This thesis uses kinetic plasma physics to study the kinetic evolution of the electron velocity distribution function (VDF) in the solar wind. We propose an analytical model for resonant wave–particle instability in homogeneous plasma based on quasi-linear theory. By using this model, we confirm that the oblique fastmagnetosonic/whistler (FM/W) instability can scatter the electron strahl in the electron VDF.
Following the study of the local scattering, we propose a global transport theory for the kinetic expansion of solar-wind electrons. We derive a gyro-averaged
kinetic transport equation that accounts for the solar-wind expansion in the geometry of the Parker-spiral magnetic field. Our kinetic transport model shows the
development of the core–strahl configuration in the electron VDF near the Sun.
Applying fits to our numerical results, we compare our numerical results with data
from Parker Solar Probe (PSP), and provide theoretical evidence that the electron
strahl is not scattered by the oblique FM/W instability near the Sun.
To confirm our theoretical results for strahl scattering, we analyse data from
PSP and Helios. We compare the measured strahl properties with the analytical
thresholds for the oblique FM/W instability in the low- and high-β∥c
regimes, where β∥c is the ratio of the parallel core thermal pressure to the magnetic pressure, as
functions of heliocentric distance. Our PSP and Helios data show that the electron strahl is stable against the oblique FM/W instability in the inner heliosphere.
Our analysis suggests that this instability can only be excited sporadically, on short
timescales.
For the numerical evaluation of the kinetic equations in the research chapters, we develop a mathematical approach based on the Crank–Nicolson scheme. This
approach numerically solves any kind of diffusion equations with any dimensions.
We note that our mathematical approach is applicable to other complex diffusion
equations
