Charged particle transport in turbulent magnetic fields: The perpendicular diffusion coefficient

The diffusion of charged particles in a static turbulent magnetic field that is superimposed on a constant magnetic field B sub(0) k is considered. Previous calculations of the particle flux in a direction perpendicular to k related the flux S to the particle number density f by S = - Kappa ( gradient f) , where Kappa is found from the power spectrum of the turbulent magnetic field. It is shown that this formula is inconsistent with the theory of Jokipii and Parker (1969), that the perpendicular particle flux arises primarily because of random walking of magnetic field lines across the direction k. For a simple example of a turbulent magnetic field, it is shown that the above expression for S is incorrect; the particle flux S is recalculated, and a new relationship between S and f is found. This new expression for S is shown to be consistent with the idea that particle diffusion across the direction k results from random walking of the magnetic field lines.