Dominant occurrence of hammerhead velocity distributions close to the heliospheric current sheet

Parker Solar Probe (PSP) has observed strong perpendicularly diffused proton beams in velocity distribution functions. These were first reported by Verniero et al 2022 and termed as so-called hammerhead VDFs. Attempts to numerically simulate the formation of hammerheads have yet to produce results in alignment with spacecraft observations. This necessitates detailed statistical studies of the occurrence conditions and the associated plasma processes in order to better guide simulations. We developed a Python-based, open-source and fast hammerhead detector called hampy and investigated 20+ recent encounters of PSP data starting from E04. We also carry out detailed field-of-view (FOV) analysis to disqualify the hammerhead detection being a consequence of FOV-biased detection. Our results show that hammerheads dominantly occur around the heliospheric current sheet (HCS). As the HCS goes from being flat to vertical over the solar cycle (going from early to later PSP encounters), the occurrence of hammerheads are seen to pile up in narrow bounds around the HCS with progressively later encounters. We also characterize the hammerhead populations across encounters and heliospheric distance to study trends in the anisotropy of the proton beam and its connection to the density of proton beams as well as the drift speed of the beam to the core.