Nonlinear simulation of toroidal Alfven eigenmode with microturbulence-induced radial diffusion

It is shown analytically and numerically that microturbulence-induced diffusivity can affect nonlinear saturation of energetic particle driven modes in the similar way as collisional pitch angle scattering does. Introducing a simple diffusion operator to the code, our numerical results have shown that a single toroidal Alfven eigenmode (TAE) can saturate at a steady state with sufficiently high diffusion rate. The calculated saturation level scales with the radial diffusion rate by the same scaling of pitch angle scattering. A criterion is derived to judge the importance of microturbulence-induced radial diffusion effect comparing to the collisional pitch angle scattering effect. According to the criterion, we find that the microturbulence-induced diffusion has a stronger effect than the Coulomb collision on the TAE saturation in present tokamak devices and future burning plasmas [International Thermonuclear Experimental Reactor (ITER)].