Effects of negative triangularity shaping on energetic particle driven Alfvén eigenmodes*

Simulations using the gyro fluid code FAR3d indicate that the profile and shape changes associated with negative triangularity (NT) can lower the growth rate of energetic particle (EP) driven Alfvén eigenmodes (AEs) in DIII-D compared to positive triangularity plasmas. There has been a renewed interest in NT plasma shaping due to observations of reduced microturbulence and higher normalized beta. An investigation of shaping effects on the EP-driven, linear AE activity in DIII-D is performed using FAR3d that identifies AEs at similar frequencies as observed in the experiments. Because AEs have a global mode structure and are caused by the couplings between adjacent poloidal modes, it is expected that plasma shaping will influence their stability. However, DIII-D experiments did not show significant effects of NT shape on AE-induced fast ion transport. The present work also extends simulations to the nonlinear regime to study the effects of different types of plasma shaping on AE-driven transport. These findings may inform the choice of plasma shapes for future fusion devices that can mitigate or suppress EP-driven AEs.