0.0,0.6] (in a(0)(-1)). In respect of the photodetachment process of H(-), we have also compared the plasma screening effect of a dense quantum plasma with that of a weakly coupled plasma for which plasma screening effect has been represented by the Debye model. Our results for the unscreened case agree nicely with some of the most accurate results available in the literature.

Elastic scattering of slow electrons by positronium atoms in weakly-coupled plasmas

Low-energy elastic scattering of electrons from the ground state of positronium atoms embedded in weakly-coupled plasmas has been studied within the framework of an effective range theory. Plasma screening effect has been taken care of by screened Coulomb potential. Highly correlated and variationally determined wave functions for Ps− are used to determine the effective range of the ion states. The results for S-wave singlet phase shifts for the incident electron momentum in the range of [0, 0.5] a.u. are reported, to the best of our knowledge, for the first time in the literature.

Application of variational method for three-color three-photon transitions in hydrogen atom implanted in Debye plasmas

Multiphoton processes, where transparency appears, have long fascinated physicists. Plasma screening effects are investigated on three-color three-photon bound-bound transitions in hydrogen atom embedded in Debye plasmas; where photons are linearly and circularly polarized, two left circular and one right circular. All possible combinations of frequency and polarization are considered. Analytical wave functions are used for initial and final states along with the pseudostate wave functions for intermediate states. The analytical wave functions are obtained from the modified wave functions for screening Coulomb potential (Debye model) using Ritz variational method. Here, we have found three-photon transparency for lower values of Debye length. This type of phenomenon occurs due to energy level shifting in the presence of Debye plasma environments. The description of resonance enhancements and three-photon transparency is reported in the present context along with the region of resonance enhancements and three-photon transparency.

Nuclear fusion reaction rates for strongly coupled ionic mixtures

We analyze the effect of plasma screening on nuclear reaction rates in dense matter composed of atomic nuclei of one or two types. We perform semiclassical calculations of the Coulomb barrier penetrability taking into account a radial mean-field potential of plasma ions. The mean-field potential is extracted from the results of extensive Monte Carlo calculations of radial pair distribution functions of ions in binary ionic mixtures. We calculate the reaction rates in a wide range of plasma parameters and approximate these rates by an analytical expression that is expected to be applicable to multicomponent ion mixtures. Also, we analyze Gamow-peak energies of reacting ions in various nuclear burning regimes. For illustration, we study nuclear burning in $^{12}\mathrm{C}$-$^{16}\mathrm{O}$ mixtures.

On the Appearance of a Cooper Minimum in the Photoionization Cross Sections of the Plasma-Embedded Li Atom

The plasma screening effect is found to uncover a Cooper minimum in the photoionization cross sections from the ground state of the Li atom embedded in Debye plasma environment. The variation of the location of this minimum with Debye screening length is discussed and analyzed in terms of the instability of the ground state.

Nonthermal effects on the symmetric resonant charge transfer in Lorentzian plasmas

The nonthermal and plasma screening effects on the symmetric resonant charge transfer process are investigated in Lorentzian plasmas. It is shown that the nonthermal character of the Lorentzian plasma enhances the symmetric resonant charge transfer probability as well as the charge transfer cross section. The plasma screening effects on the charge transfer cross section are found to be quite significant for small values of the spectral index. In addition, the nonthermal effects on the symmetric resonant charge transfer process are found to be more significant in Lorentzian plasmas with higher densities. It is also shown that the nonthermal character of the Lorentzian plasmas enhances the rate coefficient.