Antonín Brablec

Atmospheric-pressure diffuse coplanar surface discharge for surface treatments

We report results from a plasma source; a diffuse coplanar surface discharge (DCSD), which is capable of generating macroscopically uniform thin layers of diffuse plasmas in air and other reactive gases at atmospheric pressure. DCSD is a type of dielectric barrier discharge generated on the surface of a dielectric barrier with embedded electrodes, which appears to be advantageous to surface treatment and deposition processes. Preliminary results on hydrophilization of polypropylene nonwoven fabric are also presented.

Atmospheric pressure glow discharge in neon

The dielectric barrier discharge burning at atmospheric pressure usually has a filamentary non-homogeneous form. However, it was found that uniform dielectric barrier discharge can be generated in helium, nitrogen and in the mixture of argon with acetone under specific conditions. Such uniform discharge is called atmospheric pressure glow discharge (APGD). We studied dielectric barrier discharge burning in neon at atmospheric pressure and we found that the APGD can also be generated in neon. We measured the electrical characteristics of APGD in neon for different voltages and frequencies of power supply and different gas flows. We found that higher gas flow stabilizes the APGD and we determined the area of parameters in which the APGD burns. The images of discharges were recorded by a video camera and emission optical spectra were measured by a spectrometer. The properties of the discharges in neon were compared with the properties of discharges burning in argon and in the mixture of neon with argon.

Comparative study of diffuse barrier discharges in neon and helium

Diffuse dielectric barrier discharges in neon and helium at atmospheric pressure were studied. The discharges were generated between two metal electrodes, both covered by an alumina layer and driven by ac voltage of frequency 10 kHz. The discharge gap was 2.2 mm and 5 mm, respectively. The discharges were investigated by electrical measurements and by temporally and spatially resolved optical emission spectroscopy. The experimental results revealed similar discharge behaviour in both gases being considered. Although the discharges were ignited at slightly different electric field strengths, their evolutions were found to be similar. At maximum discharge current the spatial light intensity distribution was characterized by the formation of a cathode fall. A difference was observed in the magnitudes of the current density only. In addition to the regime with a single discharge pulse per voltage half period T/2, a discharge mode with two and more subsequent current pulses per T/2 (also referred to as the pseudoglow discharge regime in the literature) was obtained due to an increase in the voltage amplitude or an admixture of nitrogen.

The high pressure torch discharge plasma source

We present a plasma source which works on the principle of the arc torch discharge. The powered electrode of the arc torch discharge was made from a thin pipe that simultaneously acts as the nozzle through which the working gas flows to the discharge region. The flow of the working gas stabilizes the arc torch discharge and a well defined plasma channel is created. The advantage of this system is that it is able to work at high pressure of working gas up to atmospheric pressure inside the plasma-chemical reactor and also in free space.

Permanent hydrophilization of outer and inner surfaces of polytetrafluoroethylene tubes using ambient air plasma generated by surface dielectric barrier discharges

We present an atmospheric pressure ambient air plasma technique developed for technically simple treatment of inner and/or outer surfaces of plastic tubes and other hollow dielectric bodies. It is based on surface dielectric barrier discharge generating visually diffuse plasma layers along the treated dielectric surfaces using water-solution electrodes. The observed visual uniformity and measured plasma rotational and vibrational temperatures of 333 K and 2350 K indicate that the discharge can be readily applied to material surface treatment without significant thermal effect. This is exemplified by the obtained permanent surface hydrophilization of polytetrafluoroethylene tubes related to the replacement of a high fraction (more than 80%) of the surface fluorine determined by X-ray photoelectron spectroscopy. A tentative explanation of the discharge mechanism based on high-speed camera observations and the discharge current and voltage of measurements is outlined.

Planar UV excilamp excited by a surface barrier discharge

In the contribution, typical characteristics of planar excilamp based on KrCl* and XeCl* exciplex molecules are presented. The excitation of working mixture Kr/Xe/Cl2 is realized by means of the surface barrier discharge at pressures of 0.1 - 1 bars. They were measured and discussed spectra emitted by the plasma in UV/VIS/NIR spectral range, intensity of emitted light vs. total pressure in the discharge and a composition of the working mixture, power of emitted light, resp. The radiation power vs. input electric power, space distribution of emitted light including basic electrical parameters of the discharge were also measured. It was shown that characteristic power of UV radiation emitted in the spectral range 200 - 400 nm is about 6 mW/cm2 while the efficiency could be about 8 %.

Deconvolution of spectral line profiles: solution of the inversion problem

We present a method for the deconvolution of spectral line profiles - the subtraction of the apparatus function. This inversion problem requires solution of the Fredholm integral equation of the first kind. For this purpose we suggest the use of B-splines. The efficiency of the approach is demonstrated using test examples as well as the deconvolution of the H spectral line profile, measured by means of the Fabry-Perot interferometer. The H line was emitted by a low temperature plasma in RF discharge burning in water vapour at reduced pressure. This deconvolution method is compared with the standard least squares method, where the initial profile is described by the Voigt function.

Experimental and theoretical characterization of a multi-wavelength DBD-driven exciplex lamp operated with mercury bromide/rare gas mixtures

Emission spectra from an atmospheric-pressure dielectric barrier discharge (DBD) with HgBr2/He or HgBr2/Xe/Kr mixtures, as well as the electrical characteristics, were investigated at repetition frequencies of sinusoidal voltage pulses up to 125?kHz. In the spectra, the study revealed radiation from HgBr(B?X, C?X) exciplex molecules, atomic lines of mercury and rare gases, and in mixtures with xenon, radiation of XeBr(B?X, B?A) exciplex molecules. Regularities in the spectral characteristics of the radiation from the gas-discharge plasma were discussed. The electron energy distribution function, the specific energy lost in the processes involving electrons, the electron temperature and density, and the rate constants of elastic and inelastic electron scattering by the components of the working mixture were calculated as functions of the reduced field E/N. The high-frequency atmospheric-pressure barrier discharge in mixtures of mercury dibromide with gases can be used in multi-wavelength exciplex lamps, operating in the UV and visible regions.

A study of the electron energy distribution function in the cylindrical magnetron discharge in argon and xenon

We studied the behaviour of the cylindrical magnetron discharge in argon and xenon. We concentrated ourselves mainly on description of the transport of charge carriers in the region from the negative glow to the anode. We attempted to describe this transport using Monte-Carlo simulations as well as by standard transport parameters, mobility and diffusion coefficients. We also experimentally determined the radial shape of the electron energy distribution function (EEDF) including its detectable anisotropy caused by the presence of magnetic field. For the EEDF determination we used the planar probe whose collecting surface was adjustable at different angles to the direction of the magnetic field as well as movable in radial direction. The results of modelling and experiment are discussed.

Atmospheric-pressure plasma treatment of ultra-high-molecular-weight polypropylene fabric

Effects of an atmospheric pressure surface discharge on a woven ultrahigh molecular weight polyethylene fabric were studied. Our results show that the surface discharge can be used to achieve a higher long-term wettability and improved adhesion properties of textile materials.