Volume 86, Issue 2, 15 July 1999
Index of content:
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
86(1999); http://dx.doi.org/10.1063/1.370795View Description Hide Description
Carbon and lithium spectra are obtained from vacuum spark discharges using a grazing-incidence flat-field spectrometer. Hydrogen and helium-like lines are identified in the carbon spectrum, where only the hydrogen-like lines are found in the lithium spectrum. The absence of the helium intercombination line in the carbonplasma indicates that the electron density is greater than The electron density is found to be for carbon and for lithiumplasma using the method of Stark width analysis for hydrogen-like carbon and lithium lines of the Lyman β and Lyman δ of each element. This method was developed and implemented earlier by E. V. Aglitskii, P. S. Antsiferov, I. M. Gaisinskii, E. A. Oks, and A. M. Panin (Institute of Spectroscopy Preprint #13, Troitzk, Moskow region, USSR, 1985). The Lyman β and Lyman δ lines are chosen for our analysis because these two lines do not have the central Stark components. A pinhole picture is obtained for the carbonplasma, and the pinch diameter is measured to be 100 μm from the equal density profile scan of the pinhole photograph. The optical depth and the escape factor are incorporated into the intensity calculation of the lines using an effective plasma size of 50 μm. In this calculation, the intensity ratio of the Lyman α to the helium-like γ line yields an electron temperature of about 90–95 eV for the carbonplasma. No temperature for the lithium was possible due to the unavailability of the helium-like lines.
86(1999); http://dx.doi.org/10.1063/1.370796View Description Hide Description
Numerical simulations of radiation transport in cylindrical geometry are used to determine the effect of radially symmetric inhomogeneities. The focus of this study are inhomogeneities such as may be produced by radial cataphoresis or temperature gradients in cylindrical glow discharges, i.e., a quadratic profile of absorbing atoms which has a minimum on the axis of the cylinder. A propogator function analysis of the Holstein–Biberman equation and a Monte Carlo simulation of resonance photon scattering are simultaneously used to examine three limiting cases of interest: (i) a pure Doppler broadened atomic lineshape, (ii) a pure Lorentz atomic lineshape produced by foreign gas broadening, and (iii) a pure Lorentz atomic lineshape produced by resonance collision broadening. The fundamental mode distribution of excited atoms, the fundamental mode trapped decay rate, and the volume-averaged escape rate for a homogeneous production rate per unit volume are calculated for each of these cases. The trapped decay rates are found to change modestly (depending upon lineshape) as the degree of inhomogeneity is increased, if the volume integral of the absorbing atom density remains fixed. Correction factors for the fundamental mode trapped decay rate are reported.
86(1999); http://dx.doi.org/10.1063/1.370797View Description Hide Description
Experiments showing the dynamics in the self-organization of surface wave sustained discharges are presented. Microwave (2.4 GHz) discharges maintained in an argon gas in a continuous wave regime at a constant applied power and varying gas pressure are studied. The evolution of the discharge from a stationary plasma column at comparatively low pressure to a plasma torch at atmospheric pressure passes through different stages of self-organization of the nonlinear structure showing evidence of the general trends of behavior of nonequilibrium dissipative systems. The measurements are carried out at the stage of the discharge self-organization into a filamentary structure with an azimuthal rotation. Macroscopic characteristics (number, size, velocity of rotation) of the filaments and their dependence on the gas pressure and its time variation are given. The total light emission of the plasma considered as giving information about the plasma density is measured and different methods of signal processing (including correlation-spectrum analysis) are applied. Oscillations of the filament ends are also observed. The different types of interrelation between plasma density and field intensity, registrated in the different pressure ranges, call for variety in the instability mechanisms. Although the scenario of the discharge self-organization is stressed in the discussions, the observations are important with their relation to the discharge applications, which require avoiding conditions of development of instabilities.