Seong-Yeop Jeong
Gather.town id
MIS05
Poster Title
The Kinetic Evolution of the Electron Strahl in the near-Sun solar wind
Institution
Mullard Space Science Laboratory
Abstract (short summary)
The electrons in the solar wind exhibit an interesting kinetic substructure with many important implications for the overall energetics of the plasma in the heliosphere. We are especially interested in the kinetic evolution of the electron strahl, a field-aligned beam of superthermal electrons, in the near-Sun solar wind. We develop a kinetic transport equation for typical heliospheric conditions based on a Parker-spiral geometry of the magnetic field. We present the results of our theoretical model for the radial evolution of the electron velocity distribution function (VDF) in the solar wind. We study the effects of the adiabatic focusing, free streaming due to the electron temperature gradient, wave-particle interactions, and Coulomb collisions through a generalized kinetic equation for the electron VDF. We compare and contrast our results with the observed effects in the electron VDFs from space missions that explore the radial evolution of electrons in the inner heliosphere such as Helios, Parker Solar Probe, and Solar Orbiter.
Plain text (extended) Summary
We propose an analytical model for the kinetic evolution of the solar wind electron strahl in the inner heliosphere. We develop a kinetic transport equation that accounts for the spherical expansion of the solar wind and the geometry of the Parker-spiral magnetic field.
We initialize our model with isotropic electron distribution functions and calculate the kinetic evolution at heliocentric distances from 5 to 20 solar radii. In our kinetic evolution, the electrons evolves mainly through the combination of the ballistic particle streaming, the magnetic mirror force and the ambipolar electric field. By applying fits to our numerical results, we quantify the parameters of the electron strahl and core parts of the distributions. The strahl fit parameters show that the relative density of the electron strahl is around 5.2% at a distance of 20 solar radii, the strahl bulk velocity and strahl temperature parallel to the background magnetic field stay approximately constant from a distance of 15 solar radii, and parallel plasma beta of electron strahl (i.e., the ratio between strahl parallel thermal pressure to the magnetic pressure) is approximately constant with the heliocentric distance as 0.02. We compare our results with electron data measured by Parker Solar Probe. Furthermore, we provide theoretical evidence, supported by observations, that the electron strahl is not scattered by the oblique fast-magnetosonic/whistler wave instability in the near-Sun environment.
We initialize our model with isotropic electron distribution functions and calculate the kinetic evolution at heliocentric distances from 5 to 20 solar radii. In our kinetic evolution, the electrons evolves mainly through the combination of the ballistic particle streaming, the magnetic mirror force and the ambipolar electric field. By applying fits to our numerical results, we quantify the parameters of the electron strahl and core parts of the distributions. The strahl fit parameters show that the relative density of the electron strahl is around 5.2% at a distance of 20 solar radii, the strahl bulk velocity and strahl temperature parallel to the background magnetic field stay approximately constant from a distance of 15 solar radii, and parallel plasma beta of electron strahl (i.e., the ratio between strahl parallel thermal pressure to the magnetic pressure) is approximately constant with the heliocentric distance as 0.02. We compare our results with electron data measured by Parker Solar Probe. Furthermore, we provide theoretical evidence, supported by observations, that the electron strahl is not scattered by the oblique fast-magnetosonic/whistler wave instability in the near-Sun environment.
URL
s.jeong.17@ucl.ac.uk
Poster file