Diffusion of Plasma Ions across a Magnetic Field

Earlier work on the application of the correlation function of the electric field in a plasma is extended to the problem of diffusion of ions across a magnetic field. It is shown that the flux can be considered in three parts; one depends on the electric field correlation function and the others on the dynamic friction, which is related to the correlation function by Nyquist's theorem. When the ion and electron temperatures are unequal the present result differs from that obtained by a Chapman-Enskog type analysis of the transport equation and the interpretation of this difference is discussed. Some consequences of the diffusion formula, as it concerns impurities, are noted.