Accelerated Simulation Methods for Plasma Kinetics
Russel Calfisch, UCLA

Collisions between charged particles in plasmas are significant in a variety of regimes and are often a computational bottleneck. This is a multiscale phenomenon due to the difference between the continuum (fluid) and the collisional (particle) length scales. This talk will describe a class of simulation methods for Coulomb collisions and acceleration techniques for improving their speed and accuracy.  Starting from the nonlinear Landau-Fokker-Planck (LFP) equation, the focus will be on a binary collision model that is solved using a Direct Simulation Monte Carlo (DSMC) method. Acceleration of this method is achieved by coupling the particle method to a continuum fluid description. For systems that are not too far from (local) equilibrium, this reduces the number of simulated particles that are required for a given level of accuracy. Coupling between the continuum and the particle description is critical, and is performed through a themalization/dethermalization step. The efficiency of this method is greatly increased by inclusion of particles with negative weights. This significantly complicates the simulation method, but we have recently developed a new, more tractable approach to negative particles. This accelerated simulation method will be compared with a standard alternative and applied to some typical test problems.