Authors: Yogesh (CUA/NASA GSFC), L. Ofman (CUA/NASA GSFC), S. A. Boardsen (UMBC/NASA GSFC), V. M. Sadykov (Georgia State University), L.K. Jian (NASA GSFC), J. L. Verniero (NASA GSFC), J. Huang (SSL/UC Berkeley)

Recent in situ observations from the Parker Solar Probe (PSP) mission in the inner heliosphere near perihelia reveal evidence of ion beams, temperature anisotropies, and kinetic wave activity, which are likely linked to the kinetic heating and acceleration processes of the solar wind. During Encounter 17 (r =11.4R_sun), PSP’s FIELDS instrument detected enhanced ion-scale kinetic wave activity (~3 hours) on Sep-26-2023, which is likely associated with unstable ion Velocity Distribution Functions (VDFs) observed by PSP/Solar Probe Analyzers-Ion (SPAN-I). The central frequency of the wave activity varies rapidly by a factor of 5 in approximately five minutes. During this wave activity, the proton VDFs show the presence of strong ion beams. Using the bi-Maxwellian model, we calculate the proton core and beam populations for the duration of this event. The proton beam population increases during the wave activity and, surprisingly, becomes greater than the core proton density during a few intervals of the event. The drift velocity of beams with respect to the core remains nearly constant (at about v=0.8-1.0 VA, where VA is the Alfven speed). During this event, the initial moments of VDFs show that the alpha population is around 1% of the proton number density. We use linear instability analysis to determine if the proton beam instability can provide the energy to produce the observed enhanced wave activity. Additionally, we investigate the nonlinear evolution of ion kinetic instabilities using hybrid simulation, in several cases during this PSP observation and quantify the transfer of energy between the protons, alpha particles, and the kinetic waves.