Ion Dynamics Effects Research Articles

Ion Dynamics and Water Percolation Effects in DNA Polymorphism

The dynamics of ions and water at the surface of DNA are studied by computer simulations in a wide range of hydrations involving the zone of low-hydration polymorphism in DNA. The long-range mobility of ions exhibits a stepwise increase at three distinct hydration levels. The first of them is close to the midpoint of the water percolation transition as well as the midpoint of the transition between A- and B-DNA forms. It coincides with the onset of the dissociation of ion pairs on the DNA surface probably caused by the increase in the water dielectric permittivity due to the appearance of the spanning hydrogen-bonding network. The other two steps are attributed to the formation of percolating water layers on the surface of DNA accompanied by the progressive escape of ions from the DNA surface. The results agree with earlier experimental data and further corroborate the suggested universal mechanism of the low hydration polymorphism in DNA including intraduplex electrostatic condensation close to the water percolation threshold.

Dynamics of Mobile Ions: Fitting of CKN Frequency Response Data without an Excess Wing

Ion dynamics effects and the resulting dispersed frequency response of conducting materials have often been explained in the past by a combination of the Moynihan original modulus formalism (OMF) and the Ngai coupling model (NCM). These incorrect approaches and their inappropriate conclusions are replaced by alternate, Kohlrausch-related physically reasonable conductive-system fitting and interpretation models that are then used for the analysis of both limited-range and wide-range data for the supercooled liquid 0.4Ca(NO3)2*0.6KNO3 (CKN). Detailed analysis of the limited-range 342 K data at the electric modulus immittance level shows that OMF fitting leads to an excess wing and that more appropriate models fit the data well without such a wing. Further, although such models allow estimation of the bulk dipolar dielectric constant of the material, as well as one associated only with mobile charges, they lead to implausibly small estimates of the important Kohlrausch K1 model shape parameter, beta1, and lead to an inadequate determination of its characteristic relaxation time. Therefore, wide-range CKN data sets extending to nearly 1012 Hz for the temperatures 342, 350, 356, and 361 K were very well-fitted with a more detailed composite model but one still involving K1 response. All model parameters were well-determined with no excess wings; beta1 estimates were all much closer to the universal value of 1/3; and the estimated model parameters led to a Boson peak beyond 1012 Hz, to very large thermal activation energies, and to evidence that the mobile charge concentration reached a saturation value at about 356 K. Such results do not support assumptions about variable ion-ion correlation, a mainstay of the OMF and NCM approaches. Finally, it is shown that although excess wings can sometimes be eliminated by using just an appropriate bulk fitting model and series blocking-electrode capacitor, as shown for the present narrow-range data, adequate fitting of the present wide-range data sets over their full spans of as much as 13 decades required the addition of an additional series dispersive-response model to the composite model. This addition seems likely to be required to take adequate account of the presence of more than one species of mobile charge in CKN.

Ion dynamics effect in forming relativistic solitons in plasmas

By using one-dimensional self-consistent relativistic fluid model, moving relativistic electromagnetic solitons with high intensity in electron-ion plasmas where the ion dynamics is taken into account are investigated numerically. It is demonstrated that two types of relativistic solitons with a precisely defined group velocity can occur in underdense and overdense plasmas with a given different background density. One is single-humped with weak scalar and vector potential amplitude; the other is multi-humped with high one. For these two types of solitons, the eigenvalue spectra of the group velocity versus the background density are found. The existence of soliton solutions is investigated in plasmas with a different background density, and the properties of these solitons are presented in detail.

Application of path integral formalism in spectral line broadening: Lyman- [formula omitted] in hydrogenic plasma

In this paper the results of Lyman- α line shapes without fine structure are rederived using a path integral formalism. The method presented here is designed to provide a quantum formalism that will treat the ions and the electrons on the same physical basis. This method also has the advantage of treating cases where the dynamical effects are present. We therefore give an expression of the dipolar autocorrelation function taking into account the ion dynamics effects. At the end, some Lyman- α lines are plotted under several conditions and compared to those obtained by other methods. This comparison checks out the validity of our approach. Note here that we do not intend to show a new result in spectral line shapes but add a contribution to the path integral formalism.

Computer simulated Balmer-alpha, -beta and -gamma Stark line profiles for non-equilibrium plasmas diagnostics

Balmer-alpha, -beta and -gamma lines have been calculated using computer simulations including ion dynamics effects for equilibrium and non-equilibrium conditions. The results obtained allow us to supply diagnostic maps based on the widths of those lines, as well as the Stark broadened full line profiles and the dipolar correlation functions obtained in the simulations. These profiles and correlation functions are a better diagnostic tool than the widths of the profiles in case of non-equilibrium plasmas. Calculations cover the range of electron densities between 10 20 and 10 25 m −3 and of electron temperatures between 1000 and 175 000 K. The emitter and the perturber ions kinetic temperature may vary between the value of the electrons temperature and one tenth of it.

Experimental and calculated Stark widths within the Kr I spectrum

On the basis of the precisely recorded 20 neutral krypton (Kr I) line shapes (in the 5s-5p and 5s-6p transitions), we have obtained the basic plasma parameters, i.e., electron temperature (T) and electron density (N) using our line deconvolution procedure in a plasma created in a linear, low-pressure, pulsed arc discharge operated in krypton. The mentioned plasma parameters have also been measured using independent experimental diagnostics techniques. Agreement has been found among the two sets of the obtained parameters. This recommends our deconvolution procedure for plasma diagnostical purposes, especially in astrophysics where direct measurements of the main plasma parameters (T and N) are not possible. On the basis of the observed asymmetry of the Stark broadened line profile, we have obtained not only its ion broadening parameter (A) which is caused by influence of the ion-microfield over the line broadening mechanism but also the influence of the ion-dynamic effect (D) over the line shape. The separate electron (W(e)) and ion (W(i)) contributions to the total Stark width, which have not been measured so far, have also been obtained. Stark widths are calculated using the semiclassical perturbation formalism for electrons, protons, and helium ions as perturbers.

The He I 706.52 nm line shape characteristics in the plasma diagnostics

On the basis of the precisely recorded 706.52 nm He I line shape we have obtained the basic plasma parameters i.e. electron temperature (T) and electron density (N) using our new line deconvolution procedure in the case of five various plasmas created in a linear, low-pressure, pulsed arc discharge. Plasma parameters have been also measured using independent experimental diagnostical techniques. Excellent agreement was found among the two sets of the obtained parameters. This enables our deconvolution procedure to recommendation for plasma diagnostical purposes, especially in astrophysics where direct measurements of the plasma parameters (T and N) are not possible. Besides, on the basis of the observed asymmetry of the Stark broadened line profile we have obtained its ion broadening parameter (A) caused by influence of the ion microfield to the line broadening mechanism and also the influence of the ion dynamic effect (D) to the line shape. Our A and D parameters represent the first data obtained experimentally using the line profile deconvolution procedure. We have found stronger influence of the ion contribution to the 706.52 nm He I line profile than the existing theoretical approximations estimate. This can be important for plasma modeling or for diagnostics.

Ion contribution to the prominent Ne I, Ar I and Kr I spectral line broadening

On the basis of the observed asymmetry of the measured spectral line profiles we have obtained the ion contribution to the Ne (26 lines), Ar I (19 lines) and Kr I (20 lines) spectral line broadening due to the quasi-static ion approximation and ion-dynamical effects. The ion broadening parameters (A) and the ion dynamic coefficients (D) have been obtained directly by the use of our line deconvolution procedure which allows the determination of the basic physical properties that characterize the line profile and also the relevant plasma parameters. We are the first to publish experimental data, viz. D and A values for the Ne I, Ar I and Kr I lines. The 26 Ne I, 6 Ar I and 9 Kr I A values are the first measured data and many of them are the first published data in this field. We have found clear evidence of the quasi-static ion and ion-dynamical effects on the investigated line shapes; they play a much more important role than the approaches based on semiclassical theory provide, especially in the case of the Ne spectral lines. This is of importance for astrophysical plasma modeling and diagnostics.

Ion contribution to the astrophysical important 388.86, 471.32 and 501.56 nm He I spectral lines broadening

Characteristics of the astrophysical important Stark broadened 388.86 nm, 471.32 nm and 501.56 nm He I spectral line profiles have been measured at electron densities between 4.4·10 22 and 8.2·10 22 m −3 and electron temperatures between 18,000 and 33,000 K in plasmas created in five various discharge conditions using a linear, low-pressure, pulsed arc as an optically thin and reproductive plasma source operated in a helium–nitrogen–oxygen gas mixture. On the basis of the observed asymmetry of the line profiles, we have obtained their ion broadening parameters ( A) caused by influence of the ion microfield and also the influence of the ion dynamic effect ( D) to the line shape. Our A and D parameters represent the first data obtained experimentally by the use of the line profile deconvolution procedure. We have found stronger influence of the ion contribution to these He I line profiles than the semiclassical theoretical approximation provides. This can be important for some astrophysical plasma modelling or for diagnostics.

Spectroscopy of magnetized plasmas

The frequency fluctuation model that provides a model for the description of Stark broadening has been modified to include the effect of a uniform magnetic field. This model is a convenient framework for treating, in a non perturbative approach, simultaneously acting Zeeman and Stark effects, while retaining the effect of ion dynamics. The first applications of this model concern the Lyman- α line of hydrogen in discharge plasma conditions, and the same transition for hydrogenic argon in high energy density plasmas. Line shapes of boron-like carbon observed in Tokamak edge plasma have also been calculated, and compared to experimental profiles.

Slow electromagnetic solitons in electron-ion plasmas

A set of nonlinear differential equations that describe moving relativistic solitons is investigated analytically and solved numerically. The influence of the ion motion on the soliton structure is investigated. It is demonstrated that, depending on the propagation velocity, relativistic solitary waves can occur in the form of bright solitons, dark solitons, or collisionless electromagnetic shock waves. In the limit of a low propagation velocity, a dark soliton can trap the ions and accelerate them. In the case of a bright soliton, the effects of ion dynamics limit the soliton amplitude. The constraint on the maximum amplitude is related to either the breaking of ion motion or the intersection of electron trajectories. The soliton breaking provides a new mechanism for ion and electron acceleration in the interaction of high-intensity laser pulses with plasmas.

Asymmetry of Stark profiles

The theoretical basis is presented that allows to compute the Stark broadened line shapes of atomic ions up to the quadrupole terms in the interaction potential between the radiator and the plasma electric microfields and their gradients. The nature of the corrections due to the plasma polarization effects associated with the electron distribution around ion perturbers are carefully analyzed. The relevant universal plasma functions are evaluated in a cluster expansion or by Monte Carlo simulations, and the line shape is calculated with ion dynamic effects by the Model Microfield Method. The asymmetry of the Lyman line of hydrogenic ions is then studied.

Tables of dipolar emission and two–photon absorption Lyman$-\alpha$ profiles

This paper shows the results of calculations, obtained by computer simulation, of the Stark broadening of the dipolar Lyman line of hydrogen considering fine structure, of two–photon absorption profiles for the transition 1S2S of hydrogen and of the profiles that could be obtained using two–photon polarization spectroscopy techniques for the aforementioned transition. Calculations have been carried forward for wide ranges of electron density, between 4 1019 and 1023 m-3 and temperature, between 2 000 and 100 000 K. We have considered ion dynamics effects with perturbers of different masses. In this paper we give the obtained profiles and the autocorrelation functions. These autocorrelation functions could be used in order to add another broadening mechanisms before obtaining the spectral profiles.

Polarised hydrogen line shapes in a magnetised plasma

The general profiles entering the polarised radiation transfer matrix for the hydrogen Ly\(\) line in dense magnetised plasmas are studied. The Stark effect due to plasma electrons is treated by the Unified Theory. The contribution of fine structure is discussed. Ion dynamics effects are studied, by application of the Model Microfield Method (MMM). The validity of a simpler approach, based on the Simplified Unified Theory (SUT) is assessed, by comparison with the MMM.

Redistribution of resonance radiation in hot and dense plasmas

A method for calculating the redistribution of resonance radiation in hot, dense plasmas is developed by extending the frequency fluctuation model (FFM). This model was originally designed as a numerical procedure for the calculation of the spectral shape of Stark-broadened lines emitted by multielectron ions and has been particularly useful in computations accounting for the ion dynamics effect. The FFM is based on a numerical technique that replaces the primitive inhomogeneous Stark component contributions to the linear response line shape with the observable radiative channels. These channels can be viewed as equivalent to a system of microfield dressed two-level radiators, the Stark-dressed transitions (SDT), which emit a set of spectral lines that reproduce the main features of the first-order radiative properties of the emitter. The mixing of these transitions through a stochastic process is equivalent to random fluctuations of the local ion microfield. The SDT form the basis for the extension of the FFM to the computation of nonlinear response functions. The theory of the second-order radiative redistribution function is reviewed and examples are given.

Calculations of the polarization spectrum by two-photon absorption in the hydrogen Lyman-α line

We present calculations, obtained by computer simulation, of the polarization spectrum by two-photon absorption in the transition $1\stackrel{\ensuremath{\rightarrow}}{S}2S$ of hydrogen in plasmas at low electronic density. Fine structure and ion dynamic effects have been included. The obtained results allow one to make a map of linewidths as a function of the electronic density and temperature to be applied for diagnosis in plasmas.

Spectroscopic line shape measurements at high densities

A comprehensive spectroscopic investigation of plasmas at extreme conditions produced by indirectly driven inertially confined implosions is described. In these experiments argon is doped into the gas filled core of implosion targets and the Ar K-shell emission is used to make time resolved measurements of electron density and electron temperature. The electron density is derived from the Stark broadened Ar XVII 1s 2-1s3p line shape, the electron temperature is derived from the line intensity ratio of the Ar XVII ls 2-ls3p transition and the lithium-like dielectronic satellites 2121′, 2131′ lying on the low energy side of the resonance line. We give examples of the experimental data and compare the extracted time histories of electron density and electron temperature with simple radiation hydrodynamic simulations, where broad agreement is found. Detailed line shape measurements of the Ar XVII 1s 2-1s3p transition are presented and the absence of an intensity dip at line center in the experiment results is discussed. The validity of the quasi-static ion approximation for these plasma conditions is tested by varying the mass of the fill gas in the core. Results from deuterium, deuterated methane, and nitrogen filled implosions are presented and indicate ion dynamic effects are not responsible for the line center discrepancy. We discuss other possibilities including spatial gradients in the core affecting measurements of the intrinsic line shape.

Oscillating two-stream instability of beat waves in a hot magnetized plasma

It is shown that an electrostatic electron plasma beat wave is efficiently unstable for a low-frequency and short-wave-length purely growing perturbation (ω, k), i.e. an oscillating two-stream instability in a transversely magnetized hot plasma. The nonlinear response of electrons and ions with strong finite Larmor radius effects has been obtained by solving the Vlasov equation expressed in the guiding-center coordinates. The effect of ion dynamics has been found to play a vital role around ω ∼ ω ci, where ω ci is the ion-cyclotron frequency. For typical plasma parameters, it is found that the maximum growth rate of the instability is about two orders higher when ion motion is taken into account in addition to the electron dynamics.

Study of the Stark broadening of the Paschen alpha line in hydrogen

Stark width tables of the Paschen alpha line in hydrogen plasmas are presented, as an aid for plasma diagnosis. The calculations have been carried out by means of a computer simulation technique using particles and within the usual framework of a - ion model. With this technique, an adequate treatment of the ion dynamics effects can be achieved. The calculations cover a range of electron densities between - and temperatures that go from 5000 to 40 000 K. Four values of the reduced mass of the emitter - perturber pair have been considered, and 2.0.

Spectroscopic analysis of hot dense plasmas: A focus on ion dynamics

A brief discussion of the standard theory of line broadening is presented together with an analysis of selected laser-driven implosion experiments. The effect of improved theoretical procedures on experimental analysis is discussed. In particular, we consider the combined effects of ion dynamics and opacity on line profiles used in the analysis of these plasmas. The experiments discussed were performed at the University of Rochester Laboratory for Laser Energetics (LLE). The results presented in this paper illustrate the usefulness of plasma line broadening in diagnosing hot dense plasmas and in understanding fundamental plasma processes.