V. F. Chinnov

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.

Spectral and kinetic analysis of heterogeneous gas discharge plasma in the flow of an Al, H2O, and Ar mixture

Plasma excited by a longitudinal pulse-periodic discharge in a mixed flow of a buffer gas (Ar), oxidizer (H2O), and aluminum dust is studied. The salient features of its kinetics are the atomic and molecular electronic channels of Al atom transformation, which were not taken into account earlier. They accelerate not only the oxidation process but also aluminum vaporization because the excitation and ionization energies are finally released on the surface of aluminum particles. This work is devoted to experimental and theoretical analysis of these channels.

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.

Optical investigations of the multicomponent plasma of the capillary discharge: Subsonic outflow regime

We present the results of spectroscopic investigations of the plasma of the pulsed discharge in the capillary with the ablation wall made of a carbon-containing polymer, at the pulse energy 50–150 J, the current 50–120 A, and the discharge pulse duration of 9 ms. The system of video registration and fast spectral diagnostics makes it possible to investigate the spatiotemporal evolution of the plasma structure and parameters both inside the capillary volume (1–2 mm in diameter, 3–5 mm in depth) and in the subsonic plasma jet. On the basis of the 2D-matrix high resolution spectra containing the Hα and the Hβ lines, the CN and the Swan molecular bands, and the CuI lines, we obtain the spatiotemporal distributions of the electron density and the plasma temperature in the capillary and the subsonic plasma jet. We reveal the peculiarities of the spatial distribution of the electron density and of the spectral components intensity within both above zones conditioned, in particular, by achievement, in the hot central zone, of an electron temperature above the normal temperature (equal to 16500 K for the Hβ). We analyze the thermodynamic state of the “hot” discharge core and show the possibility of its representation as a highly ionized atmospheric pressure hydrogen plasma.

Kinetic model of Al oxidation by water vapor in heterogeneous plasma: Heterophase kinetics

The kinetic model of gas and heterophase plasma-chemical processes taking place in the working zone of a reactor is extended to the evaporation of aluminum from the surface of microparticles, which results in the mean value of the flux density and evaporation time. It is shown that the balance of aluminum atoms in the working zone is determined by the heterogeneous processes of evaporation of low-melting aluminum and adhesion of refractory oxides, which is the dominant aluminum-containing component of the plasma. The time of flight of microparticles through the working zone in a gas-discharge aluminum-water reactor with a pumping system is experimentally found, which, under the conditions created, coincides with the burnout time of aluminum microparticles. The mechanisms of burnout and reproduction of microparticles (evaporation and microexplosions) are determined, reducing the average size of microparticles in the working zone from 100 to 10 μm.

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.

The Importance of VUV-Radiation in the Anode Region of High-Current Plasma Generators with Diverging Anode Channel

It is demonstrated that a region of a stable laminar mode of arc burning with diffuse flow of current to the anode exists in high-current (I ≥ 250 A, I/d ≥ 40 A/mm) plasma generators with a self-adjusting arc length and diverging anode channel. The most important mechanism providing for the volume ionization of the “plasma-anode wall” transition layer is the photoionization of the cold surface layer of gas by dense VUV-radiation transferred to the periphery from the arc core where the fully ionized plasma has a temperature above 20 000 K. The presence of high-intensity resonance radiation of singly charged nitrogen ions and its absorption at the periphery of the energy release region of the nitrogen arc enable one to explain the experimentally observed nonthermal pattern of distribution of intensity in the radiation spectrum of molecular ion of nitrogen.

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.