Observations of energetic ion driven ion cyclotron emission and high frequency Alfvén eigenmodes in negative triangularity plasmas in DIII-D

Observations are presented for an investigation of energetic ion driven coherent ion cyclotron emission (ICE) and sub-cyclotron high frequency Alfvén eigenmodes (hfAE) in negative triangularity shaped plasmas in DIII-D obtained with a set of loops inside the vacuum wall with sensitivity to radio frequency emission at frequencies f < 200 MHz. This investigation contributes to a better understanding of the observed waves so that in the future, such observations can be used to diagnose the energetic ion population. In a 2023 negative triangularity campaign, many experiments were conducted which provided a rich data set for examining ICE and hfAE characteristics on plasma parameters in negative triangularity shaped plasmas. The ICE was observed to occur at low harmonics of the central ion cyclotron frequency and the dominant harmonic varied with plasma conditions but tended to be low (l ≈ 2). Frequency splitting was observed for some ICE harmonics, as well as hfAEs. Analysis showed that in some case the splitting was the result of the formation of propagating wave packets, suggestive of nonlinear dynamics. Work supported by US DOE under DE-FC02-04ER54698 and grant # DE-SC0020337.