M Simek

Excitation of ) and ) states in a pulsed positive corona discharge in , - and -NO mixtures

Time resolved multichannel emission spectroscopy has been applied to study emission in the 200-500 nm spectral range produced by a pulsed positive corona discharge. The discharge was driven in coaxial geometry by an HV power supply (100 kV/1 kA) at atmospheric pressure in nitrogen, and in and mixtures. Emission of NO- (-) and 2.PG (-) bands has been studied in order to trace the development of and electronic states during both discharge and post-discharge periods. Analysis of spectroscopic data indicates an evolution of the electron mean energy during the discharge pulse in the range 20-1 eV and post-discharge kinetics of the NO and electronic states which is predominantly controlled by , v = 0,1) metastable species.

Excitation and decay of N2(B 3Πg,v) states in a pulsed discharge: Kinetics of electrons and long-lived species

The vibrational excitation and decay of N2(B 3Πg) state has been investigated in a N2 pulsed rf discharge. The effect of the pulsing frequency and the duty cycle on the N2 (B,v=1–12) vibrational distribution, obtained from the 1PG spectra taken at different times in discharge and afterglow, has been examined in the N2 pressure range 2.4 mTorr–1.5 Torr. The measured (B,v) distributions have been analyzed by a steady-state kinetic model taking into account the main excitation processes, like the electron impact from N2(X 1Σg+,v) and N2(A 3Σu+,v) states, the associative excitation of N2(X,v) with N2(A,v), the pooling by N2(A,v) molecules, the atomic recombination of N(4S), as well as the quenching processes. For the various processes, experimental state-to-state rate coefficients from the literature and/or calculated data sets have been used. Measured N2(A,v) and electron energy distribution functions, and estimated N2(X,v) distributions have been used as input data for the model. The model satisfactorily re...

LIF measurement of population density in a pulsed rf discharge

A laser-induced fluorescence (LIF) technique has been applied to the measurement of population density in a pulsed parallel-plates rf discharge at 0.1 Torr pressure. The method is based on a single rotational line excitation-detection LIF scheme on the first positive band system of . This approach makes the correct application of a standard model of three-level rate equations to the description of the LIF process for the treatment of experimental results possible. Conditions for true single-line operation using a line-width pulsed tunable laser are discussed and applied to the measurement. The measured density value is then used for the absolute density calibration of a previous relative vibrational distribution of -9) obtained by a non-single-line excitation-detection LIF measurement.

{\rm N}_2 \left({A\,^3\Sigma_{\rm u}^+} \right) behaviour in a N2?NO surface dielectric barrier discharge in the modulated ac regime at atmospheric pressure

Optical, electrical and discharge product measurements were performed in order to reveal the behaviour of metastables in a surface dielectric barrier discharge (DBD) driven in N2 with small NO admixtures in a modulated ac regime. Metastable species were detected both in a thin surface plasma layer and in the space afterglow through plasma induced emission and optical?optical double resonance laser induced fluorescence, respectively. Basically, the observed species follow the discharge current oscillations in the plasma layer, while they evolve on a millisecond time scale due to diffusion through the space afterglow. Emission spectrometry provides a rough estimation of average metastable concentration in a thin surface plasma layer ~9 ? 1013?cm?3. Fluorescence measurements then allow an upper estimation of metastable concentration in the space afterglow ?1 ? 1012?cm?3.

Efficiency of hydrogen peroxide production by ac capillary discharge in water solution

Efficiency of hydrogen peroxide production by an ac driven underwater capillary discharge was investigated quantitatively. The concentration of formed hydrogen peroxide was measured by a colorimetric method using a specific reaction between H2O2 and a titanium reagent. The amount of formed H2O2 increases linearly during the first hour of the discharge duration. The initial rate and corresponding total energy yield of H2O2 formation by the capillary discharge were determined for initial electrical conductivity of aqueous solution in the range of 100–500 µS cm−1 and average applied power in the range 30–90 W. It comes out that the total energy yield of H2O2 formation, derived from the initial rate of H2O2 formation and the average applied power, increases linearly with average applied power and that solution conductivity has only a negligible effect on the energy yield. A maximum total energy yield of H2O2 formation of 0.9 g kWh−1 was obtained for a 500 µS cm−1 aqueous solution.

The NO(A) excitation mechanism in a - pulsed RF discharge

Time-resolved laser-induced fluorescence detection of metastable and NO and time-resolved emission spectroscopy of the -band of NO have been applied to a - RF pulsed discharge in order to show that the process is responsible for NO(A) excitation in discharge systems of this kind. Highly resolved spectra obtained under such conditions have revealed that there is a non-Boltzmann rotational distribution in the ) state with a large excitation of levels J>20.

ICCD microscopic imaging of a single micro-discharge in surface coplanar DBD geometry: determination of the luminous diameter of N2 and Ar streamers

Time-resolved images of a single-surface dielectric barrier micro-discharge were obtained by employing ICCD microscopy with high spatial and time resolution. The micro-discharge was repetitively produced using amplitude-modulated ac high voltage waveforms applied to the coplanar electrode geometry in a reactor, fed either with high-purity Ar or N2 at atmospheric pressure. The driving high-voltage amplitude was set to initiate just one single micro-discharge per one ac half-cycle. Images recorded within the two successive ac cycles provided evidence that the track left by the first micro-discharge influenced the propagation trajectory of consecutive streamers. Images of individual micro-discharges allowed evaluation of the luminous streamer channel diameter and its evolution along the streamers propagation trajectory. Minimum luminous streamer channel diameters of 30 ? 6??m and 50 ? 10??m were fixed in Ar and N2, respectively. Furthermore, direct comparison between a single micro-discharge image and an image integrating many micro-discharges allowed the estimation of potential errors associated with methods based on accumulating optical emission produced by many micro-discharge events.

N2(AΣu+3) time evolution in N2 atmospheric pressure surface dielectric barrier discharge driven by ac voltage under modulated regime

The relaxation of N2(AΣu+3) metastable in N2 ac (5 KHz and 7 KVpp) surface dielectric barrier discharge driven under pulse modulated regime, TON=5 ms and TOFF=20 ms, at atmospheric pressure has been investigated. N2(A) has been detected by optical-optical double resonance laser induced fluorescence in a space layer (space afterglow) at 1 mm above the discharge electrode. The time evolution clearly shows that in the space afterglow layer N2(A) builds up and decay in millisecond time scale and does not vary in the voltage cycle.

Laser triggered single streamer in a pin-to-pin coplanar dielectric barrier discharge

The effect of laser light interaction with alumina surface of a single filament coplanar dielectric barrier discharge has been investigated. It has been found that for laser photon energy lower than the pure alumina photoelectron emission threshold, the laser beam was effective in triggering single streamer discharge below regular ignition voltage threshold. This work demonstrates that triggering of the filamentary discharge occurs due to the laser induced extraction of electrons originally trapped by the plasma radiation at the dielectric surface; the trap energy levels lower than the dielectric band gap explain the easier electron detrapping due to incident laser photons.

Radar sporadic meteor rates and solar activity

The correlation of sporadic meteor rates from radar observations in January, August, and December non-show-er periods in 1958–2000, and relevant solar activity represented by the solar relative number, R, is investigated. Similar analysis of the December sporadic period was already presented by Simek 1999, and Pecina. Complete analysis indicates high correlation of both phenomena with sporadic meteor counts curve following that of solar activity after 1.5–2 years in the mean eleven year solar cycle with the correlation index exceeding 70%. This result supports the large volume of observing material of the Ondřejov meteor radar in the above mentioned span covering almost four solar cycles.