Dense Plasma Environment Research Articles

Structural properties of hydrogen-like ions ([formula omitted] 1–18) under quantum and classical plasma environment

A simple pure-exponential type wavefunction in the Ritz variational framework has been proposed to estimate precise eigenenergies and radial distributions of nl [n= 1–8; l= 0–7] states of 2L [L= 0–7] symmetry of hydrogen iso-electronic ions (Z=1–18) under classical weakly coupled plasma and dense quantum plasma environment. Critical screening parameters, beyond which the ions cease to be in a bound state, have also been estimated for both types of plasma background.

Demonstration of X-ray Thomson scattering as diagnostics for miscibility in warm dense matter

The gas and ice giants in our solar system can be seen as a natural laboratory for the physics of highly compressed matter at temperatures up to thousands of kelvins. In turn, our understanding of their structure and evolution depends critically on our ability to model such matter. One key aspect is the miscibility of the elements in their interiors. Here, we demonstrate the feasibility of X-ray Thomson scattering to quantify the degree of species separation in a 1:1 carbon–hydrogen mixture at a pressure of ~150 GPa and a temperature of ~5000 K. Our measurements provide absolute values of the structure factor that encodes the microscopic arrangement of the particles. From these data, we find a lower limit of 2{4}_{-7}^{+6}% of the carbon atoms forming isolated carbon clusters. In principle, this procedure can be employed for investigating the miscibility behaviour of any binary mixture at the high-pressure environment of planetary interiors, in particular, for non-crystalline samples where it is difficult to obtain conclusive results from X-ray diffraction. Moreover, this method will enable unprecedented measurements of mixing/demixing kinetics in dense plasma environments, e.g., induced by chemistry or hydrodynamic instabilities.

Plasma screening effects on the atomic structure of He-like ions embedded in strongly coupled plasma

The influence of plasma screening on the transition energies and radiative properties of He-like ions embedded in dense plasma environment has been analyzed. For this purpose, the multiconfiguration Dirac-Fock method and Flexible Atomic Code incorporating the analytical plasma screening potential of Li et al. (2019) [39] and uniform electron gas model potential have been implemented. Our calculated line shifts of 1s2S01→1s3pP1o1 He-β transition of Cl15+ are in excellent agreement with the recent measurements of Beiersdorfer et al. (2019) [11]. The plasma shielding effects on 1s2S01→1snpP1o3(n=2,3) and 1s2S01→1snpP1o1(n=2,3) transitions of Ar16+, Ti20+ and Fe24+ ions have also been studied. It is found that transition energies for these transitions are red shifted with respect to free electron densities. The present results should be advantageous in the modeling and diagnostics of laboratory and astrophysical plasmas.

Effect of Dense Plasma Environment on the Spectroscopic Properties of He-like Ca18+ Ion

Plasma shielding effects on the energy levels and radiative properties of He-like Ca\(^{18+}\) ion under dense plasma conditions have been studied. For this purpose, the multiconfiguration Dirac-Fock method has been implemented by incorporating the ion sphere model potential as a modified interaction potential between the electron and the nucleus. To check the authenticity of our results, independent calculations have been performed using the modified relativistic configuration interaction method. It is observed that the transition energies associated with \(\Delta n = 0\) transitions are blue shifted, whereas red shifted for \(\Delta n \neq 0\) transitions. The variation in transition probabilities and weighted oscillator strengths with plasma densities has also been analyzed. The present results should be beneficial in the plasma modeling and fusion plasma research applications.

Study of energies and radiative properties of He-like ions within a dense plasma

On the basis of the tensor expression for the Breit-Pauli Hamiltonian and the irreducible tensor theory for many-electron atoms, we have proposed a general analytical method for calculating atomic structures of highly charged ions under a dense plasma environment. In this method, the standard ion-sphere (IS) potential is used to represent the interaction between the charge particles. The Racah wave functions are obtained as the linear combinations of the multi-Slater wave functions. The angular interactions and spin sums are worked out using an irreducible theory of complex systems. Analytical formulas for the calculation of relativistic corrections, such as the mass correction, the one-body Darwin correction, the two-body Darwin correction, and the spin-spin contact interaction, are derived. Energy levels and radiative properties of He-like Al11+ and Ni26+ ions are considered for illustrative purposes. Systematic trends with respect to both the nuclear charge Z and the electron density Ne are observed for all calculated quantities. Self-consistent calculations of dense plasma effects on the atomic structure, based on the same IS potential, are also presented using fully relativistic multiconfiguration Dirac-Fock (MCDF) wave functions in the active space approximation with the inclusion of a finite nuclear size, the Breit interaction, self-energy, and vacuum polarization for comparison purposes. Comparison and analysis are made between our two sets of results and the available results in the literature. The effects of relativistic correlations are investigated in detail for the first time and are found to play an important role in the stability of these systems. The results of this study should be of great help in the modeling and diagnostics of astrophysical and laboratory plasmas.

Quantum Drift Wave Analysis for Low-Temperature Dense Non-uniform Electron–Ion Plasma Environment

Using a quantum magneto-hydrodynamic mathematical model, a set of governing equations is presented for electrostatic drift-type modes in an extremely dense plasma environment. In this regard, new local dispersion relations for coupled quantum drift modes in a magnetized plasma for two cases, (a) stationary ions and (b) mobile ions, are derived, considering the effects of exchange and correlation for electrons. The dispersion relations are then analyzed both analytically and numerically. It is found that the inclusion of exchange and correlation effects, which is the quantum effect of electrons, modifies the frequency of the quantum electron drift-acoustic mode. It is investigated that the newly found quantum drift mode exists only under low-temperature conditions. Furthermore, the results are estimated to be useful in the interpretation of electrostatic fluctuations in a dense magnetized plasma.

Impact of electron exchange-correlation on drift acoustic solitary waves

The impact of electron exchange-correlation term on the linear and nonlinear quantum ion (QIA) acoustic drift waves in a highly degenerate plasma is investigated. An analytical approach is employed to derive the differential equation which is later on turned into Sagdeev energy integral equation that can be utilized to get drift solitons under existence conditions. It is noted that phase speed/frequency of the linear drift quantum ion acoustic (QIA) waves increases with electron exchange-correlation effect, but the amplitude of the corresponding solitons decreases with inclusion of these effects. Present study is carried out with reference to highly dense plasma environments like fast ignition inertial confinement fusion and white dwarfs etc.

High-pressure chemistry of hydrocarbons relevant to planetary interiors and inertial confinement fusion

Diamond formation in polystyrene (C8H8)n, which is laser-compressed and heated to conditions around 150 GPa and 5000 K, has recently been demonstrated in the laboratory [Kraus et al., Nat. Astron. 1, 606–611 (2017)]. Here, we show an extended analysis and comparison to first-principles simulations of the acquired data and their implications for planetary physics and inertial confinement fusion. Moreover, we discuss the advanced diagnostic capabilities of adding high-quality small angle X-ray scattering and spectrally resolved X-ray scattering to the platform, which shows great prospects of precisely studying the kinetics of chemical reactions in dense plasma environments at pressures exceeding 100 GPa.

Transition energies, transition probabilities and weighted oscillator strengths of He-like Al in hot and dense plasmas

We present a detailed investigation of the transition properties for He-like Al embedded in hot and dense plasma environments. The correlation effect between the bound electrons is treated with the configuration interaction method. Plasma screening on the nucleus is described using the self-consistent-field ion sphere model. Transition energies, transition probabilities and weighted oscillator strengths decrease quickly with the increase of free electron densities, but increase slightly with the electron temperature, and approach those of the uniform electron density ion sphere model at a given average free electron density. The results reported in this work are useful for plasma diagnostics.

Effects of weakly coupled and dense quantum plasmas environments on charge exchange and ionization processes in Na+ + Rb(5s) atom collisions

The effects of weakly coupled or classical and dense quantum plasmas environment on charge exchange and ionization processes in Na+ + Rb(5s) atom collision at keV energy range have been investigated using classical trajectory Monte Carlo (CTMC) method. The interaction of three charged particles are described by the Debye-Huckel screen potential for weakly coupled plasma, whereas exponential cosine-screened Coulomb potential have been used for dense quantum plasma environment and the effects of both conditions on the cross sections are compared. It is found that screening effects on cross sections in high Debye length condition is quite small in both plasma environments. However, enhanced screening effects on cross sections are observed in dense quantum plasmas for low Debye length condition, which becomes more effective while decreasing the Debye length. Also, we have found that our calculated results for plasma-free case are comparable with the available theoretical results. These results are analyzed in light of available theoretical data with the choice of model potentials.

Two-electron atoms under spatially compressed Debye plasma

Rayleigh–Ritz variational method has been employed to estimate precise energy-eigenvalues of spherically compressed two-electron atoms (Z=1−10) embedded in Debye plasma with a view to modelling atom under dense plasma environment. The trial wave function is expanded in terms of explicitly correlated Hylleraas-type basis set satisfying Dirichlet's boundary condition. The combined effect of decrease in the size of spatial confinement domain and increase in Debye screening parameter pushes the system towards gradual destabilization and subsequent ionization or complete fragmentation of the system. Present results are in reasonable agreement with other results existing in literature. Within finite domain, the thermodynamic pressure experienced by the ions due to the plasma electrons is also estimated.

Measurements of continuum lowering in solid-density plasmas created from elements and compounds.

The effect of a dense plasma environment on the energy levels of an embedded ion is usually described in terms of the lowering of its continuum level. For strongly coupled plasmas, the phenomenon is intimately related to the equation of state; hence, an accurate treatment is crucial for most astrophysical and inertial-fusion applications, where the case of plasma mixtures is of particular interest. Here we present an experiment showing that the standard density-dependent analytical models are inadequate to describe solid-density plasmas at the temperatures studied, where the reduction of the binding energies for a given species is unaffected by the different plasma environment (ion density) in either the element or compounds of that species, and can be accurately estimated by calculations only involving the energy levels of an isolated neutral atom. The results have implications for the standard approaches to the equation of state calculations.

Atomic and optical properties of warm dense copper.

The emission of x rays from warm dense matter is of great interest for both spectroscopic diagnostics and development of intense x-ray sources. We report the results from the collisional-radiative steady-state (CRSS) modeling of atomic and optical properties of copper plasmas at near-solid and solid-state density for a range of temperatures. The CRSS model is validated against the available data on the average charge state and shifts of energy levels in aluminum and the opacity and emissivity spectra of carbon and aluminum plasmas. The average charge states, number density of ion species, and free electrons as a function of temperature are investigated for the solid-density copper plasma. Due to the dense plasma environment the four outer electrons are found to be unbounded even in the low-temperature limit ∼1eV. As the temperature changes from 1 to 100 eV, the predominant species vary from fivefold- to twelvefold-ionized copper ions. The opacity and emissivity spectra of dense copper plasmas are studied using the local thermodynamic equilibrium (LTE) and non-LTE approaches. It is found that the non-LTE effects are important in the spectral region of soft x rays emitted from the K shell. The emissivity in spectral lines is completely suppressed, indicating the importance of the energy-dissipating radiative processes in this soft x-ray region. Line broadening and redshifts of the K- and L-shell spectral lines toward higher wavelengths are observed with the increase of plasma density. These results have important implications for understanding the radiative properties of warm dense copper and can be useful for future experimental studies.

Redshift of the Lyman-αemission line of H-like ions in a plasma environment

We present a critical assessment of the applicability of the Debye-H\uckel (DH) approximation to the redshift of the Lyman-$\ensuremath{\alpha}$ emission line of the H-like ions under a dense plasma environment. By carefully considering the $2p\ensuremath{\rightarrow}1s$ transition spatially and temporally, our investigation suggests that the DH approximation may be applied to a limited number of H-like ions, such as the ones with $Z$ between 5 and 18 or with $Z$ greater than 50. Our numerical calculation, in fact, leads to quantitative agreement with the observed redshift of the well-isolated Lyman-$\ensuremath{\alpha}$ line at plasma density of the order of $1\ifmmode\times\else\texttimes\fi{}{10}^{22}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ or higher with an electron temperature of several hundred eV of H-like ${\mathrm{Al}}^{12+}$. Our study also yields simulated data consistent with those from more elaborate quantum mechanical approaches.

Relativistic Gaussian laser beam self-focusing in collisional quantum plasmas

AbstractPropagation of Gaussian X-ray laser beam is presented in collisional quantum plasma and the beam width oscillation is studied along the propagation direction. It is noticed that due to energy absorption in collisional plasma, the laser energy drops to an amount less than the critical value of the self-focusing effect and consequently, the laser beam defocuses. It is found that the oscillation amplitude of the laser spot size enhances while passing through collisional plasma. For the greater values of collision frequency, the beam width oscillates with higher amplitude and defocuses in a shallower plasma depth. Also, it is realized that in a dense plasma environment, the laser self-focusing occurs earlier with the higher oscillation amplitude, smaller laser spot size and more oscillations.

Nonrelativistic structure calculations of two-electron ions in a strongly coupled plasma environment

In this work, the controversy between the interpretations of recent measurements on dense aluminum plasma created with Linac coherent light sources (LCLS) X-ray free electron laser (FEL) and Orion laser has been addressed. In both kind of experiments, helium-like and hydrogen-like spectral lines are used for plasma diagnostics . However, there exist no precise theoretical calculations for He-like ions within dense plasma environment. The strong need for an accurate theoretical estimates for spectral properties of He-like ions in strongly coupled plasma environment leads us to perform ab initio calculations in the framework of Rayleigh-Ritz variation principle in Hylleraas coordinates where ion-sphere potential is used. An approach to resolve the long-drawn problem of numerical instability for evaluating two-electron integrals with extended basis inside a finite domain is presented here. The present values of electron densities corresponding to disappearance of different spectral lines obtained within the framework of ion-sphere potential show excellent agreement with Orion laser experiments in Al plasma and with recent theories. Moreover, this method is extended to predict the critical plasma densities at which the spectral lines of H-like and He-like carbon and argon ions disappear. Incidental degeneracy and level-crossing phenomena are being reported for the first time for two-electron ions embedded in strongly coupled plasma. Thermodynamic pressure experienced by the ions in their respective ground states inside the ion-spheres are also reported.

Plasma Diagnostics Using K‐Line Emission Profiles of Silicon

AbstractModifications of K‐line profiles due to a warm dense plasma environment are a suitable tool for plasma diagnostics. We focus on Si Kα emissions due to an electron transfer from 2P to 1S shell. Besides 2P fine structure effects we also consider the influence of excited and higher ionized emitters. Generally spoken, a plasma of medium temperature and high density (warm dense matter) is created from bulk Si the greater part of atoms is ionized. The high energy of Kα x‐rays is necessary to penetrate and investigate the Si sample. The plasma effect influences the many‐particle system resulting in an energy shift due to electron‐ion and electron‐electron interaction. In our work we focus on pure Si using LS coupling. Non‐perturbative wave functions are calculated as well as ionization energies, binding energies and relevant emission energies using the chemical ab initio code Gaussian 03. The plasma effect is considered within a perturbative approach to the Hamiltonian. Using Roothaan‐Hartree‐Fock wave functions we calculate the screening effect within an ion‐sphere model. The different excitation and ionization probabilities of the electronic L‐shell and M‐shell lead to a charge state distribution. Using this distribution and a Lorentz profile convolution with a Gaussian instrument function we calculate spectral line profiles depending on the plasma parameters. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Possibility of giant enhancement of low-frequency non-resonant Rayleigh scattering by atomic systems within dense plasmas

In this paper, we demonstrate the possibility of electron density-induced giant growth of non-resonant Rayleigh scattering of electromagnetic radiation (in the low-frequency limit) by atomic systems within dense plasmas. Non-relativistic quantum mechanical calculation is performed under electric dipole approximation, for elastic scattering of radiation by the ground states 1s of plasma-embedded hydrogen-like atomic ions treated within the framework of the ion-sphere model. The results indicate giant enhancement of the non-resonant (photon frequency ω being much smaller than the lowest resonance frequency ω1s−2p) Rayleigh cross-section by an order of magnitude, at (atomic system-specific) high enough plasma electron densities under present consideration. The Z−8-scaling of the non-resonant Rayleigh cross-section in free and isolated H-isoelectronic sequence of ions is shown to be broken in dense plasma environments.

Dense Medium Plasma Environments Used for the Synthesis of Nanoparticle Systems and Structural Modification of Liquid Media

Dense Medium Plasma Environments Used for the Synthesis of Nanoparticle Systems and Structural Modification of Liquid Media

Ion treatment by low pressure arc plasma immersion surface engineering processes

The gaseous plasma of low pressure arc discharges has been used extensively for various surface treatment applications including heat treatment, ion nitriding, ion implantation, PECVD and duplex processes. Highly ionized low pressure arc plasmas with electron density up to ~1018m−3 can be generated by a shielded vacuum arc cathode, a hollow cathode or by a thermionic cathode. In this paper, plasma properties are characterized by electrostatic probes and optical emission spectroscopy. A range of different species can be produced in low pressure arc plasma immersion processes via decomposition of precursor molecules by electron collisions. Surface treatment of different steels and metal alloys in such a dense plasma environment can substantially affect the surface profile. The ion nitriding of different types of steel in a low pressure arc plasma environment is investigated. The rate of ion nitriding as a function of plasma parameters, such as ion current density, pressure and gas composition is established for several types of steel and ranging from 0.1 to 1μm/min. Ionitrided layers can be produced in arc plasma immersion processes at substrate biases as low as −30V and substrate temperatures as low as 200°C, depending on the type of steel. Alternatively, low energy ion implantation of nitrogen can be produced at bias voltages exceeding −500V and substrate temperatures less than 100°C. The distribution of plasma density and the uniformity of ion nitriding layers in industrial scale vacuum processing chambers are investigated. Duplex coatings were also produced by ion nitriding in an arc plasma immersion environment followed by deposition of TiN coatings. The ion nitriding and duplex coating layers are characterized by structure, thickness, microhardness depth profile, surface roughness and coating adhesion. Surface treatment in conventional glow discharge compared to low pressure arc plasma immersion processes is presented. The results of processing complex shape components are discussed.