Electron Number Density Distribution Research Articles

A spectroscopic investigation of stabilized dc argon arc at atmospheric pressure by power modulation technique

Spatial distribution of delayed responses of argon and hydrogen spectral line and continuum intensity to square power modulation was investigated in order to get better insight into the processes occurring in argon dc arc plasma. The power was abruptly changed between stationary values, 9 and 3.5 A. For these currents steady state radial distributions of electron number density, temperature and emission intensity were measured. On part of the discharge radial profiles the power drop and the power jump are both accompanied by intensity peaks which may be explained by displacement of the arc core axis and change in the arc core diameter during the power modulation.

A Spectroscopic Investigation of Spatial Symmetry of Radiation in the U-shaped DC Argon Plasma with Aerosol Supply

ABSTRACT Radial distributions of plasma parameters, temperature, and electron number density, together with radial distribution of analyte absorption and emission, were investigated in order to obtain insight into the radial symmetry of low-current (≤ 10 A), atmospheric pressure, argon stabilized arc with tangential introduction of the aerosol. For plasma diagnostics, several methods were used: measurements of Hβ line profile, absolute intensity measurements of the argon 430.01-nm line, and of the spectrally adjacent continuum and power interruption technique. It was found that the inevitable asymmetry in aerosol introduction has negligible influence on basic plasma parameters but influences considerably the spatial distribution of the analyte particle spectral absorption and emission.

Extreme polar cap density enhancements along magnetic field lines during an intense geomagnetic storm

Sounding measurements from the radio plasma imager (RPI) on the IMAGE satellite are used to derive electron number density distributions along magnetic field lines in the polar cap magnetosphere during an intense magnetic storm. It is shown that electron densities along magnetic field lines in the polar cap magnetosphere were greatly enhanced on both the dayside and nightside during the storm, compared to the electron density profiles measured during periods of lower geomagnetic activities. The electron density enhancements were observed extending to 7 Earth radii (RE) in altitude on the dayside, with the electron density value reaching about 10 cm−3 at 7 RE altitude. The observed density enhancements were likely due to the enhanced cleft ion fountain during the storm although some of nightside density enhancements might be caused by the increased ion outflows locally in the polar cap. The strongest electron density enhancements observed on the dayside are possibly further associated with storm‐time transport of plasma from the midlatitude ionosphere and plasmasphere to high latitudes, which manifests as a plasma plume intruding to dayside high latitudes as seen from total electron content (TEC) maps. With an enhanced source population supplied by the plasma plume, acceleration and heating processes in the dayside cusp/auroral region may produce a large flux of outflowing plasma along magnetic field lines while the outflowing plasma is convected anti‐sunward toward the polar cap. These processes lead to strongly enhanced cleft ion fountain and thus greatly raised electron densities at magnetospheric altitudes in the polar cap. The present study captures an event of a massive redistribution of the magnetospheric and ionospheric plasma during a geomagnetic storm caused by extreme solar wind/interplanetary magnetic field (IMF) conditions.

Spectroscopic diagnostics for evaluation of the analytical potential of argon + helium microwave-induced plasma with solution nebulization

An Ar + He mixed-gas microwave-induced plasma (MIP) has been investigated for use as an excitation source for optical emission spectrometry (OES) with solution nebulization. Regarding spectroscopic diagnostics via plasma temperatures and electron number density, the study compares excitation conditions in Ar, He and Ar + He plasma. Spatial emission profiles and radial distribution of electron number density have been determined to study energy transfer in the plasmas. The addition of He to Ar produces a plasma capable of ionizing metals with ionization potential in the range of 6–10 eV more efficiently than the pure Ar plasma. The best excitation conditions for metallic elements were obtained with the Ar + 20% He plasma due to increase of rotational temperature up to 3900 K and argon excitation temperature up to 7500 K as well as Mg II/Mg I line intensity ratio. The detection limits for ionic lines of some metals for the Ar + He mixed-gas plasma are 2–7 times lower than for Ar-MIP-OES.

Numerical Investigation for $\hbox{CF}_{4}$ Decomposition Using RF Low-Pressure Plasma

Among perfluorocompounds, is considered to be one of the most stable and difficult-to-decompose gases. We investigated the decomposition of CF4 using the inductively coupled plasma (ICP) reactor with radio frequency (RF) power supply, which was used for semiconductor cleaning process as well as decomposition. This technology was confirmed to achieve an extremely high efficiency and more economical system in comparison with the conventional system. The purpose of this paper is to perform numerical simulation of CF4 decomposition using RF low-pressure plasma. The experimental investigation of CF4 the decomposition was performed to validate the computed results, and the reaction products such as CO, CO2, and COF2 upon the CF4 decomposition were measured CO2 using a analyzer and a Fourier transform infrared spectrophotometer. Then, the numerical simulations of the CF4 decomposition using commercially available code were performed to obtain the gas temperature, electron temperature, electron number density, gas velocity, and chemical species number density distribution to cope with CF4 the decomposition in the ICP reactor.

Emission spectroscopy of highly ionized high-temperature plasma jets

This paper deals with advanced studies on the optical emission spectroscopy of atmospheric pressure highly ionized high-temperature argon and nitrogen plasma jets generated by a powerful arc plasmatron. The emission spectra are taken in the 200–1000 nm range with a spectral resolution of ∼0.01–0.02 nm. The exposure times are 6 × 10−6–2 × 10−2 s, the spatial resolution is 0.02–0.03 mm. The recorded jet spectra are abundant in spectral lines originating from different ionization stages. In nitrogen plasmas, tens of vibronic bands are also observed. To interpret and process these spectra such that plasma characteristics can be derived, a purpose-developed automated processing system is applied. The use of a CCD camera at the spectrograph output allows a simultaneous recording of the spectral and chord intensity distributions of spectral lines, which can yet belong to the overlapped spectra of the first and second orders of interference. The modern optical diagnostic means and methods used permit the determination of spatial distributions of electron number densities and temperatures and evaluation of rotational temperatures. The radial profiles of the irradiating plasma components can also be obtained. Special attention is given to the method of deriving rotational temperatures using vibronic bands with an incompletely identified rotational structure.

Radiative model of post-breakdown laser-induced plasma expanding into ambient gas

The dynamics of the radiative plasma expansion into an ambient gas is considered. The model describes the evolution of the plasma emission spectrum and the dynamics of the resulting shock wave. The time frame for the applicability of the model is in the tens of nanoseconds after the laser pulse is terminated, until a few microseconds later when the plasma ceases to emit. It is assumed that local thermodynamic equilibrium is established and that the plume expands with spherical symmetry. The model outputs are spatial and temporal distributions of atoms, ions, and electron number densities, evolution of atom and ion line profiles, and the shock wave. The model should be applicable to spectroscopic analysis of the initial plasma state and plasma dynamics.

Electron and ion number densities in the space charge layer in thermal plasmas

The space charge layer near the charged surface in the thermal collision plasma has been studied. The analytical expressions describing the spatial distributions of electron and ion number densities, taking into account the nonequilibrium ionization, have been obtained. It has been shown that the nonequilibrium ionization in the space charge layer leads to the essential change of the distribution profile of these number densities.

Effect of relative humidity on electron distribution and ozone production by DC coronas in air

The effect of relative humidity on the electron distribution and the ozone production in the direct current (dc) corona discharge from a thin wire is evaluated with a numerical model. The model is based on the prior models of ozone production by dc coronas in dry air, with modifications to incorporate the effect of water vapor on the corona plasma and the plasma chemistry for ozone production. The distribution of electron number density is obtained by solving coupled continuity equations for charge carriers and the Maxwell's equation. The electron kinetic energy distribution is solved from the Boltzmann equation. Both the electron number density distribution and the distribution of electron kinetic energy are insensitive to the variation in the relative humidity due to the relatively low water content. The electron distribution data are then combined with the chemical mechanisms of ozone production in humid air and the two-dimensional (2-D) transport processes to obtain the distribution and the production of ozone. In qualitative agreement with prior experimental findings, the ozone production rate decreases with increasing relative humidity in both positive and negative coronas due to the removal of atomic oxygen by water molecules, and the ozone production rate in the negative corona is one order of magnitude higher than that in the positive corona.

Spectroscopic characterization of low power argon microwave induced plasma

The spatial distributions of radiation densities emitted by various components (major, minor and traces) of atmospheric low power (100 W) argon microwave induced plasma (MIP), generated by a resonant TM 010 cavity, were determined. The analytes (Ca, V and Zn) were introduced into the plasma in the form of aqueous solutions applying pneumatic nebulization. The obtained distributions were characterized by the value and the position of the maximum of radiation on the axis of the axially symmetric discharge of filament type. The distance of the maximum above the plasma torch depends on physical characteristics of the element. The influence of potassium on spatial radiation densities of all the mentioned species was investigated. The radial distributions of electron number density (1–9×10 14 cm −3) were determined from the Stark broadening of the H β line. From the experimentally determined ratio of ionic to atomic spectral line intensity of Ca and electron number density, the radial distributions of the non-equilibrium factor, the degree of ionization of Ca and ionization temperatures of Ca, T ion(Ca), and of Ar, T ion(Ar), were determined. The values of T ion(Ar) are ranging from 6700 to 7600 K and of T ion(Ca) from 4000 to 5600 K in the plasma region from 1.6 to 3.4 mm in axial and up to 0.3 mm in radial direction. The obtained results compared with apparent temperature data from literature confirm that this plasma is not in state of local thermodynamic equilibrium (LTE).

Radiation dynamics of post-breakdown laser induced plasma

A radiation dynamic model is developed for a post-breakdown stage of a laser induced plasma expanding into vacuum. The model describes the plasma formed on a small solid particle, which is completely vaporized by a laser. The symmetry of the expanding plasma is spherical. The time frame for the applicability of the model is somewhat between a hundreds of nanoseconds, after the laser pulse is terminated, and a few microseconds, when the plasma ceases to emit. The model is based on a system of gas dynamic equations coupled with the equation of radiative transfer. Local thermodynamic equilibrium is assumed, allowing the application of the collision-dominated plasma model as well as standard statistical distributions. Calculations are performed for a dual SiC system, although calculations for any arbitrary number of system's components are permitted. The model has two implications. First, an analytical expression for the plasma radiation dynamics is obtained by artificially setting the initial conditions. Second, from experimentally measured plasma parameters, information is deduced about the initial state of the plasma. The main model input parameters are the total number and distribution of plasma species and the initial distribution of temperature. Some of the other model inputs, such as the speed of the plasma front and the temperature profile across the plasma can be directly measured, thus providing valuable experimental feedback to the model. The model outputs are the evolution of plasma temperature, the spatial and temporal distributions of atoms, ions and electron number densities and the evolution of the plasma spectrum in a desirable spectral window (e.g. 280–290 nm for the chosen in this work SiC system).

Molecular dynamics simulation of plasma flow around two stationary dust grains

Plasma kinetics in the presence of ions flowing around two stationary dust grains aligned perpendicularly to the direction of the flow is studied by a three-dimensional molecular dynamics simulation code. The dynamics of plasma electrons and ions as well as the dust particle charging are simulated self-consistently. Distributions of electron and ion number densities and the electrostatic plasma potential are obtained for various intergrain distances, including those much less, of the order of, and more than the plasma electron Debye length.

Small scale density variations of electrons and charged particles in the vicinity of polar mesosphere summer echoes

Abstract. We present small scale variations of electron number densities and particle charge number densities measured in situ in the presence of polar mesosphere summer echoes. It turns out that the small scale fluctuations of electrons and negatively charged particles show a strong anticorrelation down to the smallest scales observed. Comparing these small scale structures with the simultaneously measured radar signal to noise profile, we find that the radar profile is well described by the power spectral density of both electrons and charged particles at the radar half wavelength (=the Bragg scale). Finally, we consider the shape of the power spectra of the observed plasma fluctuations and find that both charged particles and electrons show spectra that can be explained in terms of either neutral air turbulence acting on the distribution of a low diffusivity tracer or the fossil remnants of a formerly active turbulent region. All these results are consistent with the theoretical ideas by Rapp and Lübken (2003) suggesting that PMSE can be explained by a combination of active and fossil neutral air turbulence acting on the large and heavy charged aerosol particles which are subsequently mirrored in the electron number density distribution that becomes visible to a VHF radar when small scale fluctuations are present.

Kinetics of plasma flowing around two stationary dust grains.

The characteristics of plasma particle kinetics in the presence of ions flowing around two stationary dust grains aligned in the direction of the flow are studied using a three-dimensional molecular dynamics simulation code. The dynamics of plasma electrons and ions as well as the charging process of the dust grain are simulated self-consistently. Distributions of electron and ion number densities, and the electrostatic plasma potential are obtained for various intergrain distances, including those much less, of the order of, and more than the plasma electron Debye length.

Calculation and analysis on the wave reflected characteristics of plasma before the conductor plate

Regarding the nonuniform plasma plate as uniform multilayer slabs, the total wave energy reflectance of the interface between the plasma before a conductor plate and the atmosphere or vacuum can be calculated by applying the equivalent input impedance method. The result obtained is that the reflection characteristics are affected by electron number density, plasma thickness, frequency and transmitting direction of the incident wave. Changing any factor of them, the total wave energy reflectance can be reduced greatly. In the low frequency band, the d istribution of electron number density almost does not affect the reflectance. B ut in the high frequency band, it will affect the reflectance. The effect of pla sma thickness, wave frequency, electron number density distribution on it is alm ost independent of the wave polarizing direction.

Parametric study of an atmospheric pressure microwave-induced plasma of the mini MIP torch — II. Two-dimensional spatially resolved excitation temperature measurements

Two-dimensional mapping of the excitation temperatures have been carried out in the microwave-induced plasma torch with tangential argon flow. It is detected that the presence of wet aerosols in a nebulizer gas increases axial excitation temperature while desolvation acts in the opposite direction. The influence of low hydrogen concentration in the support gas and potassium in the nebulizer gas on the temperature distribution is studied in detail. The comparison of excitation temperature and electron number density distributions clearly indicates non-equilibrium plasma conditions.

Modeling an inhomogeneous optically thick laser induced plasma: a simplified theoretical approach

A simplified theoretical approach is developed for an optically thick inhomogeneous laser induced plasma. The model describes the time evolution of the plasma continuum and specific atomic emission after the laser pulse has terminated and interaction with a target material has ended. Local thermodynamic equilibrium is assumed allowing the application of the collision-dominated plasma model and standard statistical distributions. Calculations are performed for a two-component Si/N system. The model input parameters are the number of plasma species (or plasma pressure) and the ratio of atomic constituents. Functions are introduced which describe the evolution of temperature and size of the plasma. All model inputs are experimentally measurable. The model outputs are spatial and temporal distributions of atom, ion and electron number densities, evolution of an atomic line profile and optical thickness and the resulting absolute intensity of plasma emission in the vicinity of a strong non-resonance atomic transition. Practical applications of the model include prediction of temperature, electron density and the dominating broadening mechanism. The model can also be used to choose the optimal line for quantitative analysis.

Parametric study of the vacuum ultraviolet emission and electrical characteristics of a He–Xe microdischarge

Vacuum ultraviolet emission and electrical characteristics of a simple discharge configuration consisting of two planar cylindrical electrodes operated with a dc voltage have been measured over a wide range of He/Xe mixtures and discharge pressures. Breakdown characteristics are consistent with those found in the literature, however current–voltage characteristics and the inferred discharge resistivity suggest the presence of a complex process controlling electron emission at the cathode. Ultraviolet vacuum emission maps of atomic and molecular xenon at 147, 150, and 173 nm, respectively, have been measured as a function of pressure, from 60 to 500 Torr, and gas mixture, from pure Xe to 5% Xe in He. The calibrated ratios of each emission map help to visualize the zones of strongest ultraviolet emission over a wide range of operating conditions. One-dimensional simulations of the breakdown voltage and current discharge have been performed using the commercially available discharge-modeling package SIGLO. Good agreement with experimental results is found in the case of pure helium and xenon, however, in the case of pure xenon, the gas temperature was adjusted (elevated) in order to reproduce the measured current–voltage characteristics. Modeling of the electron number density distribution indicates that the discharge is principally composed of a thick ion sheath near the cathode.

Plasma kinetics around a dust grain in an ion flow.

The kinetics of plasma particles around a stationary dust grain in the presence of an ion flow is studied using a three-dimensional molecular dynamics simulation method. The model is self-consistent, involving the dynamics of plasma electrons and ions as well as charging of the dust grain. The effect of ion focusing is investigated as a function of the ion flow velocity. Distributions of electron and ion number densities, and electrostatic plasma potential are obtained.

Microwave Plume Measurements of a Closed Drift Hall Thruster

The plasma plume from a closed drift hall thruster has been characterized using a 17-GHz microwave diagnostic system. Electron number density profiles are obtained throughout the thruster plume via differential phase measurements. A functional model of plasma density has been developed combining a near-field Gaussian beam term and a far-field point source expansion term. An outcome of this work is a mapping of the transition region between the nearand far-field plume. An indication of slight plume asymmetry is obtained by evaluating total integrated density measurements along rays emanating from the thruster. Additional evaluations have determined the plasma plume effect on attenuation and spectral characteristics of a wave transmitted through the plume. The attenuation was small, with slightly over 2 dB loss at 0.09 m along the thruster axis. However, ray-tracing attenuation modeling based on plasma density profiles indicates a greater effect for lower-frequency operation. The spectral data of the signal transmitted through the plume exhibited clear 26-kHz harmonic sidebands and added broadband noise. Estimates of potential impact to communication and other electromagnetic satellite systems can be obtained directly from the measurements and from the electron number density distribution models derived from the measurements.