Effect of the discharge parameters on the generation of deuterium ions in the plasma of a high-current pulsed vacuum arc with a composite zirconium deuteride cathode

We have studied the mass and charge composition of an ion beam extracted from the plasma of a vacuum arc with a zirconium deuteride cathode for various durations of the arc current pulse (half width at half amplitude) of 2, 4, 7, and 17 μs. It has been established that the fraction of deuterium ions in the vacuum arc plasma increases with the current and the dependence achieve saturation for current of about 1 kA. For the fraction of deuterium atoms in the cathode at a level of 40%, the fraction of deuterium ions in the vacuum arc plasma can exceed 80%. The experimental results have been interpreted theoretically. It has been shown that the main sources of deuterium ions in a microsecond arc discharge are cathode spots. We have developed a model of deuterium desorption during the operation of cathode spots for quantitatively estimating the concentration of deuterium ions in the arc plasma.     

傅里叶变换法计算焊接电弧光谱Stark展宽研究

利用电弧光谱,采用Stark展宽法计算电子密度是测量等离子体电子密度最有效、最准确的方法。而如何从众多展宽机制复合的谱线中分离出Stark展宽是应用Stark展宽法的难点。利用傅里叶变换从测得的光谱线形中分离出Lorentz线形,从而准确获得Stark展宽,并且计算了TIG焊电弧等离子体电子密度的分布。这种方法不需要准确测量电弧温度,不需要测量仪器展宽并且对数据有去噪作用。计算结果表明：在轴线上,TIG焊电弧电子密度随着离钨极距离的增大而减小,变化范围在1.21×1017~1.58×1017 cm-3之间;在径向,电子密度随离轴距离的增大而降低,在靠近钨极区域具有离轴最大的性质。     

Investigation of the Directional Velocities of Ions in a Vacuum Arc Discharge by Emission Methods

This paper is devoted to an investigation of the directional velocities of the ions generated in cathode spots of vacuum arc discharges. By using emission methods of studying the processes in a vacuum arc discharge, which involve the determination of the parameters and characteristics of the discharge plasma by analyzing the ion current extracted from the plasma and the ion charge states, the velocities of ions have been determined for the majority of cathode materials available in the periodic table. Is has been shown that at a low pressure of the residual gas in the discharge gap the directional velocities of the ions do not depend on the ion charge state. Comparison of the data obtained with calculated values allows the conclusion that the acceleration of ions in a vacuum arc occurs by the magnetohydrodynamic mechanism.     

Temperature's optical tomography diagnosis of arc plasma jet flowing into air

An argon arc jet plasma flowing into air is chosen as a practical example to study the multiple species jet plasma's optical computerized tomography (OCT) diagnosis. The refractive index models of the pure argon and the multiple species arc plasmas are supplied. On the basis of which, the temperature reconstruction model of the multiple species arc plasma is further derived. By theoretical calculation, the effect of mixed air on the refractive index is given. For the sake of better proving the effect of directly omitting the mixed air on flow field's temperature reconstruction from the refractive index, a simulated experiment is supplied. Finally, the condition, which can be adopted to estimate that whether the pure argon arc plasma refractive index model still can be used as the temperature reconstruction model of the argon arc plasma jet flowing into air, is proposed.     

An experimental study on the characterization of electric charge in electrostatic dust removal

Automatic dust removal using the electrostatic forces of electrodynamic screen (EDS) is an emerging method for mitigation of energy yield losses caused by dust accumulation on solar collectors. Both electric field distribution and dust particles' charge acquired during the removal process play pivotal roles in thorough evaluation of EDS performance. Previous studies have comprehensively analyzed the electric field distribution in EDS. In this paper we have conducted a number of experiments to examine how two EDS design parameters, electrode width and inter-electrode spacing, and two operational parameters, applied voltage and relative humidity, affect dust particles' charge. Sixteen EDS prototypes in two sets were developed and tested in a laboratory environment to study the acquired charge by dust particles via charge-to-mass ratio measurements. It has been shown that the charge-to-mass ratio is directly affected by the electric field intensity on an EDS surface. Furthermore, we have shown the detrimental impact of relative humidity on EDS performance. The results are advantageous in the evaluation of EDS design and its optimization to attain maximum dust removal efficiency.     

The computer simulation of the vacuum arc emission center

The paper presents a two dimensional (2-D) hydrodynamic model of vacuum arc emission center-“ecton”-which is an outgrowth of the one-dimensional problem that we have solved earlier. The numerical simulation was carried out for the initial stage of the operation of the cathode spot of a low-current vacuum arc on a copper cathode. It has been shown that, in terms of this model, the current flows in the main through the edges of the cathode spot. Based on a these data, a mechanism for the motion of a cathode spot has been proposed     

Determination of the Local Parameters of a Cascade‐Arc Plasma by the Profiles of the Lines in the Radiation Spectrum

The transverse distribution of the plasma temperature in the positive column of a d.c. cascade arc in argon at atmospheric pressure has been measured. The measurements have been carried out by the conventional method involving the determination of the emissivity of plasma as well as directly from the radiation spectrum of the arc without recourse to the Abelian inversion. A theoretical and model justification of the applicability of the second method is given. The results of the determination of the temperature profile in the observation direction by the width and shift of the ArI 425.9nm line selected for the diagnostics are presented. An analysis of the data obtained supports the possibility of determining the temperature of an inhomogeneous, optically thin plasma from the profiles of lines in the emission spectrum.     

Noether's Theorem and the Conservation Laws of the KORTEWEG-DE VRIES Equation

A method developed recently by the author to derive a continuum of conservation laws by Noether's theorem from the so-called extended Bäcklund transformations is applied to the KORTEWEG -DE VRIES equation that describes various nonlinear dispersive wave phenomena in hydrodynamics, plasma physics and solid state physics. Further applications of Noether's theorem concerning this equation are given. It is shown that the Galilean transformation in the present case has an analogous function as Lie's transformation has with respect to the sine-Gordon equation.     

Computer simulation of the phenomenological transport coefficient in the lattice gas and Fick's First Law

A direct steady state computer simulation method for calculating the Onsager phenomenological transport coefficient from the gradient of the chemical potential in the one component lattice gas is presented. It is shown that the results are in good agreement with the Einsteinian method. A recent alternative formulation for Fick's First Law that had been proposed to replace the standard Fick's First Law formulation is also analysed using the same model. It is shown that the alternative formulation gives poor agreement with the simulation data whereas the standard Fick's First Law gives excellent agreement. Accordingly, the alternative formulation does not appear to have merit as a new definition of the diffusion coefficient. It is shown that the alternative formulation is a rough approximation for the dependence of the interstitial solute diffusion coefficient on solute concentration in an interstitial solid solution if information about the activity coefficient and solute diffusion coefficient at very dilute concentrations is available. However, in this role, this is not an entirely new idea.     

Unipolarbögen

Unipolar arcs have achieved considerable importance as a plentiful source of contaminations in tokamak plasmas. A definition of unipolar and plasma induced discharges is given, and the main properties of the space charge sheath between plasma and wall as well as the existence conditions of unipolar arcs (necessary voltage drop, current balance) are considered. From a simple model that includes the superposition of two completely different plasmas — the tokamak plasma and the cathode spot plasma of the arc — the radial dependencies of the current densities and voltages between plasma and wall and of the plasma parameters are derived. It is shown, that — in typical cases — the anode region is a ring-shaped area situated at distances from the arc cathode spot r > b with 0.3 cm ? b ? 1 cm, and that the density decrease of the arc plasma n ～ r^?μ necessitates an exponent 2 ? μ ? 3 because of the current balance condition (arc current = backflow current). Moreover some thermodynamic aspects (unipolar arcs as a kind of dissipative structures), the ignition problem, the effects of magnetic fields, the problems of diagnostics and the possibilities of simulations are shortly discussed.     

Effect of electron-neutral collisions on the satellites of the Thomson scattering spectrum in arc plasmas

The effect of electron-neutral collisions on the high frequency spectrum of laser radiation scattered by the free electrons of a plasma is investigated for a partially ionized H₂ are plasma at atmospheric pressure. The calculations are carried out along Gorog's theory solving the linearized Boltzmann equation for electrons with a collision term. The collision integral is approximated by a Krook relaxation model with the collision frequency determined from experimental electron-atom scattering data. The collisions influence size, half width, and position of the high frequency satellites. In a H₂ arc plasma, the change of the satellites' position is negligible as well as the change in half width within experimentally attainable error limits. The change of size is of minor importance, since the general evaluation procedure uses only normalized scattering intensities. Thus, for laser scattering experiments in are plasmas the collision-free theory can be applied.     

An Efficient Spectroscopic Control — Technique of the Parameters of Thermic Plasmas Produced under the Condition of a Variable Current

The spectroscopic diagnostics has been carried out as an example for an argon plasma from Maecker-Shumaker type electric arc supplied by periodic variable current. It is shown that the time-dependent runs of intensity of the plasma light may be determined using an ordinary oscilloscope. We have stated that the electron concentration N_e in the plasma is the most sensitive quantity to the current pulsations. In the percentage, N_e variations at the arc axis are approximately the same as the current ones.     

Modal analysis and cutoff frequencies of a doubly clad plasma loaded waveguide having a lemniscates of Bernoulli-type core cross-section

The modal dispersion characteristics of EM waves in a new unconventional plasma loaded doubly clad waveguide having a shape of the lemniscates of Bernoulli-type core cross-section have been studied analytically. The proposed waveguide has three parts namely the core with slighter high index, the inner cladding with plasma and the outer cladding with air. Now using the necessary orthogonal coordinates for the proposed structure and imposing the boundary conditions under the weak guidance condition, the modal characteristics equation has been obtained considering variations in plasma width and plasma frequency, the dispersion curves and cutoff frequencies have been obtained and presented in this paper. It is noted that as the width of plasma layer increases, the cutoff frequency also increases considerably in all considered cases. This shows that using plasma width as a new parameter we can control any particular mode on our wish.     

Determination of spatial characteristics of the chain reaction wave in silver azide

The paper presents the methodology and results of determination of the spatiotemporal characteristics of the solid-state chain reaction wave in silver azide, initiated by a neodymium laser pulsed. The wave’s leading front width at half maximum is l ₁ = (110 ± 10) μm, the wave’s rear front width at half maximum is l ₂ = (120 ± 20) μm. The spatiotemporal parameters of the reaction wave in silver azide whiskers are calculated using a phenomenological model of the process previously proposed by the authors. It is shown that the calculated values of the velocity and the wave front width are consistent with the available experimental data.     

On the problem of polarization characteristics of radio waves in a randomly inhomogeneous magnetoactive plasma

Expressions for the Stokes parameters when radio waves propagate in a turbulent magnetoactive plasma have been obtained using a refractive scattering method. The problem of the spatial coherence of polarized radiation is considered. Expressions for the correlation functions and fluctuation dispersions of the Stokes parameters are found in the case of saturated wave field fluctuation. It is shown that the fluctuation of the circular polarized component will be observed in the received radiation even if the circular polarization is absent in the radiation that is incident on the magnetoactive plasma slab. A method is proposed to define the preference orientation of the magnetic field in the inhomogeneous layer of space plasma, which is biased on the simultaneous measurement of the space correlation functions of the I, V Stokes parameter fluctuation and Faraday rotation of the radiation polarization plane from the source with known polarization characteristics.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 8, pp. 1007–1013, August, 1996.This work was supported in part by the Russian Foundation for Fundamental Research under Project No. 96-02-18632.     

Time-spatial structure of an electric arc anode region

This paper studies the anode region of an eroding anode with a nonstationary arc-root attachment. High-current free-burning short as well as long arcs at atmospheric pressure are investigated. A technique to study the anode region of the arc is suggested. An anode moving perpendicular to the arc axis was used for estimating parameters of the anode jets at a given moment of their development. The mechanism of current transfer in the anode region is considered on the basis of electrophysical and optical-spectroscopic investigations of the arc attachment traces and plasma parameters both of the anode jet and arc column. The anode jet was found to be of importance in the stationary arc operation. The near-anode plasma parameters depend on the effect of the cathode jet. In short arcs (L_a~2 mm), the plasma temperature at the anode exceeds 20000 K, while in long arcs (L_a >50 mm), it falls below 7000 K. At plasma temperature T_a >11000 K, the total arc current in the anode region is transferred through the arc plasma, while at lower temperatures, both the arc column and the anode jet take part in the current transfer     

Omni-directional reflection bands in one-dimensional plasma dielectric photonic crystals

In this paper the omni-directional reflection bands in one-dimensional plasma photonic crystal (PPC) have been studied theoretically. We present the study of plasma photonic crystal, having alternate regions of plasma?dielectric (Al₂O₃ or ZnS). Reflectances from this periodic multilayered structure in TE- and TM-modes are calculated for different angles of incidence in microwave region for omni-directional reflection bands. The reflectance is obtained by solving a Maxwell's equation using a translational matrix method. In addition to this, we have also studied the effect of variation of plasma width as well as plasma density on the reflection properties of plasma dielectric photonic crystal in TE- and TM-modes. The study of reflectance bands of such plasma photonic crystals shows that it can be used as omni-directional reflector.     

Experimental stark parameters of carbon C II 2993 Å line

Total Stark profiles of the C II 2993 Å line of a plasma jet of a slit discharge with an evaporating wall. In the interval of electron densities of 10¹⁷ to 6 × 10¹⁷ cm^?3, the electron impact width, the ionic broadening and the shift of the intensity maximum of the line are measured. It is found that, at an inversely quadratic dependence of the electron impact width on the electron concentration, the Stark shift and the ionic contribution to the total width of the profile are linear. It is noted that calculated values of the shift regularly exceed measured values, while the signs of the measured and calculated shifts coincide. The method of approximating experimental data is proposed, which takes into account the interrelation of the main Stark parameters in plasma with a strong interparticle interactions.     

Arc root dynamics in high power plasma torches — Evidence of chaotic behavior

Although plasma torches have been commercially available for about 50 years, areas such as plasma gun design, process efficiency, reproducibility, plasma stability, torch lives etc. have remained mostly unattended. Recent torch developments have been focusing on the basic understanding of the plasma column and its dynamics inside the plasma torch, the interaction of plasma jet and the powders, the interaction of the plasma jet with surroundings and the impingement of the jet on the substrate. Two of the major causes of erratic and poor performance of a variety of thermal plasma processes are currently identified as the fluctuations arising out of the arc root movement on the electrodes inside the plasma torch and the fluid dynamic instabilities arising out of entrainment of the air into the plasma jet. This paper reviews the current state of understanding of these fluctuations as well as the dynamics of arc root movement in plasma torches. The work done at the author’s laboratory on studying the fluctuations in arc voltage, arc current, acoustic emissions and optical emissions are also presented. These fluctuations are observed to be chaotic and interrelated. Real time monitoring and controlling the arc instabilities through chaos characterization parameters can greatly contribute to the understanding of electrode erosion as well as improvement of plasma torch lifetime.