Energy channeling from trapped to passing fast ions mediated by GAE/CAE activity in NSTX

In the National Spherical Torus Experiment, an increased charge exchange neutral flux localized at the neutral beam full injection energy is measured by the E\textbar \textbar B Neutral Particle Analyzer. Termed the High-Energy Feature (HEF), it appears on the beam-injected energetic ion spectrum in discharges where NTM or kink modes (f \textless\ 10 kHz) are absent, TAE activity (f $\sim$ 10-150 kHz) is weak and CAE/GAE activity (f $\sim$ 400 -- 1200 kHz) is robust. The HEF exhibits a growth time of t $\sim$ 20 - 80 ms and develops a slowing down distribution that continues to evolve over periods \textgreater\ 100 ms. HEFs are observed only in H-mode discharges with NB power P$_{\mathrm{b}} \ge $ 4 MW and in the pitch range v$_{\mathrm{\vert \vert }}$/v $\sim$ 0.7 -- 0.9. The HEF appears to be caused by a CAE/GAE wave-particle interaction that modifies the fast ion distribution, f$_{\mathrm{i}}$(E,v$_{\mathrm{\vert \vert }}$/v,r). This mechanism was studied using the SPIRAL code that evolves an initial TRANSP-calculated f$_{\mathrm{i}}$(E,v$_{\mathrm{\vert \vert }}$/v,r) distribution in the presence of background plasma profiles under drive from wave-particle resonances with CAE/GAE Alfv\'{e}n eigenmodes.