Double Electric Probe Research Articles

MEASUREMENT OF THE LOCAL ELECTRON TEMPERATURE IN SELF-COMPRESSED PLASMA STREAM

The local electron temperature measurements with the double electric probe in the compression zone are presented. Electric probes make it possible to measure the electron temperature with a reasonably good spatial resolution. Double electric probe application for electron temperature measurements in the dense self-compressed plasma stream is discussed. We have shown experimentally that the electric probe operates in a diffusion regime.

New measurements on hydrodynamics in a gas–liquid–solid expanded bed

The solid holdup, in a 150mm-ID×2460mm-height gas–liquid–solid expanded bed with air, water and glass beads (the diameter of particles is 0.6–0.8mm) was firstly investigated based on the immersion-type online multiphase measuring instrument, and bubble behavior was studied via the BVW-2 double electrical conductivity probe. The effect of the superficial gas velocity and liquid velocity on the expanded ratio, the transition ratio, the bubble rising velocity, the gas holdup and the solid holdup was studied. It is discovered that compared with the gas velocity, the liquid velocity has stronger impact on the expanded ratio, but it is opposite for the transition ratio. The average gas holdup and solid holdup increase linearly as the superficial gas velocity goes up. Among it, the gas holdup increases greater in the center, while the solid holdup increases greater near the wall. Compared with it, when the superficial liquid velocity rises, the average gas holdup hardly changes, but the average solid holdup keeps decreasing, especially the solid holdup distributes flatter with the increase of the superficial liquid velocity.

Variation of Plasma Properties in Cylindrical Inertial Electrostatic Confinement Device by Changing the Anode Transparency

Inertial electrostatic confinement (IEC) is investigated in terms of direct-current discharge in a cylindrical configuration using nitrogen gas in the pressure range between 0.028 and 0.09 Torr. Discharge characteristics are determined for different anode transparencies of 84%, 92%, and 96% corresponding to 24, 12, and 6 anode rods, respectively. I-V characteristic curves indicate that the electric discharge is in the abnormal glow discharge region. The discharge voltage has the highest values for the low anode transparency for the same value of the discharge current. A double electric probe has been used to measure electron temperature and ion density. The low anode transparency (24 anode rods) enhances field uniformity and aligns the motion of electrons into a chord so that better electrostatic confinement is achieved. This will raise the ion density and lead to thermalization of the plasma, which reduces the electron temperature. The behavior of the electron temperature and the ion density was studied as a function of the gas pressure at the center and near the edge. The variation of the density and temperature in both positions can confirm the plasma confinement. In the low-pressure regime, the confinement process is reinforced. Because of the longer mean free path, electrons cause ionization at the center, which raises the ion density to about 1.44 × 1015 m−3 and the electron temperature to about 2.9 eV.

Space potential and charged particles density variation in a glow discharge plasma during shock wave propagation

The plasma parameters in a glow discharge plasma near the front of shock wave moving perpendicularly to the discharge axis has been investigated using a double electrical probe. It has been discovered that the shock wave propagation is accompanied by an increase in the potential of discharge plasma. A relatively small change in the potential is observed before the shock wave arrival and a significant one behind shock wave front. The varying potential in the glow discharge plasma distorts the current of the double probe. A method of its correction is proposed, which consists in the joint processing of two signals obtained in separate experiments with different surface areas of the negative probe electrode. The method allows us determine the ionic current and the change in the potential of space. The magnitude of ion current corresponding to the charged particles concentration remains unperturbed before the shock wave arrival to the measurement point. A gradual increase in the ionic current is observed behind the shock wave front in contrast with the abrupt change in gas-dynamic parameters on the shock wave front.

Peculiarities of the charged particles distribution near the front of a shock wave in a glow discharge plasma

The charged particles distribution in a glow discharge plasma near the front of shock wave moving perpendicularly to the discharge axis has been investigated using a double electrical probe. It has been shown that the interaction of the shock wave with the glow-discharge plasma is accompanied by a decrease of charged particles density before the shock wave arrival to the measurement point. This decrease occurs simultaneously through the entire plasma volume. The short-term increase of charged particles density has been revealed. Its appearance caused by interaction of a shock wave with the cathode layer of a glow discharge. These peculiarities of charged particles distribution compared with the case when shock wave propagates through decaying plasma. A significant difference between the distributions of the charged particles in these two cases was revealed.

Plasma conductivity as a probe for ambient air admixture in an atmospheric pressure plasma jet

By utilizing a fully floating double electrical probe system, the conductivity of a linear atmospheric pressure plasma jet, utilizing nitrogen as process gas, was measured. The floating probe makes it possible to measure currents in the nanoamp range, in an environment where capacitive coupling of the probes to the powered electrodes is on the order of several kilovolts. Using a chemical kinetic model, the production of reactive nitrogen oxide and hydrogen-containing species through admixture of ambient humid air is determined and compared to the measured gas conductivity. The chemical kinetic model predicts an enhanced diffusion coefficient for admixture of O2 and H2O from ambient air of 2.7 cm2 s−1, compared to a literature value of 0.21 cm2 s−1, which is attributed to rapid mixing between the plasma jets and the surrounding air. The dominant charge carriers contributing to the conductivity, aside from electrons, are NO+, NO2 − and NO3 −. Upon admixture of O2 and H2O, the dominant neutral products formed in the N2 plasma jet are O, NO and N2O, while O2(1Δg) singlet oxygen is the only dominant excited species.

An experimental study of the effect of humidity on the distribution of charged particles in a glow-discharge plasma

The charged-particle distribution in a glow-discharge plasma in air with differing moisture concentration was studied using a double electric probe. An important difference is found in the distribution of charged particles in the discharge, depending on the humidity of the air. The amount of water vapor with a relative concentration of 2% does not affect the distribution of charged particles in the plasma, and, with an increase in moisture content up to 15%, a twofold increase in the ion concentration along the discharge axis is observed.

Interaction of shock wave with free glow discharge

The distribution of charge particles in glow-discharge plasma during shock wave propagation through it is measured by a double electric probe. It is established that a decrease in the ion concentration in front of the shock wave is related to the occurrence of ion-acoustic oscillations in the plasma.

Low-pressure low-frequency inductive discharge with ferrite cores for large-scale plasma processing

Electrophysical characteristics of a low–frequency (100 kHz) low–pressure (10–100 Pa) argon inductive discharge with ferrite cores have been investigated for discharge currents of 1–50 A, discharge chamber diameter of 230 mm. The dependencies of electric field strength on the argon pressure and discharge current were measured. Radial profiles of electron density and temperature were determined with double electric probes. Experimental results were compared with numerical results obtained by a self-consistent kinetic model of the low-frequency ICP, based on the simultaneous solution of a non-local Boltzmann equation for electron energy distribution function and balance equations for the metastable argon atoms density and gas temperature. Comparison of numerical and experimental results is presented.

Study of the Effect of Decrease in the Conductivity Ahead of a Shock Wave in a Glow-Discharge Plasma

The electrical conductivity of a glow-discharge plasma ahead of a shock wave moving perpendicularly to the discharge axis has been investigated using a double electric probe. The obtained results have shown that the interaction of the shock wave with the glow-discharge plasma is accompanied by a change in its conductivity in the entire investigated volume simultaneously.

Spatial distribution of the electron component parameters in the nitrogen plasma of a low-pressure electrode microwave Discharge

Spatial distributions of charged particle concentration, electron temperature, and DC potential in an electrode microwave discharge in nitrogen at a pressure of 1 Torr have been measured using the double electric probe method. It has been shown that, near the electrode/antenna, the charged particle concentration exceeds a critical value. The concentration and heterogeneity of the discharge increase with increasing microwave power.

Peculiarities of interaction of a shock wave with gas discharge plasma

Using a double electrical probe, distribution of charged particles behind the front of a shock wave in gas discharge plasma in the presence of the electric field and in decaying plasma without the electric field was studied. A significant difference between the distributions of the charged particles in these two cases was revealed.

Tailoring surface morphology of cotton fibers using mild tetrafluoromethane plasma treatment

Surface morphology of woven cotton fabrics was modified by treatment with mild plasma created in tetrafluoromethane (CF4) at the pressure of 60 Pa. Samples of dimensions 20 cm × 20 cm were mounted into a 27-cm-wide cylindrical plasma reactor powered with a radio frequency generator of frequency 27.12 MHz and output power of about 500 W. The volume of the reactor was 17 l and the corresponding power density was solely 30 W/l. The plasma density was estimated with a double electrical probe and was about 2 × 109 cm−3. The type of radicals created in plasma was determined using optical emission spectroscopy (OES). No CFx and a negligible amount of F radicals were observed by OES, and surprisingly the predominant spectral features were CO bands. The evolution of surface morphology vs. plasma treatment time was monitored by scanning electron microscopy. Originally smooth fibers became extremely rough after prolonged treatment. The results were explained by etching of fibers with gases released from the samples upon plasma treatment.

Investigation of Capacitively Coupled Argon Plasma Driven by Dual-Frequency with Different Frequency Configurations

Low pressure argon dual-frequency (DF) capacitively coupled plasma (CCP) is generated by using different frequency configurations, such as 13.56/2, 27/2, 41/2, and 60/2 MHz. Characteristics of the plasma are investigated by using a floating double electrical probe and optical emission spectroscopy (OES). It is shown that in the DF-CCPs, the electron temperature Te decreases with the increase in exciting frequency, while the onset of 2 MHz induces a sudden increase in Te and the electron density increases basically with the increase in low frequency (LF) power. The intensity of 750.4 nm emission line increases with the LF power in the case of 13.56/2 MHz, while different tendencies of line intensity with the LF power appear for other configurations. The reason for this is also discussed.

An automated system for DC and RF plasma characterization by guard double electric probes

Monitoring basic plasma parameters such as temperature (T), density (n), floating potential (Vf) or Debye length (λd) provides vital knowledge during the ion implantation processing of materials immersed in plasmas (PIII or PSII) generated either by DC or (13.56MHz) RF sources. Thus, a fully automated electromechanical system has been designed and constructed on the basis of guard double electric probes in order to prevent both probe erosion and plasma contamination. The electronic components of the system comprise a ±150V triangular and ramp wave form generator capable of supplying ±50μA to ±100mA currents at 1–2000Hz frequencies and a DAQ PCI-6023E data acquisition board with a 12 bit resolution compatible with LabVIEW graphic language. A program has been specifically developed for the latter in order to control the probe position within the discharge vessel and to capture, filter, visualize, process and store the respective information. The system has been experimentally applied to DC and RF plasmas of helium, argon, nitrogen, oxygen, and multiple gas mixtures with great success, inside several PIII reactors. Results are presented free from RF interference from the process itself or other surrounding sources.

DC pseudo-glow discharge in nitrogen gas

The plasma properties from a DC pseudo-discharge have been studied in low-pressure nitrogen gas. The discharge took place between a virtual cathode and a mesh anode similar to a pulsed virtual cathode oscillator or vircators. The electric potential, electric field and space charge density of the glow discharge have been obtained in the axial and radial part of the glow discharge. The location of the virtual cathode was found at around 0.7 cm from the mesh anode. The axial and radial distributions of electron temperature and ion density have been measured using a double electric probe. The electron temperature varied between 0.5 and 1.4 eV, while the ion density varied from 7×1012 to 12×1012 cm−3, outside the electrodes.

Red flashes in air

A red flash in a low-pressure air discharge is experimentally studied. Optical radiation, double electric probes, and the electric current of the pulsed plasma that is generated against a low-current stationary discharge are measured. The experimental data are analyzed.

Nitriding of AISI 304 stainless steel by PIII in DC and RF toroidal discharges

DC electrode. The latter is polarized with 1 kV and then the discharge is controlled by varying the gas pressure before the RF signal is applied. The main plasma parameters were established by means of double electric probes yielding electron temperature values within 0.5-1.5 eV and density values within 1.5£10 15 to 4£10 15 m i3 for the DC case while 1.5-3.0 eV and 7£10 14 to 3£10 15 m i3 were reached with RF assisted DC. We present in this work the experimental results obtained from a PIII process applied to AISI 304 stainless steel plates. The outcome shows that the Vickers hardness has been incremented according to the gas pressure within the 1£10 i1 to 1£10 i3 mbar range. The treated plates were analyzed by scanning electron microscopy (SEM) and the results point to an increased percentage of nitrogen, around 20%. By means of x-ray diffractometry (XRD) the gamma expanded phase and compounds such as Fe3NiN, Ni4N, FeNiN and Fe3N were determined.

A Plasma Source for a Microsecond Plasma Opening Switch

The results of the studies of surface plasma sources with an ФЭР-7 optical photochronograph and a double electric probe are presented. The designs of radial and axial plasma generators are described. It is shown that a radial SPS does not ensure satisfactory reproducibility of the plasma flow parameters from pulse to pulse, which influences the operation stability of plasma opening switches. Based on data obtained experimentally, a modernized axial plasma generator was constructed. Studies of plasma flows with a double electric probe have shown that, at equal energy contributions to the plasma generator, the probe's current density increases by a factor of four. The use of an axial surface plasma source on the SIGNAL (high-current pulse generator for laser pumping) installation with a plasma opening switch resulted in the front sharpening of the load current pulse (∼200–220 kA) from 60 ns obtained in earlier experiments to 30 ns for the same current amplitude.

Statistical method to calculate local interfacial variables in two-phase bubbly flows using intrusive crossing probes

This paper presents a statistical method to calculate local interfacial variables in two-phase gas–liquid bubbly flows from data taken with double-sensor intrusive probes. Firstly, one derives the geometrical relationship existing between the apparent and actual bubble velocity for a single spherical bubble flowing in a multidimensional flow field. The apparent variables are obtained from the experimental data when one assumes that the bubble trajectory is aligned with the probe axis. A similar relationship exists for the intersected chord length and bubble diameter. Then, the analysis is extended to a swarm of bubbles. The ratio between the apparent to the actual bubble velocity and the intersected chord length to the bubble diameter appear now as probability density functions. The experimental data were taken for air–water bubbly flow regime in a vertical round pipe with a double tip electrical probe. Processing the phase density function generated by the bubble events, one determines distribution function of the bubble velocity and intersected chord length, termed the apparent distributions. The variables of interest, actual bubble velocity and diameter, come out of the solution of a linear system of equations relating the probability function of the measured and estimated bubble velocity and bubble size ratio. The probability density function of the actual bubble velocity and bubble diameter, plus the bubble frequency, add up to various interfacial properties calculated with this technique: the void fraction, the bubble velocity, the bubble size, the interfacial area density and the interface velocity fluctuation intensity. To validate the method, the paper compares local and area averaged quantities with previously published results, volumetric measurements and extensively used correlation.