Stationary Ion Research Articles

Effect of spin on the electron-ion scattering and the heating rate of a plasma in very intense laser light.

An exact Volkov state solution of the minimally coupled Dirac equation is used to calculate the transition rate dR of an electron scattering via a stationary ion in the presence of a very intense laser field. A consistent picture of the scattering is presented in which the electrons' initial and final states are quasifree states. Accordingly, a modified transition rate ${\mathrm{dR}}^{\mathrm{*}}$ and a modified Maxwell-Boltzmann distribution are developed. They are used to calculate the heating rate W of the isotropic part of a quasifree neutral plasma in the presence of very intense laser light. In order to simplify the expression for the heating rate W, an important transformation, which changes an infinite sum over Bessel functions into a finite integral, is introduced. It is then shown that the leading term of the heating rate W is similar to the expression of Osborn (with corrections) for intensity I${<10}^{16}$ W/${\mathrm{cm}}^{2}$ and ${k}_{B}$T1 keV. A new correction factor is defined to show the effect of a very intense laser field when the intensity I${10}^{16}$ W/${\mathrm{cm}}^{2}$. For ${k}_{B}$T>1 keV, a spin-dependent term of order ${k}_{B}$T/${\mathrm{mc}}^{2}$ is also discovered. This represents a new term not previously known. We show that the effect of this term on the heating rate is substantial and it would be possible to measure its effect with present-day laser systems.

The limiting ionic conductivity of Na+ and Cl− ions in aqueous solutions: Molecular dynamics simulation

The molecular dynamics computer simulation technique was used to calculate the limiting ionic mobilities for Na+ and Cl− in TIP4P water. The velocity autocorrelation function and the memory kernel for the corresponding generalized Langevin equation were calculated for the mobile ion. The autocorrelation function of the force exerted on the stationary ion was also calculated and compared with the memory kernel. The two are in good agreement, especially at short times (≈0.1 ps). The diffusion coefficients obtained from Brownian motion theory (the stationary ion case) were also in good agreement with the ones obtained from mobile ion calculations. The major assumptions of the molecular theory of the limiting ionic mobility were tested and not confirmed by the simulation.

Molecular dynamics test of the Brownian description of Na+ motion in water

The autocorrelation function of the velocity of an infinitely dilute Na+ ion in aqueous solution, and the autocorrelation function of the force exerted on a stationary Na+ under the same conditions are evaluated by molecular dynamics calculations. The results are used to test the accuracy of Brownian motion assumptions which are basic to hydrodynamic models of ion dynamics in solution. The self-diffusion coefficient of the Na+ ion predicted by Brownian motion theory is (0.65±0.1)×10−5cm2/s. This value is about 60% greater than the one obtained for the proper dynamics of the finite mass ion, (0.4±0.1)×10−5cm2/s. The numerically correct velocity autocorrelation function is nonexponential, and the autocorrelation of the force on the stationary ion does not decay faster than the ion velocity autocorrelation function. Motivated by previous hydrodynamic modeling of friction kernels, we examine the approximation in which the memory function for the velocity autocorrelation function is identified with the autocorrelation function of the force on the stationary ion. The overall agreement between this approximation for the velocity autocorrelation function and the numerically correct answer is quite good.

Selected area, stationary beam cratering for high sensitivity depth profiling with a computerized Auger microprobe

The use of improved methods of “crater edge profiling” as a viable alternative to conventional depth profiling by sputter etching and Auger analysis is discussed. The emphasis is placed upon utilizing a stationary ion beam (full width at half- maximum, about 200 μm) from a differentially pumped gun, the beam of which can be selectively positioned on the sample surface for localized cratering. A variety of samples of Au/Cu, Au/Zr, Ag/Si and silicon either uncoated or coated in situ with metal were used for demonstrating different aspects of this experimental approach and for mapping with Auger, secondary and elastically backscattered electrons. A thin oxide layer on silicon ( d OX ≈ 1.2 nm) was very easily detected and measured by line scans across shallow craters (tan α ≈ 10 -5).

Electrostatic ion (hydrogen) cyclotron and ion acoustic wave instabilities in regions of upward field‐aligned current and upward ion beams

An investigation is made into the stability of electrostatic hydrogen ion cyclotron and ion acoustic waves in a model plasma where an ion beam, population 2, and oppositely directed drifting electrons pass through a stationary ion background, population 1. The excited wave properties are then compared with the characteristics of the unstable modes observed on the S3‐3 satellite. Three temperature regimes are studied: (1) Te > Ti2 ≫ Ti1, (2) Ti2 > Te ≥ Ti1, and (3) Te ∼ Ti1 > Ti2. It is found that the ion beam acts as a free energy source only in regime 1. This regime is also highly unstable to the electrons as a free energy source. Unstable modes in regimes 2 and 3 seem to best satisfy the electrostatic hydrogen cyclotron wave (EHC) properties at 1RE. For these cases the electrons are the free energy source, the beam supplies damping.

Studies in reversed-phase ion-pair chromatography : IV. The rôle of the chain length of the pairing ion

Adsorption isotherms of straight chain sodium alkanesulphonates (from butane to octane) were determined by the breakthrough method in aqueous phosphate buffer on ODS-Hypersil, along with retention data of similarly and oppositely charged ionic and non-ionic solutes. The effects on the solute retention of the chain length of the pairing ion were examined both at varying and constant counter ion (sodium) concentrations, in terms of both the mobile phase and stationary phase pairing ion concentrations. A practical consequence of the use of systems with constant counter ion concentration is that pairing ions with different chain lengths (members of a homologous series) are interchangeable in terms of their surface concentrations.

Studies in ion-pair chromatography : II. Retention of positive and negative ions and neutral solutes in tetrabutylammonium bromide-containing methanol—water eluents on lichrosorb rp-18

The retention of positively and negatively charged ions, as well as of neutral solutes, was studied in 0–70% methanol in 25 m M aqueous phosphate buffer (pH 2.1–3.4) eluents as a function of the tetrabutylammonium bromide ion pair reagent concentration. The log k′ vs. mobile phase pairing ion concentration ( P m ) plots (which showed P m - and [methanol]-dependent maxima) could be transformed into log k′ vs. stationary phase pairing ion concentration ( P s ) curves by using the simultaneously determined adsorption isotherms of tetrabutylammonium bromide. While the shape of the log k′ vs. P m curves of oppositely charged solutes changed considerably with the concentration of methanol in the eluent, the log k′ vs. P s curves were more similar, and their maxima are in the 80–120 μmole/g range. The log k′ vs. P m curves of similarly charged solutes were more alike. The methanol concentration of the eluent influences the retention of oppositely charged solutes more sensitively than that of the similarly charged solutes. At constant P m the log k′ vs. [methanol] curves of oppositely charged solutes were S-shaped, while the log k′ vs. [methanol] curves at constant P s values ran similar to the log k′ vs [methanol] curves obtained in the absence of ion-pairing reagents.

The Electron Beam Method of Production of Highly Charged Ions and Its Applications

Based on the works performed at the Joint Institute for Nuclear Research, the present-day situation and prospects of development are considered of the electron beam method of production of highly charged ions and its applications in various fields of physics.At present an ionization factor jτi (the product of electron beam density by the time of bombarding a stationary ion target with the electrons) approximately equal to 1.5 × 102 2 cm-2 has been achieved at an electron energy of Ee = 20 keV. This allows one to produce rather highly charged ions including argon nuclei (Ar18+) and He-like ions of krypton (Kr34+) and xenon (Xe52+).As regards the applications of the method, primary consideration is given to positive ion ionization by electron impact, the charge exchange of highly charged ions on atomic and molecular hydrogen targets, the interaction of the ions with the surface of solids and the nuclear properties of the ions.

Linear electrostatic instability of the electron beam ion source

Linear plasma fluid theory is used to study the stability of a cold electron beam in Brillouin equilibrium which passes through a stationary cold ion background, with particular interest in stability for parameters relevant to EBIS devices. Dispersion is studied both analytically and numerically. For l = 0, the usual infinite medium two stream instability condition is shown to correspond to a requirement that beam perveance exceed a minimum value, P > 33 μperv; hence, this mode is stable for EBIS ( P ≈ 1 μperv). The Brillouin equilibrium rotation is shown to cause an electron-ion rotating stream instability, which is convectively unstable. The l = 1 mode is also found to be unstable. Higher modes numbers, l > 1, are unstable, but have reduced growth. Instability is only weakly affected by finite beam radius and boundary conditions.

Resonant Excitation of High Amplitude Oscillations and Hydrodynamic Wave Breaking in a Streaming Cold Plasma

The excitation of large amplitude electron oscillations in a streaming cold plasma and the minimum threshold of wave breaking in the resonant region are investigated analytically as a function of flow velocity. The problem is reduced to the solution of a driven harmonic oscillator with time varying eigenfrequency ωp(t) in a self-consistent, stationary ion density profile. An analytical solution is presented and applied to the correct wave breaking criterion in a streaming plasma. Wave breaking sets in when the driver amplitude Êd obeys the inequality which shows that the threshold is proportional to the driver frequency ω and to the flow velocity at the resonance point, vc; however, it is independent of the density scale length. Resonance ends at η = π/2. The denominator assumes there the value 2.759. η is a dimensionless time which measures the transit time of a volume element through resonance.

Splitting Scheme Integration of the Two-and-One-Half-Dimensional Vlasov Equation

A numerical splitting scheme technique is applied to the integration of the Vlasov equation in two-space and three velocity dimensions. Calculations are performed for a cold, stationary ion, mobile electron plasma in the presence of a constant external magnetic field. Results for Landau damping and the two-stream instability are presented in both one and two velocity dimensions. The Landau damping results show a plateau structure in the electron velocity distribution function in both the parallel and perpendicular directions formed as a result of the damping of a high initial electric field propagating at 45° to the parallel velocity axis. The two-stream velocity distribution function shows pitch angle scattering and velocity diffusion for an electron beam initially propagating at 45° to the magnetic field direction through a low-temperature equal density background. The two-stream distribution function evolves to a stable quasi-isotropic plateau structure similar to that found in auroral sounding rocket data.

Effect of cell membrane-active antimicrobial agents on membrane potential and viability of mycoplasmas

The membrane potential ofMycoplasma mycoides subsp.capri has been determined to beEM=−48 mV±10%, inside negative. In this study we investigated the influence of cell membrane-active antimicrobial agents, viz., valinomycin, gramicidin, polymyxin, and clotrimazole, on membrane potential and viability ofM. mycoides subsp.capri. Valinomycin, an ionophore with extreme potassium selectivity, induced a membrane hyperpolarization,EM=−110 mV. Valinomycin was not cidal, but static to mycoplasmas. Obviously the potassium drain induced by valinomycin can be compensated for by the organisms. Gramicidin is an antibiotic forming cation conduction channels across membranes. It induced a rapid depolarization,EM=+23 mV, of mycoplasma membranes. At low concentrations, gramicidin had a static effect, whereas at high concentrations it was cidal to mycoplasmas. The rapid permeation of cations through the stationary ion channels formed by gramicidin obviously exerts an inhibitory or even lethal effect on mycoplasma metabolism and growth. Polymyxin B induced a depolarization,EM=−35 mV, of mycoplasma membranes only when the organisms had been pretreated and hyperpolarized with valinomycin. After treatment with both valinomycin and polymyxin B, a slight inhibition of mycoplasma growth was observed. Clotrimazole, a synthetic imidazole antimycotic, hyperpolarized mycoplasma membranes (EM=−80 mV). At high concentrations clotrimazole was cidal, whereas at low concentrations it was static to mycoplasmas.

Coupled Stationary Langmuir and Ion Acoustic Waves in the Presence of Trapped Ions

Self-consistent stationary solutions for the envelope of Langmuir waves, the ion density perturbation and the ion distribution function are obtained for a one-dimensional unmagnetized plasma. Allowance for trapped ions yields an arbitrariness for the shape of the solutions. Two special solutions are obtained: one is an envelope solitary wave in which the width is decreased due to the trapped ions compared with the case obtained by the fluid theory, and the other is an envelope shock in which the density jump is determined only by the shock width and is independent of the Langmuir wave amplitude; the propagation velocity is decreased due to the effect of trapped ions.

Sputter etch profiles of spheres, cylinders and slab-like silica targets

The intermediate and quasi-equilibrium contours generated by ion bombardment on silica targets under the condition of stationary target and ion beam direction are shown predictable by Frank's construction method. An expression based on ion reflection is reported which yields values for the apex angle of conical silica ion etch structures in agreement with those derived graphically from sputter yield data. The effect of the initial target shape on the etch topography is discussed.

High-pressure Langmuir probe in a weak flowing plasma or a plasma sheath

A theory is developed for the current to a negatively biased probe in a moving weakly ionized plasma or a stationary ion sheath. It is found that at low ionization densities the current is no longer space-charge limited but is, in fact, limited by the electric field generated by the probe. For a cylindrical probe the current per unit length I=2πμn0eV[log(I/n0evfrp)−1/2] −1, where μ is the mobility of the ion, e is the electronic charge, V is the probe potential (negative), I is the probe current, vf is the plasma flow velocity, n0 is the plasma ionization density, and rp is the probe radius. For a spherical probe the current I=4πμn0erpV. Measurements with a cylindrical probe at densities down to 1012/m3 show good agreement with theory.

A cratering analysis for quantitative depth profiling by ion beam sputtering

The depth profiling of composition by sputtering with a stationary ion beam of non-uniform intensity is treated analytically. Attention is devoted to the situation where the experimental signal originates simultaneously from all or most of the sloping, sputtered crater, as in ion scattering spectrometry (ISS) or secondary ion mass spectrometry (SIMS). As a result the signal itself does not relate directly to the composition at any specific depth in the specimen. Data processing formulas for various degrees of correction are presented, starting with a very simple result for the Gaussian intensity distribution. Simulated ISS outputs and processed data points are then illustrated for a number of selected composition profiles. An alternative use of the analysis to determine the radial intensity distribution in an ion beam is presented with experimental data supporting the Gaussian beam approximation as modified by the so-called clipping factor. Finally a practical stratagem is proposed for overcoming such extraneous problems as beam intensity transients, while determining the depth profiles of the elements in specimens of several components.

ISS imaging and depth−profile analysis using beam rastering and signal gating

Ion scattering spectrometry (ISS) has been shown to be a valuable technique for the chemical analysis of surfaces. As the ion beam (energy less than 3 keV) is sputtering the surface, a depth profile is obtained by sequential measurement of the scattered ion energy distribution. However, when a stationary ion beam is used, the true−depth distribution of elements may be distorted due to crater−edge effects. This difficulty has been overcome by rastering the ion beam over the sample, and gating the analyzer signal so that only the flat−bottomed center of the crater is analyzed.In addition, the scattered ion signal has been used to image the lateral distribution of the surface elemental composition.

Stability of large-amplitude relativistic non-linear plasma waves

Stability properties of large-amplitude, relativistic non-linear plasma waves are investigated by solving the Cauchy problem for the motion of a relativistic electron fluid with uniform stationary ion background. The development of a stationary large-amplitude relativistic wave is studied under the influence of initial perturbations of electric field and particle velocities. Stochastic initial perturbations are slightly damped with time; in the case of parametric initial perturbations, a perturbation growth is followed by non-linear saturation and decay. Under some conditions, particle interstreaming can develop but it does not significantly influence the large potential wells in the wave.

Contrastreaming Instability in a One-Dimensional Finite-Length System

Two independent and oppositely directed electron beams with equal densities and speeds are considered to interpenetrate one another in a finite-length system with a stationary neutralizing ion background. The nonlinear development of the resulting electrostatic waves is followed both in time and space by numerical simulation. The results include the time-dependent behavior of the particle trajectories governed by the equation W = 12mv2−| qφ0(t) | coskmaxz. In the cold beam case a hysteresis-like loop in phase space is observed to develop in the transition from the laminar to a turbulent state. The vortices formed in velocity space are found to be absorbed at the right-hand boundary of the finite-length system and coalesce into one another for all warm beam cases. The total electric field energy saturates at approximately 16% of the total system energy. This result is three times greater than for a one-dimensional system with periodic boundary conditions.

The Thermal Temperature Coefficient of the Calomel Electrode Potential Between 0° and 70°C: III Discussion: Moving, Transport and Stationary Entropies and Heat Capacities of Aqueous Chloride Salines and Their Ions. The Approximate Partition Function of Water and Hydronium Ion

The moving (transported) ionic properties and are partial molal properties of the ion itself and include the effect of its electrical charge on that portion of the solvation layer which travels with the ion (Eastman first and second regions). The negatives of the ionic transport properties −S* and −C* measure the influence of the ion (plus its tightly bound waters if any) on the remainder of the solvent (Eastman third region). A positive value of S* identifies the ion as a structure maker in the third region. The sums , where , measure the partial molal properties of the stationary ion, including the effect of the ionic charge on both Eastman second and third regions of the solvent. Observed values of suggest a twofold effect of the ionic charge on its entourage of water molecules: a loosening of the O‐H covalent bonds coupled with a stiffening of the O … H hydrogen bonds. The moving entropy and heat capacity of hydronium ion can be understood in terms of the hydrogen‐bonded model of water structure, in which every or can be 4‐, 3‐, 2‐, 1‐bonded to its neighbors or unbonded. By ascribing both bond and vibrational energy levels on this model, an approximate partition function is constructed for and , which can be made to fit our data for the unitary entropy and heat capacity of at 25° and standard data for the entropy and heat capacity of between 0° and 100°. This model predicts the following fraction of hydrogen bonds broken in liquid at 0°, 25°, and 100°: 0.183, 0.218, and 0.310; in at 25°, 0.094. The addition of H+ to thus introduces a distinct amount of structure to the complex since it reduces the number of hydrogen bonds broken at 25° to a level, 9.4%, equal to half the number of hydrogen bonds broken in the liquid complex at the melting point. The need to break about 12% more hydrogen bonds when the proton moves away at 25° is consistent with a calculated heat of transport of 3530 cal/mol, which compares favorably with the observed heat of transport of around 3000 cal/mole (on the Agar postulate). The single‐ion stationary heat capacities for K+, Na + , Li+, and Cl− obtained experimentally in the present study via the ‐bridge postulate compare very favorably with theoretically calculated values of for these ions based on the statistical model of Scheraga‐Griffith.