  Effects of plasma nonuniformity on zero frequency zonal structure (ZFZS)
excitation by drift Alfven wave (DAW) instabilities in toroidal plasmas are
investigated using nonlinear gyrokinetic theory. The governing equations
describing nonlinear interactions among ZFZS and DAWs are derived, with the
contribution of DAWs self-beating and radial modulation accounted for on the
same footing. The obtained equations are then used to derive the nonlinear
dispersion relation, which is then applied to investigate ZFZS generation in
several scenarios. In particular, it is found that, the condition for zonal
flow excitation by kinetic ballooning mode (KBM) could be sensitive to plasma
parameters, and more detailed investigation is needed to understand KBM
nonlinear saturation, crucial for bulk plasma transport in future reactors.
