Compressional Alfvén eigenmodes in NSTX help to explain anomalous ICRH driven fast ion energy diffusion

Observation and identification of Compressional Alfvén Eigenmodes (CAEs) in National Spherical Torus experiments (NSTX) offer new supporting evidencies to the idea of possible anomalous beam ion energy diffusion due to interaction with high frequency oscillations. Such anomaly observed in TFTR has not been explained and was earlier suggested to be driven by large amplitude cavity modes: such as CAEs. The polarization of the observed magnetic field oscillations along the equilibrium magnetic field and the instability frequency dispersion help to identify the eigenmodes responsible for the instability as CAEs. On the other hand theoretically it was pointed out that CAEs may be driven to a large amplitude by ICRH and result in strong energy diffusion of beam ions in TFTR plasma. In this work we bridge this theoretical hypothesis with observations.