UC Berkeley

Parker Solar Probe (PSP), launched in late 2018, is a mission designed to sample the near-Sun environment and solar corona, and answer broad open questions concerning coronal energy flow and solar wind dynamics. The SPAN-Ion instrument is an on-board electrostatic analyzer responsible for measuring 3D ion velocity distribution functions (VDFs). In the first part of this thesis, we give an overview of SPAN-Ion, its intrinsic uncertainties, and discuss the effect of its finite field-of-view on moment measurements. We then move on to study magnetic switchbacks, rapid radial reversals of the magnetic field. While their role in young solar wind dynamics and precise generation mechanisms are still unclear, their ubiquity marks them out as an important early PSP observation. Using MHD invariants to probe their macroscale structure, we show that they are localised S-shaped folds in the magnetic field with internally backward propagating Alfvénic fluctuations, which has important implications for studies of small-scale turbulence using such invariants. Using fits to SPAN-Ion data, we then investigate alpha particle density, abundance, and velocity fluctuations inside and outside individual switchbacks, showing that there are no consistent compositional changes inside vs outside, but argue that these findings cannot yet be used to definitively rule in favour of one particular switchback generation mechanism (although they may be able to in the future). We also show that alpha particle speeds may be enhanced, decreased, or remain constant during a switchback, depending on the relative values of the alpha proton drift and the local wave phase speed, in contrast to the always positive proton velocity spikes. In the final part we study the alpha VDFs in more detail, focussing on characterising secondary alpha populations or alpha ``beams”. These have been essentially unstudied relative to their proton beam counterparts. We find they are generally more dense and slower moving than proton beams, and occur less frequently. We report time localised correlations between proton and alpha normalised heat flux, suggesting the existence of a common mechanism for producing beams in each species. We then perform a case study of an ion scale wave event, showing for the first time an active role being played by the alphas, specifically the alpha beam population, in driving solar wind plasma unstable and locally generating right-handed fast magnetosonic waves. The predicted wave frequencies, polarisations, and times of occurrence agree remarkably well with the observations. Such wave events are important for understanding the mechanisms of energy exchange between waves and particles that may be responsible for in-situ heating of the solar wind.