Intermittent Fluctuations of Fast Ions Across Phase Space on DIII-D

Fluctuation measurements of both Fast Ion Loss Detectors (FILDs) and an Imaging Neutral Particle Analyser (INPA) show intermittent transport of fast ions during Alfvén Eigenmode (AE) induced critical gradient behavior. Previous work on the current ramp phase of L-mode, inner-wall-limited plasmas have shown bursts of losses in FILD data, increasing in frequency with total injected beam power [1]. Here, we expand on these findings with the use of an upgrade to the fast ion fluctuation diagnostics on DIII-D – the most important of which is the installation of a fluctuation measurement on the INPA to see the effect of the critical gradient on confined particles. Along with an increased number of FILD fluctuation measurements and a new optical setup for measuring fluctuations in Fast Ion D­_α (FIDA), these new measurements form a more complete picture of energetic particle transport across phase space. Beam Emission Spectroscopy (BES) data is also used to compare against recent theory suggesting that microturbulence affects the intermittent behavior of fast ions [2].



[1] C.S. Collins et al 2016 PRL 116 095001

[2] R.E. Waltz et al 2021 Nucl. Fusion 61 036043