Russel Calfisch, UCLA
Abstract:
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.