Alfven eigenmodes (AE) driven by energetic particles (EP) can cause large EP transport that degrades
plasma confinement and threaten machine integrity. Understanding the nonlinearly saturated AE
amplitude and associated EP transport level is needed for extrapolating EP confinement properties to
burning plasma experiments such as ITER. Global gyrokinetic simulations find strong cross-scale
interaction between meso-scale reversed shear Alfven eigenmodes (RSAE) driven by EP and micro-scale
ion temperature gradient (ITG) microturbulence in DIII-D plasma. In the coupling simulations, regulation
of RSAE by ITG results in quasi-steady state AE turbulence that is comparable to experimental
measurements. In turn, stronger zonal flows generated by RSAE reduce thermal ion heat transport driven
by ITG.
Building on this nonlinear validation, global GTC simulations of the ITER steady state operation scenario
find significant EP transport even in single mode RSAE simulation, and huge EP transport in the quasi-
steady state AE turbulence in the multimode simulation even with the background microturbulence
suppressed in the ITER, in contrast to the nonlinear dynamics of the RSAE in the DIII-D. The large EP
transport driven by the AE turbulence leads to significant density profile relaxation of both beam ions and
alpha particles within 0.15ms after nonlinear saturation, which indicates that the classical EP profiles in
this ITER steady state operational scenario is unrealistic.