  In this work, gyrokinetic theory of drift waves (DWs) self-regulation via the
forced driven zonal flow (ZF) is presented, and finite diamagnetic drift
frequency due to plasma nonuniformity is shown to play dominant role in ZF
forced generation. The obtained nonlinear DW equation is a nonlinear
Schr\"odinger equation, in which the linear dispersiveness, linear growth,
nonuniformity of diamagnetic drift frequency, and cubic nonlinearity induced by
feedback of forced-driven ZF to DWs are self-consistently included. The
nonlinear DW equation is solved numerically in both uniform and nonuniform
plasmas. It is shown that DWenvelope soliton may form due to the balance of
linear dispersiveness and nonlinearity, and lead to turbulence spreading to
linearly stable region. It is further found that though the threshold on DW
amplitude for soliton formation is well within the relevant parameter regimes
of realistic tokamak experiments, solitons can not extend beyond the range
bounded by the turning points of the wave packet when plasma nonuniformity is
self-consistently accounted for.
