Modeling of particulate coagulation in low pressure plasmas

In this paper we study the growth of nanometer particles in low pressure plasmas due to coagulation. We describe results of a model which involves the self-consistent determination of plasma properties, the description of particle charging, as well as the description of the particle size distribution via solution of the general dynamic equation for an aerosol. Our results show that particle coagulation in the low pressure plasma is enhanced compared to coagulation in neutral aerosols due to the attraction of oppositely charged particles. The temporal behavior of the coagulation follows the same laws as coagulation of neutral particles as long as the density of nanometer particles is larger than the positive ion density in the plasma. The positive ion density can be considered as the critical density for coagulation to occur. We also show that the details of the particle charging mechanism are only of minor importance for the coagulation dynamics but of great importance for the accurate prediction of plasma parameters.