Self-Consistent Langevin Simulation of Coulomb Collisions in Charged-Particle Beams

In many plasma physics and changed-particle beam dynamics problems, Coulomb collisions are modeled by a Fokker-Planck equation. In order to incorporate these collisions, we present a three-dimensional parallel Langevin simulation method using a Particle-In-Cell (PIC) approach implemented on high-performance parallel computers. We perform, for the first time, a fully self-consistent simulation, in which the friction and diffusion coefficients are computed from first principles. We employ a two-dimensional domain decomposition approach within a message passing programming paradigm along with dynamic load balancing. Object oriented programming is used to encapsulate details of the communication syntax as well as to enhance reusability and extensibility. Performance tests on the SGI Origin 2000, IBM SP RS/6000 and the Cray T3E-900 have demonstrated good scalability. As a test example, we demonstrate the collisional relaxation to a final thermal equilibrium of a beam with an initially anisotropic velocity distribution.