Plasma diffusion by Coulomb collisions in two-dimensional maps

Summary form only given, as follows. Nonlinear chaos theories have been used to understand many important physical phenomena in plasma physics, including various radio frequency heatings (v-space diffusion), wave-driven spatial diffusion, magnetic-ripple driven spatial diffusion in tokamaks, etc. Historically, the nonlinear chaotic diffusion problems in plasmas have been studied under the emphasis that the dissipation is provided by an intrinsic perturbation without Coulomb collisions. However, in many of the practical plasmas, the Coulomb collision can also play a significant role in the nonlinear diffusive processes In this presentation, we will report recent progresses in understanding the role of Coulomb collisions in various mapping equations. Interesting universal interplay between the intrinsic perturbation and the Coulomb collisions has been found. Above the stochastic threshold, Coulomb collisions reduce the diffusion rate. Below the threshold, however, Coulomb collisions play an important role in inducing diffusion, depending upon the mapping structure. Simple physical insights to explain the diffusion scaling law will be presented for standard map, isotropic web map, and anisotropic web map, supported by rigorous numerical simulation results.