Petr Kloc

An investigation of dielectric barrier discharge in Ar and Ar/NH3 mixture using cross-correlation spectroscopy

Dielectric barrier discharges (BDs) are known to operate in two distinctive modes. The filamentary mode of BD is characterized by a large number of short lasting spatially bounded microdischarges. This type of discharge is typical for most cases of BDs at atmospheric pressure. Under some specific conditions another form of BD may arise. In this mode plasma uniformly covers the whole electrode area. This mode is usually referred to as the diffuse or homogeneous mode of BD.This work presents studies of the filamentary mode of BD in argon and its transition to the diffuse mode by ammonia addition. The discharges were investigated by means of cross-correlation spectroscopy. Particularly, the influence of electrode shape, discharge gap and the influence of ammonia admixture on discharge development were studied. The measurement offers results with high temporal and spatial resolution which are useful for comparison with results of numerical models.The obtained results include the electrical current measurement of discharge in several ammonia admixtures to argon. The diffuse discharge appeared at ammonia admixture above 3 vol%. The observed propagation of streamer in discharge in pure argon for two different electrode configurations is presented. When compared with discharge in pure argon the streamer velocity is decreased for 0.1 vol% ammonia admixture. With increasing ammonia concentration the streamer velocity increases again. The behaviour of presented impurities was observed and the results are included in this report. The basic model of the discharge kinetic is included. For reduced electric field below 10 Td the electron drift is much higher in argon–ammonia mixture than in pure argon.

Radiation transfer in air and air-Cu plasmas for two temperature profiles

In this article we present our results from calculations of the divergence of the radiation flux in a high temperature air-Cu plasma arc. We assumed stationary plasma, with local thermodynamic equilibrium valid throughout the plasma volume. We paid attention especially to the presence of copper lines in the absorption coefficient spectra and their influence on the energy transfer. Two distinct temperature regimes were used, with one focusing on a steep temperature gradient and the other involving a slowly varying temperature profile. The temperature ranges from 25 kK at the arc center down to 3 kK at the plasma arc boundary. Uniform pressure of 1 bar was considered in all cases. The results show that a large amount of energy is emitted by the copper vapor, which helps with cooling the arc.

Atmospheric pressure barrier discharge at high temperature: Diagnostics and carbon nanotubes deposition

Atmospheric pressure dielectric barrier discharge (DBD) in Ar/H2 gas feed with C2H2 or CH4 admixture was studied at room and high temperature of 680 °C by plasma diagnostics (electrical measurements, fast camera imaging, and optical emission spectroscopy). It was shown that filamentary DBD in pure Ar or Ar/H2 can be converted into homogeneous discharge by an acetylene admixture. Fast intensified charge-coupled device (ICCD) camera proved that this homogeneous discharge is an atmospheric pressure glow discharge (APGD) at room temperature whereas at high temperature the discharge mode switches at every half-period between APGD and atmospheric pressure Townsend discharge. The high temperature discharges (610–710 °C) in Ar/H2/C2H2 and Ar/H2/CH4 were also investigated with respect to a surface bound deposition of carbon nanotubes using 5 nm thick iron layer as a catalyst. CNTs were deposited without any dedicated catalyst pretreatment phase. The quality of CNTs, namely, their density, vertical alignment, and w...

On the Selection of Integration Intervals for the Calculation of Mean Absorption Coefficients

In radiation modeling of thermal plasmas non-grey models are applied where the radiative transport is described in several frequency bands (spectral intervals). Hereby mean absorption coefficients have to be calculated by a spectral integration procedure, providing a constant mean absorption coefficient for each band. Depending on the number of bands, one or more integration boundaries have to be selected in order to do the integration. In this paper we evaluate the influence of the selection of these integration boundaries on the mean absorption coefficient and the also radiation transfer by applying the mean absorption coefficients in a radiation transport model. Using a simplified two-band model we demonstrate that the selection of the integration boundary has a large impact on the total model accuracy. We show that in some cases selecting a band boundary right at the frequency where the continuum absorption shows a jump can introduce a significant error into the radiation calculation. The process of the integration interval selection thus demands a global optimization procedure to properly evaluate the boundaries of each frequency band.

Modification of Polymer Surfaces Using Atmospheric Pressure Barrier Discharges

Abstract The objective of the present work is the development of a technique for the deposition of thin films, by means of an atmospheric pressure discharge, onto a pulp board surface, with the desired surface energy, permeability and wear resistant surface. The deposition of thin films was carried out by a surface barrier discharge at the atmospheric pressure. The films were deposited from mixtures of C4F8 with nitrogen. The properties of the thin film substrate systems were investigated by means of contact angle measurement and industrial permeability tests. The chemical composition of the films was studied by means of a Fourier transform infrared spectroscopy. The mechanical properties of the films were studied by means of depth sensing indentation tests performed on samples deposited upon glass plate. The surface topographies of coated and uncoated samples were investigated using a scanning electron microscope.

Diagnostics of Various Phenomena in LV Devices Under Real Switching Conditions

The article deals with issues to be tackled when performing experiments with low voltage devices under real switching conditions and subsequently discusses various phenomena in an experimental device. The first part describes optimum setting of diagnostic equipment mainly for optical diagnostic methods. The second part describes some phenomena encountered during switching process under real switching conditions – arc roots movement (cathode and anode spots). These phenomena are not only important for experimental study itself but also form necessary input data for numerical models and their validation.