Sawtooth-induced Fast-ion Transport in the DIII-D Tokamak: Observations and Comparison to Theory*

Tokamak sawteeth consist of a reorganization of the plasma magnetic field and various plasma parameters. The extent to which the fast-ion distribution function $F(x,v)$ is influenced can depend on the ions' distribution of pitch and energy as well as the nature of the crash. Recent sawtooth experiments at DIII-D employed the newly extended fast-ion deuterium-alpha (FIDA) diagnostic, 2D FIDA imaging, and the newly commissioned fast-ion loss detector. Consistent with theoretical predictions, the FIDA diagnostic indicates that passing particles are more strongly affected by a sawtooth crash than the trapped population. Furthermore, FIDA imaging reports a depletion of up to 50\% of the central fast-ion density. Extensive experimental data provide a rigorous test bed of theoretical models.