Velocity–Space Drag and Diffusion in a Model, Two-Dimensional Plasma

The quasilinear fluctuation integral is calculated for a two-dimensional, unmagnetized plasma ~composed of charged rods!, and is expressed in terms of Fokker–Planck coefficients. It is found that in two dimensions, the enhanced fluctuations generated by fast electrons lead to anomalously large transport coefficients. In particular, the effect of a small population of fast electrons is only weakly dependent on their density. In three dimensions, the effect of fast electrons is masked by the dominant approximation, but higher-order terms describe processes similar to those in two dimensions, and these terms can become significant for weakly stable plasmas. The differences between two and three dimensions arise from the fact that both emission and damping of plasma waves are retained to lowest order in two dimensions, while the three-dimensional dominant approximation effectively includes only wave emission by test particles. An understanding of the differences between two and three dimensions is crucial to the interpretation of two-dimensional particle simulations.