Ion Number Density Research Articles

Nonlinear dust-acoustic solitary waves and shocks in dusty plasmas with a pair of trapped ions

The propagation characteristics of small-amplitude dust-acoustic (DA) solitary waves (SWs) and shocks are studied in an unmagnetized dusty plasma with a pair of trapped positive and negative ions. Using the standard reductive perturbation technique with two different scalings of stretched coordinates, the evolution equations for DA SWs and shocks are derived in the form of complex Korteweg-de Vries and Burgers' equations. The effects of the dust charge variation, the dust thermal pressure, and the ratios of the positive to negative ion number densities as well as the free to trapped ion temperatures on the profiles of SWs and shocks are analysed and discussed.

Neutral Ingestion Effects on Plume Properties of a Radio-Frequency Plasma Discharge

To enable comparison of thruster performance across different vacuum facilities, an understanding of the effect of operating pressure on plasma plume properties generated in a helicon ion thruster architecture is required. Plasma property measurements acquired at two different vacuum facility operating pressures are used to determine the effect of neutral ingestion on the operation of a replica of the Madison Helicon Experiment at low power. The ion velocity distribution function, electron temperature, ion number density, and plasma potential are measured along the thruster axis. Plasma plume property measurements made at the “high-pressure condition” ( corrected for argon) are compared to values recorded at the “low-pressure condition” ( corrected for argon) for thruster operation at radio-frequency forward power, 340 G source region magnetic field strength, and argon volumetric flow rate. Operation at the high-pressure condition has 31–79 V lower ion energy, 0.8–6.1 eV lower electron temperature, and higher ion number densities than operation at the low-pressure condition. Changes in collision frequency and ionization balance result from increased neutral ingestion at the higher operating pressure.

Experimental and theoretical study of the near IR emission of xenon excited by a fast electron beam

Emission of xenon excited by a 120-keV electron beam at gas pressures of 100, 200, 500, and 760 Torr nm was studied experimentally and theoretically. More than 30 spectral lines were identified in the wavelength range of 750–1000 nm. A self-consistent kinetic model is developed to calculate the emission intensity of xenon atoms in the near IR range. The model includes balance equations for the number densities of electrons, ions and excimer molecules; equations for the populations of electron levels; and the Boltzmann equation for the low-energy part of the electron energy distribution function with a source of slow electrons. Excitation and ionization rates of xenon by the beam electrons and the energy spectrum of slow electrons are calculated by the Monte Carlo method. It is shown that, under these conditions, the main mechanism of xenon atom excitation is dissociative recombination of Xe3 + ions.

Kinetic Jeans instability and nonlinear damping of electromagnetic waves in self gravitating dusty plasma

A kinetic theory of the Jeans instability of a self gravitating dusty plasma has been developed in the presence of nonlinear Landau damping (NLD) term. We demonstrate that NLD alters the growth rate of the gravitational collapse of the gravitating dusty plasma. The dispersion relation of modified Jeans instability is obtained and analyzed for specific conditions. Jeans frequency is compared with the dust acoustic frequency; new definition of Jeans wave length is introduced. The maximum growth rate is obtained for a particular condition as well as the Jeans critical mass is defined. Next to address the heating of plasma through radiation processes, we investigate the nonlinear theory of high frequency electromagnetic waves (EMWs) in a collisionless dusty plasma by using a set of Vlasov-Poisson equations. The effects of the nonlocal nonlinear Landau term (appearing due to the nonlinear interaction of EMWs with gravitating dusty plasma) in the nonlinear Schrödinger equation are examined. It is found that nonlinear Landau damping of EMWs leads to transfer of effective energy to the plasma particles, the corresponding decay rate of EMWs appears to be a function of amplitude of electromagnetic pump waves, and damping can be faster in the presence of large ion number density.

Theoretical study to investigate the impact of plasma parameters on the catalyst nanoparticle growth

The plasma kinetics based model is adopted to elucidate the effect of plasma parameters on the nucleation and growth mechanism of catalyst nanoparticle. The present model considers the plasma processing of thin catalyst film, power equalization at the film surface, flux and kinetics of plasma species (electrons, ions, and neutrals). In our investigation, it is found that catalyst nanoparticle diameter decreases with increase in ion number density in plasma. Moreover, it is also found that catalyst film thickness significantly affect the catalyst nanoparticle size i.e., catalyst nanoparticle diameter increases with catalyst film thickness. In addition, it is observed that the substrate temperature increases during the plasma processing and finally achieve saturation. Our theoretical results are in good agreement with the experimental results.

Synthesis and different optical properties of Gd2O3 doped sodium zinc tellurite glasses

A series of Gd2O3 doped sodium zinc tellurite [xGd2O3-(0.8-x) TeO2−0.1Na2O-0.1ZnO] glasses are prepared by the conventional melt quenching method and their optical properties have been studied. UV–vis spectrophotometric studies within the wavelength range from 230nm–800nm are carried out in the integrating sphere mode to study the effect of Gd2O3 doping on the optical band gap (Eg), refractive index (n), dielectric constant (εr) and susceptibility (χ). Other physical properties like molar volume, molar refraction, polarizability, metallization criterion, number density of rare-earth ions (N), polaron radius (rp), inter ionic distance (ri), molar cation polarizability (∑αi), number of oxide ions in chemical composition (NO2-), optical band gap based electronic oxide ion polarizability (αO2-) and optical basicity (Λ) of glass samples have been studied on the basis of UV–vis spectra and density profile of the different glasses.

Effect of gamma radiation on the transport and structural properties of polyacrylonitrile-lithium bis(oxalato)borate films

Different doses of gamma-rays from 5 to 35kGy have been used to irradiate solid polyacrylonitrile (PAN)-lithium bis(oxalato)borate (1:1 ratio) films in order to study their transport and structural characteristics. Impedance data show that with an increase of radiation dose, conductivity (σ) of the complexes increases and exhibits a maximum of 1.02×10−4Scm−1 at γ-ray dose of 15kGy. The obtained conductivity is about 200 times higher than that of the virgin sample (σ=1.74×10−6Scm−1). By fitting the Nyquist plots with the impedance of an equivalent circuit, it is possible to calculate the dielectric constant (εr), diffusion coefficient (D), ionic mobility (μ) and mobile ion number density (n). These parameters are highest for 15kGy irradiated samples indicating that σ, εr, D, μ and n are dependent on radiation dose. FT-IR spectroscopy confirms that ɣ-irradiation causes IR peak shifting, abolishment and reformation of functional groups of PAN-LiBOB indicating bond breaking, bond deformation and/or new bond formation. At 25 and 35kGy doses of ɣ-radiation, new peaks have been observed at 833, 877, 1072, 1160 and 1225cm−1 which may be attributed to the formation of new species. Free and contact ions in irradiated films have been calculated via deconvolution of the FTIR spectra obtained from 1750 to 1850cm−1. The sample irradiated with 15kGy ɣ-radiation contains the highest percentage of free ions and the lowest concentration of contact ions. The number density of free ions is observed to have more control on the conductivity compared to ion mobility and diffusion coefficient. XRD spectrum reveals peaks at 2θ ~16.85°, ~30.5° and ~36.9° for all irradiated samples. The polymer electrolyte irradiated with 15kGy gamma-rays is the most amorphous. The FWHM values increase with ɣ-ray doses showing maximum at 15kGy and then decreases with further increase of radiation dose. Crystallite size decreases with the increase of radiation doses, reaches lowest value at 15kGy followed by additional growths as more radiation is applied. This observation is also conceivable with the EIS and FT-IR results.

Y2O3 wall interactions in Cl2 etching and NF3 cleaning plasmas

Time-dependent behavior of chlorine inductively coupled plasmas is presented for Si etching, following NF3-Ar plasma cleaning of a chamber coated with Y2O3. Optical emission intensities were recorded throughout the processes for Cl, O, F, Si, SiClx=1-3, SiF, and N2, as well as from added trace rare gases Xe and Ar for determination of number densities for selected species by actinometry. Time-dependent Langmuir probe measurements of ion and electron number densities and electron energy distributions were also carried out. Ex situ x-ray photoelectron spectroscopy measurements of the surface composition of Y2O3 coupon pieces after different etching and clean processes were also performed. Initially fluorinated yttria surfaces are shown to have a relatively high probability for loss (“recombination”) of Cl through formation of both Cl2 and SiClx. As etching proceeds, SiClx abstracts F from the surface and deposits Si and Cl, lowering of the heterogeneous recombination of Cl. The initially high recombination coefficient for Cl is explained by the weakening of the surface binding energy for Cl and SiClx at YFx sites, due to the highly electronegative nature of F, allowing recombination reactions forming Cl2 and SiClx to become energetically favorable.

Dielectric functions of Pd and Zr transition metals: an application of Drude-Lorentz models with simulated annealing optimization.

An accepted-probability-controlled simulated annealing (APCSA) method has shown to be a valuable tool to describe, in parametric form, by means of an extended Drude-Lorentz model, the dielectric function of several metals through infrared, visible, and ultraviolet photon energies [Appl. Opt.37, 5271 (1998)APOPAI0003-693510.1364/AO.37.005271]. In this work, an improved APCSA approach is used to estimate the parameters involved in an extended Drude-Lorentz type model which incorporates the dielectric constant due to a background electronic polarization in the Drude term and the normalization of the individual oscillation strengths involved in the Lorentz contributions to the dielectric function. This last approach allows us to introduce a new parameter z to be optimized: the number density ratio, i.e., the ratio between number density of conduction electrons and number density of metal ions. From the optimization of the z value within this novel approach, we evaluate other parameters: electrical resistivity, electron mean free path, effective mass of conduction electrons and relaxation time, Fermi energy, electronic density of states at the Fermi level, and electronic heat capacity coefficient. Application of the model is carried out to describe the dielectric functions of two transition metals, Pd and Zr, through ultraviolet, visible, and infrared photon energies.

Generalized sheath criterion for arbitrary degenerate plasmas

In this research, we study the generalized sheath criterion for plasmas with an arbitrary degree of electron degeneracy and temperature, ranging from the classical dilute regime to the fully degenerate quantum plasmas. The latter may be relevant to warm dense matter and/or laboratory high energy density matter or even astrophysical stellar plasmas. The hydrostatic one dimensional model is used to establish the generalized Bohm's criterion for sheath entrance ion speed limits, and the small amplitude theory of the sheath problem, which accurately describes the sheath parameters for lower ion acoustic Mach numbers, is developed. Our results indicate that the sheath characteristic parameters such as electrostatic potential and density profiles, as well as the wall potential and the sheath length, are significantly affected by plasma parameters such as the ion and electron temperature and number densities in the plasma region. In particular, there are fundamental differences between sheath structures of the dilute classical plasmas and those of dense quantum ones.

The effect of NH4NO3 towards the conductivity enhancement and electrical behavior in methyl cellulose-starch blend based ionic conductors

Solid polymer electrolytes based on methyl cellulose (MC)-potato starch (PS) blend doped with ammonium nitrate (NH4NO3) are prepared by solution cast technique. The interaction between the electrolyte’s materials is proven by Fourier transform infrared (FTIR) analysis. The thermal stability of the electrolytes is obtained from thermogravimetric analysis (TGA). The room temperature conductivity of undoped 60 wt.% MC-40 wt.% PS blend film is identified to be (1.04 ± 0.19) × 10−11 S cm−1. The addition of 30 wt.% NH4NO3 to the polymer blend has optimized the room temperature conductivity to (4.37 ± 0.16) × 10−5 S cm−1. Conductivity trend is verified by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and dielectric analysis. Temperature-dependence of conductivity obeys Arrhenius rule. Conductivity is found to be influenced by the number density (n) and mobility (μ) of ions. From transference number measurements (TNM), ions are found to be the dominant charge carriers.

Low frequency nonlinear waves in electron depleted magnetized nonthermal plasmas

A theoretical study on the ultra-low frequency small but finite amplitude solitary waves has been carried out in an electron depleted magnetized nonthermal dusty plasma consisting of both polarity (positively charged as well as negatively charged) inertial massive dust particles and nonextensive q distributed ions. The reductive perturbation technique is employed to derive the ZakharovKuznetsov (ZK) equation. The basic features of low frequency solitary wave are analyzed via the solution of ZK equation. It is observed that the intrinsic properties (e.g., polarity, amplitude, width, etc.) of dust-acoustic (DA) solitary waves (SWs) are significantly influenced by the effects external magnetic field, obliqueness, nonextensivity of ions, and the ratio of ion number density to the product of electron and negative dust number density. The findings of our results may be useful to explain the low frequency nonlinear wave propagation in some plasma environments like cometary tails, the earth polar mesosphere, Jupiter’s magnetosphere, etc.

The effect of a longitudinal density gradient on electron plasma wake field acceleration

Three-dimensional, particle-in-cell, fully electromagnetic simulations of electron plasma wake field acceleration in the blow-out regime are presented. Earlier results are extended by (i) studying the effect of a longitudinal density gradient, (ii) avoiding the use of a co-moving simulation box, (iii) inclusion of ion motion, and (iv) studying fully electromagnetic plasma wake fields. It is established that injecting driving and trailing electron bunches into a positive density gradient of 10-fold increasing density over 10 cm long lithium vapour plasma results in spatially more compact and three times larger, compared with the uniform density case, electric fields (−6.4×10 10 V m −1 ), leading to acceleration of the trailing bunch up to 24.4 GeV (starting from an initial 20.4 GeV), with energy transfer efficiencies from the leading to trailing bunch of 75%. In the uniform density case, a −2.5×10 10 V m −1 wake is created leading to acceleration of the trailing bunch up to 22.4 GeV, with energy transfer efficiencies of 65%. It is also established that injecting the electron bunches into a negative density gradient of 10-fold decreasing density over 10 cm long plasma results in spatially more spread and two and a half smaller electric fields (−1.0×10 10 V m −1 ), leading to a weaker acceleration of the trailing bunch up to 21.4 GeV, with energy transfer efficiencies of 45%. Taking ion motions into consideration shows that in the plasma wake ion number density can increase over a few times the background value. It is also shown that transverse electromagnetic fields in a plasma wake are of the same order as the longitudinal (electrostatic) ones.

Numerical study of electric potential formation in a weakly ionized plasma flowing supersonically through open magnetic field lines

We investigate the mechanism of space potential formation due to a diverging magnetic field on a rarefied weakly ionized plasma flowing supersonically by performing a hybrid simulation. Ions and neutrals are treated by the particle-based direct simulation Monte Carlo method, while electrons are treated as a fluid to save time and memory. We apply an electron continuity equation in order to treat the electron velocity independently of the ion velocity. We find the number density of ions (and electrons) distributed along the magnetic field. We also find electron rotation along the flowing direction. Since we remove the current-free condition assumed in our previous study, we find that the longitudinal variation in the space potential agrees reasonably well with our previous experimental results.

Fast and Slow Mode Solitary Waves in a Five-Component Plasma

We have investigated fast- and slow-mode solitary profiles in a five-component plasma consisting of positively and negatively charged pair ions, hydrogen ions, and hotter and colder electrons. Of these, the heavier ions and colder photoelectrons are of cometary origin while the other components are of solar origin; the electrons are described by kappa distributions. The Zakharov-Kuznetsov (ZK) equation is derived, and solutions for fast- and slow-mode solitary structures are plotted for parameters relevant to comet Halley. We found that the presence of hydrogen ions determines the polarity of the fast- and slow-mode solitary structures. Also, variations of equilibrium number density of hydrogen ions and charge numbers on the heavier pair ions act differently on the fast- and slow-mode solitary structures. The addition of hydrogen ions significantly affects the amplitude of the solitary structures for the fast mode. Further, the cyclotron frequency of the lighter and heavier ions has a noticeable effect on the width of the solitary waves.

Transport and AC Impedance Studies of Plasticized-Chitosan Based Polymer Electrolytes

Dimethyl Carbonate (DMC)-plasticized chitosan-based polymer electrolytes were prepared in the present work. The sample 37.5 wt% chitosan - 37.5 wt% NH4CF3SO3 - 25 wt% DMC showed the highest conductivity of (1.95±0.15) x 10-6 S/cm. From calculated values obtained using the Rice and Roth model, the increase in conductivity is due to the increase in the number density of mobile ions. Universal Power Law was used to analyze the AC conductivity of the sample. Arrhenius behavior was observed in the plot of hopping frequency; ωP against temperature. The AC conductivity master curve was obtained for the highest conducting sample when scaled vertically by σ and horizontally by ω .

Simultaneous simulation of microhollow cathode discharge and its sustained discharge with split third electrodes

Simultaneous simulation of microhollow cathode discharge (MHCD) and its sustained discharge in argon is attempted with a two dimensional, self-consistent, continuum fluid model. Bell-shape enlarged volume discharge is simulated with a single third electrode, and further expansion in the discharge volume of the sustained discharge is demonstrated with split third electrodes. In the sustained discharge region, monomer metastable is a dominant species and the number density of dimer ions is higher than that of monomer ions. The expansion in the sustained discharge does not alter the characteristics of the MHCD observed with a single electrode. But electrons and metastables in the sustained discharge region are expanded when the third electrodes are turned on. The simulated distribution of metastable species shows a rake-like structure that is also observed in experiments. As the pressure increases, a ratio of dimer-to-monomer metastable number density increases.

Monte Carlo simulations of Kα source generated by hot electrons-nanobrush target interactions

We focus on the transport processes from hot electrons to Kα x-ray emission in a copper nanobrush target. The physics on the enhancement of Kα photon yield and conversion efficiency from laser to Kα x-ray ηL→Kα is studied by combining Monte Carlo simulations and previous particle-in-cell simulation results. Simulation results show that Kα photon yield and electron-Kα photon conversion efficiency ηe−→Kα from nanobrush targets rise gradually and then stay nearly constant. Kα photon yield from the structured nanobrush target increases with peak number density n0, but the yield is a little less than that from the same-size planar target when the electron temperature T=400 keV and n0=1021 cm−3. It is because the number density of atoms and ions in the nanobrush target is almost one half of the foil target. Compared to the planar target, Kα photons after the nanobrush target are more than those before the target. Because it is easier for the electrons to enter the structured target surface, and Kα x-ray source is produced in the deeper position of the structured nanobrush target. Considering the realistic number of hot electrons produced by laser-nanobrush and -planar targets interaction, Kα photon yield in nanobrush targets has a significant enhancement of over 2–6 folds relative to laser-foil irradiation. The yield and ηL→Kα from the nanobrush target are, respectively, 5.42×109 sr−1 and 7.32×10−5 when laser strength Iλ2≈2×1018 W cm−2 μm2. The yield and ηL→Kα decrease gradually with the laser strength, but the values are always higher than that from the planar target. Therefore, the laser-nanobrush target interaction can produce brighter and smaller-size Kα photon source, compared to a planar target.

Ionic transport on composite polymers containing covalently attached and absorbed ionic liquid fragments

The ionic transport of five supported ionic liquid-like phases (SILLPs) based on 1-butyl imidazolium ion covalently attached to a polymeric matrix has been analysed by means of electrochemical impedance spectroscopy (EIS) using the electrode polarization analysis. The structure of three of the SILLPs contains variable amounts of 1-butyl-3-methyl imidazolium chloride (BMIM[Cl]) strongly absorbed on the functional polymeric surfaces. The impedance spectra of the SILLPs show different ionic conductivity processes at different regions of the spectra. At higher frequency, the high conductivity observed is associated to the bis-((trifluoromethyl)sulfonyl)imide) (NTf2−) anion mobility. The ionic conductivity of SILLPs is increased up to 3 orders of magnitude in the presence of BMIM[Cl]. In this case, the highest ionic conductivity obtained was 2.56×10−3S/cm at 30°C and 1.3×10−2S/cm at 80°C. The experimental results show than the variation of ionic conductivity with the temperature is of VFT type. From the maximum loss tangent the inverse of Debye length has been obtained being 100 times higher when free bulk BMIM[Cl]is absorbed into the polymeric matrix. Finally the electrode polarization analysis overestimates the free ion diffusivity while underestimates the free ion number density.

Influence of transport parameters on conductivity of lithium perchlorate-doped poly(vinyl alcohol)/chitosan composites

This article focuses on the calculation of transport parameters (number density of ions and time travel of ions between sites, mobility, diffusion coefficient, and number of transitions per unit time) of the lithium perchlorate (LiClO4)-doped poly(vinyl alcohol)/chitosan (PVA/CS) composites using Rice and Roth model. The thermal study reveals a decrease in glass transition temperature for LiClO4-doped PVA/CS composites. The highest ionic conductivity of 3 × 10−6 S cm−1 at room temperature is observed for the 20 wt% LiClO4-containing composite. The temperature-dependent conductivity follows Arrhenius relation and lowest activation energy of 0.153 eV is observed for highest conducting sample. The mechanical properties such as Young’s modulus, stiffness, and tensile strength decreases and its percentage elongation at break increases with increase in LiClO4-doping level in PVA/CS polymer matrix. The scanning electron microscopic images exhibit smooth and homogeneous surface of PVA/CS composite.