Alex Samarian

EMISSION PROPERTIES AND STRUCTURAL ORDERING OF STRONGLY COUPLED DUST PARTICLES IN A THERMAL PLASMA

Abstract Micron-sized dust particles are found to form a Coulomb liquid-like structure in a bulk of a thermal plasma under atmospheric pressure and a temperature of 1700 K. The particles are charged positively and have about 10 3 electron charges. The work function of the electron is found to be 2.1 eV.

CRYSTALLINE STRUCTURES OF STRONGLY COUPLED DUSTY PLASMAS IN DC GLOW DISCHARGE STRATA

Abstract Strongly coupled dusty plasmas are formed by suspending micron-sized dust particles in strata of a dc glow neon discharge. We have observed for the first time an ordered structure of the negatively charged particles trapped in the strata region. Image analysis reveals the crystalline structure, which is consistent with a large value of the Coulomb coupling parameter.

Experimental observation of Coulomb ordered structure in sprays of thermal dusty plasmas

A macroscopic Coulomb-ordered structure of polydisperse CeO2 particles is observed experimentally in a laminar spray of weakly ionized thermal plasma under atmospheric pressure and temperature of about 1700 K. Diagnostic instruments are used to measure plasma parameters. The particles are charged positively and carry about 103 electron charges. The calculated values of Coulomb coupling parameter γp is > 120, corresponding to a strongly coupled plasma.

Temperature measurements of optically non-gray particles in high-temperature dusty media

A technique for determining the temperature of optically nongray particles is considered. Novel approximate relationships are proposed for the spectral emissivity of dusty media. The spectral approximations of a single-scattering albedo are derived for the particles of combustion products. The polydispersions of CeO2 and ash particles in the flow of propane-air flame combustion products have been measured. The particle temperature, refractive index, and mean diameter are obtained.

Analysis of the Formation of Ordered Dust-Grain Structures in a Thermal Plasma

The possibility is studied of the formation of ordered dust-grain structures in a low-temperature thermal plasma consisting of electrons, ions, and micron-sized charged dust grains. The range of the required values of the coupling parameter Γ defining the degree to which the plasma is nonideal is calculated using the results of diagnostic measurements carried out in a plasma consisting of combustion products of propane in air with grains of different materials. The results obtained show that the most favorable conditions for the formation of strongly correlated grain structures (for both positively and negatively charged grains) take place at the maximum grain number density and a plasma temperature close to the minimum flame temperature (∼1600 K). In this case, the optimum grain radii lie in the range 4–10 µm and the maximum value of the parameter Γ is less than 200. Since the calculated values of Γ give an upper estimate, liquidlike ordered structures are most likely to form in a thermal plasma. Based on the results of the analysis, it is stated that an increase in the parameter Γ and, accordingly, the formation of plasma-crystal structures in a thermal plasma can only occur for positively charged grains.

Parameters of Dusty Particles in Plasma Flows

Publisher Summary This chapter describes the various parameters of dusty particles in plasma flows. The parameters are: particle temperature, particle mean sizes, and refractive index of dusty plasmas. This chapter presents a combination of optical methods for determining the particle temperature, Tp, mean size, D 32 , concentration, N p , and refractive index, m( λ )=n( λ )-ik( λ ), in high-temperature flows. The temperature of particles can be obtained from emission-absorption measurements in an emission line of the gas. It is preferable to measure the particle temperature, Tp, and their parameters in a wide wavelength range beyond the gas emission line. The classic pyrometric two-color method can be employed for the determination of Tp in optically grey medium. The equation for the determination of the spectral dependence of dusty plasmas is illustrated; with the known particle sizes and real refractive index, the spectral absorption index, k{X), can be easy measured. For determination of the particle mean size, concentration, and real refractive index, a technique based on measurements of forward angle scattering transmittance (FAST) at different aperture angles of the detector is used. The unknown particle parameters are obtained by minimizing a meansquare error between the measured and calculated data. Calculations are performed by using the Mie theory.