Using Kinetic Entropy to Understand Dissipation in Re-connection and Turbulence
This report summarizes results obtained at Space Science Institute (SSI) under a collaborative project funded by the NSF-DOE partnership in Basic Plasma Physics. The overall goal of the project was to perform a study of kinetic entropy as a diagnostic of dissipation in several archetypal models, such as magnetic reconnection and decaying plasma turbulence. The specific task of the SSI group was to perform collisionless and weakly collisional Particle-in-Cell (PIC) simulations modeling these systems. Overall, the project has demonstrated that, as expected, kinetic entropy carries an imprint of weakly collisional processes commonly thought to be associated with dissipation and thus provides an important diagnostic of dissipation. Specific entropy-related metrics have been proposed that could be used as quantitative measures of dissipation. These metrics have been implemented as diagnostics in PIC simulations and their utility, as well as relation to other, previously proposed, measures of dissipation have been demonstrated. Further, PIC simulations were used to investigate a general question of how energy is dissipated in magnetized weakly collisional turbulence in both non-relativistic and relativistic plasmas.