The Experts below are selected from a list of 222 Experts worldwide ranked by ideXlab platform
N Sadeghi - One of the best experts on this subject based on the ideXlab platform.
-
influence of the excitation frequency on the density of helium Metastable Atoms in an atmospheric pressure dielectric barrier discharge
Journal of Applied Physics, 2017Co-Authors: N Sadeghi, J Margot, J S Boisvert, F MassinesAbstract:Diffuse dielectric barrier discharges in atmospheric-pressure helium can be sustained over a wide range of excitation frequencies (from, but not restricted, 25 kHz to 15 MHz). The aim of the present paper is to identify the specific characteristics of the discharge modes that can be sustained in this frequency range, namely, the atmospheric-pressure Townsend-like discharge (APTD-L) mode, the atmospheric-pressure glow discharge (APGD) mode, the Ω mode, the hybrid mode, and the RF-α mode. This is achieved experimentally, by measuring the density of helium Metastable Atoms, which are known to play a driving role on the discharge kinetics. This density is measured by means of two absorption spectroscopy methods, one using a spectral lamp and the other one using a diode laser as a light source. The first one provides the time-averaged atom densities in the singlet He(21S) and triplet He(23S) Metastable states, while with the second one we access the time-resolved density of He(23S) Atoms. Time-averaged measure...
-
space time resolved density of helium Metastable Atoms in a nanosecond pulsed plasma jet influence of high voltage and pulse frequency
Journal of Physics D, 2016Co-Authors: Claire Douat, N Sadeghi, Issaad Kacem, G Bauville, Michel Fleury, V PuechAbstract:Using tunable diode laser absorption spectroscopy, the spatio-temporal distributions of the helium He(23 S1) Metastable Atoms’ density were measured in a plasma jet propagating in ambient air. The plasma jet was produced by applying short duration high voltage pulses on the electrodes of a DBD-like structure, at a repetition rate in the range 1–30 kHz. In addition to the Metastable density, the spatial distribution of helium 587 nm emission intensity was also investigated to give insight into the excitation mechanisms of the He(33 D) excited state inside the dielectric tube, in which no laser measurement can be performed. It is demonstrated that the shape of the radial distribution of helium He(23 S1) Metastable Atoms strongly depends on the polarity of the applied voltage and on the repetition frequency. For positive applied voltages, a dramatic constriction of the excited species production is observed whenever the pulse repetition frequency is higher than 6 kHz, and the voltage higher than 5 kV. This shrinking of the jet structure induces an increase by one order of magnitude of the Metastable Atoms’ density in the jet centre which reaches values as high as 1014 cm−3. Beyond a critical distance, associated to a transition between a positive streamer and a negative one, the distribution of the excited Atoms gets back to an annular structure. For the negative polarity, no shrinking effect correlated to the pulse repetition frequency was observed. The on-axis constriction of the excited species for the high repetition rate and positive polarity is attributed to a memory effect induced by the negative ions, having a lifetime of hundreds of microseconds, left between successive pulses at the periphery of the helium gas flow.
-
the spatio temporal distribution of he 23s1 Metastable Atoms in a mhz driven helium plasma jet is influenced by the oxygen nitrogen ratio of the surrounding atmosphere
Plasma Sources Science and Technology, 2015Co-Authors: Jorn Winter, N Sadeghi, Santos J Sousa, Ansgar Schmidtbleker, Stephan Reuter, V PuechAbstract:The density of helium He (23S1) Metastable Atoms is measured in a 1.6 mm diameter MHz-driven atmospheric pressure helium plasma jet by laser absorption spectroscopy with spatial and temporal resolution. The surrounding atmosphere of the jet is varied from pure oxygen to pure nitrogen with a gas shielding device. The highest Metastable density of 1.3 × 1013 cm−3 is obtained in the center of the jet close to the nozzle exit at normal atmospheric air conditions. Within 0.3 mm in the radial direction and 2 mm in the axial direction, the He Metastable density drops below the detection limit. The obtained He Metastable lifetime is almost independent of the shielding gas composition. By analyzing the diffusion of shielding gas species into the effluent it is concluded that their density is too low to explain the observed He Metastable lifetime. Instead, impurities from the feed gas, especially water molecules, are more likely to be responsible. However, a drastic change in Metastable He density is observed when decreasing the amount of oxygen in the shielding gas. The lower the oxygen amount, the lower the Metastable He density. For pure nitrogen, no He Metastables are detected at all. By exchanging nitrogen with argon, a similar behavior is observed. Thus, it is concluded that it is the absence of ambient oxygen rather than the elevated presence of nitrogen, which is responsible for the observed decrease in the He (23S1) density.
-
space resolved density measurements of argon and helium Metastable Atoms in radio frequency generated he ar micro plasmas
European Physical Journal D, 2010Co-Authors: B Niermann, Marc Boke, N Sadeghi, J WinterAbstract:Space resolved concentrations of helium He* (3S1) and argon Ar* (3P2) Metastable Atoms in an atmospheric pressure radio frequency micro-plasma jet were measured using tunable diode laser absorption spectroscopy. Even small absorptions down to 10-4 could be measured using lock-in technique. The absolute density of Metastable Atoms densities at different rf-power, flow rate and gas mixture was deduced from measured absorption rates. Metastable concentrations range from 109 to 1011 cm-3. Analysis of spectral profiles provided the pressure broadening coefficients of both Metastable Atoms by helium. The spatial distribution of Metastable Atoms in the plasma volume was obtained for various discharge conditions. Density profiles between the electrodes reveal the sheath structure and reflect the plasma excitation distributions in the discharge volume. It reveals the dominance of the α-mode discharge.
-
determination of the non relaxation reflection probability of Metastable ar 3p2 Atoms on a pyrex surface
Plasma Sources Science and Technology, 2004Co-Authors: Peter Macko, N SadeghiAbstract:Two techniques allowing us to measure the probability for the non-relaxation of Metastable Atoms impinging on glass surfaces are presented. In the first one, the radial distribution of Ar*( 3 P2) Metastable Atoms in the proximity of the glass wall is determined by a resonant absorption technique in the afterglow of a low pressure (8.5 Pa) argon discharge. The comparison of the experimental density profile with model profiles predicted by a simple model, permits the determination of an upper limit, R 0.45, for the non-relaxation probability. In the second experiment, the Doppler-shifted laser-induced fluorescence technique is used to deduce the velocity distribution function of Ar*( 3 P2) Metastable Atoms in the vicinity of a Pyrex wall in very low pressure (0.09–0.5 Pa) argon plasmas. The non-relaxation probability is deduced from the ratio of the flux of Metastable Atoms having their radial velocity oriented towards the cell axis to the flux of those with their radial velocity oriented towards the wall. This latter technique is much more precise and gives a value of R = 0.28 ± 0.05 for the non-relaxation probability. It is also shown that Metastable Atoms moving away from the surface have somehow been accommodated to the surface and acquired a velocity distribution corresponding to the wall temperature.
G Popa - One of the best experts on this subject based on the ideXlab platform.
-
Investigation of Oxygen Metastable Distribution in Atmospheric-Pressure DBD Using TDLAS
IEEE Transactions on Plasma Science, 2011Co-Authors: G Borcia, R Cazan, G PopaAbstract:The absorption coefficient corresponding to the oxygen Metastable Atoms is recorded with time, as a function of the laser-absorbing path, in an axially symmetrical discharge. The bidimensional Abel transform is used to reconstruct the radial distribution of the Metastable Atoms. The results show that the oxygen Metastable Atoms have wavelike time-space dynamics.
-
time space resolved distribution of oxygen Metastable Atoms in an axially symmetrical atmospheric pressure barrier discharge
Plasma Sources Science and Technology, 2008Co-Authors: R Cazan, G Borcia, A S Chiper, G PopaAbstract:Tunable diode laser absorption spectroscopy is used as a non-invasive method for the diagnosis of a helium atmospheric pressure dielectric barrier discharge, containing oxygen as contaminant. The time evolution of the absorption coefficient corresponding to the oxygen Metastable Atoms on the 35S2 level is recorded as a function of the laser absorbing path, in the axial symmetrical electrode geometry. The bi-dimensional Abel transform is used to obtain local information on the space distribution of the Metastable Atoms in the discharge. The results show that the oxygen Metastable Atoms have distinct time–space dynamics, in relation to plasma kinetics involving helium high-energy species and to the marked role of the dielectric barrier.
-
Time–space resolved distribution of oxygen Metastable Atoms in an axially symmetrical atmospheric pressure barrier discharge
Plasma Sources Science and Technology, 2008Co-Authors: R Cazan, G Borcia, A S Chiper, G PopaAbstract:Tunable diode laser absorption spectroscopy is used as a non-invasive method for the diagnosis of a helium atmospheric pressure dielectric barrier discharge, containing oxygen as contaminant. The time evolution of the absorption coefficient corresponding to the oxygen Metastable Atoms on the 35S2 level is recorded as a function of the laser absorbing path, in the axial symmetrical electrode geometry. The bi-dimensional Abel transform is used to obtain local information on the space distribution of the Metastable Atoms in the discharge. The results show that the oxygen Metastable Atoms have distinct time–space dynamics, in relation to plasma kinetics involving helium high-energy species and to the marked role of the dielectric barrier.
R Cazan - One of the best experts on this subject based on the ideXlab platform.
-
Investigation of Oxygen Metastable Distribution in Atmospheric-Pressure DBD Using TDLAS
IEEE Transactions on Plasma Science, 2011Co-Authors: G Borcia, R Cazan, G PopaAbstract:The absorption coefficient corresponding to the oxygen Metastable Atoms is recorded with time, as a function of the laser-absorbing path, in an axially symmetrical discharge. The bidimensional Abel transform is used to reconstruct the radial distribution of the Metastable Atoms. The results show that the oxygen Metastable Atoms have wavelike time-space dynamics.
-
time space resolved distribution of oxygen Metastable Atoms in an axially symmetrical atmospheric pressure barrier discharge
Plasma Sources Science and Technology, 2008Co-Authors: R Cazan, G Borcia, A S Chiper, G PopaAbstract:Tunable diode laser absorption spectroscopy is used as a non-invasive method for the diagnosis of a helium atmospheric pressure dielectric barrier discharge, containing oxygen as contaminant. The time evolution of the absorption coefficient corresponding to the oxygen Metastable Atoms on the 35S2 level is recorded as a function of the laser absorbing path, in the axial symmetrical electrode geometry. The bi-dimensional Abel transform is used to obtain local information on the space distribution of the Metastable Atoms in the discharge. The results show that the oxygen Metastable Atoms have distinct time–space dynamics, in relation to plasma kinetics involving helium high-energy species and to the marked role of the dielectric barrier.
-
Time–space resolved distribution of oxygen Metastable Atoms in an axially symmetrical atmospheric pressure barrier discharge
Plasma Sources Science and Technology, 2008Co-Authors: R Cazan, G Borcia, A S Chiper, G PopaAbstract:Tunable diode laser absorption spectroscopy is used as a non-invasive method for the diagnosis of a helium atmospheric pressure dielectric barrier discharge, containing oxygen as contaminant. The time evolution of the absorption coefficient corresponding to the oxygen Metastable Atoms on the 35S2 level is recorded as a function of the laser absorbing path, in the axial symmetrical electrode geometry. The bi-dimensional Abel transform is used to obtain local information on the space distribution of the Metastable Atoms in the discharge. The results show that the oxygen Metastable Atoms have distinct time–space dynamics, in relation to plasma kinetics involving helium high-energy species and to the marked role of the dielectric barrier.
V Puech - One of the best experts on this subject based on the ideXlab platform.
-
space time resolved density of helium Metastable Atoms in a nanosecond pulsed plasma jet influence of high voltage and pulse frequency
Journal of Physics D, 2016Co-Authors: Claire Douat, N Sadeghi, Issaad Kacem, G Bauville, Michel Fleury, V PuechAbstract:Using tunable diode laser absorption spectroscopy, the spatio-temporal distributions of the helium He(23 S1) Metastable Atoms’ density were measured in a plasma jet propagating in ambient air. The plasma jet was produced by applying short duration high voltage pulses on the electrodes of a DBD-like structure, at a repetition rate in the range 1–30 kHz. In addition to the Metastable density, the spatial distribution of helium 587 nm emission intensity was also investigated to give insight into the excitation mechanisms of the He(33 D) excited state inside the dielectric tube, in which no laser measurement can be performed. It is demonstrated that the shape of the radial distribution of helium He(23 S1) Metastable Atoms strongly depends on the polarity of the applied voltage and on the repetition frequency. For positive applied voltages, a dramatic constriction of the excited species production is observed whenever the pulse repetition frequency is higher than 6 kHz, and the voltage higher than 5 kV. This shrinking of the jet structure induces an increase by one order of magnitude of the Metastable Atoms’ density in the jet centre which reaches values as high as 1014 cm−3. Beyond a critical distance, associated to a transition between a positive streamer and a negative one, the distribution of the excited Atoms gets back to an annular structure. For the negative polarity, no shrinking effect correlated to the pulse repetition frequency was observed. The on-axis constriction of the excited species for the high repetition rate and positive polarity is attributed to a memory effect induced by the negative ions, having a lifetime of hundreds of microseconds, left between successive pulses at the periphery of the helium gas flow.
-
the spatio temporal distribution of he 23s1 Metastable Atoms in a mhz driven helium plasma jet is influenced by the oxygen nitrogen ratio of the surrounding atmosphere
Plasma Sources Science and Technology, 2015Co-Authors: Jorn Winter, N Sadeghi, Santos J Sousa, Ansgar Schmidtbleker, Stephan Reuter, V PuechAbstract:The density of helium He (23S1) Metastable Atoms is measured in a 1.6 mm diameter MHz-driven atmospheric pressure helium plasma jet by laser absorption spectroscopy with spatial and temporal resolution. The surrounding atmosphere of the jet is varied from pure oxygen to pure nitrogen with a gas shielding device. The highest Metastable density of 1.3 × 1013 cm−3 is obtained in the center of the jet close to the nozzle exit at normal atmospheric air conditions. Within 0.3 mm in the radial direction and 2 mm in the axial direction, the He Metastable density drops below the detection limit. The obtained He Metastable lifetime is almost independent of the shielding gas composition. By analyzing the diffusion of shielding gas species into the effluent it is concluded that their density is too low to explain the observed He Metastable lifetime. Instead, impurities from the feed gas, especially water molecules, are more likely to be responsible. However, a drastic change in Metastable He density is observed when decreasing the amount of oxygen in the shielding gas. The lower the oxygen amount, the lower the Metastable He density. For pure nitrogen, no He Metastables are detected at all. By exchanging nitrogen with argon, a similar behavior is observed. Thus, it is concluded that it is the absence of ambient oxygen rather than the elevated presence of nitrogen, which is responsible for the observed decrease in the He (23S1) density.
G Borcia - One of the best experts on this subject based on the ideXlab platform.
-
Investigation of Oxygen Metastable Distribution in Atmospheric-Pressure DBD Using TDLAS
IEEE Transactions on Plasma Science, 2011Co-Authors: G Borcia, R Cazan, G PopaAbstract:The absorption coefficient corresponding to the oxygen Metastable Atoms is recorded with time, as a function of the laser-absorbing path, in an axially symmetrical discharge. The bidimensional Abel transform is used to reconstruct the radial distribution of the Metastable Atoms. The results show that the oxygen Metastable Atoms have wavelike time-space dynamics.
-
time space resolved distribution of oxygen Metastable Atoms in an axially symmetrical atmospheric pressure barrier discharge
Plasma Sources Science and Technology, 2008Co-Authors: R Cazan, G Borcia, A S Chiper, G PopaAbstract:Tunable diode laser absorption spectroscopy is used as a non-invasive method for the diagnosis of a helium atmospheric pressure dielectric barrier discharge, containing oxygen as contaminant. The time evolution of the absorption coefficient corresponding to the oxygen Metastable Atoms on the 35S2 level is recorded as a function of the laser absorbing path, in the axial symmetrical electrode geometry. The bi-dimensional Abel transform is used to obtain local information on the space distribution of the Metastable Atoms in the discharge. The results show that the oxygen Metastable Atoms have distinct time–space dynamics, in relation to plasma kinetics involving helium high-energy species and to the marked role of the dielectric barrier.
-
Time–space resolved distribution of oxygen Metastable Atoms in an axially symmetrical atmospheric pressure barrier discharge
Plasma Sources Science and Technology, 2008Co-Authors: R Cazan, G Borcia, A S Chiper, G PopaAbstract:Tunable diode laser absorption spectroscopy is used as a non-invasive method for the diagnosis of a helium atmospheric pressure dielectric barrier discharge, containing oxygen as contaminant. The time evolution of the absorption coefficient corresponding to the oxygen Metastable Atoms on the 35S2 level is recorded as a function of the laser absorbing path, in the axial symmetrical electrode geometry. The bi-dimensional Abel transform is used to obtain local information on the space distribution of the Metastable Atoms in the discharge. The results show that the oxygen Metastable Atoms have distinct time–space dynamics, in relation to plasma kinetics involving helium high-energy species and to the marked role of the dielectric barrier.