Parker Solar Probe Observations of Ion Velocity-Space Diffusion Associated with Ion-Scale Right-Hand Polarized Waves

Parker Solar Probe (PSP) continues to shed light on the fundamental nature of the inner heliosphere with each orbit around the Sun. Characterizing the energy transfer between electromagnetic fields and particles improves our understanding of the complex dynamics that govern our universe. Particle velocity distribution functions (VDFs) that possess sufficient asymmetries may supply a source of free energy for plasma wave generation. We present SPAN-I measured VDFs from Encounter 4 with beams that exhibit unique `hammerhead' shapes that are seen simultaneously with ion-scale right-hand polarized waves observed from FIELDS. We provide a plausible explanation for these `hammerhead' features as a signature of ion velocity-space diffusion resulting from resonant interactions with parallel-propagating fast-magnetosonic/whistler waves.