  Nonlinear excitation of low frequency zonal structure (LFZS) by beta-induced
Alfven eigenmode (BAE) is investigated using nonlinear gyrokinetic theory. It
is found that electrostatic zonal flow (ZF), rather than zonal current, is
preferentially excited by finite amplitude BAE. In addition to the well-known
meso-scale radial envelope structure, ZF is also found to exhibit fine radial
structure due to the localization of BAE with respect to mode rational
surfaces. Specifically, the zonal electric field has an even mode structure at
the rational surface where radial envelope peaks.
