The investigation focuses on the optical emission spectroscopy of plasma generated by breaking arc between single-component Cu and composite Cu-W electrodes manufactured using shock sintering technology at temperature of 750°C. The electrodes were subjected to arc currents of 4, 50, and 104 A. Optical emission spectroscopy with high spectral and temporal resolution was employed to investigate the plasma with copper and tungsten vapour admixtures. The temporal evolution of temperature in the plasma was determined by the Boltzmann plot technique based on the emission intensities of Cu I spectral lines. Temporal evolution of electron densities were determined from the full width at half maximum of Cu I 515.3 nm spectral line. These initial plasma parameters integrated over the volume of breaking arc were utilized to calculate the temporal evolution of plasma compositions and contents of metal vapours admixtures in discharge gap.

Plasma of electric arc discharge burning between different types of composite Cu-W electrodes was investigated. Electrodes manufactured of Cu-W composite materials (30/70% by mass) by shock sintering technology at temperatures of 750, 850, 950, and 1050°C were used. Optical emission spectroscopy techniques were applied to determine the main plasma parameters. Specifically, the side-on spectra of plasma emission were registered using a space-resolved spectrograph with a CMOS camera as a sensor device. The plasma thermodynamics properties were calculated based on the equilibrium plasma composition, which was determined using experimentally obtained radial distributions of temperatures and atom concentrations of the metals.

This work is a part of acomplex investigation of the interaction of Cu-W composite materials with thermal electric arc discharge plasma. The plasma of 3.5 A DC arc discharge between novel Cu-W composite materials, fabricated by shock pressing technology at the temperature of 750°C, was studied at this stage. Spectra of such plasma emission were registered and treated to determine the radial distributions of plasma temperature in three different cross-sections of the plasma channel, namely in near-cathode, near-anode and middle cross-sections.

Mean Absorption Coefficients (MACs) represent a potentially suitable way of calculation of radiation transfer in relatively complex geometries. They allow utilization of well established radiation transfer models such as DOM or P1 approximation while removing the complexity of the real spectrum, thus greatly reducing the computation power and time requirements of these models. However, no generally accepted method of MAC prediction was proposed so far, which would be applicable in the wide variety of conditions. This paper presents but a small, yet important step in a search for the ultimate MAC method. It provides an accuracy evaluation of three different MAC methods, namely line-limited Planck MAC, Rosseland MAC and hybrid MAC, while applied to the case of air plasma at various pressures. The line limited Planck MAC proved to be the most accurate method at low pressure, but its reliance on predefined spatial parameter called Characteristic absorption length makes it hard to apply in real situations. The other two methods proved unsatisfactory results for low pressure thermal plasma. However, the hybrid MAC was found to be superior at elevated pressure providing possibly the most universal option for radiation evaluation.

This study presents a numerical model of the hybrid-stabilized argon–steam thermal DC plasma torch of a new design for generating an argon–steam plasma suitable for efficient abatement of persistent perfluorinated compounds. The model includes the discharge region and the plasma jet flowing to the surrounding steam atmosphere contained in a plasma-chemical chamber. Compared to previous studies, the torch had a smaller nozzle diameter (5.3 mm) and a reduced input power (20–40 kW) and arc current (120–220 A). The outlet region for the plasma jet extends to 20 cm downstream of the exit nozzle. Fluid dynamic and thermal characteristics together with diffusion of argon, hydrogen and oxygen species, and distribution of plasma species in the discharge and the plasma jet are obtained for currents from 120 to 220 A. The results of the calculations show that the plasma jet exhibits high spatiotemporal fluctuations in the shear layer between the plasma jet and colder steam atmosphere. The most abundant species in the plasma jet are hydrogen and oxygen atoms near the jet center, and molecules of H 2 , O 2 and OH in colder surrounding regions. Satisfactory agreement is obtained with measurements of the radial temperature and electron number density profiles near the jet center close to the nozzle exit.

The results of optical emission spectroscopy (OES) investigation of plasma of electric arc discharges in steadystate mode between Cu-Cr composite electrodes, manufactured at different sintered temperatures: 750, 850, 950 or 1050 °C, is presented. In particular, the impact of sintering temperature on erosion resistanceof such composite materials, which was determined in indirect manner by estimation of metal vapours content in the midsection of discharge gaps, is studied by the analysis of plasma parameters. These contents were calculated in assumption of local thermodynamic equilibrium (LTE) on the base of experimentally obtained radial distributions of plasma temperature and electron density.

Numerical simulation of mixing of argon- and water-plasma species in argon-steam arc discharge has been investigated in thermal plasma generator with the combined stabilization of arc by axial gas flow (argon) and water vortex. Mixing process is described by the combined diffusion coefficients method in which the coefficients describe the diffusion of argon “gas”, with respect to steam “gas”. Calculations for currents 150–600 A with 15–40 standard liters per minute (slm) of argon reveal inhomogeneous mixing of argon and oxygen-hydrogen species with the argon species prevailing near the arc axis. However, calculations for currents higher than 400 A were not straightforward and a phenomenon of premixing of argon and steam species in the upstream discharge region was predicted from modelling to obtain reasonable agreement with experimental data. Premixed argon-steam plasma has a global impact on the plasma jet parameters near the exit nozzle as well as on the overall arc performance. The results of thermo-fluid fields, species mole fractions and radiation losses from the discharge are presented and discussed. Our former calculations based on the homogeneous mixing assumption differ from the present model in temperature, enthalpy, radiation losses, and flow field. Comparison with available experiments exhibits very good qualitative and quantitative agreements for the radial temperature profiles and satisfactory agreement for the velocity profiles 2 mm downstream of the exit nozzle.

This work deals with investigations of thermal plasma of electric arc discharge between sintered composite Cu-Cr electrodes, which can be used in electrical contacts of vacuum circuit breakers. Breaking arcs between composite Cu-Cr as well as single-component copper electrodes were used to study the electrical properties, plasma optical emission and electrodes surface modification behavior. In particular, the temporal evolution of plasma emission spectra of electric breaking arcs in air atmosphere was investigated by Optical Emission Spectroscopy (OES). Scanning Electron Microscopy (SEM) with Energy-dispersive X-ray Spectroscopy (EDXS) were applied to analyze the cross-section of working layer of electrodes surface modified by the heat flux from the discharge.

This paper deals with the evaluation of radiation properties of air arc plasma with various admixtures of Cu, Ag, and Fe, respectively. Under assumption of isothermal plasma cylinder, the net emission coefficients were calculated for various arc radii as a function of the plasma temperature up to 30000K. For plasma with prescribed temperature profile, the equation of radiation transfer was solved in the P1approximation, and the radiation flux and its divergence were calculated.

In this work the plasma of electric arc discharges between Cu-Cr composite electrodes, which material were pressured and sintered at different temperatures 750 or 1050°С, are investigated by Optical Emission Spectroscopy (OES). The Scanning Electron Microscopy (SEM) with Energy-Dispersive X-ray Spectroscopy (EDXS) are used to study the working surface of electrodes, modified by thermal effect of breaking electrical arc in the air atmosphere. The erosion intensity of electrodes’ material due to plasma-surface interaction is estimated in indirect way by determination of metal vapours content in the discharge gap in an assumption of local thermodynamic equilibrium (LTE). The plasma composition is calculated in this case on the base of experimentally determined plasma parameters: temperature and electron density.

This work deals with investigations of model plasma source realised as electric arc discharge in gas atmosphere between Cu-Cr composite electrodes. Radial distributions of temperature and electron density in arc plasma column were studied by optical emission spectroscopy. The content of electrode metals' vapours in discharge was calculated on the base of experimentally obtained plasma parameters as initial data. So, in this way the erosion properties of such composition can be determined.

The aim of this paper is to evaluate radiation properties of air arc plasmas with various admixtures of copper vapours. The first order of the method of spherical harmonics (P1-approximation) has been used as the way to solve the equation of radiation transfer. Calculations of the absorption coefficients for a thermal plasma have been performed as a function of the temperature and the frequency. The frequency variable in the equation of transfer was handled by means of multigroup method. Methods for prediction of the average absorption coefficients were described and compared in detail. The net emission coefficients have been determined for comparison.

Noise diagnostics was performed on a tungsten hairpin cathode that was used in conventional scanning electron microscope (SEM) which operates in a high vacuum. The focused beam was firstly measured and its power spectrum obtained in order to characterize its slope in the lower frequencies which are connected with the events occurring on the cathode surface during the emission of electrons. Further experiments involved additional noise measurements which evaluated electron beam with altering beam energy, in particular at 5 kV, 10 kV and 20 kV up to 30 kV; with and without electron beam scanning involved and with different levels of cathode heating. Obtained results were evaluated in relation to a 1/f type noise component, generation-recombination process on the cathode surface, on the shot noise and on the velocity fluctuations caused by the ion oscillations. Achieved results were discussed.

Thermal plasma of electric arc is widely used in various technological applications: welding, cutting, lamps, spraying, protection of electrical installations, etc. Process efficiency is defined by different parameters that determine arc operation and influence the energy transfer within the medium. All energy exchanges depend on the medium, which is modified by the presence of the arc and more particularly by the appearance of new species from contact erosion. Sintered Cu-Cr composites are widely used as electrical contacts for vacuum circuit breakers. These materials take advantage of the high thermal and electrical conductivity of Cu and of the refractory and oxygen getter properties of reinforcing Cr particles. The aim of this paper is to give results of the calculation of the equilibrium composition of argon and air plasma with various admixtures of Cu and Cr.

Mean absorption coefficients (MACs) offer great potential for fast numerical calculation of radiation heat transfer. They are based on replacing complex absorption coefficient spectrum by a handful of frequency bands with a single, temperature dependent value assigned to each band. Accuracy of radiation transfer calculation thus depends on the accurate interpretation of the mean value inside each frequency band as well as on the proper band distribution. Yet finding optimal band distribution is not an easy task often requiring numerical optimization process. This contribution focuses on the parameters of such optimization process, namely selection of an objective function and its effect on the optimal band distribution. It demonstrates, that improper objective functions can produce physically unreasonable artifacts in the calculation of radiation heat transfer. Optimal formulation of the objective function is proposed in this contribution.

Radiation heat transfer plays an important role in the energy balance of plasma in an electric arc and its accurate prediction is essential for the development of new electrical devices. Unfortunately, a very complex spectrum of the absorption coefficient makes accurate radiation heat transfer calculations a very challenging task, especially with complex geometries. Numerical approximation of the absorption coefficient is therefore commonly used to reduce computing demands. This paper presents our contribution to the topic of computing requirements reduction, namely the problem of frequency band selection for mean absorption coefficients (MACs). We show that, with the proper band distribution and averaging method, even a very low number of bands can be sufficient for an accurate approximation of the real radiation heat transfer. The band selection process is based upon numerical optimization with a mean value of each band being calculated as a line limited Planck MAC. Both the line limiting factor and associated characteristic plasma absorption length are investigated in detail and an optimal value equal to the three plasma radii is proposed. Tables for three bands mean absorption coefficients in air at the pressure of 1 bar and temperature range spanning from 300 K to 30 kK are included in this paper. These tables serve as input parameters for a fast evaluation of radiation transfer using either the P1 or discrete ordinates method (DOM) approximation with satisfactory accuracy.

The objective of this work is to compare the accuracy of several approximate models of radiative properties for the prediction of radiative transfer in air arc plasma at the temperatures in the range of 300 - 25 000 K and the pressure of 0.1 MPa. Calculated absorption coefficients are used to generate the parameters of different models. The radiative transfer inside the cylindrically symmetrical air plasma with prescribed temperature profile was studied. The equation of radiative transfer was solved using the P1 and SP3 approximations, calculated radiative source term in the energy equation (net emission) was compared with results obtained by spectral integration.

In this paper, attention has been given to the absorption properties of argon arc plasma at the pressure from 0.1 MPa to 5 MPa. The frequency interval (0.01–10) x10 s has been divided into several frequency groups. Depending on the absorption properties of the medium for the given frequency group, the average absorption coefficient has been taken as either a group Rosseland or group Planck mean. These mean absorption coefficients were calculated for thermal plasma Ar as a function of plasma temperature in the range (1 000, 35 000) K for each of frequency groups. Different splitting procedures of the frequency interval have been used to find the optimal values of mean absorption coefficients for further calculations of radiation characteristics. Attention has been given to calculation of net emission coefficients which determine the radiation losses in the arc centre. Net emission coefficients have been derived for isothermal cylindrical plasmas of radii from 0.01 to 10 cm. Spectral coefficients of absorption Spectral coefficients of absorption (absorptivities) are proportional to the concentration of the chemical species occurring in the plasma. Concentrations of argon atoms, ions and electrons calculated under assumption of local thermodynamic equilibrium [1] are shown in Fig. 1 for pressures of 0.1 MPa and 2.0 MPa. Spectral absorption coefficients  were calculated using semi-empirical formulas described in [2] to represent both continuum and line radiation. Continuous spectrum is formed by boundfree transitions (photo-ionization) and free-free transitions (bremsstrahlung). Spectral variation of the absorption coefficient of a spectral line depends on the profile of the line. The line shape is given by simplified Voigt profile. Our calculations of line broadening account for Stark and Doppler half-widths and line shifts, resonance broadening and polarization shift. Theoretical formulas are given in [2]. The total absorption coefficients given by both continuous and line radiation at temperatures of 5 000 K and 20 000 K are given in Fig. 2. 43 EPS Conference on Plasma Physics P1.113

Summary form only given. The paper focuses on numerical simulation of mixing of plasma chemical species under extreme temperature and density gradients in the arc discharge with hybrid stabilization of an electric arc by axial argon flow and tangential water vortex (hybrid-stabilized arc). This arc is being used at present for plasma spraying and for production of syngas (CO + H 2 ) from municipal waste or biomass.We assume one-fluid, two-dimensional, axisymmetric, unsteady, compressible and generally turbulent plasma flow, with mixing of water and argon plasma species considered using the so called combined diffusion coefficients method. Diffusion processes due to pressure, temperature and concentration gradients, and due to an external electric field are taken into account [1, 2]. Energy losses from the argonwater plasma by radiation are calculated by the partial characteristics method [3]. Turbulent effects (even though very small) are treated by Large Eddy Simulation (LES) with the Smagorinsky subgrid-scale model. Results carried out for currents 150-300 A and for argon mass flow rates 15-22.5 standard liters per minute show that: a) Mixing of plasma species is inhomogeneous under the studied conditions: argon species are dominant in the central regions of the arc, water ones in arc fringes. b) Temperature and ordinary (concentration) diffusions are the principal contributions in the argon mass diffusion flux. c) The combined ordinary diffusion is highest in the regions with steep radial temperature gradients while the combined temperature diffusion in a shear layer between argon and water plasmas.