Langevin representation of Coulomb collisions in PIC simulations

In order to treat electron-electron and electron-ion collisions, an efficient mesh generated Langevin formulation is developed for a particle-in-cell plasma simulation code. The Langevin equation is used to formulate these collisions in a probabilistic way analogous to the Monte Carlo method that is used for non-coulomb scattering. The only difference is that the coulomb collisions are very frequent and weak so that the Langevin equation represents the net probabilistic effect of many small angle scatterings