Friday

Following on from Helios, the advent of Parker Solar Probe provides unprecedented high-resolution measurements of the pristine solar wind, which helps us to bridge the gap between local and global kinetic processes. This project uses a combination of a Levenberg-Marquardt fitting routine and a machine learning technique to determine and classify the electron populations in SWEAP/SPAN-E measurements of the electron distribution function. Our method fits a bi-Maxwellian distribution function to the core electron population, a bi-Kappa to the halo and another bi-Maxwellian to the strahl. We present the evolution of these populations, such as density, bulk velocity, temperature, the kappa index and temperature anisotropy from 0.13 to 0.5 au. Our findings show that the core density radial evolution is in excellent agreement with isotropic expansion while the suprathermal populations have a more complex radial evolution. We report that at the closest distances the distribution can be well modelled with a core and a strahl model with little/no halo model, which is observed for the first time. A novel finding through consideration of the fractional densities of these three electron populations, we find evidence for the growth of the suprathermal halo and strahl populations from 0.13 to 0.17 au, indicating growth of the suprathermal particles. Moreover, the growth in the halo population is not matched by a decrease of the strahl population, as has been reported for previous observations outside of 0.3 au. In addition, at the near-Sun distances sampled, we observe a new feature where there is a statistical deficit in the core population in the direction opposite to that of the main strahl beam. Based on our results, we discuss possible local kinetic links between the electron populations and their impact on the thermodynamics of the solar wind at an early stage of their evolution.