Diagnostics of an RF Plasma Flash Evaporation Process Using the Monochromatic Imaging Technique

The high densities and high gas temperature of rf plasmas at pressures near 1 atm are favorable for the development of plasma sources capable of evaporating solid precursors in the plasma zone. In the cooler region downstream of the plasma, the evaporated material condenses to nanoparticles and/or coatings. The complete evaporation of precursors injected into a thermal plasma depends on plasma and precursor parameters and is studied in this paper. Since many parameters contribute to the evaporation, fast experimental techniques are necessary to carry out a systematic study of the evaporation process. The monochromatic imaging technique applied in this work uses an intensified CCD camera with optical filters for the detection of characteristic plasma emission lines. The high spatial and temporal resolution of this technique results in a detailed picture of plasma emission and particle evaporation for different process parameters. These results are compared to model calculations for particle evaporation.     

Investigation of a Xenon-plasma produced in cascaded arcs

This investigation extends earlier measurements and calculations performed on cascaded arcs burning in the noble-gases He, Ne, Ar and Kr to a Xenon discharge. Starting from intensity and line width measurements of some Xe lines, temperature and electron density profiles as well as transition probabilities are determined.E-I characteristics evaluated in conjunction with intensity profiles and temperature measurements lead to accurate results for the electrical conductivity. The pressure inside the arc chamber is variable. In a broad region of parameters LTE is established.     

Holographic Interferometry of Arc Discharges Displaced by Magnetic Fields

The first part of the paper gives a survey of some theoretical aspects of the behavior of a free burning arc in transverse cross-flow and magnetic field. After a short discussion of the variety of forces acting on the arc, the low current case is investigated, in which the external magnetic field is assumed to change aperiodically with time. In the second part, an arc experiment is described which allows the examination of the theoretical aspects of the arc motion. As a diagnostic method, a holographic technique is applied which visualizes the position of the arc as function of time. The calculated and measured displacements of the arc agree within the error limits.     

Laser diagnostics of a low-pressure hollow-cathode arc

We report the use of resonance fluorescence induced by a repetitively pulsed tunable dye laser in measuring electron collisional transfer rates between fine-structure levels, electron density and neutral particle temperature in a low-pressure hollow-cathode arc. Excitation by a narrow bandwidth laser is analyzed to obtain correct interpretation of the results. A power-broadening formula, which is valid for large saturation parameters, has been derived and experimentally verified.     

CARS diagnostics of a CO2-laser pyrolytic experiment for the production of nanosized ceramic powders

Spatial distributions of rotational temperatures and molecular number densities of C₂H₂ and H₂ were measured with CARS during the production of ultrafine SiC powders in a laser pyrolytic process flame. By means of a CO₂ laser, the reaction gases SiH₄ and C₂H₂ (or alternatively C₂H₄) are converted into SiC and H₂. From the CARS measurements temperature gradients are determined between 8.8 × 10⁵ K/m and 1.6 × 10⁶ K/m with corresponding heating rates of 1.8 × 106 K/s and 1.3 × 10⁶ K/s. The CARS data also allow an estimation of the gas expansion behaviour in the reaction zone. Moreover, they show that diffusive velocity components of the hydrogen in the hot reaction zone do not exceed 0.4 m/s.     

Experimentelle und theoretische Untersuchungen von Nichtgleichgewichtseffekten an stationären Heliumplasmen unter Normaldruck

Measurements and calculations of temperature, densities and field-strength-current-characteristics of cascaded arcs (0.15 and 0.3 cm radius) burning in Helium under normal pressure are reported. It is shown that the evaluation of measured arc data assuming Saha equilibrium is not in agreement with the detailed solution of the balance equations. The temperature of electrons and heavy particles as well as the density of electrons and neutrals must be determined as independent variables from the rate equation for ground state neutrals, from the equation of state, and from the energy balance of the electron gas and of the total plasma. The latter equation can be replaced by relations between measured intensities and the state variables. The deviations from Saha equilibrium are mainly caused by diffusion of neutral particles into the arc core and of charged particles into the opposite direction. The theoretical results derived from the balance equations are compared with spectroscopic line intensity and line width measurements. The agreement is good even if the equilibrium conditions are strongly violated.     

Resonant Coherent Anti-Stokes Raman Scattering Applied to Vapor Phase InI

The metal halide indium iodide (InI) is used as an important additive to mercury discharge lamps. The aim of this paper is to prepare resonant coherent anti-Stokes Raman scattering (RECARS) experiments for measuring concentration and temperature profiles of InI in commercially available metal halide lamps. The spectral positions of possible RECARS lines of InI (double and triple resonances) are calculated up to rotational quantum number J = 280 and vibrational quantum number v = 10. There is evidence for triple resonances leading to strong RECARS signals at J = 174 and J = 231. Dipole transition moments are calculated, which are important input data for the determination of the RECARS spectra. A degenerate-folded BOXCARS setup with a frequency-tripled Nd:YAG laser at 355 nm pumping two dye-laser systems oscillating near 411 nm is utilized to detect RECARS signals of the rovibronic transitions between X:(1)Sigma(+) and A:(3)Pi(0)(0(+)) states of InI. The laser output is attenuated to prevent saturation of the spectra. The tunable dye-laser systems have good beam-pointing stability and a small spectral width (<0.07 cm(-1)). Measured RECARS spectra from a pure InI vapor quartz cell at p = 120 Pa and T = 880 K are compared with theoretical data and good agreement is obtained with respect to the spectral position and RECARS intensity. The scatter signals are achieved with laser-pulse energies of less than 1 μJ. A collision-constant Gamma = 0.0025 cm(-1) describes the line broadening best. The experiments are also performed at a partial InI pressure of 1.12 kPa, a partial Hg pressure of 112 kPa, and a temperature of T = 1073 K and could be interpreted with a broadening constant Gamma = 0.23 cm(-1). Temperature measurements were performed between 900 and 1200 K with an accuracy of 7%. Copyright 2000 Academic Press.     

Untersuchung des Nichtgleichgewichtszustandes an stationären Edelgasplasmen unter Normaldruck

It is shown that in wall stabilized rare gas arcs under normal pressure deviations from Saha-equilibrium occur. These deviations are very strong for Helium and Neon, smaller for Argon and Krypton discharges and are caused by diffusion of neutral and charged particles. A numerical method is described for the evaluation of temperature and density distributions from measured line intensities in the case of non-equilibrium, based on the balance equations of the arc plasma. Results are given for Neon, Argon and Krypton arcs of 0.15 and 0.3 cm radius. A simple validity condition for local thermal equilibrium in a plasma with diffusion effects is derived. The influence of non-equilibrium on the determination of transition probabilities is discussed.