Non-Linear Turbulence and Fluid Resonances in Magnetized Plasmas: Kinetic and Statistical Methods

Dear Colleagues,

The path to a commercially viable fusion reactor is fundamentally challenged by the turbulent behavior of magnetically confined plasmas. In tokamak devices, the nonlinear interplay between micro-instabilities, zonal flows, and energetic particle modes governs the anomalous transport of heat and particles, directly dictating plasma confinement and performance. Understanding these dynamics is not merely an academic pursuit; it is a critical prerequisite for predicting reactor-scale operation, mitigating disruption events, and optimizing fusion power output.

While linear gyrokinetic theory has successfully identified the primary drivers of turbulence (e.g., Ion Temperature Gradient (ITG), Trapped Electron Mode (TEM), and Kinetic Ballooning Mode (KBM)), the saturated state of these instabilities—and the resulting transport levels—is determined by complex nonlinear processes. These include inverse cascades, coherent structure formation, phase-space zonal structures, and nonlinear wave-particle resonances (such as the nonlinear Landau damping and modulational instabilities). However, the most important nonlinear wave-particle process is resonance broadening. While this process has been able to completely cancel the wave-particle resonance, nonlinear Landau damping can be seen as a part of the resonance broadening. Furthermore, the interaction between thermal plasma turbulence and suprathermal populations (alpha particles and fast ions) introduces a new layer of nonlinear complexity that is essential for burning plasma scenarios.

The Topic aims to describe the present theoretical understanding of plasma behavior in tokamak experiments used for obtaining a background knowledge for building a working fusion reactor. Particular emphasis will be on nonlinear effects. We seek contributions that push the boundaries of current models, moving beyond quasi-linear approximations to capture the full non-Markovian, non-Gaussian nature of plasma turbulence.

Dr. Jan Weiland
Dr. Tariq Rafiq
Topic Editors