Validating Quasi-linear simulations of a single Alfven eigenmode in a tokamak

The oscillatory behavior of a single unstable toroidicity-induced Alfvénic mode (TAE) observed in DIII-D experiments [M. Van Zeeland et al, Nucl. Fusion Nucl. Fusion 61 (2021) 066028] and excited by suprathermal beam ions is investigated numerically. One goal of this study is to validate the quasilinear approach used in recently developed Resonance Broadened Quasilinear code RBQ [N.N. Gorelenkov, Duarte, Phys. Lett. A 386 (2021) 126944]. We are showing that the realistic time dependence of fast ion growth rate is essential to reproduce the observed overshoot phase emerging within a few milliseconds after the start of NBI blip. Another goal is to quantify the TAE oscillations in the saturated state. The comparison helps to understand the multiscale intermittency observed in experiments and predicted in simulations. An interplay between the growth, damping rates and the effective scattering frequency in RBQ simulations exhibits a predator-prey behavior of the mode amplitude evolution. Additionally, studied beam blip experiments exhibit a rapidly changing drive which needs to be factored into simulations.