Structure of an extended plasma jet in a vacuum arc in an axial magnetic field

The motion, heating, and ionization of a plasma in a ring anode vacuum arc in an axial magnetic field are studied using a quasi-one-dimensional MHD model. The region between the cathode and anode (a current-carrying plasma jet), as well as the region behind the anode (a current-free plasma jet), is considered. It is shown that, over a long portion of a current-free plasma jet, the electron density and temperature remain high and the ion charge increases substantially due to electron-impact ionization.     

On the macroparticle flux from vacuum arc cathode spots

The macroparticle contamination of vacuum-arc-deposited thin films generated by a plasma source with an optional axial magnetic field is studied. Emphasis is placed on the macroparticle flux near the discharge axis. The arc current, metal species, deposition system geometry and axial magnetic field strength are varied. Distribution functions for macroparticles of Pb, Ag, Cu, Pt, W, and Ni are determined, normalized to the film thickness deposited or the charge transferred. The application of the axial magnetic field leads to a considerable reduction of the normalized macroparticle flux since the plasma is effectively focused by the field, whereas the macroparticle production is not influenced. The macroparticle content normalized to the deposited film thickness is reduced to about 20-35% of that without an additional magnetic field     

Analysis of macroparticle charging in the near-electrode layer of a high-frequency capacitive discharge

Spatial variation of dust particle charges are estimated numerically for typical laboratory experiment conditions in a radio-frequency (rf) capacitive discharge. The surface potentials of macroparticles levitating in the upper part of the near-electrode layer of the rf discharge are measured. A model is proposed for the formation of irregular dust oscillations due to stochastic motion of dust in the bulk of a spatially inhomogeneous plasma (in the presence of a dust charge gradient). This mechanism is used for analyzing the results of measurements of the amplitude of vertical vibrations of dust particles in the near-electrode layer of the rf discharge. It is found that the dust charge gradient may be responsible for the development of such vibrations.     

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.     

Heterodyne detection of CO2 laser radiation scattered from a plasma arc jet

Observations have been made of CO₂ laser radiation scattered incoherently from an argon arc jet plasma. The heterodyne detection technique employed is discussed.     

Non-LTE diagnostic of an argon arc plasma

The plasma of an argon arc has been investigated by applying the partial LTE model (overpopulation of the ground state) and accounting for different kinetic temperatures of electrons and atoms. The plasma analysis is performed without making use of atomic constants (e.g. transition probabilities) from the literature. The experimental results show that LTE is obtained in the 4mm arc at atmospheric pressure for electron densities above 6×10¹⁶cm^-3. Below this value, increasing under-population of the excited levels with decreasing arc current can be observed. This deviation from LTE may explain some not understood results from previously published spectroscopic observations of argon plasmas.     

Anode jet in a high-current vacuum arc

A stable intense jet with a clear-cut bright sheath has been detected on the anode of a 10-ms-long high-current vacuum arc with a current amplitude of 15 kA. The jet is adjacent to the hot spot of a molten metal on the anode surface. The primary light of the jet is emitted by neutrals. The sheath of the jet is surrounded by an ion-induced diffuse glow. The anode jet arises from interaction between the cathode and anode plasmas. Because of this, the size of the jet inversely depends on the current of the arc and the jet becomes observable only by the end of the current pulse. This object (anode jet with a bright sheath) is well reproducible when the arc is initiated between copper-chromium electrodes. In the case of pure copper electrodes, such objects occur randomly and appear at long projections of the molten metal, where heat release is hampered, and at large drops moving in the interelectrode gap. This means that the anode evaporation intensity is crucial for the appearance of bright-sheath jets.     

Analysis of an arc-formed gas-plasma jet in the arc method of fullerene production

A two-component fan-shaped gas jet forming in the discharge gap of a chamber for fullerene production is analyzed. Under standard fullerene production conditions, the averaged parameters of the jet can be found with a reasonable accuracy using the well-known solution for an incompressible liquid jet. Based on the analysis performed in this work, a simple model of gap-jet transition, and the fullerene formation kinetics considered earlier, the dependences of the fullerene yield on observable experimental parameters (current, helium pressure, gap width, and electrode radii) are constructed. The calculated and experimental results are in good agreement. The analytical data obtained in this work may be helpful in considering the fullerene production kinetics in a real, finite-dimension chamber of a given geometry.     

Fluctuation of arc plasma in arc plasma torch with multiple cathodes

Fluctuation phenomena commonly exist in arc plasmas, limiting the application of this technology.In this paper,we report an investigation of fluctuations of arc plasmas in an arc plasma torch with multiple cathodes.Time-resolved images of the plasma column and anode arc roots are captured.Variations of the arc voltage, plasma column diameter, and pressure are also revealed.The results indicate that two well-separated fluctuations exist in the arc plasma torch.One is the high-frequency fluctuation(of several thousand Hz), which arises from transferring of the anode arc root.The other is the low-frequency fluctuation(of several hundred Hz), which may come from the pressure variation in the arc plasma torch.Initial analysis reveals that as the gas flow rate changes, the low-frequency fluctuation shows a similar variation trend with the Helmholtz oscillation.This oscillation leads to the shrinking and expanding of the plasma column.As a result, the arc voltage shows a sinusoidal fluctuation.     

Laser interferometric measurements of electron density in an arc plasma

The paper describes the application of a laser interferometric technique to arc discharges operating at atmospheric pressure. The limitations of this method are discussed in detail. Results are given for the axial electron density in an argon arc, tube 5 mm diameter, over a current range 30–75 A. In addition the decay of the electron density following rapid arc interruption is also given. It is shown that the time constant of the conductance decay which can be derived from the preceeding measurements is in very good agreement with experimental values determined directly.     

纵磁作用下真空电弧单阴极斑点等离子体射流三维混合模拟

真空电弧的特性直接受到从阴极斑点喷射出的等离子体射流的影响,对等离子体射流进行数值仿真有助于我们深入了解真空电弧的内部物理机制.然而,磁流体动力学和粒子云网格仿真方法受限于计算精度和计算效率的原因,无法有效地应用于真空电弧等离子体射流仿真模拟.本文开发了一套三维等离子体混合模拟算法,并在此基础上建立了真空电弧单阴极斑点...     

O--ion radiation in the spectrum of an oxygen arc plasma

The radiation emitted from the axis of a wall-stabilized, low-current cylindrical arc in pure oxygen at temperatures around 9000 K was measured quantitatively in the wavelength range from 2000 to 9000 A. In the near i.r. region, the two first thresholds of the affinity continuum appear at 8615 and 8465 A, respectively, yielding an electron affinity (EA) of 1.465 eV and a ground-state splitting Δ = 26 meV for the negative oxygen ion. Another threshold occurs in the u.v. region at 3630 A and involves a transition to O^- from the first exited state of atomic oxygen. The continuous spectrum can be shown (Fig. 17) to be dominated in the u.v. and visible regions by the affinity continuum due to the negative oxygen ion. Additional contributions, which become increasingly important towards longer wave-lengths, are the Kramers-Unsöld continuum and O₂⁺-association radiation. In the u.v., the recombination of two neutral oxygen atoms forms a small contribution. A broad peak structure centered around 7000 A cannot be definitely explained. Applying Kirchhoff's law, the photodetachment cross section of O^- is obtained as a function of photon energy. Deviations from local thermodynamic equilibrium (LTE) are accounted for.     

On the transformation of carbon vapor in the gas-plasma jet of an arc discharge

Experimental data on measuring the amounts of fullerene-containing soot deposited in different areas of a fullerene arc are obtained. It is shown that, relying on a fairly general model of the spectra of clusters, a simple gas-dynamic model, and existing knowledge of the transformation stages of carbon clusters, the area of the arc where fullerenes are produced can be determined.     

Synthesis of nano-sized antimony-doped tin oxide (ATO) particles using a DC arc plasma jet

Nano-sized antimony-doped tin oxide (ATO) particles were synthesized using DC arc plasma jet. The precursors SnCl₄ and SbCl₅ were injected into the plasma flame in the vapor phase. ATO powder could conveniently be synthesized without any other post-treatment in this study. To control the doping amount of antimony in the ATO particles, the Sb/Sn molar ratio was used as an operating variable. To study the effect of carrier gas on the particle size, argon and oxygen gases were used. The results of XRD and TGA show that all Sb ions penetrated the SnO₂ lattice to substitute Sn ions. With the increased SbCl₅ concentration in source material, the Sb doping level was also increased. The size of the particles synthesized using the argon carrier gas was much smaller than that of the particles prepared using the oxygen carrier gas. For the argon gas, PSA results and SEM images reveal that the average particle size was 19 nm. However, for the oxygen gas, the average particle size was 31 nm.     

A laser interferometer for measuring electron densities in an arc plasma

A Michelson interferometer working simultaneously at two wavelengths is used to follow the decay of the electron density n_e along the axis of a short-circuited dc-argon arc. Using optical isolation, compensating mirrors and quadrature signal detection results in a random error of 1% for n_e=5×10¹⁶ cm^-3.