Modeling the effect of particle size and plasma parameters on dust grain charge fluctuations in non-thermal complex plasmas using Langevin Dynamics

Dust grains in a complex plasma, typically of nanometer to several microns in size, collect charge primarily through collisions with ions and electrons. While the grain charge usually fluctuates around an equilibrium value, for particles of size<100nm, the extent of these fluctuations can be relatively significant. This work focuses on modeling the charge fluctuations considering the effect of ion concentration, gas pressure, particle size, and electron temperature. Langevin Dynamics is used to simulate the motion of multiple ions around a non-emitting spherical particle in a periodic domain. The particle, initially neutral, is assumed to lose charge through continuous electron current following the traditional Orbital Motion Limited theory and to gain charge through discrete ion collisions. Ion-ion and particle-ion interactions are assumed to be simple Coulombic. The velocity distribution of the ions is observed to be Maxwellian within our parametric space of interest. The magnitude of the fluctuations relative to the steady state charge will be presented as function of the aforementioned parameters.