Abstract Details
Abstracts
Author: Georgia O. Acton
Requested Type: Consider for Invited
Submitted: 2026-03-11 08:22:39
Co-authors: E. Rodriguez, G. Roberg-Clark, P. Costello, A. Zocco
Contact Info:
Max-Planck-Institut fur Plasmaphysik
Wendelsteinstrase
Greifswald, Mecklenburg-Vorpomme 17491
Germany
Abstract Text:
In this talk, the problem of zonal-flow generation is revisited within the framework of local gyrokinetic theory. We introduce a systematic ordering in the amplitudes of interacting modes, which enables us to isolate regimes in which zonal-flow dynamics can be classified according to the structure of their nonlinear coupling. We term these the weak, strong, and fully developed regimes, and discuss how each connects to and clarifies existing results in the literature. Their temporal evolution and phase-space structure are obtained in the “weakly nonlinear regime” from a truncated spectral representation and validated through numerical solutions. A Laplace analysis, in the spirit of the Rosenbluth–Hinton treatment of zonal-flow residuals, demonstrates that when early nonlinear dynamics are governed by the linear response of unstable primary modes, no marginal stability threshold exists for zonal-flow destabilisation. Instead, in a weakly nonlinear regime, zonal growth is controlled by a nonlinear frequency-selection rule arising from convolution in the zonal system equation and is determined entirely by the spectrum of linearly unstable modes. During this initial growth phase, the zonal-flow phase-space structure is tightly constrained by the structure of its turbulent drive, resulting from the driven nature of zonal-flow formation. This constraint selects a natural phase-space structure for the zonal mode, which significantly modifies the residual response. We show that adopting this natural zonal structure leads to an enhanced residual level as compared with the Rosenbluth-Hinton prediction.
Characterization: 1.0
Comments: