Ion Dynamics Effects Research Articles

On Considering the Effects of Ion Dynamics In Modeling the Spectra of Multicharged Ions

On Considering the Effects of Ion Dynamics In Modeling the Spectra of Multicharged Ions

Review of Rydberg Spectral Line Formation in Plasmas

The present review is dedicated to the problem of an array of transitions between highly-excited atomic levels. Hydrogen atoms and hydrogen-like ions in plasmas are considered here. The presented methods focus on calculation of spectral line shapes. Fast and simple methods of universal ionic profile calculation for the Hnα (Δn=1) and Hnβ (Δn=2) spectral lines are demonstrated. The universal dipole matrix elements formulas for the Hnα and Hnβ transitions are presented. A fast method for spectral line shape calculations in the presence of an external magnetic field using the formulas for universal dipole matrix elements is proposed. This approach accounts for the Doppler and Stark–Zeeman broadening mechanisms. Ion dynamics effects are treated via the frequency fluctuation model. The accuracy of the presented model is discussed. A comparison of this approach with experimental data and the results of molecular dynamics simulation is demonstrated. The kinetics equation for the populations of highly-excited ionic states is solved in the parabolic representation. The population source associated with dielectronic recombination is considered.

Study of Stark broadening of krypton helium-β lines and estimation of electron density and temperature in NIF compressed capsules

The National Ignition Facility (NIF) diagnostic instrument manipulator (DIM) - based high resolution (dHIRES) x-ray spectrometer was used to measure the time evolution of the electron density (n e) and temperature (T e) in the hot spot of four NIF compressed capsules with 25 ps time resolution during the ‘stagnation’ phase. The electron density was inferred by comparing the measured Stark broadening of the krypton (Kr) Heβ spectral complex with theoretical calculations that include ion dynamic effects, and the electron temperature was inferred by comparing the measured ratio of the intensity of a dielectronically excited Li-like Kr line to the intensity of the Kr Heβ resonance line with calculations using the spectroscopic collisional radiative atomic model (SCRAM) and CRETIN collisional-radiative models. The inferred, time averaged n e values mainly agree with n e values from neutron diagnostics within uncertainties, but the neutron time-of-flight values of T ion are consistently higher than dHIRES T e values by 200–700 eV. The dHIRES measurements and measurement techniques, method of uncertainty analysis, and discussion of comparisons with measurements from neutron diagnostics are presented.

Calculating the simultaneous effect of ion dynamics and oscillating electric fields on Stark profiles

We calculate hydrogen line shapes resulting from the simultaneous Stark effect of the plasma microfield and an oscillating electric field. Like laboratory plasmas, many kinds of space plasmas are affected by oscillating electric fields with a magnitude similar to that of the microfield. Here we focus on conditions where we expect that the effect of ion dynamics and oscillating electric are both significant. The combined effect of their dynamics on the quantum emitter is retained by a computer simulation coupled to a numerical integration of the Schrödinger equation. Our calculations are applied for conditions and transitions where significant changes in the line shape allow for a diagnostic of the plasma and oscillating field.

Stark–Zeeman line-shape model for multi-electron radiators in hot dense plasmas subjected to large magnetic fields

We present a Stark–Zeeman spectral line-shape model and the associated numerical code, PPPB, designed to provide fast and accurate line shapes for arbitrary atomic systems for a large range of plasma conditions. PPPB is based on the coupling of the PPP code—a Stark-broadened spectral line-shape code developed for multi-electron ion spectroscopy in hot dense plasmas—and the MASCB code developed recently to generate B-field-dependent atomic physics. The latter provides energy levels, statistical weights, and reduced matrix elements of multi-electron radiators by diagonalizing the atomic Hamiltonian that includes the well know B-dependent term. These are then used as inputs to PPP working in the standard line-broadening approach, i.e., using the quasi-static ion and impact electron approximations. The effects of ion dynamics are introduced by means of the frequency fluctuation model, and the physical model of electron broadening is based on the semi-classical impact approximation including the effects of a strong collision term, interference, and cyclotron motion. Finally, to account for polarization effects, the output profiles are calculated for a given angle of observation with respect to the direction of the magnetic field. The potential of this model is presented through Stark–Zeeman spectral line-shape calculations performed for various experimental conditions.

New results from exact solution of the dispersion relation for nonextensive electron-ion plasma in the framework of collisionless kinetic theory

The electrostatic (ES) oscillations, spatio-temporal Landau damping and growth in an electron-ion (EI) plasma is investigated by taking into account the effect of ion (electron) dynamics on the electron (ion) oscillations in the context of nonextensive particle distributions. The dispersion relation is exactly solved without employing approximations on the phase velocity, in contrast to the procedure developed by Landau where some approximations are applied on the phase velocity. This enables us to obtain some results which are not shown previously duo to approximate numerical and analytical studies. It is remarked that four kinds of ES modes; a high frequency mode (well-known Langmuir wave), two low and high intermediate frequency (LIF and HIF) modes and a very low frequency mode (well-known IA wave) may propagate in desired plasma system. In particular, these ES modes represent very different behavior when moving to left and right directions, from the point of view of spatio-temporal damping and growth. In addition, it is shown that exact solution of the dispersion relation gives rise to some interesting phenomena; such as the existence of non-acoustic electron and ion modes, the frequency and wavelength cutoffs and the existence of backward waves.

ZEST: A Fast Code for Simulating Zeeman-Stark Line-Shape Functions

We present the ZEST code, dedicated to the calculation of line shapes broadened by Zeeman and Stark effects. As concerns the Stark effect, the model is based on the Standard Lineshape Theory in which ions are treated in the quasi-static approximation, whereas the effects of electrons are represented by weak collisions in the framework of a binary collision relaxation theory. A static magnetic field may be taken into account in the radiator Hamiltonian in the dipole approximation, which leads to additional Zeeman splitting patterns. Ion dynamics effects are implemented using the fast Frequency-Fluctuation Model. For fast calculations, the static ion microfield distribution in the plasma is evaluated using analytic fits of Monte-Carlo simulations, which depend only on the ion-ion coupling parameter and the electron-ion screening factor.

On the nature of ion dynamics

A study of physical mechanisms responsible for the ion dynamics effects is presented. It is shown that the effect is primarily caused by the fluctuations of ion microfield direction, which can naturally be represented as rotation of the electric-microfield vector. Various aspects of this problem are discussed.

Line shape models for magnetized hydrogen plasmas

We report on Stark-Zeeman line shape models for the diagnostic of magnetic fusion plasmas. Computer simulations, which serve as a reference for an evaluation of the ion dynamics effects, are usually CPU time consuming, so that they cannot be used in a real-time diagnostic. In this framework, a database that allows a fast evaluation of Stark-Zeeman line shapes is currently under preparation. We present preliminary results. Analytical models based on ion collision operators and suitable for strong (near-impact) ion dynamics regimes are also discussed.

Effects of parallel ion motion on electromagnetic toroidal ion temperature gradient modes in a fluid model

Effects of ion dynamics along the background magnetic field have been added to an advanced fluid model which has been developed, tested, and successfully used in transport code applications during the last decades. Introducing electrostatic (ϕ) and electromagnetic (ψ) potentials, a system of two coupled second order differential equations in these potentials is derived. The mode solution is interpreted as a coupling between an Ion Temperature Gradient (ITG) mode and an ion motion driven acoustic wave. The mode may be stabilized by electromagnetic effects and by minimizing the ITG parameter ηi(=LnLTi). Interestingly, the addition of kinetic Landau resonance effects may enhance the ηi stabilization.

Investigation of thermodynamic equilibrium in laser-induced aluminum plasma using the Hα line profiles and Thomson scattering spectra

We have studied isothermal equilibrium in the laser-induced plasma from aluminum pellets in argon at pressure of 200 mbar by using a method which combines the standard laser Thomson scattering and analysis of the Hα, Stark-broadened, line profiles. Plasma was created using 4.5 ns, 4 mJ pulses from a Nd:YAG laser at 1064 nm. While electron density and temperature were determined from the electron feature of Thomson scattering spectra, the heavy particle temperature was obtained from the Hα full profile applying computer simulation including ion-dynamical effects. We have found strong imbalance between these two temperatures during entire plasma evolution which indicates its non-isothermal character. At the same time, according to the McWhirter criterion, the electron density was high enough to establish plasma in local thermodynamic equilibrium.

Spectral-Kinetic Coupling and Effect of Microfield Rotation on Stark Broadening in Plasmas

The study deals with two conceptual problems in the theory of Stark broadening by plasmas. One problem is the assumption of the density matrix diagonality in the calculation of spectral line profiles. This assumption is closely related to the definition of zero wave functions basis within which the density matrix is assumed to be diagonal, and obviously violated under the basis change. A consistent use of density matrix in the theoretical scheme inevitably leads to interdependence of atomic kinetics, describing the population of atomic states with the Stark profiles of spectral lines, i.e., to spectral-kinetic coupling. The other problem is connected with the study of the influence of microfield fluctuations on Stark profiles. Here the main results of the perturbative approach to ion dynamics, called the theory of thermal corrections (TTC), are presented, within which the main contribution to effects of ion dynamics is due to microfield fluctuations caused by rotations. In the present study the qualitative behavior of the Stark profiles in the line center within predictions of TTC is confirmed, using non-perturbative computer simulations.

Ion Dynamics Effect on Stark-Broadened Line Shapes: A Cross-Comparison of Various Models

Modeling the Stark broadening of spectral lines in plasmas is a complex problem. The problem has a long history, since it plays a crucial role in the interpretation of the observed spectral lines in laboratories and astrophysical plasmas. One difficulty is the characterization of the emitter’s environment. Although several models have been proposed over the years, there have been no systematic studies of the results, until now. Here, calculations from stochastic models and numerical simulations are compared for the Atoms 2014, 2 300 Lyman-α and -β lines in neutral hydrogen. Also discussed are results from the Helium-α and -β lines of Ar XVII.

Thermal ion effects on kinetic beta-induced Alfvén eigenmodes excited by energetic ions

Kinetic beta-induced Alfven eigenmodes (KBAEs) driven by energetic ions are numerically investigated using revised AWECS code. The thermal ion density and temperature gradients are taken into account. It is found that the growth rate of the KBAEs increases with the thermal ion pressure gradient, and the contributions from the density gradient and temperature gradient of the thermal ions to the enhancement of the instability are comparable. The damping effect of thermal ion dynamics on the modes is also observed.

Effect of ion dynamics on the evolution of electron phase-space holes

The evolution of two-dimensional (2D) electron phase-space holes (electron holes) has been previously investigated with electrostatic Particle-in-Cell (PIC) simulations, which neglect ion dynamics. The electron holes are found to be unstable to the transverse instability, and their evolution is determined by the combined action between the transverse instability and the stabilization by the background magnetic field. In this paper, the effect of ion dynamics on the evolution of an electron hole is studied. In weakly magnetized plasma (<em>Ω</em>_e < <em>ω</em>_pe, where <em>Ω</em>_e and <em>ω</em>_pe are electron gyrofrequency and plasma frequency, respectively), the electron hole is still unstable to the transverse instability. However, it evolves a little faster and is destroyed in a shorter time when ion dynamics is considered. In strongly magnetized plasma (<em>Ω</em>_e > <em>ω</em>_pe), the electron hole is broken due to the lower hybrid waves, and its evolution is much faster.

Stark broadening tables for the helium I 492.2 line

Context. We studied the Stark broadening of the He I 492.2 nm line, which is sometimes used for plasma diagnostics or to obtain information on different stellar parameters. Aims. The final aim of this study is to obtain tables of lines shapes as well as the relationships between different line parameters and the plasma electron density, temperature, or composition. The tables of profiles and the mathematical expressions obtained will be used in plasma diagnostics. Methods. We performed computer simulations and used a physical model that considers a weakly coupled plasma. Our computer simulations naturally take into account ion dynamical effects, which has permitted us to study the influence on the line shapes of imbalances in the plasma caused by different electron and gas temperatures. Results. Our computer simulations considered electron densities between 10 19 and 10 24 m −3 , electron temperatures between 5000 and 40 000 K, and plasmas of different compositions. The dependences obtained in the simulations for the line width, the ratio of intensities between the allowed and the forbidden components, or the distances between those components’ peaks on the plasma conditions are shown and compared with experimental data. Numerical expressions for the line width and for the peak distances against the electron density were obtained from the simulation results and can be applied to obtain the electron density from experimental results. Full line profile tables are also supplied for use in plasma diagnostics.

Time-dependent density-functional-theory calculation of high-order-harmonic generation of H2

The observation of the isotope effect in the high-order-harmonic generation (HHG) of H${}_{2}$ presents a challenge for time-dependent density-functional-theory (TDDFT) methods, since this effect is related to the dynamics of the ion created in the tunneling ionization step of HHG and it depends on the harmonic order. As an initial step toward describing this effect within current computational capacity, we benchmark a method in which the nuclear and electronic degrees of freedom are separated and both treated quantum mechanically. For the electrons two TDDFT formalisms are adopted. Although the ion-dynamics effect is not described in our method, it reproduces the measured D${}_{2}$-to-H${}_{2}$ HHG ratios up to the 25th harmonic when the 35th is the classical cutoff. Beyond the 25th harmonic, however, our results show substantial deviation and are sensitive to the laser intensity. A higher intensity reproduces the experimental results. Analysis reveals an $R$-dependent phase factor as the cause of the isotope effect in our calculation. We isolate this phase factor and propose a strong-field-approximation-phase model, which reproduces experimental data, including those for which the ion-dynamics model has to be further modified. We show that the model that we propose is intrinsically related to the ion-dynamics model. Our model provides a correction to the TDDFT approach when the ion-dynamics effect becomes significant. It also indicates that the isotope effect is not only a probe for the ion created by the external field but is ultimately a more useful probe for the ground-state nuclear wave function. For all molecules whose vertical ionization potential strongly depends on the nuclear geometry, HHG may serve as a sensitive ultrafast probe of nuclear dynamics.

Hydrogen Stark Broadened Brackett lines

Stark-broadened lines of the hydrogen Brackett series are computed for the conditions of stellar atmospheres and circumstellar envelopes. The computation is performed within the Model Microfield Method, which includes the ion dynamic effects and makes the bridge between the impact limit at low density and the static limit at high density and in the line wings. The computation gives the area normalized line shape, from the line core up to the static line wings.

Time Ordering Effects on Hydrogen Zeeman-Stark Line Profiles in Low-Density Magnetized Plasmas

Stark broadening of hydrogen lines is investigated in low-density magnetized plasmas, at typical conditions of magnetic fusion experiments. The role of time ordering is assessed numerically, by using a simulation code accounting for the evolution of the microscopic electric field generated by the charged particles moving at the vicinity of the atom. The Zeeman effect due to the magnetic field is also retained. Lyman lines with a low principal quantum number n are first investigated, for an application to opacity calculations; next Balmer lines with successively low and high principal quantum numbers are considered for diagnostic purposes. It is shown that neglecting time ordering results in a dramatic underestimation of the Stark effect on the low-n lines. Another conclusion is that time ordering becomes negligible only when ion dynamics effects vanish, as shown in the case of high-n lines.

Stark broadening tables for the helium I 447.1 line

Context. Stark broadening of the 447.1 line of neutral helium in a weakly coupled plasma has been studied. This spectral line has a very close forbidden component. This means it is very sensitive to the plasma electron density, which is similar to hydrogen lines, for which the Stark effect is linear. Aims. The aim of this work is to supply information to be used in the spectroscopic diagnostics of plasmas. Methods. We used computer simulations in the frame of a physical model for a plasma with weak coupling between charges. The calculation includes the so-called “ion dynamics effects” in a natural way. The electron density, the ionic and electronic temperatures, and the perturber mass were the parameters in the calculations. Results. Simulation results relate the line width, shift, shape, and especially the ratio of intensities between the allowed and forbidden components, with the plasma parameters. These results are supplied as tables of line shapes.