In this paper results of optical emission spectroscopic study of microwave 915 MHz plasma in atmospheric pressure nitrogen with an addition of ethanol vapour are presented. The plasma was generated in waveguide-supplied cylinder-type nozzleless microwave plasma source. The aim of research was to determine the rotational T_{rot} and vibrational T_{vib} temperatures of CN and C_2. A method called bubbling was employed to introduce alcohol (ethanol) into the plasma. The T_{rot} and T_{vib} were determined by comparing the measured and simulated spectra. Obtained rotational and vibrational temperatures of CN and C_2 were ranged from 4400 to 5400 K and from 2800 to 3400 K, respectively, depending on the location in the plasma and the microwave absorbed power P_{A}.
Using spectroscopic measurements vibrational and rotational temperatures were determined in the "ferroelectric" plasma source for different gas mixtures. It was shown that in this time-periodical, atmospheric pressure non-equilibrium discharge, both plasma temperatures differ strongly, and that the vibrational temperature is much higher (≈ 3 kK) than the rotational one (< 1 kK).
The aim of this paper is to present a novel microwave microplasma source generated in different gases at atmospheric pressure. The design, rule of operation and experimental investigations of the new microwave microplasma source are described. The main advantage of the presented microwave microplasma source is its small size, simplicity, and low cost of construction and operation. The microplasma has a form of a small plasma jet of dimensions of a few mm, depending on the kind of gas, gas flow rate, and absorbed microwave power. Presented in this paper results of experimental investigations were obtained with an atmospheric pressure argon, krypton, nitrogen, and air microplasma, sustained by microwaves of standard frequency of 2.45 GHz. The absorbed microwave power was up to 70 W. The gas flow rate was from 2 to 25 l/min. The miniature size, simplicity of the source and stability of the microplasma allow to conclude that the presented new microwave microplasma source can find practical applications in various fields.
Using spectroscopic and electric measurements, vibrational and rotational molecular gas temperatures as well as free electron temperature and concentration were determined in different regions of a time-periodical type, atmospheric pressure non-equilibrium low current gliding arc. It was shown that this discharge includes an initial quasi-equilibrium zone, with the quasi-equilibrium temperature of 4 to 6 kK, and the non-equilibrium zone with the electron temperature about 10 kK, the vibrational temperature about 3 kK, rotational and translational temperatures from 1 to 1.5 kK. The transition between two mentioned zones coincides with the phenomenon of the arc "length explosion" already observed in moderate-current gliding arc.
In this paper, results of spectroscopic study of microwave (2.45 GHz) plasma at atmospheric pressure and high CO_2 flow rate are presented. The plasma was generated by waveguide-supplied nozzleless cylindrical type microwave plasma source. Working gas flow rate and microwave absorbed power varied from 50 up to 150 l/min and from 1 up to 5.5 kW, respectively. The emission spectra in the range of 300-600 nm were recorded. The rotational and vibrational temperatures of C_2 molecules, as well as the rotational temperature of OH radicals were determined by comparing the measured and simulated spectra. The plasma gas temperature inferred from rotational temperature of heavy species ranged from 4000 to 6000 K. It depended on location in plasma, microwave absorbed power and working gas flow rate. The presented microwave plasma source can be used in various gas processing applications.
We study the intensity distribution of the A^{2}Δ-X^{2}Π system of CH molecule at 430 nm in a low pressure plasma jet. This system shows an overlap of vibrational bands with Δv=0. By comparing simulated and experimental emission spectra, we obtain rotational and vibrational temperatures using Boltzmann plots or some thermometer functions. The thermometer functions are the integrated intensities of line-like transitions composed of several rotational transitions. The result of the Boltzmann plots and the thermometer functions method that we propose are in good agreement.
We investigate the pulsed flashover voltage of dielectric samples at up to 4 bar SF_{6} in the simultaneous presence of a high current (>10 kA, ∼20 microsecond pulse) volume discharge nearby. The chosen distance, ∼7 cm, between surface and volume breakdown is consistent with conditions found in the Sandia-Z-machine type rimfire switch. For a flashover gap distance of 24 mm and a simultaneous excitation within ∼ 5 microseconds, we observe an average reduction in the flashover voltage from 164 kV to 142 kV at 3.7 bar when the volume discharge is turned on. The test setup utilizing a magnetic switching scheme operating at 320 kV and 10 kA is briefly discussed along with the breakdown properties and the spectral characterization of the volume/surface flashover discharge plasma. In general, UV light propagates relatively unattenuated for wavelengths >160 nm in the high pressure SF_{6} from the volume discharge to the dielectric surface, setting up conditions which are conducive to photoelectron emission from the dielectric.
Silicon organic thin films have been prepared by RF hollow cathode plasma chemical vapor deposition system, from hexamethyldisilazane (HMDSN) as the source compound, under different plasma conditions, namely feed gas and applied RF power. The feed gas has been changed from argon to nitrogen, and the power has been varied between 100 W and 300 W in N_{2}/HMDSN plasma. The plasma active species (electrons, ion flux rate, and UV radiation) contributing to the films growth mechanisms have been identified by electrical probes and optical emission spectroscopic analysis. The films have been investigated for their thickness and deposition rate, using quartz crystal microbalance, and sensing properties relating to humidity and gas (NH_{3}, CO_{2} and O_{2}) sorptive investigations, using the piezoelectric effect of quartz crystals of the quartz crystal microbalance. The effect of the different plasma conditions on the plasma phase characteristics and deposited thin films properties, as well as the correlations between deposition rate and plasma characteristics and between sorptive properties, water contact angles and thin films surface morphology are reported.
Gas cleaning using plasma technology is slowly introduced into industry nowadays. Several challenges still have to be overcome: increasing the scale, safety, life-time and reducing costs. In 2006 we demonstrated a 20 kW nanosecond pulsed corona system. The electrical efficiency was > 90%. O-radical yields were found to be very high (3-7 mole/kWh). However, to be competitive, high costs of the pulsed power technology are still a major hurdle. Here we present a novel modulator for efficient generation of large volume corona plasma. Only a small amount of expensive high-voltage components are required. Switching is done at an intermediate voltage level of 1 kV with standard thyristors. At the high-voltage side, only a diode and a pulse transformer are needed. The estimated costs are about 5 kEuro/kW, whereas for state-of-the-art pulsed power technology these costs usually are about 20-30 kEuro/kW. Detailed investigations on the modulator and a wire-plate corona reactor will be presented. Modulator parameters have been varied systematically as well as reactor parameters (number of electrodes, electrode-plate distance). The O-radical yield was determined from the measured ozone concentrations at the exhaust of the reactor. With a detailed kinetic model, ozone concentrations could be calculated back to the initial O*-yields. The following conclusions will be discussed: for all parameters, an electrical efficiency of > 90% could be obtained. With fast imaging, the average streamer width was found to be ∼ 737 μm and an estimate for the plasma volume was made. The obtained yields of O-radicals (1-4 mole/kWh) are excellent. The conditions to obtain high yields will be discussed.
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