Efficient evaluation of the EP-driven stability landscape and nonlinear states using Landau closure methods*

The FAR3d global gyro-Landau moments model provides an efficient kinetically-closed reduced model for energetic particle (EP) – driven instabilities in tokamaks and stellarators. Two examples of this are: (a) the linear eigenvalue structure of the moments equations, allowing rapid scans of multiple unstable modes as parameters/profiles are changed, and (b) the feasibility of long-time scale nonlinear simulations in strong mode coupling regimes. These capabilities are demonstrated based on selected discharges from the DIII-D tokamak. Under (a) we examine a sequence of low-frequency EP-driven instabilities (BAE frequency and below) as the q-profile is varied. Low frequency EP instabilities are of interest due to the increased EP transport they can drive. Under (b) a nonlinearly saturated TAE state is examined with respect to turbulent transport rates, effects of source/sink variations, fast ion critical gradient profiles, and intermittency levels. The simulation of instability-driven fast ion transport and intermittency is an important factor for integrated modeling and performance predictions of future fusion systems.