  Following the analysis on linear spectra of shear Alfv\'en fluctuations
excited by energetic particles (EPs) in the Divertor Tokamak Test (DTT)
facility plasmas [T. Wang et al., Phys. Plasmas 25, 062509 (2018)], in this
work, nonlinear dynamics of the corresponding mode saturation and the
fluctuation induced EP transport is studied by hybrid
magnetohydrodynamic-gyrokinetic simulations. For the reversed shear Alfv\'en
eigenmode driven by magnetically trapped EP precession resonance in the central
core region of DTT plasmas, the saturation is mainly due to radial decoupling
of resonant trapped EPs. Consistent with the wave-EP resonance structure, EP
transport occurs in a similar scale to the mode width. On the other hand,
passing EP transport is analyzed in detail for toroidal Alfv\'en eigenmode in
the outer core region, with mode drive from both passing and trapped EPs. It is
shown that passing EPs experience only weak redistributions in the weakly
unstable case; and the transport extends to meso-scale diffusion in the
strongly unstable case, due to orbit stochasticity induced by resonance
overlap. Here, weakly/strongly unstable regime is determined by Chirikov
condition for resonance overlap. This work then further illuminates rich and
diverse nonlinear EP dynamics related to burning plasma studies, and the
capability of DTT to address these key physics.
