Adaptive particle management in a particle-in-cell code

In particle-based plasma simulation, when dealing with source terms such as ionization, emission from boundaries, etc., the total number of particles can grow, at times, exponentially. Problems involving the spatial expansion of dynamic plasmas can result in statistical under representation of particle distributions in critical regions. Furthermore, when considering code optimization for massively parallel operation, it is useful to maintain a uniform number of particles per cell. Accordingly, we have developed an algorithm for coalescing or fissioning particles on 2D and 3D orthogonal grids that is based on a method of Assous et al. [F. Assous, T. Pougeard Dulimbert, J. Segre, J. Comput. Phys. 187 (2003) 550]. We present the algorithm and describe in detail its application to particle-in-cell simulations of gas ionization/streamer formation and dynamic, expanding plasmas.