Calculation of Laminar Flows of Plasma in the Channel of a Plasmatron with the Self-Adjusting Length of the Electric Arc

A simplified method is suggested for the calculation of the parameters of laminar flows of plasma in the channel of a plasmatron. A new analytical solution of the Elenbaas–Heller equation is derived, which generalizes the channel model of electric arc to the case when the volume radiation makes a significant contribution to the electric arc energy balance. Numerical calculations are performed in order to determine the electric field intensity, the longitudinal pressure gradient, and the heat transfer to the electric arc channel wall depending on the working parameters of the plasmatron in a laminar flow of gas in a stabilized section. In determining the arc length, it is assumed that the electric arc is shifted downstream of the flow and, at the same time, performs random walks over the channel cross section. The walks occur under the effect of vortexes whose characteristic size is of the order of the arc diameter.     

Features of pulse substrate bias voltage generation with electron tubes

Features of pulse substrate bias voltage generation with electron tubes in different operation modes are considered. The overstressed mode with low anode voltage and return of electrons to the grid has practical significance at bias voltages in the kilovolt range under the conditions of large substrate current fluctuations. This mode ensures small bias voltage fluctuations and effective use of the primary DC voltage. When the substrate current spontaneously rises above the critical value, the tubes automatically decrease the bias voltage and suppress current spikes and arcing. Such approach may be used in PVD processes, for ion surface treatment and ion plasma immersion implantation.     

Anode mode in cathodic arc deposition apparatus with various cathodes and ambient gases

The anode mode of a vacuum arc in a cathodic arc deposition apparatus was observed as a function of ambient gas pressure ranging from 0.01 to 300 Pa. The chamber (400 mm in diameter and 600 mm in length) made of stainless steel (SUS304) acted as the anode. The arc was operated at a relatively low constant current of 50 A. The cathode materials used were Al, Ti, Fe, Ni, and Cu, and ambient gases were He, Ne, Ar, H₂, N₂, O₂, and CH₄. The principal results are as follows. (1) As the pressure was increased, the anode mode changed from diffuse-arc to footpoint to plane luminous to anode-spot mode. (2) The anode mode and resultant arc voltage increase were strongly dependent on gas species, and weakly on the cathode material. (3) Comparing diatomic and polyatomic (H₂, N₂, O₂, and CH₄) with mono-atomic molecule gases (He, Ne, and Ar), the onset pressure of the anode mode transition in the former was lower, the arc voltage higher, and the footpoints more numerous, smaller, and clearer. Both the dependence of the ambient pressure and the influence of the cathode materials and gas species on the anode mode changes were explained by the ion deficiency theory.     

Equilibrium states of an ion-beam plasma with magnetized electrons at low pressures

Results are presented of an experimental investigation of an ion-beam plasma with magnetized electrons in the cathode channel of an ion accelerator with an anode layer. New data are reported on the spatial distributions of the local plasma parameters (plasma potential, electron temperature, electron and ion densities) as functions of the external parameters of the discharge (magnetic field strength, anode voltage, and working gas pressure) in regions with strong, nonuniform electric and magnetic fields. Pis’ma Zh. Tekh. Fiz. 24, 33–38 (March 12, 1998)     

Metal transfer modes of twin-wire indirect arc welding

Metal transfer modes of twin-wire indirect arc welding are studied and the effects of welding parameters on transfer modes are investigated in this paper. The progress of transition is captured by a high speed camera system with a xenon lamp as light source in order to remove the intense arc light. An oscilloscope is used to record the values of the parameters. Results show that anode and cathode have different transfer modes under certain conditions because of different melting rates. All the transfer modes are classified as short-circuiting transfer and free-flight transfer. The latter could be subdivided into globular transfer, projected transfer, streaming transfer, etc. The metal transfer modes of TWIAW are influenced by the welding current, arc voltage and shielding gas. With an increase in welding current and arc voltage, the transition frequency increases and droplets become smaller. Images indicate that the metal transfer modes influence arc shape periodically because of the detaching force and retainable force changing periodically.     

Metal transfer modes of twin-wire indirect arc welding

Metal transfer modes of twin-wire indirect arc welding are studied and the effects of welding parameters on transfer modes are investigated in this paper. The progress of transition is captured by a high speed camera system with a xenon lamp as light source in order to remove the intense arc light. An oscilloscope is used to record the values of the parameters. Results show that anode and cathode have different transfer modes under certain conditions because of different melting rates. All the transfer modes are classified as short-circuiting transfer and free-flight transfer. The latter could be subdivided into globular transfer, projected transfer, streaming transfer, etc. The metal transfer modes of TWIAWare influenced by the welding current, arc voltage and shielding gas. With an increase in welding current and arc voltage, the transition frequency increases and droplets become smaller. Images indicate that the metal transfer modes influence arc shape periodically because of the detaching force and retainable force changing periodically.     

Analysis of high-frequency processes in an electric-discharge chamber of a three-phase plasma torch at high working gas pressure

The paper deals with electrophysical processes in an electric-discharge chamber of a three-phase AC plasma torch with nitrogen as working gas. The frequency characteristics of voltage pulsations depending on current, gas mass flow rate, power, and pressure are obtained. Photos of arc burning processes in the plasma torch discharge chamber at different parameters are presented. It is shown that two arcs burn simultaneously in the plasma torch chamber and the third one either extinguishes or arises. These investigations might be useful when creating various technological processes by applying three-phase AC plasma torches operating on inert gases.     

Transverse Electric Discharges in Supersonic Air Flows: Space-Time Structure and Current-Voltage Characteristics of Discharge

The space-time evolution of potential distribution in a pulsed transverse discharge in a supersonic jet of air is studied in a mode close to the current generator mode. The current dependences of the longitudinal electric field intensity and of the discharge channel diameter are measured for different values of pressure in the jet. It is demonstrated that the electric field intensity decreases with increasing discharge current by the power law, with the exponent being close to that for a highly contracted glow or arc discharge in the absence of flow. The increase in current is accompanied first of all by an increase in the discharge channel cross section. The characteristics of the oscillatory mode of discharge burning are studied for discharge power supplies, which are close to the current generator mode. The obtained dependences of the oscillation period on the external parameters of discharge, namely, current, pressure, and interelectrode spacing, are interpreted. An expression is derived which describes the maximal extent of discharge along the flow in the case of instability due to external electric circuit. This extent may increase further only in the case of transition to supplies close to current generators; in this case, the extent is restricted by the mechanism of repeated breakdown.     

6063铝材微弧氧化最佳电流密度和槽液温度的探讨

目前的铝合金微弧氧化工艺存在电流密度高、槽液温度范围窄等不足,使其应用受到了限制.为此,从铝材低电流密度和宽槽液温度方面研究了6063铝材的微弧氧化工艺,探讨了微弧氧化工艺中电流密度及槽液温度对起弧电压、起弧时间及膜层厚度等的影响.结果表明,同等条件下,电流密度越大,则起弧电压越低,起弧时间越短,膜层越厚;槽液温度越高,则起弧电压越低,起弧时间越短,膜层越厚;在10 min内,得到12μm厚度的膜层,同等时间内比普通阳极氧化膜厚提高4倍;微弧氧化膜的表面显微硬度相对6063铝材高7倍以上.     

Fluctuations of DC atmospheric double arc argon plasma jet

An original DC double anode plasma torch has been devised and tested, which generates a long-time and highly stable argon plasma jet at atmospheric pressure. The arc unsteadiness and dynamic behaviour are investigated through the fluctuations of electrical signals combined with the classical tools, such as the statistic method, fast Fourier transform (FFT) and correlation analysis. The current-voltage characteristics of the argon plasma jet show an increasing tendency. The takeover mode is identified as the typical fluctuation behaviour of the double arc argon plasma jet in our experiment. The FFT and correlation calculation results of electrical signals exhibit the only characteristic frequency of 150 Hz, whereas the high frequency fluctuations are totally disappeared. Such low frequency fluctuation (150 Hz) can be attributed to the inherent characteristic of the torch power source and is independent of any change in the operating parameters. These results indicate that the nature of fluctuation in an argon plasma jet is mainly induced by the undulation of tri-phase rectified power supply. In addition, both arcs are characterized as the one and only system, and each arc root attachment is rather evenly diffused than located at a fixed position on the anode surface. The time shift derived from the cross correlation between the arc voltage and current intensity can be used as an independent parameter to reflect the fluctuating behaviour in the plasma jet.     

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.     

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 criterion of similarity and transition to turbulence for electric arc flows

A method is suggested for determining the similarity criterion and the criterion of transition of an electric arc flow in a plasmatron channel from a laminar regime to a turbulent one (equivalent Reynolds number) that does not require using any reference temperature. Application of this method to the available experimental data on the transition to turbulence demonstrates its correctness and efficiency. The critical value of the proposed similarity criterion corresponding to the boundary of the transition from a laminar regime to a turbulent one has been revealed. A marginal curve separating the regions of the laminar and turbulent regimes of the plasma flow has been plotted in the space of the operating plasmatron parameters. A phenomenon of a double change of the electric arc flow regime with electric current rise upon constant plasma-forming gas flow rate has been discovered.     

Generalization of volt-ampere characteristics of the electric arc in a double-jet plasmatron with tubular single-chamber electrode units

On a double-jet plasmatron with cylindrical single-chamber electrode units, an experimental study of volt-ampere characteristics of the electric arc is conducted at current 105–550 A, voltage 400–1320 V, total flow rate of the plasma-forming gas (air) (0.76–9.83)∙10⁻³ kg ⁄ s, angle between the cathode and anode parts 45–62°, distance between the cathode and anode axes at the outlet from nozzles 0.07–0.2 m, and outlet pressure of ~0.1 MPa. Correlations for these characteristics are obtained.     

Calculation of the Characteristics of the Initial Section of the Plasma Generator Channel

An equilibrium magnetogasdynamic model of plasma is used to calculate the flow and heating of gas in the initial section of the plasma generator channel. The gas is heated by an electric arc. The distribution of the electric field intensity, temperature, velocity, and pressure drop is obtained depending on changes in the current strength, gas flow rate, and the wall thickness of the electrode nozzle. It is found that axial zones of return flow are formed in the vicinity of the initial section of the channel. The calculation results are compared to the experimental data.     

The volt-ampere characteristics of a DC arc plasmatron with a distributed anode spot

A new DC plasmatron with a hot rod cathode and cold nozzle anode was proposed and tested at atmospheric pressure, generating nearly spectrally clean plasmas of air, air/diesel fuel mixture, oxygen, and CF₄. The arc Volt-Ampere characteristic (VAC) is an integral indicator reflecting the general behavior of all the arc parts, among which the most important are the by-electrode layers and positive column. The sensitivity of the VAC to the gas flow velocity in the technologic channel confirmed the external vortex nature of the anode arc spot, which does not hide inside the anode orifice, but exits it and interacts with the gas flow.     

An experimental study concerning the electrical and the thermal characteristics of stabilized arcs

Results are shown of an experimental study concerning the electric field intensity and the useful power of a plasma jet as well as the electron and the atom-ion gas temperature in an argon arc under atmospheric pressure.Notation l _a length of arc - E electric field intensity in the arc column - d diameter of arc channel - d₀ unit diameter - H enthalpy - I _a arc current - Re Reynolds number - T_e electron temperature - T atom-ion gas temperature Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 1089–1095, June, 1972.     

Analysis of a Swirling Flow of Gas in the Diaphragmed Channel of a Plasma Generator

A two-temperature magnetogasdynamic model of plasma is used to calculate a swirling flow of gas (argon) in the diaphragmed channel of a plasma generator and the heating of this flow and to investigate the dependence of the flow on the strength of the current, geometry of the channel, and the flow rate and swirling moment of gas. The effect of the velocity field of swirling flow on the disequilibrium of plasma and on the arc characteristics in varying-area channels is treated. The calculation results are in qualitative agreement with the experimental data.     

Oscillations of the Hall current in a Hall thruster with an anode layer

Burning of an intense discharge in crossed electrical and magnetic fields in a Hall electrojet engine (Hall thruster) is considered. An engine of this type is an azimuthally symmetric device in which the discharge burns in an annular channel between the poles of the magnetic circuit. The anode is usually made in the form of a cavity through which the working gas is supplied (thruster with anode layer, TAL) or in the form of a planar ring mounted in a dielectric channel in a weak magnetic field (stationary plasma thruster, SPT), and the role of the cathode is played by the plasma surrounding the engine. The electrons trapped in the magnetic field between the poles of the magnetic circuit oscillate in the electric field between the anodic and cathodic regions of the discharge, forming the Hall current closed in the azimuthal direction. It is known from practice that discharge of this type is always nonstationary and the main self-sustained oscillations are excited on the atomic time-of-flight frequency (“accelerative” regime). In addition, there exists a region of parameters in which the self-sustained oscillations become stochastic and the discharge current increases sharply (“stochastic” regime). This work is devoted to the induction measurements of the oscillations of the Hall current arising in various regimes of operation.