Using Alfvén eigenmode control tools to improve steady state performance in DIII-D

Alfvén Eigenmodes (AEs) can significantly reduce performance in DIII-D steady state scenarios with negative central shear and qmin>2, resulting in measured neutron rates that are typically half of the classically expected values. In recent experiments, AE activity was altered by transiently increasing the density, broadening the density profile with injected deuterium pellets, radially scanning electron cyclotron current drive or heating, reducing neutral beam voltage, or applying n=2 resonant magnetic perturbations. In all cases, AEs remained strongly driven and improvement to performance was minimal. Experiment data are compared to AE simulations using the NOVA code and fast ion transport simulations using the kick model, which includes the impact of AEs on beam slowing-down and scattering calculations in TRANSP. Modeling will be used to understand and predict whether upgrades that are currently underway to increase DIII-D’s off-axis current drive will significantly affect AE stability and improve performance in this scenario.