Charged Particle Density Research Articles

Ionization waves in the PK-4 direct current neon discharge

The PK-4 system is a micro-gravity dusty plasma experiment currently in operation on-board the International Space Station. The experiment utilizes a long DC discharge in neon or argon gases. We apply our 2D particle-in-cell with Monte Carlo collisions discharge simulation to compute local plasma parameters that serve as input data for future dust dynamics models. The simulation includes electrons, Ne+ ions, and Ne m metastable atoms in neon gas and their collisions at solid surfaces including secondary electron emission and glass wall charging. On the time scale of the on-board optical imaging, the positive column appears stable and homogeneous. On the other hand, our simulations show that on microsecond time scales the positive column is highly inhomogeneous: ionization waves with phase velocities in the range between 500 m s−1 and 1200 m s−1 dominate the structure. In these waves, the electric field and charged particle densities can reach amplitudes up to 10 times of their average value. Our experiments on ground-based PK-4 replica systems fully support the numerical findings. In the experiment, the direction of the DC current can be alternated, which has been found to favor dust particle chain formation. We discuss possible mechanisms for how the highly oscillatory plasma environment contributes to the dust particle chain formation.

Modeling characterisation of a bipolar pulsed discharge

We apply particle based kinetic simulations to explore the characteristics of a low-pressure gas discharge driven by high-voltage (∼kV) pulses with alternating polarity, with a duty cycle of ≈ 1% and a repetition rate of 5 kHz. The computations allow tracing the spatio-temporal development of several discharge characteristics, the potential and electric field distributions, charged particle densities and fluxes, the mean ion energy at the electrode surfaces, etc. As such discharges have important surface processing applications, e.g. in the treatment of artificial bones, we analyse the time-dependence of the flux and the mean energy of the ions reaching the electrode surfaces, which can be both conducting and dielectric. Our investigations are conducted for argon buffer gas in the 40–140 Pa pressure range, for 1–5 cm electrode gaps and voltage pulse amplitudes ranging between 600 V and 1200 V.

PEDOT:PSS nano-particles in aqueous media: A comparative experimental and molecular dynamics study of particle size, morphology and z-potential

PEDOT:PSS is the most widely used conducting polymer in organic and printed electronics. PEDOT:PSS films have been extensively studied to understand the morphology, ionic and electronic conductivity of the polymer. However, the polymer dispersion, which is used to cast or spin coat the films, is not well characterized and not well understood theoretically. Here, we study in detail the particle morphology, size, charge density and zeta potential (z-potential) by coarse-grained MD simulations and dynamic light scattering (DLS) measurements, for different pH levels and ionic strengths. The PEDOT:PSS particles were found to be 12 nm–19 nm in diameter and had a z-potential of −30 mV to −50 mV when pH was changed from 1.7 to 9, at an added NaCl concentration of 1 mM, as measured by DLS. These values changed significantly with changing pH and ionic strength of the solution. The charge density of PEDOT:PSS particles was also found to be dependent on pH and ionic strength. Besides, the distribution of different ions (PSS−, PEDOT+, Na+, Cl−) present in the solution is simulated to understand the particle morphology and molecular origin of z-potential in PEDOT:PSS dispersion. The trend in change of particle size, charge density and z- potential with changing pH and ionic strength are in good agreement between the simulations and experiments. Our results show that the molecular model developed in this work represents very well the PEDOT:PSS nano-particles in aqueous dispersion. With this study, we hope to provide new insight and an in-depth understanding of the morphology and z-potential evolution in PEDOT:PSS dispersion.

Study of charged-particle multiplicity fluctuations in pp collisions with Monte Carlo event generators at the LHC

Proton–Proton ([Formula: see text]) collisions at the Large Hadron Collider (LHC) are simulated in order to study events with a high local density of charged particles produced in narrow pseudorapidty windows of [Formula: see text] = 0.1, 0.2, and 0.5. The [Formula: see text] collisions are generated at center of mass energies of [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] TeV, i.e., the energies at which the LHC has operated so far, using PYTHIA and HERWIG event generators. We have also studied the average of the maximum charged-particle density versus the event multiplicity for all events, using the different pseudorapidity windows. This study prepares for the multi-particle production background expected in a future search for anomalous high-density multiplicity fluctuations using the LHC data.

Rydberg Level Shift due to the Electric Field Generated by Rydberg Atom Collision Induced Ionization in Cesium Atomic Ensemble

We experimentally studied the Rydberg level shift caused by the electric field, which is generated by Rydberg atom collision induced ionization in a cesium atomic ensemble. The density of charged particles caused by collisions between Rydberg atoms is changed by controlling the ground-state atomic density and optical excitation process. We measured the Rydberg level shift using Rydberg electromagnetically-induced-transparency (EIT) spectroscopy, and interpreted the physical origin using a semi-classical model. The experimental results are in good agreement with the numerical simulation. These energy shifts are important for the self-calibrated sensing of microwave field by the employing of Rydberg EIT. Moreover, in contrast to the resonant excitation case, narrow-linewidth spectroscopy with high signal-to-noise ratio would be useful for high-precision measurements.

Controllable synthesis of terminal carboxyl hyperbranched polyester and their retarding effect on concrete

Concrete retarders could efficiently extend the hydration time of cement and maintain the plasticity of concrete slurry. However, some inherent shortcomings, such as a short setting time and poor compatibility, severely limits their application. To solve these problems, in this work, a series of carboxyl-terminated hyperbranched polymers (CTHP) were controllably synthesized and their retarding effects on the concrete setting were investigated. The results showed that the final setting time of concrete was increased by nearly 4 times as the addition amount of third generation CTHP was 1.5%, demonstrating an excellent retarding effect. Furthermore, the compressive strength was increased by 43% after 7 d of curing. The results of resistivity and Zeta potential demonstrated that CTHP could change the surface charge density of cement particles and affect the flocculation of cement particles and thus extend the retarding time. The results of Tg、XRD and SEM demonstrated that the CTHP could induce a decrease in the content of Ca(OH)2 and an increase in the content of ettringaite (AFt) during the hydration procedure, drastically enhancing the strength of the concrete. These CTHP would demonstrate the enormous potential to commercial concrete for the rapid demand in the engineering field.

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.

Model predictions of charge particle densities and multiplicities in the forward region at 7 TeV

We simulate proton–proton interactions to study densities and multiplicities of charged particles at center-of-mass energy, [Formula: see text] TeV in the forward region and compare predictions with experimental findings of LHCb detector. We use different event generators: Sibyll2.3c, EPOS (1.99 and LHC tunes), and DPMJETIII for the simulations. The kinematic region for momentum [Formula: see text], transverse momentum [Formula: see text] and [Formula: see text] in pseudorapidity is kept same as in the LHCb experiment for forward region. Predictions of different models and experimental data are presented and compared as a function of transverse momentum and pseudorapidity.

Investigation of Arc Erosion Mechanism for Tin Dioxide-Reinforced Silver-Based Electrical Contact Material Under Direct Current

To get an in-depth insight into the arc erosion mechanism for tin dioxide-reinforced silver-based (Ag-SnO2) contact material, the contact pairs made of Ag-4wt%SnO2 contact material were, respectively, performed for 20,000 switching operations under the direct currents of 19 A and 29 A and the voltage of 12 V, together with the electrode gap of 4 mm. The eroded surfaces and cross-sectional morphologies and the chemical compositions were characterized by scanning electron microscopy equipped with an energy dispersive spectrometer (EDS). The results show that there is a deep erosion pit at the cathode and an apparent protrusion at the anode, suggesting that a serious material transfer generates from cathode to anode. The EDS results show that the Sn contents at the protrusion and at the region around the crater are below 0.75 wt.% and 4 wt.%, respectively. This reveals that SnO2 undergoes severe evaporation during electrical contact testing. Moreover, arc stability decreases with increasing the load current, and the Ag-SnO2 contact material has larger arc power (make arc: 68.2 J/s; break arc: 58.53 J/s at 29 A) as compared to Ag-TiB2 contact material (make arc: 62.85 J/s; break arc: 50.01 J/s at 29 A). As a result, it is thought that SnO2 evaporation reduces Ag dissipation, thus shortening the lasting time of the make arc. However, the emission current is increased owing to the low work function of SnO2, which further promotes the improvement in the density of the charged particles, thereby enhancing the arc power. Additionally, the large density of charged particles can sustain arc burning for a longer time, resulting in an extended break arc duration.

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.

A hybrid approach for corona discharge in needle electrode configuration: in a large-scale space

Needle electrodes are widely used as the discharge electrode in charged particle-generating apparatus to study discharge characteristics due to their high efficiency. However, for the charged particle distribution of needle electrode corona discharge in a large-scale space (tens or even hundreds of centimeters), there is still a lack of an effective numerical simulation method. To solve this problem, a hybrid approach based on the combination of a hydrodynamic fluid model and an ion flow transport equation (ion drift model, based on the Kaptzov hypothesis) is put forward in this paper. The principle and implementation of the proposed method is introduced in detail. Further, the good consistency of the numerical simulation and a series of experiments under various applied voltages with two type sphere (radius 25 cm) apparatus, by comparing the charged particle density and discharge current, has demonstrated the accuracy and feasibility of the hybrid approach. This research provides an approach for the further study of corona discharge in a large-scale space, and implies the precise control potential in the application of low-temperature plasma, such as plasma material treatment, water treatments, gas disposal and so on.

Effects of charge density and molecular weight of papermaking sludge-based flocculant on its decolorization efficiencies

The charge densities (CD) and molecular weights (MW) of the flocculants are closely related to their application performances, but seldom researches focus on the effects of flocculant CD and MW on decolorization efficiencies. Herein, a series of flocculants with various CD and MW levels, named as PBF1–9, were designed and synthesized from papermaking sludge. The physicochemical characteristics of the PBF1–9 were measured by fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS) and particle charge density analyzer (PCD). The efficiencies of PBF1–9 were studied in the reactive blue (RB) dye removals by flocculation under different process conditions. The operation costs of the flocculants were evaluated at their optimal dosages. Also, the pH-independences and ion-tolerances of the aforementioned flocculants were studied in terms of the molecular levels. The experimental results exhibited that the flocculants CD or MW values were relevant to their flocculation behaviors and operation costs. CD values played a dominant role in color removal efficiencies and the costs, whereas MW values were critical to the floc structure. The pH or ion-independences of the flocculants were significantly dependent on the CD and MW values. However, some conclusions, conflicted with prior studies, were observed in this work. For instance, flocculant with the highest CD and MW levels was not the most effective one in enduring pH variation and the coexisting ions. The floc properties, including floc size, resistance and recovery ability, were relatively insensitive to flocculant intrinsic CD and MW levels when the flocculants were used at their optimal dosages. Furthermore, the possible relevance between CD or MW levels and the flocculation mechanisms have been proposed in this work. Exploring the effects of flocculants CD and MW levels could precisely control the flocculant characteristics to achieve satisfactory decontamination efficiencies with low costs.

Underlying event measurements in p+p collisions at s=200 GeV at RHIC

Particle production sensitive to non-factorizable and non-perturbative processes that contribute to the underlying event associated with a high transverse momentum ($p_{T}$) jet in proton+proton collisions at $\sqrt{s}$=200 GeV is studied with the STAR detector. Each event is divided into three regions based on the azimuthal angle with respect to the highest-$p_{T}$ jet direction: in the leading jet direction ("Toward"), opposite to the leading jet ("Away"), and perpendicular to the leading jet ("Transverse"). In the Transverse region, the average charged particle density is found to be between 0.4 and 0.6 and the mean transverse momentum, $\langle p_{T}\rangle$, between 0.5-0.7 GeV/$c$ for particles with $p_{T}$$>$0.2 GeV/$c$ at mid-pseudorapidity ($|\eta|$$<$1) and jet $p_{T}$$>$15 GeV/$c$. Both average particle density and $\langle p_{T}\rangle$ depend weakly on the leading jet $p_{T}$. Closer inspection of the Transverse region hints that contributions to the underlying event from initial- and final-state radiation are significantly smaller in these collisions than at the higher energies, up to 13 TeV, recorded at the LHC. Underlying event measurements associated with a high-$p_{T}$ jet will contribute to our understanding of QCD processes at hard and soft scales at RHIC energies, as well as provide constraints to modeling of underlying event dynamics.

Formation of solitary structures and envelope solitons in electron acoustic wave in inner magnetosphere plasma with suprathermal ions

AbstractThe propagation of electron acoustic solitary waves is investigated in magnetized two‐temperature electron plasma with supra‐thermal ion. By using the reductive perturbation technique, the Korteweg de‐Vries (KdV) equation is derived. Later solving this equation, a solitary wave solution has been derived. These are mainly in astrophysical plasmas where changes of local charge density, temperature, and energy of particles produce considerable effects on the plasma system. The effects of supra‐thermality, density, and Mach number on solitary structures are studied in detail. The results show that the supra‐thermal index (κ) and ion to electron temperature ratio (σ) alters the regime where solitary waves may exist. While studying the solitary profile for different parametric variation some interesting conclusion can be drawn; it is shown that the solitary profile becomes flatter. This can be due to the thermal energy associated with the hot electrons. However, with the increase in ion density with respect to the cold electrons' density, the solitary waves become steeper and sharper. This is due to the comparatively heavier mass of ions. The density of cold electron also increases the solitary structures in a similar manner. The higher the density of cold electrons, sharper will be the profile. The above findings will be helpful in understanding many astrophysical phenomena and data obtained by space missions. For a further study, we keep the investigation of the formation of other kinds of stationary structures like shocks, double layers, etc.

Charged Particle Oscillations in Transient Plasmas Generated by Nanosecond Laser Ablation on Mg Target

The dynamics of a transient plasma generated by laser ablation on a Mg target was investigated by means of the Langmuir probe method and fractal analysis. The empirical data showcased the presence of an oscillatory behavior at short expansion times (&lt;1 μs) characterized by two oscillation frequencies and a classical behavior for longer evolution times. Space- and time-resolved analysis was implemented in order to determine main plasma parameters like the electron temperature, plasma potential, or charged particle density. In the motion fractal paradigm, a theoretical model was built for the description of laser-produced plasma dynamics expressed through fractal-type equations. The calibration of such dynamics was performed through a fractal-type tunneling effect for physical systems with spontaneous symmetry breaking. This allows both the self-structuring of laser-produced plasma in two structures based on its separation on different oscillation modes and the determination of some characteristics involved in the self-structuring process. The mutual conditionings between the two structures are given as joint invariant functions on the action of two isomorph groups of SL(2R) type through the Stoler-type transformation, explicitly given through amplitude self-modulation.

Influence of operating parameters on high‐pressure microhollow cathode discharge with a cylindrical hole

AbstractAs a promising candidate for generating large‐scale plasma at high pressure, microhollow cathode discharge (MHCD) with a cylindrical hole has been numerically simulated at an argon pressure higher than 50 Torr by a two‐dimensional particle‐in‐cell Monte Carlo collision method. Results indicate that MHCD is operated in a confined phase at the beginning, which transits to an expanded phase and reaches a steady‐state at about 160 ns. In a steady‐state MHCD, the majority of electrons have a low energy of several eV, and some electrons have a high energy up to 480 eV. High‐energy electrons mainly appear adjacent to the cathode surface. With increasing applied voltage, there is a transition from the confined phase to the expanded phase for a steady‐state MHCD. Moreover, maximal density of charged particles increases for the expanded phase with increasing applied voltage and argon pressure or decreasing hole diameter. Besides, discharge morphology has been investigated in detail with varying operating parameters. All these results have been compared with those simulated by the fluid model.

Discharge properties of helicon oxygen plasma in the source and expansion chambers

In this paper, a study of a helicon discharge with O2 gas, operating at 13.56 MHz frequency and powers between 0–1500 W and pressure between 3 × 10−3 and 8 × 10−3 mbar is presented. Measurements of plasma parameters were made in the plasma production chamber as well as in the downstream expansion chamber. In the source chamber, transition from E to H and finally to W mode appears by increasing the input radio frequency (RF) power. To the best of our knowledge, this is the first detailed report of Helicon mode transition in Oxygen discharge. Mode transition is further confirmed by studying the radial density profile and by external matching circuit parameters measurement. Comparison of Langmuir probe I-V measurements and electron energy distribution function (EEDF) in source and expansion chambers confirms formation of negative ions. Negative ion fraction is measured in the expansion chamber by using two-probe method and densities of charged particles (electrons, positive and negative ions) are calculated using standard Langmuir probe theory and quasi-neutrality condition.

Surface charging parameters of charged particles in symmetrical electrolyte solutions.

Surface electric charge of dispersed particles is an essential determinant of physicochemical properties, coagulation and flocculation processes, and stability of colloidal solutions. Size-dependence of surface potential, charge density, and total surface charge of suspended charged particles has recently received attention in the literature. Despite the clear significance of understanding such dependence, very few studies have been devoted to this problem, with contradictory results of the relationship type. Currently, there is no analytical formula to represent explicit relationships between surface charging parameters and particle size. This research work is directed at development of accurate physics-based formulas for quantification of curvature-dependence of surface potential, surface charge density, and total surface charge for cylindrical and spherical charged particles immersed in a symmetrical electrolyte solution. First, a non-dimensional approach is adopted to simplify the problems, overcoming the difficulty of dealing with multiple influential variables. Then, to reduce the degrees of freedom of the problems under consideration, Gauss's law is combined with the condition of electro-neutrality in an electrical double layer (EDL). Next, the resulting complex integral equations are solved to construct characteristic curves and to express the dimensionless surface charging parameters explicitly as a function of the dimensionless particle radius. The new theoretical expressions are founded on approximate analytical and numerical solutions of the nonlinear Poisson-Boltzmann (PB) equation in cylindrical and spherical geometries. Afterwards, the solutions of the non-dimensionalized problems are dimensionalized to derive accurate explicit closed-form expressions, describing how surface charging parameters are related to the radius of a charged particle, properties of the solution, and thermodynamic conditions. These analytical formulas enable researchers to properly determine surface potential, surface charge density, total surface charge, and radius of dispersed particles by characterizing only one of them. Finally, the validity of the commonly-held hypothesis that surface charge density is independent of particle size is examined at the end of this study.

Фазовые превращения в азотированном феррованадии под действием мощного пучка ионов углерода

The phase and elemental composition of the near-surface layer of nitrided ferrovanadium irradiated with a high-power ion beam has been investigated by XRD and SEM methods. The impact of a powerful beam of the Temp-4M setup with an energy of carbon ions of 250 keV at a radiation pulse duration 10–7 s and a power density of charged particles qi ≥ 106 W/cm2 causes melting of the Fe-VN composite and partial evaporation of elements with a high vapor pressure from the surface layer. High-speed solidification of the melt on the surface of the Fe-VN target leads to the formation of highly dispersed vanadium nitride and tetragonal carbide Fe23C6 in the modified layer. After irradiation of Fe-VN with a high-power beam with qi ≈ 107 W/cm2 at a dose of ~ 1015 cm–2, a violation of the translational invariance of the distribution of intercalated carbon atoms, a structural redistribution of Fe and V atoms, and the formation of X-ray amorphous microliquations of Fe-V and gas-carbon complexes are observed in the modified layer.

Effects of reflection of electrons and negative ions on magnetized electronegative and collisional plasma sheath

The effects of the reflection of electrons and negative ions in magnetized electronegative and collisional plasma sheath on the Bohm criterion and the sheath structure are numerically investigated. The Bohm criterion expression of the sheath with considering the reflection of electrons and negative ions is derived theoretically. The lower limit of ion Mach number versus parameters and the distribution curve of charged particle density in sheath are obtained by numerical simulation when Boltzmannian model and reflection model are applied to electrons and negative ions. The results show that the upper limit of ion Mach number is identical to that of Boltzmannian model, but their lower limit expressions are different. The lower limit of ion Mach number in the reflection model is also related to the wall potential, and with the increase of the wall potential, ion Mach number first increases and then remains unchanged after reaching the same value as that from Boltzmannian model, and the speeds of their reaching the maximum values are different due to the difference in sheath edge negative ion concentration and temperature. In both Boltzmannian and the reflection model, the lower limit of the ion Mach number decreases with the concentration of the negative ion at the sheath edge increasing and the negative ion temperature decreasing, but the maximum value is smaller in the reflection model. The lower limit of ion Mach number for each of the two models increases with sheath edge electric field increasing, but increases faster and the final value is larger in Boltzmannian model. The lower limit of ion Mach number for each of the two models decreases with the increase of collision parameter or magnetic field angle, but decreases faster in Boltzmannian model with the increase of collision parameter or magnetic field angle. The lower limits of ion Mach number in the two models tend to be the same with the increase of magnetic field angle. When the wall potential is small, the reflection of electrons and negative ions has a great influence on the sheath structure. When the wall potential is large, the reflection of electrons and negative ions have little effect on the density distribution of charged particles in the sheath.