"Measurements of Critical Gradient Behavior of Fast-Ion Transport Due to Alfvén Eigenmodes in DIII-D"

 

 

 

Recent experiments in the DIII-D tokamak show that many overlapping small-amplitude Alfvén eigenmodes (AEs) cause stiff fast-ion transport above a critical threshold. Three key features of critical gradient behavior have been observed; (1) a sudden increase in transport occurs above a threshold that varies in fast-ion phase space, (2) fast-ion losses become intermittent above threshold, and (3) stiff transport causes the fast-ion density profiles to become fixed despite increased source. These measurements can be used to quantitatively validate transport models that aim to predict alpha profiles, beam ion profiles, and losses in future burning plasma devices.