Event Details

Space and Planetary Physics webinar

In this seminar, we will present the results of two-dimensional fully kinetic Particle-In-Cell (PIC) simulations performed to shed light on the fundamental role of whistler waves in shaping the electron velocity distribution functions (VDFs) in the near-Sun solar wind. The simulations are initialised with electron VDFs modelled after those observed by Parker Solar Probe during its first perihelion at 0.166 au, consisting of a dense core and an anti-sunward strahl population. We will show that, as a consequence of the evolution of the electron VDF, different branches of the whistler heat flux instability can be excited, which can drive whistler waves propagating in the direction oblique or parallel to the background magnetic field. The excited waves interact with the electrons via resonant scattering processes. As a consequence, the strahl pitch angle distribution broadens and its drift velocity reduces. Strahl electrons are scattered in the direction perpendicular to the magnetic field and an electron halo population is formed.

We will also show how the solar wind expansion can be the main driver of the onset of whistler heat flux instabilities and hence how can contribute to the generation of whistler waves in the inner heliosphere. This has been done by using the EB-iPic3D code, which models solar wind expansion self consistently within a fully kinetic PIC semi-implicit approach. Also in these simulations, the onset of whistler heat flux instabilities deeply affects the shape of the electron VDFs as the solar wind expands.

All the simulated wave-particle interaction processes are accompanied by a substantial reduction of the solar wind heat flux. The implications of our results for the understanding of kinetic instabilities in the solar wind and for the interpretation of in situ observations will be discussed.

If someone from outside of the SPP group would like to join the webinar, please send a request to w.gould@lancaster.ac.uk