On fast radial propagation of parametrically excited geodesic acoustic mode

TL;DR

This paper investigates the nonlinear propagation of parametrically excited geodesic acoustic modes (GAMs), revealing they propagate faster than linear predictions and deriving their nonlinear dispersion relation, with implications for experimental interpretation.

Contribution

It provides the first analytical and numerical analysis of nonlinear GAM propagation and derives a nonlinear dispersion relation driven by finite amplitude pump.

Findings

GAM propagates at a group velocity much larger than linear theory predicts.

Derived a nonlinear dispersion relation showing frequency increment.

Discussed implications for experimental observations.

Abstract

The spatial and temporal evolution of parametrically excited geodesic acoustic mode (GAM) initial pulse is investigated both analytically and numerically. Our results show that the nonlinearly excited GAM propagates at a group velocity which is, typically, much larger than that due to finite ion Larmor radius as predicted by the linear theory. The nonlinear dispersion relation of GAM driven by a finite amplitude drift wave pump is also derived, showing a nonlinear frequency increment of GAM. Further implications of these findings for interpreting experimental observations are also discussed.