Microturbulence-mediated route for energetic ion transport and Alfvénic mode amplitude oscillations in tokamaks

Highlights: • A novel channel for transport of energetic ions is proposed. It can impact the success of tokamaks as a viable design. • A quasilinear theory self-consistently derived from a first-principles near marginal instability is employed. • Microturbulence increases the effective scattering of fast ions and becomes a mediator for energetic particle relaxation in tokamaks. New regimes of Alfvén eigenmode (AE) induced fast ion transport in tokamak plasmas are reported, in which microturbulence plays the role of a mediator of fast ion relaxation. Coulomb collisional scattering alone leads to small AE amplitudes and does not reproduce the steady state regimes observed in experiments. We show that in nonlinear regimes the sufficiently large effective pitch angle scattering due to microturbulence can lead to steady state AE amplitude evolution. This indicates a new route for fast ion losses, which is beyond the scenarios described in "Energetic ion transport by microturbulence is insignificant in tokamaks" [Pace et al. (2013) [9]]. As a result, microturbulence can significantly increase the amplitude of AEs in predictive simulations of burning plasma experiments such as ITER.