Nonlinear dynamics of geodesic-acoustic-mode packets

The dynamics of finite-amplitude, undamped geodesic-acoustic-mode (GAM) packets is shown to be well described by a nonlinear Schrödinger equation. GAM supposed generated through an appropriate initial perturbation, and its coupling with other possible modes in the plasma disregarded. However, modifications dispersion properties due itself are retained. A theoretical approach based on variational method compare successfully particle-in-cell simulations. Typical phenomena, as known, e.g., from optics, like phase shift, phase-front shape, wave breaking analyzed. Depending electron-to-ion temperature ratio hence regime (normal or anomalous), synergy competition between dispersive packet broadening takes place. In latter regime, existence “GAM solitons” reported.