  A new strategy is presented to explain the creation and persistence of zonal
flows widely observed in plasma edge turbulence. The core physics in the edge
regime of the magnetic-fusion tokamaks can be described qualitatively by the
one-state modified Hasegawa-Mima (MHM) model, which creates enhanced zonal
flows and more physically relevant features in comparison with the familiar
Charney-Hasegawa-Mima (CHM) model for both plasma and geophysical flows. The
generation mechanism of zonal jets is displayed from the secondary instability
analysis via nonlinear interactions with a background base state. Strong
exponential growth in the zonal modes is induced due to a non-zonal drift wave
base state in the MHM model, while stabilizing damping effect is shown with a
zonal flow base state. Together with the selective decay effect from the
dissipation, the secondary instability offers a complete characterization of
the convergence process to the purely zonal structure. Direct numerical
simulations with and without dissipation are carried out to confirm the
instability theory. It shows clearly the emergence of a dominant zonal flow
from pure non-zonal drift waves with small perturbation in the initial
configuration. In comparison, the CHM model does not create instability in the
zonal modes and usually converges to homogeneous turbulence.
