Diffusion of electrons by multicharged ions

Here we consider a magnetized plasma composed of electrons of low mean dens ity and of one species of multicharged ions. Starting with the Vlasov-Fokke r-Planck equations for both particles, we derive a diffusion model for the electrons, with explicit transport coefficients which are related to the io ns. Finally, we study the kinetic boundary layers in the case of a bounded domain in space variables. For that purpose, we are led to study a Milne pr oblem and to introduce a generalized extrapolation length.