Theory of Classical and Anomalous Diffusion of a Plasma across a Magnetic Field

Abstract

The diffusion coefficient of the electrons across a magnetic field (with strength B) is calculated in terms of the spectral function of the electric field fluctuations. The calculation is based on the microscopic evaluations of the first and second moments of the guiding-center displacements under the action of the fluctuating electric field in an inhomogeneous plasma. For a Maxwellian plasma, it is found that the diffusion coefficient contains an anomalous term D_⊥^* in addition to the usual classical term; D_⊥^* is proportional to B⁻¹ when ω_e²(1+T_e⁄T_i)>>Ω_e², and to B⁻²lnB when ω_e²(1+T_e⁄T_i)<<Ω_e², where ω_e is the electron plasma frequency, and Ω_e, the electron cyclotron frequency. The contributions of the like-particle interactions vanish identically in the idiffusion coefficient.