Computer Experiment of Anomalous Diffusion

Abstract

A computer model of the diffusion of a fully ionized plasma across a constant magnetic field is described. The two‐dimensional motion of one thousand charged rods is followed as they move according to Newtons law of motion under the action of their mutual electrostatic forces. A square region is considered which is perpendicular to a constant magnetic field. Plasma rods are injected thermally from one side of the square, and the transport of rods to the opposite side is observed. The model is virtually collisionless, and the observed diffusion can be attributed to the effect of the coherent electric field arising from the spontaneous growth of plasma instabilities. The magnitude of the diffusion is given by the Bohm drain diffusion formula. The dominant instability is an m = 1 drift wave which occurs when the electron drift motion is in synchronism with an electrostatic ion wave. The results of the calculation have been displayed in a short two‐minute movie which shows the time variation of the potential surface.