Microturbulence-mediated route for energetic ion transport and Alfv\'enic mode intermittency in tokamaks

TL;DR

This paper reveals a new mechanism where microturbulence mediates Alfvén eigenmode-induced fast ion transport in tokamaks, potentially increasing energetic ion losses beyond previous models, with implications for ITER simulations.

Contribution

It introduces a novel nonlinear regime where microturbulence enhances Alfvén eigenmode amplitudes, advancing understanding of ion transport in tokamak plasmas.

Findings

Microturbulence mediates steady state AE amplitude evolution.

Microturbulence can significantly increase AE amplitudes.

This mechanism impacts predictions for ITER plasma behavior.

Abstract

We report on a theoretical discovery of new regimes of Alfv\'en eigenmode (AE) induced fast ion transport in tokamak plasmas, where 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 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" [D. C. Pace et al., Phys. Plasmas 20 (2013) 056108]. As a result, microturbulence can significantly increase the amplitude of AEs in predictive simulations of burning plasma experiments such as ITER.