Two-temperature channel model of a direct current arc

A relatively simple method is proposed for computing the gas and electron temperatures in an arc plasmotron channel within the framework of the self-consistent two-temperature channel model of an arc discharge. This method affords the possibility of obtaining the gas and electron temperature distribution with good enough accuracy for given discharge parameters (current intensity in the discharge, power inserted in the discharge, etc.) as a function of the radial coordinate in both nonequilibrium (T_e T_ai) and quasi-equilibrium (T_e = T_ai within the current conducting channel) cases. The results obtained can be utilized in model computations to estimate the gas and electron temperatures as well, possibly, as in a number of engineering computations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 80–86, July, 1990.The author is grateful to L. A. Rachevskii for useful discussion of results of the research.     

Influence of a current jump on vacuum arc parameters

Based on time of flight method, influence of short time vacuum arc current jump on arc plasma parameters were investigated. Superposition of the current pulse of a vacuum arc with a high operating voltage results in the appearance of ions of higher charge state in the discharge plasma and in an increase in the mean ion charge state for most of the cathode materials used in the experiment. The method of a “short-time current jump” can be also used to investigate the parameters of a vacuum arc, in particular to estimate the ion direct velocities in vacuum arc plasmas. Our estimates show that in the presence of a current step the ion velocities are almost identical for all differently charged ions and depend only on the peak current and the ion mass     

Preliminary investigation of arc stabilization with a forced vortex

The stabilization of an arc using a forced vortex was studied experimentally. Measurements on the arc characteristics were made as a function of the stabilizing flow parameters. It was found that the behaviour of the arc may be understood in terms of measurements made on the stabilizing flow without the arc. It is concluded that stable arc operation may be achieved using forced vortex stabilization, but that in open-ended systems end effects on the vortex are likely to cause severe convective losses in the arc.     

Spectroscopic studies of a plasma temperature and radiation standard based on a wall-stabilized arc

The absolute determination of the axial temperature (12,000 K ≤ T ≤ 14,500 K, 0.9×10²³ m^-3 ≤ N_e ≤2.5×10^-3 m^-3 of a 3 mm bore wall-stabilized arc operating in argon at 1.75×10⁵ Pa is described using spectroscopic techniques both in the visible and vacuum u.v. spectral regions. Computer simulation techniques to predict the line wing correction for the A(I) line at 430 nm and a detailed study of sources of systematic error have been applied. The reproducibility of the temperature results and the establishment of LTE demonstrates the suitability of the source as a plasma temperature and radiation standard. A detailed study of the Stark broadening of H_β and the comparison of the experimental profiles with the theories of Kepple and Griem and Vidal, Cooper and Smith has shown the former giving N_e values some 11% lower and the latter 1% higher than the pure argon diagnostics at N_e ? 2 × 10²³ m^-3. New values for the argon transition probabilities of two lines and continuum factors at two wavelengths are presented.     

Spectroscopic investigation of structure transformation in wavellite

The Electron Spin Resonance of VO²⁺, and the Infrared and Nuclear Magnetic Resonance of protons were studied in wavellite. Interpretation of¹H NMR by shape function calculation allows us to determine the distribution of protons between molecular water, OH-groups, the three-spin magnetic configuration H₃O⁺ and to ascertain the characteristic distances between protons. The spin-Hamiltonian parameters, Fermi contact interaction parameters and dipolar hyperfine coupling parameterPK were calculated. Three types of VO₂₊ complexes were detected in wavellite. It is found that VO²⁺(1)- and VO²⁺(2)-centres disappear and a new VO²⁺(3)-centre appears during annealing. VO²⁺(1) is more stable than VO²⁺(2). The parameters of the VO²⁺(3) complex change in the process of annealing. The transformation of VO²⁺(1) is connected with the destruction of acidic H₃O⁺-groups, and the transformation of VO²⁺(2) correlates with the loss of weakly-bonded water molecules in the wavellite structure. ThePK parameter and Δg?Δg _⊥ ratio can be used as markers of disorder in the wavellite structure.     

Plasma expansion and current flow in a vacuum arc with a smallanode

A low-density plasma flow in a vacuum arc with a small anode, which intercepts only part of the cathodic plasma jet, was studied theoretically using a two-dimensional approximation. The plasma expansion was modeled using the sourceless steady-state hydrodynamic equations, where the free boundary of the plasma was determined by a self-consistent solution of the gasdynamic and electrical current equations. Magnetic forces from the azimuthal self-magnetic field were taken into account. The influence of the ratio of the anode radius to initial plasma jet radius on the plasma density, velocity, current distribution, and anode sheath potential drop is analyzed. It is shown that the mass and current flow in a 500 A arc are compressed near the axis. This leads to an increase in the plasma density by a factor of two and in the axial current density by a factor of 1.5     

Spectroscopic investigation of iron ions in soda-tellurite glasses

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 52, No. 3, pp. 434–438, March, 1990.     

High current density spotless vacuum arc as a glow discharge

Vacuum discharge burning between a broad cathode and a point anode made of Mo, Cu, and Cd has been studied. This discharge operates in anode vapors and shows major arc characteristics, although no craters were examined on the cathode. The secondary electron emission is involved to explain current transport within the cathode region. This discharge is interpreted as a high density low voltage glow discharge. Having discussed the present and previous findings, the conclusion has been drawn that the secondary electron emission and “hump of potential” are dominant in the vacuum arc cathode spot     

Experimental investigation of current modulation in a planar Cs-Batacitron

The Cs-Ba tacitron is being considered as a switch, or as an inverter consisting of two switches operating in a push-pull mode, for power conditioning of low voltage/high current dc power sources operating in high radiation/high temperature environment, beyond the limits of semiconductor switches. This paper presents new experimental results delineating the effect of the various operating parameters on the grid potential needed for ignition, V_g⁺, and extinguishing, V_g^-, during stable current modulation of a planar Cs-Ba tacitron. Parameters investigated are Cs pressure, emitter temperature, T_E, discharge current, I_C , and modulation frequency, f_g. The value of V_g ⁺, which is independent of T_E, decreases as Cs pressure increases, but increases as either I_C or f_g increases. Increasing the emitter temperature from 1100-1200°C only slightly decreases the forward voltage drop in the device by ~0.2 V. The value of |V_g^-| increases with Cs pressure, decreases with increased T_E, and is sensitive to changes in fg. At I_C=5 A, the value of |V_g ^-| for stable modulation shows a maximum between 8 kHz and 10 kHz. The Cs pressure, I_C, fg, and V_g⁺ all affect the ignition delay time; depending on the operating conditions, it increases from 5-30 μs to an equilibrium value of 10-45 μs during the first 2 ms in the pulse train