E. Kh. Isakaev

Investigation of low-temperature plasma generator with divergent channel of the output electrode and some applications of this generator

A review is made of experimental and theoretical investigations of processes occurring in low-temperature plasma generators (LTPG) with divergent channel of the output electrode, and the possibilities of utilizing these generators in new plasma technologies are analyzed. Comparison is made of the characteristics of discharge (including the current-voltage characteristic) in a divergent channel and in a cylindrical channel of uniform cross section. The effect of divergent channel of the output electrode and of its expansion ratio on the pattern of physical processes in LTPGs of different designs is studied. Investigations are performed of the distribution of electric current and heat flux density along a channel with a segmented output electrode. The voltaic equivalents of heat fluxes to cathode and anode are determined. The process of “shunting” of discharge is investigated, which causes fluctuations of electric arc-burning voltage. The investigations involving an LTPG with divergent channel reveal that the voltage amplitude in the case of shunting decreases with increasing current strength and, at high currents of argon arc, does not exceed 1–2 V. Results are given of spectral and visual investigations of LTPG. It is demonstrated that, in an LTPG with divergent channel, the plasma temperature in the region of energy input at currents of 300 A and higher exceeds 30 000 K. The significant part is found which is played by vacuum ultraviolet radiation in the process of closing the arc to anode. The mechanisms of erosion of the tungsten cathode tip are investigated, which play an important part in increasing the cathode service life by way of recirculation of tungsten atoms because of their ionization in the discharge gap. Results are given of using an LTPG with divergent channel of the output electrode in plasma technologies of surface hardening, cutting, and hard-facing of metals. The technology of plasma hardening of wheel pairs, adopted by the RZhD (Russian Railroads) Joint-Stock Company, provides for increasing the service life of railroad wheels by a factor of 1.5–2.

Emission spectroscopy of highly ionized high-temperature plasma jets

This paper deals with advanced studies on the optical emission spectroscopy of atmospheric pressure highly ionized high-temperature argon and nitrogen plasma jets generated by a powerful arc plasmatron. The emission spectra are taken in the 200?1000?nm range with a spectral resolution of ~0.01?0.02?nm. The exposure times are 6 ? 10?6?2 ? 10?2?s, the spatial resolution is 0.02?0.03?mm. The recorded jet spectra are abundant in spectral lines originating from different ionization stages. In nitrogen plasmas, tens of vibronic bands are also observed. To interpret and process these spectra such that plasma characteristics can be derived, a purpose-developed automated processing system is applied. The use of a CCD camera at the spectrograph output allows a simultaneous recording of the spectral and chord intensity distributions of spectral lines, which can yet belong to the overlapped spectra of the first and second orders of interference. The modern optical diagnostic means and methods used permit the determination of spatial distributions of electron number densities and temperatures and evaluation of rotational temperatures. The radial profiles of the irradiating plasma components can also be obtained. Special attention is given to the method of deriving rotational temperatures using vibronic bands with an incompletely identified rotational structure.

Study of a low temperature plasma generator with a divergent output electrode channel

Results of experimental studies of a plasma generator with a divergent output electrode channel are presented, and a comparative analysis is performed of operation of this plasma generator and plasma generator with cylindrical channel of constant cross section. Studies of sectioned output electrodes are performed along with plasma generators with solid electrodes. The influence of sectioning on the parameters of electric discharge is studied. It is shown that the optimal degree of divergence of the output electrode channel is a complex function of different parameters.

Investigation of temperature fields on the surface of tungsten cathode of a high-current arc using a high-speed matrix

A method is suggested of time-space analysis of temperature fields on the surface of tungsten cathode of a high-current electric arc using a VS-FAST high-speed video camera (manufactured by VideoScan, Moscow). The importance of contribution made by plasma radiation to the cathode surface emissivity being measured is considered, and the methods of taking this contribution into account are identified. Experiments reveal the possibility of using this high-speed video camera as a pyrometer providing for time resolution up to 2 μs and space resolution of about 30 μm.

Spectroscopic Analysis of Spatial Distribution of the Electron Temperature and Concentration in High-Enthalpy Flows of Argon and Nitrogen Plasma

The paper deals with the spectral determination of the temperature and number density of electrons in high-enthalpy flows of highly ionized plasma of argon and nitrogen at atmospheric pressure. Radial distributions of these parameters in different cross sections of the plasma jet are obtained. An automatic system of data acquisition and processing is used to investigate the distribution of atoms and ions of argon and nitrogen over excited states. Different methods of spectral determination of ne and Te are compared with one another in application to the plasma being investigated.

Spectral determination of local values of electron concentrations and temperatures in a strongly ionized nitrogen plasma using a CCD sensor

Using an earlier described automated measuring system and the procedure of processing “matrix” spectra, we detect and process the set of NI, NII, and NIII spectral lines, which allows independent determination of local electron concentration and temperature values in a strongly ionized nitrogen plasma in the temperature range 15–35 kK. From measurements of local contours of lines NI and NII, we obtain the radial electron concentration distributions in the space of an inhomogeneous plasma and compare them with the results of diagnostics on continuous radiation of the plasma. We study local distributions of excited nitrogen ions according to excitation states in order to elucidate the question on the possible quasi-Boltzmann description of these distributions with local electron temperature values.

Spectral Measurements of Local Parameters of Plasmas Using CCD Matrices

The possibility of obtaining local contours of spectral lines of strongly inhomogeneous doubly ionized nitrogen plasma with the help of a system that involves a spectrograph and a megapixel CCD matrix is shown. An automated measuring system based on a CCD matrix is described, and a procedure for processing matrix spectra is presented. The results of the Abel transform of the chord distributions of spectral line intensities of ions with different degrees of ionization are presented. Determined local contours of spectral lines can be used for estimating local temperatures and electron concentrations in strongly ionized spatially inhomogeneous plasmas.

Analysis of Metrological Potentialities of a High-Current Arc in Plasma Generators with a Diverging Channel

The paper is concerned with substantiating a high metrological “quality” of the cathode section of a stationary electric arc in plasma generators which have a current density of over 2 kA/cm2, a diverging anode channel, and vortex stabilization. An automated spectroscopic system and a system for fast visualization of plasma filament are used to demonstrate the high reproducibility and stability of the electrical parameters of the arc and of the space and time radiating characteristics of highly ionized plasma of the cathode region of the discharge. The results of analysis of the thermodynamic state of plasma in the cathode region of the discharge point to the validity of the conditions of partial local thermodynamic equilibrium in this region. The use of the developed system of automatic acquisition and processing of spectroscopic information enables one to obtain unique (as regards the scope and accuracy) data on the radiating characteristics of lines of atoms and ions of different multiplicity.

A high-power low-temperature air plasma generator with a divergent channel of the output electrode

We have developed and studied a powerful high-enthalpy (H ≥ 20 kJ/g) air plasma jet generator with a divergent channel of the output electrode, which belongs to the class of dc plasmatrons with a thermionic cathode. The plasma generator possesses an efficiency of about 80% and ensures the formation of slightly divergent (2± = 12°) plasma jet with diameter D = 50 mm and a mass-average temperature of 6000–9000 K.

Synthesis of carbon nanotubes by high current divergent anode-channel plasma torch

In this study we propose the high-performance technology to produce carbon nanotubes (CNT) in plasma jet reactor by means of a direct current plasma torch. This technology provides excellent opportunities to investigate a direct evaporation of materials and their subsequent condensation on the carbon surface. Experiments were carried out at the electric power of a plasma torch up to 30 kW. Helium and argon served as plasma gases. CNT synthesis at pyrolysis of soot was catalyzed by the metal disperse powders of Ni, Co, Y2O3. We applied x-ray diffraction and electronic microscopy to investigate the structure of obtained products. Also we utilize the thermogravimetric analysis to determine the phase structure of carbon nanomaterials. Using available experimental data we were able to sequentially scale the production process of CNT of desirable space structure. Finally we established that structural and morphological properties of CNT produced at evaporation of soot in the presence of high- percentage combined catalysts depend upon the catalyst structure.