Weakly-coupled Plasmas Research Articles

Accurate computation of screened Coulomb potential integrals in numerical Hartree–Fock programs

The frequently-used Zk and Yk functions in the framework of numerical Hartree–Fock method are formulated for atomic systems embedded in weakly-coupled plasmas modeled by Debye–Hückel potential. The Gegenbauer expansion is used to decompose the screened interelectronic Coulomb potential. Two numerical methods, the integration and differentiation ones, are developed to accurately and efficiently calculate the Zk and Yk integrals with each one showing special advantages in the implementation of numerical Hartree–Fock programs. Comparing to the analytical results specialized for Slater-type radial functions, it is generally concluded that the integration method possesses more accuracy and robustness than the differentiation one. Calculations on the two-electron C4+ ion in three different screening models are performed to demonstrate the applicability and stability of present methods in a wider range of screening parameters than existing Hartree–Fock calculations. With benchmark Hartree–Fock energies obtained in this work and accurate non-relativistic energies calculated based on Hylleraas-CI basis functions, it is found that the correlation energies are smallest in the fully screening model.

Industrial plasmas in academia

The present review, written at the occasion of the 2014 EPS Innovation award, will give a short overview of the research and development of industrial plasmas within the last 30 years and will also provide a first glimpse into future developments of this important topic of plasma physics and plasma chemistry. In the present contribution, some of the industrial plasmas studied at the CRPP/EPFL at Lausanne are highlighted and their influence on modern plasma physics and also discharge physics is discussed. One of the most important problems is the treatment of large surfaces, such as that used in solar cells, but also in more daily applications, such as the packaging industry. In this contribution, the advantages and disadvantages of some of the most prominent plasmas such as capacitively- and inductively-coupled plasmas are discussed. Electromagnetic problems due to the related radio frequency and its consequences on the plasma reactor performance, and also dust formation due to chemical reactions in plasma, are highlighted. Arcing and parasitic discharges occurring in plasma reactors can lead to plasma reactor damages. Some specific problems, such as the gas supply of a large area reactor, are discussed in more detail. Other topics of interest have been dc discharges such as those used in plasma spraying where thermal plasmas are applied for advanced material processing. Modern plasma diagnostics make it possible to investigate sparks in electrical discharge machining, which surprisingly show properties of weakly-coupled plasmas. Nanosecond dielectric barrier discharge plasmas have been applied to more speculative topics such as applications in aerodynamics and will surely be important in the future for ignition and combustion.Most of the commonly-used plasma sources have been shown to be limited in their performance. Therefore new, more effective plasma sources are urgently required. With the recent development of novel resonant network antennas for new advanced large area or large volume plasma sources, an important step towards high performance plasmas and new fast processes is made.

Dynamics of ionization with exponential cosine-screened Coulomb potential

Dynamics of ionization in dense quantum plasmas (DQPs) has been studied by the classical trajectory Monte Carlo method. The interactions between charged particles have been described by the exponential cosine-screened Coulomb potential. It is found that ionization cross sections in plasma environments are obviously larger than those in plasma-free environments due to the screening effects. Cross sections for also have been calculated for comparison. For , cross sections increase with the increase of screening effects. However, for , cross sections begin to decrease in strong screening effects at intermediate energies. Furthermore, impact ionization cross sections in weakly coupled plasmas (WCPs) also have been calculated. The interactions have been described by the static screened Coulomb potential. It is found that when screening effects are weak, cross sections in DQPs and WCPs are approximately the same. As screening effects increase, cross sections in DQPs become larger than those in WCPs at high energies. However, when screening effects are strong enough, cross sections in DQPs become smaller than those in WCPs at low and intermediate energies.

The relation between cross section, decay width and imaginary potential of heavy quarkonium in a quark–gluon plasma

Abstract Computations with weakly-coupled plasmas and some lattice results suggest that the heavy quarkonium potential has an imaginary part that is important in order to study dissociation. This imaginary part is due to the scattering with partons in the medium in a process called quasi-free dissociation. At temperatures much below dissociation another process that is known to be important is the gluo-dissociation. The aim of this work is to clarify in a perturbative framework the relation of the different expressions for the quarkonium cross sections that can be found in the literature with the quarkonium thermal width. Finally, with the use of effective field theories we evaluate the quasi-free and gluo-dissociation cross sections in a wide range of temperatures ranging from the binding energy to the dissociation temperature. The work presented here is based on [N. Brambilla, M. A. Escobedo, J. Ghiglieri and A. Vairo, preprint number TUM-EFT 27/11, in preparation].

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.

Positron scattering from hydrogen atom embedded in weakly-coupled plasmas

Elastic scattering of positrons from the hydrogen atoms in weakly-coupled plasmas has been studied using an expression for partial wave scattering amplitude that has been derived within the framework second order distorted wave Born approximation. The interactions among the charged particles in the plasma have been represented by Debye-Huckel potentials. A detailed study has been made on differential and total cross sections in the energy range 20–300 eV. To the best of our knowledge such a study on the differential and total cross sections for elastic positron-hydrogen collisions in a weakly-coupled plasma environment is reported for the first time in the literature.

Classical Electron‐Ion Coulomb Bremsstrahlung in Weakly Coupled Plasmas

In weakly coupled plasmas the classical electron-ion Coulomb bremsstrahlung process are investigated. The cross section for the electron-ion Coulomb bremsstrahlung in weakly-coupled plasmas is obtained by the Debye-Huckel model with the modified hyperbolic-orbit trajectory method. The results show that the plasma-screening effects on the scaled doubly differential bremsstrahlung radiation (SDDBR) cross section increase as the radiation frequency increases. For a given projectile electron energy, the SDDBR cross section obtained by the modified hyperbolic-orbit trajectory method and by the straight-line trajectory method tend to the same value with increasing radiation photon energy. The SDDBR cross sections using the modified hyperbolic-orbit trajectory method are increased by the plasma screening in the small impact parameter domain and decreased for large and intermediate impact parameters with increasing radiation frequency.

A review of the stark widths and shifts of spectral lines from non-hydrogenic atoms and ions in weakly-coupled plasmas and experimental results for XeI and XeII lines

In this paper, we present a review of experimental work on the Stark broadening and shift of non-hydrogenic spectral lines of neutral and ionized atoms in weakly-coupled plasmas. The most important factors determining the quality of the line profile and of the shift measurements are discussed. Comparisons of experimental results show large disagreements between various sets of data. In an attempt to find the cause for this discrepancy, an experiment was conducted to study the broadening and shift of XeI and XeII lines in the plasma of a pulsed xenon flashtube. Shifts and widths of the observed lines were found to be in good agreement with extrapolated low-density data obtained by other authors.

Simulation microfield method for plasma spectroscopy

A computer simulation method has been developed to analyze the effect of the ionic microfield fluctuations on the spectral line shape of hydrogenic emitters. The simple simulation model involves use of independent perturbers interacting with the emitter through a Debye potential and is valid for weakly-coupled plasmas. The dipole autocorrelation function of the emitters are obtained by numerical integration of the Schrödinger equation for the time- evolution operator. For a large domain of plasma parameters, our calculations demonstrate that the ion-broadening mechanism belongs to a regime which is intermediate between the limiting impact and quasistatic approximations. The effect of ion-microfield fluctuations on the redistribution function has also been analyzed. This function enters into radiative transfer calculations and is often approximated by complete redistribution, which assumes that the emission profile is the same as the fluorescence profile. For highly charged emitters, this approximation is no longer valid and we have partial redistribution conditions. The occurrence of partial redistribution depends critically upon competition of the rates of spontaneous emission, Stark shifts, electron broadening, and the rate associated with ion-microfield fluctuations. By using the simulation model for an estimate of the latter rate, it is possible to analyze the role of ion-microfield fluctuations in partial redistributions.

Weak interaction mediated by Regge particles: C. Iso, Physics Department, Brandeis University, Waltham, Massachusetts

A computer simulation method has been developed to analyze the effect of the ionic microfield fluctuations on the spectral line shape of hydrogenic emitters. The simple simulation model involves use of independent perturbers interacting with the emitter through a Debye potential and is valid for weakly-coupled plasmas. The dipole autocorrelation function of the emitters are obtained by numerical integration of the Schrödinger equation for the time- evolution operator. For a large domain of plasma parameters, our calculations demonstrate that the ion-broadening mechanism belongs to a regime which is intermediate between the limiting impact and quasistatic approximations. The effect of ion-microfield fluctuations on the redistribution function has also been analyzed. This function enters into radiative transfer calculations and is often approximated by complete redistribution, which assumes that the emission profile is the same as the fluorescence profile. For highly charged emitters, this approximation is no longer valid and we have partial redistribution conditions. The occurrence of partial redistribution depends critically upon competition of the rates of spontaneous emission, Stark shifts, electron broadening, and the rate associated with ion-microfield fluctuations. By using the simulation model for an estimate of the latter rate, it is possible to analyze the role of ion-microfield fluctuations in partial redistributions.