Using Kinetic Entropy to Understand Dissipation in Reconnection and Turbulence

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This project will contribute to a detailed understanding of a mysterious plasma process called magnetic reconnection, a process behind explosive events in space including solar flares and so-called geomagnetic storms that drive space weather. It occurs where a magnetic field embedded in a superheated (ionized) gas, a plasma, changes directions and rapidly releases large amounts of energy into the plasma. The project will also contribute to understanding of plasma turbulence, where energy injected at large scales cascades down to small dissipation scales. This project will pursue a systematic approach to determining where dissipation occurs in plasmas. The approach is to develop the tools to apply the concept of entropy, known since the late 19th century, to this modern problem where it has been underutilized. This project has the capability to be truly transformative to the field of geospace sciences since it will provide the infrastructure for using entropy as a diagnostic for dissipation which should be useful in many subareas of this field, and will be directly comparable to existing satellite measurements. It fosters education through the support of a graduate student and a postdoctoral researcher.The goal is to perform the first systematic study using kinetic entropy as a diagnostic for dissipation in reconnection and turbulence, and to compare the results with observational data from the Magnetospheric Multiscale space mission. The kinetic diagnostic was recently developed for particle-in-cell (PIC) codes by the research team, so the new diagnostic will be used to assess the numerical dissipation in collisionless PIC codes and implemented into a collisional PIC code that self-consistently contains dissipation. The two will be compared to provide strong insights into where dissipation occurs and what physical mechanism causes it. As needed, the results will be compared directly with a new Vlasov-Maxwell solver that was recently developed by a collaborator at the Los Alamos National Laboratory. The simulation study will be carried out on standard test problems in magnetic reconnection and turbulence. The expected contribution of this work will be a systematic approach to study dissipation in nearly collisionless systems which can broadly be used for plasma science, and a newfound understanding of what causes irreversible dissipation in reconnection and turbulence. This project is being supported as a part of the NSF/DOE Partnership in Basic Plasma Science and Engineering, with a collaborating effort at the Space Science Institute supported by the Department of Energy, Office of Fusion Energy Sciences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.