Diffusion and equilibration in 2D fluid codes

Abstract

The problems associated with diffusion and rapid equipartition of energy between electrons and ions in two-dimensional fluid codes are investigated numerically. It is shown that a commonly used procedure of averaging the exchange term over the hydrodynamic timescales of interest can be problematic in modelling the equipartition unless very small timesteps are used. A simple model, in which the electron and ion diffusion equations are solved simultaneously, is found to prevent the problems introduced by the average exchange model. The simultaneous solution method increases storage requirements as large scale matrix equations have to be solved. Various algorithms are considered in terms of the increase in storage and execution time required to implement the simultaneous solution method. In particular, a new simple point-iterative algorithm is introduced which is particularly efficient at solving the above problem and offers much scope when applied as a solution method for multi-species diffusion and equilibration problems.