Multi-phase simulation of fast ion profile flattening due to Alfvn eigenmodes in a DIII-D experiment

Todo, Yasushi*; Van Zeeland, M. A.*; Bierwage, A.; Heidbrink, W. W.*

The hybrid code MEGA, which simulates the interaction between fast ions and an MHD fluid, is extended with realistic beam deposition profile and collisions. It is used for multi-phase simulations, where classical simulations (fast ion source + collisions) and hybrid simulations (source + collisions + MHD) are run alternatingly. In a multi-phase simulation of DIII-D discharge 142111, it is found that the stored beam ion energy is saturated due to toroidal Alfvn eigenmodes (TAE) at a level lower than in the purely classical simulation. This is consistent with the experimental observation. After the stored fast ion energy is saturated, it is demonstrated by hybrid simulations that the fast ion spatial profile is significantly flattened due to the interaction with the multiple TAEs with amplitude / and / of order 10e-4. The temperature fluctuations caused by TAEs are of the order of 1% of the equilibrium temperature. This is also comparable with ECE measurements in the experiment.