Fast Ion Losses Driven by Applied Magnetic Perturbations and Plasma Response on DIII-D

Externally applied resonant magnetic perturbations (RMPs) on DIII-D alter fast ion confinement, leading to an increase in prompt losses from beam ions born inside the last closed flux surface (LCFS). Experimentally, the light ion beam probe (LIBP) technique [1] is used to infer fast ion orbit displacement using signal from the midplane fast ion loss detector (FILD) during application of n=1 and n=2 RMPs. The applied n=1 RMPs analyzed are rigidly rotated around the vessel at a set phase offset between the upper and lower internal coils △φ_UL. Plasma response to RMPs with △φ_UL=0 increases with plasma β, and is strongest when the RMP is coupled with an internal kink. Simulations of these shots in ASCOT5, using the plasma responses calculated by M3D-C1, show high concentrations at the midplane of losses induced by RMPs. With n=2 RMPs, a continuous scan through △φ_UL was achieved by holding the lower coil perturbation constant while the upper coil current was rotated. Experimental losses at the midplane vary with △φ_UL as does the simulated response.

[1] X.Chen et al, Rev Sci Instrum 85, 11E701 (2014)