Number Density Of Charged Particles Research Articles

Electromagnetic Response of Clustered Charged Particles

Electromagnetic response of clustered charged particles is the foundation of electromagnetic wave interaction with various natural phenomena, such as sandstorm, cloud, and volcano eruption. Previous studies usually employed assumption of independent charged particles, without considering the coupling between them. Here, we build up a general numerical model considering the multiple scattering effect, and test it with a charged two- and four-particle system. The numerical results show that independence assumption fails, while the number density of clustered charged particles is getting larger. This work may pave the way for deeper understanding on the electromagnetic interaction of clustered charged particles.

Effects of additive NaI on electrodeposition of Al coatings in AlCl3-NaCl-KCl molten salts

Effects of NaI as an additive on electrodeposition of Al coatings in AlCl3-NaCl-KCl (80-10-10 wt-%) molten salts electrolyte at 150 °C were investigated by means of cyclic voltammetry, chronopotentiometry, scanning electron microscopy and X-ray diffraction (XRD). Results reveal that addition of NaI in the electrolyte intensifies cathodic polarization, inhibits growth of Al deposits and increases number density of charged particles. The electrodeposition of Al coatings in the AlCl3-NaCl-KCl molten salts electrolyte proceeds via three-dimensional instantaneous nucleation which however exhibits irrelevance with NaI. Galvanostatic deposition results indicate that NaI could facilitate the formation of uniform Al deposits. A compact coating consisting of Al deposits with an average particle size of 3 µm was obtained at a current density of 50 mA·cm−2 in AlCl3-NaCl-KCl molten salts electrolyte with 10 wt-% NaI. XRD analysis confirmed that NaI could contribute to the formation of Al coating with a preferred crystallographic orientation along (220) plane.

Underlying event properties in pp collisions at sqrt{s} = 13 TeV

This article reports measurements characterizing the Underlying Event (UE) associated with hard scatterings at midrapidity (|η| < 0.8) in pp collisions at sqrt{s} = 13 TeV. The hard scatterings are identified by the leading particle, the charged particle with the highest transverse momentum ( {p}_{mathrm{T}}^{mathrm{leading}} ) in the event. Charged-particle number-densities and summed transverse-momentum densities are measured in different azimuthal regions defined with respect to the leading particle direction: Toward, Transverse, and Away. The Toward and Away regions contain the fragmentation products of the hard scatterings in addition to the UE contribution, whereas particles in the Transverse region are expected to originate predominantly from the UE. The study is performed as a function of {p}_{mathrm{T}}^{mathrm{leading}} with three different pT thresholds for the associated particles, {p}_{mathrm{T}}^{mathrm{track}} > 0.15, 0.5, and 1.0 GeV/c. The charged-particle density in the Transverse region rises steeply for low values of {p}_{mathrm{T}}^{mathrm{leading}} and reaches a plateau. The results confirm the trend that the charged-particle density in the Transverse region shows a stronger increase with sqrt{s} than the inclusive charged-particle density at midrapidity. The UE activity is increased by approximately 20% when going from 7 TeV to 13 TeV pp collisions. The plateau in the Transverse region (5 < {p}_{mathrm{T}}^{mathrm{leading}} < 40 GeV/c) is further characterized by the probability distribution of its charged-particle multiplicity normalized to its average value (relative transverse activity, RT) and the mean transverse momentum as a function of RT. Experimental results are compared to model calculations using PYTHIA 8 and EPOS LHC. The overall agreement between models and data is within 30%. These measurements provide new insights on the interplay between hard scatterings and the associated UE in pp collisions.

Characteristics of a radio-frequency cold atmospheric plasma jet produced with a hybrid cross-linear-field electrode configuration

Cold atmospheric plasma (CAP) jet has wide applications in various fields including advanced materials synthesis and modifications, biomedicine, environmental protection and energy saving, etc. Appropriate control on the volume, temperature and chemically reactive species concentrations of the CAP jet is of great importance in actual applications. In this paper, an radio-frequency atmospheric-pressure glow discharge (RF-APGD) plasma generator with a hybrid cross-linear-field electrode configuration is proposed. The experimental results show that, with the aid of the copper mesh located at the downstream of the traditional co-axial-type plasma generator with a cross-field electrode configuration, a linear field between the inner powered electrode of the traditional plasma generator and the copper mesh can be established. This liner-field can, to some extent, enhance the discharges at the upstream of the copper mesh, resulting in small increments (all less than 12.5%) of the species emission intensities, electron excitation temperatures and gas temperatures by keeping other parameters being unchanged. And due to the intrinsic transparent and conducting features of the grounded copper mesh to the gas flowing, electric current and heat flux of the plasma plumes, a plasma region with higher concentrations of chemically reactive species and larger plasma plume diameters is obtained at the downstream of the grounded copper mesh on the same level of the gas temperature and electron excitation temperature compared to those of the plasma free jet. In addition, the charged particle number densities at the same downstream axial location of the grounded copper mesh decrease significantly compared to those of the plasma free jet. This means that the copper mesh is also, to some extent, helpful for separating the chemically reactive neutral species from the charged particles inside a plasma environment. The preceding results indicate that the cross-linear-field electrode configuration of the plasma generator is an effective approach for tuning the characteristics of the RF-APGD plasma jet in order to obtain an appropriate combination of the plasma jet properties with higher chemically reactive species concentrations, especially relative higher number densities of neutral species, larger plasma volumes and lower gas temperatures.

Jet properties in PbPb and pp collisions at sqrt{s_{mathrm{N};mathrm{N}}}=5.02 TeV

Modifications of the properties of jets in PbPb collisions, relative to those in pp collisions, are studied at a nucleon-nucleon center-of-mass energy of sqrt{s_{mathrm{N};mathrm{N}}}=5.02 TeV via correlations of charged particles with the jet axis in relative pseudorapidity (Δη), relative azimuth (Δϕ), and relative angular distance from the jet axis varDelta mathrm{r}=sqrt{{left(varDelta eta right)}^2+{left(varDelta phi right)}^2} . This analysis uses data collected with the CMS detector at the LHC, corresponding to integrated luminosities of 404 μb−1 and 27.4 pb−1 for PbPb and pp collisions, respectively. Charged particle number densities, jet fragmentation functions, and jet shapes are presented as a function of PbPb collision centrality and charged-particle track transverse momentum, providing a differential description of jet modifications due to interactions with the quark-gluon plasma.

Spatially resolved electron density and electron energy distribution function in Ar magnetron plasmas used for sputter-deposition of ZnO-based thin films

Langmuir probe and trace rare gases optical emission spectroscopy were used to analyze the spatial structure of the electron density and electron energy distribution function (EEDF) in a cylindrical Ar magnetron plasma reactor used for sputter-deposition of ZnO-based thin films. While a typical Bessel (zero order) diffusion profile was observed along the radial direction for the number density of charged particles at 21 cm from the ZnO target, a significant rise of these populations with respect to the Bessel function was seen in the center of the reactor at 4 cm from the magnetron surface. As for the EEDF, it was found to transform from a more or less Maxwellian far from the target to a two-temperature Maxwellian with a depletion of high-energy electrons where magnetic field confinement effects become important. No significant change in the behavior of the electron density and EEDF across a wide range of pressures (5–100 mTorr) and self-bias voltages (115–300 V) was observed during magnetron sputtering of Zn, ZnO, and In2O3 targets. This indicates that sputtering of Zn, In, and O atoms do not play a very significant role on the electron particle balance and electron heating dynamics, at least over the range of experimental conditions investigated.

Computer modelling of electronegative plasma sheaths and their mutual interaction

Our paper focuses on investigation of sheath structures formed in the vicinity of biased solid objects immersed in electronegative plasma. In Particular, phenomena during mutual interaction of several plasma sheaths were investigated. Our results show the manner in which the sheath of a cylindrical probe is affected by the presence of another cylindrical probe with smaller radius in its surroundings. Number density of charged particles, electric field intensity and fluxes of charged particles on the probes were observed to quantify the mutual interaction of sheaths. The study was done by means of the 2D particle-in-cell model with Monte Carlo treatment of collisions.

Numerical Study on Acceleration and Deceleration Mechanism of Weakly Ionized Plasma Flowing Supersonically Through Open Field Line

We study supersonic flow of rarefied weakly ionized plasma at diverging magnetic field. While the flows of ions and neutral are treated by particle-based direct simulation Monte Carlo method, the electron is treated as a fluid, i.e., we carried out hybrid simulation. We calculate number density, velocity, temperature, and electric potential of charged particles and neutrals when the arc plasma flows out of the uniform magnetic field into lower pressure region in a steady state. We find the velocity increase just after passing the open magnetic field line, followed by deceleration due to collisions with residual molecules. We also find the temperature increase during the deceleration. In this acceleration/deceleration phenomena, the velocity difference between the neutrals and charged species are found, which also changes the electric potential. We discuss the mechanisms of potential formation along the plasma flow mainly by the pressure difference and the friction force between the charged particles and neutral species. The numerical results are, at least qualitatively, consistent with our previous experimental results.

Studying Heavy Ion Collisions Using Methods From Cosmic Microwave Background (CMB) Analysis

We present and discuss a framework for studying the morphology of high- multiplicity events from relativistic heavy ion collisions using methods commonly em- ployed in the analysis of the photons from the Cosmic Microwave Background (CMB). The analysis is based on the decomposition of the distribution of the number density of (charged) particles expressed in polar and azimuthal coordinates into a sum of spherical harmonic functions. We present an application of the method exploting relevant symme- tries to the study of azimuthal correlations arizing from collective flow among charged particles produced in relativistic heavy ion collisions. We discuss perspectives for event- by-event analyses, which with increasing collision energy will eventually open entirely new dimensions in the study of ultrarelaticistic heavy ion reactions.

On the role of ion number density disturbances in VLF sprite relaxation

VLF sprites are identified by VLF signal perturbations due to upward electric discharges which lead to an appearance of vertical plasma columns. An analytical relaxation model for the charged particle number densities has been developed in order to explain the observations of very strong VLF sprites. A rapid increase in the negative number density during the first a few seconds after the onset of relaxation has been determined. Employing the developed model, the electron conductivity, the positive ion conductivity, and the negative ion conductivity have been calculated. The efects of the disturbance in the ion number density result in an increase in the relaxation time for VLF sprites in the middle atmosphere.

Considerations on the role of the Hall current in a laboratory-model thruster

Hall current magnitude and spatial distribution are presented for the plasma discharge in the University of Michigan/Air Force Research Laboratory P5 5 kW laboratory-model Hall thruster. The data are calculated from direct, probe-based measurements of the electric field, static magnetic field, and charged particle number density. Thruster discharge voltage was fixed at 300 V and two current levels investigated: 5.4 A (1.6 kW) and 10 A (3 kW). The results indicate that, for both cases, the bulk of the Hall current is confined to a region centered several millimeters upstream of the exit plane and is asymmetric about the centerline of the discharge channel. At 1.6 kW, the axial plasma potential drop occurs over a much shorter distance, resulting in a more sharply peaked Hall current zone, as compared to the 3-kW case. Comparison of the Hall current and ion number density distribution suggests that the azimuthal electron drift may contribute significantly to the ionization process in the discharge channel. Integration of the Hall current over the entire discharge volume yields total current values that are a factor of 3.5-4.6 times larger than the discharge current. Estimates of the self-magnetic field induced by the drifting electrons indicate no significant modification to the applied magnetic field during thruster operation, at the power levels considered. Using the Hall current density distribution derived from probe measurements, the electromagnetic body force on the ions was calculated and compared to measured engine thrust for both power levels.

Continuum plasma flow past a sphere

Flow of a collision-dominated weakly ionized gas over a solid sphere is investigated in the limit λm≪λD≪rp, where λm is the mean free path, λD is the Debye length, and rp is the sphere radius. Such flow is encountered in plasma heating of metallic/ceramic powders in rf plasma-aided manufacturing processes. The flow Reynolds number (Re) based on sphere diameter is in the intermediate range (Re∼5–100). The continuity, the momentum conservation, and the energy conservation equations for the neutrals and those for the charged particles are simultaneously solved with the Poisson’s equation for the self-consistent electric field. A model for production and recombination of the charged particles is incorporated in the formulation. The surface of the sphere is considered as a sink for the charged particles and is at the floating potential. A finite difference method is employed to solve the governing equations. The flow field, the temperature distributions, the charged particle number density variations are obtained and the heat transport to the sphere surface is determined for a range of flow Reynolds number. The effects of Reynolds number, the far field temperature, and the surface temperature on the electric sheath around the sphere surface and on the heat transport to the sphere, are delineated.

Thermal plasmas in material processing

Thermal plasmas are partially ionized gases at atmospheric pressures, characterized by temperatures in the range of 2000–20,000 K and charged particle number densities in the range of 1019–1021 per m3. Thermal plasmas are produced by plasma torches as a highly constricted jet. The high temperatures, enthalpies and heat fluxes in the plasma jet make it amenable to many chemical and metallurgical processes of industrial importance. The processing environment can be inert as in the case of argon or nitrogen plasmas or can be made reactive by introducing suitable gases. Reactive thermal plasma processing is a novel technique, wherein the plasma enters the reaction scheme, with ions and excited species opening up new channels. This technique is versatile in producing a wide variety of materials like oxides, carbides, borides, aluminides and coatings of diamond, superconductors and bioceramics. In this paper, the basic design of the plasma devices and some of the significant materials-related activities carried out recently at BARC are reported.

Langmuir Probe Determination of Charged Particle Number Density in a Flowing Afterglow Plasma

AbstractExperimental study of the electron and ion density determined by Langmuir probe is presented. The probe data have been obtained on FALP apparatus for electron (and ion) number densities ranging from 1012 m−3 to 1016 m−3, at electron temperatures equal to room temperature and also roughly ten times higher and at neutral pressures from 60 Pa to 150 Pa.The number densities of electrons for all measured probe data have been deduced from the electron current to the probe at the space potential and also by means of OML method from the electron current measured for positive probe with respect to the space potential. In the paper it is shown that in the flowing afterglow plasma the values of the electron density determined according both methods are in a good agreement and it is possible to take them as the reference number density for comparison with apparent ion densities obtained from the ion current.The number densities obtained from the ion currents in the ion accelerating region (negative probe with respect to the space potential) according to different applicable probe theories have been compared with reference value. It is found that the best agreement between the number densities evaluated from the electron current and from the ion current gives the theory of ion collection by Tichý et al. [16], which takes into account the collisions of ions with neutrals in the space charge sheath around the probe provided that the conditions correspond to the OML regime.

Effect of negative ions on electrical breakdown in a nonuniform air gap between a wire and a plane

Electrical breakdown of an axisymmetric, atmospheric pressure air gap between a wire and a plane has been investigated for a gap length of 0.5 mm. O− and O−2 have been identified as the negative ions affecting the discharge development in air, besides electrons and positive ions, and have been included in the electrical breakdown model. Five coupled two-dimensional transient partial differential equations describing the discharge evolution in the air gap have been solved using a finite difference algorithm developed earlier. Temporal development of the charged particle number densities, electrostatic potential, electric field, and current at both the electrodes is presented when the wire is negatively biased at 2500 V. The impact of negative ions on gap breakdown has been assessed by comparing the results of analyses with and without negative ions. It is concluded that the negative ions have negligible effect during the early stages of the discharge development. However, as the discharge evolves, the negative ions cause a net loss of electrons from the discharge. The effect is most pronounced away from the discharge axis, where peaks in the electron density occur as breakdown proceeds. Radial spread of discharge and current growth rate are relatively unaffected by the presence of negative ions, but the magnitude of total current at the electrodes has been found to decrease by a decade when the negative ions are present.

Extended two-dimensional analysis of electrical breakdown between a wire and a plane

The formation of a discharge between a wire and a plane has been simulated numerically through the development of large electron and positive ion number densities. When the number densities grow sufficiently large and equal a new region within the computational model is formed, within which the governing equations of the quasi-neutral region are solved for the common ion and electron number density and electric potential. Results for the temporal development of the quasi-neutral region, radial profiles of charged particle number density, electric potential, and electric field strength from discharge initiation to program termination are described. The quasi-neutral region is shown to develop first off of the discharge axis, above the wire-to-plane gap. Near the quasi-neutral region the electric field strength and electric potential are highly distorted and within the quasi-neutral region are greatly diminished.

Two-dimensional analysis of electrical breakdown in a nonuniform gap between a wire and a plane

Electrical breakdown of a gap between a wire (modeled as a hyperboloid) and a plane has been investigated numerically by solving the two-dimensional form of the diffusion flux equations for the charged particle number densities and Poisson’s equation for the self-consistent electric field. Electron impact ionization, thermal ionization, and three-body recombination have been considered as the charged particle production and loss mechanisms. The electrode surfaces are considered to be absorbing and the initial density of the particles is small, but nonzero. A gap length of 0.5 mm is investigated and the gas medium is air or argon at atmospheric pressure. The temporal development of the profiles of ion and electron number densities, potential and electric field, and current growth on both the electrodes are presented when the applied voltage is 1500 and 2500 V for both positive and negative wires. When the wire is negatively biased, the peaks in the radial distribution of both of the charged particle densities near the wire occur off the axis except during the very early part of the breakdown. With positive polarity, the electron density maximum always occurs on the discharge axis, while for ions it moves away from the axis, later in the transient, due to the reverse particle drift in the electric field from the negative polarity case. The discharge spreads farther out into the ambient (almost two times the gap length) when the wire is negatively biased than with positive polarity. The effect of charge separation on the externally applied electric field is significant at voltages 2500 V and higher. Ionization is greater in argon than in air for a fixed potential difference between the electrodes.

The Influence of Particles Interaction in Low‐Temperature Plasma on its Composition and Optical Properties

AbstractA model theory of the influence of particles interaction in plasma on its composition and optical properties is developed.The interaction of charged particles in plasma reduces the ionization energy of atoms and ions. The action of internal microfields in plasma on atoms and ions reduces the statistical weight of electron levels which affects the populations of excited states. The latter effect leads to an effective cutoff of partition functions and determines the behaviour of optical properties of plasma (of absorption coefficient and emissivity) at increased number densities of charged particles.The formulas are obtained for calculation of the continuous and discrete spectrum in plasma taking into account the particles interaction. A non‐monotonic dependence of optical plasma density upon number density of charged particles is quantitatively explained. A satisfactory agreement is obtained with a large number of experimental data some of which were considered to be contradictory.The method developed can be used for calculations in the field of atomic spectroscopy and low‐temperature plasma physics including increased densities of charged particles. The use of the formulas obtained in plasma diagnostics will enable one to avoid considerable errors.

Charged Particles in Sooting Flames II. Determination of the Fraction of Charged Soot

AbstractA new technique has been developed allowing the determination of the relative amounts of charged and neutral soot in fuel‐rich premixed low‐pressure flames. Results on C2H2 and C6H6 flames are reported and used, together with charged particle number densities, to calculate soot mass fractions and particle sizes. The occurrence of charged soot particles is discussed within the adopted mechanism of soot formation.

Hollow Probe for Measuring Ion Density in a Slightly Ionized Plasma Flow

In order to measure the number density of charged particles in a high speed flow on slightly ionized argon, the hollow electric collector probe has been shown to be useful. This work is to investigate effects of the dimension of hollow probes and the strength of applied electric field on capture of charged particles. The experimental results show that the lower aspect ratio (=the ratio of the distance between electrodes to the electrode length) and the higher applied electric field are effective for capturing all charged particles entering into the probe. Even when an ion number density is relatively high (≤10 13 cm -3 ), the hollow probe can be used for measurement of plasma density in a flowing plasma, though there are restrictions on minimum dimensions of probes and maximum strength of applied electric field.