Unraveling momentum transport in turbulent plasmas: This research presents an in-depth analysis of local momentum balance within electromagnetic gyrokinetic systems, crucial for understanding plasma behavior in fusion energy research. The study derives governing equations using an Eulerian variational formulation, extending previous work on spatial coordinate transformation invariance. Key aspects of finite gyroradii and electromagnetic microturbulence are meticulously described through the gyrokinetic Poisson equation and Ampère's law, both derived from the variational principle. Furthermore, the influence of collisions and external sources on momentum balance is explored, highlighting momentum transport via a symmetric pressure tensor. The research clarifies the relationships between axisymmetry, quasi-axisymmetry of toroidal magnetic fields, and the conservation form of the local momentum balance equation. By using the WKB representation, the study provides a detailed expression of the ensemble-averaged pressure tensor due to microturbulence. It is verified to reproduce toroidal momentum transport, aligning with previous findings for axisymmetric systems. This work's detailed analysis provides a valuable reference for simulation studies of momentum transport, promising advancements in controlling and optimizing plasma confinement in fusion reactors. The obtained local momentum balance equation and pressure tensor enhance the precision of gyrokinetic simulations.
Published in Physics of Plasmas, this paper aligns with the journal's focus on plasma physics, ionized gases, and electromagnetic phenomena. The investigation into momentum balance in electromagnetic gyrokinetic systems directly contributes to the theoretical understanding and simulation capabilities relevant to plasma confinement and fusion energy research, core areas of interest for the journal and its readership.