P. Michel

University of Greifswald, Greifswald, Mecklenburg-Vorpommern, Germany

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Publications (12)7.01 Total impact

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    ABSTRACT: The techniques of spatially resolved cross-correlation spectroscopy (CCS) and current pulse oscillography were used to carry out systematic investigations of the barrier discharge (BD) in the binary gas mixtures N2/O2 at atmospheric pressure. In the case of the BD filamentary mode, which is characterized by the formation of microdischarges (MDs) of short duration, the spatio-temporal distributions of the BD radiation intensities were recorded for the spectral bands of the 0-0 transitions of the 2nd positive (λ = 337 nm) and 1st negative system of molecular nitrogen (λ = 391 nm). The velocities of the cathode-directed ionising waves as well as the effective lifetimes of the excited states N2(C3Πu)υ ′=0 and N+2 (B2Σ+u)υ ′=0 were evaluated from the CCS data. The two-dimensional optical scanning of the MD channel (in axial and radial directions of the MD) was carried out for the BD operated in the gas mixture consisting of 6 vol.% of O2 and 94 vol.% of N2. In the middle of gap, the MD channel diameter was found to be about 0.3 mm and to expand towards both electrodes. On the dielectrics, outward propagating discharges were observed. In pure nitrogen the diffuse mode of barrier discharge was investigated. Surprisingly, under the conditions studied, the transition to the filamentary mode already starts for O2 admixtures to nitrogen of ≥400 ppm. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Beiträge aus der Plasmaphysik 07/2005; 45(5‐6):338 - 347.
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    ABSTRACT: The techniques of spatially resolved cross-correlation spectroscopy (CCS) and current pulse oscillography were used to carry out systematic investigations of the barrier discharge (BD) in the binary gas mixtures N 2 /O 2 at atmospheric pressure. At very low oxygen concentrations (<500 ppm), the BD was observed in a so-called diffuse mode (also referred to as atmospheric pressure glow discharge, glow silent discharge or homogeneous BD). In the case of the BD filamentary mode, the spatio-temporal distributions of the BD radiation intensities were recorded for the spectral bands of the 0–0 transitions of the second positive (λ = 337 nm) and first negative system of molecular nitrogen (λ = 391 nm). In the case of the diffuse mode, the spectral bands λ = 337 nm, λ = 260 nm (0–3 transition of the γ -system of NO) and λ = 557 nm (radiation of ON 2 excimer) were used for this purpose. The velocities of the cathode-directed ionizing waves as well as the effective lifetimes of the excited states N 2 (C 3 u) υ =0 and N + 2 (B 2 + u) υ =0 were evaluated from the CCS data. Special attention was devoted to the investigation of the transition between the filamentary and diffuse modes of the BD, this transition being caused by the variation of oxygen content within the range 500–1000 ppm.
    Journal of Physics D Applied Physics 01/2005; 38:518-529. · 2.53 Impact Factor
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    ABSTRACT: Barrier discharges (BDs) produce highly non-equilibrium plasmas in a controllable way at atmospheric pressure, and at moderate gas temperature. They provide the effective generation of atoms, radicals and excited species by energetic electrons. In the case of operation in noble gases (or noble gas/halogen gas mixtures), they are sources of an intensive UV and VUV excimer radiation. There are two different modes of BDs. Generally they are operated in the filamentary one. Under special conditions, a diffuse mode can be generated. Their physical properties are discussed, and the main electric parameters, necessary for the controlled BD operation, are listed. Recent results on spatially and temporally resolved spectroscopic investigations by cross-correlation technique are presented. BDs are applied for a long time in the wide field of plasma treatment and layer deposition. An overview on these applications is given. Selected representative examples are outlined in more detail. In particular, the surface treatment by filamentary and diffuse BDs, and the VUV catalyzed deposition of metallic layers are discussed. BDs have a great flexibility with respect to their geometrical shape, working gas mixture and operation parameters. Generally, the scaling-up to large dimensions is of no problem. The possibility to treat or coat surfaces at low gas temperature and pressures close to atmospheric once is an important advantage for their application.
    Vacuum 01/2003; · 1.53 Impact Factor
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    ABSTRACT: Dielectric barrier discharges can be operated in a diffuse (glow-like) mode at atmospheric pressure in nitrogen, helium and neon, provided that the feeding sinusoidal voltage is within the kHz range. These homogeneous discharges have been investigated by spatio-temporally resolved emission spectroscopy. The analysis of experimental data including their comparison with the corresponding results of numerical modelling enables to clarify the mechanisms of discharge development. These mechanisms appear to be essentially different for the cases of noble gases and nitrogen. For example in nitrogen the maximum of light intensity is located at the anode, while in helium and neon a cathode directed propagation of a luminosity wave is observed.
    10/2002;
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    01/2002;
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    ABSTRACT: The technique of spatially resolved cross-correlation spectroscopy (CCS) is used to carry out diagnostic measurements of the barrier discharge (BD) in air at atmospheric pressure. Quantitative estimates for electric field strength E(x, t) and for relative electron density n e (x, t)/n max e are derived from the experimentally determined spatio-temporal distributions of the luminosity for the spectral bands of the 0–0 transitions of the second positive system of N 2 (λ = 337.1 nm) and the first negative system of N + 2 (λ = 391.5 nm). These results are used to test the validity of some physical models of electrical breakdown in a BD. The influence of the spatio-temporal structure of the discharge on the chemical kinetics of ozone synthesis is studied by means of a semi-empirical method based on the results of spatially resolved CCS measurements.
    Journal of Physics D Applied Physics 01/2001; 34:3164-3176. · 2.53 Impact Factor
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    01/2001;
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    ABSTRACT: The entire range of gas phase reaction products, depending on the composition of initial binary mixtures of methane and carbon dioxide in dielectric barrier discharges, has been determined (saturated as well as unsaturated hydrocarbons and oxygenated organic compounds). The macro-kinetics of the basic chemical pathways of the system under consideration has been investigated. This system is found to display a strong feedback effect (positive or negative, depending on the initial state of the surfaces, as well as the chemical composition of the feed-gas mixture). It is demonstrated that these properties undergo significant changes during operation, due to surface modification processes (polymer film deposition, its oxidation or reduction). They are found to exert a considerable influence on the chemical efficiency of the discharge (for example, on the absolute and relative chemical yields of the reaction products), the Lissajous figures appear to be a sensitive tool to monitor the operation conditions of the discharge.
    Plasmas and Polymers 11/2000; 5(3):129-150.
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    ABSTRACT: The electrical and optical characteristics of the dielectric barrier discharge (DBD) in nitrogen with a trace admixtures of oxygen (
    10/2000;
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    ABSTRACT: The temporal and spatial development of a single filament barrier discharge was investigated at atmospheric pressure. The used technique allows spectral and phase resolved measurements in the time scale 1 ... 200 ns at a spatial resolution of 0.1 mm. The single filament is produced with the frequency of about 6 kHz. A symmetrical electrode arrangement with both electrodes covered by the dielectrics (glass or alumina, discharge gap width of 1mm) was used. The time resolution in the sub ns scale was realized by a correlation technique in single photon counting mode /1/. The spectral investigations are focussed on the second positive system (wavelength 337 nm) and the first negative system (wavelength 391 nm) of nitrogen. The measurements allow a detailed visualization and interpretation of the streamer development. In combination with a kinetic model of the dominant excitation as well quenching processes there is the possibility to get informations on the temporal and spatial development of the reduced field strength E/n, too. /1/ K. V. Kozlov et al, Proc. XIth Conf. on Gas Discharges and their Applications (1995) II-42
    10/2000;
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    ABSTRACT: The influence of the chemical composition of the feeding gas mixtures CH4-He on the physical properties of dielectric barrier discharge was investigated experimentally as well as theoretically. Certain changes in the shape of charge-voltage characteristics (Lissajous figures) were observed when the content of He was varied within the range 0–90%. An increase of the He concentration was found to cause monotonous but not linear decrease of the ignition voltage as well as of the burning voltage of the discharge. Measurements of the burning voltage were used to estimate the characteristic energy of electrons in the mixtures under consideration. These estimates were compared with experimentally determined values of the energy consumption for the synthesis of C2H2, C2H4 and C2H6, respectively. It was demonstrated that the observed dependencies of the energy consumption upon He content can be explained taking into consideration the influence of the chemical composition of feeding gas mixture upon the characteristic energy of electrons in the dielectric barrier discharge.
    Czechoslovak Journal of Physics 09/1998; 48(10):1199-1207. · 0.42 Impact Factor
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    ABSTRACT: The technique of spatially resolved cross-correlation spectroscopy is used to carry out diagnostic measurements of the barrier discharge (BD) in flowing synthetic air (80%N 2 + 20%O 2) at atmospheric pressure. Quantitative estimates for electric field strength E(x,t) and for relative electron density n e (x,t)/n e max are derived from the experimentally determined spatio-temporal distributions of the luminosity for the spectral bands of the 0-0 transitions of the 2 nd positive system of N 2 (λ = 337.1 nm) and the 1 st negative system of N 2 + (λ = 391.5 nm). These results are used to test the validity of some physical models of electrical breakdown in a BD.