PLASIMO’s Particle Growth Model describes the spatially averaged time-dependent nucleation, coagulation, charging and surface growth of dust particles due to one or more nucleation species.
The nucleation describes the onset of the particle growth process and typically corresponds to nucleation species formed due to the plasma activities. The coagulation processes are described in a sectional approach, meaning that the mass distribution is given by discrete mass values. A continuity equation is solved for each mass. Each mass can have a charge distribution and for each mass-charge combination one equation is solved. The charging of the particles due to collisions with electrons and ions is calculated using the collision frequencies from the orbital motion limited (OML) theory. Surface growth is assumed to take place via the ion collisions.
Example: Particle growth in acetylene plasma
The model describes the charge resolved mass coagulation, starting from acetylene (C2H2) with an initial density of 1e18 m−3. 15 mass species are considered and 12 charge states for each mass bin are taken into account. Typical mass distribution plots are produced for nucleation and coagulation systems.
Figure 1: Calculated mass densities as a function of time. The total mass density in the system can be seen to increase due to the constant nucleation rate.
Figure 2: Calculated mass distribution at the end of the simulation. The smaller masses have a relatively large density due to the constant nucleation. Larger masses form arround 10 000 amu due to coagulation.
Figure 3: Normalized charge distribution at the end of the simulation.