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

Abstract

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.