Langevin equation vs. kinetic equation : Subdiffusive behaviour of charged particles in a stochastic magnetic field
The running diffusion coefficient D(t) is evaluated for a system of charged particles undergoing the effects of a fluctuating magnetic field and of internal collisions. The latter coefficient can be expressed either in terms of the mean square displacement (MSD) of a test particle, or in terms of a correlation between a fluctuating distribution function and the magnetic field fluctuation. These approaches are shown to be not necessarily equivalent. A hybrid kinetic equation is developed to ensure equivalence with the Langevin results. The BGK model for the collisions also yields a wrong result for the general Fokker-Planck equation. A linear approximation to the hybrid kinetic equation yields an inexact behaviour model, which is acceptable in the strongly collisional limit.
Bibliographic Reference: Report: EUR-CEA-FC-1512 EN (1994) 55 pp.
Availability: Available from CEA, Département de Recherches sur la Fusion Contrôlée, Saint-Paul-lez-Durance (FR)
Record Number: 199411572 / Last updated on: 1995-01-10
Original language: en
Available languages: en