Analysis of the formation of ordered dust-grain structures in a thermal plasma

The possibility is studied of the formation of ordered dust-grain structure s in a low-temperature thermal plasma consisting of electrons, ions, and mi cron-sized charged dust grains. The range of the required values of the cou pling parameter Gamma defining the degree to which the plasma is nonideal i s calculated using the results of diagnostic measurements carried out in a plasma consisting of combustion products of propane in air with grains of d ifferent materials. The results obtained show that the most favorable condi tions for the formation of strongly correlated grain structures (for both p ositively and negatively charged grains) take place at the maximum grain nu mber density and a plasma temperature close to the minimum flame temperatur e (similar to 1600 K). In this case, the optimum grain radii lie in the ran ge 4-10 mu m and the maximum value of the parameter Gamma is less than 200. Since the calculated values of Gamma give an upper estimate, liquidlike or dered 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 Gam ma and, accordingly, the formation of plasma-crystal structures in a therma l plasma can only occur for positively charged grains. (C) 2000 MAIK "Nauka /Interperiodica".