Investigation of collective fast ion instability-induced redistribution or loss in the National Spherical Torus Experiment

Medley, S. S.*; Andre, R.*; Bell, R. E.*; Darrow, D. S.*; Fredrickson, E. D.*; LeBlanc, B. P.*; Levinton, F. M.*; Menard, J. E.*; Stutman, D.*; Roquemore, A. L.*; Shinohara, Koji; Tritz, K.*; Yuh, H.*; NSTX Research Team*

The National Spherical Torus Experiment (NSTX) is particularly well suited to investigate fast-ion driven instabilities. These instabilities are observed in the wide range of frequency from 0 kHz to the ion cyclotron frequency. Two recently implemented diagnostics on NSTX, the Motional Stark Effect (MSE) and scintillator Fast Lost Ion Probe (sFLIP), facilitate separation of redistribution and loss effects. Outward redistribution of the core-peaked energetic beam ions modifies the beam-driven current profile and hence the core q-profile. For certain H-mode discharges where NPA measurements of the NB energetic ion spectra exhibit MHD-induced fast-ion depletion, the sFLIP data confirm the existence of an ion loss that occurs primarily for passing particles near the NB full injection energy. Observations and TRANSP simulations representing fast ion instability-induced redistribution/loss phenomena in NSTX are presented.